Protective Structures for Civilian Populations

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          Proceedings of the Symposium
               held at Washington, D. C.
                 April 19-23, 1965 by the
.,&ubcommittee on Protective Structures,
   Advisory Committee on Civil Defense,
   ><
        National Academy of Sciences-
              National Research Council
                                                             PROPERTY OF
              "

                                                              t p~ p~     1996
                                                              l!!jLSrr-u
                                       tfrotectiv
                                       Structures
                                        for

                                       CIVILIAN
                                       POPULATIONS


                                              NAS-NRC
                                              JUL G 1966

                                               UBRARY




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                                                PREFACE
This publication contains papers presented at the          f1 survival. Second, as protection from fallout is
Symposium on Protective Structures for Civilian             accomplished, the effort will move to protecting
Populations at Washington, D.C., during the week c:l        those segments f1 the population threatened by more
April 19-23, 1965, conducted by the Advisory Com-           than fallout alone.
mittee on Civil Defense, National Academy c:l                    Whether or not a fire storm will develop can be
Sciences and sponsored by the Office of Civil               predicted with reasonable reliability from estimates
Defense, Department f1 the Army.                            of fuel density, according to Dr. Leutz. Likelihood
    The stated purposes f1 the Symposium were to            c:l fire is related to probabilistic considerations of
review applicable effects, to define technical require-    atmospheric tranSmissivity, humidity, and tempera-
ments for shelters and associated equipment, to             ture, together with antiCipated weapon characteris-
describe design procedures, and to discuss specific         tics. Furthermore, the region in which fires can be
cases of shelter construction, especially those in-        an antiCipated threat to shelter occupants can be
volving unusual or novel techniques or achieving           predicted from the presence c:l combustibles.
outstanding economies. Thus, all papers at the                  It is clear from Dr. White's paper that the bio-
Symposium relate to the technical feasibility of           logical effects c:l blast have been well defined for
shelter construction. No two readers c:l the papers        some subhuman mammalian species in certain
in these proceedings will be impressed by the same         limited but carefully specified blast environments.
points, but certain points will impress most readers,      Major uncertainties sWI exist in the extent f1 varia-
as will some of the more obvious implications. It is       tions introduced by environmental geometries and
the purpose here to touch upon the major implica-          materials and in extrapolating results to humans.
tions inherent in the papers presented.                    Especially lacking is the ability to estimate effects
   In the first paper, Dr. Brode has shown that the        in marginal shelter environments. Dr. White em-
superior efficiency f1 nuclear weapons makes their         phasized that it may very well be simpler to define
threat transcend that of conventional bombs or f1          a shelter to shield from the effects rather than to
chemical or biological weapons, although the latter        predict accurately the result c:l a fallure to provide
cannot be excluded in consideration of a balanced          adequate protection; viz., design away from the
protective system. New or unusual weapons are not          hazard.
to be expected within the foreseeable future, nor are           In the case f1 radiation, Dr. Conrad demonstrated
spectacular advances in nuclear weapons to be an-          our knowledge f1 the tolerances of the individual hu-
ticipated. Numbers and yields of nuclear weapons           man to sublethal exposures to radioactive fallout.
may be expected to increase with time, bringing            By Omission, however, he calls attention to our
about the most probable changes in threat-more or          lesser understanding of the collective tolerances f1
larger weapons on locations that would be targeted         an entire population, which might serve as a crite-
today and additions to today's list of targets with        rion for designing a nationwide system of protective
time. One cannot but be impressed by the fact that         structures.
output phenomena are known and that these phe-                  The biological effects c:l fires and their accom-
nomena are predictable with much greater preCision         panying combustion products are well known and
than that with which we can predict how and where          protective measures are either available or the
the weapons will be used. Efficient weapon employ-         knowledge for their design exists, but protective
ment, however, does provide limitations within which       measures are expensive.
the most probable threat lies.                                  Dr. Spencer's paper outlined the problems of
   Dr. Knapp showed the nature of fallout radiation        analyzing structures for protection against initial
that has properly occupied, to the present time, the       radiation. Shielding against initial radiation has
greatest attention of all the nuclear-weapon effects.      lagged because of emphasis on fallout, and because
Two future trends bearing on protective construction       of the inherent complexity c:l the radiation field
emerge from the presentations of Brode and Knapp.          which combines gamma ray neutrons from several
First, as more weapons and delivery systems permit         different generating mechanisms. Dr. Spencer
assignment c:l additional weapons to a given target        expects substantial progress toward more accurate
or addition of targets, the fallout levels will increase   and more manageable systems for estimating
due to overlap c:l fallout patterns, and a greater         shielding during the next year or two.
shielding will be required to achieve the same level            In the Design Procedures seSSion, the paper by


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Dr. R. V. Whitman and Dr. U. Luscher summarized            conventional structures if, during design, proper
.in a qualitative fashion some recent observations         attention is given to details and if the protection goal
 concerning soil-structure interaction, particularly       is kept in mind.
footing behavior, one of the major problems in                 The shelters described in the case studies ranged
designing for moderate overpressures. Dr. Newmark          from those for a few occupants (Canada, Sweden,
elaborated further on the soil-structure interaction       Denmark, and Great Britain) to those that accom-
problem insofar as design recommendations are con-         modate a large number of people (Netherlands,
cerned, and summarized some of the latest informa-         Germany, and the United States). Swiss shelters
tion relating to design against shock and vibration,       cover a range of sizes. Of special interest were
which will be of great importance in the future, as        Hudgins' example of a corporation formed for pri-
there is a necessity to design for upgraded blast          vate shelter construction in the United States and a
criteria. Mr. Davies described a number of case            suggestion by Harrenstein and Narver for a close-
histories of structures employing models carried           in shelter system with built-in egress from the
out in Great Britain, and specifically called attention    damage area to a region of relative safety. The
to the great structural strength that can be achieved      former is an example of what can be accomplished
with slabs that are restrained against in-plane de-        by small groups acting independently and the latter
formation at the edges. Although there are no struc-       is an example within the capability of a determined
tural uncertainties that preclude shelter construction     city to accomplish independently. Hopefully these
as the blast design criteria become more severe, it        examples will lead to other independent solutions
is apparent that there are· many aspects of the design    for commercial, industrial, and educational groups.
problem that will need further investigation and              Mr. Panzhauser raised a difficult question as to
clarification.                                             whether the best goal for a shelter program is to
    With respect to design details, the situation is       provide all citizens with an equal chance for survi-
essentially the same. While blast propagation              valor to maximize the number of survivors for any
through entrances and ducts is not equally well            given expenditure at all times until the protective
understood for all configurations, there are no            system is complete. He also points out that to opti-
uncertainties Significant enough to require defer-         mize protection from radiation requires a systematic
ment of construction. Likewise, the technology            consideration of all the interrelating factors: period
exists for determining ventilation and cooling re-        of occupancy, shielding factor, expected radiation,
qUirements of shelters with sufficient accuracy to        and acceptable dose.
permit construction to proceed. One point made                The case studies were especially useful in bring-
clear by the foregOing and by the case studies,           ing out differences. Some of the differences are
described later, is that there have been no major         logical since they are due to geographic differences
economic breakthroughs in prOviding protective             (Netherlands and Denmark with their high water
construction. Minor savings can be made in light-         table, Norway and Switzerland with availability of
weight pre-formed shelters for a few occupants or         rock). Other differences appear, on the surface at
through planned dual use of larger shelters in whic~      least, to be more arbitrary. A disparity exists from
most or part of the shelter cost is written off against   one nation to another in the emphasis placed on the
the primary purpose of the structure. Cost continues      weapons from which protection should be provided.
to increase rapidly as the level of protection is in-     For example, some provide protection from conven-
creased. Other factors are also important in deter-       tional weapons or bacteriological or chemical weap-
mining unit costs; e.g., size and material.               ons, as well as from nuclear weapons, while others
    A wide variety of case studies provided illustra-     find the effects of nuclear weapons so awesome that
tive examples of protective construction efforts in       the effects of more conventional or less-efficient
Europe, Canada, and the United States. Included           weapons pale to insignificance. Also, for those con-
were dual-use garages (Switzerland and Germany),          sidering nuclear effects, it is not always clear how
subways (Netherlands and SWitzerland), schools            the weapon yield against which protection must be
(United States), and single-purpose shelters              provided has been chosen. Because of the foregoing
(Denmark, Sweden, Switzerland, and the United             considerations, there are differences in the antici-
States). Experiments under way in Canada light            pated duration of shelter occupancy. There are
the way to the use of less conventional materials         differences in the per capita space allocations and
for blast shelters. Work in Norway shows that             ventilation requirements. There are differences
commercial shelter eqUipment can be used by pro-          from one nation to another in the degree of incentive
viding simple protection against ground shock-            or even legal requirements to provide shelter. These
consideration of which reflects an interest in pro-       apparent disparities are even more remarkable when
tection against relatively high levels of blast.          one considers that weapon effects and human biologi-
Mr. Roembke's paper illustrated how some addi-            cal response to them is not a function of national or
tional fallout protection can be obtained from            cultural dissimilarities. Clearly, each of the diver-




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gent solutions to protective construction can hardly   sented at the Symposium for more uniform criteria
constitute an optimum solution to the problems of      and improved means of providing a greater degree
protection.                                            of balanced protection at less expense.
   Let us hope that this Symposium will have pro-
vided the motivation for better understanding of the            Luke J. Vortman
underlying reasons for the differences in require-              Acting Chairman
ments, for an lntensive re-evaluation of proposed               Subcommittee on Protective Structures
solutions, and for striving among the nations repre-




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                                          GENERAL REMARKS

                                              Eugene P. Wigner
                                             Princeton University


I would like to tell you a little about my own experi-    defense and the antiballistic measures, could supple-
ence during the first six months of the project at the    ment each other so that the joint protection they
Oak Ridge National Laboratory on civil defense. As        provide would be greater than the sum of the
many of you know, this is a small project as projects     protection provided by them separately. The third
go nowadays; we are about a dozen people. In a way        problem is to gauge the behavior of people in an
it is an outgrowth of the Harbor Project, which was       emergency and to look for ways and means to im-
a study under the auspices of the same National           prove that behavior. There have been many disasters
Academy of Sciences which sponsors the present            in the past, both man-made and natural, which tried
meeting. It took place one and a half years ago and       the moral quality of people, and even though, on the
had as a purpose a general appraisal of the possi-        whole, man acquitted himself rather better than one
bilities, promise, and also the side effects of civil     might expect in the face of such emergencies, the
defense. Two of the participants in the Harbor Study      behavior varied enormously. The purpose of the
joined the study at Oak Ridge. All of us have read        study is, of course, to find ways for bringing out the
not only the Harbor Summary Report and some of            best in man so that he helps his fellow rather than
the detailed report itself, but also, of course, the      thinking only of himself. The problem of recovery
reports of several other studies.                         is the last question, and is the one that the Harbor
    At the time the Harbor Study was in progress, it      Study considered perhaps most carefully, but never-
was generally believed that the full fallout-protection   theless not adequately, in view of its immense mag-
program would pass Congress and would soon be-            nitude. This is principally the question of prepara-
come a reality. The study therefore took off from         tions ahead of time, which should alleviate the
that point, and its main theme was the discussion of      after-effects of the catastrophe as far as possible.
more elaborate protective measures than fallout           As I said, this is a question of immense difficulty
shelters for the period of the hostilities, and eco-      and also of immense importance, and we decided
nomic preparations for the aftermath, the period of       not to tackle it with our very modest means.
recovery. It was a great shock to many of us when             Thus the Oak Ridge study was left with three
the bill then pending before Congress was not             questions to consider: the locations of shelters in
passed. Nevertheless, the preoccupation and interest      very densely populated areas, that is, centers of
in measures that go beyond protection against fall-       cities; the correlation of passive and active defense;
out radiation proved to be lasting, and the Oak Ridge     and the behavior of people in disaster or, as it is
project took off where the Academy study ended. We        put more euphemistically, in an emergency. We
all recognized the necessity of implementing the          wanted to tackle these problems, and tried to find
fallout-shelter program before more could or should       collaborators for each of them. We soon noticed,
be done on a nationwide scale. We also felt, however,     however, with some surprise, the many intercon-
that the plans for this program had progressed to a       nections between our problems-the fact that the
degree at which a small group, such as ours, could        study of each problem involved the study of a great
contribute little to it, and we also felt that it was     many other factors-so that the subjects broadened
important to think further. As I said, we took off        to such a degree that their original boundaries were
from the point where the Harbor Study concluded and       hardly recognizable. Hand-in-hand with this broad-
set as our goal the investigation of the problems that    ening of the subject matters went our increasing
the Harbor Study left open.                               realization of the scope of earlier work on so many
    There were four such problems .that appeared to       facets of the broadened problem that by now we
us most important. The first of these concerned the       hardly feel like a team investigating new problems
location of shelters in cities, particularly at the       and feel, to a much greater extent, like people
centers of cities where space is at a premium and         adding a few building blocks to an existing supply
the density of people to be taken care of highest.        of building blocks-and perhaps like planners, along
The second problem concerned the ways in which            with many others, of the use of these building blocks.
passive and active defense, that is, principally, civil   This realization of the magnitude of earlier work,



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even jf not on our own problems, has been heightened         blast damage, or it may strike the countryside, to
at the present conference, which my friends and I            cause fallout. I may lRterject here that, right now,
found immensely instructive.                                 I am most worried about this last alternative. All
    You may be interested in an earlier experience.          these are possibilities that the passive defense may
During the last war, in the forties, Mr. Young and           have to face, but the ways of thwarting the active
Mr. Weinberg, now respectively Assistant Director            defense are even more numerous: decoys, chaff,
and Director of Oak Ridge National Laboratory, and           multiple warheads, saturation, exhaustion, and so on.
I were given the charge of designing nuclear reactors        It is evident that the problem of visualizing the
to produce plutonium or, to pUt it more precisely, to        events surrounding an attack is much more djfficult
irradiate uranium with neutrons. We thought, first,          than to visualize what happens, in ilie large and in
that we had two tasks: to find the conditions for            the small, in the temperature motion and in terms
chain reaction, and to discover a method for trans-          of non-equilibrium phenomena, when the control rod
ferring heat from the fuel elements to some heat             is withdrawn in a reactor.
sink outside the reactor so as to avoid overheating              It would be good to be able to claim that at least
of the uranium. However, we soon found ourselves             as much thought has gone into visualizing the func-
 trying to imagine all the events in the reactor-the         tioning of a passive-defense system as has gone,
way neutrons travel around in the moderator, caus-           before any reactor was tested, into visualizing the
 ing the atoms of the moderator to recoil under the          events in the reactor when it would be tested. As
 impact and in this way losing energy; the recoil            some of you know, we are intensely interested in the
atoms colliding with other atoms, sharing their              defensive system that Dr. Harrenstein described
kinetic energy with them and becoming ionized,               today and which we have re-invented. Mr. Narver
 that is, losing some of their electrons; what happens       will describe this shelter complex more in detail
 to these electrons; how they recover an ion to re-          tomorrow, as it has evolved in our thinking. HI
 combine with; what the neutron does further on; and          start visualizing the functioning of this shelter com-
 so on. In other words, we came to realize that it is        plex, I see people scrambling out of the doors of
 necessary not only to solve definite problems but to        high-rise buildings. I do not know whether they
 visualize all the events that go on. 'The magnitude of       might run or just rush, whether they might scream
 some of these events, such as the total energy de-          and try to push past, others on the sidewalk, or go
 posited in the moderator, or the total number of            on the main road, whether there will be any of the
 dislocations caused by them, is not of crucial im-          vehicles there. I do not know how they will behave
 portance and, if one knows them within a factor of 2,       when past the entrance of the shelter, how they can
 one knows enough. The magnitude of other effects            best be induced not to stop there in the hope that the
 must be gauged with high accuracy, such as that of           "all clear" signal will be given soon, but will move
 the multiplication constant. A certain amount of            away from the entrances to let others in. There is
 flexibility must be built into the system-in the case        no clarity in my mind how they might act jf the
 of a reactor, for instance, by a control rod-but the        attack indeed materializes, how much coaxing they
 important thing we came to realize was that we did           need to do what is expected. There is no clarity in
 not have separated problems but had to try to imag-          my mind even how the shock-wave will set the earth
 ine all the events that would take place when the           and the shelter into motion if the explosion is high
 installation would be used.                                  up, whether the electromagnetic pulse will interfere
     It seems to me now that the situation fs the same        with the light. There is even less clarity in my mind
 with respect to civil defense, except that the visuali-     about what might happen jf the concrete pipe should
 zation of the use of the installations is more difficult,    crack some place and the system were even breached
 and also more important. Also, the importance of the         somewhere.
 visualization increases with increasing expected ef-             Let me not continue with describing all that is
 fectiveness of the system, that it is more important         difficult to foresee. It is clear that the list could be
 to know what might happen in a blast shelter than in a       continued beyond what your patience would stand.
 simpler fallout shelter. The djfficulty of visualizing      What follows from all this? It seems to me that there
 this is greater than in the case of a reactor because        are several consequences. First, that a determined
 the reactor is built by us; the attack against us, if it     effort should be made to visualize the consequences
 comes, is mounted by others. Thus, many of the               of a test of any proposed defensive arrangement.
 circumstances are outside our control. The attack            The visualization should extend to the physical
 may come by day, when people are at work, or at              effects: blast, that is, pressure, wind, heat, radia-
 night, when they sleep. It may come-and jf it comes,         tion, earthmovement, sound, shock, and so on. It
 probably will come-after demands by the enemy that           should also- extend to the behavior of people, the
 our government has to refuse, or it may come-                tensions and anxieties generated in them at the time
 though probably will not-as a surprise. It may con-          of the attac,'k, the effect on their resolution, after the
 sist of bursts at high altitude, to cause fires and          attack, to build anew, more secure nation and me




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for themselves. All this must be explored whether         think of shielded vehicles, able to withstand a heavy
or not you believe, as I do, that if our defense is       shock-wave, for stamping out incipient fires, for
good, the attack will never come and the defense w1ll     clearing rubble, for evacuating people from too
not have to be tested. Because the defense is only        heavily affected areas, perhaps for transporting
good and only effective for discouraging an attack if     some to locations where they may be able to per-
it is really good, if no one can find an Achilles heel    form some useful function. There may be a need
on it. The one who wishes to destroy the defense has      for inner gates in the shelters to be opened when
as much imagination as we do, who want to prepare         the attack seems to have ceased. It is not clear to
it; his desire for destruction may give him more          me even that we cannot have airplanes, manned or
imagination.                                              unmanned, that can survive a shock-wave and can
    The three problems that the study at the Oak          survey the terrain for damage and radiation. Flexi-
Ridge National Laboratory started to investigate          bility is particularly important if our knowledge is
are still with us, and they are still very important      limited.
problems. However, they become parts of a much                There is another proposition that seems unavoid-
larger and much more difficult and much more im-          able; it has been made already in·the course of the
portant problem: to build a passive defense, to build     Harbor Study: that we must build, if we want to be
its details, but also to build the whole conSistently     effective, as many components of the defense sys-
and coherently.                                           tem ahead of time as possible. What the Harbor
    That we must learn more is the first thing that       Study said is that we should build a prototype and I
follows from our ignorance of many factors that may       believe we all agree with that.
be relevant. We must try to reduce-in fact to                Above all, however, we must try to increase our
eliminate-our ignorance. The second conclusion            ablllty to foresee the functioning of our defense sys-
is, it seems to me, that we must build flexibility        tem in as much detail and with as much certainty and
into our system. In the case of a nuclear reactor,        accuracy as possible. This w1ll take a lot of thinking,
I mentioned the control rod; I could have mentioned       a lot of experimenting, a lot of cooperation and ex-
the arrangements to heat up the moderator, to dis-        change of views. In this regard, this conference was
charge various parts'of fuel at different intervals.      a wonderful beginning and I wish to close with thanks
It seems to me that perhaps we have so far paid too       to those who have conceived this conference, to those
little attention to flexiblllty. We spoke about every     who have made it possible-our Office of Civil
civilian seeking the protection of the shelter. Is this   Defense in the first place-and, last but not least, to
really possible or desirable? Can we abandon the          those who have not spared any effort to organize it
outside completely if only temporarily? I do not          and who have put in a great deal of effort to make it
think so. It is necessary to maintain some measure        a success.
of control over it-it may mean so much. One can




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                           CONTENTS


DESIGN CRITERIA/WEAPON EFFECTS                                                             1

  Blast and Other Threats
     Harold Brode  0   0   0   0   0   0       0   0   0   0   0   0   0
                                                                                           3 '
  The Intensity and Distribution of Initial and Residual
   Radiation
    Harold Knapp   0   0   0   0   0   0   0       0   0   0   0   0   0                  21
  PossibUities of Occurrence of Area Conflagrations and
   Firestorms with Respect to Fuel Density
    Hermann Leutz      0   0   0   0   0   0       0   0   0   0                          31

DESIGN CRITERIA/TOLERANCES AND INTERNAL
 ENVIRONMENT                                                                              39

  Tentative Biological Criteria for Estimating Blast Hazards
     Clayton So White  0   0   0   0   0   0       0   0   0   0   0   0   0              41
  Radiation Tolerance from Fallout in Protective Structures
     Robert Ao Conard  0   0   0   0   0   0       0   0   0   0   0   0   0              55
  Fire and Noxious Gases: Effect on Internal Environments
   of Protective Shelters
     J Enoch Johnson and Eugene Ao Ramskillo
      0                                                                                   58
  Gamma- Ray Streaming through Ducts
     Charles Mo Huddleston     0   0   0   0       0   0   0   0                          65

DESIGN PROCEDURES/RADIATION                                                               87

  Problems of Shielding against Initial Radiations
     Lewis V Spencer
             0         0   0   0   0   0   0       0   0   0   0   0                      89
  Shielding Experiments
     A. B. Chilton . . . . . . . . . . . .                                                95
  The PasSing Parade of Shielding-Analysis Methods: A
    Review of the State of the Art
     Kenneth Go Farrell    0   •   •   •   •       •   •   •   •   •   •   •   •     •   107
  ICHIBAN: The Dosimetry Program for Nuclear Bomb
    Survivors of Hiroshima and Nagasaki
     John Auxier. •    0   •   •   0   0   •       •   •   •   •   •   •                 121

FIRE-SAFE SHELTER DESIGN                                                                 127

  Fire-Safe Shelter Design
     John "Go Degenkolb • • • • • • • • • • •                                            129
  Fireproof Shelters with Secured Ventilating Systems
     Hermann Leutz •       0   •   •   •   •       •   •                             •   134
  Fire-Safe Shelter Design-Swedish Views
     COsta Smitt • • • • • • • •                   0   •   •                         •   139
  Fire-Safe Shelter Design-Canadian Views
     Gordon Shorter    0   •   •   •   •   •       •  • • • •
                                                       0                                 146




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DESIGN PROCEDURES/BLAST                                            149

  Footings for Protective Structures
     Robert V. Whitman and Ulrich Luscher • • • •            •   • 151
  An Engineering Approach to Protective structures
     Neal FitzSimons • • • • . • • • • • •                   •   • 159
  State of the Art in Dynamic Analysis and Techniques for the
   Design of Underground Protective Construction
     Nathan M. Newmark. • • • • • • • • •                        • 166
  Model AnalysiS
     I. LI. Davies                                           •   • 180

DESIGN DETAILS                                                     191

  The Behavior of Shock Waves in Ducts and When Entering
   Entrance Structures
     H. Schardin and H. Reichenbach. •                     • • 193
  Blast-Closure Systems
     Edward Cohen and Samuel Weissman •                      • 207
  Ventilation and Air Cooling in Protective Structures
   . Eugene E. Drucker • • • • • • •                   • • • • 226
  A Prefabricated Blast-Resistant Shelter
     E. Basler                                       • • • • • 237

CASE STQDIES                                                       245

  Activities in the Field of Protective Recommendations,
   Measures, and Construction in The Netherlands
     P. J. M. Ruyters. • • • • • • • • • • • • • •                 247
  A Swedish 200-psi Blast-Resistant Seven-Man Shelter
     Sune Granstrom • • • • • • • • • • • • • • •                  263
  The Use of Underground Parking Lots and Garages for
   the Protection of Civilian Populations
     Hans Walter • • • •               ••••••••••                  269
  Public Shelters in Denmark
     H. W. Rich. • • • • •                             • • • •     275
  Canadian Use of Reinforced Plastics in Blast Shelters
     s. N. WIllte. . . . . . . . • . . . . .                  •    281
  Technical Aspects of the Austrian Shelter Program
     E.P~hauser • • • • • • • • • •                           •    286
  Examples of Swiss Protective Structures
     G. Schindler • • • • • • • • •                 •••••          292
  The Protection against Fallout Radiation Afforded by Core
   Shelters in a Typical British House
     D. T. Jones. . . . . . . . . . . . . . . . .                  298
  Public Shelters in Norway- Protection against Ground Shock
     Arnfinn Jenssen • • • • • • • • • • • • • • •                 304
  Cooperative Group Shelter near Livermore, California
     Arthur J. Hudgins. • • • • • • • • • • • • • •                307
  Actual versus Hypothetical Fallout-Shelter Case Studies
     James Roembke • • • • • • • • • • • •                    •    316
  Targeting Assumptions for Attacks against Populations                  ../
     Harold A. Knapp • • • • • • • •                      • • •    322
  Metropolitan-Area Blast-Shelter System
     David L. Narver, Jr. • • • • • • •
  A Risk-Oriented SoluUon for a Target Community
                                                          • • •    333   J
     Howard P. Harrenstien •                        • • • • •      338

PARTICIPANTS • • • • •                                    • • • 349



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DESIGN CRITERIA/WEAPON EFFECTS

     Lyndon Welch, Chairman




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                                  BLAST AND OTHER THREATS*

                                           Harol d Brode
                             The RAND Corporation, Santa Monica, California


 INTRODUCTION                                                 purpose bombs or even block-busters must strike
                                                              (or nearly strike) a structure in order to cause
  The current prevalence of nuclear weapons and their         heavy damage. Underground shelters are not vul-
  dominance as a threat to civil populations requires         nerable to such explosives unless the weapons
  that some assessment of their direct physical effects       penetrate to or into the shelter. World War n saw
  be included in any comprehensive civil-defense              the mClWlting of enormous load-carrying capacities
  study. The emphasis in this pa,per reflects the rela-       in the bomber fleets then constructed. Such air
  tive importance of nuclear weapons as wartime               armadas no longer exist, nor are they necessary for
  hazards to a nation's populace. Threats from weap-          delivery of nuclear weapons, but their absence from
  ons other than nuclear may be somewhat more                 current air forces precludes immediate or near-
  serious for some nations than for the United States,        future threats of heavy bombardment by chemical,
  because of variations in their size and in their            explosive weapons. Missile accuracies and load-
  proximity to potential attackers. In some circum-           carrying capacities, although seemingly ever-
  stances, bacteriological weapons pose a potential           increaSing, do not promise effective delivery and
  threat; however, chemical agents and high explosives        city-target destruction in the foreseeable future.
  are less of a threat than nuclear weapons in the               Although still very much a force in tactical and
  context of large-scale population-center attacks.           limited warfare engagements, high-explosive weap-
. Although there is no guarantee that novel, "Sunday          ons are currently less of a threat to civil populations
  Supplement" type, super-effective weapons will not be       and national survival than they were 20 years ago.
  developed in the future, there is no current develop-           Nonetheless, there are numerous situations that
  ment program or any research effort that shows              could favor a resurgence of high-explosive weapon
  promise of finding one that will be effective against       employment. At present, both cold-war skirmishes
  large areas and large populations. Many new de-             and limited wars of liberation (or insurgency) either
  velopments have interesting lethal applications; but,       threaten or actually employ high-explosive bombard-
  we have not been able to identify any that present          ments. If such wars become more intense and con-
  threats likely to be of major civil-defense concern         tinue for long periods, it is highly likely that suffi-
  for the next few decades. Practical logistics limita-       cient aircraft will be assembled to make aerial attack
  tions on delivery and distribution of any new offen-        a serious threat even to civilians in towns and cities
  sive weapons have so far always overwhelmingly              of involved states.
  favored more compa,ct and far-reaching nuclear                 At some future time, with the happy advent of a
  weapons. The virulence and potential lethality of           successful nuclear disarmament, chemical explosives
  other agents should not be minimized or dismissed;          may again become the most serious threat to survi-
  their role in modern, large-scale war is more a             val of structures and materials.
  grim tribute to the high efficiency (for destruction
  and lethality) of nuclear weapons variously employed
  and delivered.                                              Biological Warfare

                                                              Biological warfare as currently conceived depends
 NON-NUCLEAR WEAPONS                                          on the exploitation of pa,thogenic organisms known in
                                                              nature. Since the development of entirely new orga-
 Chemical High-Explosive Weapons
                                                              .Dr. Brode's presentation is derived from his report:
 As in pa,st aerial warfare, bombs and missiles                "A Review of Nuclear Explosion Phenomena Pertinent
 carrying chemical explosives to targets are capa,ble          to Protective Construction," May 1964. published by the
 of extensive damage only when delivered in large              RAND Corporation (R-425-PR). Space limitations of these
 numbers and with high accuracy. The usual general-            Proceed1ngs prevent reprinting that report in its entirety.


                                                          3

                                                                                           Digitized by   Google
nisms is highly improbable, the future threat from            describe the very much less effective use of col-
biologic agents may be limited to somewhat more               lected radioactive wastes in aerosol spray or powder
virulent or resistant strains of existing organisms.          form, could be used to increase the level of local
    Biological agents can cause. great suffering and          fallout. Such special nuclear weapons might produce
loss of Ufe. Further, there exist credible military           some particular isotopes that give off more ener-
and political situations that could make their use            getic, and so more penetrating, gamma rays than
attractive, particUlarly in nations of smaller area           are present in the normal fission products, or
and with high concentrations of population. For               could concentrate activity in particular half-lives
instance, it is possible to be defended against nuclear       so as to maximize radiation hazard in a particular
attack and still be wlnerable to biological agents.           time period. Another possible modification might
The most intense lethal-agent development has been            be aimed at producing a particUlar isotope that,
concentrated on those for attack on humans, but               because of chemical or physical properties, might
agents damaging to crops and livestock are also               more easily enter and concentrate in living orga-
available. Although the impact on our economy                 nisms and so increase biological effectiveness.
could be enormous, in view of the huge effort neces-              The advantages of such modifications are much
sary to deliver such an attack, and the rather in-            less real than apparent. In all weapons delivered by
direct and problematic results, there appear to be            missiles, minimizing the payload and total weight is
a number of more serious threats.                             very important. If the total payload is not to be in-
    Most biological agents are inexpensive to produce;        creased, then the inclusion of inert material to be
their effective dissemination over hostile territories        activated by neutrons must lead to reductions in the
remains the chief deterrent to their effective employ-        explosive yield. If all the weight is devoted to nuclear
ment. Twenty square miles is about the area that can          explosives, then more fission-fragment activity can
be effectively covered by a single aircraft; large            be created, and it is the net difference in activity
area coverage presents a task for vast fleets of              that must be balanced against the loss of explosive
fairly wlnerable planes flying tight patterns at              yield. As it turns out, a fission explosion is a most
modest or low altitudes. While agents vary in                 efficient generator of activity, and greater total
virulence and in their biologic decay rate, most are          doses are not achieved by injecting special inert
quite perishable in normal open-air environments.             materials to be activated. The increase of dose
Since shelter and simple prophylactic measures can            rate at one time, using special isotopes, can be
be quite effective against biological agents, there is        bought at the expense of lower rates at earlier
less likelihood of the use of biological warfare on a         and/or later times. The maximum increase of
wholesale basis against a nation, and more chance             intensity above that from fission products alone is
of limited employment on population concentrations            not great compared to the usual uncertainties in
-perhaps by covert delivery, since shelters with              fallout intensities due to details of the meteorology
adequate filtering could insure rather complete               and the point of burst. The possible advantages in
protection to those inside.                                   radiological weapons are complicated and uncertain,
                                                              while the disadvantage in giving up explosion energy
                                                              available for blast and thermal damage is obvious
Chemical Weapons                                              and frequently serious.

Chemical weapons, like biological weapons, are
relatively inexpensive to create, but face nearly             The Neutron Bomb
insurmountable logistics problems on delivery.
Although chemical agents produce casualties more              The neutron bomb, so called because of the deliber-
rapidly, the greater amounts of material to deliver           ate effort to maximize the effectiveness of the neu-
seriously limit the likelihood of their large-scale           trons, would necessarily be limited to rather small
deployment. Furthermore, chemical research does               yields-yields at which the neutron absorption in air
not hold promise of the development of significantly          does not reduce the doses to a point at which blast
more toxic chemicals for future use.                          and thermal effects are dominant. The use of small
                                                              yields against large-area targets again runs into the
                                                              delivery problems faced by chemical agents and ex-
SPECIAL WEAPONS                                               plosives, and larger yields in fewer packages pose a
                                                              less stringent problem for delivery systems in most
Radiological Weapons                                          applications. In the unlikely event that an enemy
                                                              desired to minimize blast and thermal damage and
Radiological weapons, a term that has been applied            to create little local fallout but still kill the populace,
to nuclear weapons arranged so as to produce larger           it would be necessary to use large numbers of care-
amounts of radioactivity, but sometimes used to               fully placed neutron-producing weapons burst high


                                                          4


                                                                                      Digitized by   Google
                 [zlast damage 0:&1                                                       increasing numbwBu  Bn[[lear weapons
enou[[[[           neutrons down~              how-                                     klnt previously         *,**,rth attack-
ever, adequate radiation shielding for the people                      ing may become important. (2) Future views of
would leave the city unscathed and demonstrate the                     weapon employment will surely be colored as much
attack to be futile.                                                   by the changes in the numbers, aiming accuracies,
                                                                       and efficiencies of new weapons as by other possibly
                                                                       novel characteristics of new weapons systems. (3)
                                                                            u**,*,-"**,,%[[,,Ctllon rates, W       be influenced
                                                                                    BGklCepts of warfaBG,         lGcreased
                                            Y:;JI'BBibility of
                                    ~C'U*,~S?"'JJ",                                        for penetratiukl      mlissile war-
                                                    avoiding                           ,~,%,rrespondingly    -%[[li[[s11e defenses,
                                                       to                           [[{"leration of entieGlb              resulting
blast ,i"mage.       special consRuction anY:; fuzing,                 from ttie appearance of weapons SYS%[[*"lS not cur-
nuclear weapons can be made to penetrate the ground                    rently anticipated.
before detonation. Such penetration is, for a number
of reasons, limited to depths of, at most, about 100
ft, unless new and more elaborate concepts of dig-in                   NUCLEAR EXPLOSIONS
mechanisms are discovered and made practical.
UnI:a',B        [[,,%[[ll-yield weaY:;Oklkl        in con-
                     penetration,
               [[oy:;raded, buttheBo                                                                          [['Z[[%,%[[panied by a
                      thermal radiatiBB,                                                                                    radiations
will                  intensified VklU[[          Uze point                                                            Gnd of the
of destruction, and much reduced at larger distances                   scattering and absorbing properties of the explosion
down-wind.                                                             surroundings. Enormous amounts of energy are very
                                                                       suddenly released in rather small masses and
                                                                       volumes, creating such high temperatures that a
Nuclear Weapons                                                        considerable fraction of the energy must escape
                                                                       from the weapon as radiated light or heat. But since
    Num[zklUkl, [["ugets, and yieldf~                                                      energy releau,*         *,fmGsphere or
singlu               ,;:uplosion are                                                     ,unnot escape               immediately
stoo[[;        UUUUUBment of damay:;u                                                      extreme pre[[G%'GGU       [[*,eated by
atta,:[[            c:u:etain because                                       ",J,~~~~~~'~ kating and are               lGng enough
of th"                   weapons empIBY:;uY:;,                                          GtGong blast-wavG~       lGb[[uGities of all
the intended targets. Thus, when projecting into the                   these initial phenomena are so high as to be capable
future, estimates differ on yields and numbers of                      of causing significant damage to people or to struc-
weapons that a nation may possess. Using a country's                   tures and equipment at far greater distances than
total capabilities as a basis, without regard to either                would result from attack by any other type of
intent or competing demands within the country or                      explosive weapon.
outsiY:;u,              ,zonstruct uppe*,            [[ields and
numbUUB                  frequently too               useful.
Put                      there are no                  over-
                     liu,ltations on eW~,u,~           of weap-
on                      bield) or the nUInbnB    wUklpons that                       GGITkltions, both                   klGd long-
can      ll'*,'IITUe[[nred. Therefore                 brofitable                           required                    Y:;B"tection from
in making future projections to consider some other                    them are discussed in subsequent papers. Generally,
equally indefinite factors. A vague, but historically                  for large-yield (multi-megaton) explosions, the
supported, conclusion from past attempts at predict-                   prompt or initial radiations cannot penetrate the
ing future enemy weapon stores is that, for the next                   surrounding air in sufficient intensity to be a serious
few years and perhaps well into the next decade, the                   hazard at the greatest distances at which serious
                       l",rge-yield weaRn,le            class)                            or thermal ra[['*'Uon             can still
             "~J'nli' "" in tens, while            (tins sian)                         ",UITmize the arnn               bnstruction
                          class may nun1be!~          bundreds.                          ignitions, nuclnnB               %[[ust be
But                    ",ust inevitably                                   '~J"JH~~'~~, wdl above the eaGtb
                          continue to be n%[[wwte,                                         extensive local J",'J~'",'~
additional sovereign nations develop R,eir own atomic                  reason, atb*,cbs directed agaRwt urtnnn centers
forces.                                                                could well be devoid of nuclear-radiation hazards,
    A most important caution follows from the easy                     either prompt or fallout.


                                                                   5
FIREBALL FORMATION                                             scale) for a 1-mt surface burst. The earliest
                                                               curve-0.075 millisecond (ms)-is characteristic of
In the explosion of a I-megaton (mt) bomb, energy              the nearly isothermal fireball formed by the radia-
equivalent to 1015 calories (cal) is released in much          tion diffusion. At later times, the shocked air beyond
less than a millionth of a second and in a mass of a           the isothermal sphere (which itself is expanding and
very few tons. Such high-energy density leads to               cooling) shows a region of lower temperature. As
temperatures of millions of degrees and leaves much            the shock decreases in strength, it heats the air less,
of the energy in the form of radiation. This radiation         so that the air behind the shock is hotter than that
quite quickly diffuses into the air. The radiation             just at the shock, and a steeply increasing gradient
from the bomb materials at such high temperatures              in temperature exists from the shock front back to
is primarily in the form of ultraviolet rays and X-            the nearly uniform hot interior.
rays; and "light" from these high frequencies, unlike
ordinary visible light, does not travel great distances
                                                                       ~-""""'I0.12mHC
                                                                                                                   I               I   :
in air. Rather, it is absorbed in the air immediately
                                                                                                                                       -
around the bomb, causing that air to be heated to
temperatures in the neighborhood of 1,000,OOOoC.
                                                                                      ""\2.2
                                                                                                                                       -
                                                                       ~.                                                              :
                                                                                                                                       -
                                                                                                \
                                                                                                                 ~"
However, air at 1,000,000°C becomes quite trans-                                                            \
parent, even to X-rays and ultraviolet light, so that                                                                                  -
subsequent radiation from the bomb can traverse
this region of hot air more freely and can be ab-                      -                             II                44
                                                                                                                                  ~:
sorbed only when it reaches the cold outer air. By                                                                                     -
such a process, this initial region of hot air grows
rapidly as energy pours out of the bomb and is                               ..          .          .                                  =
                                                                                                                                       -
absorbed in surrounding cold air. The cold air is                      -          I                                I               I
                                                                                                                                       -
so opaque to soft X-rays that a rather sharp, fast-                                       200               400             600
                                                                                                           R(m)
moving front is maintained between the cold outside            Figure 1. Fireball temperature versus radius at early
air and the hot inside air.                                    times in the fireball history (l-mt surface burst).
    The initial radiative growth of this high-tempera-
ture sphere takes place before hydrodynamic shocks
can develop. But as the energy expands by this                    Since the radiation-diffusion growth is initially
radiation-diffusion process into larger and larger             too fast to induce appreciable motions in air, the air
volumes of air, its temperature begins to drop and             is left at essentially normal air density, while its
the speed of the expansion decreases, until, at about          temperature and pressure are raised to values on
800,000°C, the rate is comparable to a shock speed             the order of 1,000,000°C and 1,000,000 pounds per
at the same temperature. After that, an extremely              square inch (psi). As the radiation wave slows in its
strong spherical shock front develops and races                growth and the high pressures begin to build a
onward at extremely high speed. For a 1-mt surface             strong shock, air in the hot interior begins to ex-
burst, this transition should occur at a radius of             pand to lower denSities, while the shock that forms
about 170 ft from the bomb. The extremely strong               at the outer radius compresses the air there to _
shock, driven by high pressures in this hot sphere,            many times normal air density (PQ = 1.293 x 10- 3
begins to compress the air some tenfold above                  grams per cubic centimeter, or g7cm3). (See
normal air density and to force it outward close               Figure 2.) The interior of the fireball is rapidly
behind the shock front. Since the shock is expanding
into continuously larger volumes of air, its strength,
and consequently its ability to heat the air it engulfs,
decreases rapidly with increasing shock radius.
Although the shock-heated air is initially at tem-
                                                                  1.0 .....""""-...,...-t--I----+--+---""--t-+--.....
peratures well below the interior temperatures, it
is hot enough to be intensely luminous (with inten-             PIPo
sities many times that of the sun). This shock front
is the source of early thermal radiation. As the                   O.II-----t-#---fl------,f-t----I
shock decreases in strength, its luminosity decreases
so rapidly that the total radiation from the fireball
also decreases, in spite of the increasing area of the
expanding shock front.                                           0.01 L....&.:::±:::::E::=I=c=:cz:::t::;:,......L--I._~..I-..L...J
    Figure 1 illustrates the early temperature history               o              200             400
                                                                                                          R(m)
of such a blast-wave, showing the temperature in de-           Figure 2. Fireball density versus radius at early times in
grees on the Kelvin scale (the absolute centigrade             the fireball history (l-mt surface burst).


                                                           6

                                                                                                    Digitized by   Google
evacuated, 80 that by the time the shock has de-                                              the visible spectrum; and only that fraction that is
creased to a peak pressure of 1,000 psi (-74 ms at                                            in wavelengths in the visible or infrared spectrum
1,500 ft for 1 mt), the interior density is about one                                         can travel to great distances. The power or rate of
hundredth of normal air density-a fairly good.                                                thermal radiation at the earlier times can be ex-
vacuum I                                                                                      pressed as proportional to the surface area of the
   The pressure profiles at these early fireball                                              nearly hemispherical fireball (2W'R2) and to the spe-
times are shown in Figure 3. The earliest air over-                                           cific black-body radiation rate at tRe shock tempera-
pressures are indeed on the order of 1,000,000 psi,                                           ture (dr:), but modified by a factor f(Ts) represent-
but they rapidly drop as the fireball grows, so that                                          ing that fraction of the spectrum that can plSS
a peak overpressure of 100,000 psi occurs at about                                            through cold air:
350 ft (for 1 mt) and an overpressure of 10,000 psi
at about twice that distance.                                                                 P = IfR2 aT 4 f(T )
                                                                                                     s    s    s
      100

              Ft'
                                          I                I                      I   _
              ~      o.I2mMC
                                                                                      -
                                                                                      -
                                                                                                  At times as late as those shown in Figure 4, the
                                                                                              shock front itself is becoming 10 cool that it is no
         10                2.2
                                                                                              longer strongly luminous, and the hotter air behind
              ~                                                                       :
  p
 (Kb)
              ~/
                      ~                                                               -       begins to shine through. The hot interior is stUl
                                                                                      -       expanding, and its radiation intensity is increaSing
          1                                                                                   rapidly with the increased effective temperature that
                                       ./ tt                         ,   ...          :
              =-                                                          "
                                                                            .         -       can be seen from outside the fireball (as the outer
                                                       ~       44                     -       air becomes more transplrent). ConsequenUy, the
      o.1
              ."                                                                              thermal power rises sharply at this time. As the

                                                                          ~:
                                                                                              rate of radiation increases, it becomes a significant
                       I                                                      •   I
                                                                                              heat loss to the fireball and depletes the store of
          I                                                                                   energy in the hot interior. This loss drops the inner
                                 200             400                600
                                               R(m)                                           temperatures and the thermal power again decreases.
Figure 3. Overpressure versus range at early times In the                                     The subsequent depletion and COOling rates become
shock-wave growth (l-mt surface burst).
                                                                                              less rapid as the temperature drops, so that the
                                                                                              thermal intenSity trails off over a period of 10 sec
THERMAL RADIATION                                                                             or more.
                                                                                                  This sequence of optical-hydrodynamic events
Figure 4 shows temperature profiles at late fireball                                          results first in a fast maximum in the thermal
times for the same 1-mt surface burst. As men-                                                radiation, followed by a minimum at about 1/10 sec,
tioned, most of the earliest light from the bomb                                              and then by a second maximum at about 1 sec. Since
cannot travel far in air, but, as a shock develops                                            the time duration of the first maximum is short and
and the surface of the fireball becomes a sharp                                               the size of the fireball is small, less than half of 1
shock front, this surface begins to radiate strongly                                          per cent of the bomb's energy is radiated before the
in the visible spectrum at an intensity characteristic                                        first minimum in the power pulse is reached. The
of a black body at the shock temperature.                                                     second pulse is longer and radiates from a larger
   At times earlier than those illustrated here, oniy                                         effective surface, and it emits nearly one third of
a fraction of the black-body rate (which is propor-                                           the total energy of the bomb. The main pulse of the
tional to the fourth power of the temperature) is in                                          thermal radiation reaches a maximum in about 1
                                                                                              sec (for the 1-mt case) and lasts about 10 sec
                                                                                              Figure 5).
                                                                                                  At very close-in locations, the thermal phenome-
                                                                                              non may be characterized as an intensely hot ''bath''
                                                                                              of fireball gases rather than as light impinging on
                                                                                              exposed surfaces. Figure 6 illustrates the time
                                                                                              history of the air temperature at some peak over-
TC'"K)
                                                                                              pressure levels. The 40-psi point is outside the
                                                                                              fireball's maximum radius so that, as the shock
                                                                                              strikes, the air temperature is raised about 150°C
                                                                                              but cools again within a few seconds to near normal.
                   1=0.115 sec           0.10              2.2                                At the 100-psi station, which is on the edge of the
      1000~~~~~~~~-2~~~~~3~~~~                                                                fireball, the temperature continues to rise some-
                                               R(Km)                                          what after shock arrival. The shock, being stronger
Figure 4. Late fireball temperature versus radius (i-mt                                       here, heats the air to a higher initial temperature
surface burst).                                                                               of about 400°C. The air behind the shock is still


                                                                                          7
                                                                                                                         Digitized by   Google
                                                                           temperature has returned to normal. The other
                                                                           high-temperature curves would be similarly reduced
                                                                           at late times and by the same effect.
                                                                              At the 400-psi and 1,OOO-psi levels, the tempera-
                                                                           tures rise even higher but subsequently show a more
                                                                           rapid drop (at times less than 1 sec) because of
                                             1/2
               IIUD Tbermal Palae: tmu: :II WIIT.ec:
                                                                           thermal-radiation loss, which becomes significant
                                                                           even before the fireball has begun to rise.
                    P         .. 100 wi/2 ! 110ft KT/.ec:                     The thermal energy radiated in such relatively
                        mu:
                                                                           short times will result in impressive heat loads on
                Tbermal BDarlD':II    i WilT· i      10111 WilT cal.
                                                                           any exposed surface, even far beyond the fireball.
                lI'n'_.' tmin:ll          1/2
                                      .1 WilT aec:                         One fourth to one half of the yield "shines" away in
                                                                           a matter of seconds. The intensity (measured in
                Firat Palae: p..     twa!" T! t(T.)                        calories per square centimeter, or cal/cm2) must
                    BDa. Ia Drat palM        < • 0011 WIlT                 decrease faster than the inverse square of the dis-
Figure 5. Thermal radiation rate.                                          tance from the burst because of absorption and
                                                                           scattering in the intervening air.
                                                                               For purposes of approximately estimating the
expanding, but since it was shocked to even higher                         thermal load from various-yield explosions as a
temperatures, it exposes the 100-psi point to higher                       function of distance from the burst, the following
and higher temperatures until the expansion stops.
                                                                           formula should suffice for air- burst weapons:
The air flow reverses and eventually ends in the
general rising away of the hot remains of the                                           EcalT       1012WKTT(R) WKTT(D/V)
fireball.                                                                  Q(cal/cm2) = - - - : : :            ::: -.,;;:;..;;:......,,--
       I~                                                                               4trR2         121TR2              D2
                                                                                             cm            cm                 mi
                                                                           where Ecal represents the thermal energy emitted
                                                                           (in calories) and is here approximated as one third
                                                                           of the total yield (W) in kilotons (kt); D is the dis-
                                                                           tance from point of burst in miles (mi); R is the
                                                                           same distance in centimeters; and T is the transmis-
                                                                           sion factor. The transmission factor T in the above
                                                                           approximation depends on the atmospheriC conditions
                                                                                                                             f
                                                                           and may be estimated in terms of the usual visibility
                                                                           criterion. Recent estimates(2) of transmissivities for
        ~.~~~~~~~~~~~~~
         O.t 0.3 1
                                                                           great distances in clear sea-level air follow approxi-
                                                                           mately the nearly exponential form T = (1+1.4D/V)
                                 Tim. (sec)
                                                                           exp (-2D/V). This form is represented in Figure 7.
Figure 6. Temperature versus time at high peak over-                           The thermal radiation from a surface burst is
pressures (l-mt surface burst).
                                                                           expected to be less than half of that from an air
                                                                           burst, both because the radiating fireball surface
   The 200-psi point is well inside the maximum                            is truncated and because the hot interior is partially
fireball radius, where the temperature rise after                          quenched by the megatons of injected crater mate-
shock arrival indicates that much hotter air engulfs                       rial. Such degrading factors as attenuating clouds,
this station. Here the temperature rises from a                            smoke, haze, fog, dust, or chance shielding by inter-
shock value of 1,000'1c (-700°C) to about 4,OOO'1c in                      vening topography, structures, or natural growth
less than a second.                                                        further limit the coverage and the exposure at great
   Since the fireball is like a bubble in the atmos-                       distances from surface or low-altitude bursts. At a
phere, it begins to rise and pulls away from the                           number of miles from low-altitude or surface bursts
earth's surface in only a few seconds. Using a very                        even those of large yield, these combined effects of
approximate model for the effect of this fireball rise                     atmospheric attenuation and obscuration by surround-
on temperature history at the distance corresponding                       ing terrain features very greatly degrade the thermal
to a peak overpressure of 200 psi, it appears that the                     loads to exposed surfaces.
hot temperatures of the fireball interior will be re-                          Even closer, at the higher levels, heavy thermal
duced at this ground range in approximately the                            damage to protective structures is not expected,
manner indicated by the decreasing tail on the 200-                        since the duration of heating is too short for appre-
psi curve of Figure 6. Thus a decrease begins after                        ciable conduction beyond the surface layers of ex-
4 or 5 sec of exposure, and in 15 to 20 sec the air                        posed materials. Some pitting and charring, even


                                                                       8

                                                                                                           Digitized by   Google
     '~~---'r----r----'-----r---~----~                            Electromagnetic Pulse

                                                                  Strong electromagnetic signals are observable from
                                                                  nuclear explOSions. These signals, which extend
                                                                  through the entire radio and radar spectra, are a
                                                                  result of the intense ionizing radiation from nuclear
                                                                  reactions and their asymmetries and earth-field
   .'0" t-----~~-----"~ri_----__I                                 interactions •
                                                                      Where electronic equipment in a protected sys-
                                                                  tem is required to operate continuously throughout
 I                                                                a nuclear attack, care must be exerted to provide
                                                                  magnetic shielding and electrical isolation from
 J           =
           Y villbility (diltance)
                                                                  transients induced in external conductors.
                                                                     If an installation involves long lines of conduct-
    'O~t-----~-----~-~~--~                                        ing cables or extensive wired connections beyond a
                                                                  localized facility, some provision should be made
           Curve 1. DASA '376 IIItrapoiation af ENW               for protection against permanent damage due to
           Curve 2. M. G. Gibbons, USNRDL TR 236                  excessive currents induced by the low-frequency
           Curve 3. DASA '376 .trapoIation to ICIfge
                     dilfancn of IIIIOtWIIMfIfI made              component of the electromagnetic pulse. Such pulses
                     at 1..01 AnteI.. -and at tile Nftada         and protective provisions may be thought of as
                     Tnt Sit.                                     analogous to those for natural lightning strokes.
    'O~~-~~-~--~--~--~-~                                             The induced pulses are, in general, character-
       °                                        2
                  Oiltonc:e in It"'" of vllual rGII9I (DIY)
                                                                  ized by high power but low energy, which is the
                                                                  consequence of their highly transient nature.
Figure 7. TransmissIvity as a function of distance in units       However, very-low-frequency components of the
of vlsIbll1ty.
                                                                  pulse may exist to such an extent that both electric
                                                                  and magnetic fields may be propagated to consider-
                                                                  able depths below the earth's surface (correspondini
                                                                  to large "skin depths"). Electronic gear that re-
some evaporation or blowoff from steel or concrete                sponds adversely to such very-low-frequency field
surfaces may occur; but reinforced-concrete doors                 changes should be mounted and protected with these
mounted flush with the ground surface do not suffer.              phenomena in mind.
Elements exposed above ground-level mayexperi-
ence more thermal damage, and such structures
will also be more subject to blast damage.                        Cratering and Direct Ground Shock
    Inside the fireball, hot air enveloping a protected
structure produces a very corrosive environment,                     Cratering. The crater that results from a nuclear
but even here the transient nature of the thermal                 detonation on hard rock has dimensions roughly 20
load works to limit the damage. At typical fireball               per cent smaller than those of a similar burst on
temperatures, the air itself does not readily trans-              soil or soft rock; i.e., a burst on rock excavates a
port the radiant energy, 8.\ld the first vaporized                crater volume only about one half of that expected
material from the surfaces forms a protective                     from a burst on soil. The efficiency of cratering by
screen that inhibits the subsequent flow of heat to               nuclear explosives depends on more than just the
the remaining solid surface. Calculations of ther-                nature of the medium (hard rock, soft rock, dry soil,
mal damage are necessarily complicated by such                    saturated soil, etc.); it varies also with the depth of
obscuration considerations, but observed effects                  burst and with the yield of the explosive, and is
are indeed negligible despite what simple heat-                   further sensitive to some details of the weapon and
transfer notions would predict.                                   of its immediate surroundings at the instant of
   Designers must work to avoid damage to door                    detonation.
seals or to interiors that occur through contact with                 The effect of depth of burst is particularly dra-
hot fireball gases. Ingestion by ventilating systems              matic for nuclear explosives near the surface. The
and other openings generally must be prevented, but               relatively small mass and physical dimensions of a
the major design problems do not hinge on the tem-                nuclear charge (in comparison with the mass and
perature or thermal-radiation effects that charac-                size of its high-explosive equivalent) makes the
terize the fireball. There are other, even more                   crater from a low air burst or contact burst much
undesirable environmental conditions within the                   less impressive, while, for an adequately buried
fireball than the brief, but intense, high-temperature            and tamped nuclear charge, the surrounding earth
exposure.                                                         in large part compensates for the disparity in ex-


                                                              9

                                                                                             Digitized by   Google
plosive mass and size. The dependence of crater
radius and crater depth on depth of burial of a 1-kt
nuclear charge is illustrated in Figure 8. Some
typical data points are included. The sharp change
in crater efficiency at the exact surface of the earth
is exaggerated.                                                      -
                                                                     E
                                                                     j   100
                                                                     •
                                                                     c
                                                                     •
                                                                     E
                                                                     ~

                                                                     i
                                                                     u
                                                                          10




                                                                         0 .0
                                                                                             Yield
                                                                 Figure 9. Crater scaling.

                                                                 crater formation.
             o             20          40           60
                                                                    Although such a calculation may include the
                 Scali depth of bunt (m/KT lIs)
                                                                 effects of both the high pressures of the bomb-vapor
Figure 8. Crater dimensions versus depth of burst (1 kt).        residual energies and the pressure or impulse from
                                                                 the air-blast slap (see Figure 10), early results have
                                                                 shown that only the extremely high-pressure impact
    Crater dimensions may be approximately scaled                of the bomb material itself is important in the exca-
for other-yield weapons by multiplying depth by the              vation process. The air slap does indeed send a
fourth root of the yield (WO.25) and diameter by the             shock into the ground, but it is over a wide area and
yield to the three-tenths power (WO.30). Such an                 at pressures several orders of magnitude less than
empirical scaling is used in Figure 9 to approxi-                those within the direct shock out of the bomb. While
mate crater dimensions for three types of bursts in              the air blast is born in a great fireball, which begins
hard rock: for surface or contact bursts, for shallow-           pushing on an area many times that of the eventual
buried bursts, and for bursts deep enough to maxi-               crater, the remaining energy in the bomb vapors is
mize the crater volume.                                          so concentrated as to vaporize and quite forcefully
    Theoretical work in recent years has contributed             eject the immediately surrounding material. Out
considerably to an understanding of the crate ring               along the surface beyond the region of the crater,
action of nuclear explosives. Viewed in axial sym-               the air-blast slap will induce ground stress that will
metry, the early soil dynamics has been modeled                  exceed any stress directly propagated that far from
with two-dimensional hydrodynamic numerical                      the initially intense bomb shock (that will arrive
methods. Such a model is far from complete. The                  later). But for the cratering action, and for shocks
use of hydrodynamics is strictly justifiable only in             immediately below the crater, the effect of air slap
that region where the ground medium is subject to                is negligible.
stress well in excess of its shear strength, while                   Thus the internal and kinetic energies delivered
final crater dimensions are likely to be influenced              directly to the ground from the bomb are a most
as much by the subsequent lesser stresses and mo-                important aspect in forming a near-surface-burst
tions characteristic of solids under compression and             crater and inducing ground motion below it. For
shear.                                                           this reason, the precise height or depth of burst
    The extremely high-energy densities and tempera-             and the details of the bomb disassembly have an
 tures of a nuclear explosion guarantee the validity of          important influence on the crater and on the energy
a hydrodynamic treatment in studying close-in soil               initially delivered into the soil. Shallow burial and
 response, since the initial strong shock will vapor-            denser bomb cases may enhance crate ring efficiency
 ize the earth for some distance. Because the geome-             by Significant factors.
 try of the burst relative to the interface of ground                A true contact burst might be expected to deliver
and air strongly influences the formation of a crater,           half its momentum downward into the soil and half
a hydrodynamic model in two dimensions, including                upward into the air. However, only a fraction of the
vertical and radial motions, is vital to a description           bomb energy finds its way into kinetic motion of the
of pressures and velocities during and following                 bomb materials. Further, since the soil is at least

                                                            10

                                                                                             Digitized by   Google
a thousand times denser than the air, the dynamics                                            100        -...- .
of a surface burst require, for conservation of
momentum, that the velocities imparted to the soil
be less than those created in the air by just this                                                                       L1~   \
                                                                                                                   ...
                                                                                                  10
                                                                                                                    ~     ~ ~~
                                                                                                                          ~ ~

                                                                                        PEAK
                                                                                       STRESS
                                                                                        (Kilo,)                            \
                     HoI 01"
                                                                                                    I
                                                                                                                          1\ \1\
                           Rodl .. -&Om
                     T.......' ...... - 2 million "K
                         Pr....... - IlO Kba,
                          V.I•• it, - 1 KmlHC                                                                                  1\        \



                     -.   Radiua .... 2m
                     T.mpera"n - 4 million "K
                       Pre..." ..... to' Kbor
                                                                                                  o.1
                                                                                                        10



                                                                                    surface or shallow-buried bursts).
                                                                                                                         100
                                                                                                                                    1\
                                                                                                                           DEPTH (1ft)
                                                                                                                                         1\\ \
                                                                                                                                       1000

                                                                                    Figure 12. Peak stress versus depth in hard rock (beneath
                                                                                                                                                 10,000




                        V.lac", - 1000 KmlHC

Figure 10. Initial conditions for surface-burst cratering                               These calculations are not sufficiently accurate
motion.
                                                                                    at low stress levels to provide direct predictions of
                                                                                    peak earth stress beneath such a crater, but they
                                                                                    are useful in manipulating data from buried bursts
 ratio of densities. The kinetic energy imparted in
                                                                                    to provide such estimates.
this way will be proportional to the square of the
                                                                                       It should be noted that early decay of peak pres-
velocity, and so will be proportionately much less
                                                                                    sure follows an inverse cube of the slant distance
in the dense material. In one example, approxi-                                     from the burst point, as is expected for a strong
mately 15 per cent of the energy from a 4-mt
                                                                                    shock in any medium. At lower pressures, the decay
surface explosion started out into the ground.
                                                                                    approaches a more gradual decay-more like the
    Figure 11 illustrates pressure contours typical
                                                                                    inverse square or inverse three-halves power of
of a surface burst of a few megatons on a relatively
                                                                                    the radius. The pressures shown are intentional
soft volcanic rock material at about 50 ms after
                                                                                    overestimates based largely on the hydrodynamic
detonation. Pressures are in kilobars (kb). Early
                                                                                    calculations. Experience with contained explosions
response is centered in a downward hemispherical
                                                                                    indicates that other dissipative mechanisms provide
shock several meters below the burst point. The
                                                                                    an even more rapid decay of peak stress with
presence of the surface has already caused some
                                                                                    distance.
relief of pressure at shallow depths, but the main
                                                                                        Based in large part on these early calculations,
shock appears to be fairly uniform and spherically
                                                                                    Figure 13 shows peak stress contours for both a
diverging in a vertical cone about 90 degrees (deg)
                                                                                    surface and a shallow-buried burst of 1 mt. Levels
in width.
                                                                                    from 1/2 to 2 kb correspond to the onset of gross
    Direct ground shock. Figure 12 presents some                                    rock failures for most formations and thus repre-
rather arbitrary bands of peak earth stress as                                      sent the range of survival for the best examples of
functions of the depth below surface bursts of 1,                                   underground construction. From the relatively
10, and 100 mt.                                                                     small lateral extent of these contours it is clear
                                                                                    that a weapon must be delivered with great accuracy
                                                       Rodl .. 1m)
                                                                                    to be effective against a structure set deep in hard
      ISO    100     50                        50          100       150            rock, and even a direct hit will not destroy an in-
        --- ------ ---                                                              stallation that is deep enough. Since these dimen-
                          ---                                              2        sions should increase no faster than as the cube
                                                                                    root of the yield, an increase in attacking weapon
                                                                                    yield does not rapidly require excessive depths of
                                                                                    burial.
                                                                                    Air Blast

                                                                                       Shock parameters. Returning to the history of the
  -50mltc
                                                                                    blast, we see in Figure 14 the overpressure profiles
                                    200                                             extended to later times, larger distances, and lower
Figure 11. Earth pressure contours from surface burst                               overpressure levels. The pressure-time relation-
(t= 50 ms).                                                                         ship may be more easily understood by noticing the

                                                                               11

                                                                                                                               Digitized by   Google
                                                                           depend on the energy of explosion, being greater by
                                                                           the cube root of the yield in megatons for yields
                                                                           greater than 1 mt. On shock arrival, the pressure
                                                                            jumps within a fraction of a millisecond (or within a
                                                        112 Kilo,          few milliseconds for precursed shocks) to the peak
                                                                           pressure. The subsequent decay of the pressure
                                                                           pulse is initially dominated by the passage of the
                                                                           pressure spike associated with the shock front
                                                                           itself. As the spike moves on, continuing decay is
                                                                            dictated by the general rate of pressure decrease
                                                                            in the more uniform shock-wave interior, which
                                                                            has by then engulfed the position in question. This
                                                                          . time history can be quite well described at all
  •
  ~
   .                                                                        pressure levels by the sum of three decreasing
  •
  E
                                                                            exponential functions of the time:
  &
  A.                                                                                      -aT          -8T          -yT
                                                                          AP = APs (ae          + be         + ce         )(1 - T),
  •
  Q

       ~c=~~~-;--'~r---+---;---~                                          where   T   is the time after shock arrival measured in
                                       - - - - - Surface burtt            units of positive phase duration.
                                       - - - Shallow burial                  To force this curve to go to zero overpressure at
                                                                          the end of the positive phase, a linear factor has
                                                                          been included that becomes zero at a time equal to
                                                                                                                            +
                                                                          the duration of the positive phase (T = 1 or t =Dp),
       ~O~-~~--t~OO~-~--~200~--~-~~~                                      where time is measured as the time after shock
                               Rodlul, mete"                              arrival.
Figure 13. Peak stress contours for 1-mt bard rock.


nature of these profiles. Note that at these smaller
radii the pressure drops rapidly just behind the
shock, while in the interior there are essentially no
pressure gradients. The interior is the very hot
region of the fireball where pressure pulses of any
sort are transmitted outward very rapidly because
of the high sound speeds accompanying these high
temperatures. Near the front, however, the positive
pressure gradient (as a function of radius) is a
necessary feature of the spherically expanding shock,
in which the interior gas is constantly decelerated as
the shock runs into more and more stationary air.
    Figure 15 shows the shock arrival time ts and the
shock radius R for various overpressures resulting
from the detonation of a I-mt bomb. These values

           4
                                       '-

           3                       i        1.4_



•.!.':o,   2
                                  / /              2_

                               ) /            V         /3_

                            ~/
                                                   ~V
                                            I                41iV1


           o
                                       /       V
               o
Figure 14.
                                 _IKM'         2

                   Overpressure versus radius (1-mt surface
                                                                 3
                                                                                                       1.0                  10
                                                                          Figure 15. Shock radius (Rs) and arrival time (ts) versus
burst).                                                                   peak overpressure for a 1-mt surface burst.


                                                                     1~


                                                                                                             Digitized by    Google
   Figure 16 gives the values of all shock para me -
ters and coefficients necessary to obtain the
pressure-time curve for a given peak overpressure.
   Similarly, Figure 17 gives the shock parameters
and coefficients for obtaining the dynamic pressure-
time curve based on the analytical fit

Q = Qs (1 -       ~2 (de- 6w + fe -~w),
where
   Col)
           t -
          =--,
                 ts
             D+
              u
 D: = duration of positive velocity       (-w!{;),
 Qs       = peak dynamic pressure.

   Curves showing the pressure-time relations
based on these analytic expressions are given in
Figures 18 and 19.
    Figure 20 displays positions of the shock front
from a I-mt surface burst, illustrating generally
the relative positions of the fireball and crater.
The higher peak overpressures at distances closer
to the burst point are strikingly evident. Note that
100 psi occurs just at the edge of the fireball. The
high transient winds or air velocities accompanying
the shock emphasize the importance of placing pro-
tective structures below, or at least flush with, the
surface. The short solid lines below the ground
indicate schematically an expected attenuation of
peak overpressure with depth at a given range; the
dashed lines indicate the general relationship be-
tween the air-shock poSition and the wave front in
the soil at corresponding times. At the higher over-         Figure 17. Approximate analytic form for dynamic
pressures (down to 200 or 300 psi) the air-shock             pressure versus time for nuclear blast wave in terms of
speed is faster than the seismic velocity of most            peak overpressure.




                                                                         Figure 16. Approximate analyt1c form for
                                                                         overpressure versus time for nuclear blast
                                                                         wave in terms of peak overpressure.




                                                        13

                                                                                         Digitized by   Google
     II


     ,
                 ....
                u..
                        _-
                        --
                 ....1"1 I
                 ... ·UlIIlI_
                        P,-Pt
                        "'-Po
                                                ~ .. J ... J'LI .....V
                                                        /
                                                            ,
                                                                ,
                                                                    ~



                                                                          V
                                                                                  1-:'- rI.
                                                                                   ,/


     •          APt,

 j
                                                  "/1~:;t.
                                                                    I-'
                                                                                   ,     -
 r   •                                      //  "~
                                                        :--
                                                       ~~ . . _
                                                                    1-

                                                                          ...   7'1.4~



                                       ~ ~ ~~ ......
                                                V

                -
                            ....:::;
                                                                                                                     20'   30"      40"      30"        60"   70"   10"   90"
            ~           -V V                                                                                                     ..... of incicleftce
     ,

level.
      0.1

                                        --,-     10


Figure 24. Reflection factors for normal shocks at sea
                                                                        tOO              _         Figure 25. Reflection factors versus 1Dcldent angle &lid
                                                                                                   shock strength.



some distortion of the "Mach stem" and a precursor                                                  maining wlnerab1l1ty may be associated with the
shock in front of it, both being results of thermal                                                violent movements of the surrounding earth.
radiation heating of the ground surface ahead of the                                                   In addition to the intense direct shock in the
shock. The pressure in such a precursed state does                                                 ground that is responsible for crater formation,
not have ideal properties but generally shows a                                                    ground motions are induced by the passage of air
slower rise to peak and a more irregular decay                                                     blast over the surface. For most surface or
after maximum than those exhibited by normal                                                        shallow-buried structures, this air-induced ground
shocks. For certain diffraction-type targets, such                                                 shock is of great significance since it is extended
slow-rising pressures can greatly reduce the                                                       to large distances by the air blast, while the direct
damage potential. For drag-type targets, the dam-                                                  ground shock is more rapidly attenuated below
age may actually increase because of precursed                                                     damaging levels in passing through the intervening
shock effects, since higher dynamic forces and                                                     earth mass.
greater irregularity in the duration and direction                                                     As long as the shock wave in air is strong and is
of destructive winds usually result.                                                                moving at very high speed, shock induced in the
   When the shock front strikes an exposed surface                                                 ground can only trail behind and below the air
normal to the shock (Q = 0), the overpressure is                                                   shock. In such a case, ground shock can be conven-
raised almost instantaneously to a reflected over-                                                 iently characterized by the intensity and duration of
pressure. Normally reflected shock pressures can                                                   the air blast passing nearly directly above. As the
be calculated and are given in Figure 24, which                                                    air shock slows and moves at speeds approaChing
provides reflection factors versus initial peak                                                    the speed of sound in undisturbed air, the shocks
overpressures. For shocks less than about 50 psi,                                                  generated in the ground may disperse because of
an approximate ideal gas formula may be used to                                                    their higher speeds (several times faster than the
predict reflection factors: .                                                                      speed of sound in air) and so may move ahead as
                                                                                                   well as below and behind the air-shock position.
 _ APr _ (7PO + 4APs)                                                                              The wave histories in this latter case are generally
R- AP -2 7P +AP       ,                                                                            more complex and show greater variation from soil
            s                   0           s
                                                                                                   inhomogeneities and stratifications.
where P is the ambient atmospheric pressure.                                                           Unfortunately, there is no entirely satisfactory
Figure 2q, gives values of reflected overpressures                                                 method of extrapolating the meager test results to
as a function of angles of incidence of the shock                                                  other soil types or other burst positions or yields.
front and of the incident overpressure up to 70 psi.                                               Theoretical efforts are not yet sufficiently sophisti-
These curves demonstrate a trend toward a simpler                                                  cated to provide the physical interpretation neces-
reflection with less ''Mach stem" enhancement at                                                   sary for such extensions, so that at present more
increasing overpressures.                                                                          direct empirical correlations are more useful. A
                                                                                                   set of approximate formulas of this kind are pro-
                                                                                                   vided by F. M. Sauer(3,4) for the peak values of
                                                                                                   acceleration, velocity, and displacement near the
Air-Blast-Induced Ground Shock                                                                     surface. These formulas, given below, differ for
                                                                                                   situations in which air shock is superseism1c
A shallow-buried structure may be made quite safe                                                  (i.e., faster than the seismic velocities in the soil)
from nuclear and thermal radiations and from the                                                   and where the ground shock can arrive before the
direct effects of air blast, so that the primary re-                                               air shock (identified as "outrunning" by Sauer).

                                                                                              16

                                                                                                                                       Digitized by       Google
SUPERSEJSMIC GROUND-8HOCK MAXIMA                                 displacement is estimated to be between 5 and 10 in.,
(AT 5-FT DEPTH)                                                  with a best value being 7.5 in.
                                                                    In the outrunning region, consider the same soil
Vertical acceleration: Q vm ::: 340 APs/CL :i: 30 per            and a l-mt surface burst at the loo-psi point. Since
cent. Here acceleration is measured in g's and over-             the shock radius at the 100-psi point for 1 mt is
pressure (4Ps) in pounds per square inch. An em-                 about 3,500 ft, the reduced radial parameter in these
pirical refinement requires CL to be defined as the              formulas becomes 3.5. The predicted acceleration at
seismic velocity (in feet per second) for rock, but              this range is about 5 g's, with a range from 2 to 20
as three fourths of the seismic velocity for soil.               g's equally possible. Such wide ranges stem largely
     Vertical velocity: llvm =:-75 AP /SC L ft/sec :i: 20        from the complexities imposed on the ground motions
per cent. The specific gravity of rite earth medium              by the signals refracting or reflecting from other
is denoted as S. In the following, the overpressure              surface points and from possible layered strata in
impulse (positive phase only) is designated as !t,.              the ground. In this outrunning phase, such signals
     Vertical displacement: ~::: 20tp (APs)I/4/SCL               can overtake, and indeed overpower, the motions
ft :i: 30 per cent. Since no attenuation is presumed,            stemming more directly from the overhead blast
the stress is taken to be the same as the loading                load at any instant.
overpressure, but an exponential decay may be more                  Following the same example at 100 psi, the ex-
reliable.                                                        pected maximum velocity lies between 3 and 9 ft/sec,
                                              t
     Vertical strain: (vm.:::.1.1 x 105 APs / SC parts           with a mean prediction of 5.4 ft/sec. Similarly, the
per thousand :i: 30 per cent. Values of maximum                  expected maximum displacement for this case is
horizontal displacement are likely to be half (or                10 in.; but here, as is the case with the rest of these
less) of the vertical maxima, while maximum hori-                semi-empirical formulas, there is need for caution.
zontal acceleration and velocity are expected to be              These expressions are inapplicable when extrapo-
more nearly comparable to vertical maximum                       lated into regions of overpressure, weapon yield, or
values.                                                          type of soil or rock much outside the realm of our
                                                                 test experience.

OUTRUNNING GROUND-SHOCK MAXIMA
(AT -10-FT DEPTH)                                                ATTENUATION WITH DEPTH

Vertical acceleration: Q vm ::.2 x 105 /C Lr 2                   Data taken on a low air-burst shot in Nevada. indicate
+ factor 4 or -factor 2. Acceleration is measured in             an exponential decay of maximum displacement with
gis, and r is the scaled radial distance-i.e., r =               depth. For the particular case of a burst of - 40 kt
R/Wl/3 kft/(mt)I/3.                                              at 700 ft, some measurements were made as deep
      Vertical velocity: Uvm':::' 4 x 105/SCLr2 ft/sec           as 200 ft below the surface of Frenchman Flat, a dry
:t   50 per cent.                                                lake bed, which led to the following approximate
      Vertical displacement: dvm':::' 6 x 104w1/ 3/SCLr 2        decay law, according to Perret.<5)

ft. Horizontal motions in this outrunning phase may              6 = 60 exp (-O.017D),
be quite comparable to vertical movements.                       where 6 represents the maximum vertical displace-
    Using these formulas in two examples may help                ment induced at depth D, 60 is the maximum dis-
to establish their limited usefulness. Consider a                placement at the surface, and D is the depth in feet.
Boil with a seismic velocity of 4,000 ft/sec (thus,                 Estimates of maxima at great depths can be
CL = 3,000), and introduce a ground shock from an                made by accounting for attenuation by means such
air-blast load of peak overpressure equal to 500 psi.            as those suggested by Perret. However, care should
The air-shock speed for this overpressure (see                   be taken to distinguish the attenuation due to geome-
Figure 21) is faster than this seismic velocity above            try from that due to dissipative mechanisms in the
- 400 psi, so one should refer to the superseismic               soil dynamics. The latter will depend primarily on
relations, which for this level give a maximum                   the travel path of the earth shock and on dominant
vertical acceleration of 57 gls with an uncertainty              periods or frequencies in the wave. Since the period
of 30 per cent-allowing the expected value to be                 of blast load changes quite slowly with explosion
anywhere between 40 and 74 g's.                                  yield, the dissipative attenuation for a given depth
    If this soil has a specific gravity of about two,            and given peak overpressure level will not be a
then the peak vertical velocity predicted for this               sensitive function of the yield except at very great
500-psi load is about 6.25 ft/sec, or between 5 and              depths or very high overpressure levels. This dis-
7.5 ft/sec.                                                      pe"rsion does reduce the peak stress by smearing the
    For a l-mt surface burst, and again at the 500-              wave fronts and causing longer rise times to peak
psi point, the overpressure impulse is about 40                  stress, "'hich often means more uniform loading of
psi . sec, so that for this same soil example the                buried structures.

                                                            17

                                                                                           Digitized by   Google
    In some contrast, the effect of geometry may be                                            It is obvious, but worth further emphasis, that
negligible for shallow-buried structures subject to                                         the wave fronts of Figure 26 do not represent sur-
loading by large yields, but may be very pronounced                                         faces of equal pressure. In fact, the lack of spheri-
for comparable loading from small-yield explosions.                                         cal divergence in the wave front directly below the
To illustrate, Figure 26 shows the wave fronts in the                                       point of burst would suggest that less geometric
air-induced ground shock. In the examples used, the                                         attenuation will occur there than in a more sym-
earth media have seismic velocities of 2,500 and                                            metric explosion. In the same vein, the ground
5,000 ft/sec, and fronts are shown at times when the                                        shock just below the shock front at the 3OO-psi point
peak air overpressures are 10,000, 1,000, 300, and                                          for the 5,000-ft/sec seismic speed case includes
100 psi. The curves represent positions achieved at                                         signals from pressures considerably higher than 300
uniform seismic velocities and take no account of                                           and could, in that region, show ground stresses
faster ground-shock propagation at the highest stress                                       higher than the air overpressure.
levels or of variations in seismic velocity with depth.                                        It is equally certain that as we go to greater
It is interesting to note that the effect of the rapid                                      depths or to smaller yields-they are the same thing
slowing of the air shock at around 300 psi (where it                                        since both depth and distance scale with the cube
approaches the 5,000-ft/sec seismic speed) results                                          root of the yield-the spherical divergence of the
in a steepening of the wave front and in a piling-up                                        shock energy into the below-ground space must
of the signal or waves from a considerable range of                                         further attenuate the shock strength.
earlier shock positions. A similar condition is
beginning at 100 psi for the slower seismic speed
case (2,500 ft/sec), but it is less pronounced since                                        Debris and Fallout
the air-shock speed is decreasing more gradually
and so permits less of the ground wave to be super-                                         Immediately following the blast-wave positive phase,
imposed. For the case of a 5OO-ft/sec seismic                                               a negative phase sets in, in which the winds reverse
velocity soil and an air shock at 100 psi (therefore                                         to blow toward ground zero, and the overpressure
traveling at less than 3,000 ft/sec) clearly some                                           becomes an underpressure (less than ambient). This
signal in the soil can propagate ahead of the air                                           negative overpressure can approach as much as 3
shock, thus representing a region where one must                                            psi of suction, which could exert considerable 11ft
expect ground-shock signals to arrive even before                                           on a sealed, pressurized installation. (A 3-psi
the air-blast arrival (the "outrunning" phase                                               partial vacuum could 11ft a concrete lid 3 ft thickl)
previously described).                                                                      The reversed winds may be strong enough to bring
                                                                                            back some debris to clog openings or revetments.
                                                                                            These winds do not stop within a few seconds, but


                       /
                           /
                               ,
                                                            ./
                                                                 .......    --              fade into the circulation set up by the riSing fireball.
                                                                                            The late fireball is still hot but at nearly normal
                                                                                            pressure, so that its interior is at low density-




          I
           /
               /
                   /
                           AIR
                                       /
                                           /
                                               /
                                                   /.
                                                        /

                                                                            ---             forming a kind of buoyant balloon in the atmosphere.
                                                                                             Figure 27 shows the densities versus radius at times
                                                                                            as late as a few seconds. This several-thousand-
                                                                                            foot diameter, lOW-density sphere begins immediately
                                                                                            to rise as a bubble as the denser air around it forces
         I                         /                    /                                   it upward. The rate of rise after a few seconds
                                   300 psi
         I
                                                                           ~O,oooP'1
                                                                                            approaches 400 ft/sec. The circulation is such that
                                                    'toOOPSI
                                                                                            the air velocities in the dust-laden stem that flows
                                                                                            up through the riSing cloud are about twice the cloud-
                                                                                            rise velocities, or as much as 900 ft/sec. The con-
                                                                                            sequences of such wind velocities can be better
                                                                                            appreciated when it is considered that the drag
                                                                                            created by this flow could hold aloft a boulder
                                                                    --------                weighing as much as 7 tons or could loft lesser
                                                                                            rocks and debris to very high altitudes. The cloud
                                               WAVE FRONTS ARE NOT                          continues to rise for 4 to 6 min, which can take it
                                                 GENERALLY SURFACES                         to altitudes over 60,000 ft, depending on meteorologi-
                                                 OF EQUAL PRESSURE                          cal conditions. Even after the cloud has stabilized,
                                                                                            the stem continues to rise as the circulation persists.
                                                                                            During the time of initial cloud rise, much of the
Figure 26. Air-shock-induced ground motion wave fronts                                      cratered debris is aloft on various trajectories.
for peak overpressures of 10,000, 1,000, 300, and 100 pSi,                                  Much of this material will be excavated at pressures
and for seismic velocities of 2,500 ft/sec and 5,000 ft/sec.                                below that needed to pulverize or vaporize the rock

                                                                                       18

                                                                                                                        Digitized by   Google
or soil, and some of it will be lofted in essentially                     Height of Burst
its original sizes and shapes. If the soil is rocky,
or if concrete and steel structures are involved,                        Damaging effects of blast from air bursts extend to
some large fragments must be expected at ranges                          greater distances than from ground bursts prinoi-
at least as large as the stem radius; and there is                       pally because a shock wave, where reflected, can
some chance that rocks may rain down over a wide                         result in pressures several times the incident shock
area for many minutes after a burst.                                     pressure. This height-of-burst effect can double the
   Again, if the wind circulation closely corresponds                    area of blast damage to ordinary urban structures,
to the visible cloud and stem movements, wind veloc-                     although it is relatively less impressive against
ities of the same order of magnitude (-100 ft/sec)                       hardened structures and is entirely ineffective
may be expected at the base of the stem-i.e., in the                     against deeply buried shelters. The Hiroshima and
dust-laden air above shelter.                                            Nagasaki explosions were made at altitude in order
                                                                         to take advantage of this increase in area of cover-
                                                                         age by overpressures sufficient to damage homes
Uncertainties Influencing Attack Planning                                and industrial buildings.
                                                                             For somewhat similar reasons, an air burst pro-
Many factors that greatly influence the hazards from                     vides greater coverage by thermal radiation fluxes
a nuclear attack can never be known in detail by an                      capable of igniting fires. Both by shining down more
attacker. They may have a great influence upon the                       effectively on a larger area (extensive exposure) and
effects of a given explosion. For instance, several                      by providing a more efficient radiant source, an air
aspects of the local weather influence the resulting                     burst poses a more serious thermal threat. At suf-
damage. Wind patterns at all elevations, cloud                           ficiently high altitudes of burst, both the greater
cover, preCipitation, presence or absence of snow                        distance from the earth's surface and the decreasing
on the ground, temperature, visibility near the                          ability of the thirming atmosphere to contain and con-
ground, humidity at the time of attack and during                        vert the weapon energy into thermal radiation leads
the preceding few days-all these may modify either                       to less threat, i.e., to lower radiant exposures on
the fallout pattern or the area of thermal damage.                       the ground. For every weapon yield, then, a particu-
The area of blast damage is less dependent on local                      lar altitude of burst will maximize the thermal
weather and is only slightly affected by wind patterns                   effectiveness, and some other altitude (perhaps not
at low overpressure levels.                                              very different) should optimize the blast effective-
    The enemy has control over the approximate lo-                       ness. One such case (burst heights to maximize the
cation, the probable elevation, and the yield of the                     area covered by pressures of more than 3 psi) is
explosion. However, for bursts on or in the ground,                      illustrated in Figure 28, showing the range for 1, 3,
he cannot accurately control the kind and condition                      and 10 psi, as well as the ranges for thermal-ignition
of surrounding materials at the time of explosion,                       limits for fire kindling with various cloud conditions,
and such details can influence fallout and cratering.                    all as a function of yield.
   Since most of these uncertainties apply to fallout,
thermal effects, cratering, and ground shock, but not
to blast, an attack planner may be led to count most
heavily on blast damage and thus arrange to maxi-
mize blast effects on property and people.



   10r---~--~--~---.----r---.----r--~

    6             , . 0.10_                                              10'


                                                          l.6           =
                                                                        ~
   1.0 b------+,------,'-.... -"'7"C----:lt.:-......:;----~_:I          :!
   0.6                                                                  '!
                                                                         ~
                                                                        ....
{ 0.'
                                                                         10'
  0.101:-------:1----/--#----------------------:1
  0.06


                                                                        3000
                                                                               1            10                  100             1000
  0.01 0          2000          ~             6000          8000                                   YIeld (MTI
                                _(It)                                   Figure 28. Bursts at altitudes to maximize range for 3-psi
Figure 27. Late fireball densities (l-mt surface burst).                overpressure.

                                                                   19

                                                                                                     Digitized by     Google
    Surface or contact bursts are required if crater-           put them at depths of burst much beyond 30 m, so
ing, ground shock, fallout and very high blast damage           that only at quite small yields « 1 kt) can such burial
are desired, The details of burst, whether it occurs            effectively confine the fallout to the immediate vicin-
ju'st above or just below the earth's surface, or               ity of the crater. For large yields, such burial will
whether it occurs inside a building or under water.             appear as fairly shallow, thus enhancing cratering
can make very significant differences in these                  but not seriously degrading blast or thermal radia-
effects, A buried burst, even at shallow depth, can             tion below that resulting from surface or contact
be enormously more effective than a contact burst               bursts, at the same time impressively increasing
at digging craters, at creating downwind fallout, or            the downwind fallout intensities. Such subsurface
at causing intense ground motions, while a low air              delivery is more difficult, but for some weapon
burst is likely to be quite inefficient at producing            applications could be justifiable. More complete
such effects. Figure 29 illustrates ranges versus               disruption and longer denial of harbor facilities
yield for 1, 3, 10, 30, and 100 psi, and for thermal            or concentrated commercial areas could be
ignitions and for various prompt radiation doses                achieved by such weapons.
from surface bursts.
    As mentioned earlier, straightforward means of
delivering weapons to detonate underground do not               References

                                                                1.   Glasstone, S. (ed .), The Effects of Nuclear Weapons,
                                                                     rev. ed., U.S. Department of Defense, U.S. Atomic
                                                                     Energy Commission, April 1962.
                                                                2.   National Academy of Sciences, Future Weapons and
                                                                     Weapon Effects, Project Harbor (Group B), September
                                                                     1963.
                                                                3.   Sauer, F . M., "Ground Motion from Above-Ground
                                                                     Nuclear Explosions," Chapter IV -1 in Nuclear Geo-
!:                                                                   plosics, Defense Atomic Support Agency, DASA-1285,
~                                                                    May 1964.
:.!
1!                                                              4.   _ _ _ _ _ _., "The Nature of Ground Shock Induced
~
~                                                                    by Airblast from Above-Ground Nuclear Explosions,"
      10'                                                            in Proceedings of the Symposium on Scientific Prob-
                                                                     lems of Protective Construction at the Swiss Federal
                                                                     Institute of Technology, July 25-30, 1963, Bundesamt
                                                                     fUr Zivilschute, Berne, Switzerland, pp. 351, 352.
                                                                5.   Perret, W.R., Ground Motion Studies at High Incident
                                                                     Overpressure, The Sandia Corporation, Operation
                      10                 100       I(xx)
                            Yield (MTI                               PLUMBBOB, WT-1405, for Defense Atomic Support
Figure 29. Effects of surface bursts.                                Agency Field Command, June 1960.




                                                           20

                                                                                             Digitized by   Google
                             THE INTENSITY AND DISTRIBUTION
                           OF INITIAL AND RESIDUAL RADIATION*
                                                Harold Knapp
                            Institute for Defense Analyses, Arl ington, Virginia


General Considerations                                         specified limits. Shelter-stay times are also
                                                               affected by fallout levels in other than the immediate
In contrast to the blast and thermal effects of nuclear        area of the shelter, and by the level of radiation ex-
weapons, the initial gamma rays and neutrons from              posure to be permitted over various intervals of
a nuclear burst and the delayed gamma and beta                 time. In fact, almost every way in which fallout
rays from fallout are a threat to biological systems,          affects civil defense activities outside the shelter
but not to structures. The hazard is complex and               has an influence on shelter-stay times, and thus on
subtle in that the potentially harmful radiations are          the space requirements within the shelter for food,
not sensed by the body and the many different bio-             supplies, and equipment.
logical effects are delayed in time from an hour or               In developing estimates as to the levels of blast,
so to many years following exposure. The individual            thermal pulse, and initial nuclear radiation that
fallout particles, which contain the radioactive by-           might reasonably be anticipated at specific locations
products of the fission and fusion processes im-               in the United States, in the event some fraction of a
bedded in or on a mass of inert materials, cover a             nuclear attack on this country were targeted to maxi-
wide range in size. Some are as large as grains of             mize population fatalities, the principal variables are
sand, others as small as particles of dust. In highly          the numbers and yields of the weapons employed,
contaminated areas, the total bulk of fallout material         whether they are assumed to be burst in the air or
deposited from a surface burst would be clearly                on the surface, and the targeting criteria.
visible in daylight as long as meteorological condi-               Comparable estimates of the external gamma
tions permitted the particles to settle and be retained        doses and dose rates from the fallout involve
on foliage or on smooth surfaces. It is very difficult         additional important uncertainties:
to predict when the fallout will come to earth, but it             1. The speed and direction of the wind at all
is known that potentially lethal concentrations of             altitudes up to the top of the mushroom cloud, and
radioactivity can be deposited hundreds of miles               at all locations throughout the United States
from the point of detonation, and that it can cover                2. Precipitation patterns throughout the United
an area an order of magnitude greater than the area            States
where fatalities are produced by blast. The hazard                 3. The level and distribution of attack on mili-
persists in time. Although the immediate and great-            tary targets
est danger is from gamma radiations from the fall-                 4. The fraction of the total yield of each weapon
out particles, these particles also emit beta rays,            due to fission
which can cause burns if fresh fallout comes in                    5. A method for estimating the distribution and
contact with the skin and is not promptly washed               deposition times of the radioactivities from a single
off. There are several short- and long-lived radio-            surface burst, when all the factors listed above are
nuclides among the fission products, notably 1131              specified precisely
 (half-life eight days), Sr90 (half-life 28 years), and            Large uncertainties and variations in estimates
Cs137 (half-life 30 years) that can produce an                 of fallout doses and dose rates at specific locations
internal hazard via the food chain.                            are introduced by each of these factors, in addition
    The type and amount of radioactive material that
may be deposited in an area where shelters are to
be constructed affect shelter design directly by               *Dr. Knapp's presentations at the Symposium on Protec-
                                                                tive Structures have been published in full by the Institute
indicating the amount of shielding necessary to hold            for Defense Analyses. July 1965. uDder the title: "Magni-
radiation exposure of the shelter occupants to with-            tude &lid Distribution of Weapon Effects fer the Design of
in specified limits, and indirectly by influencing the          Shelters for Protection Against Fallout" (Research Paper
length of time the shelter must be occupied, con-               P-I94). Because of space limitations. these Proceedings
tinuously or partially, to hold dose levels within              contain somewhat shortened versions.

                                                          21

                                                                                              Digitized by   Google
to the uncertainties present in estimates of the                 b. shortening of life and the development of vari-
distribution and intensity of the immediate effects.             ous kinds of malignant neoplasms 1-20 years
                                                                 following exposure,
                                                                 c. changes in the genetic material of the indi-
Radiation Dose Units (1,2)                                       vidual exposed that may result in the genetic
                                                                 death of a future descendant-perhaps many
The effect of nuclear radiations on a biological                 generations later-and/or in some degree of
system is expressed in terms of an "absorbed dose."              physical disability to several descendants.
The rad is defined as the absorbed dose of any
nuclear radiation that is accompanied by the libera-             Damages of type (b) and (c) are probably also
tion of 100 ergs of energy per gram of absorbing              dependent on the dose rate and the time interval
material. Although all ionizing radiation-gamma               over which the dose is delivered, but to a lesser
rays, X-rays, beta rays, neutrons, protons, alpha             extent than the type of injury listed under (a).
.-rt1cles-are ca.-ble of producing similar biologi-              The notion of biological dose or equivalent
cal effects, the absorbed dose measured in rads that          residual dose (ERD) is an attempt to equate the
will produce a certain biological effect may vary             clinical manifestations of radiation injury of type (a)
appreciably from one type of radiation to another.            resulting from a protracted dose (i.e., a dose de-
This difference in behavior is expressed by means             livered over a period greater than about four days)
of the "relative biological effectiveness" (RBE) of a         with a brief dose (a dose delivered over a period less
.-rticular nuclear radiation. The RBE is defined as           than four days). The assumptions made for comput-
the ratio of the absorbed dose in rads of gamma               ing the equivalent residual dose (ERD) may be de-
radiation to the absorbed dose in rads of the given           scribed as follows. Any radiation dose may be con-
radiation having the same biological effect.                  sidered as consisting of two parts, a reparable dose
   The value of the RBE for a .-rt1cular type of              Oft, and an irreparable (permanent) dose Dp. The
nuclear radiation depends on several factors, in-             irreparable dose Dp consists of 10 per cent of the
cluding the energy of the radiation, the kind and             total dose. The reparable dose Da is constantly
degree of biological damage, and the nature of the            being repaired by the body at a rate of about 2.5 per
organism or tissue under consideration.                       cent per day. Thus if r(t) is the dose rate in
    The rem is defined as dose in rads x RBE.                 roentgens/hour,
    The roentgen is a measure of radiation-exposure           dD p
dose from gamma or X-rays, as opposed to absorbed             Cit    = 0.1 r(t)
dose, and is defined as the quantity of X- or gamma
radiation such that the associated corpuscular emis-          dDR
sion per 0.001293 grams of air produces, in air, ions         Cit    = 0.9 r (t) - 0.00104 DR
carrying one electrostatic unit of electricity.
    The RBE for gamma rays is approximately unity,                At any time after irradiation stops, the dosage
by definition, although it varies somewhat with the           which has been accumulated over a period of time
energy of the radiation. Because 1 roentgen-                  is assumed to correspond, in its clinical manifesta-
exposure dose gives rise to about 1 rad absorbed              tions to a brief dose = D~ + DR.
dose in tissue for photons of intermediate energy                 The implications of Ws concept is that one-tenth
(0.3 to 3 Mev), the absorbed dose for gamma rays              of any dose accumulated is permanent as regards
or X-rays is often stated, somewhat loosely, in               damage of type (a) above, and that the effect of the
roentgens.                                                    remaining 9/10 of the accumulated dose is con-
    The RBE for beta. particles ie close to unity. The        stantly being repaired in such a way that any time
RBE for alpha .-rticles from radioactive sources              irradiation stops; only half the reparable dose Da
has been variously reported to be from 10 to 20, but          will remain after 30 days.
this may be too large. For nuclear-weapon neutrons,               The decay rate from a given amount of fallout
the RBE for acute radiation injury is now taken as 1,         deposited on the ground is such that the equivalent
but it is appreciably larger where the biological             residual dose accumulated at a point three feet
effect considered is the formation of opacities of            above the ground from 1 hour following detonation
the lens of the eye-cataracts.                                reaches a maximum about four days following
    Equivalent residual dose (biologically effective          detonation and this maximum is approximately equal
dose). Human exposure to fallout radiations can lead          to the four-day total dose. If the equivalent residual
to different types of biological damage:                      dose is computed starting 6 hours after detonation,
                                                              it reaches a maximum at about one week following
   a. siclmess or death in two hours to six months,           detonation; this maximum is apprOximately equal
   depending on the total dose delivered and the dose         to the total dose accumulated from six hours to one
   rate and time interval over which it is delivered,         week. Since the total dose from six hours to four


                                                         22

                                                                                       Digitized by   Google
days is about 90 per cent of the total dose from six                        a l-mt burst. These estimates are qualified in
hours to one week, and an even larger fraction of                           paragrapb 8.27 of The Effects of Nuclear Weapons.
the one-week dose is accumulated from one bour                                 The data of ngures 1 and 2 illustrate an impor-
to four days, the maximum biological dose from                              tant consideration for the design of blast shelters in
any fallout deposited between one and six hours                             the 30-to-l00-psi range, namely, that protection
(or thereabouts) will be approximately equal to the                         aplnst blast and residual radiation does not auto-
total dose accumulated during the first week.                               matically guarantee protection against 1n1ual radia-
    The clinical features of radiation injury of type                       tion. Suppose, for example, a 30-psi shelter las a
(a) resulting from various levels of brief or equiv-                        PF of 1,000 ap.lnst residual radiation-i.e., the
alent residual doses are described in detail in                             protection equivalent to about 36 inches of earth.
Reference 11.                                                               The same thickness of earth would give a protection
                                                                            factor of about 25 from the 1n1ual radiation. A pro-
                                                                            tection factor of 25, applied ap.lnst a dose of 104
ln1ual Nuclear Radiation
                                                                            rem at the 30-psi blast level, would result in a total
                                                                            in-shelter dose of 400 rem. Similarly a l00-psi
The 1n1ual nuclear radiation from a weapon burst 18
                                                                            blast shelter with a PF of 10,000 (48" earth) ap.lnst
defined as that emitted by a weapon burst and its
                                                                            residual radiation gammas might offer a PF of only
radioactive by-products within 1 min from the
                                                                            70 against the 1n1Hal gammas. Since 100 psi corre-
instant of deto..tion. As a civil defense hazard, it
                                                                            sponds to 2.6 x UP rem for a l-mt surface burst
consists of high-energy gamma pbotons and neutrons.
For a 20-ld device, about 80 per cent of the total
                                                                             100.000
gamma dose received is delivered within 3 sec. For
a 5-mt device, 80 per cent is delivered in about 8
sec. The neutrons are released essenually                                                                                                                                 ,
                                                                                                                                                                          I

instantaneously.                                                                                                                                                      /
   An estimate of the relative contribution to the                                                                                                         If
total dose (in rads or rems) from the 1n1ual gamma                            10.000                                                                      J~
pbotons and neutrons is shown in Table 1 below:                                                                                                           ...i


           Inlttal Dose versus DiataDce - 1 MT

            Gamma-Ray
                                 TABLE 1


                    (from Ref. 2. p. 15).

                                                        Overpressure
                                                                                                                           if
                                                                                                                           .
                                                                                                                           .t
                                                                                                                               "s~
                                                                                                                               ~.t

                                                                                                                               ~
                                                                                                                                ~~
                                                                                                                                   .f"P
                                                                                                                                   "/l
                                                                                                                                        .::'
                                                                                                                                        ~
                                                                                                                                            o     .
                                                                                                                                                ...
                                                                                                                                                      ~




                                                                                                                                                                                       .L
Distance       Dose                Neutron Dose                                                                            ~                                                       /
  (mi)      (roentgens)               (rads)               (pSi)                                                     J                                                        V_
  2.0
  1.5
                        ....44
                     .... 700
                                             ..... 15
                                          ....11
                                                                  10
                                                                  20                   ~---- ~----
                                                                                                                 I                                                    L
  1.0           ....14.000              ....1.050                 40                                                                                  ~.
  0.5        .... 500.000          .... 173.000             .... 200                                         ,   I             ~~~
                                                                                                                                ~" .. ~+
                                                                                                                                   ,~
                                                                                                                                   ,,:j>
                                                                                                         /                           ..to
   An important feature of the 1n1ual gamma radia-                                                               I       ~...~~
tion as opposed to the residual gamma radiation is
the greater penetrability of the iniHaI nuclear radia-                            °
                                                                                                     /           'L
tion. The tenth-value thiclmess of earth for initial
gamma radiation is about 26 in., whereas it is only                                         L        /           I
12 in. for the residual gamma radiation. The over-                                      L
                                                                                                                 I
all radiation reduction (protection) factor for a given
thickness of earth for each of these two types of                                  I~           10
                                                                                                                 1    30                 c                       50           to        IQ

radiation is shown in Figure 1.                                                                                  EAITH THICKNESS (INCHES I

    ngure 2 shows the initial nuclear radiation and                         Figure 1. Rad1ation protection factor versus earth thick-
ove»pressure as a function of range and yield for a                         ness for inittal and residual gamma radiation.
                                                                            ~: Fig. 8.38. par. 12.52. Ref. 3.
surface burst. According to Figure 2 the initial
nuclear radiation from a l-mt surface burst is less
than 1 rem whenever the overpressure is less than
5 psi. However, an overpressure of 30 psi (the                              .The numerical values given in Table 1 were received from
approximate radius of the fireball) corresponds to                           Dr. Brode on 19 AprU 1965. They differ from the values
an 1n1tial dose of 104 rem, and an overpressure of                           given on page 15 of Ref. 2. but are consistent with the
100 psi to an 1n1Hal dose of about 2.6 x 105 rem, for                        formulas presented on page 14 of Ref. 2.


                                                                       23
                                                                                                                               Digitized by                      Google
(Figure 2), there is a possibility at the 100-psi level                                                                                             When a nuclear weapon is burst in the air, the
of an in-shelter dose of about 3,700 rem. These                                                                                                 mass of the fallout particles consists of the weapon
estimates are very rough because no consideration                                                                                               casing and the fission fragments. The particle diame-
has been given to the different geometrical relation-                                                                                           ters lie largely in the range of 2 to 12 microns, and
ship between the radiation source and the shielding                                                                                             most of the particles take weeks or months to reach
material in the two cases, and because of the large                                                                                             the earth. Under these circumstances most of the
uncertainties in the initial radiation dose level noted                                                                                         radioactivities that give rise to an external gamma
above. Further, they are based on a I-mt surface                                                                                                radiation hazard decay harmlessly in the air. How-
burst. They do illustrate, however, the necessity of                                                                                            ever, long-lived internal emitters such as strontium-
taking initial radiation into account when designing                                                                                            90, with a half-life of 28 years and cesium-137, with
blast shelters in the 30-to-l00-psi range, and the                                                                                              a half -life of 30 years, if deposited in sufficient
very large amount of shielding that may be required                                                                                             concentrations, can still present an internal hazard
to protect against initial nuclear radiation at these                                                                                           via the food chain.
levels of blast.                                                                                                                                    The approximate distribution of the radioactive
                                                                                                                                                material from a surface burst on particles of differ-
                                                                                                                                                ent sizes and the time required for these particles
Residual Nuclear Radiation                                                                                                                      to fall from different altitudes is shown on Figure 3.
                                                                                                                                                The approximate height and radius of the top of the
Residual nuclear radiation is defined as that radia-                                                                                            mushroom cloud into which the fallout particles are
tion emitted from the radioactive by-products of a                                                                                              lifted by rising air currents before being scattered
nuclear explosion later than 1 min from the instant                                                                                             by the winds is shown in Figure 4.
of the explosion. (3) The sources and characteristics                                                                                               Many different mathematical models of varying
of this radiation vary with the percentage contribu-                                                                                            degrees of complexity have been developed to pre-
tion of fission and fusion to the energy release of                                                                                             dict when and where the particles of different sizes
the weapon. Those radioactivities induced by neutron                                                                                            will be redeposited on the earth. It is evident that
capture in earth and bomb materials are of immedi-                                                                                              the answer must depend on the speed and direction
ate interest only in weapons whose fission fraction                                                                                             of the winds, or more exactly, on the speeds and
is less than about 10 per cent.* Otherwise, as shown                                                                                            directions of the wind at different altitudes and
later, the gamma radiation they emit is dominated                                                                                               different locations of the fallout pattern. The results
by that from the fission products.                                                                                                              of the various models differ widely and no one is
   When uranium (or plutonium) undergoes fission,                                                                                               sure which model is more correct or whether or not
about one tenth of 1 per cent of the mass of the fis-
sioning atoms is converted to energy. The rest is
accourlted for by over 200 different isotopes of 36
different elements. Each fissioning uranium atom
gives rise to a pair of fission products whose mass
                                                                                                                                                ~ '10I'it·, 'rll 'i ·
                                                                                                                                                ~lOO ~~Hr~~~~~1-~Y1-+~1-~~~~~~
                                                                                                                                                                                                     V                           ~/'
is almost that of the unsplit atom. For each kiloton                                                                                            a ilf~ lkiJ /                                                 ~/-+v+--t-++--b-I
                                                                                                                                                ~ ..   /1' S-.,yr- V         L-1-t-t-:;,f-vt-VI-+--+--t"
of energy released, ** 56 grams of uranium = 1.45 x                                                                                                                                                                         ~             I

102 3 uranium atoms are fissioned.                                                                                                              g        J     / /   ...';   01'+ / '                /v         pO'!         ...... ...... v~
                                                                                                                                                E"        II
                                                                                                                                                '"       ljll/lv V ,~!.....)./v                            !--""""!--"~K
                                                                                                                                                                                                                       ~r-
     s.o,....------r-----..-------r---7--..----,
                                                                                                                                                5
                                                                                                                                                g ..
                                                                                                                                                <..
                                                                                                                                                        VI II, /
                                                                                                                                                        ~~ V v/'~~ . . . !--"
                                                                                                                                                        UJ. /' /'
                                                                                                                                                                   '
                                                                                                                                                                     ...... ~ -
                                                                                                                                                                                        I
                                                                                                                                                                                                     ~~~~
                                                                                                                                                                                                                           .,

                  1'_                                                                                                                           ~ .l~ ~~:~:.                 1 ••   ~. ~:~:'C,~£ .:'::U:... 11 11 ,~'::' .. 22 13 2.
i
~ 1.0
                                                                                                                                                                                            TIME (HOURS)
                                                                                                                                                Figure 3. Times of fall of particles of different sizes from
                                                                                                                                                various altitudes and percentages of total activity carried.
                                                                                                                                                (Reproduced from The Effects of Nuclear Weapons, Ref. 3,
                                                                                                                                                Fig. 9.187.)



                                                                                                                                                 *For some weapons, neptunium-239 (half-life 2.3 days,
                                                                                                                                                  average gamma photon energy = 0.27 Mev) may be
                                                                                                                                                  created in such quantity as to constitute a significant
    0 .01 ~'.':""T........;...............~,O'::.T--'-'-........~,OO~.':""T........................~,M~T--'-'-........~,OM...,,--::!20MT
                                                                                                                                                  hazard in addition to the fission products. See Table 3.
                                                             vlno.     w                                                                        **By definitions, 1 kiloton is 1012 calories
Figure 2. Initial nuclear radiation and overpressure as a                                                                                           = 4.2 x 101 9 ergs
function of range and yield for surface bursts.                                                                                                     = 1.15 x 106 kilowatt hours
Source: Fig. 2.16, Ref. 4.                                                                                                                          = 2.64 x 10 25 Mev

                                                                                                                                           24

                                                                                                                                                                                              Digitized by      Google
any of them is sufficiently accurate to give a reli-                           An alternate, time-independent method of describ-
able estimate of what doses and dose rates will                            ing a fallout contamination level is in terms of the
actually be experienced at various locations on the                         roentgens/hour infinite plane dose rate, normalized
ground at various times following a nuclear                                to 1 hr-that is, assuming that all the fallout that
detonation'(5)                                                              is eventually deposited at a given location has in
   An illustration of the difference between a pre-                        fact been deposited 1 hr following the detonation.
dicted and an actual fallout pattern is shown in                           The relation between those two descriptions is
Figure 5 (see also Figures 9.58a and 9.58b, Ref. 3).                       indicated in Table 2, i.e., 1 kt/mi2 = 3,720 r/hr at
    In spite of the great difference possible between                      1 hr.
predicted and actual fallout patterns, it is assumed                           It is clear from Table 2 that the doses and dose
that idealized patterns are useful as an indication                        rates experienced at a given location at various
of the shapes and levels of fallout deposition patterns                    times following a nuclear burst will depend very
which could reasonably be anticipated as a result of                       much on how long it takes for all the fallout which
surface bursts of different yields, under different                        is going to be deposited at a particular location to
conditions of wind. It should be noted that currently                      be deposited. Fallout deposition times, as with other
available fallout models assume that no precipitation                      features of the fallout models, are subject to large
or irregular wind conditions occur in the area where                       uncertainties. At areas close to the point of detona-
fallout particles are deposited.                                           tion-in areas of 30 psi overpressure or more-some
                                                                           fallout or throwout will begin within minutes. At
                                                                           greater distances it is estimated (Ref. 3, par. 9.84)
Doses and Dose Rates from a Uniform Distribution                           that the time of fallout arrival is about 24 min. One
of Fission Products on the Ground                                          hundred miles from the point of detonation, the fall-
                                                                           out may not begin for 4-6 hours and may last for
It is a common assumption of most fallout models                           several hours.
that only the fission product radioactivity will be                            An estimate of the approximate contribution of
directly considered in the computations, and that                          induced activities to the infinity (approximate 1 yr)
the fission products will be considered unfraction-                        dose from clean and normal weapons is shown in
ated-that is, the relative concentrations of the many                      Table 3.
different radionuclides present in any sample of
fallout is the same as for the radioactive debris
taken as a whole.                                                          Contamination Levels and Accumulated Doses
    With this assumption, there exists a simple, time-                     in an Idealized Fallout Pattern: Scaling with
invariant description of the fallout-contamination                         Yield and Wind
level at a given location, namely, the number of
kilotons-equivalent of fission products deposited                          Fallout particles of a size large enough to be visible
per unit area. External gamma dose rates and                               against a white sheet or paper-those with diameters
accumulated doses 3 ft above a smooth, infinite                            in excess of 50 microns*-are for the most part
plane contaminated to a level of 1 kt per square
mile are shown in Table 2 (abstracted from Ref. 6).                        *1 micron        = 10-6   meter = 10-3 millimeter.




                                                             .
•                                                            .. I

         --t.----------4-
                                                                                                        I 100 MILES I
~                                                                 i           (R.t. 3 .•    'is'9.82a). IdeaU&ed un1t-tu.. retereace close-rate
t.
I                                   ---+2-~-                 ..   i
                                                                  I
                                                                                CODtourS tor an 8-_pton, 50-percent nsdon, surtace

I   ~------~------    __ ------4-~~~~--_4
                                            .. !                  I
                                                                                burst (Iio IIIPh ettecti ve w1lld speed).


    -+----t ----+-----::.,...q---7""9L--~~-r. I




                                           __--
                                           ~'




Figure 4. Approximate nuclear cloud dimensions.
                                                 ..
                                                _ _ _ _ 'l
                                                                              (Ret.   3 ,   '18. 9.82b). Correspoad1n8 actual close-rate
                                                                                CODtour. (hJpotheUcal).
(From Fig. 1. Ref. 7.)                                                     Figure 5.


                                                                      25
                                                                                                                   Digitized by   Google
                                                     TABLE 2

                   Gamma Dose Rate aDd Accumulated Dose 3 Feet above a Smooth, Infinite Plane,
                Uniformly Contaminated with Unfractionated Fission Products from the Thermal Fission
                  of U-235 at a Density of 1 Kiloton Equivalent of Fission Products per Square Mile,

                                                    Accumulated
 Beta Activi,                      Dose Rate         Dose from
  curies/mi.                         r/hr.            1 hr. in r
(NRDL TR-187                    (NRDL TR-247      (NRDL TR-247       Interval
  p 7 et seq.    Time after      p. 13 et seq.      p. 31 et seq.     Dose           Dose from Time Indicated to:
 from graphs)      Fission       from graphs)       from tables)       inr      1 Day    1 Week   1 Month 1 Year

                   1/2 br.          8,560             -2,680
 4.43 x 108        1 br.            3,720                 0                     7,597     9,567        10,723   11,820
                                                                       2,382
 1.96 x 108        2 brs.           1,530             2,382                     5,215     7,185         8,341    9,438
                                                                       1,139
 1.22 x 108        3 brs.             853             3,521                     4,076     6,046         7,202    8,299
                                                                         700
 8.62 x 10 7       4 brs.             577             4,221                     3,376     5,346         6,502    7,599
                                                                         495
 6.74 x 107        5 brs.             432             4,716                     2,881     4,851         6,007    7,104
                                                                         382
 5.49 x 107        6 brs.             340             5,098                     2,499     4,469         5,625    6,722
                                                                       1,347
 2.55 x 10 7      12 brs.             152             6,445                     1,152     3,122         4,278    5,375
                                                                         706
 1.57 x 107       18 brs.              91.0           7,151              446      446     2,416         3,572    4,669
 1.10 x 107        1 day               60.4           7,597                         0     1,970         3,126    4,223
                                                                         856
 4.59 x 106        2 days              21.8           8,453                               1,114         2,270    3,367
                                                                         392
 2.74 x 106        3 days              12.5           8,845                                 722         1,878    2,975
                                                                         250
 2.02 x 106        4 days               8.90          9,095                                 472         1,628    2,725
                                                                         189
 1.61 x 106        5 days               7.02          9,284                                 283         1,439    2,536
                                                                         155
 1.33 x 106        6 days               5.82          9,439                                 128         1,284    2,381
                                                                         128
 1.15 x 106        7 days               4.99          9,567                                   0         1,156    2,253
                                                                         296
 8.08 x 105       10 days               3.'3          9,863                                               860    1,957
                                                                         274
 5.88 x 105        2 weeks              2.34         10,137                                               586    1,683
                                                                         321
 3.84 x 105        3 weeks              1.51         10,458                                               265    1,362
                                                                         265
 2.55 x 10 5       1 month                .984       10,723                                                 0    1,097
                                                                         432
 1.16 x 105        2 months               .368       11,155                                                        665
                                                                         199
 7.25 x 104        3 months               .213       11,354                                                        466
                                                                         128
 5.17 x 104        4 months               .149       11,482                                                        338
                                                                          93
 3.80 x 104        5 months               .111       11,575                                                        245
                                                                          70
 2.90 x 104        6 months               .0832      11,645                                                        175
                                                                         121
 1.47 x 104        9 months               .0354      11,766                                                         54
                                                                          54
 8.74 x 10 3       1 year                 .0146      11,820                                                          0
                                                                          59
 1.88 x 10 3       3 years         1.11 x 10- 3      11,879
                                                                         115
 2.43 x 102       30 year.         3.54 x 10-4       11,994




deposited within 24 hours from the time of detona-             following detonation. Figure 7 shows the time-
tion. They contribute the most immediate and most              invariant level of contamination, and may be used in
predictable threat from the fallout of a single weap-          conjunction with Table 2 to obtain accumulated doses
on burst. That portion of the fallout which occurs .           and dose rates once all the fallout at a given loca-
within 24 hours is somewhat arbitrarily called early           tion has been depoSited.
fallout, as opposed to delayed fallout which occurs                The dose rates and doses shown in Figures 6 and
after 24 hours. It is the doses and dose rates from            7 are for a 1-mt surface burst of 100 per cent fission
early fallout which one attempts to define with an             yield. They must be scaled down by a factor equal to
idealized fallout plttern. For land surface bursts             the fraction of the total yield due to fission. This
in the megaton range, it is estimated that from 50             fraction is normally taken as one half for illustra-
to 70 per cent of the radioactivity created by the             tive purposes, although fractions as low as one third
nuclear explosion will be deposited as early fall-             and as high as two thirds indicate the general range
out.(3)                                                        of uncertainty introduced by this factor.
    Sample fallout pltterns from the fallout model                 An important factor to consider in connection with
described in The Effects of Nuclear Weapons are                the fallout contours given in Figure 7 is how they
shown in Figures 6 and 7. Figure 6 illustrates how             scale with yield and wind. This is described in
the total dose may accumulate during the first 18 hrs          Ref. 3, par. 9.75-9.81.


                                                         26

                                                                                        Digitized by   Google
                                                                                            TABLE 3
                                                                                          (Ref. 8, p. 538)

                 IDustrat1ve Chart Showing Approximate Contributions of Induced Activities and Unfractionated Fission
                     Products to the Infinity Dose of Fallout from Air and fllrface Bursts of a Normal Weapon for a
                Contamination Level of 1 kt Total Yield/mi 2 Together with an Estimate of the Inflnlty Doses from Fission
                                    Products and Inducted Activlties in a Surface Burst Clean Weapon
                                                                                                                   Inflnltt Dose in Roen~ns
                                                                                        Normal Weapon                         Normal Weapon                           Clean Weapon
                                                  Aver~ge  Mev/                          fllrface Burst                          Air Burst                            Surface Burst
Activlty              Half Life                   Disintegration                    Low      Typical    High             Low      Typical   IUgh                         Typical

U-240               14.2 hours                        .34                            10       60                 300         10         60                 300
Na-24               15 brs.                         4 .1                             50      250                 600          1          5                  10
Np-239              2.33 days                         .27                            40      250                 900         40        250                 900
U-237             . 6 .75 days                        .16                            35      150                 350         35        150                 350
Fe-59               45.1 days                       1.1                               0        1                   2          0            1                  2
Co-58               72 days                           .97                             1        2                  20          1           2                  20
Co-57               270 days                          .13                             0        1                  10          0           1                  10
Mn-54               300 days                          .84                             1        3                  30          1           3                  30
Co-60               5.3 yrs .                       2 .5                              3       20                  30          3          10                  30
Mn-56               2.6 hrs.                        1.8                              15      100                 600          0           0                   0
                      Total Induced                                                          837                                       482                                   500
                      Fission Products                                                     6,000                                     6,000                                   600
 Note: Normal weapon assumed 50 per cent fission yield
       Clean weapon assumed 5 per cent fission yield
       No fractionation assumed



   The ENW model differs in a number of ways                                                        subsequently modified by Pugh in 1961 in conjunc-
from a more comprehensive and detailed model                                                        tion with a special subcommittee of the Advisory
developed by Pugh and Galiano of WSEG(9) and                                                        Committee on Civil Defense, National Academy of

       -
       ,.1 Jt
                                                                               11
                                                                                                    Sciences, for use by the National Resources Evalua-
                                                                                                    tion CeRter (see Ref. 10). Results for a number of
                                                                                                    yields and winds have been calculated.

         ,.
         ".
         1M
                                                                               11

                                                                               10
                                                                                                        One difference between these models is that the
                                                                                                    maximum H+1 hr dose rate in the 1961 modification
                                                                                                    is not limited to 10,000 r/hr at 1 hr. For example,
                                                                                                    it indicates an H+1 hr contour of 30,000 r/hr at 1 hr
                                                                                                    over a 742-square - mile area for a 100-mt, 100 per
                                                                                                    cent fission surface burst, a 10-knot wind, and an
                                                                                                    effective fallout shear of 0.1 kt per 1,000 ft altitude.·
                                            lOR




                                                                                                     I~t 4¥>-:>-
      ••
      i:
       •
          •                                                                                           •      ~         .:.   J.
          11

                                                                                                          ( Ret . 3 . P1« . 9 . 73) . Ideal1zed unlt .. t1 m refertnte <so •• -rate
                                                                                                                                                            e
                                                                                                             pattem t o r ear l y Cal l out trom a l-me g a ton naslon yield
           II.   'I   •   11   •   •   I~    :    10.   10   .0 ; 1~       •                                 ."reace burat (15 mph effect1ve w1nd speed).
                      DlrTAllCI . . . . OIIOUIID &1110 ( _ ,
                  1lI0II1              • __                  II lI0II111                            Figure 7.
  (Ref. 3 , Pig . 9.67b) . Total - dose contours from early
    fallout at 1, 6, and 18 hours after surface bprst
    with I - megaton fission y1eld (15 mp h effective
~~ w1nd speed) .
                                                                                                    -See Ref. 9 for a deflnltion and discussion of effective
Figure 6.                                                                                            fallout shear.


                                                                                               27

                                                                                                                                                  Digitized by      Google
Meteorological Data for Use with                                                         area covered by the 5-psi blast level has a con-
Fallout-Prediction Models                                                                tamination level of at least 1,500 r/hr at 1 hr.
                                                                                         About half the total 5-psi area and somewhat more
The principal information needed to apply the models                                     of the downwind area outside the 5-psi circles is
described above to determine the fallout at any                                          contaminated to a level of at least 5,000 r/hrat
designated point is:                                                                     1 hr. Significant areas within the 5-psi blast level
                                                                                         and downWind of it are contaminated to levels in
   1. the yield, fission yield, and burst points of the                                  the range of 5,000 to 10,000 r/hr at 1 hr. The
weapons contributing fallout to that point,                                              highest levels indicated by the patterns are about
   2. the effective wind speed and direction and the                                     13,000 r/hr at 1 hr. Very extensive areas downwind
effective fallout shear at the points of detonation of                                   are overlapped by all three patterns, for a total
the weapons contributing fallout to that point.                                          contamination level of at least 4,500 r/hr at 1 hr.
   The wind speed and direction could, of course, be                                        From Figure 9, it is seen that a maximum biologi-
almost anything'. There are, however, seasonal                                           cal dose approximately equal to the total dose during
regularities in wind conditions at given places                                          the first week, through most of the 5-psi area is at
throughout the country. These are described in                                           least 5,000 r, that it is about 15,000 r over significant
some detail in Reference 7. The most important                                           positions of the blast area and beyond; that it reaches
data are reproduced in Table 4.                                                          about 26,000 r in the area of greatest intensity.
                                                                                            These results are for a fission yield of 50 per
Doses and Dose Rates in Overlapping                                                      cent. They should be increased by one third if the
Fallout Patterns                                                                         fission yield is increased from one half to two thirds.
                                                                                         They would increase if the effective wind were less
Since no attempt has been made to estimate the                                           than 10 knots, or if there were heavy fallout from
possible level of attack on military targets, or the                                     other targets. They would decrease if the effective
distribution of such an attack throughout the United                                     wind were greater than 10 knots, or if the fission
States, it is not possible to give an example of the                                     yield were less than 50 per cent. They would essen-
integrated fallout pattern throughout this country for                                   tially disappear if the weapons were airburst.
even one set of wind conditions. What will be con-                                           One cannot draw reliable general conclusions as
sidered instead is an estimate of the maximum level                                      to the level of fallout contamination against which
of fallout that might reasonably be anticiplted in and                                   protection should be sought in and around all urban
around a reasonably large populated area subjected                                       areas by use of a single illustrative example using
to a' direct attack. Specifically, it will be assumed                                    one of several fallout models, and considering only
that three 10-mt, 50 per cent fission-yield weapons                                      an area subject to heavy attack. For with fallout, as
have been surface-burst in such a way that the 5-psi                                     with blast and heat, each area requires special
circles are just tangent to each other. The wind                                         study, and each area must be considered in light of
speed selected is 10 mots-the average for the                                            many postulated attacks on the country as a whole.
Washington, D.C. area in the summer (see Table 4).                                           There is, perhaps, one tentative conclusion of
The model used will be the 1961 modified WSEG                                            some importance, namely, that in areas in and
model, the effective wind shear 0.1 kt/1,000 feet                                        around a target subjected to multiple attack with
altitude. One may wish to examine how the H+1 hr                                         high-yield surface-burst weapons, contamination
contour levels, and the first-week dose (maximum                                         levels in the range of 5,000-10,000 r/hr at 1 hr, and
biological dose) contour levels can overlap under                                        first-week doses in the range of 15,000-30,000 rare
these conditions. The individual patterns, with                                          not unreasonable fallout levels to consider-along
overlap indicated, are plotted in Figures 8 and 9.                                       with other factors such as cost-in the design of
    It may be seen from Figure 8 that most of the                                        shelters and in planning recovery operations.




     -
     W INQ.o,OlClS
                         KAL(INMIIlS

                                       ("'t(TM fAu.OUT SttW. 0.1 cTSlIOOO IT. AU.
                                                                                             -
                                                                                             WIN) -10 leTS
                                                                                                                   SCALE IN MILES

                                                                                                                           lFflCTM FALLOUT SHEAI·O.' 1CT5I'IIOO". ALI.

Figure 8. Overlapping fallout H + 1 hour dose rate contours                              Figure 9. Overlapping maximum biological dose contours
for 310-mt. 50% fission surface bursts.                                                  for 310-mt. 50% fission surface bursts.
(1961 Modified WSEG Model)                                                               (1961 Modified WSEG Model)

                                                                                    28

                                                                                                                    Digitized by        Google
                                                                       4

            Climatological Mean WiDd Direction (D) &Dd Average Speed (8) in Knots in the Layer from 80,000 ft. Altitude
                            to Surface of the Earth &Dd Vector Standard Deviation (V) (Table I, Ref. 7)

    Location               Spring                  Summer                        Fall                   Winter             Annual

                      D     8        V       D       S        V             D     8              D        8
Albrook                             08.3    277                            275   08.8           044      02.2                      6
AIbuquerque                         19.4    035                            095   17.1           U92      28.9     2Z?              8
~dhd:lchorage                       19.4    049                            053   14.7:          (180     17.7     2Z?Z?          iO
Annette                             22.4    098                            076   22.0           U90      24.0     27:~7:         i6
Aig Spring                          18.7    284                            093   15.5           U84      35.6     21               9
lI,smarck                           20.0    085     16.8    15.1           087   23.9    20.5   109      27.8     20.5     095   21
Boise                096   16.6     20.0    062     15.7    14.8           097   19.4    20.7   102      25.9     22.9     092   19
Brownsville          078   24.4     15.4    275     12.8    10.7           088   08.2    17.7   077      29.5     16.5     075   13
Buffalo              096   26.3     23.1    107     16.6    16.5           083   28.8    22.6   089      37.4     23.7     092   27
Burrwood             087   28.1     18.7    261     09.5    11.8           088   14.0    19.4   083      37.0     17.8     086   18
Caribou              089   19.0     22.7    093     16.4    18.7           080   29.9    23.3   081      29.7     24.1     084   23
IIharleston                         22.3    229                            079   19.7:          U88      42.4     1UA            02
{I"lumbia                           22.6    099                            096   23."           U91      38.5     2U~            7:4
ilihyton                            23.5    115                            089   24.7:          (190     41.5     2U~£)          ;'6
IIlInver                            20.2    073                            103   18.e£          i04      26.0     2Z?~Z?           8
Dodge City                          20.4    072                            096   20.7:          U93      32.2     2;17:          00
i:dmonton                           17.8    076                            102   23.Z?          l09      27.1     lS~i           17
Ely                  095   17.7     20.0    052     12.9     13.0          092   16.9    19.0   102      24.0     23.0     089   17
Fairbanks            067   06.8     18.2    060     04.6     14.8          061   15.3    18.4   085      18.7     25.5     072   11
Fort Worth           082   31.5     20.4    282     03.7     13.2          095   16.5    20.7   085      37.8     22.3     087   20
Great Falls          095   18.8     19.4    069     16.8     15.3          102   24.1    20.3   106      30.0     21.8     098   22
Green Bay            096   21. 7    21.5    105     17.3     16.1          097   26.2    22.1   098      32.4     23.0     099   24
Greensboro           092   30.2     22.8    137     05.0     14.5          081   22.3    21.5   087      43.4     21.2     090   25
Adhmpstead                          24.4    104                            081   29.£)          U89      42.7     2U             09
futernat'l Falls                    20.2    098                            106   24.Z?          107      27.9     2,             01
bb""ksonville                       20.8    253                            OB3   16.7:          U88      39.0     17:U           00
       Charles                      19.0    263                            094   15.            Z?82     38.8     17::3          7:9
I~±bbue                             15.0    289                            123   Ol.Cz            06     15.1     1£;~Z?         Z?7
lIittle Rock                        21.8    212                            096   19.1           U85      40.5     27:~U          02
Long Beach           093   20.7     20.4    029     07.6     13.2          082   12.7    17.1   101      22.2     23.3     098   14
Maniwald             097   20.5     22.7    108     16.2     17.0          085   27.3    23.0   089      30.8     22.2     092   23
Medford              100   18.8     21.2    064     12.0     16.0          092   17.0    22.2   099      26.3     24.3     092   18
Miami                097   21. 8    17.2    267     12.4     10.7          080   06.5    18.4   088      29.5     17.2     092   11
Montgomery           092   30.7     22.5    246     05.4     13.4          087   18.5    21.5   086      42.2     21.4     091   21
Mt. Clemens          089   26.2     24.0    109     16.2     16.4          088   26.9    22.3   090      37.0     24.7     093   26
rrantucket                          24.3    091                            077   30.            U85      42.6     2e;7:          09
rrashville                          22.7    146                            089   22.7:          <p86     42.7     27:U           04
7:~"me                              18.8    040                            066   11.            U81      17.4     2U~            09
7:""rfolk                           23.0    124                            079   23.7:          Z?89     44.9     2Z?3           Z?6
08kland                             21.5    060                            093   14.7:          7: 05    25.1     2;d;              7
lI~aha                              22.0    089                            100   24.7:          U98      32.3     2U~U           l3
Pittsburgh           093   29.5     23.7    110     13.1     15.8          083   27.3    22.2   089      43.0     23.6     092   29
Rantoul              092   28.2     23.5    110     11.9     14.8          095   25.3    21.4   091      39.0     24.9     096   27
Rome                 094   26.8     24.2    104     17.0     18.1          081   29.2    23.7   088      37.5     24.4     090   27
San Juan             105   10.5     12.7    276     13.4     09.0          250   05.7    13.1   114      11.8     13.6     172   02
Seattle              093   16.8     21.8    076     11.0     18.0          091   21.4    21.8   097      25.7     24.0     092   18
Sault Ste. Marie     098   19.9     22.0    110     17.7     17.0          095   25.3    22.9   098      30.4     23.5     100   21
   Cloud                            21.0    095                            103   25.7:          U03      29.1                    03
1I""son                             20.3     349                           085   14.4           U88      27.4     2;'~           16
\kJasbington                        24.1     112                           080   26.            Z?89     44.7                    17
fulIxitehorse                       19.7     071                           066   17.7:          087      21. 3    2~§~           12




                                                                  29

                                                                                                 Digitized by (
References                                                       7. DOD-OCD, Federal Civil Defenae Guide Part E,
                                                                    Chapter 5, Appendix 6, Applicat10n of Yeteorolos1cal
 1. Hearings on the Department of Defense Appropriations            Data to RADEF, December 15, 1963.
    for IT 1964, U.S. House of Representatives. Part L
                                                                 8. USAEC External Gamma Doses and Dose Rates from
    page 110 (Secretary McNamara's statement given on
                                                                    the Fallout of Nuclear Explosfog, B. A. KDapp. Fallout
    February 7, 1963).
                                                                    Studies Branch, Div. Biology and Medicine, May 16,
 2. RAND R-425-PR A Review of Nuolear Explosion Phe-                1960, reprinted p. 527 at ~ Bearings on Civil
    nomenon Pertinent to Protective Construction. B. L.             Defense before a subcommittee of the Committee on
    Brode, May 1964.                                                Government Operations, 86th Congress, Marcb 1960.
 3. Tbe Effects of Nuclear Weapons, Prepared by the              9. WSEG Research Memorandum No. 10, An Analytic
    United States Department of Defense, Published by               Model of Close-in DepoSition of Fallout for use in
    the United States Atomic Energy Commission, April               Operational-Type Studies, George E. Pugh, Robert J.
    1962, Samuel Glasatone, Editor, U.S. Govt. Printing             GallaDo, October 1959.
    Office.
                                                                10. Ferber, Gilbert J. and J. L. Heffner. A CoIDl!!1'i8on of
4. USAEC CEX-62.2 Nuclear Bomb Effects Computer,                    Fallout Model Predictions with a Consideration of
   Fletcher !1 al., February 1963.                                  Wind Effects, p. 122. ~ seq. AEC TID-7632.
5. TID-7632 Radioactive Fallout from Nuclear Weapons            11. National Committee on Radiation Protection and
   Teats, Prooeedings of a conference beld in Germautown,           Measurements Report No. 29. Exposure to Radiation
   Maryland, November 15-17,1961, USAEC.                            in an Emerll!DOY. J8IIU&!')' 1962.
6. AEC-TID 16457 Gamma Ray ElQ?Osure Dose to Non-               12. Tabulations of Caloulations made from the 1961
   Urban Populations from the &lrfaoe Deposition of                 Mod1f1ed WSEG Model. an unpubl1shed report.
   Nuolear Test Fallout, B.A. Knapp, July 1,1962.




                                                           30

                                                                                              Digitized by   Google
                        POSSIBILITIES OF OCCURRENCE OF AREA
                        CONFLAGRATIONS AND FIRESTORMS WITH
                             RESPECT TO FUEL DENSITY
                                               Hermann Leutz
                                 Federal Ministry for Housing, Urbanization,
                                             and Land Planning
                                        Federal Republic of Germany


Causes of Area Conflagrations                                 Rome fire in 74 B.C., the Moscow fire in 1812, and,
                                                              more widely known and more disastrous, the area
According to Besson, an area conflagration can be             conflagrations and firestorms that occurred during
recognized by the following three essential charac-           the Second World War and destroyed many German
teristics. First, a spreading fire front that moves           cities. Offensive fire weapons in these recent cases
along under the wind's effect behind a volume of              consist of high-explosive and incendiary bombs, in a
overheated gas from low-pressure, smoldering car-             1:1 ratio, which were utilized in such numbers that
bonization. Second, fire fighting can be successful           during the air attack on Hamburg in 1943 two out of
only up-wind and on the flanks. And third, the fire           every three houses were set on fire in an area of
spreads, in the case of insufficient fire-fighting            several sq km. Other examples are found in the
caplcity, up to the point where it is no longer fed.          bombing of cities such as Cologne, Berlin, Dresden,
   Causes of the phenomenon can be classified into            Wuppertal, Kassel and Darmstadt.
three types. The first of these types is the area                The third cause of area conflagration is the simul-
conflagration that develops from a single fire site.          taneous ignition of everything caplble of burning over
This is completely typical of the type of fires that          large surface areas through use of nuclear weapons.
occur during peacetime. Under favorable weather               Examples are the area conflagrations that occurred
conditions (e.g., dryness and wind), the original fire        in Hiroshima and Nagasaki. The type of city con-
could easily be spread to adjacent buildings by flying        struction no longer plays a role in ignitions of this
splrks and radiant heat in crowded inner cities of            type. However, weather conditions have a great
predominantly wood construction. It also could                influence. Thus it is estimated that the thermal
occur because fire-fighting equipment did not have            radiation of a 100-mt bomb exploded at a height of
the caplc1ty it has today. Examples of area con-              100 km can scorch an area of 30,000 sq km under
flagrations that spread, essentially with the prevail-        UDfavorable weather conditions, whereas under
ing wind, are the fires that occurred in Hamburg in           favorable weather conditions it will scorch 200,000
1842, Chicago in 1871, and Baltimore in 1904.                 sqkm.
   Second is the area conflagration due to the grow-             It can be authoritatively stated that area confla-
ing together of numerous small fires. In this case            grations of the first type can no longer occur for
individual fires are spread by the prevailing ground          numerous reasons. Above all, the efficiency of
wind and are brought together into a fire front,              modern fire-fighting forces is so great that individ-
which moves down-wind and carries hot combustion              ual fires can at least be prevented from spreading
gases in front. Weather conditions also have a great          into area conflagrations. Nonetheless, area confla-
effect in this type of conflagration, whereas con-            grations of the second and third type are quite
struction type plays a secondary role. These large            conceivable, especially as a result of war-time
numbers of small fires can come about as results              occurrences.
of natural catastrophes, as occured in area confla-
grations in San Francisco in 1906 and in Tokyo and
Yokohama in 1923. In these cases fires were pre-              Conditions for the Occurrence of Firestorms
ceded by earthquakes. Buildings fell together and
combustible material1gn1ted in family fireplace,..            Although three fourths of the damage that occurred
   Tbey may also be caused by arson, including                in Germany during the Second World War was caused
deliberate wartime destruction. Examples are the              by fires, and many cities were burned, only a few


                                                         31
                                                                                        Digitized by   Google
firestorms occurred. This is due to the fact that,                 We can differentiate three zones of building
apparently, special conditions must exist before a              density:
firestorm can develop.
    Explanation of the physical process of a fire storm
                                                                o - 5%          Zone of individual fires that do not
                                                                                spread beyond their original center
is simple. Because of the merger of a large number
                                                                                of activity.
of individual fires during lulls in the wind, the air
above is heated to such a great extent that it unites           6 - 2~          Zone in which a fire can spread
into a single column of smoke and hot air and, be-                              beyond the original fire center but
cause of its reduced specific weight, develops such                             where no area conflagration danger
a powerful upward draft that it draws the surround-                             or fire storm danger occurs.
ing air masses strongly toward the fire's center.
                                                                Above 2~        Danger zone from area conflagration
This strong suction or pressure effect causes wind
velocities of greater than 150 km per hr, and                                   and firestorm.
smoldering fires are further fanned into flames. Air                Fuel density. Building density and fuel density
movement can also be explained by comparing tem-                are directly related and together indicate the extent
perature differences. In natural meteorology, these             of fire threat. A high fuel density directly follows
differences generally amount to 20 to 30 degrees                from a high building denSity. Fuel density will be
centigrade; but in the case of firestorms, we are               discussed later.
dealing with temperature differences of 600, 800,
or even 1,000 degrees centigrade. In contrast to an                Size of the area. Of the three geographic require-
area conflagration, a firestorm is a boiler-type fire.          ments this is the least significant. Generally, a
Centripetal air current greatly hinders lateral ex-             surface of 1 sq km is taken as the lower limit for
pansion of the fire; nevertheless, due to the ex-               the occurrence of a firestorm. However, with
tremely high temperature, expansion is possible by              present-day weapons having the capability of
means of radiation.                                             suddenly igniting everything that will burn, a much
   A firestorm is characterized by: rapidity of                 smaller area should suffice.
development (e.g., it can be fully developed within
half an hour after a conventional air attack, passing              Number of fires. It has already been pointed out
its greatest intenSity within four to five hours);              that only a large number of individual fires can re-
small degree of fire spread; complete destruction of            sult in this form of catastrophe. Fires of this type
everything combustible; hopelessness of any type of             are rarely created by natural forces. Planned
fire fighting; and a large number of deaths. Death              destruction, as in World War n, is the cause of
comes as a result of heat and carbon monoxide                   most.
produced by incomplete combustion.
    Besson classifies the special factors contributing             Wind. Calm wind conditions promote the forma-
to firestorms as geographical and tactical. Geo-                tion of firestorms because smoke and heated air can
graphical factors are subdivided into building density,         rise unimpeded over the fire area. On the other
fuel denSity, and size of the area. Tactical factors            hand, in cases of prevailing ground winds, fires
are subdivided into number of fires, wind, and at-              spread in the direction of the wind and lead to area
mospheric conditions. These factors are considered              conflagrations.
here in detail.
                                                                   Atmospheric conditions. Dryness, in particular,
    Building density. The building density indicates            favors the development of firestorms. Records
the degree of utilization of an area, and signifies the         indicate that, during World War II, dry weather
ratio between the area occupied by buildings and the            prevailed in all German firestorm areas.
total available space in an area.
   A differentiation is made between net building
density as related to net area (i.e., the area of built-        Comparison of Firestorm and Area Conflagration
up plots of land-buildings, yards, and lawn areas)
and the gross building density as related to the gross          All factors that have been enumerated as necessary
area of the location under study, including net areas           for the development of a firestorm are equallyappli-
plus areas of streets, public parks, railways, etc.             cable for the formation of an area conflagration,
   The firestorm area of Hamburg-Hammerbrook,                   except wind. If calm prevails during a large area
which was investigated in very great detail, showed             conflagration, the probability is great that a fire-
a net building density of 0.654 and a gross building            storm will result. Area conflagrations occur in
density of 0.438. Generally, building density of 0.3            cases of ground winds.
is the lowest limit that will allow the development                Besson clearly presents the following differences
of a firestorm.                                                 between firestorms and area conflagrations:


                                                           32

                                                                                          Digitized by   Google
 Firestorm                    Area Conflagration                 ing's susceptibility to fire is the amount of combus-
                                                                 tible material (referred to as the fuel density). The
        Usually involve a large city area, and
                                                                 concept of combustibility (Geilinger refers to this as
        the growing together of several fires.
                                                                 the "fire load"), first introduced in England and
 Initially there is no        Strong initial ground              America, was subsequently used by Professor
 ground wind or only a        wind.                              Virtala and since that time has come into use in
 weak ground wind.                                               German technical literature.
                                                                     Thus fuel density is the sum of calorific values of
 Occurrence of a cen-         Presence of a fire front
                                                                 all combustible materials present in a building
 tripetal pressure that       that is driven forward             (which includes both built-in building materials and
 limits the fire surface      by the wind.
                                                                 furniture or stored materials), related to the total
 to the periphery but
                                                                 area occupied by the building. The unit of measure-
 brings about a simul-
                                                                 ment is kcal/m2 • Expressions in terms of wood
 taneous setting ablaze
                                                                 equivalents per square meter are more useful. This
 of the entire area
                                                                 is the amount of wood which would develop the same
 afflicted.
                                                                 amount of heat as the combustible materials actually
 Forms within a few           Lasts up to several                present. The total available amount of heat, the so-
 hours.                       days.                              called burning potential, is related to the total area
                                                                 occupied by the building.
 Fire-fighting work           Fire fighting sometimes
                                                                     The following relation exists:
 practically impossible.      possible (in certain
                              sectors).                                %: (Gi . HI)
 Complete destruction         In certain cases zones             ~ = H           ·A
                                                                          wood
 by fire of the entire        which have been more
 area afflicted.              or less spared remain                              %:QI               2
                              intact.                                     4,000 kcal/kg • A (kg/m wood equivalent)

 Very large number of         The number of deaths is                     = Weight of the individual combustible mate-
 victims.                     relatively small.                             rial in kilograms
                                                                          = Calorific value of the individual combustible
      Fuel density (calorific value). The most impor-
                                                                            material in kcal/kg
  tant factors influencing the progress of a fire are:
  the type and amount of combustible material; the                        = Sum of all amounts of neat of the burning
  ratio of surface to mass, i.e., the distribution of the                   parts in kcal
  combustible material; and the supply of oxygen.
  Other factors of significance are: the size of the
                                                                 H    d   =Calorific value of wood (here:  average
                                                                  woo       value = 4,000 kcal/kg) for converting into
  fire from one fire-proof wall to the next; the size                       the wood equivalent
  of window-opening surfaces, and other similar
  opening surfaces; and special danger points.                   A        = Surface of the burning parts in sq m
      The evaluation of combustible material present
  in a potential fire area is made in terms of calorific
                                                                 ~        = Wood equivalents per sq m
  value. This is the amount of heat released from the               Although factors other than the number of kilo-
  combustion of one kilogram of the material in                  calories per unit area, determine the course of a
  question.                                                      fire-above all, locally-produced conditions-the
     In most cases of fire, a decisive role is played            evaluation of susceptibility to burning of a building
  by wood, in particular wood used as building mate-             based on fuel density is a useful criterion for de-
. rial-stairs, walls, wood shingles, framing, furm:ture.         termining fire danger.
  According to data provided by Geilinger, the calo-                According to Geilinger, the fuel density is a
  rific value of available wood varies between 4,350             simple criterion for determining the fire risk of a
  kcal/kg and 4,780 kcal/kg. In order to obtain a clear          building or part of a building. It presents a yard-
  picture of the danger represented by the calorific             stick for determining necessary fire-protection
  values of various combustion materials, Geilinger              measures.
  proposes that the mean calorific value of w~od be                 Fuel-density index. Up to now, fuel density has
  set at 4,400 kcal/kg (other authors have calculated            been a factor in evaluating mdividual buildings. It
  a figure of approximately 4,000 kcal/kg) and that              is also useful in connection with city-wide analyses,
  the calorific values of other materials be related to          that is to say, the evaluation of entire districts.
  that of wood.                                                     Suppose we observe an area occupied by several
     Fuel density (combustibility). It is evident that           buildings that are not close together. Between them
  the principal starting point in determining a build-           are yards, streets or other open areas. If we think

                                                            33

                                                                                                Digitized by   Google
of total burning potential in terms of the gross area          Investiption of the Fuel Density in Large
rather than as just the area occupied by buildings,            Modern Cities
we obtain the so-called fuel-density index, which is
a criterion for judging the susceptibility to fire of              Combustible construction parts and combustible
an entire city district.                                       construction volume. An evaluation of reports con-
   The fuel-density index, referred to as the i-value,         cerning the destruction of German cities by bombing
is obtained as the product of mean fuel density and            attacks shows that in many cases area conflagrations
building density of the area being studied. The nu-            occurred but only rarely did they develop into fire-
merical value is consequently always smaller than              storms. We can conclude that in these cities there
the numerical value of the fuel density.                       were present the prerequisites for fires of this type
   The following formula holds:                                and, in particular, a high i-value. Actually, we sub-
                                                               stantiated this assumption from the narrow, angular
i = q x D kcal/m2 gross land area, with
                                                               construction and predominant use of wood in parts
i = fuel-density index                                         c1 old German cities prior to 1945. Because of ex-
q = fuel density in kcal/m2                                    tremely high building density and high fuel density
D = building density                                           these city areas suffered area conflagrations.
                                                                   This high fuel density (which, in the case of the
   In order to simplify the expression, a continuously
recurring factor, 105 (F), is included in the equation.        surviving town of Regensburg, was 8.4 x 105 keal
   The extent of risk can be related to the fuel-              per sq m gross ground area prior to reconstruction)
density index as follows:                                      was largely in the residential portion of the city aDd
                                                               was a result of the high proportion of combustible
Group 0:                                                       material, I.e., wood. The use of wood was encouraged
  i < 2 F           (keal/m2)    No great danger               and is still being encouraged because of its dura-
                                 from fuel density.            bility, light weight, and workability, which make it
                                                               usable in conjunction with heavier construction mem-
Group 2:                                                       bers in windows, floors, doors, and wall paneling.
  i is between      (keal/m2 )   Danger of extensive               If any judgments are to be made concerning the
  2and4F                         fire spread; under            possibility c1 area conflagrations and firestorms in
                                 unfavorable condi-            today's cities, it must be determined whether the
                                 tions an area confla-         situation has changed since 1945. It must, in partic-
                                 gration or firestorm          ular, be determined whether the proportion of wood
                                 is also possible.             in homes being built today has changed. In the ease
                                                               c1 commercial and office buildings the situation is
Group 4:                                                       evident. A number of authors have attempted this
  i is between      (kcal/m2)                                  task, but they have usually limited their investiga-
                                 Increased danger c1
  4 and 6 F                      area conflagration            tions to a definite object, for instance, a damaged
                                                               area or a type of home. Beeause of the quantity of
                                 or firestorm.
                                                               published material, however, it is possible to
                                                               determine a definite trend.
Group 6:                                                           The fuel density c1 a building is determined not
  i is between      (keal/m2)    Probability of area           only by the amount of built-in wood but also to a
   6 and 8 F                     conflagration or              great extent by other combustible contents such as
                                 firestorm.                    furniture, books, clothes, fuel in cellars, and trash
                                                               on floors. On this baSis, the ratio of combustible
Group 8:                                                       construction to combustible contents was previously
   i> 8 F           (kcal/m2)    Area conflagration            about 3 or 4 to 1.
                                 of firestorm is                   Examples of comparative investiptions. Until
                                 inevitable.                   just before the beginning of the second world war,
                                                               German housing construction generally had the
   City analyses with the help of the fuel-density             following characteristics:
index show how much an entire area may be en-
dangered, where area conflagrations and firestorms             Foundation walls and        brick masonry or
are poSSible, and where reconstruction measures                cellar walls                concrete
are necessary. An example of the effectiveness of
changes in construction in seriously endangered                Cellar ceilings             ferro-concrete or side-
areas of a city is provided in the reconstruction of                                       rite or as arches be-
Regensburg, where the i-value was reduced from                                             tween steel girders
8.4 to 4.4 • 105 kcal/m2 •                                     Floor construction          wood joists


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                                                                                        Digitized by   Google
~                            wood                             entirely eliminated. In this manner we obtain an
                                                              astonishing correlation with earlier results.
Stairs                       wood, steel, or concrete
                                                                 In addition, statistical data were assembled
Floors in liviDg rooms       wood                             concerning the tendency for massive construction,
                                                              including concrete slabs in lieu of wooden rafters.
Floors elsewhere             sheet metal or flagstone
                                                              The following pattern was obtained after inquiry at
Windows and doors            wood                             the Office of Building Inspection af Hamburg concern-
                                                              ing new construction in the first nine months of 1953:
   In this type of construction, a typical three-story
home with six rooms would require 89 cu m of wood                                        Publicly        Freely
for every 79 sq m of living space.                                                       Assisted        Financed
   The percentages of wood used in major compo-                                          House           House
nents of houses to the total wood consumption are                                        Building        Building
as follows:                                                   Solid construction           90%            70%
                                                              Wooden rafter ceilings        2%            20%
Floor construction           38 to 42 per cent, corre-
                                                              Mixed construction            8%            10%
                             spondiDg to 33.6 - 37.6
                             m3 of wood                          Dr. Schubert feels that a primary reason for the
                                                              great reduction in wood utilization is the ''Decree
Roof construction            16 to 18 per cent, corre-
                                                              for Increasing Fire Safety," according to which only
                             sponding to 13.9 - 15.8
                             m3 of wood                       one- and two-story buildings should have joist ceil-
                                                              ings, and in the relatively high price of Wood.
Floor covering with          19 to 20 per cent, corre-           Other interesting investigations by the author
tasebcards                   sponding to 17.8 m3 of           concerning area conflagration and fire storm areas
                             wootl                            in Hamburg, Elnsbuttel, and Hammerbrook led to
                                                              results similar to those previously described.
Doors and windows            10 per cent, correspond-
                                                              Areas subsequently investigated were primarily
                             ing to 9.9 m3 of wood.
                                                              residential. In this case, similarly constructed
   The remaining uses of wood are distributed                 19th century, four- or five-story buildings were
among other construction parts and construction               examined. Joist ceilings, made of wood plastered
work.                                                         on the bottom, and wooden roof trusses were, in
   The use of wood in home building was considerably          conjunction with high building density, decisive
reduced in the reconstruction period after 1945.              factors in determining fire susceptibility.
Ferro-concrete ce1l1ngs on all floors and concrete               A report was given for three home types that
and solid stairs are being increasingly. used to re-          had or still have wood in attics, in floors, and in
place wooden construction. Using the same theoreti-           basements. They were classified as:
cal house with more economical roof construction
                                                              Type 1 Residential building of old construction
and without wooden floors and wooden ceilings, we
obtain a wood use of 25 cu m.                                        with wood framing, joist ceilings, and
                                                                     wooden stairs
   As a limiting value, wood consumption of 16 m3
appears attai-.ble. This becomes possible when                Type 2 Residential buildings of a type prevalent
roof construction, ceilings, and floors are made of                  during reconstruction, i.e., solid ceilings
non-combustible materials. Large consumers of                        and non-combustible stair construction, but
wood are primarily windows and doors, as well as                     wooden roof construction
lattice doors in cellars.                                     Type 3 Residential buildings of fireproof construc-
    The above results were confirmed by investiga-                     tion, i.e., solid ceilings and non-combustible
tions published by Dr. Schubert concerning wood con-
                                                                       stair and roof construction
sumption for an attic in a similar home constructed
in 1912. He found a built-in wood factor of 33 m3                Following are the calculated values in kilograms
which, during reconstruction, was reduced to 10 m3            af wood per sq m of floor or building space:
by more economical usage.
                                                                                Type 1         Type 2        Type 3
   When considering all built-in wood, the density                               55.5            26
                                                              Atticfioor                                        4
per unit building ground-floor area for city residen-                            70.0            24             24
                                                              Living floor
tial areas is about 0.51 m3/m2 for prewar homes
                                                              Cellar floor       22.5            11             11
and about 0.14 m3/m2 for postwar homes. This is
a reduction of 73 per cent in utilization of built-in            If the average wood load per sq m for a three-
wood for home building. According to Dr. Schubert,            story house is calculated from the above figures,
this value can be brought up to a limiting value of           values of 96, 36, and 29 kg result. In Type 2 con-
84 per cent when combustible roof construction is             struction this corresponds to a reduction of 63 per


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                                                                                         Digitized by   Google
cent and in Type 3 to a reduction of 70 per cent            This refers to zones where buildings have approxi-
over Type 1, which was popular in prewar days.              mately SO to 90 per cent non-combustible building
   Dr. Gelbert has made public the results of               materials. It is therefore valid to assume that no
similar investigations that largely agree with those        appreciable fire can occur in these areas where
discussed above.                                            there is complete destruction. Small individual
                                                            fires are pOSSible, but they cannot lead to area
                                                            conflagrations.
Summary                                                        At greater distances from ground zero, remain-
                                                            ing standing ruins of buildings form a shielding
It can be concluded that, in German cities rebuilt          effect against the spread of fire by thermal radia-
 following the war, buildings contain far less combus-      tion. Only window openings can permit heat radia-
 tible material because of increased avoidance of           tion to pass through, and higher parts of a house are
 lumber use. Therefore, fuel density of the buildings       more endangered than lower parts. Here one must
 is likewise less than prior to the war. The reduc-         provide for blocking of window openings.
 tions in the use of wood have occurred primarily in           In addition to fires caused by thermal radiation,
 heavy construction parts. Principal current utiliza-       fires caused by damage from collapse should also
 tion of wood is for windows, doors, floors and panel-      be watched for. Among the many reasons for such
 ing. But even here, wood can be replaced so that it        fires are:
 may be said that an unburnable home is already a              a) Igniting of combustible materials as a result
 reality. The ratio of combustible furnishings of           of room contents being thrown about by the shock of
 buildings to total combustible material will become        the explosion
 greater as progress is made in this area. Whereas             b) Igniting of gas from bursting gas pipes
 the ratio of built-in wood to the combustible contents        c) Igniting of combustible liquids and vapors, or
was 2.9:1 in the case of the four-story old-type con-       combustible materials dangerously near by
 struction, this ratio shifts in the case of Types 2           d) Igniting of easily inflammable objects by hot
 and 3 to 0.S5:1 or even 0.66:1. Generally, a ratio         metallic parts of the bomb
 1:1 is given in technical literature. The advantage           e) Dust ignition in certain industrial plants
 of the shift in this ratio is that during periods of
 crisis the fuel density can be quickly and effectively         Generally, in this type of fire there is no danger
 reduced by decreasing the combustible contents.            of further spreading. If a house is damaged and
     Generally, it may be stated that, in German cities     small fires occur in the debris, embers from these
 reconstructed after the war, the fuel-density index,       fires may continue to glimmer for a time or may
or i-value, is considerably smaller than before the         even ignite adjacent materials. But once the wind
war, first because of the reduction in fuel density         slackens it is usually simply a question of time until
and second because of more satisfactory building            the fire dies. In this case, the general danger of fire
density. It has been possible in this way to reduce         is not very great.
the danger of area conflagrations and fire storms. A            The increase in ignition area in the case of ground
typical example of how this has been achieved is the        or air explosions amounts to only 65 per cent for a
well-known reconstruction of the Hansa Quarter in           ten-fold increase in the explOSion value of the weap-
West Berlin. Prior to the war the ratio of building         ons. This does not apply in the case of explosions
area to non-building area was 1:1.5, today this ratio       occurring at very high altitudes, where only a small
is 1:5. Further, it was found that the amount of wood       portion of the total energy occurs as pressure, and
building materials could be reduced by SO per cent          where the effective heat energy is radiated over a
of the pre-war figure. If one allows for the combus-        very short period of time. If a value of 5 kcal/cm2
tible contents, there has been a reduction of 45 per        is taken as the critical energy, then, in the case of
cent in the total combustible material.                     a 100-mt weapon which is exploded at an altitude of
    It still remains to be seen to what extent the re-      30 miles, the ground area for the ignition of easily
sults achieved in fighting area conflagration and           inflammable materials is approximately SO sq miles.
firestorm danger during the war have been made                 In today's German cities, it is assumed that fire
impossible by the development of offensive incendiary       danger is no greater from nuclear weapons than
weapons, and especially thermonuclear weapons.              from massive utilization of conventional ones. Sur-
    Statements made by G. R. Stanbury present a view        vival appears possible in fireproof blast-protection
of the possibility of ignition and spread of fire during    shelters with sealed ventilating systems.
nuclear attacks. According to this view, it is assumed
that destruction in the central zone will be so com-           Death during air attack through fires. As early
plete that every initial fire will be smothered by the      as 1945 a report, "Death During Air Attack," was
masses of debris and dust flying about, somewhat            published by Dr. S. Graf of Hamburg. The author
similar to the action of fire -extinguishing powder.        compiled eye-witness accounts of the attack on


                                                       36

                                                                                       Digitized by   Google
Hamburg and post-mortems ~ persons Idlled during              tions above the fioars were still bearable. On the
the attack. The results of his investigations are ~           other hand, in some basement shelters people
utmost importance in establishing construction re-            perished without being aware of the danger. It can
quirements for fireproof inaulated shelters and their         be determined from these results and from general
ventilating systems.                                          considerations that death by means of oxygen defi-
   Temperatures above 50 degrees centigrade                   ciency or carbon dioxide poisoning was only possible
occurred in all basement shelters that were investi-          in streets or in homes when especially unfavorable
gated and in which victims were found.                        conditions came together.
   According to statements 01. persons who remained              The occurrence of carbon monoxide in basements
in basement shelters during the fire in the firestorm         in which there had not been any fire can only be ex-
area, it seemed that survival was possible only               plained by firestorms adjacent to the houses bringing
where penetration ~ heat into the basement shelter            smoke and fire into the basements. This resulted in
was prevented by means ~ barriers and sufficient              burning doors crashing into the basement and occa-
thickness of enclosure walls.                                 sionally igniting wooden partitions, coal and other
   In the large tower bunkers of Hamburg, which               fuel stored there, and other combustible objects.
provided a seating capacity ~ approximately 1,200                For the great majority 01. fire victims, the only
persons each but which were overcrowded by 3,000              causes of death were overheating and occasionally
to 4,000 persons during the attacks, air conditions           carbon monoxide poisoning. Together with burns,
were supp>sed to have been poor. However, no one              the most frequent cause of basement deaths was
                                                                                          '--
was seriously harmed.                                         hypertbermia-excessive heat. Hyperthermia also
   In several basement shelters occupants owed                claimed many victims among those in streets anclin
their survival to the fact that basement ceilings held        the firestorm area. Death due to other causes
up; large tubs ~ water were available so that, during         occurred only under special circumstances. Oxygen
the period of maximum beat, wet pieces 01. cloth              deficiency and carbon dioxide poisoning played either
could be placed on the face and body; and air condi-          a very insignificant role or no role whatsoever.




                                                         37

                                                                                          Digitized by   Google
DESIGN CRITERIA/TOLERANCES AND
     INTERNAL ENVIRONMENT

   Wayne J. Christensen, Chairman




                                    Digitized by   Google
                           TENTATIVE BIOLOGICAL CRITERIA FOR
                              ESTIMATING BLAST HAZARDS*

                                              Clayton S. White
                                          The Lovelace Foundation
                                          Albuquerque, New Mexico


INTROOUCTION                                                  follows. First, the nature of the blast-related
                                                               phenomena that may be significant to occupants of
 Since experience at Hiroshima and Nagasak1(I,2)              protective structures will be noted and categorized.
 and studies at the Nevada Test Site(3-6) have in-            Also, relevant information from field studies will
 dicated that chances of survival following nuclear           be reviewed.
 explosions can be sharply enhanced by suitable                  Second, criteria for estimating human hazards
 exposure inside open and closed structures, it is            from such phenomena will be presented even
 appropriate that a symposium on protective con-              though those available are tentative and incom-
 struction include an examination of selected biologi-        plete and only a beginning has been made in their
 cal information to help improve, if possible, sur-           formation. (2,11-14)
 vivability when structures are either modified or               Third, supporting material and references from
 designed to function as shelters. Tlat the material          the literature, including those from a long-term,
presented should encompass biomedical air-blast               continuing program sponsored by the Division of
criteria stems at least in part from the fact that the        Biology and Medicine of the U.s. Atomic Energy
combination of lazardous variations in the environ-           Commission since 1951, and by the Defense Atomic
 ment resulUng from nuclear explosion not only can            Support Agency of the Department of Defense since
be markedly altered by the conditions of exposure,            1959, will be summarized briefly. Such information
but also can be favorably influenced to assure blast          will aid those who would better understand the tenu-
survival at ranges relatively close to ground zero.           ous nature of the criteria and better appreciate the
This fact has been demonstrated for animals in field          intraspecies biological studies, as well as the re-
tests at free- field overpressures near 90 psi for            lated biophysical and physical investigations that
open(4,7,8) and about 175 psi for closed(6,9)                 lave not only improved understanding of the effects
underground structures. Also, test data are avail-            of blast from conventional explosives, but also
able on a simple structure buried at a location               extended the data to include nuclear blast as well.
subjected to approximately 245 psi(10) which in-
dicate that survival from blast-related hazards
could have been highly probable.                              TENTATIVE BIOLOGICAL CRITERIA FOR
    To the contrary, events inside some structures,           ESTIMATING BLAST HAZARDS
due, for example, to pressure reflections and to
wiDds funneling through entryways and other open-             Primary Effects (Pressure)
ings, can, for certain locations and designs, enhance
hazardOus conditions considerably. In fact, danger-           It is now known that mammalian tolerance to blast-
ous translational effects for large yields and for            induced variations in air pressure, as far as lethality
certain burst conditions and exposure geometries,
may extend to ranges that are close to those for              *Tbe background for Dr. White's presentation is contained
significant free-field thermal effects on a hazy               in the report ''Biological Tolerance to Air Blast and Re-
day, and they can easily occur at ranges far                   lated Biomedical Criteria," prepared by Clayton S. White,
exceeding those for thermal burns when the latter              I. Gerald Bowen, and Donald R. Richmond, Lovelace
                                                               Foundation for Medication Education and Research,
must be due to scattered thermal radiation or hot,             Albuquerque, New Mexico, Aprlll965, which has been
dust-laden air or debris because the geometry d.               published by the Atomlc Energy Commission (CEX 65.4).
exposur.e precludes direct-l1ne-of-site application            Because of space limitations, these proceecUlIgs contain
of thermal energy.                                             only Sections L In, and VI of that report. They are given
    This presentation will attempt to deal with three          in full with figures and reference numbers unchanged, but
related areas in a reasonably systematic way as                with page numbers conforming to these proceedings.

                                                         41
                                                                                             Digitized by   Google
and effects on the lungs are concerned, is dependent                Neither the effects of rise time and pulse duration,
upon the rate, magnitude, character, and duration fA.           as they might influence the pressure tolerance fA. the
the pressure rise and fall, the size of the species fA.         eardrum, nor the effects of age on blast tolerance has
interest, and probably the ambient pressure at which            been systematically studied thus far, but a few data
exposure occurs'<2,4,13,17,29-38) Also, it is clear             are available iDdicating that young rats are more
that, for major effects, biological tolerance to                susceptible than adult rats.(44) However, a system-
atypical or disturbed wave forms is different from              atic investigation of the effects of ambient pressure
that for pulses of classical or near-classical con-             in blast tol~rance has been under way for some
figuration'<2,4,13,29-32,39-42) The latter will be              time'<46,47) To date, one exploratory study with
discussed first.                                                mice indicates that tolerance to overpressure is
                                                                indeed a function of the ambient pressure at which
                                                                exposure occurs.(47) If work with other species
Classical or Near-Classical Wave Forms                          continues to support the same conclusion, then bio-
                                                                logical scaling to ootain figures appUcable for
For a given species of mammal, the response of the              exposure at different altitudes will become feasible.
thoraco-abdominal system to "fast"-rising over-                 If it does, this probably means that the lung and
pressures is determined both by the magnitude and               lethaUty data in Table 28, derived at Albuquerque
by the duration of the pulse.(2,4,13,17,29"-39,41,42)           altitude, can be scaled to sea level using the factor
Tentative estimates appUcable to human adults are               1.2, which is the ratio of sea-level pressure (14.7
available for "long"-duration waves; viz., for ex-              psi) to the ambient at Albuquerque (12 psi).
plosive yields down to at least 1 let. These are                    Also, regarding the lung and lethality data in
summarized in Table 28,<2,4,5,11-14,31,43-45) The               Table 28, it is important to reaUze that they were
first column of numbers in Table 28 refers to maxi-             derived using many hundreds of animals all exposed
mum effective pressures measured at or near a                   side-on against an end-plate closing an instrumented
biological target. The last column gives the incident           shock tube. In each instance, therefore, the effective
overpressures from which these may occur if                     maximum pressure was the reflected pressure.
pressure reflects maximally.                                    This pressure was appUed almost instantaneously
                                                                to the side fA. the animal mounted against the sbock-
                         TABLE 28
                                                                tube end-plate, but occurred in two steps on the
    Tentative Criteria for Primary Blast Effects In             upstream side fA. the animal; viz., the incident
   Adults AppUcabie to "Fast"-Rislng, ''Long''-Duration         followed a very short time later by the reflected
                 0gerpressures In Air                           pulse passing back over the animal from the end-
          (adapted from References 11, 14, 31)                  plate of the tube.
                                                                    Work is under way to learn how to scale the
                    Related Maximum 0gerpressure, psi           shock-tube data to other exposure geometries such
 Critical                  Maximum      Incident with           as side-on and end-on to the advancing pulse in the
 Orpnor                    Effective      Maximum
                                                                open-as well as the various angles in between-and
  Event                    at Target      Reflection
                                                                prone on the ground with the source of the blast
Eardrum Fallure*                                                varying on an arc from immediately overhead down
 Threshold                    5                2.3              to the surface fA. the ground.
 50 per cent                 15 - 20           6.2 - 8.0
Lwyr Damage+
 Threshold                   10 - 12           4.4 - 5.1        Disturbed Wave Forms
Lethal1tyt                                                          Stepwise increase in overpressure. For certain
 Threshold                 30 - 40          11 - 15
                                                                locations of exposure, such as varying distances
 50 per cent               42 - 57          15 - 18
 Near 100 per cent         57 - 80          19 - 24             away from reflecting surfaces stepwise increase
                                                                in overpressure can occur.<2-5,1l-14,30-32,39-42)
*Data from Zalewsld,(43) WT-1179,(4) WT-1467,(5)                This can involve the initial appUcation of the incident
 Richmond. (44)                                                 followed by the reflected pulse.(l3,32,39-42) If the
+Data from Richmond, (44) Pratt et aI. (45)
tData from CEX-58.8,(12) DASA 1341,(11) CEX-63.7,(2)            interval between the incident and reflected pressures
 DASA 1335.(13).                                                is very short-J)8rhaps 0.1 to 0.4 msec for small
                                                                animals (13,32,-39,40) and 0.5 to 1.0 msec for the
Note: The lung and letballty data, derived using IIhook tubes   dog (l3)-the animal "appreciates" the pressure
      In Albuquerque at 12 psi using a side-on exposure
     pometry ap1nat a refieoting surface, apply str10tly        rise as one pulse. For longer intervals of time,
     to conditions wherein the max1mal refieoted pressure       perhaps a few msec for animals as large as man, the
     was the maximal effective pressq.re. There may soon        biological target "sees" the pressure as two sepa-
     be enough ev1deDCe to scale the data to sea level (see     rate pulses. As a consequence, tolerance rises by
     tex:t) and to other pometries of exposure.                 a factor fA. about 1.6 for the guinea pig (2,13,32) and



                                                                                          Digitized by   Google
 may be as much as a factor of 2 for large animals,                                     TABLE 29
 including humans.
    Unfortunately, it will not be possible to make a                 TentaUve Criteria for SeooDdary Blast Effects
 more precise statement until studies of stepwise                         (adapted from Refe1'8llOeS 11, 14, 31)
-increases in overpressure are extended to the larger                                                               Related
 and to more of the smaller mammalian species.                                                                      Impact
                                                                                        CriUcal Organ               Velocity
    Other wave forms. If the riSing pbase of a pres-            Kind of MissUe            or Event                   ft/s8C
sure pulse inc~ases smoothly or in small, incre-
mental steps, it is known that the tolerance of                 Nonpenetratlng
mammals to overpressure increases by factors of                  lo-lb object       Cerebral CoDedslon:.
from 3 to 5 providing the very early pbase of the                                    Mostly "safe"                   10
                                                                                     Threshold                       15
increase in pressure is not great and fast enough
to be letbalin its own r1ght'<2,48,49) Again, the                                   SIrull Fracture:.
lack of data does not allow tolerance to be more                                      Mostly "safe"                  10
fully defined. However, it is known that mammals                                     Threshold                       15
                                                                                     Near 100 per cent               23
weighing about 35-40 lbs and exb1biting 50-per cent
letbal1ty .at a P max of 50 psi if the wave is "fast"           Penetrating
rising and of ''long'' duration, will tolerate well over         10-gm glass        9dn Laceratlon:+
200 psi if the p.tJ.se increases to a maximum in 20              fragments           Threshold                       50
or more msec'<2,48,49)                                                              Serious Wounda:+
                                                                                     Threshold                      100
                                                                                     50 per cent                    180
Secondary Effects (Missiles)                                                         Near 100 per cent              300

                                                                *Data from Lissner and EvaD8i(52) Zuckerman and
A variety of materials may be energized by blast                 Blacki(53) GurdJlan, Webster and Lis8Der.(54)
overpressures, winds, ground shock, and gravity.                +Data from AECU-3350(51) and WT-1470i(50) figures
Even if they should strike man as missiles, they                 represent impact velocities with unclothed skin.
might or might not be hazardous depending upon
several exigencies: i.e., the kind, character, mass
and velocity of the missile; the angle at impact;               ative experiences related thereto that are induced
whether or not penetration or perforation occurred:             by blast pressure, winds, ground shock and gravity,
and the area and organ of the body involved. Though             represent one of the major and, under certain cir-
the situation is fraught with complexities and any              cumstances, the most far-reaching effects of blast
biological criteria to help assess possible hazards             on man.<11,12,14,29-31,55,56) Whether or not the
from blast-induced debris are Ukely for some time               effect is of consequence depends upon a variety of
to be incomplete and.inadequate, some that are                  factors. Among them are the magnitudes of the
tentatively useful have nonetheless been formulated             forces involved; the time, distance, and angle over
using data from several sources'<2,12,50-54)                    which they are applied; the character of the contact
    In these, reproduced in Table 29,(11,14,31) 10-             surface concerned: and the area of the body
gram window-glass fragments were employed to                    traumatized.
simulate the effects of a penetrating missile, and                  Mostly for the sake of simplicity, but also be-
the nonpenetrating hazard was exemplified by a                  cause it is difficult to know which portions of the
10-pound object assumed to strike the head, the                 body to relate to acceleration-time data, tentative
latter being regarded as the critical organ for                 tertiary blast criteria were developed on the basis
minimal hazard. That the liver and spleen, as well              of impact velocity. These are shown in Table 30.
as other abdominal organs and even the eye, may                 They were assembled using data for skull frac-
be more susceptible to accelerative impact loading              tures;(54) information on whole-body impact derived
than the head bas been recogn1zedJ2,lf,14) However,             from an lDtraspecies study of small anima1s;(57)
 the lack of relevant quantitative data currently pre-          figures for foot, ankle, and leg fractures;(53,57-59)
 cludes regarding them as more critical organs than             and work with human volunteers subjected to i~ct
 the head.                                                      loads in the seated and s~nd1ng positions.<60-62)
                                                                    Even though the data are crude and incomplete,
                                                                the criteria are helliu!. pot only in assessing the
 Tertiary Effects (Whole-Body Displacement)                     various levels of decelerative injury that may follow
                                                                translation, but also in evaluating some of the pos-
 In add1tiOD to translational phenomena involving               sible hazards from accelerative loading that can
 penetrating and nonpenetratlng missiles, whole-                occur in shelters' respondinc to ground shock. In
 body displacement and the accelerative .and deceler-           either case, the sharply challenging loads are likely

                                                           43
                                                                                              Digitized by   Google
                          TABLE 30
                                                                   show) to the "high"-G but "short"-duration loads.
        Tentative Criteria for Tertiary Blast Effects              The msec-duration figures in the charts refer to the
            (adapted from References 11, 14, 31)                   time the average G must act to give the velocity-
                                                  Related
                                                                   acceleration-time relationships shown.
       Condition                                  Impact              The vertical iso-acceleration lines define toler-
    Critical Organ                                Velocity         ance when the acceleration pulse is constant and
       or Event                                    ft/sec          prolonged; viz., since it is reported that 1,500 lbs
                                                                   applied statically produced fracture in one leg, and
 Standing Stiff-legged Impact.                                     therefore 3,000 Ibs will be required if one is stand-
  Mostly "safe"                                                    ing stiff-legged on both feet, 20 G applied to a 150-
    No significant effect                          <8 (7)          Ib man can be expected to be near the fracture level,
    Severe discomfort                               8 - 10         a fact noted in the left illustration of Figure 71 by
   Injury                                                          the vertical portion of the shaded area, which was
    Threshold                                      10 - 12         drawn parallel with the 20-G line.
    Fracture threshold                             13 - 16             The right illustration in Figure 71 contains three
     (heels, feet, and legs)                                       "low"-acceleration asymptotes. One refers to the
 Seated Impact.                                                    design limit for ejection seats and the other two
  Mostly "si1fe"                                                   (the heavily shaded area and the dotted line), accord-
    No effect                                      <8 (7)          ing to Hirsch, (61) span the tolerance values ranging
    Severe discomfort                               8 - 14         from 15 to 28 G given in the literature for the limit
   Injury                                                          of the spine's tolerance to fairly static loads.
    Threshold                                       15 - 26
 Skull Fracture+
  Mostly "safe"                                         10         Miscellaneous Effects
  Threshold                                             13
  50 per cent                                           18         Non-Line-of-Site Thermal. Hazards
  Near 100 per cent                                     23
 Total-Body Impactt                                                   Hot, debris-laden gases. Apparently the thermal
  Mostly "safe"                                         10         biology literature contains no laboratory data rele-
  Lethality threshold                                   20         vant to the exposure of animal or human skin to
  Lethality 50 per cent                                 26         moving, hot, dust-laden air. Also, experimental
  Lethality near 1 00 per cent                          30         information about burns produced by hot, moving
 ·Data from Draeger, Barr, Dunbar, Sager, Schelesnyak;(58)         gases, when the exposure time is measured in a
  Black, Christopherson and Zuckerman;(59) SWearingen,             few fractions of a second, seems to be sparse indeed.
  McFadden, Garner and Blethrow;(60) mrsch(61) and                 Accordingly, it is not possible to formulate biologi-
  Eiband. (62)                                                     cal criteria that are germane to the conditions under
 +Data from GurdJian, Webster and LisBner;(54) Zuckerman           which non-line-of-site thermal burns were noted in
  and Black. (53)                                                  the "open" shelters at the Nevada Test Site; viz.,
 tData from DASA 1245. (57)                                        hot, dust-laden air, moving at high velocity over
                                                                   biological targets for time periods ranging about
. to be of "short" duration when collision with a hard             75-120 msec, the "fill-time" of the shelters. These
  object occurs, mainly because the stopping time and              intervals represent the time it took for the inside
  distance are a function mostly of the cushioning                 shelter pressures to become equal to the outside
  effects of the body tissues themselves.                          pressures due to the positive winds moving into
     This factor and the concept of iso-velocity values,           the structure with the blast wave.
  being the phYSical parameter with which one might                   However, data shown in Figures 72 and 73, from
  relate biological response, was given considerable               a study by Ashe and Roberts,(67) involving the ex-
  meaning by a perceptive and much more refined                    posure of human volunteers to air of various tem-
  analytical contribution recently published by                    peratures blown at 6 liters per minute through a
  Hirsch.(61) Figure 71, in which Figures 7 and 8 are              tube 1 cm in diameter, have some relevance to
  reproduced from Hirsch's work in a David Taylor                  thermal hazards when calories are delivered to
  Model Basin report,(61) shows estimated iso-velocity             the skin mostly by convection. Figure 72 shows the
  asymptotes as criteria for impact tolerance in                   temperature-time relationships found to be associ-
  standing and seated positions.                                   ated with a minimal thermal insult to the skin;
     The horizontal iso-velocity lines at 10 ft per                namely, the occurrence of an initial erythema
  sec for the stiff -legged standing man, and at 15 ft             (redness) within 15 minutes, which disappeared,
  per sec for the seated man, apply (as the illustrations          however, within 24 hours.


                                                              44
                                                                                             Digitized by   Google
    Figure 73, in addltion, shows the temperature-                                                        mal singeing ~ the vibrissa and the fur of animals
time conditions necessary to produce the indicated                                                        bas been observed.(44)
burns on the forearms ~ five volunteers, eacb
undergoing five exposures at temperatures of 100°,                                                           Other blast-induced thermal hazards. Blast-
200°, 300°, 400° , and 500° C. It is of interest to                                                       induced fires and burns from sizable pieces of bot
point out that Asbe and Roberts regarded a burn                                                           debris are known to occur. Tbose interested in
showing erythema for longer than 24 bours, but                                                            temperature-time criteria for hazards from flames,
without vesiculation, as a first-degree burn. Second-                                                     radiant surfaces and hot circumambient air and for
degree injuries were defined as blistering burns.                                                         bot objects are referred to the work Qf. Henriques;(68)
The vesicles noted varied from 0.5 to 1.0 cm in                                                           Henriques and MOritz;(69) MOritz;(70) Moritz and
diameter. Tbey were accomplished by a surrounding                                                         Henriques·(71) Moritz Henriques, Dutra and
erythematous area from 0.8 to 2.0 cm in diameter.                                                         WeiSiger;(72) Biittner(73) and others, including the
   It sbould be emphasized that the data in Figures                                                       many contributors to the recent text edited by
72 and 73, shown here mostly because they do involve                                                      Hardy.(74)
exposure times ranging from a few seconds down to
a few tens cl. msec, apply to low-velocity air that                                                           Dust inhalation. Whether or not the inhalation of
contains no materials that might significantly in-                                                        dust and other aerosols, radioactive or not, can be
crease the thermal capacity ~ the moving gas.                                                             bazardous to man poses a number of complex ques-
Tberefore, the curves in Figures 72 and 73 need be                                                        tions to whicb only the furure holds firm answers.
regarded as useful for orientation only, and not to                                                       Among the factors involved are the following: the
belp interpret thermal events that occurred in the                                                        physical and cbemical properties of the inhaled
Nevada sbelters and were associated with exposure                                                         material; the concentration acblally inhaled; the
to very high-velocity air carrying considerable                                                           particle size, shape, and density; the respiratory
quantities of quite bot dust into the structures.                                                         rate and volume; the relative amount of nasal versus
                                                                                                          mouth breatbing; the time cl. exposure; the amount
   Compression beating. It may serve some purpose                                                         and location of the inhaled material initially deposited
here to point out that experience with shock rubes                                                        in the airways; the subsequent fate and residence
clearly shows that mammalian lethality occurs well                                                        time of the materials in the body; and for insoluble
below pressures associated with temperatures higb                                                         particulates, perhaps soluble aerosols also, the
enough to burn animals. Occasionally, at pressures                                                        ciliary clearance time under conditions of continu-
near the upper portion of the lethality curve, mini-                                                      ous exposure may be quite important indeed.


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                  Tolerance of stIff-legQed standing men to shock                                                     Tolerance eX seated men to shock motion of short
                            motion of Ihort duration 61                                                                                 duration 61

Figure 71. For references numbered 6. 8, 10, 14, and lS in these graphs, see blbl10graphy Items 58, 63, 64, 65, and 66,
respectively.


                                                                                                     45

                                                                                                                                                                   Digitized by      Google
   Lung deposition. Figure 74, reproduced from a                              Inert dusts-dust axphyxia. Inert dusts or particu-
report of the Subcommittee on Inhalation Hazards.                          lates of low solubility and toxicity may be hazardous
chaired by H. A. Kornberg, (75) is helpful in that it                      simply because deposition in the lower portions of
summarizes the results of many estimates of per-                           the respiratory tree is sufficient to mechanically
centage of disposition in the lower and total respira-                     occlude the airways and produce suffocation'(24)
tory tract as this varies with particle size and                           Desaga called attention to this problem, reported
respiratory rate. Findeisen,(76) and Abram80n(77)                          relevant experiments using dogs, and computed the
(noting some of Findeisen's data) estimated that                           amount of dust required to produce suffocation in
10-30 micron particles are deposited as low as the                         adults to be about 30 cc: i.e., 30 gm for a unit-
terminal bronchioles of the lungs, while those> 30                         density material; 45 gm for a dust having a specific
microns are deposited only in the trachea, larynx,                         gravity of 1.5 (fly ash from soot traps in the coaI-
pharynx, and the nasal passages and sinuses. Also,                         operated Klingenberg power plant in Berlin and
much of the inhaled material is swallowed, including                       similar to plaster dust and dust developing in re-
that swept into the throat by ciliary action in the                        inforced concretet bunkers(24»; 75 gm for material
tracheobronchial tree.                                                     having a density of 2.5 gm/cm 3 (that of reinforced
   Figure 74 shows the marked variability, from                            concrete itself).
about 20 to near 90 per cent, in the amount of inhaled                        Using any of the applicable values noted above
material that is deposited, depending upon particle                        along with appropriate parameters, order-of-
size as well as respiratory rate. For particles 1                          magnitude calculations can be made of the time it
micron in diameter, the deposition percentage may
vary by a factor of 4 (from 20 to 80 per cent) due
only to changes in respiratory rate. To produce a
similar variation in deposition at constant respira-
tory rates, a change in particle size by a factor of
near 10 is required-from around 0.5 to 5 microns.
   Since the weight of a given particle is propor-
tional to the cube of the radius, the dose or amount
of material deposited in the lung is mostly associated
with particle sizes above 0.5 microns. Particles
smaller than this are probably significant only for
very toxic material and perhaps only for very
prolonged exposures.



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                    _... -
                                                                                •        IE D4     .ceDIllO      Z          .4"" D
                                                    \Il                                                       TIME IN SECONDS

                                                                           Figure 73. Temperature -time relationship produclDg


                                                      ~
                                                                           iDd1cated degree of hot-air burns of human sldD. 67
                W. .!!!: ' .!:!.' II-a,      It4I
 0.10
 CIDI
 D.OI                                                     .lo.
                        I
 om
 D.OI o     ~         ~
                        I
                                       ~             ~    ~
                                                              "   ~        . *Ol the Committee on Pathological Effects of Atomic
                            TEMPEIIATlIIE IN DEGREES Co                       Rad1at1on, Dr. Sbields Warren, Cha1rmaD.
Figure 72. Time-temperature relationship required to                         tCement bas a deDS1ty of 0.82 - 1.95 &lid silica a density of
produce erythema without a burn. 67                                          2.66 lHandbook of Chemistry, 9th Edition, edited by Laq).


                                                                      46

                                                                                                                          Digitized by   Google
                                                           TABLE 31

                   Computed Order of Map1tude-Tlme-Concentration Relationship to Produce Dust Asphyxia.

         Dust                           Amount Inhaled                 Amount Deposited                 Time to Deposit
    Concentration                         in m2lmin                        in m2lmiD                   45 lID in Minutes
pn/m3        mg/l1ter               10 lpm         90lpm              10lpm         90lpm           101pm          90lpm

 100              100                1000          9000                 500          4500             90            10
  50               50                 500          4500                 250          2250            180            20
  25+              25                 250          2250                 125          1125            360            40
  10               10                 100           900                  50           450            450            50
   5                5                  50           450                  25           225            900           100
.Assumed dust density was 1.5 pn/cc. 50 per cent of the 1nha.led material by weight was retained aDd 45 lID deposited in
 the lung would produce asphyxia.
+Nonhazardous in 1 hr for dogs exposed to Klingenberg dust (1.5 gm/cc) apparently because ciliary action mostly kept the
 deeper reaches of the lung free of particulates.



might tate to prodllce dust asphyxia in a variety of                 First, dust concentrations of 31.8 and 88 gm/m3
coDditions. As an example, Table 31 was prepared                     were reported by Desaga(24) as found in two com-
assuming the following conditions:                                   partments of a reinforced concrete bunker of the
   a. Density of the inhaled dust, 1.5 gm/cc                         Maginot Line following the experimental detonation
   b. Lung retention to be 50 per cent by weight of                  of ''H'' charges (magnetic antitank hollow charges).
material lnbaled                                                     Second a dog inhaling in a chamber containing 80
   c. Lung retention of 45 gm sufficient for asphyxia                gm/mi of Klingenberg dust was practically asphyxi-
   d. Respiratory volumes to be 10 and 90 liters per                 ated in one hour .(24)
minute, these values being approximate for sitting at                   Also, it is prohably significant that Desaga re-
rest and a maximal work effort, respectively                         ported that a dog Inhaling 25 gm/m'3 of Klingenberg
   e. The concentration of inhaled materials ranged                  dust for 60 minutes showed no change in respiration
from 5 to 100 gm/m3, but remained constantfor                        within 30 minutes, was panting and coughing at the
each exposure                                                        end of the exposure, and that slimy dust sediment
   Table 31 shows that suffocation of an individual,                 was found only in the upper one third of the trachea.
breathing 10 liters per minute and lnbaling dust                     Some dust was discernible in the alveoli. Apparently,
having a concentration of 50 aDd. 100 gm/m3, might                   ciliary action served to clear the lung at a rate
occur in 180 and 90 minutes, respectively. If, how-                  nearly equal to the deposition rate of particles.
ever, the ventilation rates were near the maximum                    Thus, the 25 gm/m3 concentration prohably is a
(90 liters per minute), asphyxia could ensue in 10                   marginal concentration for the dog, and perhaps
minutes for the higher and in 20 minutes for the                     so for man. Desaga personally inhaled this con-
lower dust concentrations. Tbe figures ·of 50 and                    centration of Klingenberg dust for 0.5 minutes
100 gm/m3 are interesting for at least two reasons:                  (16 deep inspirations) and reported coUghing,
                                                                     copious nasal secretion, and mUd conjunctivitis
                                                                     as long as six hours after the exposure.
          o     TOTAL RESPIRATORY TRACT
                                                                        Toxic-particulates .:net aerosols. No attempt will
 -        ~ LOWtR RESI'IRATOIrI TRACT
                                                                     be made here to deal with the complex problems of

 •
 i
                                                                     moderately and highly toxic materials, including
                                                                     those that are radioactive and usually classed as
                                                                     internal emitters. Suffice it to say that serious


I!:~~t~~~
                                                                     technical difficulties are involved, that much rele-
                                                                     vant research Is under way and that many more data.
                                                                     are required before it will be possible to formulate
                                                                     mea.nJndul biomedical criteria for animals and
 i~r--~~~=~--~~                                                      man. (75) Also, it is helpful for orientation purposes
 !                  OJ                    1.0              10
                                                                     to study the useful illustration, compiled in 1952 by
                                                                     First and Drinker (78) and reproduced here as
                     MRTICLE DIAMETDt (NICfIONS)                     Figure 75. A study of the figure shows that toxicity
Figure 74. Depoa1tion in Respiratory Tract.                          for radioactive elements, beiDg in the range of about
(Reproduced from NAS-NRC Publloatlon 848. (75»


                                                                47

                                                                                               Digitized by   Google
10- 11 to 10-20 gm/m3, is many orders of magnitude                                        SUMMARY
separated from the concentrations of dust occurring
in storms that range from about 0.5 to 10 gm/m3•                                          The nature of the blast-induced hazards related to
Thus the dust concentration in the shelters in Nevada,                                    protective construction was illustrated by summariz-
being from 2 to 5.5 gm/m 3, were comparable to those                                      ing experience with animals exposed in above- and
seen in severe dust storms. They pose no hazard as                                        below-ground structures subjected to rmclear blast
far as suffocation is concerned, but might be other                                       during the field operations carried out at the Nevada
than annoying and irritating, depending upon the                                          Test Site in 1953, 1955, and 1957.
chemical nature of the particulates. Should these be                                         Environmental variations of consequence that
silicates-and there are bound to be some from the                                         occurred in shelters tested "open" and well as
sand and aggregates used in the concrete-then                                             "closed" were:
Figure 75 shows that around 10-4 gm/m3 has proven
a troublesome range in industry.                                                             1. Variations in pressure.
    Finally, it is well to say that the settling rates of                                    2. High-velocity winds, aided sometimes by
the various-size particulates in a shelter can be a                                       ground shock and gravity that energized penetrating
significant factor in determining the particle size                                       and nonpenetrating missiles and debris arising from
of material inhaled as well as the dust concentration.                                    inside, outside, and in the entryways of the structures.
This follows because, as sedimentation proceeds,                                             3. Whole-body displacement as a consequence of
the spectrum of concentration and particle sizes                                          high-velocity winds, ground shock, and gravity, and
passing the face of an individual will vary. One                                          the damage related thereto.
result is that the time of initial exposure will be                                          4. Non-Une-of-site thermal phenomena due to
a function of settling velocity, and the time of sub-                                     hot, dust-laden gases and debris, sufficiently severe
sequent exposure, among other things, will be a                                           in some instances to produce carbonizing third-
function of the level of post-shot activity in the                                        degree burns in pigs and complete loss of hair and
shelter, producing resuspension of the dust that                                          severe skin burns in dogs.
was previously deposited on the floor.                                                       5. Macroscopic particulates and reSpirable dust




                                                            GRAMS        PER      CUBIC      METER
 lOll   I               I~                                                        10           I                          I            I                    KTI
 -LOW-PRESSURE PNEUMATIC CONVEYING ......                                               ~      DUST               _    StlORM    ---+-
            ~ EXPLOSIVE CONC. OF AIRBORNE DUSTS                            ~                  ~CLOUDBURST                             - MODERATE RAIN ....
                                    fLOUR  COAL                                                               -FLY-ASH EFFLUENT __
                                                                                                             IALTIMOIII AlME STD IIIILWAUlCf:E
                                                       lAND I STOllE DII'tlNt      ILAIT I'UIINACE OPEN HEARTH ELECTltIC ITHL IIIAII fOllY. DIIILUil
                                          _              STACK                     EFFLUENT                  CONCENTRATION              ~ ...-MINE AIR -
                                                                                    I IREY IItON fOUllD.....              SMELTERS                COAL CUTTINt

                                                                                                                                                           10-'
                                                                                                                                                      -
 I(fl       I                      10il            I                             IO-~          I                       10-4            I

 04 1
    DRIZZLE -
                 _
                  ~FOG        It MIST! - . .
                         FOUNDRY - W RKROOM AIR
                                                   --'--Hl~ :1ft
                                                      -       CITY                                  AIR
                                                                                                            ~                     ~         POLLEN
                SHAICEOUT          CLEMIII POURINt MOUIINI
                    _    COTTON -MILL - WORKROOM AIR                                         . . - RURAL"        SUBURBAN AIR _


 --MINE AIR --+-
 MUCIC...  HAUUNt
                            lItEAICINt _III              CARDINt
                                                                        .... I  WEAVINt

                                                                                                             .
                                                                                                   VllCOUS fiLTERS
                                                                                                                          I
                                                                                                                  AlR-COIIDITIOII ... flLUItl
                                                                                                                       I EFFLUENT AIR
                                                                                                                      SlOt
                                                                                                                                     INDUSTRIAL CLOTH fiLTERS
            WlLDINI                                                           COiL                      SILl CATES
                                                       THRESHOLD         LIMITS IFOR        MINERAL DUSTS       AND TOXIC METALS
                  FIaOa     z,.o              MN                                              SI             AI Pi 00 He CetOa

                                                   I                                           I                                  •    I
                                                                                 Icfl                                  ICTII                               10--
                 ELECTROSTATIC      ItREClltlTATORS
        f A I RIC                E~ENT
                      f I L T E Rs i -~I----------~------
                                               AIR cELLULOIE - ADEITOI IW'E1ti

                                                   I                                                                                   I
 10--                                                                            I<TII      I                                                              ICT'II
   ......_ - - THRESHOLD                                             ~           THflESHOLD   LIMITS       FOR                        ELEMENTS
                                                                     PuN           IRA"
                                                          GRAMS       PER       CUBIC      METER


Figure 75. Chart, plotted on lOgarithmic scale, showing atmospheric conditions dealt with in practice. (Reproduced from
Firat aDd Drinker, Arch. Indus. Ilyg. Occup. Med., §.: 387, 1952,(78»


                                                                                  48
                                                                                                                                Digitized by   Google
even in "closed" shelters, arising from the walls                Serious wounds
and cellings as a consequence of ground-shock-                      Threshold         100 ft/sec impact velocity
induced spalUng and, in some instances, pro..bly                    50 per cent       180 ft/sec impact velocity
from air blowing through the ventilation systems                    Near 100 per cent 300 ft/sec impact velocity
protected by sand traps (or other "leaky" devices).
                                                              Impact, Standing Stiff-Legged
   Except for the loss of one dog from violent im-
pact subsequent to wind-induced translation and 17               Mostly "safe"
of 20 mice pro..bly from transient spikes of high                  No significant effect        < 8 (?) ft/sec
reflected pressure, blast survival of "large" and                  Severe discomfort            8-10 ft/sec
"small" animals located Inside "open" below-ground
shelters was demonstrated at free-field overpres ..              Injury
                                                                    Threshold                   10-12 ft/sec
sures of over 90 psi (ground range of 1,050 ft from
a 29-kt explosion on a 500-ft tower). Blast survival                Fracture threshold          13-16 It/sec
was also demonstrated with mice exposed in "closed"           Impact, Seated
structures located at 175 psi (804-ft ground range
from a 44-kt explosion on a 700-ft tower).                       Mostly "safe"
                                                                   No effect                    < 8 (?) ft/sec
   For "open" shelters of certain configurations,
the blast-related environmental variations inside                  Severe discomfort            8-14 ft/sec
proved to be greater than those outside the shelter.             Injury
For other configurations the opposite was true. Thus,               Threshold                   15-26 ft/sec
the geometric conditions of exposure may either
enhance or attenuate hazards from blast phenomena.               Skull Fracture from Head Impact
   Tentative biological criteria for estimating                     Mostly "safe"      10 ft/sec
human tolerance to blast-induced environmental                     Threshold           13 ft/ sec
variations were presented In tabular form as follows:              50 per cent         18 ft/sec
                                                                    Near 100 per cent 23 ft/sec
"Fast"-Rising Overpressures of "Long" Duration                   Total-Body Impact
   Eardrum failure                                                  Mostly "safe"               10 ft/sec
     Threshold                 5 psi (2.3 psi)*                     Lethality threshold         20 ft/sec
     50 per cent               15-20 psi (6.2-8.0)                  Lethality 50 per cent       26 ft/sec
                                                                    Lethality near 100
   Lung damage
                                                                     per cent                   30 ft/sec
     Threshold                 10-12 psi (4.4-5.1)
                                                                 Non-Line-of-Site Thermal Burns
   Lethality
     Threshold                 30-42 (11-15)                        The lack of criteria for non-line-of-site ther-
     50 per cent               42-57 (15-18)                        mal burns caused by hot, dust-laden air
     Near 100 per cent         57-80 (19-24)                        moving at high velocities was noted, but data
                                                                    from Ashe and Roberts (67) were cited to show
Atypical or Disburbed Wave Forms of "Long"
                                                                    temperature-time conditions for transient
Duration
                                                                    redness of the skin, and for first- and second-
   Tolerance was estimated to increase by a factor                  degree burns in human volunteers when air at
   of about two for pressures rising to a maximum                   various temperatures was blown at 6 liters per
   in two ''fast'' steps and by a factor of 3 to 5 for              minute through a tube 1 cm in diameter onto
   wave forms rising smoothly to a maximum in                       the subject's skin.
   30 or more msec.
                                                                 Dust Asphyxia
Nonpenetrating Missiles (10-1b Object)
                                                                    No attempt was made to formulate criteria for
   Cerebral concussion                                              particulates of low, intermediate, or high
     Mostly "safe"          10 ft/sec impact velocity               toxicity due to radioactivity or otherwise.
     Threshold              15 ft/sec impact velocity               However, a calculation, following Desaga, (24)
                                                                    was made of the time it might take in adults
  Skull fracture                                                    to produce dust asphyxia for "normal" and
     Mostly "safe"          10 ft/sec impact velocity               maximal ventilation of 10 and 90 liters per
    Threshold               15 ft/sec impact velocity               minute, respectively, at various assumed dust
     Near 100 per cent      23 ft/sec impact velocity
                                                                    concentrations.
Penetrating Missiles (10-gm Glass Fragments)
                                                              *The figures In parentheses represent overpressures that
  Skin lacerations                                            on normal reflection will give the maximal value of
     Threshold              50 ft/sec impact velocity         pressure noted.

                                                         49

                                                                                          Digitized by   Google
   Supporting data from the literature and ongoing                      tect1ve Shelters," USAEC Civil Effects Test Group
programs in environmental medicine from which the                       Report, WT-1467, Office of Tecbn.ical Services, De-
tentative biological blast criteria were drawn were                     partment of Commerce, Washington, D.C., June 30,
cited not only to help the reader assess the validity                   1959.
of the criteria, but to elucidate the use of extrapola-              6. Richmond, D.R., C.S. White, R.T. Sanohez, and
tions from animal data, to point out the employment                     F. Sherping, ''The Internal Environment of Underground
of "best estimates" where data were inadequate or                       struotures Subjeoted to Nuolear Blast. n. Effects on
absent, and to note wherein "state of the art" con-                     Mice Located in Heavy Concrete Shelters," USAEC
cepts bear upon attempts to estimate human blast                        Civil Effects Test Group Report, WT-1507, Office of
                                                                        Technical Servioes, Department of Commerce,
tolerance at the present time.                                          Washington, D.C., May 31, 1960.
    The implications of the full-scale field experi-
ence with shelters, tentative criteria for assessing                 7. Vortman, L.J., "Evaluation of Various Types of Per-
blast hazards, and selected data supporting the latter                  sonnel Sbelters Exposed to an Atomic Explosion,"
                                                                        USAEC Civil Effeots Test Group Report, WT-1218,
were briefly discussed. Among other things empha-
                                                                        Office of Technical Services, Department of Com-
sized was the fact that while "open" structures had                     merce, Washington, D.C., May 10,1957.
without question enhanced survival, they also proved
extremely hazardous on a variety of occasions. As                    8. Vortman, L.J., "Effects of an Atomio ExplOSion on
a consequence, and even though no "open" structures                     Group and Family Type Sbelters," USAEC Civil Effects
                                                                        Test Group Report, WT-1161, Offioe of Technical
carefully designed to serve as shelters had been                        Services, Department of Commerce, Washington, D.C.,
tested, proof of adequacy as means of protection                        January 21, 1957.
was considered a responsibility of those who might
favor "open" rather than "closed" designs.                           9. Cohen, E. and A. Bottenbofer, "Test of German
                                                                        Underground Personnel Shelters," USAEC Civil Effeots
                                                                        Test Group Report, WT-1454, Office of Technical
                                                                        Services, Department of Commerce, Washington, D.C.,
                                                                        June 25, 1962.
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                         RADIATION TOLERANCE FROM FALLOUT IN
                                PROTECTIVE STRUCTURES*

                                             Robert A. Conard
                                        Medical Research Center
                             Brookhaven National Laboratory, Upton, New York


This paper is concerned with the protective role of            whole-body dose of 175 rads of gamma radiation,
shelters as related primarily to the hazards of close-         and sufficient contamination of the skin to result
in fallout radiation associated with nuclear detona-           later in widespread beta burns and loss of hair. In
tions. Tile formation of such fallout occurs in the            addition, measurable amounts of radionuclides were
following manner. The intense heat of the fireball,            detected in their urine from internal absorption of
as it touches the surface of the ground, incinerates           fallout materials. Gamma radiation caused a reduc-
earthen material to an ash-like state, drawing it into         tion in their blood cells to about half-normal levels
the cloud where it becomes mixed with radioactive              and proved to be the most serious of the hazards to
residue from the bomb detonation. Because of the               which they were exposed. Fortunately, the dose was
heavy particulate nature of the material it is depos-          just short of lethal, and no deaths or serious conse-
ited within an area of several hundred mUes. 'Ihe              quences (such as bleeding or infections from lower-
hazards associated with fallout are due primarily to           ing of their blood levels) were apparent. The return
gamma and beta irradiations associated with the                of blood levels toward normal was evident within
fission products in the fallout material. In some              one year. Beta burns and epilation began to appear
 cases alpha-emiWng isotopes may be present, but               about two weeks after exposure in about 90 per cent
these are likely to be present only in small amounts.          of the people. They occurred largely on areas that
 Neutron radiation is not associated with fallout but          were not covered by clothing at the time of exposure.
is emitted with gamma radiation at the time of deto-           Most burns were superficial and healed within a few
nation, and, as is true with blast and thermal effects,        weeks, though there were a few that were more seri-
is of concern only in the immediate area of the                ous, resulting in p~ul ulcerations and requiring
 detonation.                                                    longer healing time. Loss of hair on the head was
                                                                spotty and temporary with regrowth occurring within
                                                                six months. Based on radiochemical urine analyses
Effects of Fallout in an Open Field                             it was estimated that during the two days prior to
                                                                evacuation, the average individual body burdens for
When an individual is exposed to fallout in an open             the princi~alisotopeS were as follows: Sr89 , 1.6-
field, there are three types of hazards to which he             2.2 ~. Ba 40,0.34-2.7 I'C; Rare Earth Groue& 0-1.2
is subjected: first, that of penetrating whole-body            I'c; 11~1 (in thyroid gland), 6.4-11.2 I'c; Ru1 ,
gamma radiation; second, that due to irradiation of             0-0.013 I'C; Ca45 , 0-0.19 I'c; and FessUe Material
the skin from deposit of fallout material on the body;          0-0.162 gm.(l) Absorbed material radioiodines
and third, that of internal absorption of radioactive           were the most hazardous isotopes, and it was
materials from air breathed and food and water                  calculated that the dose to the adult's gland was
consumed. Our experience with 82 Marshallese                    150 rads and to the child's gland approximately
people who were accidentally exposed to such fall-              1,000 rads. The rapidity of isotope elimination from
out on Rongelap Island in the Pacific in 1954, follow-          the body was noteworthy: no acute effects associated
ing the experimental detonation of a thermonuclear              with the presence of these isotopes were detected.
device, exemplifies these three types of hazards.(l,2)              The findings of subsequent surveys suggest that
The island was dusted with white ashen material                 possibly some late radiation effects are evident in
which fell for a time estimated at up to 16 hours               the Marshallese'(2) These include slight retardation
following the detonation. Since their flimsy, thached '
palm huts offered little protection, the natives lived
under the most extreme conditions of fallout con-
tamination for the two-day period before evacuation            *Reaearoh supported by the U.S. Atomio Energy
was possible. The majority received an estimated                Commission.

                                                          55

                                                                                            Digitized by   Google
                                                                                                                                                                        --
of growth and development in some exposed male                   of exposure. Later, the appearance of fe~er, Infec-
children; a slight increase in miscarriages and                  tions, and bleeding from the gums or other parts of
stillbirths in exposed women during the first five               the body will also serve as indications of severity of
years after exposure; and an increase in pigmented               exposure (see Figure 1).
moles in areas of beta burns. During the past three
years, six cases of nodules of the thyroid glands                    Importance of bone marrow dose. It is clear that
among the exposed people have occurred. Five of                  the degree of destruction of blood-forming cells is
these were not malignant and appeared in children,               the critical factor in the "survival possible" dose
and one was a cancerous nodule in an adult woman.                range of radiation. The dose to the bone marrow,
These are undoubtedly related to exposure of the                 where blood cells are formed, thus becomes the
thyroid gland to radioiodines absorbed from the                  all-important consideration. Blood-forming marrow
fallout, and emphasize the importance of radio-                  is encased in bone that varies considerably in depth
iodines in early fallout situations.                             in various parts of the body (from a few cm to 11 cm
    These studies have helped place the hazards of               or more, with an average depth of 5 cm).(4) There-
fallout in proper prospective. It is clear that                  fore, the critical dose could be considered roughly
penetrating gamma radiation is by far the most                   at the 5-cm body depth. Attermation of the gamma
serious hazard.                                                  radiation through the shielding structures will re-
                                                                 sult in considerable degradation and scattering of
The Role of Protective Structures in Fallout                     the incident radiation so that a good portion of the
Situations                                                        measured radiation may be too soft to reach much
                                                                 of the critical organ system (the bone marrow).
Let us examine the importance of protective struc-                Furthermore, bone covering the marrow may further
tures as related to each of the hazards of fallout.              attenuate radiation. It is not believed likely that the
                                                                 photoelectric effect produced in bone will seriously
    Gamma hazard. Attermation of the gamma radia-                alter the dose to the bone marrowJ5,6) If one can
tion is the most important role of protective struc-             insure a dose to the bone marrow of not over 200
tures in regard to fallout. In order to understand the           rads in 24 hours in an uncomplicated case, survival
importance of this fact, let us examine the possible             should be probable. It would be ideal to have radia-
effects of such radiation on man when delivered to               tion-detection instruments in protective structures,
the whole body in a relatively short period of time.             which would measure the total absorbed dose at 5 cm
Several categories of effects can be based on the                body depth.
prognosis related to radiation dose.(3) With very                    The dose rate is another important factor to be
large:doses, greater than 600 rads, survival ,is im-             considered. Protraction of radiation is lmown to
probable. With doses greater than 600-700 rads,                  reduce the effect. Thus, further radiation at more
and in the thousands of rads, brain damage and gas-              protracted dose rates over the ensuing days after
trointestinal damage would be so severe that death               fallout could be tolerated, perhaps 100 rads the
would occur within the first 4- 5 days and no treat-             second day and lesser amounts thereafter. This
ment would be capable of life-saving. With doses be-             dose schedule would allow for more free movement
tween 200-600 rads survival is possible. With this               of personnel after the first day or so.
degree of exposure, blood-cell destruction is the
predominant effect, and may result in infections,
bleeding, and possibly death. Figure 1 shows blood
changes and clinical signs in cases where survival                       I-~~~?N~~~
                                                                           ~
is possible (200-600 rads). With doses below 200                               of';"o




                                                                                                               ,
                                                                                          0....
rads survival is probable, since the blood-cell de-
struction per se will be insufficient to result in death.                      ... ...           ~(
                                                                                                        ~~
                                                                                         ...             ~~
One must remember that other stresses, such as                                                 "'''',
physical trauma, blast injury, thermal burns, sick-
ness, starvation, and thirst will undoubtedly lower
                                                                                                        '~.ft.
                                                                                                         ,                                                         ~
                                                                                                                                                             -" ...~
                                                                                                                                                            ~~

the dose at which survival is possible.                                                                      '...                  CRITICAL PERIOD     ~~; 000
                                                                                                                                                         ..
                                                                                                                    \                   FEVER      'ioo~
   Since reliance on blood counts as an index of the                                     PLATELETS~                                   IN;~i:~~~S                        ,/
degree of blood cell destruction will not be likely                                                                     \             POSSIILE DEATH               /'
under the conditions considered, it should be noted                                                                         \
                                                                                                                                , ..... ----------' ........   ~


that there are certain signs that will roughly indicate             0~--~--L---L---~--~--~--~--~--~
the severity of radiation exposure. The severity of                  o     ~                    10             I~           20        U       30       3~        40      4~
                                                                                                               OAYS AFTER EXPOSURE
the nausea, vomiting, and diarrhea during the early              Figure 1. Schematic graph showing major blood changes
period after exposure and the duration of these                  and clinical signs for radiation doses where survlvalis
symptoms are important indications of the extent                 possible (200-600 rads).


                                                            56

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   The quality of the radiation (specific ionization,          and inadequate. It is important to recognize that
linear energy transfer) would be a consideration               fatal radiation casualties, for which treatment will
only in regard to the neutron irradiation. However,            be c1little avail, will succumb within a few \\eeks
some experimental work indicates that in dogs, at              after exposure, whereas those who may survive, and
least, the relative biological effectiveness of fast           can be benefited even by limited treatment, will
neutrons for bone-marrow dam~ is about the                     probably not develop full signs of radiation illness
same as for gamma radiation. (7)                               for two to three weeks. By that time radiation levels
                                                               will be greatly reduced and such persons may be
   Skin irradiation. In regard to the hazard of skin           channeled to aid stations or hospitals for more
burns from fallout, shelters would offer complete              definitive treatment than can be offered in most
protection. The small amounts of fallout material              shelters.
that might sift into a closed shelter would be negli-
gible with regard to skin irradiation. In personnel
                                                               References
who are contaminated when they enter the shelter,
radiation skin burns can be prevented simply by                 1. Cronkite, E.P. et al., Effects of Ionizing Radiation on
removing contaminated clothing and washing the                     Human Beings. Report on Marshallese and Amerioans
skin, or simply wiping the skin with a damp cloth.                 Accidentally Exposed to Radiation from Fallout and
Clipping the hair or even shaving the head may be                  Discussion of Radiation Injury in Human Beings, U.S.
indicated If the hair and scalp are heavily                        Government Printing Office. 1956, pp. 1-106.
contaminated.                                                   2. CoD&rd, R.A. and A. Bicking, Medical Findings in
                                                                   Marshallese People Exposed to Fallout Radiation.
   Internal irradiation. The hazard of internal                    Results from a Ten-Year Study. J.A.M.A. 191, No.
absorption of fallout should not be significant in                 19, May 10, 1965.
the shelter. Except for closed underground shelters,            3. Cronkite, E.P., V.P. Bond, and R.A. Conard, DIagnosis
most will require no air filtration or special ventila-            and Therapy of Acute Radiation Injury, Chapter 10 in
tion systems, since sufficient air to maintain life                Atomic Medicine, Fourth Edition, Eds. C.F. Behrens
will filter through cracks in doors, windows, etc.(8)              and E.R. King, The William and W1lk1na Co., Baltimore.
In such situations, it is possible that temperature                1964. pp. 238-250.
and body odors might cause some discomfort, but                 4. International Commission on Radiological Protection,
under the circumstances they would be of negligible                Report of Committee IV (1953-1959) on Protection
importance. During the period when fallout is                      against Electromagnetic Radiation above 3 mev and
actually falling-only a matter of hours-the shelter                Electrons, Neutrons, and Protons, Pergamon Press,
should be kept closed except for short periods when                Inc., New York, 1964, pp. 1-44.
a door or window may be opened to refresh the air.              5. Wilson. R. and J.A. carruthers, Measurement of Bone
Thereafter no special ventilation precautions should               Marrow Dose in a Human Phantom for C0 60 " Rays and
be necessary.                                                      Low Energy X-Rays. Health Physics 1: 171, 1962.
                                                                6. Spiers, F.W., The Influenoes of Energy Absorption and
                                                                   Electron Range on Dosage in Irradiated Bones. Brit. J.
Treatment of Radiation Casualties                                  Radiol. 22: 521, 1949.
                                                                7. Bond, V.P. and J.S. Robertson, Comparison of Mortality
With regard to treatment of radiation casualties                   Responses of Different Msmmalfan Species to X-Rays
associated with rmclear warfare, the importance of                 and Fast Neutrons; in Biological Effects of Neutron and
using protective structures as a prophylactic treat-               Protron Irradiation, Vol. 2, pp. 365-377. International
ment for avoiding exposure to penetrating radiation,               Atomic Energy Agency, Vienna, 1964.
skin contamination, or internal absorption cannot be
                                                                8. An Evaluation of the Need for Filtration Systems to
overemphasized. Because of the chaotic circum-                     Protect Sheltered Personnel from RadIoactive Fallout;
stances at such a time, and the shortage of trained                Naval Research Co. 3-9 Brookhaven National Labora-
medical personnel, the use of active treatment for                 tory, Upton, New York, Offioe of Naval Research
serious radiation effects will necessarily be limited              ACR-72, May 1962.




                                                          57

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                          FIRE AND NOXIOUS GASES: EFFECT ON
                              INTERNAL ENVIRONMENTS OF
                                 PROTECTIVE SHELTERS

                                 J. Enoch Johnson and Eugene A. Ramskill
                                      U.S. Naval Research Laboratory


Introduction, Assumptions, and Definitions                     Condition A - No power (i.e., temporarily unable to
                                                                             use emergency power), therefore no
Common to all protective shelters are environmental                          external ventilation or internal re-
problems related to the metaboHc processes of the                            circulation available.
human occupants: viz., (a) consumption of oxygen               Condition B - Power available, but external atmos-
(02)' (b) production of carbon d10xide (C~) and                              pheric cond1tions are such that only
water, and (c) production of metabolic heat. In                              internal recirculation can be used.
add1tion to these normal problems, we must face
the complications of possible internal and external            Condition C - Power available, external atmosphere
fires with attendant oxygen consumption, evolution                           suitable for ventilation of the shelter.
of noxious gases, and heat release. The considera-
tion of the effects of these fires will be limited in
this paper primarily to the internal environments              Cond1tions A and B-No VentUation
of protective shelters for the survival do the civilian
population. In order to focu8 our attention on this            It is considered impossible to depend on anything
problem realistically, we must first select and de-            external to the shelter being as planned or desired.
fine a working model-a typical shelter unit for the            For example, although the shelter may be built in a
protection and survival of the civilian population. In         cleared area as far as possible from other struc-
add1tion, we must define the external and internal             tures or trees, a large fire may be in the immediate
conditions facing the occupants.                               vicinity consuming material that was moved into the
    We have chosen for our model a structure de-               cleared area by blast. At any rate, because of poSSi-
signed to shelter 100 occupants for a period of two            ble external fires in the area, several requirements
weeks following one or more nuclear blasts. This               must be fulfilled before normal ventilation with ex-
structure was deHberately chosen to provide only               ternal air is advisable. In this paper, the term
the minimum space and vent1lat1on recommended by               "ventilation" is strictly reserved to mean introduc-
the Office do Civil Defense.<l) These recommenda-              tion do external air into the shelter.
tions require that each occupant shall have 10 sq ft               It is assumed that the emergency power system
of floor space, 86 cu ft do volumetric space, and a            can be activated within a reasonable time, i.e., well
ventilation rate of 3 cfm. Hence, our model has a              before C~ increase becomes a problem. However,
total volume of 6,500 cu It and is capable of being            during the period before power is available (Condi-
ventilated at the rate of 300 cfm. It is assumed that          tion A), lighting should be supplied only by electric
the shelter is stocked with the food, water, and other         flashlights. The use do matches, candles, and ciga-
suppHes required for survival.                                 rette lighters must be absolutely controlled to con-
    It is assumed further that the occupants, although         serve 02, minimize CO2 and carbon monoxide (CO)
having survived the effects do one or more nuclear             production, and reduce the probabtHty of internal
explosions, are now without any support facilities             fires. As is done in naval submarines during emer-
external to the shelter, such as communications,               gency no-ventilation periods, only those persons
pubHc water supply, and power. It is considered                doing necessary jobs should be up and about. All
mandatory that emergency electrical power be made              other persons should He or sit down. All unneces-
a part of our model to provide the required venUla-            sary movement should be denied. Smoking must be
tion. Without mechanical ventilation, it is doubtful           absolutely forbidden.
that survival is possible. It is reasonable, therefore,            During Cond1tion A or B, the importance do avoid-
to specify three cUfferent cond1tions based on ventila-        ing combustion of oxygen by burning lighted candles,
tion possibilities as follows:                                 for example, is explained by the following data. An

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ord1nary 3/4-inch-diameter candle bul'Ding quietly            concentration of cigarette smoke cannot be stated
(no draft) in ordiD8l'y air was found to be consumed          to have an immed1ate toxic effect, it certainly is
at the rate of 9 grams per hour. The candle Is                a condition to be avoided.
assumed to be composed of paraffin hydrocarbon,                  The air in the shelter at the time the ventilation
which burns essentially to COJ and water as follows:          ducts are valved shut should approach the usual
                                                              concentrations of normal atmosphere which are, at
- CH2- + 3/2 O J - COJ + H20 •                                sea level: 21 per cent OJ, 0.03 per cent CO2, and
Therefore, the candle burning at 9 grams per hour             O.SO ppm CO. As long as ventilation is secured, the
will consume 0.84 cu ft of OJ and evolve 0.56 cu ft           air in the shelter will lose OJ and gain CO as well
of COJ per hour. Particularly In a small shelter              as COJ through human respiration; it is assumed
(e.g., family-size), the burning of one such candle           that the shelter is sufficiently tight to prevent sig-
will be important when ventilation is restricted or           nificant exchange with external air. It bas just been
not available, since it consumes approximately as             shown that CO concentrations that can reach 40-70
much 02 and produces as much CO2 as one man.                  ppm even with limited smoking should not be a
Obviously, where heat is an important factor, the             serious problem.
                                                                 It bas been established that, under conditions of
candle output of 90 Kcal per hour cannot be ignored.
   It hardly needs to be emphasized again that                no ventilation and no smoking, the limiting factor
                                                              for sbelter occupancy wW be the CO2 levedS,5)
tobacco smoking must be forbidden during periods
of no ventilation. However, the following comments            At any given level of C02' more d1stress wm
are made for completeness. If 100 cigarettes (one             result from this metabolic product in the atmos-
per man) were smoked during this condition, the               phere than from 02 depletion. Table 3 contains a
total CO2 evolved from the cigarettes would be less           conv,~ent summary of physiological effects of
than one cu ft; this Is approximately the COJ pro-            CO2 •    It is noted immediately that ventilation
duced by one man in one hour. The CO produced, at             should be started, if possible, before the CQa con-
48 ml per cigarette, would add 26 ppm to the pre-             centration reaches 3 per cent. Under no conditions
va1l1ng CO concentration.(2) In a 100-man trial, the          should the ventilation be delayed beyond 5 per cent
amounts ol CO exhaled during the initial no-smoking           CO2. At this exposure, it is very difficult to make
periods were as given in Table 1.(S) These data               rational decisions. Figure 1 shows the concentra-
show that in the first two hours about SO cc/man was          tion of COJ versus time in the unventilated shelter.
exhaled into the shelter atmosphere. This would add           Consideration of Table 3 and Figure 1 indicates
16 ppm CO to the atmosphere of our hypothetical               that the endurance limit Or the shelter occupancy
6,500 cu ft shelter. The total of 42 ppm would not            during Cond1tion A or B is reached within 3.5 to
be troublesome. Table 2 contains a convenient                 5.5 hours. It is obvious that application of Condition
summary ol CO toxlcity. (4)
    The most serious effect ol such smOking, however,
Is the h1gb concentration of irritating aerosol (ciga-                               TABLE 2
rette smoke), which would amount to about 8 micro-
grams per liter. This concentration of cigarette                     Toxioity of Carbon Monoxide to Bumans(4)
smoke Is very high and is very irritating to most
                                                              Concentration (ppm)          P~siologloal     Effect
personnel. Poorly ventilated night clubs would
seldom have concentrations this high. Highly con-                                          MAC -         effect in 8 hours
                                                                      100                          DO
tam1nated industrial areas seldom have aerosol
concentrations in excess of 1 microgram per liter,                    200                  Headaches in 2-3 hours
while ''fresh country air" Is generally stated to be                  400                  Headaches and nausea in
less than 0.1 microgram per liter. While the high                                           1-2 hour.
                                                                      800                  Headaches and nausea in
                                                                                            45 min. and oollapse in
                                                                                             2 hours
                          TABLE 1
                                                                     1600                  Headaches and nausea in
      Average Exhalation of Carbon Monoxide DIlr1Dg                                         20 min. and possible
        No-Smoking Periods of Shelter Trial.(3)                                             death in 2 hours
                                                                     3200                  Headaches and dizziness in
                   CO Exhaled (oo(STP)/Man(hour)
                                                                                             5-10 min. and possible
               Two-Day Trial         Two-Week Trial
                                                                                            death in 30 min.
1st                  18                        20                    6400                  Headaches and dizziness in
2nd                  11                        13                                           1-2 min. and possible
3rd                   7                                                                     death in 10-15 min.


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                                                                                          Digitized by   Google
B (recirculation) w1ll not alleviate the situation,              external air into the shelter for this purpose ID1J8t
because it will not add 02 or remove COz. In fact,               be prov1dec:l; a Simple, inexpensive means COD8ists
if heat build-up were the limiting factor, the added             af a l/4-inch copper tube.
heat from operation of a motor blower would aggra-                  We believe that a test for CO is the most urgent
vate the situation. Minimizing all unnecessary                   requirement. It is likely that the gas mixture re-
physical exertion will extend the viab1l1ty of the               sulting from any fire, especially if Oz is already
atmosphere as well as cut the heat output of the                 low, will contain CO in concentrations of up to
occupants, and extinguishing all unnecessary light-              several per cenl.(6) Exposure to high concentraUoDS
ing w1ll help reduce the heat load.                              of CO can be fatal in a short time (Table 2). UtiUziDg
                                                                 outside air with CO concentrations higher than 100
                                                                 ppm will depend on the urgency of alleviating a high
                                                                 concentration of C02 which has accumulated in the
                        TABLE 3                                  shelter air. Suitable, inexpensive means (detector
                                                                 tubes) are available for determining CO concentra-
        Toxicity of carbon Dioxide to Humans(4)
                                                                 tions and should be provided in each chamber for
Concentration
                                                                 establlshing that the CO content of external air is
(% by Volume)         Physiological Effect                       within safe limits before starting ventilation.
                                                                    Once the CO criterion is satisfied, it is believed
      0.5             MAC - no effect in 8 hours                 safe to assume reasonable COz and Oz concentration
      1.0             Slight increase in lung-ventilation
                                                                 limits in the incoming air. However, it is possible
                        rate                                     that the outside air temperature may be higher than
                                                                 desired, or, as an unusual case, that a fire is present
      2.0             Lung-ventilation rate up 50%               overhead which is producing scarcely any CO. A
      3.0             Lung-ventilation rate up 100%,             second safety check on the incoming air can be pro-
                        headaches appear                         vided inexpensively by installing a temperature
      5.0             Lung-ventilation rate up 300%.             measuring device (e.g., dial thermometer) in the
                        severe headaches and breatb1ng           inlet duct inside the shelter immediately prior to
                        is laborious                             the filter system.
     10.0             Can be endured for only a few
                                                                    Satisfaction of the requirements in the incoming
                        minutes                                  air for both CO and temperature should permit opera-
                                                                 tion under Condition C, that is, normal ventilation of
     12.0             Quick loss of oonsoiousness                the protective shelter as planned.
                                                                    If no particulate filter or carbon filter is provided,
                                                                 the hazard do using external air goes up considerably
Condition C-Normal Ventilation
                                                                       6r--------------------------------------------,
Once power is available again, electric lights may
be energized. However, no ventilation should be pro-
                                                                 .-
                                                                 .-
                                                                 2
vided until this outside atmosphere has been found               W5         ----------
to be safe. It must be assumed that the shelter is               ~
                                                                 W
                                                                 Cl.
provided with a properly designed filter unit com-
prised of a fireproof particulate filter and activated           24
carbon. Without such protection, the problems of                 o
                                                                 i=
prOviding the necessary equipment to verify the                  c:t
safety of the atmosphere are 80 numerous and                     ~ 3
                                                                 2
immense that they cannot be considered here. With                W
such protection, however, we can immediately as-
sume that outside air after filtration w1ll be safe
                                                                 ~
                                                                 0     2
from radioactive materials, biological and chemical              ~
warfare agents, and nearly all extraneous products               §
from a damaged industrial complex. This filtered                 o
air may still be hazardous if it contains high con-              ~
                                                                 ID
centrations do CO or COz or low concentrations of                0::
Oz; these conditions are immediately recognized as               c:t
                                                                 o
describing a fire in the viCinity of the air intake to                                                                   6
the shelter. Therefore, before the external atmos-
phere is brought into the chamber it must be tested              Figure 1. JDcrease of carbon diOxide concentration in
and found suitable. A means of drawing samples do                unventilated 100-man shelter (6500ou. ft.).

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                                                                                            Digitized by   Google
since in addition to increased heat, CO, C02, and                    at 1 elm would not be expected to exceed 25 ppm,
decreased ~, the external atmosphere may contain                     which is acceptable for continuous exposure.
toxic and irritating aerosols, gases, and vapors due                    It may not be generally appreCiated that a maxi-
to combustion and decomposition in fires. Many of                    mum ventilation rate of 3 elm per man is entirely
these possible irritants and toxicants have not been                 inadequate under some conditions. Under many
characterized or identified. Because of the multi-                   warm weather conditions, the highest possible
plicity of possible molecular species represented,                   practical ventilation rates will also be inadequate.
it would be impossible to provide adequate analytical                It was demonstrated in a recent study that highly
equipment to identify them. Furthermore, no mowl-                    motivated, healthy young men had reached their
edge of threshold limits of toxicity is available for                limit of endurance after about one week at an
many of these materials. Consequently, because of                    average effective temperature of 85 0 F .<7,8) This
the cost, time, and uncertainty of detection, test for               finding has been confirmed by other studiesJ9)
such speCies is not recommended. Since activated                     Continuation of this exposure would not Simply have
carbon will remove the vast majority d. these com-                   added to their discomfort but would soon have re-
pounds from the incoming air, its use is highly rec-                 sulted in many deaths. An appreciable increase in
ommended. There seems to be no reasonable                            ventilation rate would have lowered the effective
substitute for collective protection that can be                     temperature by an insignificant amount because of
provided by a filter unit utilizing a fireprod. high-                high outside temperatures. Hence, the heat-dissipa-
efficiency particulate filter and activated carbon.                  tion problem in shelters in the summer cannot be
                                                                     minimized.
                          TABLE 4

             Equilibrium Concentrations of Gases                     Effects of Fire within the Shelter
              as a Function of Ventilation Rate.
                                                                     In any situation in which a large number ci persons
                              Equilibrium conc. (percent)
                                                                     are packed into a relatively small chamber, the
Ventilation Rate (cfm)        CO2                       °2           possibility d. an accidental internal fire must be
         3 (max)             0.33                      20.5
                                                                     seriously considered. The presence of an adequate
         2                   0.5                       20.3          fuel supply is undeniable (see Table 5), probably
         1                   1.0                       19.7          consisting mostly of cellulosic material such as
                                                                     clothing, paper, and wood products. The only real
.caJ.cuJ.atlons based on 02 consumption of 0.73 cu.ft./1Il&D/        remaining requirement then is a source of ignition,
  hour and C02 output of 0.6 cu.ft./man/br.
                                                                     such as an electrical breakdown or glowing match.
                                                                     Such a likelihood is quite possible especially in
                                                                     emergency situations with untrained personnel.
                                                                     Knowing then that a fire is indeed possible, we
 Heat Dissipation in Shelters                                        should consider its potential effects as follows:

A brief mention of the heat problem in shelters
                                                                                            TABLE 5
seems appropriate at this point because of lateral
impact on the toxic gas problem. It is possible in                     Fuels Required to Produce Dangerous Concentrations
cold weather that maintaining the maximum ventila-                         of carbon Monoxide in a 6500 cu. ft. Shelter
tion rate will kee~ the shelter air temperature un-                                      (No Ventilation)
comfortably lowJ3) Naturally, the air flow rate can
be reduced by a suitable control valve. However, it                                           Cellulose          Hydrocarbon
1s strongly suggested that the flow of air through the                carbon Monoxide         Required            Required
filter unit be maintained at the maximum rate by                     Concentration (ppm)       (grams)             (grams)
recirculating increasing volumes of internal atmos-
                                                                            1000                 460                 230
phere to compensate for any decrease in incoming                            2000                 920                 460
air. This will provide at all times the maximum                             4000                1850                 920
purification rate in terms d. removing aerosols,
odors, and irritating vapors from the shelter air.
However, it is obvious that the equilibrium level of
C~ will increase, and 02 will decrease as the utili-                    Production d. CO. It is not unreasonable in a
zation of outside air is decreased as shown in Table                 fire involving carbonaceous material to expect that
4. The conclusion is that a flow rate of 1 cfm of                    up to one half ci the carbon consumed will yield
fresh air will maintain tolerable levels. Even with                  CO'<6) Assuming this to be the case, we can calcu-
unlimited smoking, the CO equilibrium concentration                  late the minimum amounts of fuel (cellulosic mate-


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rials being assigned an average composition of                                          TABLE 6
CH20} required to yield significant amounts of CO.
We must assume that the fire will be discovered and                Useful Percent Decay Values for Ventilated   ~es.
extinguished within a short time (perhaps one minute).
Then in our model shelter of 6,500 cu ft, we find that                                                Time (minutes)
fuel requirements are as given in Table 5. Thus, we             Percent Decay               General               Model'"
can quickly reach hazardous concentrations of car-
bon monoxide with small quantities of fuel. For                      50                   0.69 ViR••              14.9
                                                                     63                       ViR                 21.7
example, 40 pages of an ordinary newspaper is
                                                                     90                   2.3 ViR                 49.8
approximately 460 grams of cellulose, and half a                      95                     3 ViR                65.0
pint of kerosene is 230 grams of hydrocarbon. Even                    99                  4.6 ViR                 99.6
1,000 ppm of CO is extremely dangerous, and 4,000
ppm is lethal in a short time (Table 2). Once the                 .Based on C = Coe-Rt/V
fire is extinguished, the maximum ventilation rate               **V = volume of ventilated space (cu.ft.).
                                                                   R = ventilation rate (cfm).
(300 cfm) will cause the CO concentration to fall as
                                                                ."This calculation is made for the model shelter speci-
shown in Figure 2.                                                 fled in this paper where V = 6590 cu.ft. and R= 300 cfm.


                                                                                         TABLE 7

                                                                    Production of CO2 and Consumption of 02 During
                                                                           a Cellulose Fire (No Ventilation)

~4                                                              Cellulosic Fuel      C02 Increase          02 Consumption
)(



to
z
                                                                Burned (gramS)

                                                                     460
                                                                                       (percent)

                                                                                         0.2
                                                                                                              (percent)

                                                                                                                0.2
2
II:
                                                                    1850                 0.8                    0.8
~     0                               70   80   90   100

Figure 2. Decrease in carbon monoxide concentration in
100-man shelter at maximum ventilation rate.


   The curve shown in Figure 2 is simply the classi-            onset of fire. Although priceless 02 has been con-
cal exponential decay curve,                                    sumed, and a substantial quantity of CO2 has entered
                                                                the shelter atmosphere, it would not be immedi-
               -Rt/V                                            ately disastrous. If maximum ventilation rate is
C = Coe                ,
                                                                available, recovery will occur in about one hour in
where C is the concentration at any time t, Co is the           terms of C02 and 02. It is obvious, however, that
initial concentration (in this case 1,000 ppm), R is            should the fire occur during the no-ventilation peri-
the ventilation rate (300 cfm) and V is the ventilated          ods (Condition A or B), it would shorten the time
volume (6,500 cu ft). It is perhaps instructive to              allowable before outside ventilation must commence
point out that the time required to remove a certain            due to CO2 build-up and 02 depletion. The above
percentage of the CO is dependent only on R and V               statements are based on the assumption that water
and not on the CO concentration. For example, the               or smothering has been used to extinguish the fire,
CO concentration will be reduced to one half of the             not C~. The use of a C02 extinguisher during
initial concentration in a time given by                        Conditions A or B should definitely be discouraged
                                                                and is probably not advisable under Condition C.
           V                V
to.5      =i    In2   = 0.69 R
                                                                   Other chemical vapors and aerosols. It is not
regardless of the initial concentration value. For              possible to predict reliably the amounts of aerosols
our model, to.5 = 14.9 minutes. Table 6 gives other             and noxious vapors from a modest fire such as that
decay percentage values that may be of general                  described. It is a universal experience that irritat-
interest.                                                       ing, choking aerosols and lachrymatory, irritating
                                                                vapors (such as aldehydes) often result from fires.
   C~ and 02. If we take the position that, in a                This would be a c:Ufficult, uncomfortable period until
smaI Ire similar to that above, all the fuel involved           ventilation has reduced these products of combustion
burns to yield C02' the changes in gas composition              to a comfortable level. If outside ventilation Is not
will be as given in Table 7. These changes will be              possible, It would be very helpful to recirculate the
superimposed on the concentrations existing at the              internal air through the fllter system (Condition B).

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Moat of the irritants, both aerosol and vapor, would             grams of activated coconut carbon exposed to 2
be removed as rapidly by recirculation through the               literS/min of air at 280°C in a one-inch tube ignited
filter unit, as by actual ventilation.                           spontaneously and burned actively with the CO and
                                                                 CO2 each reaching concentrations of greater· than
   Temperature effects. It Is of interest to calculate           10 per cent of the effluent gas, whereas the ~ con-
the heat released by the combustion of the fuels                 tent approached zero.(10) As the carbon becomes
mentioned above, and the effect of this heat on the              saturated with organic compounds such as hydro-
shelter atmosphere. For purposes of these calcula-               carbons, the situation worsens. For example, 8 g
tions we wID use the following data: The specifiC                of used activated coconut carbon (containing 22.5 per
heat do combustion of cellulose is 5 Kg cal per gram,            cent of hydrocarbons adsorbed during exposure in a
and for hydrocarbons 10 Kg cal per gram. The spe-                main filter in a nuclear submarine) exposed to 2.1
cific heat of ordinary air Is 0.25 calorie per gram,             liters/min of air at 200°C in a similar apparatus,
and the air density at 3008 K is 1.18 g/Uter at 760              burned actively with CO2 of > 10 per cent, and CO
mm Hg. As the worst situation, the combustion must               approaching 10 per cent of the effluent gas.<l1) Other
occur very quickly and adiabatically, i.e., none of the          contaminated carbon samples exposed in similar ex-
heat generated is dissipated to walls or equipment.              perimentation have kindled at temperatures as low
The results of these calculations are given in Table 8.          as 180°C. However, occurrence of fires in the car-
                                                                 bon bed of the shelter is considered to be most
                                                                 unlikely for at least three reasons. First, the
                          TABLE 8
                                                                 shelter carbon bed should be essentially free of
                                                                 adsorbed hydrocarbons, since the ventilation system
  Heat Release from a Small Fire in a 6500 cu.ft. Shelter        should have been operated previously only during
                                                                 brief test periods. Second, the fireproof particulate
                                           Adiabatic             fUter will be effective In preventing ignition sources,
 Fuel CoDBUDled (gramS)     Heat Released Temperature            such as a glowing ember, from reaching the carbon
Cellulose   Iqdrocarbon       (K. cal)     Rise (C)              bed. Third, frequent observation of the inlet-air
                                                                 temperature (e.g., using the dial thermometer recom-
    460          230            2300               42
    920
                                                                 mended earlier) will largely eliminate the possibility
                 460            4600               84
   1840          920            9200              168            of fire due to spontaneous ignition by hot inlet air.
                                                                 The inlet-air temperature should be monitored con-
                                                                 tinuously at the time of start-up of the ventilation
    It is advisable to consider carefully the figures in         blower.
Table 8. The heat produced by the combustion of one
pound of cellulose, or one half pint of kerosene, Is                Unusual fires. 2. Halogenated compounds. The
enough to raise the average temperature of the air               materials considered as fuel for the fires discussed
In the shelter by 42°C (75°F)-admlttedly, this cal-              thus far in this paper have contained the elements
calation assumes no heat loss by other means, but                C, H, and O. It can be generally stated that materials
this will be essentially the case if the fire is fast.           containing such other elements as the halogens, sul-
Moreover, note that a 75° F rise is the average-                 fur, nitrogen, etc., should be avoided in a protective
greater increases can be expected closer to the fire.            shelter as much as possible. Combusion and degra-
The effect of a 75°F increase in shelter temperatures            dation products from such materials are often con-
depends to some extent on the starting temperature.              siderably more irritating and toxic than simple
Using temperatures of 6O-800 F encountered during                compounds of C and H.
winter occupancy, it Is seen that a 75° increase is                 One example of the combustion of halogenated com-
approaching an intolerable levet.<3) It has already              pounds has been chosen from the work of Coleman
been stated that any increase in temperature during              and Thomas(12) to illustrate the hazardous poten-
the summer trials would have been intolerable. As                tial of such combustion. Small samples of various
soon as the fire has been extinguished, normal ven-              chlorinated plastics in common use were burned or
t1lat1on (300 elm) will reduce the air temperature to            pyrolyzed in air. Although 0.25-gram samples were
normal in about one hour. Thus, it Is concluded that             actually burned in a bench scale apparatus, the
the heat liberated by an accidental fire in the shelter          products from these plastics are given in Table 9
may well be its most dangerous aspect.                           in terms of amounts extrapolated to a 6,500 cu ft
                                                                 shelter. The CO and C~ concentration calculated
    Unusual fires. 1. The activated carbon bed. It is            from these data are not alarming, but HCl concen-
generally considered that activated carbon is not a              trations of 50 to 100 PJ)m can be tolerated for a
fire hazard, that it Is not readily Ignited. However,            maximum of one hour'< 4) Greater exposures can
a bed do carbon deserves to be treated with respect              result in laryngeal spasm which illustrates the
as a fire hazard. A recent study has shown that 8                severity of this hazard.


                                                            63

                                                                                            Digitized by   Google
   It seems fruitless to discuss all the possible                   References
effects of burning materials containing elements                     1. Department of Defense OCD Technical Memorandum
other than C, H, and 0. However, this subject was                       61-3 (Revised), ''Technical Requirements for Fallout
treated briefly to emphasize the need to consider                       Shelters, " August 1964.
the selection of materials to be used in shelters to
                                                                     2. Anderson, W.L. and J.L. Bitner, "AtmospheriC Con-
avoid such elements as far as possible.
                                                                        tamination by Cigarette Smoke," NRL Report in
                                                                        preparation.
                                                                     3. Bogardus, H.F., E.A. Ramskill, !! al., "Studies of
                         TABLE 9                                        the Bureau of Yards and Docks Protective Shelter, I.
                                                                        Winter Trials," NRL Report 5882, December 31, 1962.
         Evolution of Gases from Combustion of
             Chlorinated Plastics at 300° C                          4. Sax, N.I., "Dangerous Properties of Industrial Mate-
                                                                        rials," Reinbold, New York, 1963.
                                Concentration in 6500 cu.ft.         5. Leutz, H., ''Test Results in Continuously Occupied
                      Amount          Shelter (Ppm)                     Shelters," Proceedings of the Meeting on Environ-
   Material           (gramS)   HCI       CO                            mental Engineering in Protective Shelters," NAB-NRC,
                                                                        February 8-10, 1960, pp. 139-144.
Polyvinylchloride       650     1000      400           460
 (unstabUized)                                                       6. Wilson, C.C., "Forest Fire Research Helps Develop
                                                                        Shelter Criteria," Proceedings of the Meeting on
Polyvinylchloride/      650     1075      150           300             Environmental Engineering in Protective Shelters,
 Polyvinylidene                                                         NA8-NRC, February 8-10, 1960, pp. 273-295.
 chloride copolymer
                                                                     7. Bogsrdus, H.F., E.A. Ramsk1ll, et al., "Studies of the
                                                                        Bureau of Yards and Docks Protective Shelter, n.
                                                                        Summer Trials," NRL Report in preparation.
                                                                     8. Newburgh, L.H., "Physiology of Heat Regulation and
Conclusions                                                             Science of Clothing," PhUadelphia: Saunders, 1949.
                                                                     9. Yaglou, C.P., ''Tolerance Limits of People for Cold,
The foregoing data and considerations have shown                        Heat and Humidity in Underground Shelters," Proceed-
conclusively that a fire inside the protective shelter                  ings of the Meeting on Environmental Eng. in Protec-
must be considered as a serious menace because of                       tive Shelters, NA8-NRC, February 8-10, 1960, pp. 29-40.
the possible lethal effects on humans. This is true                 10. Woods, F.J. and J.E. Johnson, "Further Studies of the
of fires that would ordinarily be considered of                         Combustion Properties of Activated Carbon," NRL
minor importance in everyday life, where occupants                      Report in preparation.
of a structure can flee to outside safety. The limit-               11. Woods, F.J. and J.E. Johnson, ''The Ignition and
ing factor in the shelter fire is shown to be not                       Combustion Properties of Activated Carbon Containing
necessarily the depletion of 02' evolution of C02 or                    Adsorbed Hydrocarbons," NRL Report 6090, July 28,
CO, or the output of noxious vapors and aerosols.                       1964.
The limiting factor may be, in fact, the output of                  12. Coleman, E.H. and C.H. Thomas, ''The Products of
heat (i.e., the calories released) during the process                   Combustion of Chlorinated Plastics," J. Applied Chem.,
of combustion of as little as one pound of fuel.                        1.: 379-383, 1954.




                                                               64

                                                                                               Digitized by   Google
                            GAMMA-RAY STREAMING THROUGH DUCTS

                                            Charles M. Huddleston
                                     U.S. Naval Civil Engineering Laboratory


INTRODUCTION                                                  DI = Dose rate in mr/hr at first corner of duct

In the problem of shielding of personnel against
                                                              L     = Total length of the duct in feet as measured
gamma radiation from nuclear weapons, an impor-                         along the axis; i.e., L =Ll + L2 for a two-
tant aspect is consideration of the hazard caused by                    legged duct, and L = Ll + L2 + L3 for a three-
radiation which is scattered off interior surfaces of                   legged duct
entranceways and air ducts into the shelter area.             Ll = Length of first leg in feet, measured from
The duct-streaming problem has been investigated                   the source to the center of the first corner
both experimentally and theoretically at several
laboratories. Current understanding has progressed            1.1   =   Distance in feet from source to detector in
to the stage where a review of progress is indicated.                   the first leg
This report proposes to survey information on:                ~ = Length of second leg in feet, measured from
some experimental determinations of the attenuation                     the center of the first corner to the end of
of gamma-ray dose within concrete ducts as a func-                      the duct in the case of a two-legged duct, or
tion of distance from the radioactive source; albedo,                   from the center of the first corner to the
which is an important concept in gamma-ray scatter-                     center of the second corner in the case of a
ing; and theoretical approaches to the duct-etreaming                   three-legged duct
problem.
                                                              1.2   = Distance in feet from center of first corner
                                                                      to detector in second leg of a two-legged or
                                                                        three-legged duct
EXPERIMENTAL INVESTIGATIONS
                                                              L3 = Length in feet of third leg of a three-legged
Several investigators have conducted experiments                   duct, measured from the center of the second
giving information on the distribution of radiation                corner to tlie end of the duct
along the axis of air ducts in concrete with square,
                                                              1.3   =   Distance in feet from center of second corner
rectangular, and round cross- sections. Some of the
                                                                        of a three-legged duct to detector in third leg
ducts have one right-angle bend, and some have two
right-angle bends. In each case treated here, the             T     = Some distance in feet measured along the
measurements were made with a gamma-ray point                         axis of the duct
source.
   The signUicant results of these investigations will        W/2 = Half-width of duct in feet: for a square,
be discussed and compared with each other and with                  W/2 is half of the width of a side of the cross-
theory. A systematic effort will be made to give as                 section of the duct; for a rectangle, W/2 is
much information as is available concerning actual                  the geometric mean of the half-height and
experimental results so that the data may be con-                   half-width of the duct (i.e., w2 is the area of
venient to other investigators.                                     .the cross-section of the duct); for a round
                                                                    cross-section with radius R, W/2 is given by
                                                                    W/2 = Ji R/2 (i.e., W2 is the area of the
DEFINITION OF TERMS                                                 cross- section of the duct)

A uniform terminology is used for various sources             W2 = Area of cross- section of the duct
of data:
                                                              L-shape refers to a duct with a single right-angle
D    = Measured dose rate in mr/hr at some dis-                      bend
           tance along the axis of the duct                   U-shape refers to a duct with two right-angle bends
Do = Dose rate in mr/hr at 1 foot from source in                    of the same sense such that radiation reach-
     air                                                            ing the detector streams in the opposite

                                                         65

                                                                                            Digitized by   Google
        direction to radiation streaming from the              the U-shaped duct and the Z-shaped duct. An exami-
        source down the first leg                              nation of the figures reveals no striking differences.
Z-shape refers to a duct with two right-angle bends               The last section of this paper includes a descrip-
      of opposite sense, such as a tunnel with an              tion of the theory developed by Eisenhauer to account
      offset                                                   for the results of his experimental findings.
                                                                  Extensive experimentalinvestigat10ns d. gamma-
S    = Source strength in curleD                               ray streaming through air ducts in concrete have
                                                               been carried out by Terrell and his co-workers at
Do = 10.76 SF(Eo)' where F is taken to be                      the Armour Research Foundation, (2,3,4) and reports
       0.235 for Au 198
           0.320 for Cs137
           1.32 for Co60
           1.84 for Na24                                        _
                                                                ~          _ _ L.
                                                                            I
                                                                                                                                                ".ctl.tlon Tr.


                                                                                      I

Experimental Findings

One of the earliest investigations of gamma radiation            Ins Ide Cont.r I I
streaming through air ducts in concerete was per-
formed by Eisenhauer, (1) who studied scattering of
radiation from a collimated Co60 gamma-ray source.
He made measurements in the second leg of a two-
legged duct and in the third leg of a three-legged
duct. The ducts Eisenhauer considered all had
square or rectangular cross sections. The gamma-               Figure 1. Schematic diagram of duct.
ray source was on the axis of the first leg of the
duct, and all dose measurements were made on the
axes of the second and third legs.
   A significant finding was that the dose rate along                                           I    -L,Il-
                                                                                                    LI ·3.21 ..
                                                                                                                                           -&,Il-
                                                                                                                                           Lz • 3.21 ..
the second leg of a two-legged duct decreased as the                                                                                         t--I)
inverse cube of the distance from the detector to                         10. 1
the geometrical center of the first intersection; l.e.,
D      1
-""- •                                                                                                                        •
Do 1, 3                                                                   10-2
                                                                                                                                  •
       2                                                           {                                                                  •
                                                                                                                                       •
    Eisenhauer also performed trapping experiments                 I                                                                        •
                                                                                                                                                ,,
by recessing one of the back walls of the corner of                 •     10-3                 Axlot       0I00erw0I

a two-legged duct a distance of one mean free path                 eO                      ~.
                                                                                                1ft)        ...
                                                                                                           Dooo ....
                                                                                                              "",)
                                                                                                                                                       •
for Co60 gamma rays in concrete. He found that                     If!0                        3.21
                                                                                               3. 76
                                                                                                           1155
                                                                                                               14                                          ••
                                                                   J
                                                                   iCI
such a radiation trap was not highly effective; i.e.,                     10-4
                                                                                               3.93
                                                                                               4. 0'1
                                                                                                                75. 0
                                                                                                                49. 0
it resulted in only an approximate 15 per cent de-                                             4.25             33.0
                                                                                               4.58             14.9
crease in dose rates along the axis of the second
leg of the duct.
    Decrease in dose rate, of approximately a factor
d. two, were achieved by substituting lead for con-
                                                                   i      10~
                                                                                               4••
                                                                                               4.91
                                                                                               5. 21
                                                                                               5. 24
                                                                                               5.53
                                                                                               5. 16
                                                                                                                 .. 40
                                                                                                                 7.10
                                                                                                                 4.10
                                                                                                                 4.40
                                                                                                                 3.04
                                                                                                                 2.07
                                                                                               6. 19             1. 46
crete at the inside corner lip of the intersection.
This striking decrease illustrates the importance d.                      10"'
scattering and penetration effects at the inside

                                                                          10.7~1--,:--,:-----,:~.......I;:--:-'.
corner lip. (See Figure 1.)
    The results of Eisenhauer's experiments with
L-shaped ducts are given in Figures 2, 3, and 4.                                  o       .1        .2    .3       .4    .5   .6    .7            .1       .9    1.0
                                                                                                               &atIo Til (I.. 6. SU)
    Eisenhauer also investigated three-legged ducts            Figure 2. L-sbaped 0.630 x 0. 952-foot rectangular ooncrete
with both a U-shape and Z-shape . Results are shown            duct with W/2 = 0. 3815 foot; 0.6-curie Co60 point source.
in Figures 5 and 6. Figure 7 compares results for              (From Reference 1. supplemented by correspondence.)




                                                          66

                                                                                                                         Digitized by           Google
                                                                                                                                    -Ly'L-                                 ~yt-
                              ~Ly'L-
                                                                                                                                    LI - 3.21"                                   1.64 ..
                              LI   -3.2I ..                                   ~ - 3.21 ..
                                                                                                                                                                             ~
                                                                               ~                                   10- 1
          10- 1




          10-2
                                                                •                                                 10-2
    ~
    g
    iii
    1\
                                                                 "
    a"                               .,.. .....
                                     0IMrve0I
                                      ..,,,,,,)
    ~*'                                                                                                                                                                         •
    j     10-4
                       3.21
                       3.76
                                        Ulm
                                         135                                                ••
                                                                                                                            ""101
                                                                                                                            0_             .,.. .....
                                                                                                                                            0IMrve0I
                       3.89
                       3.93
                                          76.1
                                          67.0
                                                                                                                               ~)            ...."",1                                   •
     j                                                                                                                        5.49            6.00
                       4.06               42.1
                                                                                                                              5.62            5.20

    I
                       4.09               39.0
                       4.22               26.8
                                                                                                                              5.78            4.60
                       4.25               23.5                                                                                5.94            3.60
          10-6         4.58               10.3                                                                    10-6        6.11            2.50
                       4088                5.70                                                                               6.27             1.74
                                           3. 15                                                                                               1.24
                                           1.97                                                                               ~0~6            0.63
                                           1.30                                                                                               0.42
                                           0.90




          10-7!---':,.-L~_-':-_L-----':_....L._-':---'~--'=_:-I                                                   10-7 !--':....J....-';:-_-':---'':-'--';:_-':-_"''="".......~-';;:--:-'
              o   .1      .2        .3        .4        .5       .6            .7    .1     .9    1.0                  o            .2.3.4.5.6.7.1.9                                    1.0
                                         IIotIo   TIL    (L -    6.56")                                                                       ....10 TIL (L - 7. 13 "I
Figure 3. L-sbaped 0.630 x 0.630-foot square concrete                                                        Figure 5. U-sbaped 0.925 x 0.925-foot square concrete
duct with W/2 = 0.3149 foot; 0.6-curie Co60 point source.                                                    duct with W/2 = 0.4625 foot; 0.6-curie Co60 point source.
(From Reference I, supplemented by correspondence.)                                                          (From Reference I, supplemented by correspondence.)



                              ~oLy'L_
                                                                                                                                     -Ly'L-                                -yt-
                                   ·3.21 ..                                                                                                                                       1.64 ..
                                                                                                                                     LI - 3.21"
                                                                                                                                                                             --I
                                                             •
                                                                 •
                                                                     0



    i                                                                         ,
                                                                         ·0




    I
    as'                             .,.. .....
                                    0IMrve0I
                                     ..,,,,,,1
                                     1050
    ~
    CI                                  934                                                                                                                                      •
                                        216                                                                                                                                         0

    j                                   100
                                         61.4                                                                                             .,.."",1
                                                                                                                                                .....
                                                                                                                                          0II00tv.d
                                                                                                                                                                                        0
                   4.25                  64.5                                                                                              ....

    i              4.55
                   4.58
                   4 ••
                   4.91
                   5.21
                   5.53
                                         30.2
                                         27.6
                                         15.6
                                         14.4
                                          9.00
                                          5.10
                                                                                                                                           3.50
                                                                                                                                           3.10
                                                                                                                                           4.00
                                                                                                                                           3.90
                                                                                                                                           3.15
                                                                                                                                           2.00
                   5.86                   3.70                                                                                             1.25
                   6.19                   2.72                                                                                             0.60
                                          2.02
                                                                                                                                           0.32




                                   .3       .4    .5                                             1.0                                 .2     .3       .4     .5                   .9         1.0
                                        ....10 TIL (L. 60 'S4                                                                                    ....10 TIL
Figure 4. L-sbaped 0.925 x 0.925-foot square concrete                                                        Figure 6. Z-sbaped 0.925 x 0.925-foot square concrete
duct with W/2 = 0.4625 foot; 0.6-curie Co60 point source.                                                    duct with W/2 .. 0.4625 foot; 0.6-curie Co60 point source.
(From Reference I, supplemented by correspondence.)                                                          (From Reference I, supplemented by correspondence.)

                                                                                                        67
            ,
            10- 3

            a
                                                           •
                                                           )(
                                                                 U-,h.pe
                                                                 Z-,hope
                                                                                                                                                           -y..-
            7                                                                                                                                              &, •   19.0 It
            6        ••                                                                        10. 1
                     )C x )C


      ~
             It
                                •   )C                                                                               •
      ~
      -::
      •                             •
                                                                                         ~
                                         )C
      2                                                                                        10.2
      ::
       •
                                         •                                               ...
                                                                                         E

      e
      0°
                                              •                                          ~
                                                                                         •
      ~     10-                                                                          eO 10-3
       ~
             9
      !      8
             7                                        t                                  0.°                                                               •
       X
      ...                                                                                d
             6
      !                                                                                  !
                                                                •                        .l    10-4                                                                    •
       i
       C
              It                                                )C

                                                                                         j                 Axlol
                                                                                                          DI,tance
                                                                                                            (It)
                                                                                                                              0I0MNed
                                                                                                                              Dooo Ita,.
                                                                                                                               .../Iv)
                                                                                         00(
                                                                                                           5.00                243.6
                                                                                               10.5       12.00                 ".08
                                                                                                          19.00                  2 . .0
                                                                                                          23.00                  0.71
                                                                                                          31.00                  0.18

            10-     '----of---lrl.II"'"""---;-1.7_ __
                                               5                                               10-6

                               Dilt~c.   in fH' .101"1, thi rd leg




                                                                                               , -' i
Figure 7. Comparison of attenuation factors for L-sbaped
duct and Z-sbaped duct. (From Reference 1. supplemented
by correspondence.)                                                                                   o      .1          .2       .3        .4    .5    .6      .7         .8       .9   1.0
                                                                                                                                       Ratio T/I. ( l . 31.0 It)
                                                                                     Figure 8. L-shaped 6 x 6-foot concrete entranceway with
                                                                                     W/2 = 3.0 feet; 1.52-curie Cs137 point source. (From
were published in 1960, 1961, and 1962. This series                                  Reference 2. Table 4.)
of studies included Co 50, Cs137, Na24, and Au 198 •
All ducts had square cross sections, some 6 x 6 ft
                                                                                                             I
and some 1 x 1 ft. Some ducts had one right-angle
bend, and some had two right-angle bends. Results                                                                                                      -y..-
                                                                                                                                                       &, •    19.0 It
are briefly summarized for each of these three
reports:
                                                                                                                     •
   1960. Four principal sets of measurements were
made using gamma- ray point sources in two-legged                                                                                           •
ducts with one right-angle bend'(2) The ducts in-
vestigated were concrete with square cross sections
of 6 x 6 ft, chosen because this cross section is
                                                                                         ~     10-3
reasonable for a shelter entranceway. Figures 8,                                         •                                                             •
9, 10, and 11 de~cribe these measurements.                                               eO
    For one of the cases direct comparison can be                                        ~o                                                                       •
made between attenuation factors as a function of
axial distance for C0 60 and Cs137. A later figure
                                                                                         J     10-4                                                                             •
will show such a comparison.
   As expected, it is seen that greater attenuation
is achieved for the higher energy case.
   Terrell also measured gamma-ray dose attenua-
                                                                                         i     10.5
                                                                                                                                            Axlel
                                                                                                                                            DI_
                                                                                                                                                (It)
                                                                                                                                              5.00
                                                                                                                                                           0II0erwd
                                                                                                                                                           Dooo Rat.
                                                                                                                                                            ...,Ihr)
                                                                                                                                                           2037
                                                                                                                                              '.00          731
tion for 8-in. x 8-in. lead ducts with 4-in. walls. The                                                                                      11.00          669
                                                                                               10-6                                          15.00           37.3
results are shown below:                                                                                                                     19.00           11.7
                                                                                                                                             23.00            4.75
                      LI                   L2               Dose Attenuation                                                                 27.00            2.41

Source              (inch)               (inch)                  Factor
                                                                                               10Ji
Cs l37                                                                                             o         .1      .2          .3     .4    .5     .6      .7            ••       .9   1.0
                     20                        0                     .00700                                                        Ratio TI\. ( l . 27.0 It)
Cs137                20                       20                     .0000103        Figure 9. L-sbaped 6 x 6-foot Concrete entranceway with
Co 60                20                        0                     .00636          W/2 = 3.0 feet; 3.67-curie Co60 point source. (From
Co 60                20                       20                     .0000147        Reference 2. Table 5A.)


                                                                                68

                                                                                                                                                Digitized by       Google
                                                                                                              The effect of a radiation trap was investigated by
                                                                -yt-                                       removing the entire roof section over the rlgbt-
                                                                ~ • 19.01t                                 ~ bend d. the 8-ft x 8-ft concrete duct. For
                                                                                                           Co ,removal of the roof section increased the
                                                                                                           dose attenuation ratio at the end d. the second leg
                                                                                                           from 424 to 517 •
                                •
                                                •                                                             1961. In order to obtain information on gamma-
                                                                                                           ray dose attenuation in ducts at both higher and
                                                                                                           lower photon energies, Terrell(3) made measure-
                                                                                                           ments using Na24 and Au198 gamma radiation. The
                                                                •                                          measurements were all made in 8-ft x 8-ft concrete
   f!0                                                                                                     ducts with one right-angle bend. Various values
   Q
   ~     10"
                                                                            •                              were chosen for Ll and L 2. Results are shown in
   .!                                                                                  •                   Figures 12-17 •
                                                                                                               It would be desirable to show a plot of dose attenu-
                                                 ~
                                                    AllIoI

                                                     It)
                                                                        .,.. ....
                                                                        0IIMrvM
                                                                         ..,/hr)
                                                                                                           ation factors as a function of axial distance for each
                                                                                                           of the four gamma-ray energies used by Terrell for
                                                     7.'"               1065                               one particular duct. Unfortunately, Terrell did not
                                                    10.'"                462                                make measurements in the same duct for each of
                                                    13. ...              465
                                                    17.'"                 21.WI
                                                                           7.29
                                                                                                           the four energies involved. He used a duct with
                                                                                                           Ll =12 and L2 =19 only for the cases of Co 60 and
                                                    21.'"
                                                    25.'"                  2.73
                                                    29.'"                  1.31
                                                                                                           Cs137. It is possible on the basis d. certain assump-
         10.,11
            o     .1       .2       .3        .4    .5  .6     .7                 ••       .,   1.0
                                                                                                           tions, however, to construct from available data the
                                                                                                           expected attenuation factors within a duct having
                                                                                                           Ll = 12 and ~ = 19 for Au198 and Na24 • The
                                         IIItIo TIL (L. 29.0 It)
Figure 10. L-shaped 6 x 6-foot concrete entraDoeway with
W/2 = 3.0 feet; 3.67-curie Co60 point source. (From                                                        assumptions involved are:
Reference 2. Table 5B.)                                                                                       1. The ratio of the dose at some pOSition in the
                                                                                                           second leg to the dose at the center of the intersec-
                                                                                                           tion D(.t2)/Dl is independent d. the length of the first
                                                                                                           leg Ll' Analysis d. the data shows that this assump-
                                                                    -yt-                                   tion is valid provided Ll is several times as large
                                                                    ~   • 19.0 It
                                                                                                           as the duct half-width W/2.
                                                                                                              2. The dose at some position in the first leg
                       •                                                                                   D(.tl) is independent of the length of the first leg Ll'
                                                                                                           This assumption is valid, as the data show, provided
                                    •                                                                      Ll is se.veral times as large as W/2 •
                                                    •                                                          On the basis of these two assumptions, hypotheti-
                                                                                                           cal dose attenuation curves have been constructed for
                                                                                                           Au 198 and Na24 for a duct with Ll =12 and L2 =19.
                                                                                                           Figure 18 shows a comparison of dose attenuation
                                                                 •                                         factors for pmma radiation from Au198, Cs137,
                                                                                                           Co 60, and Na24 • It is seen, as expected, that pro-
                                                                             •                             tection factors are greater for the higher energy
                                                                                       •                   cases. That is, radiation from Na24 (2.75 Mev and
                                                                                                           1.37 Mev) is attenuated more than the radiation from
                                                    01_
                                                        AllIoI

                                                         (II)
                                                                         .,.. ....
                                                                          a..r-I
                                                                          ..,/hr)
                                                                                                           Co 60 (1.17 Mev and 1.33 Mev) which, in turn, is
                                                                                                           attenuated more than the radiation from Cs137
                                                         4.'"
                                                         ,....            3204
                                                                           552                             (0.662 Mev). The results for attenuation d. the radia-
                                                        12.'"              397
                                                                                                           tion from Au198 (0.411 Mev) are unexpected, i.e.,
                                                        .,....
                                                        15.'"

                                                      23.'"
                                                                           346
                                                                            15.3
                                                                             4.56                          the attenuation factor falls between those for Co60

         ~-,~
                                                      27.'"                  1.71                          and Cs137. Such a finding cannot be explained on the
                                                      31.'"                  0.93
                                                                                                           basis of current theory. The experiment for Au198
           o      .1       .2       .3         .4   .5  .6      .7               .8        .,   1.0        should be repeated in case there was some system-
                                         IIItl0 TIL (L. 31.0 It)                                           atic error in measurement. *
Figure 11. L-shaped 6 x 6-foot concrete entranceway with
W/2 = 3.0 feet; 3.67-curie Co60 point source. (From                                                        *Th11 experiment has recently been repeated at NCEL. and
Reference 2. Table 5C.)                                                                                     better agreement with theory has been found.

                                                                                                      69

                                                                                                                                          Digitized by   Google
                                                                                                                   1
                                                                                                             1

                                                                        -Ly'L-                                               -Ly'L-                                     -L2"'l-
                                                                                                                           • Ll • 10.0 tt                               ~       • 19.0tt
                                                                        Ll • 17.0 It
                   •
                       •
                                                                                                                                •
                              •
                                                                                                                                            •
                                    •                                                                                                           •
                                          •                                                                                                              •••
                                                  •• ••

                                         .,.. ....
                                         a.......                                                                                                               •
                            2.00
                                          ..,/hr)
                                         11000
                                                                •                                                            .,...... .,.. ....
                                                                                                                               Ax...
                                                                                                                                 ~)    ..,/hr)
                                                                                                                                                    a--I            ••
                            3.00
                            5.00
                                          1760
                                          3306
                                                                    •
                            .. 00         1332                       •                                                           1.00            79310
                           11.00           7...                             •                                                    2.00
                                                                                                                                 4.00
                                                                                                                                                 20400
                                                                                                                                                  5016
                                                                                                                                                                                        •
                           16.00           474                                                                                   7.00             1691
                           15.50           399                                                                                   .. 50               II•                                         • •
                           17.00
                           1.. 50
                                            330
                                            327
                                                                                  •                                             10.00                 112
                                                                                                                                11.50                 152
                           20.00            300                                         ••                                      13.00                 774
                           21.00               43.6                                                                             14.00                 7U8
                           22.00               16.5                                                                             15.00                  15.2
                           23.00                9.14                                                                            16.00                  39.6
                           24.00                6.30                                                                            17.00                  25.3
                           •• 00                1.93                                                                            21.00                    6.71
                           32.00                0.12                                                        10"
                                                                                                                                25.00                    2.10
                           34.00                0.63



                                                                                                            Ji
                                                                                                                                27.00                    2.45
                ~          :::                  0••
                                                0.40
                                                                                                                                29.00                    1.50


        10.7   ~1L...1..J-_L...---'_-'--..I.""""'_L...~""""-L.._.J,-......J
               o    .1    .2    .3    .4    .5    .6    .7    .1    .9   1.0                                      o        .1          .2       .3
                                                                                                                                                     I .• 4   .5   .6     .7                .1   .9       1.0
                                          IIotIoTI\. (L. :!LOtt)                                                                                     .... TI\. (L. 29.0 tt)

Figure 12. L-shaped 6 x 6-foot ooncrete entranceway with                                              Figure 14. L-lhaped 6 x 6-foot ooncrete entranoeway with
W/2" 3.0 feet; 4.2-curie NaM point source. (From                                                      W/2" 3.0 feet; 4.2-cur1e NaM point source. (From
Reference 3, Table 1.)                                                                                Reference 3, Table 3.)

         I
                "I            -   L11L-                             -~-
                     •        LI • 13.0 It                          ~       • 19.0tt
                                                                                                                       •
        10. 1
                              •
                                    •                                                                                           •
        10-2                               ••                                                                                            •
   ~                                                                                                                                            •
   !•
                                              • •                                                                                                        •
                                                            •                                                                                                       •
   If
   •    10-3
                      Aldol
                     01_.
                         (tt)
                                        .,.. ....
                                        a.......
                                         ..,/hr)
   eO
                        1.00            10lIO                   •                                                                                                       •
   ~o
   a
                        2.00
                        4.00
                                        20400
                                         5106                       •                                                        ""..I
                                                                                                                            01_.                .,.. ....
                                                                                                                                                a--I                        •
                                                                                                                                                                                •
                        7.00             1716                           •                                                       (tt)             ..,/hr)
                                                                                                                                                                                    •
   j    10-4           10.00
                       11.50
                                          164
                                          614                                                                                 2.00
                                                                                                                              5.00
                                                                                                                                                 4026
                                                                                                                                                  642
                       13.00              537                                   •                                                                                                           •
  I                    14.50              529                                                                                 .. 00               213
                       16.00              413                                                                                11.00                160
                       17.00              216                                          • •                                   14.00                 97.2                                          •
        10"            1.. 00              37.2                                                                              17.00
                                                                                                                             20.00
                                                                                                                                                   56.4
                                                                                                                                                   59.4
                                                                                                                                                                                                      •
                       19.00               19.1
                       20.00               12.6                                                                              21.00                 11.1
                       24.00                3.64                                                                             22.00                  6.06
                       21.00                1.66                                                                             23.00                  3.17
                       30.50                1.05                                                                             24.00                  2.71
        10-61-         32.00                0.91                                                            10"              28.00                    0.15
                                                                                                                             32.00                    0.35
                                                                                                                             34.00                    0.24
                                                                                                                   f?
        ...Ii
                                                                                                                             36.00                    0.18


               o         .1       .2      .3        ., . • 5   .6      .7           • • • 91.0
                                                                                                            10.7   )-11-.1 .2 .3 .4 .5 .6 .7 •• .9 1.0
                                                                                                                   o
                                                                                                                     I.J,-_~-I,_....L-..I.~----I'-~-~-~..,.J
                                               tatlo TI\. (L. 32.0 It)                                                                           tatlo TIL (L. 36.0 It)
Figure 13. L-shapecl 6 x 6-foot ooncrete entranceway with                                             Figure 15. L-shaped 6 x 6-foot ooncrete entranoeway with
W/2 = 3.0 feet; 4.2-cur1e NaM point source. (From                                                     W/2" 3.0 feet; 8.1-curie Aul98 point source. (From
Reference 3, Table 2.)                                                                                Reference 3, Table 4.)

                                                                                                 70

                                                                                                                                                      Digitized by              Google
                                                                                                                                  It will be shown later that detailed calculations
                                                                               -Y'--                                         give good agreement with the results of the measure-
                                                                               L, •    19.0 It                               ments for Co60, Cs137, and Na24 ; whereas the cal-
                                                                                                                             culations give an answer quite different from the
                                                                                                                             measurements in the case of Au198 •
                                •                                                                                                 Terrell made an attempt to determine the relative
                                                                                                                             importance of various scattering areas within a duct •
                                          •                                                                                  One way of determining this was to cover a scatter-
                                                   •
                                                                   •                                                         ing area with lead, which has a much lower albedo
                                                                       •                                                     than does concrete. A 1/8-in. thiclmess of lead was
                                                                                                                             used to cover the floor of the corner of the duct (6 ft
                                                                           •                                                 :It 6 ft). With a Co60 source positioned in the entrance-
   ~o
                      Alllal
                     os-.
                                              a..rv..I
                                              0 - ....
                                                                               •                                             way, the dose rate at the end of the second leg of the
   a                       (tt)                ..,/Iv)                             •
   J                                                                                                                         duct was reduced by 11 per cent by the addition of the


   J
         10'"
                       2.00
                       4.00
                       7.00
                      10.00
                      13.00
                      16.00
                                               I.
                                              4062
                                               924
                                               229

                                               112
                                                97.2
                                                                                            •
                                                                                                       ••
                                                                                                                             lead. The addition of further thiclmesses of lead did
                                                                                                                             not appreciably reduce the dose rate. Covering the
                                                                                                                             corner wall which faced the detector with 1/8 in. of
         10~          17.00                     35.7
                                                                                                                             lead reduced the dose rate by 18 per cent.
                      18.00                     13.6
                      19.00
                      20.00
                                                 9.00
                                                 5.19
                                                                                                                                  Another means of studying the relative importance
                      24.00                      1.66                                                                        of various scattering areas was to remove sections
                      28.00                      0.71
         10'"         30.00                      0.56                                                                        of the corner. The removal of the ceiling of the cor-
                      32.00                      0.36
                                                                                                                             ner caused an 18 per cent decrease in dose rate. The

         .~,i
                                                                                                                             removal of that wall of the corner which faced the
                                                                                                                             detector caused a 22 per cent decrease. The re-
                 o         .1            .2        .3        .4      .5    .6      .7            ••        .f     1.0        moval of that wall of the corner which faced the
                                                        ....... T/I. (I.. 32.0 It)                                           source caused an 18 per cent decrease •
Figure 16. L-sbaped 6 x 6-foot concrete entranceway with
W/2 = 3.0 feet; S.l-curie Au19S point source. (From
Reference 3, Table 5.)

                                                                                                                                                                     ","      0
                 I -L~-                                                -Y'--                                                                                         c,'n )(
                     • LI • 1000ft



                           •
                                                                       L, •        19.01t


                                                                                                                               '.1
                                                                                                                                       • 6
                                                                                                                                                                     ~I"
                                                                                                                                                                     ..14     6
                                                                                                                                                                               D




                                         •
                                                             ••                                                                                         .            POIitlon of rlpht ..., ' . ltenil




                                                                                                                               ."
                                                                                                                                               ••
                                                                                                                                               "   0I
                                                                  •
                                                                      ••
                                                                                                                                                               6
                                                                                                                                                               a
                              Alllal
                            D"-
                                                   a..r-I
                                                   0 - ....
                                                                                       •                                                                       a
                                  (tt)               ..,/Iv)                                          ••                                                       6


                                                                                                                                                                   :~
                              2.00                  4032
                              4.00                   914
                              7.00                   343
                             10.00                   11M
                             13.00                   156
                             14.00
                             15.00
                                                     146
                                                      22.5                                                                                                             i
                             16.00
                             17.00
                             21.00
                                                      15.0
                                                      10.5
                                                       3.22
                                                                                                                               ....'                                               I
                             25.00
                             27.00
                             29.00
                                                        1.37
                                                       1.00
                                                         0.73
                                                                                                                                                                                   t          I I        X
                                                                                                                                                                                                             a
                                                                                                                                                                                                             X

         711
       10-                                          I                                                                                                                                        t •6 g          0
                                                                                                                                                                                                             6
             o        .1            .2        .3         .4    .5    .6      .7             ••        .f        1.0
                                                   ltatlo T/I. (I.. 29.0 It)
Figure 17. L-shaped 6 x 6-foot concrete entranceway with                                                                                                 Axiel DIUence '" ' •• t

W/2 = 3.0 feet; S.l-curie Au19S point source. (Frcm                                                                          Figure 18. Comparison of dose attenuation faotors as a
Reference 3, Table 6.)                                                                                                       function of axial distance for Au198, Cs137, C0 60, and Na24 .


                                                                                                                        71

                                                                                                                                                                   Digitized by         Google
     1962. In later work, Terrell extended his experi-          ing on the value of L l , the value of W, and the nature
mental investigations to include two right-angle                of comer-lip material.
bends'(4) He used gamma-ray sources of Co60 and                    The corner of the ducts was constructed so as to
Cs137. For a large (~ft x ~ft) duct, he chose                   facilitate trapping experiments. For dose attenuation
Ll :: 13, L2 :: 14, L3 = 10. For a small (l-ft x I-ft)          measurements, a point rather well down the second
duct, Ll =3.5, ~ =4.0, L3 = 5.5. Both U-shaped                  leg was selected in order to make the corner-lip in-
and Z-shaped ducts were investigated. Results are               scatter contribution do reasonable proportions. so
shown in Figures 19-26. It was shown that the sense             that the results might have more general significance.
of the second right-angle bend is not a significant             The various scattering areaS are shown in Figure            30: .
factor, at least as long as the axes of all three legs              The data repreSenting the-contributions ofthe
do a duct lie in the same plane.                                various primary scattering areas proved to be
    An experimental study concerning the streaming               rather confusing. For example, removing Al
rJ. the gamma radiation of Co 60 through an II-in.              dropped the counting rate 53 c/sec out of a total of
square duct with one right-angle bend was performed             250 c/sec. Removing A2 dropped the rate 46 c/sec.
by Green. (5) His objectives were:                              Removing both dropped the rate 87 c/sec instead of
                                                                the expected 99 c/sec. Similar effects were 0b-
   1. To repeat some of Eisenhauer's measure-
ments(l) on the penetration of gamma rays through                served between Al and the ceiling and between A2
                                                                and the ceiling. The most likely conclusion to be
an ll-in. square duct.
    2. To study, in some detail, the relative impor-            drawn, and the one actually adopted, was that a
                                                                 multiple scatter existed between these areas, and
tance of various scattering surfaces within the duct.
                                                                 that removing one area eliminated not only the pri-
    3. To investigate the importance rJ. the corner
                                                                 mary contribution but the multiple- scatter contribu-
lip inscattering effect.
                                                                 tion as well. Evaluation of the multiple-scatter effect
    4. To study the effect of positioning either the             required removal of each area with and without the
source or detector off the center axis.                          other areas in place. The effect existing between the
      Green's findings in these four areas are described        floor and Al and A2 was assumed to be equal to the
  in the following paragraphs.                                  effect between the ceiling and Al and A2. No effect
     The reSults of dose attenuation measurements               was observed between the floor and celling.
  along the axis rJ. the duct are shown in Figures 27               The results of this series do measurements are
. and 28. For comparison, Green's results are shown             summarized in Table 1.
 together with Eisenhauer's in Figure 29. The 20 per
  cent difference between the two measurements may                                         TABLE 1
  not be significant since measurements were nor-
  malized to Dl' a troublesome quantity to measure                    Relative Contributions of Various Sources in the
  accurately. More important are the slopes of the                        Comer to the Total Dose at L2 = SO em
  lines, and here agreement is excellent.
                                                                                                          Contribution of Total
      The slopes of the lines in Figure 29 are both                       Source                                   (%)
  about -2.9, which indicates that the dose falls off
  very nearly as the cube of the distance down the              ~                                                   9
  second leg. In general, the dose in the second leg                                                               10
                                                                A2
  is composed of radiation coming from various points
  in the scattering areas. From any particular point,           Ceiling                                             9
  the intensity falls off as the square of the distance          Floor                                              9
 from that point. It might be expected then that the                                                                S
                                                                AS
  dose in the second leg would fall off as the square
  of the distance down the leg and that the slope of the        A6                                                  3
  line would be about -2.0 rather than -2.9. There are          A7 and AS                                           S
 four reasons why it is not. First, the inscatter con-          In-scatter (G s )                                  16
  tribution from the lip falls off as some power,
  greater than 3, of the distance. Second, the effective        Al - A2 (Multiple Scatter)                          S
  geometrical scattering areas contributing to the dose         ~    - Ceiling (Multiple Scatter)                   S
  are gradually decreasing in size as .t2 increases.            ~    - Floor (Multiple Scatter)                     S
  Third, the albedo values for the various scattering
  areas gradually decrease as .t2 increases. And                A2 - Ceiling (Multiple Scatter)                     3
 fourth, the areas are not effectively concentrated at          A2 - Floor (Multiple Scatter)                       3
  the point from which .t2 is measured. These four              Residual                                           10
 factors have various degrees of importance depend-


                                                           72

                                                                                           Digitized by   Google
   The residual contribution was what remained after            was not very sensitive to the axial position of the
all the corner blocks were removed and a lead cor-              source, particularly when "2 > 4W. This would imply
ner lip was installed. It is assumed that there was             that an adequate treatment of. a source, distributed
primarily a multiple-scatter effect between the                 uniformly across the entrance, could be effected by
remaining surfaces of the first and second leg.                 assuming the source to be concentrated at the center
   It would be well to describe at this point three             of the entrance. If this proves to be true for all duct
additional pertinent results from the trapping                  configurations, then it has particular Significance in
experiments:                                                    the case of radiation originating from fallout de-
                                                                posited on the entrance door.
    a. Trapping a surface to a depth of 1.8 in. (W/6)
                                                                    Finally, Green developed an empirical formula
produced a 15 per cent drop in its contribution. A
                                                                for dose in the second leg of a square duct when
depth of. 5.5 in. produced a 75 per cent drop, and a
                                                                Co 60 is the gamma-ray source. He finds:
depth of 11 in. produced a 90 per cent drop. This
information is of limited value because it is con-
fused by the additional corner-lip effects introduced
by trapping the surface.
    b. Forming the walls and ceiling of. the corner                  The factor of 1.4 accounts for build-up observed
with concrete blocks 1.8 in. thick produced a con-              in the first leg. The factor 0.067 can be thought of
tribution equal to 85 per cent of that produced by              as the value of a bend.
                                                                     Dose-rate measurements and gamma-ray spec-
walls 17 in. thick and ceiling 6.5 in. thick. This
                                                                trum measurements for CoSO were made inside a
suggests that the corner scattering processes re-
                                                                square concrete duct with a 3 ][ 3 ft cross section by
quire only one half of a mean free path in wall
                                                                J. M. Chapman'(6) Results of his duct-streaming
thickness to give close to full effect.
                                                                measurements are presented in Figures 31 and 32.
    c. Trapping experiments performed on the
                                                                In order to evaluate the importance of the various
second leg (removing walls and ceiling) suggest
that 15 per cent of. the dose at ~ = 80 cm comes                primary scattering areas, AI' A2' A3' A4 of Figure
                                                                30, Chapman used a collimated l:.in. ][ I-in. Nal(T1)
from multiple scatter in the second leg. Half of.
                                                                crystal together with a stepwise scanning spectrome-
this comes from the far wall and half from the floor
                                                                ter to measure the gamma- ray spectra scattered
and ceiling.
                                                                from the various surfaces of interest.
   The most significant conclusion to be drawn from                  The spectra showed a prominent peak at about
the trapping data is that trapping is not a feasible            300 kev, corresponding to the energy rJ. a Co 60
method of increasing the attenuation from a corner.             photon after a single Compton scatter of approxi-
Even in a 6-ft duct, it is doubtful that complete               mately 90°. The spectra also showed a large amount
trapping (to a depth of 3 ft, for example) of all sur-          rJ. lower energy multiple-scattered gamma rays in
faces would reduce the dose more than 70 per cent.              the 50-kev to 250-kev range.
Since most entranceways for personnel will have                      To study the multiple-scatter effects, a spectrum
second legs of perhaps 9 ft in length, an extension             of the area Al (see Figure 30) was taken with a
cI. 4 ft would produce about the same change in dose.           shadow shield in place. This shadow shield, a 2-in.
It is obvious that increasing the length of. the second         thick lead block, was positioned so that Al was
leg 4 ft would be much less expensive than moving               shielded from direct radiation from the Co 60 source,
each wall of. the corner back 3 ft. Furthermore, most           all other parts of the duct being unaffected. Thus,
personnel entranceways will have the first leg slant-           any gamma rays coming from Al would have been
ing downward and the second running horizontally.               scattered before arrival at AI' Figure 33 shows the
Normal construction of. such an arrangement would               spectrum me.asured with the shadow shield in place
automatically trap the ceiling. Because of the                  for L1 = ~ = 6 ft. Also shown are the unshielded
multiple-scatter effect, once one area is trapped,              spectrum and the difference spectrum. As can be
trapping an adjacent area would produce a much                  seen, the previously scattered gamma rays account
reduced additional contribution. With the ceiling               for most rJ. the low-energy gamma rays in the
naturally trapped, little would be gained by moving             spectrum.
the two side walls back. However, it must be kept                   Some conclusions drawn from Chapman's work
in mind that for such an intersection, the surfaces             are:
make different angles with the incident radiation.
This might have a pronounced effect on the relative                 (1) Multiple scattering has an important effect on
contributions •                                                 the dose rate throughout the duct. About 40 per cent
    A matter of particular interest to Green was the            of the dose-rate contribution from Al is due to
effect of. moving the source to positions off the center        gammas that were previously scattered in the first
cI. the axis rJ. the duct. He found, for the duct geome-        leg, and this will probably be found to be true for
try considered, that the attenuation in the second leg          the other basic scattering areas.


                                                           73
                                                                                             Digitized by   Google
                                                       -yL-                     -LiL-                                                                      -LzlL-                -L~­
                                                       ~   •    1~.011          L3 = 10.0 It                                                               ~    • 14.01t         L3 • 10.0 It


                        •
                               •
                                    •
                                        •• •
                       Axial            Oboe......     •
                      Distonce          Dote Rote
                        (II)             (mr/hr)
                        ~.OO            s.IOOO
                        6.00            2~                                                                                    4.00             57600
                                                                                                                              6.00             24720
                        8.00
                       10.00
                                        13572
                                         9090
                                                           •                                                                  8.00             13728        •
                                                                                                                             10.00              9330
                       11.50
                       13.00
                                         752~
                                         5839                   •                                                            11.50              7482               •
                                                                                                                             13.00              5863
                       1~.50             5952                       •                                                        16.00              ~9O                    •
                       17.00             ~7
                                                                                                                                                                           •
                       18.00
                       20.00
                       22.00
                                          ~7~
                                             190
                                             105
                                                                         •
                                                                             ., ....                                         17.00
                                                                                                                             18.00
                                                                                                                             20.00
                                                                                                                                                4802
                                                                                                                                                 485
                                                                                                                                                 217
                                                                                                                                                                               ••
                                                                                                                                                                                  ••
                       2~.00
                       26.00
                                              61.0
                                              37.2                                     •
                                                                                                                             22.00
                                                                                                                             24.00
                                                                                                                                                 107
                                                                                                                                                  66.0                                 •
                       27.00                  34.9                                                                           26.00
                                                                                                                             27.00
                                                                                                                                                  37.9
                                                                                                                                                  35.4
                                                                                                                                                                                           •
                       28.00                  36.0
                       29.00                  36.6
                                                                                           ••
                                                                                                                             28.00
                                                                                                                             29.00
                                                                                                                                                  32.5
                                                                                                                                                  26.8
                                                                                                                                                                                               •
                       30.00
                       31.00
                                             31.~
                                             25.1                                               ••                           30.00                25. I                                            •
        "'             32.00                 12.6                                                                            31.00                17.9                                                 ••

             i
      10               33.00                  3.31                                                               10"'        32.00                 8.64
                       34.00                  2.37                                                                           33.00                 3.63

                                                                                                                        ~
                 I,    35.00                  1.68                                                                           34.00                 2.28
                       36.00                   1.2~
                                                                                                                        II   35.00                 1.24
                       37.00                  1.00                                                                           36.00                 1.21
      10-7             ~I.oo                  0.37
                                                                                                                 10_7!-,-~37;-._00~_-,:_yL.·97-':-_~_':----I::-'-~_....I:---'.J
             o        .1           .2   .3       .~        .5.6    .7            .8        .9    1.0                o        .1       .2       .3     .4     .5  .6     .7        ••           .9       1.0
                                              Ratio TIL (l = 37.0 It)                                                                               Ratio TIL (l. 37.0 It)
Figure 19. Z-ahaped 6 x 6-foot concrete entranceway with                                                    Figure 21. U-ahaped 6 x 6-foot concrete entranceway with
W/2 = 3.0 feet; 50-curie Co60 point source. (From                                                           W/2 = 3.0 feet; 50-curie Co60 point source. (From
Reference 4, Table 1.)                                                                                      Reference 4, Table 3.)


                                                                                                                              I

                                                                                                                              -L;/L-
                                                           -~­                   -L~­
                                                                                                                                  LI • 13.0 It
                                                       ~ ~          14.011      L3 • 10.01t

                        •                                                                                                     •
                               •                                                                                                    •
                                    •                                                                                                      •
                                        ••                                                                                                     ••
                        01_
                            Axial          •
                                          a.....d
                                          DooeRote
                                                      ••                                                                      Axial
                                                                                                                             DI_
                                                                                                                                               0bMrv:,· •
                                                                                                                                               DooeRote
                             (It)               /hr)
                                             ....                                                                             (It)              (mr/hr)

                            4.00          24492                                                                               4.00             22950
                                                                                                                              6.00             10608
                            6.00
                            8.00
                                          10356
                                           6300
                                                           •                                                                  8.00              6426           •
                                                                                                                             10.00              4212
                           10.00
                           11.50
                                           4284
                                           3061
                                                                •                                                            11.50              3168               •
                           13.00
                           16.00
                                           2376
                                           2067
                                                                     •                                                       13.00
                                                                                                                             14.50
                                                                                                                                                2657
                                                                                                                                                2585
                                                                                                                                                                       •
                           17.00           1978                          • •                                                 16.00              2343                       •
                           18.00            267                              ••• •                                           17.00
                                                                                                                             18.00
                                                                                                                                                2079
                                                                                                                                                 269
                                                                                                                                                                               • •••
                           20.00            115
                           22.00               60.'                                    •
                                                                                                                             20.00
                                                                                                                             22.00
                                                                                                                                                 118
                                                                                                                                                  62.7
                                                                                                                                                                                    •
                           24.00               33.1
                           26.00            24. I                                                                            24.00                37.8                                     •
                           27.00            20.3                                                                             26.00                22.0
                           28.00            20.6                                           ••                                27.00                18.9                                         •
                           29.00            18.2                                                                             28.00                17.4                                             •
                           30.00            17.3                                             ••                              29.00
                                                                                                                             30.00
                                                                                                                                                  16.1
                                                                                                                                                  15.6
                                                                                                                                                                                                       ••
                           31.00            14.1
                           32.00             7.56                                                                  "'        31.00                 9.80



             I :::         33.00             1.99                                                                10          32.00                 4.93



                                                                                                                        ~ :::
                                                                                                                                                   2.32
                                                                                                                        '
                                             1.44
                                             1.02                                                                                                  1.42
                         36.00               0.76                                                                            35.00                 1.02
                                                                                                                             36.00                 0.75
             I           37.00               0.61
                                                                                                                                                   0.5.
        -7               41.00               0.26                                                                  -7        37.00
                                                                                                                 10
      10 0            .1     .2         .3    .4    .5     .6     .7             .8        .9    1.0                    o    .1         .2     .3       .4   .5    .6     .7      ••           .9           1.0
                                           Ratio TIL ( l . 37.0 It)                                                                                 RatlaTIL ( l . 37.0 It)
Figure 20. Z-ahaped 6 x 6-fcot concrete entranceway with                                                    Figure 22. U-ahaped 6 x 6 -fcot concrete entranceway with
W/2 = 3.0 feet; SO-curie Ca137 point source. (From                                                          W/2 = 3.0 feet; SO-curie Ca137 point source. (From
Reference 4, Table 2.)                                                                                      Reference 4, Table 4.)


                                                                                                       74
                                                                                                                                                          Digitized by          Google
                                                  -7"--                                                               ty'l-         -7"'--
                                                  7 = ~.O h                                                             3.5 h       7' 4.0h
                                                                                                                        •
           10. 1




    {      10.2
     E                                            •                                                                                  •
    §
    0
    ;:::

    eO                                                    •
    ~o
    0                                                         •                                                                                      •
    1                                                                                               ~
    ~      10""               Axial          a.--t
                                                                                                    ~   10""
                            DhIanc.          Dooo 1tate
    j                                                                                               j
                               (ft)           .../hr)

    I
    ~
                               3. SO
                               ~.SO
                               5.SO
                                             89120
                                              6996
                                               828
                                                                        •                           J   10.5
                                                                                                                       A.ial
                                                                                                                      Distance
                                                                                                                         (h)
                                                                                                                                        Oboerved
                                                                                                                                     Dooo late
                                                                                                                                         I/nr/hr)
                                                                                                                                                          •
           10-5                6. SO           239                                                                      3. SO           9GI8O
                               7,SO            109                                                                      ~.SO             6960




            .~ ? I.....J':------L~....L-"'""'="-_':_-'=____:_'
                                                15.9                                                                    5.SO              87~
                                                 2.11                                                                   6. SO             2~7
                                                 0.57                                                                   7. SO             111
                                                                                                                        8. SO              11.5
                                                                                                                        9. SO               1.60
                                                                                                                       10.50                0.56
                                                                                                                       11. SO               0.19



           10.7~
                                                                                                                                                                       •
                                                                                                        10·7!-..L.1~-':.....J'-':---':---':-...J...J':---':~--,=--':-....,-J
                   o   .1      .2      .3       .~    .5    .6     .7       .8   .9   1.0                      o                 .3      .~  .5    .6    .7       .8   .9   1.0
                                            Ratio T/L (I.. 11.0 h)                                                                 Ratio T/L (I.. 110 h)
Figure 23. Z-sbaped 1 x 1-foot concrete entranceway with                                         Figure 25. U-shaped 1 xl-foot ooncrete entranceway with
W/2 = 0.5 foot; 50-curie Co60 point source. (From                                                W/2 = 0.5 foot; 50-curie Co60 point source. (From
Reference 4, Table 6.)                                                                           Reference 4, Table 8.)


                                                                                                                       1/L-
                                                                                                                       3.5h




   {                                                                                                                                •
     E

    ~
    ~                                                                                                                                      •
    eO
   fi!0
                                                                                                                                                     •
    0

    j                                   DoN Ia••
                                                                                                                        Axial
                                                                                                                       Dlstanc.
    Ii                      (ft)            "r/hr)                                                                       (ft)

   1~ 10.5
                            2. SO
                            3. SO
                            ~.SO
                                        72780
                                        37572
                                         2818
                                                                        •                                                3. SO
                                                                                                                         ~.SO
                                                                                                                                         37170
                                                                                                                                          2870
                                                                                                                                           ~~
                                                                                                                                                          •
                                                                                                                         5.SO
                            5. SO            ~M                                                                          6. SO             129
                            6. SO            1M                                                                          7. SO              62.7
                            7. SO
                            8. SO
                                              65.3
                                               6.82
                                                                                 •                                       8. SO               5.99             •
                                                                                                                         9. SO               1.03
                            9,SO               1.18                                                                     10.SO                O.M
                                               O.~I                                                                     11. SO               0.15




                                                                                                                      L
                                                                                                                                                                       •


                                                                                      1.0                               .2       .3     .~          .5                 .9   1.0
                                        Ratio T/L (I.. 11.0 h)                                                                     Ia.lo T/L        (I.

Figure 24. Z-sbaped 1 x 1-foot concrete entranceway with                                         Figure 26. U-sbaped 1 xl-foot ooncrete entranceway with
W/2 = 0.5 foot; 80-curie Csl 37 point source. (From                                              W/2 = 0.5 foot; 80-curie Cs137 point source. (From
Reference 4, Table 7.)                                                                           Reference 4, Table 9.)

                                                                                            75
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                              ., .•                                                                                            1\
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                                                                                                                                                                                                                     4-
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                                                         •                                                                            \\
                                                                                                                                       \1
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                                                                 •                                                                                                                                      ,
                                                                                                                                                    l~
   1                Alelol
                    ow-.
                                  ~
                                  0 - .....                             •
                                                                                                                                                    ~\                                                                      I
   !                 (It)          ..,/hr)
                                                                             •                                         01.-
                                                                                                                                                                                  ~. I I I
                                                                                                                                                        ~R
         10-3       1.67          2300
   eO               1.84          2000                                           •
                    1.17          1900                                                 • •                                                                                            Co"
   ~o
                    2.16
                    2.49
                                  1550
                                  1150
                                                                                               •                           I                                                                                    -
                                                                                                                                                                                                                -
                                                                                                                                                          ~
   0                                 ~
   j     10-4
                    2.12
                    3.02
                    3..2'
                                     740
                                     645
                                                                                                                                                             ""IT
                                                                                                                                                              \~
                    3..97             99. 0
                                                                                                                                                               ~\

   I
                    4.41              34.0
                    4.10
                    5.17
                                      14. 3
                                       7.30
                                                                                                                                                                    \\,
                                                                                                                                                                     ~
         10-5       5.53               4.30
                    5.90               2.73
                    6.21               1.91
                    6.66               1.33                                                                                                                               1:\
                                                                                                                                                                              \\
                                                                                                                                                                              ~
         10"'


                     ~                                                                                                                                                                ~
         10.7 !--L1...l.-
             o .1 .2
                         I..J,-.....JI:---L-L~-':-~-...I;-.....JI:-...,.J
                                  .3     .4        .5          .6       .7           ••   .9       1.0
                                                                                                                         ." ,                   U        2      U         J                   s         •    7      •       t   •


                                   lotio T/I.     (I.. 7. II It)                                                                           ~
Figure 27. L-shaped 0.9167 x 0.9167-foot square concrete                                                      Figure 29. Compari80n between results of Green (NCEL)
duct with W/2 = 0.4583 foot; O.34-curie Co60 point source.                                                    and Eisenhauer (NBS) for dose attenuation of Co60 in
Source in corner for 4 measurements. (From Reference                                                          second leg of ll-inch x ll-inch duct.
5, Figure 12 and Table 8C-C.)




                                                         -7"'--
                                                          ~      • 3..131t



                                              •                                                                           ---
                                                                                                                           ~
                                                                                                                                't
                                                     •
                                                             •                                                                  I \1 II


                                                                                                                                      II
                                                                            •                                                   I         1\
                                                                                                                                          \\
    ~o                                                                                                                                     \    \
                                                                                                                                               I I

    J    10-4                                       Ale 10 I
                                                  DI.tanc.
                                                                        Oboerved
                                                                        Do.. Rate
                                                                                                                                               \ I
                                                                                                                                                I \
                                                                                                                                                1 \


    j    10-5
                                                    (ft)
                                                     1.74
                                                     2.43
                                                                            (mr/hr)
                                                                            2010
                                                                             680
                                                                                                                                                    I




                                                     2.87                    210
                                                     3,26
                                                     3.63
                                                     3.99
                                                                             125
                                                                                61
                                                                                30.5                                                                                  -_... -------
                                                                                                                                                                              -. .                          ..........
                                                                                                                                                                                                                         ....
                                                                                                                                                                                                                                    1
         10"'                                                                                                                                            -+~_                 L -_____                      ~~~ ~



         10.7~_1Ll:-~~---I:--~~:--+~-...,.J
                o   .1       .2   .3     .4    .5    .6
                                    lotio T/I. (I.. 5.57 It)
                                                             .7                      ••   .9       1.0
                                                                                                                                                                                                                                    J
Figure 28. L-shaped 0.9167 x 0.9167-foot square OODCrete
duct with W/2 = 0.4583 foot; O.34-cur1e Co60 point source.                                                    Figure 30. nact geometry lDdicatSq primary I.IId traD8-
(From Reference 5, Table 10C-C.)                                                                              mission 8C&tterlng are&s.


                                                                                                         76

                                                                                                                                                               Digitized by                        Google
                                                                                                                     (2) Insight into scattering processes going on in
                      ..
                      \
                               e
                                                                                                                  the duct, and knowledge of the dose- rate contributions
                                                                                                                  of given areas will help in determining the best
                                                                                                                  methods for decreasing the radiation in the duct.
           10-1
                                    • •                                                                           For instance, since low-energy gammas contribute
                                                                                                                  a large amount to the dose rate, a shield in the
                                                                                                                  second leg, such as a steel door, might greatly
     "C'   10-2       -Ly'L-                                         -y..-                                        increase the attenuation, and experiments should
     ~                Ll • 6.00 ft                                   '2 •      13.17 ft
                                                                                                                  be made to determine the effectiveness of such
     ...
     E
     ...                                                                                                          shields.· Further spectral measurements should
     t
     •     10-3
                                                         e
                                                             e
                                                                 e                                                also be made with different sources and source
     eO                                                                                                           poSitions, and possibly with different duct
                                                                          e
     ~O                                                                       •                                   configurations •
     a                                                                               e
     ~ 10-4
                                                                                                                     Chapman is currently engaged in an experimental
                                                 Axlol                   0I00erwcI
     lc                                         ~                        0- ....                                  program which should contribute toward better
                                                  (tt)                    ..../hr)
                                                                                                                  understanding of duct-streaming phenomenology.··
     i
     ~
           10-5
                                                  1.50
                                                  2.00
                                                  3.00
                                                  4.00
                                                  5.00
                                                                         14150
                                                                         10250
                                                                          4715
                                                                          2550
                                                                          1790
                                                                                                                  Three aspects of the program are:
                                                                                                                     (1) Using a 3 x 3-in. Nal(Tl) crystal and a
                                                  6.00                    1212                                    multi-channel analyzer, Chapman is repeating and
                                                  9.00                      17.0
                                                  9.50                      58.0                                  expanding his previous work on gamma-ray energy
           10"'                                  10.00                      41.0
                                                 11.00                      17.5
                                                                                                                  spectra within a duct.


           .~ i
                                                 12.00
                                                 13.00
                                                                            12.1
                                                                             7.10
                                                                                                                     (2) Chapman is working on an experimental study
                                                                                                                  initiated by J. Jacovitch of the possibillty of a gamma-
                                                                                                                  ray polarization effect which may improve the pro-
                  o       .1        .2      .3     .4  .5     .6     .7                      .1   .9   1.0
                                                                                                                  tection afforded by a three-legged duct if one of the
                                            IatIo TIL (L. 19. 17 ft)
Figure 31. L-shaped 3 x 3-foot square coDCrete entrance-
way with W/2 = 1.5 feet; 2.4-curie Co60 point source.
(From Reference 6. Table lA.)

                                                                         -y..-                                     *ReceDt experiments at NeEL supported this hypothesis.
                                                                          '2 •    13. 17ft                        **Tbis experimental program bas now been completed.

                                   •e
                                        e
                                            e
                                                                                                                           ,
                                                                                                                           10
                                                                                                                                                      ....           t,- _$ _
                                                                                                                                                                          _•
                                                                                                                                                                              UnIM....d CrOi. COu"t .. 10lf.ec
                                                                                                                                                                                      GrOll Coun. • 11
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     J                                                                        ••                                     ..
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                                                                                                                                                                        ~,
           10-4
                                   AxI.1
                                   Dls_
                                    (tt)
                                                OIooeNeCI
                                                0- ....
                                                 ..../hr)
                                                                                         e                           010
                                                                                                                     :::
                                                                                                                     :                     :
                                                                                                                                               ,"            ,
                                                                                                                                                    ['-Dlffe,.nc.              ,
                                                                                                                                                                                                        \,
     L.                             3.50
                                    '.00
                                    4.50
                                    6;00
                                    7.50
                                    9.50
                                   10.00
                                                3320
                                                2...0
                                                1950
                                                1150
                                                 729
                                                 200
                                                   74.0
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                                                                                                                     j
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                                                                                                                           .,
                                                                                                                           .7

                                                                                                                           .S
                                                                                                                                                                               \
                                                                                                                                                                                   ...
                                                                                                                                                                                         \
                                                                                                                                                                                                 '..
                                                                                                                                                                                                            ,
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                                   10.50           38.0                                                                    .It
                                   11.00
                                   12.00
                                                   31.0
                                                   13.5                                                                    .,                                                                           ~
                                   13.00            9.10
                                   13.50            6.40
                                   15.00             3.~                                                                   .2



                  o       .1        .2      .3
                                                 I
           10-7~-,:_-,:--'~,-,:-_~-,:_-,:-----!:--'.::---:-,
                                                   .4   .5   .6      .7                      .8   .9   1.0
                                             lotio TIL (L. 20.67 ft)                                                       .1
Figure 32. L-shaped 8 x 3-foot equare OO1lorete entraDCe-
                                                                                                                                               100         ISO    100
                                                                                                                                                          _ f ..,,,(_)
                                                                                                                                                                         2SO             )C            "0 . .       ..!

way with W/2· 1.5 feet; 2.4-ourle Co60 point source.                                                              Figure 33. Shadowed and unshadowed spectra of Al.
(From RefereDOe 6. Table lB.)                                                                                     Ll ... L2      = 6 feet.

                                                                                                             77

                                                                                                                                                                         Digitized by                       Google
legs is noncoplanar with the other two. This problem
was suggested by L. V. Spencer, who pointed out that
a gamma-ray photon is unlikely to scatter out of its
plane of polarization. It is not clear whether gamma-                    I
                                                                                        -•• •
ray polarization will be important in the crude geom-                            -lll-                     -yt-                                -Ly'l-
etryof a concrete duct. Recent experiments at NCEL                               LI = 3.00ft               ~       - 4. 17ft                   L3 ·3.33ft
show that, in certain cases, a noncoplanar third leg
may provide twice the protection of a coplanar                   f    10.2
                                                                                                           •
third leg.                                                       I
   (3) Another experiment is underway to evaluate                rS                                              --
the effectiveness of metal doors within a duct, as               • 010.3
                                                                 e                                                 •
suggested by Chapman's conclusion in Number 2.                                                                               •
                                                                 ~o                                                              ••
The work is being done by Chapman and J. S. Grant.               o                                   DI _ _
                                                                                                      Axial                OlIN.....
   Dose-rate measurements along the axis of a 12-                j    10-4                               1ft)
                                                                                                                           Dole .....
                                                                                                                              Im,/hr)
in.-diameter concrete duct with two right-angle

                                                                 I                                                                                 -•
                                                                                                         2.00                l1li25
                                                                                                         2.25                8064
bends were made by T. R. Fowler and C. H. Dorn.                                                          2.50                6685
Results are shown in Figures 34 and 35. Fowler                                                           2.75                5488                       •
                                                                      10-5                               3.00                4592
and Dorn(7) analyzed their results with Co60 and                                                         4.10                 258
                                                                                                         4. SO                114
compared them with previous measurements in                                                              4.17                  61.0
                                                                                                         5.25                  36.0
square ducts.                                                                                            5.62                  23.0
                                                                      10-6                               6.00                  16.0
   Measurements were also taken at points c1f the                                                        6.38
                                                                                                         8.17
                                                                                                                               14.6
                                                                                                                                1.50
axis in the first leg of the duct. The spread d. data
was less than 10 per cent, confirming the earlier
finding for a square duct(5) that build-Up depends
only on the position along the axis of the duct, and
                                                                      10·7
                                                                             o
                                                                                  1
                                                                                  .1    .2      .3
                                                                                                         8.55
                                                                                                         8.92


                                                                                                          .4    .5  .6
                                                                                                     Itotlo TIL Il' 10.5 ft)
                                                                                                                             .7
                                                                                                                                0.90
                                                                                                                                0.60


                                                                                                                                                   .8       .9   1.0

does not vary appreciably over the cross section              Figure 34. Z-shaped I-foot-diameter round concrete duct
of the duct.                                                  with W/2 = 0.443 foot; 2.1-curle Co60 polnt source; 0.3-
    Fowler and Dorn compared their results with               curle source used for Ll (D/7 = actual dose). (From
Green'~ formula for dose attenuation in an 11-in.             Reference 7, Tables I, III, IV.)
duct. (5) Green found:

                                                                                 _L!Il-              -yt-                                      -ly'l-
                                                                         1 II • 2.00ft               ~     • 4. 17 It                          ~   • 3.33 It
   Fowler and Dorn found that, for L1 = 2 feet,
                                                                                                     •
D(t2) = 1.33 Do L1- 1•84 (0.201) (t2/wf 3•28                                                              •
                                                                         2
                                                                                                              •
   For L1 = 3 feet,                                                                                                •
                                                                                                                       •
D(t2) = 1.40 Do L1- 1•84 (0.0634) (t2/Wf 2 •36                                                                             •
                                                                                                                                 •
   Fowler and Dorn conclude that there are not large
or important differences between round ducts and
square ducts as far as the behavior of gamma radia-                                                                                            •
                                                                                                                                                   0
tion is concerned.                                                                              Axlol                  0I00e0wcI
                                                                                               DhIanc•
                                                                                                 1ft)
                                                                                                3.17
                                                                                                                        ...
                                                                                                                       Dole ....

                                                                                                                       1141
                                                                                                                             "",)
                                                                                                                                                        •
                                                                                                3.50                    547
Review of Experimental Findings                                                                 3.17                    276
                                                                                                4.25                    149
                                                                                                4.62                     83.0
A study of the various experiments(1;.7) leads to                                               5.00
                                                                                                5.38
                                                                                                                         49.9
                                                                                                                         32.9
several conclusions of interest to the design of                                                7 17
                                                                                                7.55
                                                                                                                          4.30
                                                                                                                          2.10
shelter entranceways:
   1. If a duct is to have two legs at right angles
with total length L, best attenuation is obtained with
                                                                         7
                                                                      10· 0
                                                                                   j
                                                                                   .1   .2
                                                                                                7.92



                                                                                                .3            .4        .5
                                                                                                                          1.20



                                                                                                                                     .6   .7       ••       .9   1.0
L1 ~ ~ ~ L/2.                                                                                        ItotIo TIL ~             • 9.5 It)
                                                              Figure 35. Z-shaped I-foot-dtameter round ooncrete duct
                                                              with W/2 = 0.443 foot; 2.1-curle Co60 polnt souroe. (From
                                                              Reference 7. Tables III, IV.)

                                                         78

                                                                                                                   Digitized by                Google
    2. The cross- sectional area of a duct should be             For such a case the differential dose albedo a is
kept to a minimum size consistent with functional                defined by the equation:
requirements because better attenuation is obtained                        D a (E , I , I, tp) cos I dA
with smaller ducts.                                              dD=        0         0        0            0
    3. For a given total length L, it is preferable to                                             2   2
                                                                                               r1 r2
have two right-angle bends instead c1 one right-
angle bend, so long as Lt ~ 3W for i = 1,2,3.                    where
    4. Radiation traps are not generally an efficient
means of increasing the protection factor of a duct.
                                                                 dD    = differential dose at point of measurement
It is preferable, for the same excavation, simply to             Do = dose in air at unit distance from source
make one of the legs longer. Of course, advantage
                                                                 Eo = energy of incident radiation
should be taken of any naturally available radiation
traps.
    5. Because of the relative softness of gamma
                                                                 '0    = polar angle of incidence of radiation
                                                                 ,     =   polar angle of backscattered radiation
radiation after a right-angle bend, steel doors are
very useful for improving attenuation in the second              tp    = azimuthal angle of backscattered radiation
or third leg of a duct.
                                                                 dA = differential area of scattering surface
    Efforts have been made at the U.s. Naval Civil
                                                                 r 1 = distance from source to dA
Engineering Laboratory to find an empirical ex-
preSSion relating dose to such factors as number                 r 2 = distance from dA to detector
~ legs, lengths of legs, initial gamma-ray energy,
                                                                     Note that D/r1 2 is the dose at area dA due solely
and duct width. Recent work at NCEL has resulted
                                                                 to the incident beam. If the beam has broad, parallel-
in the development of the empirical formula:
                                                                 ray geometry, one cannot, strictly speaking, assume
               H)0.907                                           a point source, and DoIr12 can be replaced by the
              (-         .. 2864                                 dose measured in the incident beam, called, say, Dr
D     0.214    W         W-.                                         Thus one has in this case:
            L 2.534 L _2.667 E 0.710
             1      -Z        0                                           D1a cos I            dA
This formula gives results which are usually valid
                                                                 D    =               2
                                                                                           0

to within 30 per cent for a wide variety of rectangu-                            r2
lar air ducts through concrete.
                                                                    It is seen that a may be a function of Eo and of
                                                                 the three angles: '0' I, and tp, where a can be thought
ALBEDO                                                           of as a coefficient c1 dose reflection.
                                                                    Attempts have been made to determine a as a
Theory                                                           function d. angles and incident famma-ray energy;
                                                                 Monte Carlo technlques,(l0,l1, 2,13) analytical
An important concept in gamma-ray scattering is                  appro~ches~(14) and experimental measure-
 "albedo," or reflection. The term "differential dose            ments\15i~ ,17,18) have all been used.
albedo" is discussed by Rockwell(8) and Chilton and                 Raso( ) performed Monte Carlo calculations for
 Huddleston. (9) The definition of differential dose             a broad, parallel monoenergetic beam of gamma
.albedo is reproduced here since it is important to              rays incident on a semi-infinite slab of concrete •
 theoretical arguments that follow. The scattering               From backscattering histories, differential dose
 of radiation from a point source incident on a slab is          albedo was computed as a function of initial gamma-
 diagrammed as follows:                         eIItlctor        ray energy, polar angle of incidence, and polar and
                                                                 azimuthal angles of reflection. Using Kaso's data,
                                                                 Chilton and Huddleston(9) developed a semiempirical
                                                                 formula for the differential dose albedo of gamma
                                                                 rays on concrete. The formula can be expressed
                                                                 as:
                                                                           C K('s)        102 6 + C'
                                                                 a =
                                                                                   cos I
                                                                                1+ _ _   0
                                                                                   cos I
                                                                 where K(ls ) is the Klein-Nish1na differential energy-
                                                                 scattering cross section, C and C' are parameters
                                                                 dependent on the initial energy, Eo; and a, '0' and I

                                                            79

                                                                                                           Digitized by   Google
are as previously defined. 8s is the spatial angle c1                 Experimental Measurements
gamma- ray scatter.
   Derivation c1 the above formula rests on the                       Measurements of the differential dose albedo of
assumption that scattered radiation can be divided                    gamma rays from Co 60 and Cs137 on concrete were
into two parts: that part which remembers the                         made at the U.S. Naval Radiological Defense
original direction of incidence, and that part which                  Laboratory. (17) Analysis do those measurements
has forgotten the original direction of incidence.                    yields results for the parameters C and C', which
The former part is to a great extent singly scattered                 are shown in Table 4.
radiation, or radiation where only one of its scatter-
ings is through a significantly large angle. The latter
part is composed either of radiation scattered many
times or of positron-annihilation radiation (under                                                      TABLE 4
circumstances leading to such a contribution). It is
                                                                              Comparison of Theoretioal aDd Experimental
also assumed that the effective energy attenuation
                                                                                       Values of Parameters
coefficient for a gamma-ray photon does not change
greatly during a scattering history.                                  Energy          RASO                      NRDL               CLIFFORD
   A least-squares technique has been used to fit                      (Mev)        C           C'          C          C'          C      C'
the semiempirical formula to the results c1 Raso's
Monte Carlo calculations.                                              .662       .0435       .0161       .0669       .0091       .0545       .00S3
   The best values for C and C' are given in Table 2.                           :1::.0010   :1::.0006   :1::.0023 :!::. 001 0   :I::.001S   :1::.0012
                                                                      1.250      .0665     .0107          .0706       .0123
                                                                               :1::.0013 :!::.0004      :1::.0045   :1::.0009
                          TABLE 2

          Parameters for Semiemp1rical Formula for
            DIfferential Gamma-Ray Dose Albedo

Energy                                                                   Another set of experimental measurements using
 (Mev)                     C                    C'                    Cs137 was made by Clifford'(18) The best values
                                                                      for C and C' based on Clifford's data are also
 0.2                .0224 :I:: .0010      .0366    :I:: .0017         presented in Table 4. Also shown, for comparison,
 0.5                .0364 :I:: .0009      .0200    :I:: .0007         are the best values for C and C' based upon Raso's
 1.0                .0557 :I:: .0011      .0117    :I:: .0004         Monte Carlo calculations.
 2.0                .0846 :I:: .0016      .00S14   :I:: .00026           A more detailed intercomparison of experimental
 4.0                .1222 :I:: .0029      .00761   :I:: .00020        and theoretical results is given by Huddleston. (20)
 6.0                .1439 :I:: .0041      .00767   :I:: .0001S
10.0                .1653 :I:: .0056      .0070S   :I:: .00014
                                                                      A conclusion of that study is that the Chilton-
                                                                      Huddleston semiempirical equation, based on Raso's
                                                                      Monte Carlo results, gives values which are suffi-
                                                                      ciently accurate for shielding calculations.
                                                                          Another experimental study of gamma-ray back-
                                                                      scattering was performed by Kaminishi(21) who
   By interpolation, Chilton(19) derived values of C
                                                                      showed that the amount do Cs137 gamma radiation
and C' at several other energies of interest. His
values are shown in Table 3.                                          backscattered from concrete, iron, or lead was
                                                                      independent of the thickness of the backscattering
                                                                      slab, so long as the slab was greater in thickness
                                                                      than two mean free paths of the gamma radiation
                                                                      in the scattering medium.
                           TABLE 3

   Interpolated Parameters for Some Selected Isotopes                 Some Tests and Uses of Albedo Theory

                         Energy                                       The semiempirical formula for differential dose
  Isotope                 (Mev)          C                C'          albedo has been used by Chilton(22) to calculate the
                                                                      backscatter by an inifinite concrete slab do the
Au19S                      .412         .0344          .021S
                                                                      radiation from isotr~ic point sources do Na24,
C s 137                    .662         .0435          .0161          Co 60, Cs 137, and Au 8. Agreement was found with
Co60 (average)           1.250          .0665          .0107          the experimental results of Clarke and Batter(23)
                                                                      within Umits of experimental error.


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                                                                                                           Digitized by     Google
   It has been shown by Shoemaker and Huddleston(24)            with a Co60 point source in two-legged and tbree-
that variations in the azimuthal angle", are redun-             legged rectangular air ducts in concrete. He ob-
dant in experimental measurements d. differential               served that dose fell off in the second leg of a duct
dose albedo provided the Chilton-Huddleston albedo              according to the relationship:
equation, or a generalization of, is valid. Once                            1
differential dose albedo has been determined for a                   Ge-


complete set of incident and reflected polar angles                       t 3
                                                                           2
with zero azimuth, albedo at any azimuth is shown
to be calculable .by a suitable mathematical trans-             Seeking another relationship, Eisenhauer found:
formation. Specifically, what Shoemaker has shown
is that for every set d. three angles {'o,8,,,,) there          ~    Ge   _1_
exists another set d. angles {'o', 8',01 such that              Dl        t ,3
                                                                           2
a (80 ,8,,,,) = a ('0 ',8' ,0)
                                                                where:
   The primed angles are related to the unprimed                                 W    1
angles by the relationships                                     .t2' = .t2 -     "2 - ~
cos  '0'
       =. g cos      '0                                         and '" is the absorption coefficient of Co60 gamma
cos 8' = g cos 8                                                rays in concrete.
                                                                   Eisenhauer was thus able to show that dose rates
where                                                           along the axis d. his ducts were proportional to solid
                                                                angle, provided the proper origin was selected. In
                       tan2, tan2, 0 Sin2",         ]1/2        the second leg, then, Eisenhauer had:
g= [ 1+          2                            2                 D     K1
             tan 8 + 2 tan'o tan 8 cOS!p + tan 80
                                                                Do = .t ,2
    This simplification implies that in future experi-                     2
mental determinations d. differential dose albedo it            where K1 is an empirical constant which can be
is sufficient to vary only the polar angles of inci-            justified approximately from theoretical arguments.
dence and reflection. Values d. albedo at any                   In the third leg d. a duct, the expreSSion would
azimuthal angle can subsequently be derived.                    become:
    Comparison with experiments such as Hurley's(17)
shows that Shoemaker's angle-substitution formula
is highly reliable and is much more accurate than
the Chilton-Huddleston formula.
    Huddleston and Shoemaker(25) have also demon-
strated how to derive iso-albedic contours in order             where the definition d. L2' , .t3' , and ~ are obvious
that contour lines for constant albedo can be plotted.          by analogy with .t2' and K1•
The contours procJuced reveal several features d.                  Most treatments d. the streaming of gamma
scattering geometries. Inspection reveals, for                  radiation through air ducts in concrete are based
example, where the maxima and minima d. albedo                  on the method d. LeDoux and Chilton.(26) Their
occur, as well as when albedo varies over a large               method can be explained by reference to Figure 30.
range and when albedo varies only slightly. The                 Areas A1, A2, AS, and A4 are called basic scattering
graphs also give indications d. how rapidly albedo              areas because they are visible from both the source
varies with angles and energy. Information presented            and detector positions. It is reasonable, therefore,
in the form d. contours is intended primarily as a              to suppose that most radiation reaching the detector
visual aid for understanding how albedo varies with             should be scattered from the basic scattering areas.
energy and angles. This understanding should be                 Using appropriate values for differential dose albedo
useful to radiation experimenters and to designers              and invoking solid-angle arguments, LeDoux and
d. personnel shelters who want to mow the impor-                Chilton were able to calculate the basic scattering
tance d. the orientation d. scattering materials.               effects. Not having available to them values for
                                                                differential dose albedo, they used total albedo
                                                                values, assuming isotropic scattering. LeDoux and
THEORY OF DUCT STREAMING                                        Chilton also developed an analytical method for
                                                                treating corner-lip transmission effects and corner-
Eisenhauer(1) developed a theoretical model to                  lip in- scattering effects. Their results generally
account for the results d. his experimental findings            gave good qualitative agreement with experiment,


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                                                                                             Digitized by   Google
but theoretical predictions were low because of                       It remained for Chapman, (31) using Ingold's
neglect of multiple-scatter contributions.                        method, to devise a computer program to extend
    Chilton(27) subsequently extended the analytical              the LeDoux-Chilton technique for two-legged ducts
method to cases where the source and/or detector                  to include double-scatter effects. The first-order
is located off the axis of the duct.                              effects described by LeDoux(26) are included as
    Terrell (2) used the best values then available for           part of the program. Second-order scatterings are
differential dose albedo. He integrated numerically,              handled in the manner described by Ingold,(30) In
dose scattering contributions fram the various                    addition, Chapman treats other second-order effects,
interior surfaces of a duct. Multiple scattering was              such as a wall backscatter followed by a corner-lip
accounted for by the use of a build-Up factor.                    inscatter. Chapman's method also gives relative
   Subsequently, Terrell(3) described a computerized              dose contributions of various first- and second-order
method for performing numerical integrations of                   effects. Results of calculations are compared with
backscattered dose, still using a build-up factor to              experimental data for ducts whose widths vary from
account for multiple scatter. This method appeared                11 inches to 6 feet, using CoSO, Cs137, Au 198, and
to give good results but remains subject to question              Na24 gamma-ray sources. The calculated dose rates
because reliable values for differential dose albedo              agree to within ± 30 for all ducts and all sources,
were not then available.                                          except for small ducts with Cs137 sources, ducts
   Another computer code to perform numerical                     with very short first legs (Ll/W ~ 1.33), and for
integrations of dose backscatter of gamma rays.                   Au98 sources.
from interior walls of ducts was written by Silver-                  With the geometry of rectangular ducts it should
man and his co-workers.(28) The computer code                     be possible to use the AOONIS(32) computer code for
treated only single scattering; however, a method                 calculating gamma-ray dose attenuation. Efforts are
was outlined for treating second reflections, be-                 currently underway at NCEL to perform such calcu-
cause the spectral distribution of gamma rays                     lations. ADON1S is an mM-7090 Monte Carlo com-
backscattered from concrete was not well known.*                  puter code which can compute the neutron or gamma-
   Ingold(30) made calculations on C0 60 and Cs137                ray dose anywhere within a configuration composed
gamma-ray penetration through straight air ducts in               c1 rectangular parallepipeds. Such a code is expected
concrete. By using the single-scatter approximation               to be useful for calculations of dose rates within
and the albedo formula of Chilton and Huddleston, (9)             ducts.*
as well as a computerized numerical integration,
Ingold showed that square and round ducts of the
same cross sectional area have almost identical                   Conclusion
attenuation properties for all duct lengths and for
each energy studied. This conclusion is in agree-                 It is evident that there exists a wealth of experimen-
ment with the experimental finds of Fowler and                    tal data regarding the penetration of gamma radia-
Dorn.(7)                                                          tion through rectangular air ducts in concrete.
   Ingold also wrote a computer program to treat                  There are also theories that result within accept-
second reflections within a straight cylindrical duct.            able accuracy for engineering calculations of dose
A difficulty arose because albedo value for second                attenuation. Although the gamma-ray streaming
reflection depends on the energy of the once-scat-                problem is by no means solved, important advances
tered photon incident at the second reflection surface.           in recent years have greatly added to our under-
Even if backscattered gamma- ray energy spectra                   standing.
were well known, an integration over the spectra
would be required for exact calculation. As an
approximation, Ingold assumed that the gamma-ray
energy incident to the second reflection was single-
valued. The value taken was that computed for the
emergent ray c1 the first reflection, assuming a                  "'Some success has recently been achieved at NCEL in
single Compton scatter.                                            computing gamma-ray dose rate in ducts using ADONIS.




                                                                  References
"'Measurements of the energy spectra of gamma rays from
 C0 60 and Cs137 backsoa.ttered from semi-infinite slabs           1. Eisenhauer, C., National Bureau of Standards Techni-
 of paraffin, aluminum, iron, tin, and lead have been per-            cal Note 74, Scattering of Cobalt-60 Gamma Radiation
 formed by Hyodo. (29)                                                in Air Ducts, 1960.



                                                             82

                                                                                             Digitized by   Google
 2. Terrell, C.W., A.J. Jerri, R.O. Lyday, aDd D. Sperber,        17. Hurley, J.P., private communication.
    Armour Research Foundation Report ARF 1158-12,                18. Clifford, C.E., Defense Research Board of canada,
    RadIation Streaming In Shelter EntraDceways, 1960.                Defense Research Chemioal Laboratory Report No.
 3. Terrell, C.W. and A.J. Jerri, Armour Research                     412, Differential Dose Albedo Measurements for 0.66
    Foundation Report ARF 1158A01-5, Radiation Stream-                Mev GaDlma's Incident on Concrete, Iron, and Lead,
    Ing In Sbelter Entranceways, 1961.                                Ottawa, CaDada, 1963.

4. Terrell, C.W., A.J. Jerri, and R.O. Lyday, Armour              19. Chilton, A.B., private communication.
   Research Foundation Report ARF 1158A02-7, Radia-               20. Huddleston, C.M., U.S. Naval Civil Engineering Labora-
   tion Streaming In Ducts and Shelter Entranoeways, 1962.            tory Teclmioal Note N-567, Comparison of Experimen-
 5. Green, D.W., U.S. Naval Civil Engineering Laboratory              tal and Theoretioal Gamma Ray Albedo - An Interim
    Teclmical Report R-195, Attenuation of Gamma Radia-               Report, January 1964.
    tion In a Two-Legged. 11-Inch Rectangular Duct, 1962.         2l. Kaminishi, T., EngiDeering Testing Laboratory Report
 6. Chapman, J.M., U.S. Naval Civil Engineering Labora-               12-9, Scattering of Gamma Rays, September 1963.
    tory Teclmioal Note N-443, Gamma Dose Rates and               22. Chilton, A.B., Backsoattering by an Infinite Concrete
    Energy Spectra In a 3-Foot Square Duct, 1962.                     Plane of Gamma Radiation from a Point Isotropic
 7. Fowler, T.R.and C.H. Dorn, U.S. Naval Civil Englneer-             Source, Trans. Am. Nucl. Soc. 6, I, (1963), p. 200
    Ing Laboratory Teclmioal Note N-465, Gamma Ray                23. Clarke, E.T. aDd J. Batter, Gamma-Ray Scattering
    Attenuation In a 12-Inch Diameter Round Concrete                  by Nearby Surfaces, Trans. Am. Nucl. Soc., 5, I,
    Duct, 1962.                                                       (1962), p. 223.
 8. Rockwell, T., m. Editor, U.S. Atomic Energy Commis-           24. Shoemaker, N.F. and C.M. Huddleston, A Mathematioal
    sian Report TID-7004, Reactor Shielding Design Manual,            Simplification of the Gamma-Ray Albedo Problem,
    1956.                                                             Trans. Am. Nucl. Soc., 6, I, (1963), p. 198. Also see;
 9. Chilton, A.B. and C.M. Huddleston, U.S. Naval Civil               Shoemaker and Huddleston, A Mathematioal Approach
    Engineering Laboratory Teclmical Report R-228, A                  to Economy of Experiment In Determinations of the
    Semiemp1rioal Formula for Differential Dose Albedo                Differential Dose Albedo of Gamma Rays, U.S. Naval
    for Gamma Rays on Concrete, 1962.                                 Civil Engineering Laboratory Teclmioal Note N-478,
                                                                      (1962).
10. LeimdOrfer, M., AkUebolaget Atomenergl Report AE-
    92, The Backsoattering of Gamma Radiation from                25. Huddleston, C.M. and N.F. Shoemaker, U.S. Naval
    Plane Concrete Walls, Stockholm, Sweden. Also,                    Civil Engineering Laboratory Teclmioal Note N-539,
    M. LeimdOrfer, AkUebolaget Atomenergl Report                      A Mathematical Derivation of Contour Lines for
    AE-93, The Backscattering of Gamma Radiation from                 Constant Albedo of Gamma Rays on Concrete,
    Spher1cal Concrete Walls, 1962. Also, M. LeimdOrfer,              October 1963.
    AkUebolaget Atomenergl Report AE-94, Multiple
    Scattering of Gamma Radiation In a Sperioal Concrete          26. LeDoux, J.C. and A.B. Chilton, U.S. Naval Civil Engl-
    Wall Room, 1962.                                                  neering Laboratory Technioal Note N-383, Attenuation
                                                                      of Gamma Radiation through Two-Legged Rectangular
11. Raso, D.J., Teclmical Operation, Inc., Report To-B                Ducts and Shelter Entranceways, 1961.
    61-39 (rev1sed), Monte Carlo Calculations on the
    Reflection and Transmission of Scattered Gamma
    Radiation, 1961.                                              27. Chilton, A.B., U.S. Naval Civil Engineering Laboratory
                                                                      Teclmical Note N-412, Further Analysis of Gamma
12. Perkins, J.F., Monte Carlo Caloulation of Gamma-                  Ray Attenuation In Two-Legged Rectangular Ducts,
    Ray Albedo of Concrete and Aluminum, Journal of                   May 1961.
    Applied Physics, Vol. 16, No.4, June 1955.
                                                                  28. Park, C.M., C.B. Agnihotri, and J. Silverman, Depart-
13. Berger, M.J. and J. Doggett, Journal of Research of               ment of Chemioal Engineering, University of Maryland,
    the NatioDa! Bureau of Standards, Researoh paper                  Report UMNE-2, Interim Report on Scattering of
    2653, Reflection and Transmission of Gamma Radia-                 Gammas through Duots, 1962.
    tion by Barriers: Semianalytio Monte carlo Calcula-
    tion, Vol. 56 (89), 1956.                                     29. Hyodo, T., Backscatterlng of Gamma Rays, Nuclear
                                                                      Science and Engineering, Vol. 12 (178-184), 1962.
14. Corner, J. aDd R.H.A. Liston, The Scattering of
    Gamma Rays In Extended Media, Proc. Roy. Soc.,
                                                                  30. Ingold, W.C., U.S. Naval Civil Engineering Laboratory
    Ser. A, Vol. 204 (323), 1950.
                                                                      Teclmical Note N-469, Some Applications of a Semi-
15. Hayward, E. and J.H. Hubbell, An Experiment on                    empirical Formula for Differential Dose Albedo for
    Gamma-Ray Backsoattering, National Bureau of                      Gamma Rays on Concrete, 1962.
    standards Report 2264, 1953.
                                                                  3l. Chapman, J.M., U.S. Naval Civil EngiDeering Labora-
16. Hayward, E. and J.H. Hubbell, The Backscatterlng of               tory Teclmioal Report R-264, Computer Calculation of
    the Co60 Gamma Rays from Infinite Media, J. of Appl.              Dose Rates In Two-Legged Ducts Using the Albedo
    PhySiCS, Vol. 25, No.4, 506-509, 1954.                            Concept, October 1963.




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32. Eisenman, B. and E. Hennessy. ADONIS - an IBM-7090        DimensioD&l Bectangular Geometry. l1D1ted Nuclear
    Monte Carlo Shielding Code Which Solves for the           Corporation, UNUCOR - 63&. (1963).
    Transport of Neutrons or Gamma Rays in Three-




                                                         84


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,
-




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DESIGN PROCEDURES/RADIATION

 Charles M. Eisenhauer, Chairman




                                   Digitized by   Google
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                                  PROBLEMS OF SHIELDING AGAINST
                                        INITIAL RADIATIONS
                                                     Lewis V. Spencer
                                              National Bureau of Standards and
                                              Ottawa University, Ottawa, Kansas


Many scientists who have been active in research on                    is unknown, we cannot discount completely the
shielding anticipate that shielding against the radia-                 possibiUty of small bursts.
tions produced initially by a nuclear explosion will                      If shelters should be constructed with any thought
be studied systematically during the next few years.                   of blast resistance, we would expect that they meet
In this paper such studies will be considered as a                     hitherto unspecified criteria for minimum radiation
whole, so that individual problems that are essential                  shielding. On the basis 01. Table 1, for example, it
elements f1 the field can be viewed in the context of                  might not be unreasonable to expect that 100-psi
the total effort.                                                      shelters should reduce radiation levels by at least
                                                                       a factor 01. 104 • More comments about criteria of
                                                                       this type will be given later.
The Importance of Initial Radiation
                                                                       Problems in the Development 01. Engineering
In view of recent publicity, which has focused on                      Methods for Initial Radiation Shielding
very large nuclear weapons, it is important to ex-
amine whether or not an initial radiation problem                      People sometimes assume that since work was in
exists. As a general rule, initial radiation hazards                   progress long ago on the shielding against initial
decrease relative to blast and thermal hazards as                      racilation, the problem has been solved. This is not
the size 01. the explosion increases.                                  so, for many reasons:
   The last edition of Effects of Nuclear Weapons                         The shielding problems are quite difficult and
contained a very useful slide rule that can be used                    complex; and serious efforts to solve them really
to obtain at least tentative answers to this question                  began at the time when digital computers became
despite its limited accuracy Jl) Table 1 presents                      widely available, about a dozen years ago. Through-
data so obtained, for surface bursts.                                  out the last 12 years, two things, at least, have
                                                                       inhibited work on these problems: the federal policy
   Note that if the psi level is kept fixed, say at 100,
the initial radiation intensity does indeed go down
                                                                       on fallout shelters, and the state 01. neutron-cross-
                                                                       section data. Because there has been no federal
as the size of the explosion increases. But even at
                                                                       policy encouraging shelters against initial radiation
20 mt, it is reasonable to take some account of an
                                                                       effects, there has been neither strong incentive nor
incident dose as large as 35,000 rems. Further,
                                                                       funds to support substantial efforts in this field.
since the nature 01. the weapons of foreign countries
                                                                       And while the neutron-cross-section data have been
                                                                       increasing, they were skimpy in the early 1950's and
                                                                       are not complete today.
                          TABLE 1                                         Different people would certainly make up differ-
                                                                       ent lists 01. the typical elementary problems in
         Initial Radiation-Intensities for DIfferent                   initial radiation shielding.
                    Surface-Burst St.zes                                  The following list of problems represents my
                                                                       own picture of this field, which is influenced by the
                                lnit. Radiation      Distaoce
Size     Max. Overpressure           (rems)          (mileS)
                                                                       problem of restricted data.
                                                                          a) Sources
 20 mt         100 psi               .... 35,000       ....1.7            b) Spectra, angular distributions at the shield
200 kt         100                  -400,000            ..... 4
                                                        ..... 8
                                                                          c) Shielding calculations
                20                   ....15,000
 2tt            20                   .... 90,000        -.17
                                                                          d) Dose definition
                 4                      .... 3,000      ..... 4           e) Design and analysis criteria
                                                                          f) VaUdation of data

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    ''Sources'' denotes radiation emerging from the            the prompt-gamma spectrum.
device, e.g., reactor, primarily, but it also includes             Presumably the fission-product spectrum should
gamma rays produced by neutron interactions with               be integrated over the first minute after the explo-
air and other nearby materials.                                Sion, perhaps omitting the very short-lived compo-
    The radiation incident at the shield will be               nents. Dr. Walton is making such calculations in
affected by penetration through a very substantial             addition to his experiments, and may eventually
amount of air. It also depends on the many variables           provide us with a standard spectrum.
of the detailed configuration.                                     These spectra do not describe the radiation
    The shielding calculations, for different shield           produced in an explosion very well, however, be-
configurations, represent the primary shielding                cause prompt neutrons and gamma rays will be
problem; this is where most of the effort should               attenuated during their passage through bomb mate-
go, in prinCiple.                                              rials. As a result, the penetration curves through air
    The problem of definition of dose arises because           will be unrealistic if based on the reaction spectra.
the radiation field at the detector is in general a            Oddly enough, the fission-produced gamma rays may
mixture of fast neutrons, slow neutrons, and gamma             be accurately described so far as spectrum is con-
rays. The "dose" concept requires one or more                  cerned; but compression of the air by the blast-the
decisions as to how these may be combined.                     so-called hydrodynamic effect-produces even
   The problem of the criteria has been touched on             greater modification of the penetration law than
already. These clearly depend on radiation-intensity           occurs in the case of the prompt radiations.
levels against which the shield must be effective, as
well as expected mixtures of incident-radiation types.
    Finally, the problem of validation arises because          Spectra at the Shield
nearly all the most useful data will be the product
of calculations. Experiments to validate a complete            Despite the problems just mentioned, we do not
shield configuration are apt to be very difficult.             expect the reaction spectra to give misleading

                                                                II

The Problem of Usable but Unclassified                           •                                                     hIF _ _
                                                                                                                       1111 D-T _ _
Radiation Sources                                              ARBITRARY
                                                                •
                                                               ~~                .......                               UIIlP . . . . . . _ ..,.
                                                                                                                       1Iv) PI_.,.-t _ . . , .
                                                                                                                       IYI ......• _ _ ..,.
Data on radiation spectra and intensities produced                       ....   ~
by nuclear weapons have always been classified. For
this reason the question as to whether it is possible
to identify unclassified source data that will give
meaningful results must be faced at the outset of
any initial radiation study. Since only the basic
reaction spectra are freely available at the moment,
we must rephrase this question to inquire whether
use of these spectra can give meaningful results.
                                                                •
                                                                •
                                                                     I




                                                                 1~\IIt11
                                                                            \\
                                                                                           '"                    "\.
                                                                                                                       III

                                                                                                                       \
                                                                                                                                                                      (III




For reference we summarize these spectra in
Figure 1.                                                            I
                                                                                 ~.                                            \
    The fission-neutron spectrum (I), the prompt-
gamma spectrum (m), and the gamma rays pro-                      •                         x.
duced by capture of thermal neutrons by nitrogen                •                           l.
                                                                                                \
                                                                                                                                        \.
                                                                                                                                          \.
in the air were all copied from the compila.tion in                                                 \
                                                                                                                                             \
Vol. m, Part B, of the Reactor HandbookJ6) It is
                                                                                                        \
                                                                 I

known that the fusion process produces many 14-
Mev neutrons from the D-T reaction. Finally, the                 I
                                                                                                            \                                    \
gamma rays emitted by fission products during the               •
first minute or so after fission are well known by              •                                                \'
                                                                                                                  \'       I
                                                                                                                                                        '\

now, due particularly to the work of Zobel et al., (2)          •                                       •    t                 t
                                                                                                                                                            \.
                                                                                                                                                                 \.
SUnd and Walton of General Atomics,(3) andFisher                                                 IYI II                l\~
and Engle'(4) The curve (IV) represents gamma                    I
                                                                                                        i               I                                    t\
                                                                                                                  I 1\\ I
rays resulting from slow-neutron fission of U235
0.2 to 0.5 sec after fission. It will serve here to                  I                                       "
                                                                                                            Jl I I f, I               I              10.0
                                                                                                                                                             ! \         14.0
illustrate the data available, though it is probably
not the best choice on which to base extensive further         Figure 1. Reaction speotra for different types of radiation
calculations. Note that it does not differ greatly from        produced in nuclear explosions.


                                                          90

                                                                                                                                   Digitized by      Google
spectra at the shield, if the shield is far enough             spectra. But one might expect the greatest inter-
from the burst. There is a strong tendency for most            face effects to be due to radiation backscattered
components of a neutron or gamma spectrum to                   from the ground in the neighborhood of the shield.
come to relative equilibrium with one another for              This radiation would be directed upward and re-
large penetrations; and this relative equilibrium is           duced in energy by the backscattering; correspond-
not greatly affected by details of the source spec-            ingly, we would not expect such spectral modifica-
trum, provided different sources extend up to the              tions to change the (shielded) detector response
same maximum energies.                                         greatly.
   Whether thi.. effect is strong enough to mask the              More complicated interface effects exist; but it
source differences that occur must be, but has not             is expected that they would affect the intensity much
been, thoroughly studied. I believe that studies will          more strongly than the spectrum. It should be noted,
bear out the usability of reaction spectra.                    however that this problem ought to be studied
    The distances given in Table 1 vary from about             further.(6) Most interface effects have been ex-
.4 to 1.7 miles. Some idea about the effectiveness             plored thus far in terms of intensity rather than
of such penetrations in producing a relative equilib-          do spectral distortion. (7 ,8)
rium in the radiation spectra can be obtained from                Figure 2 clearly shows that the nitrogen-capture
Figure 2. This gives penetration data through un-              gamma rays are much more penetrating than the
disturbed air for most of the reaction spectra of .            neutrons. From the neutron spatial distributions, it
Figure 1. It can be observed that in all cases a               would appear that most of the capture gamma rays
distance of .4 mile is great enough to establish               originate within perhaps .5 mile of the burst point,
the slowly changing exponential trend that charac-
terizes large penetrations. As a general rule,
establishment c1 such spatial trends is accompanied
by establishment of relative spectral and angular                                                               111 _ _ _ _

equilibria. In addition, there is some possibility                 •
that the actual weapons spectra, which involve some                •,                                           (II)
                                                                                                                (III)
                                                                                                                            , ....... - .......... _ . ,.,.
                                                                                                                            P-... ...,,..
                                                                   4
                                                                                                                1111114_ .._
penetration albeit in materials different from air,                         Y
                                                                              ,,
will come to relative spectral equilibria more
                                                                                "
                                                                           IlATIONS,
                                                                                       \
quickly than do reaction spectra.
                                                                   I
                                                                             , " ,
   One should not be misled at this point about the                    I
                                                                           ~\      ,
fact that relative equilibrium is not a true equilib-              •
rium. Spectra in relative equilibrium do change                    •
with distance, particularly in the energy regions
that are most penetrating. But we would expect the
                                                                   4
                                                                                           +
                                                                                                ".~,
                                                                                                                 '. ,
                                                                                                     '\\                       "
change to be slow enough to make it possible for a                 I

representative spectrum to be applicable to a wide                                             "VI +
                                                                                                       ~                               "",
                                                                                                            \
range of distances.                                                    I

   In order to standardize the shielding calculations,             •
we propose that these calculations be based on spec-
                                                                   •                                                                                         ,II

tra one mile from the burst point, and that they be
                                                                   4
                                                                                                            +           \     '"                               "
made in undisturbed dry air at 20°C and 760 mm                                                                          II
                                                                                                                            ,~ {"I
                                                                                                                                .,
                                                                   I
pressure, with both vertical density variations and
the ground interface ignored in the calculations.
From Figure 2 (and Table 1) it is clear that one
                                                                       I
                                                                                                                                 \\
 mile is realistic, is evidently great enough to estab-
lish relative equilibria for large parts of the rele-              4
                                                                                                                                             , .,
vant spectra, and corresponds rather well to earlier
                                                                                                                                               \         '.,
experiments. (5)                                                   I

    The use of undisturbed air and the omission of
the ground interface in determining spectra at the                     I
                                                                                                       .5
                                                                                                                 ilLES
                                                                                                                                              +

                                                                                                                                                   1.0
                                                                                                                                                         \         L4
shield must be examined. We would not expect the
hydrodynamic effect to modify the spectrum in                  Figure 2. Penetration curves for different radiaUon types.
                                                               The data for I and n oorrespond to a plane normal souroe
important ways if there is enough air between burst
                                                               and are comparable with the point isotropio source data
point and shield to reduce the radiation intensity to          after removal of the inverse-square effect (Ref. 12.) The
manageable levels. This is because the type of                 data for m and IV are for point isotropic SOUl'08S; inverse-
spectral equilibrium occurring is quite insensitive            square effects have been removed. These particular curves
to density variations.                                         represent unpublished results of C. Eisenhauer. Comparable
    More serious questions concern neglect of the              data have been published by D1&Dy other autbors; in particu-
ground interface, which would certainly distort the            lar, see Refs. 9 and 13-15.

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                                                                                                                               Digitized by              Google
although this question needs further study. If thia           over different burst orientations that gives equal
is so, and perhaps even if not so, we would expect            weight to all points on a direction hemisphere.
the spectrum at one mile to be so strongly influ-             (e) We have some reason to believe that calculations
enced by the pseudo-equilibrium that we need not              of this type will give results comparable with a
perform a cascade-type calculation that includes              fairly wide range of. specific burst orientations.
neutron travel. Our intention is to adopt the one-            (d) It would greatly simplify duct and entranceway
mile spectrum for these gamma rays, as if they all            calculations. (e) Above-ground structures are
originated at the burst point.                                multi-sided, and the combined contributions tend
    Not included in Figure 2 are gamma rays pro-              toward such an "average" result.
duced by neutron inelastic scattering interactions                Two other cases have been proposed as standard:
with oxygen and nitrogen nuclei. While not so                 The worst case of a burst-point-to-shield line that
penetrating as the capture gamma rays, these also             is normal to the shield interface, and the best case
should be more penetrating than the neutrons; and             of a burst-point-to-shield line that is parallel to the
we propose to make the same assumption for them.               shield interface. Both of these proposals require
   It may be that further study will show this simple         Joint angle-energy distributions. The latter would be
assumption to be inadvisable; but it seems to be              particularly suitable to horizontal shield interfaces
quite reasonable at the moment to try it out.                 if one can make the assumption that burst heights
    Before leaving these questions, we might note             are low. The former is consistent with our feeling
that some data of. the type we are streSsing does             that the shielding calculations should be conservative.
exist, and it may be very useful,(9) But the attempt              The assumption of a cosine current for all com-
to standardize will require new calculations for the          ponents and all shield interfaces may be too non-
standard conditions assumed, even thouih the result-          conservative, although we do not expect this at the
ing spectra are not changed much. Many of. the data           present. Studies should be made in comparison with
do not exist at all. Not many neutron-gamma cas-              specific configurations. If, in fact, it should turn
cade calculations have been made, although many               out to be a seriously non-conservative assumption,
results are in prospect, particularly as a result of          a more peaked angular distribution such as cos2e
the work of Dr. Wendell Biggers, at Los Alamos. (10)          could be substituted, even though it would have much
                                                              less logical appeal.

Angular Distributions at the Shield
                                                              Shielding Calculations
Angular distributions and spectra are linked together,
and are strongly dependent on the configuration; for          Radiation can enter a sheltered area by penetrating
any given configuration that might be examined, it            through a bulk shield or through a hole in the shield.
would be necessary in principle to calculate a spec-          If the shield is inside another structure, more com-
trum for each of. perhaps a half dozen component              plicated configurations are possible; and if the shield
angular distributions for each radiation type. Or             is, say, part of a moving vehicle, it may be quite
else it would be necessary to determine by Monte              complicated in shape. We must assume, therefore,
Carlo methods the joint energy-angle distribution             that penetration through thick slabs into cavities
for each radiation type, at large penetrations, for           needs to be studied, as well as penetration through
any given configuration.                                      entranceway-duct-cavity combinations. It is hoped
    At the same time, it must be remembered that              that complicated strUctures can be reduced in some
burst-point position relative to the shield is one of         way to a modification of these two types, or else to
the important parameters of. the configuration                one of a small set of special cases.
affecting angular distributions; and this cannot be               What makes the shielding calculations burdensome
known in advance.                                             is the number of radiation types that must be con-
    We hope to avoid these complications by adopting          si~ered. A list of these types is given in Table 2.
a very simple convention: All spectral components                 Note that in the case of the 14-Mev neutrons we
of all radiation types will be assumed incident on            treat the unscattered component separately to gain
the exposed surfaces of the shield with a cosine              greater flexibility in the specification of shield
angular distribution (for the current crossing the            criteria. Each of the other six radiation types will
shield interface). This corresponds to a flux                 presumably be represented by a one- mile spectrum,
isotropic over the incident hemisphere at the shield.         and they all, including the 14-Mev unscattered neu-
    There are many reasons for adopting this par-             trons, would be assumed to be incident with a cosine
ticular convention, if it turns out to be workable:           angular distribution as already discussed.
(a) Many spectral components, particularly those                  In the case of incident neutrons, note that the
at lower energies, have isotropic-flux angular                detector will be subjected not only to a fast neutron
distributions. (b) This represents a type of average          flux, but also to a thermal neutron flux and a gamma-


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                       TABLE 2                                     A fourth que8tion has to do with the dose contri-
                                                               bution ~ thermal neutrons captured in the detector.
     BacUation Types Ino1dent on the Sbield aDd the            If the detector should be vanlsh1ngly small, this
  Correspond1nc RadJation ContribuUons at the Detector         would be negligible. If the detector were ~ exactly
                                                               the same material as the surroundings, we would
                                 hat Gamma- Thermal
                                Neutron Ray  Neutron
                                                               again be able to assume this to be zero. To the
                                 Dose   Dose  Flux             extent that a flesh-equivalent detector is not small,
                                                               and not concrete-equivalent, a non-zero contribution
Flaaion neutroDa                  ..;    .,j      ..;          due to thermal neutrons is appropriate. At present,
14-Mev (aoattered) neutrons       ..;    I        .j           I think I would favor neglecting the thermal neutrons
14-Mev (uDacattered) Deutrons     I      I        .,j          altogether, letting their effect on a small detector
Prompt gamma rays                        I                     through capture gamma rays suffice to take account
Flaldon-product gamma rays               I                     ~ them.
Air-capture gamma rays                   I
Air-scatter gamma rays                   I
                                                               Design and Analysts Criteria

ray flux, due to the capture or inelastic scattering           It may well not be pos8ible to establish design and
of neutrons in the shield.                                     analySi8 criteria without use ~ clas8ified data. But
   Presumably shielding calculations DlUSt be made             it may be pos8ible to publish and use such criteria
for each ~ the seven radiation types; and in the               freely in the literature after they have been
case ~ neutrons, these calculations not only should            establi8hed.
include the flux of thermal neutrons, but also should             The problem i8 that the criteria w1ll involve
be accompanied by calculations of the accompanying
                                                               weighted combinations ~ the seven different type8
                                                               ~ incident radiation; and they may be entirely differ-
flux of secondary gamma rays.
                                                               ent for different type8 ~ sheltering structure. Thus,
                                                               they require 8tudy ~ both absolute and relative in-
                                                               tensitie8 ~ the different type8 ~ incident radiations.
The Dose Problem                                               This cannot be done satlsfactorUy from unclas8ified
                                                               information alone, although it i8 po88ible that the
In view  ~ the obvious requirement for combinlng               criteria may be justifiable solely on the basi8 ~
neutron and gamma contributions to the dose, the               unclas8ified data.
do88 deflDltiona present a problem. I am rl. the                  Thi8 i8 one ~ the place8 where Dr. Bigger8 may
oplDion that thi8 type 01. question will not be quickly        be able to make a considerable contribution.
settled, and that it may be settled by use of more
than one type.~ dose. For thi8 reason, it seems
wise to keep track ~ all 13 type8 ~ data indicated             Validation Problems
in Table 2, as separate items, to permit different
combinations.                                                  It has already been mentioned that the angular dis-
    One major que8tion has to do with whether one              tribution and spectra incident at the shield interface
should U88 a doee concept appropriate to a 8mall               are not easUy realizable experimentally. Full- 8cale
detector or one appropriate to a large detector. The           mockup8 do not appear to be very practical. Even
large detector represents the human body matter,               field teSt8 with actual weapons have very limited
but the 8mall detector i8 conceptually simpler; and            Uselulne88. Both approache8 may give some uselu1
I tb1nk I prefer the latter.                                   information; but thi8 would constitute only a com-
    A second que8tion has to do with the relative              paratively crude type ~ validation.
effectivene88 ~ neutrons and gamma rays in pro-                    In my opinlon there is a substantial possibWty
ducing biological damage, that is to say, the appro-           that scale- model experiments will provide the be8t
priatene88 ~ an RBE approach. Here, I tend to                  mockup-type data for neutrons as well as gamma
favor use ~ the 8imple Kerma concept if it i8 at all           rays.
feasible, that i8 to 8ay, determination ~ the Kinetic              A 8pecial problem that will be encountered in
~nergy ~leasedin the MAterial comprising-the                   making compari80ns between experiment and theory
detector. Kerma value8 for neutrons and gamma                  is the effect ~ the interface. Note that the spectra
rays are comparable and additive.<l1)                          that we assume to be incident on the shield are ob-
    Third, there i8 the question of the material ~ the         tained by neglect of the interface, which will be
detector. I tb1nk I would favor a tissue-equivalent            present in realistic experiments. Further, we are
detector; although it appears that a strong case can           apt to normalize theoretical detector response in
be made for a concrete-equivalent detector.                    terms 01. the theoretical 8pectra incident; but experi-


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                                                                                           Digitized by   Google
mentalists will be inclined to normalize shielded             4. Fisher and Engle, Delayed Gammas from Fast Neutron
detector responses to the detector response outside              Fission of Th232, U233. U235, and Pu239, Pbys. Rev.
the shield. We thus expect to encounter problems of              ~ B796, 1964.

determination 01. the detector response outside the            5. Ritchie. R.H. and G.S. Hurst, Penetration of Weapons
shield in terms 01. the detector response that would              Radiation; Application to the H1roshima-Napsaki
occur due to the free-field spectra obtained without              Studies, Health PhySiCS 1.0 390. 1959.
reference to any interface.                                    6. H. Goldstein, "Sources of Neutrons and Gamma Rays,"
   The best validation may be that provided by                    Reactor Handbook, V. m, Chapter 8, E.P. Blizard,
simple penetration and duct studies with available                Editor, Inter science Publishers, 1962 Edition.
neutron and gamma sources. When calculations are               7. French, R.L. and C.W. Garrett, Gamma-Ray Energy
in detailed agreement with such elementary experi-                and Angular Distributions near the Air-Ground inter-
ments, it will be possible to perform more elaborate              face from Plane Fallout and Point Co60 Sources,
and relevant calculations with confidence, for use in             RRA-M42, June 1. 1964 (Radiation Research Associ-
practical analyses.                                               ates, Fort Worth, Texas).
                                                               8. M.J. Berger, Calculation of Energy Dissipation by
                                                                  Gamma Radiation near the Interface between Two
The Possibility of Shortcut Methods                               Media, J. Appl. Physics 28, 1502. 1957; also R.L.
                                                                  French, A First-Last Collision Model of the Air-
The approach to initial radiation shielding discussed             Ground Interface Effects of Fission Neutron Distri-
in this paper appears to be feasible. The complica-               butions, RRA-M32, November 1, 1963 (Radiation
tions arise naturally from the multiplicity 01. radia-            Research Associates, Ft. Worth, Texas).
tion and configuration types, together with the                9. See, for example. M.B. Wells, A Monte-Carlo Calcu-
boundary conditions imposed by the problems of                    lation of Gamma Ray and Fast Neutron Scattering in
restricted data.                                                  Air. Shielding Symposium Proceedings, RilL No. 110,
   Simpler calculations are always possible. Per-                 308, 1960; and D. Spielberg, Neutron Fluxes from a
haps the most reasonable shortcut calculation that                Point Fission Source in Air; Moments Method Calcula-
has been suggested to me would assume that the                    tion, ibid., p. 116.
concrete shield is air-equivalent and an extension            10. Biggers, W.A., L.J. Brown, and K.C. Kohr, Space,
of the atmospheric penetration. This is more                      Energy, and Time Distribution of Neutronsartii8
reasonable for neutrons than for gamma rays, I                    Ground-Air Interface, LA 2390, January 29, 1960
think, because they are less affected by the shield               (Office of Tech. Services, U.S. Department of
interface. Also, it is not clear that this concept                Commerce).
can be appUed to entrances and ducts through the              11. International Commission on Radiological Units and
shield. But it may be useful, nevertheless, for the               Measurements (ICRU). Radiation Quantities and Units,
purpose of obtaining rough estimates.                             NBS Handbook 84, Report lOa, November 14,1962.
                                                              12. Spencer, L.Y. and J.C. Lamkin, Slant Penetration of
                                                                  Rays: Mixed Radiation Sources, NBS Report 6322,
                                                                  February 27, 1959.
References                                                    13. Marcum, J.I., Neutron Fluxes from a Vertically
                                                                  Collimated Source of 14 Mev Neutrons at an Air-
 1. The Effects of Nuclear Weapons, S. Glasstone, ed.,            Ground Interface, RM-4120-AEC, August 1964,
    U.S. Government Printing Office (1962 edition).               Rand Corporation.
 2. Zobel, W., T.A. Love, G.M. Estabrook, R.W. Peelle,        14. Wells, M.B., Studies in Shielding - m, Monte Carlo
    Characteristics of Fission-Product Gamma Rays                 Calculations of Neutron Scattering in Air, Convair-
    Emitted from 1 to 1800 Sec. after Thermal Fission             Ft. Worth Report FZK-0-120A, NARF-59-49T,
    of U235, ORNL 2609, pp. 50, 51, February 15,1958.             December 1957.
 3. Walton, SUnd, Haddad, and Young, Delayed Gamma            15. Mebl, C.R., A Monte Carlo Calculation of the Neutron
    Rays from Photo-Fission of U238, U235, and Th232,             Flux from a Monoenergetic Point Source in Air,
    Pbys. Rev. 134, B824, 1964.                                   SC-4174(TR), Sandia Corporation, AprU 1958.




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                                    SHIELDING EXPERIMENTS

                                              A. B. Chilton
                                           University of III inois


Introduction                                                  Ceiling- shine

Many experiments have been carried out over the               No OCD engineering publications make explicit men-
past few years for testing the adequacy of. fallout           tion of ceiling-shine, or the radiation reflected off a
shelter design procedures from the radiation point            ceiling to the floor or floors below. Nevertheless, it
d. view and the validity d. the functional data upon          is impliCitly included in a somewhat empirical fash-
which such procedures are based. In addition, a               ion as described by Eisenhauer in the skyshirie func-
number of experiments have been conducted to                  tion, Ga , d. the Engineering Manual.(3) It appears
provide guidance in the development of procedures             that this approach is generally adequate under usual
for handling the problem of protection against initial        conditions, but there are exceptional circumstances
radiation. Fallout is stressed here in preference to          under which it appears desirable to determine
initial radiation, since others are reviewing recent          ceiling-shine separate from skY.shine. LeDoux has
progress in that area.                                        discussed this matter in detail.(4)
    R is assumed that each of you is familiar with                Though LeDoux proposes a new approach, some
what is popularly mown as the Engineering Manual(1}           experimental data on ceiling- reflection contributions
in one of its several editions, as well as Spencer's          are necessary if it is to be useful. This has been
Monograph, NBS 42,<2) Very little will be said here           provided through steel-model experiments made by
concerning experiments already reported in techni-            Velletri and Batter, in which fallout radiation is
cal literature. For those who feel insufficiently             simulated by a radioactive source pumped through a
conversant with this body of literature, reference            plastic tube coiled about the area adjacent to the
is made to articles published from time to time               model structure'(5) For complete details of their
in the following journals: Nuclear Science and                experiments and suggested engineering methods,
Engineering; Health Physics; Transactions of the              one must refer to the original report; however, for
American Nuclear SoCiety; Journal of Research of              the situation indicated in Figure 1, their approach
the U.S. National Bureau of Standards; and Canadian           reduces to a simple formula.
Journal of Physics.
    I will concentrate on very recent experiments
that have not yet been reported in the professional
literature, and that concern the analysis and de-
sign d. shelters providing protection against fallout.
    So that my statements will not be interpreted as
unduly harsh with respect to present standardized
techniques, let me point out that most experiments
are carried out to check those aspects of. the subject
believed to be in greatest need of critical examina-
tion. Considering the overview, it is remarkable
that a technology based largely upon theoretical
reasoning with highly idealized models has stood
the test of experimental verification as well as it
has.
    Appreciation is extended to A. L. Kaplan of                                                                             •   I   •   II
                                                              J   I   X I   I
Technical Operations, Inc., and to J. Velletri of
Conesco, for sending advance copies of their un-                                D5c ·1.I7· Gc(wc)' F(H)' R(X c) 'G~ (W s)
published results and extending permission to quote           Figure 1. Cening-sh1ne contrlbuUon (the sidewalls are
from them.                                                    opaque).




                                                         95

                                                                                                     Digitized by   Google
   In this formula:                                             tions of the Engineering Manual of protection factors
                                                                for basements with no exposed walls may be sub-
   (a) Dsc is the ceiling-shine contribution, nor-              stantially in error; unfortunately, this is usually in
malized to a reference exposure of one unit at a                the non-conservative direction. Eisehnauer(3) has
point three feet above an infinite, smooth, contami-            briefly reviewed this situation and found that ex-
nated plane;                                                    posure rates calculated within the basements may
   (b) Gc and GC' are functions of geometric charac-            be too low by a factor of 2, both for simple and
ter dependent upon ue and "'5, respectively;                    complex structures. He cites several experiments
   (c) F(H) is a correction factor if H is other than           conducted by Technical Operations, Inc., as in
10 ft;                                                          support of his statement.(6,7,8) The source, for
   (d) R(X c ) is a correction factor for finite ceiling        each of these experiments, is the equivalent of a
thiclmess. For a thickness of 20 psf, it is about 0.9;          distributed source on the ground surrounding the
for 40 psf or more, it is essentially 1.0.                      structure, and does not include roof contamination.
   The functions Gc ' GC" R, and F are given in                 It might be noted in passing that, if roof contribution
Figures 2, 3, 4, and 5, respectively.                           is a substantial proportion of the basement exposure,
                                                                as in the case of an average one-story building, the
   It should be remembered that whenever ceiling-
shine is considered separately in an engineering
problem in a manner such as the LeDoux-Velletri-
                                                                      ~O~---r----'r----.-----r----I
Batter approach, the skyshine function Ga in the
Engineering Manual should be correct to remove
the component inserted to account approximately
for ceiling-shine.


Protection Factors for Basements

This largely involves a problem of radiation penetra-
tion into the above- ground portion of a structure and
its subsequent scatter down into the basement,
attended by the shielding effects of outer walls and
floors above the basement. It is, therefore, often
referred to as the "in-and-down" problem. Regard-
ing the possibility of direct radiation penetration of
the ground surrounding the basement, it is also
closely related to the foxhole problem. For a num-
ber of years it has been recognized that the predic-            I' _I
                                                                -10
                                                                _u
                                                                (l)




                        o IRON
                        aCONCRETE




                                                                       -2
                                                                      10 L-_ _.&...-_ _L..._ _L -_ _L - _.......
    -3 "'=""_........._
                                                                          o  0.2       0.4    0.6   0.8       1.0
   10 10-2             /'             10'"
                                                                                    SOLID ANGLE FRACTION "',
                        CEILING SOLID ANGLE FRACTION lOe
Figure 2. The function Gc '                                     Figure 3. The function Gc "


                                                           96

                                                                                            Digitized by   Google
discrepancy between theory and experiment is greatly              small building with a basement brings out this
reduced, since penetration from a roof source has                 point.(6) The structure in question is shown in
been generally found to be satisfactorily predicted               Figure 6, and the results ci both measurements and
by standard engineering methods'(9)                               engineering calculations are shown in Table 1.
   Experiments made at the Kansas State University                   It can be seen that the observed variation with
Summer Institute on Radiation Shielding during 1962               height of the detector above the basement floor is
and 1963, with a distributed source on the ground                 much less pronounced than the theoretical increase.
around a blockhouse with basement, showed a simi-                 The experimental results indicate that the part ci
lar discrepancy between predicted and experimental                the dose contribution which differs most from the
exposure readings: experimental values were high                  over-all theoretical trend is from sources on the
by a factor ci about 2 at the middle ci the basement,             ground very near the building. For these sources,
three feet above the floor.                                       the detector readings at the center position in the
   Because measurements on the first floor ci a                   basement actually decrease as height above the
structure are generally believed to be much more                  basement floor increases. This behavior is con-
closely predicted by the Engineering Manual than                  sistent with the concept that only skyshine contri-
are those in the basement, suspicion has been                     bution that arises from more distant sources has
centered on the standard method for handling                      a directional distribution consistent with theory.
attenuation effect ci the first-floor (basement                   Nearby sources contribute heavily to side-wall
ceiling) slab. The Engineering Manual uses the S'                 scatter and to ceiling- shine near the edges ci the
function of Spencer's Monograph<2) as this barrier                ceiling, and thus provide a very strong grazing
factor; this use involves the key assumption that the             component to the radiation incident upon the first
radiation incident upon the first floor has the energy            floor.
spectrum and directional distribution ci skyshine.
The essence of the difficulty is as follows. Radiation
incident upon the first floor is derived from three
secondary sources:                                                                        TABLE 1
   1. skyshine penetrating the vertical side walls;
   2. radiation reflected from the first floor ceiling;                      Variation of Detector Readings with
                                                                               Height above Basement Floor
      and
   3. radiation from the ground outside, which is                                                    PoiDts in Basement
      scattered in a direction toward the first-floor
      slab by the side walls.                                     Height above basement
                                                                                                      1    3.5     6           8.5
                                                                   floor (ft)
The skyshine functions are reasonable for the first               Computed dose rates, mr/hr      0.70     0.94    1.34        2.30
and possibly the second ci these sources, but is a                Observed dose rates, mr/hr      1.48     1.73    1.75        1.87
dubious one for the third.                                        Ratio obs/calc                  2.12     1.84    1.30        0.81
   An interesting and possibly significant aspect of
this is the variation ci the detector reading in the
basement as a function of the height ci the detector                1.4 ,......~....,.."T"IrTTnr-"T"""T"1~rml-y-yTmm
above the basement floor, or, rather, the depth ci
the detector below the basement ceiling. The experi-
mental measurements of Batter and Starbird on a                     1.2                    _ _ TOT'ALDOIIE FALLOUT
                                                                                                   RADIATION (SPENCER REF 4)
                                                                                           -       DIRECT DOSE COIA1J'-SO
                                                                    1.0



                                                                   0.'

                                                                   O.S
                   • DATA FROIII ua' MDIII       .. 00J08
                   • DATA FROIII 'S ItADUI       .. 00.101
                   • DATA FROIII 111.0' IUOIU8   ...0.108
                   a DATA FROIII t2S RADIUS      ... 0.101
                   • DATA FROM5.211' IUOIU8      .. =0.101
                   + DATA FROIII ,iI RADIUS      ... 0.108




                                                                     oLI---JLJL~~~~---~~~~~~~~~~~~
                                                                                        CEILING HEIGHT, H(ft)
                                                                  Figure 5. The function F(H).


                                                             97

                                                                                                 Digitized by   Google
    This same effect is shown in model experiments                         the side walls than with a picture of a source well
by Batter, Starbird, and York, previously referred                         distributed overhead.
to in reference 8. As is shown in Figure 7, their                             Very recently, A. L. Kaplan and co-workers have
work was done with steel models of a multistory,                           done further steel- model work, using simple cylin-
non-windowed structure.                                                    drical shapes in order to provide a schematization
   Results of measurements in the middle of the                            as close as possible to that assumed in the theory
basement are shown in Figure 8.                                            behind the Engineering Manual.(10) The results of
   One can see the cUfference in theoretical trends                        these basement studies can be summarized by
and experimental observations. The experimental                            Figures 9-12.
values are generally higher than theory predicts;                             These figures show approximate agreement be-
but, for detector positions very near the ceiling, ex-                     tween Engineering Manual methods, suitably modi-
perimental values may be lower than theoretical                            fied, and experimental values. Modifications of the
ones. Experimental data are more consistent with                           calculational method are minor in effect for the
a picture which has the source coming strongly from                        zero first-floor thickness case, which indicate. that
                                                                           the present Engineering Manual might be reasonable
                                                                           for thin first floors. However, modifications make a
                                                                           substantial cUfference when the floor is about 20 par
                                                                           (1/2 inch of iron). An explanation of the noted
                                                                           moc:Ufications is as follows:
                                                                              (a) As previously discussed, the so- called
                                                                           "LeDoux modification" is a separation of the sky-
                                                                           shine and ceiling-shine effects into two parts.
                                                                              (b) The so-called "Tech/Ops modification"
                                                                           involves handling the air- scatter contribution as



                                                                                    f---
                                                                                    raw...       Ie)
                                                                                                          METHOD ENG. MANUAL
                                                                                                          METHOD A+E GUIDE
                                                                                    ~            •        MODEL BUlLDlNG2OP9F w.u..s,20PSF FLOORS
                                                                                    -            +        MODELIUILDING IOP8F WALLS,IOPSF FLOORS
                                                                                                 a        MODEL IIUI.DING 0F8F WALLS,2Ol'SF FLOORS
                                                                                    -            •        MODEL IUl.OING 2OPS!' WALLS,80" FLOORS
                                     C:IIOII Hc:TION '.                                           I                         I
Figure 6. stucture for Batter-Starbird experiment.
                                                                                        "         ,,!                       1
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                                                                                                              ........      a                       ~
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                                                                                                                         "l                     T
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                                                                                                                                                                                                             20 PSI'
                                                                                                                                      ........                                                           WALLS
                                                                                                                                                 I'........                                                  eoPSI'
                                                                                                                                                                                                             F1J)()R

                                                                                                                                                                       ~~                                    eoPSI'
                                                                                                                                                                                                             WALL
                                                                                                                                                                                                             eoPSI'
                                    _11.'OIIC1D _CUTI _ _ _                  10"4                                                                                                                            FLOOR
                                      "Lua. . .'" .... a • •aCII                    o             3                         e                   9                     12                   III          18             21
                                                                                                                  DEP1lI, MEASURED FROII BASEMENT CEILING, FT.
Figure 7. Typical steel model structure of multistorled                    Figure 8. Variation of deteotor reading with depth below
building used by Tech. Ops., Inc., experimenters.                          basement oeWng for multistory model.


                                                                      98

                                                                                                                                                     Digitized by                      Google
undergoing wall scatter rather than being absorbed                                         Whether these recommended modifications will
without scatter. This particular modification may,                                      solve the problem rl. theory-experiment discrepan-
to some extent, be an artificiality of the modeling                                     cies with detector depth below the first floor re-
technique since the air-scattering portion does not                                     mains to be determined. Further experiments are
model in the same way as other contributions be-                                        required with other first-floor thicknesses.
cause it is impossible to scale air density. At any                                        Finally, one must be careful in applying relation-
rate, the effect is minor.                                                              ships established on a model basis to full-scale
   (c) The major modification introduced by Tech/                                       structures, so as not to introduce the artificialities
Ops is the replacement d. the first-floor barrier                                       inherent in the modeling experiments into the
factor by a function other than that employed by the                                    engineering prediction system.
Engineering Manual. It appears on the basis of
preliminary results, that the function cosfbS(X,cos~
found in Spencer's Monograph. (2) has the proper                                        Interior Partitions
directional distribution to allow good predictions.
'0. the average angle of incidence d. the radiation
incident on the first floor with respect to the angle
                                                                                        The presence rl. interior partitions complicates the
                                                                                        problem rl. predicting radiation penetration, partly
normal to the floor, is estimated as being roughly                                      because of possible complexity of the barrier con-
60°                                                                                     figuration. The Engineering Manual approach divides
                                                                                        the structure into sections or zones, which can be
   Since the Engineering Manual does not give
                                                                                        considered separately as simple cases of multiple
functions equivalent to Spencer's cos8oS(X,cos'O>,                                      barriers, each with its own barrier factor. The
Kaplan et al. recommend the use of the wall-barrier
                                                                                        standard approach is to use the barrier factor for
factor, Bw, rather than the present floor-barrier
                                                                                        a first-floor exterior partition for interior partitions,
factor. Bo' • until such a time as a better function is
                                                                                        and to use normal slab thicknesses for the argument
included.
                                                                                        of such function, regardless of the directional orien-
                                                                                        tation of the interior partition within the sector.
        12                                                                                  Much experimental work has been carried out on
              ~
                                                                                        structures containing interior partitions, but rela-
              ~
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                                              IY UDOUX
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                                                                             ::
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                                                                                                    ~           I ,                     o   EXPERIMENTAL
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 8
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              o                       ~                         ~            1.5                    o                            QI                             1.0                                LI
                                  STRUCTURE WALL THICKNESI !INCHES)'                                                         ITRUCTURE WALL THICKNUS (INCHES)
Figure 9. In-and-down aoatterlng results for steel                                      Figure 10. m-aod-down aoatterlng results for steel
cyl1Ddr1cal model structure.                                                            oyl1Ddrloal model structure.



                                                                                   99
                                                                                                                                               Digitized by           Google
tively little of. it has been done to check existing                                                                                  property but takes no account of scattering prop-
design procedures. One of. the few outstanding works                                                                                  erty .(12) In this respect, they are handled differ-
in this regard is that d. Starbird et al., (ll) which                                                                                 ently from exterior walls. He points out the curious
was concerned with experiments on model multi-                                                                                        result which can occur when the outer wallis very
storied structures without windows, as shown in                                                                                       thin or has extensive apertures.
Figure 13.                                                                                                                               To study this effect, Kaplan et al., (lO) have ex-
   A fallout field was simulated by the pumped                                                                                        perimented with Simple model strUCtures, consist-
source technique previously mentioned. Note from                                                                                      ing of concentric iron cyUnders, with and without
the figure that three different situations were                                                                                       apertures. Results without apertures are as indi-
studied.                                                                                                                              cated in Table 2; with aperture results are shown in
   Results and comparisons with engineering pre-                                                                                      Table 3.
dictions are shown in Figures 14, 15, and 16,                                                                                            Results for structures without apertures are
respectively.                                                                                                                         fairly consistent with predictions, being within the
    One can see that there is generally good agree-                                                                                   same 15 to 20 per cent discrepancy previously en-
ment between theory and experiment for all cases.                                                                                     countered by Starbird and his co-workers. On the
The fact that experimental results vary by as much                                                                                    other hand, for the aperture case, serious discrep-
as 15 per cent from calculations is probably not                                                                                      ancies are found, especially for detector locations
significant clue to certain artificialities inherent in                                                                               which are opposite the apertures. In such cases,
usual modeling techniques.                                                                                                            the discrepancy may be in the order of magnitude
    LeDoux has pointed out that the present approach                                                                                  of a factor of 2, with experimental values higher
to interior partitions emphasizes their attenuating                                                                                   than theoretically predicted values.




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Figure 11. In-and-down scattering results for steel                                                                                   Figure 12. In-and-down scattering results for steel
cylindrical model structure.                                                                                                          cylindrical model structure.


                                                                                                                                100

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Other Recent Findings

Rese$ilrrh '04?orkers                 Protectlr$il hlructurer
    el(>hrr£>TI1t Center               recenith rh'04?h1ed the
                                                                                                                            'L_ _II
tration of radiation through concrete barriers, with
                                                                                                                        I         •            4            •         •
the source being the equivalent of a circularly dis-                                                    .4~-r------~----'~----r------~----'~
tributed source on the face of the barrier .(13) Good
agreeili£>$ilt with                     curve$il       L(X) .
was U'04?'04?4l44'04?r
    Kaplan and his co-workers have found that,
although there are some theoretical reasons for
believing the building shape factor approach could
                                                                                                   !
be                                   $ilecogn1zi$ilit the exist$il$il$il$il
                                                                                                    i
                  rffect fO$il hl$il£>ct as W$ilU       for wall~




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Figure                                                                                       Fiurrr a. Com£>rri444rr of oalor444TIt'04?£> and 8xtlAr44444444r1bffiill
                                                                                             exposure rates, box geometry.


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                        b. Deteator PG.ltlOD A                   o. Detector PoeltlODa F, D, B
               Figure 15. Comparison of calculated and experimental exposure rates, cornc1Or geometry.




scattered radiation-in actuality predictions based                   estimating the mass thiclmess of a foot of concrete results
upon the Engineering Manual approach without                         in an error of at least a factor of 2 in radiation contribu-
further complication are still adequate for                          tion. Concrete densities can vary cOnsiderably.
                                                                          A blockbouse was constructed••.for shielding studies.
engineering purposes,(10)
                                                                     Plans called for concrete blocks filled with poured con-
                                                                     crete. The contractor actually used cinder blocks ...
                                                                          A fallout shelter under a house was studied ... Estimates
Conclusion                                                           by owner and contractor varied from 18 to 30 inches. After
                                                                     several days, the original plans were found, and showed a
The experiments discussed in this paper were de-                     thiclmess of 24 inches.
signed to detect possible errors in calculational                         ... A building was studied... Visual lnBpection of a wall
methods currently in use. However, there is another                  indicated it was oonstructed of light material. However, a
possible source of error that should be emphasized.                  detailed lnBpection, experimental data, and an examination
                                                                     of the architectural plans showed that the lower portion
This has been brought out by Zolin Burson in one of                  was composed of about 12 inches of concrete. Because of
his reports:(14)                                                     this error the local fallout-survey team had estimated the
    ... The sensitiveness of protection-factor calculations          protection factor to be lower by a factor of 8 to 10 than
to exact mass thiclmesses Is evident. A 20% error in                 that based on experimental data.


                                                              102


                                                                                                                     Digitized by   Google
                                                TABLE 2

                       Exposure Rates in struotures with Interior PartttiODB -
                              Comparison of Theory and Experiment

                                                  Cyl1ndr1oal Steel Structure
Deteotor Height
   (inches)                 3            6                9            15          18              21

Xe = O. "t = 1/2
Dexp                      436.8        429.5                         396.0       404.7        381.5
DcaldDexp                   1.01         1.04                          1.03        0.97         0.98

Xe = 1/2. Xi = 1/2

Dexp                      278.9        291.9            804.9       288.4        277.8        288.8
D    /D                      .84          .84              .88         .88          .82          .88
 calo exp
Xe = 1. Xi = 0
.                         240.9        256.7            270.9       257.2        258.8        240.8
Dexp
D    /D                     1.10         1.08             1.02        1.02          .97          .97
 calc exp
Xe = 1. Xi = 1/2

Dexp                      188.5        208.2            208.5       199.1        184.0        178.8
D    /D                      .87          .84              .82         .88          .87          .86
 calc exp
Xe = 1-1/2. Xi = 1/2

Dexp                      122.8        138.0            138.4       182.1        127.2        119.8
D    /D                      .89          .82              .82         .83          .84          .87
 calc exp

                                                    Square Steel Structure
Detector Height
   (inches)                 3            6                9            15          18              21

Xe" 1/2. Xi" 1/2
Dexp                      228.2        267.6            288.8       261.2        263.6        238.6
Dcalc/Dexp                  1.00          .93              .89         .88          .87          .89

Xe = 1/2. Xi .. 1
Dellp                     143.7        186.8            170.9       183.1        169.0        148.7
D     /D                    1.02          .93              .89         .91          .91             .98
 calo ellp
Xe = 1. Xi .. 1/2
Dellp                     146.0        189.8            177.0       189.7        186.3        163.4
Dcal/Dexp                   1.08          .97              .92         .93          .92          .96

Xe = 1. "t-1
Dellp                      94.6        107.6            118.3       107.9        103.8         98.6
D     /D
 calo ellp
                            1.07          .99              .94         .96          .98         1.06

Xe = 1-1/2. Xi - 1/2
Dellp                      93.0        109.1            118.1       112.6        108.4        101.0
D     /D                    1.11          .99              .94         .92          .96          .98
 calc exp




                                                  103

                                                                                    Digitized by   Google
                                                 TABLE 3

                         Exposure Rates in Structures with Outer Wall Apertures -
                                Comparison of Theory aDd Experiment

                                                      CyllDdr1cal Steel Structure
Detector Height
  (iDeheS)                    3            6                 9             15          18            21

Xe   = 1-1/2, XI = 1/2
0-6
Dexp                        433.2        322.4             198.9         152.7       141.4         127.8
Dcal/Dexp                      .52             .78               .71        .80         .81           .86
6 -12
Dexp                        140.1        242.4             402.5         200.6       153.8         137.4
D    /D                        .73          .40               .53           .68         .79           .84
 calc exp
12 - 18
Dellp                       140.9        151.4             148.3         338.1       307.4         177.1
D     /D                       .78          .74               .73           .60         .73           .73
 calc exp
18 - 24
Dexp                        134.7        146.7             136.6         138.0       203.4         312.4
D    /D                        .83          .79                  .84        .77         .46           .61
 calc ellp

                                                           Square Steel Structure
Detector Height
  (1nches)                     3            6                9             15          18            21

Xe   = 1, X. = 1/2
0-6
Dexp                        422.1        355.4             265.5         217.8       203.8         191.1
D    /D                        .55          .76               .72           .81         .82           .83
 calc exp
6 -12
Dexp                        200.6        295.6             385.7         245.8       212.9         189.9
Dcalc/Dexp                     .76          .48               .60           .74         .80           .86

12 -18
Dellp                       213.6        220.1             218.5         374.2       325.4         227.8
D     /D                       .77          .77               .75           .59         .74           .74
 calc exp
18 - 24
Dexp                        205.2        209.9             214.6         206.5       239.0         344.9
D    /D                        .82          .83               .81           .77         .56           .60
 calc exp




                                                     104

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                                                                               .03 . -                            II", I'UIOIt - ;
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                                                                                            ~~:
                            DIUotor Po.IUCID B                          f
                                                                        ;:
                                                                        i
                                                                        i
                                   fUIOItllUllKW
                                                                        5       .1
                                                                                      -
                .4                      •                               u ."
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                      ~                                                          .~
                            -IDINIIIMI1mIL
                            -  ..., _ _ IIIMIUI&.                              ."



                      b. DIUotor Po.ltlOil A                                    o. Detector Po.ltlou G, F, E, D.
                                                                                          C,B
           Figure 16. Comparison of calculated and experimental exposure rates, compartment geometry.




   Tbese statements undoubtedly come as no sur-                    3. EiseDhauer, C., IIAn Engineering Method for calculat-
prise to those who are knowledgeable In engineering                   ing Protection Afforded by Structures against Fallout
construction practices. Those who are radiation-                      Radiatlon. 1I NBS MoDO graph 76 (July 1964); orig1nal1y
shielding specialists might consider such matters                     written as NBS Rept. 7810 (Feb. 1963).
when they are concerned with the preciseness of                    4. LeDoux. J.C., tlCelling-shine Contribution within
our computational models and techniques.                              BuIldings from Fallout Radiation Shield, II NCEL
                                                                      Tech. Study No. 30 in At. Def. Eng. (Feb. 1963).
                                                                   5. Velletri, J.D. and J.F. Batter, IThe Effect of Radia-
                                                                      tion Reflected from the CeUing on the Dose Rate
References
                                                                      within Structures, II Tech. Ops., Inc., Rept. TO-B
                                                                      63-25 (AprU 1963).
 1. IlDeSign and Review of Structures for Protection from
    Fallout Gamma Radiation. II Draft OCD Publication              6. Batter, J.F. and A. W. Starbird, tlAttenuation of
    (Oct. 1961); IIShelter Design and AIIalysls, Volume 1,            Cobalt-60 Radiation by a Simple Structure with a
    Fallout Protection. II OCD Publication TR-20-(Vol. 1)             Basement, tI Tech. Ops., Inc., Rept. TO-B 61-38
    (Sept. 1962-May 1964); l'Design and Review of Struc-              (July 1961).
    ture. for Protection from Fallout Gamma Radiation. II
                                                                   7. Batter, J.F., A. Kaplan, and E.T. Clarke, IIAn Ex-
    Draft OCD Publication PM 100-1 (Dec. 1963).
                                                                      perimental Evaluation of the Radiation Protection
 2. Spencer, L.V., IIStructure Shielc:Ung against Fallout             Afforded by a Large Modern Concrete Office Build-
    Rad1at1on from Nuclear Weapons, II NBS Monograph                  ing,lI Tech. Ops., Inc., Rept. TO-B 59-5 (May 1959);
    42 (June 1962).                                                   also publlshe,d as AEC Rapt. CEX-59. 1 (Jan. 1960).


                                                             105

                                                                                                           Digitized by        Google
 8. Batter, J.F., A.W. SI:arb1rd, ad N.-B. York, ''The              11. SI:arb1rd, A.W., J.D. Velletr1, ILL. MacNeil, and
    Effect of IJm1ted Strip. of CoDtamfnatf.on on tile DoH              J.F. Batter, ''The Effect of Interior Part1t1oIUI on tile
    Rate in a Kult1ltory, WiDdowle •• Bu1lc:I1na," Teoh.                Do.e Rate in a Multlltory Windowle•• BlIUding."
    Op•• , Ino., Kept. 62-68 (Aug. 1862).                               Teoh. Op•• , Inc., Kept. TO-B 68-6 (Jan. 1863).
 9. Borella, H., Z. BurIlOll, ad J. Jaoovitoh, ''Evaluation         12. LeDoux, J.C., ''Interior Wall Scatter CoDtr1batton,"
    of tile Fallout Protection Afforded by Brookhaven                   UDPUblisbad manueorJpt (Dec. 1863).
    Na.t1oD&l Laboratory Medical Kesearch Center,"
                                                                    13. Ve11etri, J., perlOD&l oommunioatton (March 1966).
    AEC Kept. CEX-60.1 (Oct. 1861).
                                                                    14. BurIOn, Z.O., ''Experimental EvaluatIon of tile
10. Kaplan, A.L., J. Waldman, J.L. Jones, W.E. Barch,
                                                                        Fallout-Radtatlon Pl'Oteot1on Provfded by Seleoted
    and ILL. MacNefl, "Struoture Sh1elc:UDg from Fallout
                                                                        Struotures in tile Los ADgeles Area, " AEC Kept.
    Gamma Radtatlon, F1Dal Report - Phase L" to be
                                                                        CEX-61.4 (Feb. 1863).
    published as Teoh. Ops., Inc., Kept. No. TO-B 66-26.




                                                              106
                                                                                                Digitized by   Google
                             THE PASSING PARADE OF SHIELDING-
                              ANAL VSIS METHODS: A REVIEW OF
                                   THE STATE OF THE ART

                                          Kenneth G. Fa"ell
                             Emergency Measures Organization, Ottawa, Canada


Introduction                                                    meteorological conditions, spatial distributions of
                                                                the fallout material are assumed to be uniform aDd
Bow many engineers, wbo have successfully com-                  roofs of buildings are assumed to receive fallout
pleted a course on fallout-shielding analysis aDd               uniformly according to their borizontal projections.
returned to their places of labor exhilarated by the            It is also assumed that the fallout remains wbere it
chase and overcome with the sweet smell of victory,             lands aDd that it does not stick to trees aDd shrubs.
endeavor to do battle with practical analysis prob-             Tbls convenlently avoids the problem of considering
lems only to discover a certain inner frustration,              irregularities of busb shapes.
whicb, though DOt readily identifiable, usually stems               Tbe energy spectrum of fallout gamma radiation
from insufficient background knowledge of the sub-              changes with the passage of time during which the
ject? Tbls background is DOt easily acquired eltber,            many products of the fission process are continually
particularly by the practicing engineer, wbose time             changing. As a result, a tremendous range of ener-
is always at a premium. Unfortunately, there is no              gies is presented from whicb a single spectrum
sbort-cut to its acquisition, aDd only by constant              must be selected.
readiDg of current literature coupled with diligence                Tbe particular cboice of the energy spectrum,
in analyzing structures aDd comparing results can              that of fiSSion products 1.12 bours after detonation,
a person bope to achieve a feel for the subject aDd            was made because it is relevant at the time fallout
gain sufficient confidence to know that be is correct,          radiation has great intensity aDd more closely
at least within the limits of precision of the method           resembles the penetrability of the gamma radiation
being used.                                                    in the first few bours. Some calculations were
    Since 1956, a considerable number of methods               formerly performed using the average energy of the
has been developed by which the fallout gamma-                 spectrum, whicb is close to that of cesium-137, but
radiation PF of structures may be determined. Tbe              the results produced were underestimated some-
following paragraphs review some of these methods.             what because the penetrability of fission-product
This paper is des1gnecl principally for practicing             radiation is greater than that of cesium-137.
engineers involved in protective construction aDd is               An item worthy of mention bere concerns barrier
intended to be neither a deta1led scrutiny of eacb             aDd geometry separation. It is convenient to con-
method DOr a judgment of their relative merits, but            sider these two separately wbere the barrier factor
rather a discussion of their more salient character-           is considered to be a function only of the mass thick-
istics, whicb, it is boped, will belp reduce the back-         ness of the barrier. Tbe geometry factor is a ratio
ground vacuum, if only a liWe, aDd perhaps provide             expressing all the other features of the actual con-
some motivation to dig below the crust.                        figuration of the structure.
                                                                   Tbe fundamental data on which most of the cur-
                                                               rent methods of shielding analysis are based were
Basic Assumptions                                              determined by the moments method developed by
                                                               Spencer aDd Fano aDd the Monte Carlo tecbniques
Certain basic assumptions are fundamental to all               of Martin Berger.
the methods discussed bere, aDd these concern the                  The moments method allows solution to trans-
fallout, its energy spectra aDd distribution, aDd              port equations, whicb describe the transport, dif-
bu11c:U.ng configuration.                                      fusion, aDd energy loss of gamma radiation, for
    Because of the many uncertainties involved in              sources in infinlte mecl1a, by the approximation of
the physics of fallout, aDd the impossibility of being         functions from numerical values obtained from
able to preclict with any certainty the wind aDd other         integrals. Tbese integrals are referred to as


                                                         107
                                                                                          Digitized by   Google
"moments." The functions presented in Spencer's                     In 1956, Dr. L. V . Spencer headed a group at the
monograph are all developed using moment methods,                National Bureau of Standards in a study of the pene-
except for those involving boundary effects such as              tration of plane isotropic sources in infinite media.
barriers, which were developed using Monte Carlo                 By that time, electronic computers had developed
techniques.                                                      to a state that permitted analytical work that was
   A Monte Carlo radiation calculation is essentially            manually impossible because of the tremendous
an experiment with pencil and paper or computer,                 amount of calculation necessary. These studies
by which the actual physical process of the path of              led to the development of the moments methods
a particle through a barrier is simulated by the use             for determining the penetration of radiation into
of random numbers. H gamma rays left tracks,                     thick shields, and ultimately, to the publication of
they would look something like those sketched in                 Spencer's monograph, written principally for the
Figure 1, which shows the expected paths of parti-               phYSicist or nuclear engineer. This work consti-
cles scattering through a barrier.                               tutes the scientific basis for the majority of sub-
                                                                 sequent methods of shielding analysis.
                                       NO INTERACTION
                                                                    British points scheme. The document, Assess-
                                                                 ment of the Protection Afforded by Buildings against
                                       SCATTERED                 Gamma Radiation from Fall-out, was published by
  GAMMA                                                          the British Home Office, Scottish Home Department,
  RAYS                                                           in 1957, followed by a revision in 1963. The points
                                        ABSORBED
  ENTERING
                                                                 concept was introduced as a convenient idea on
                                                                 which to base the calculation of fallout protection.
  BARRIER                                                        In all methods of analysis, the reduction factor of a
                                        8ACKSCATTERED            structure is compared with a normalized radiation
                                                                 contribution received by a detector in an unprotected
                                                                 location in an infinite field of contamination. It was
                                                                 this standard unprotected location that was assumed
                                                                 to receive an arbitrary number of points, and, by
                                                                 considerations of attenuation by mass and distance,
Figure 1. Particles in a barrier.
                                                                 the corresponding number of points received inside
                                                                 the structure was calculated. The ratio of the num-
                                                                 ber of points received in the standard unprotected
                                                                 location to that received inside the structure was
    When a particle enters the barrier, it has a free            then the protection factor. Although the result is
flight until there is an interaction. H this is a scat-          the same, the 1963 edition refers solely to per-
tering interaction the particle will lose some energy            centages rather than numbers of points.
and change its direction.
    In the Monte Carlo technique, the new energy                     (a) Assumptions. Almost all shielding-analysis
and direction are determined by a random process                 methods assume that the buildings are rectangular,
applying the laws of probability. Therefore, by gen-             and this method is no exception. Structures having
erating case histories for a large number of gamma               peculiar shapes must be simplified and approxi-
photons, the path of gamma radiation for specific                mated as realistically as possible to an appropriate
Situations can be determined by statistical means.               rectangular shape. The distribution of fallout is
                                                                 taken to be uniform; variations in this distribution
                                                                 on and around the building are not considered. It is
Review of Methods of Analysis                                    further assumed that fallout neither enters the
                                                                 building nor adheres to the walls, windOW-Sills, or
   Introduction. Despite the fact that fallout-gamma-            other minor projections.
radiation shielding methods today are still consid-                 Roof-contribution calculations are based on a
ered an art, considerable ground has been covered                square roof, replaced by a centered circular disc
since the early days of atomi.c;-weapons technology.             having the same area. Ground contributions are
Fallout produced by atomic explosions over Hiro-                 based on a square building and also on a fixed height
shima and Nagasaki did not appear to be suff1c1enUy              of detector above the contaminated plane; however,
significant to be a problem and it was not. until 1954,          a height-correction chart is included to provide a
with the historic Rongelap detonation, that the mag-             correction for this variation in height when consid-
nitude of the hazard of fallout really became appar-             ering upper stories. This method was developed for
ent. As a result, the first major attack on the fallout-         a structure in an infinite field of contamination, a
gamma-radiation shielding problem was begun.                     differencing technique being used for limlted fields.


                                                           108
                                                                                           Digitized by   Google
    The limited strip contribution is found by calcu-                     fore, those that are mentioned here are merely
lating the contribution for a building of fictitious                      observations based on a nodding acquaintance.
area (W + 2 We) (L + 2 Wc) for the infinite field dose,                       The method is obviously quite simple mathe-
as shown in F1gure 3.                                                     maticallyas the majority of the methods are, and
   (b) Advantages and disadvantages. It would be                          it is not particularly cumbersome. The charts are
rather preswnptuous to try to set down all the ad-                        well laid out and provide reasonable consistency of
vantages and disadvantages of a system without being                      results, although they would be more convenient to
exceptionally familiar with it and without having                         handle if reduced to half their width. With simplifi-
considerable experience in its application. There-                        cation, however, come the usual approximations and
                                                                          restrictions that are prevalent in a method of this
                                                                          type. An example of the type of format used for
                                                                          calculations is given in Table 1.
                                                                              (c) Comments. Bearing in mind that this method
                                                                          was developed for assessing relative fallout protec-
                                                                          tion of structures, and not for detailed analysis work,
                                                                          it can be said that it satisfies this requirement, con-
                                                                          sistent with the present state of the art. Results
                                                                          appear to be generally on the conservative side,
                                                                          compared with those obtained by the OCD engineer-
                                                                          ing method. It is interesting to note that this method
Figure 2. Building                    Figure 3. Limited strip             is the one proposed for adoption by countries in the
assumptions.                          contribution.                       NATO alliance.


                                                                TABLE 1

                                                      Format for Calculations

                                                      Contributions through walls
Data
       Floor area of building (sq. ft.)                                       A.                          8760
       Perimeter of building (ft.)                                            p.                           412

                                                                               N               E              S            W

       Weight of exterior wall (p.s.!.) .                            We       135              135           135          153
       Length of exterior wall (ft.).      .                         I         60              146            60          146
       Fraction of apertures in wall      •                          f         .3               .4             .3            0
       Distance to shielding building (ft.) .                        d                          60                          44

Calculation   case 1.
1.     Contribution from Fig. 2 using We and"fA'                              .35%             .35%          .35%          .23%
1. (i) Contribution from Fig. 2 using We and JA+ 2d                                            .15%                        .12%
2.     ContrJ!lution from Fig. 2 using a weight of 90 p.s.f.
       andJA                                                                  .92%             .92%          .92%
2. (i) Contribution from Fig. 2 using 90 p.s.f. and./A + 2d                                    .45%
3-     ( Item 1 ~
        -Item 1 (i) x (l-f)
                              +( -Item 2 J x f
                                  Item
                                       2(i) .                                 .52%             .31%          .52%          .11%
                                                41
4.     Corrected wall contribution = (Item 3) x -                             .30%             .43%          .30%          .15%
                                                  p
                                  Roof contribution                            .023%
                                  Wall contribution                           !..:.!!i.
                                      Total                                   ~
                                                                               100
                                  Protective factor for position X   =        --=
                                                                              1.203
                                                                                          83



                                                                 109

                                                                                                      Digitized by   Google
    OCD Engineering Method. The OCD Professional                  (2) Roof sources. The two pr1nclpal assumptions
Manual PMI00-l: Design and Review of Structures                concerDing calculation of rad1at1on from roof sources
for Protection from Fallout Gamma Radiation, more              are:
commonly referred to as the Engineering Manual,
                                                                   (a) Total overhead mass thickness is uniformly
was developed to fill a very necessary gap in the
                                                                       distributed between source and detector.
teclm1ques of engineering analysis of fallout pro-
                                                                   (b) Rectangular-roof source areas are replaced
tection afforded by structures. The gap was not one
                                                                       by circular ones subtendlng the same solid-
of knowledge or information, because the primary
                                                                       angle fraction at the detector.
calculations on penetration of fallout gamma radia-
tion were thoroughly reported by L. V . Spencer in                 The smeared barrier arrangement was selected
NBS Monograph 42, but rather one of procedures by              as the schematic coDf1gurat:1on because it more
which engineers and architects could conveniently              closely resembles the actual configuration of the
analyze structures. Such a method was developed                majority of structures, in that they have a series
by Charles Eisenhauer of the National Bureau of                of barriers fairly evenly distributed between source
Standards in 1960, with the help of Neal FitzSimons            and detector. Most of Spencer's calculations apply
of the Office of Civil Defense, and the results first          to circular disc sources for the simple reason that
appeared in a review draft form in 1961. There                 it is much more convenient to geDerate data for
have been some amendments to the data used in the              these than for rectangular ones.
method and some minor adjustments in the method
itself, but the principal changes involved are the re-            (3) Ground sources. The calculatlon of radiation
arrangement of charts to account for changes result-           contributions inside buildings from ground sources
ing from experimental analysis and changes to                  is much more complicated than calculation of those
facilitate greater precision in chart reading.                 from roof sources, and consequently more assump-
    In this method, application of the principle of            tions are involved in procedure developments.
solid-angle geometry and the use of charts for
barrier-attenuation factors and directional re-                   (a) Barrier factors
&pOnses for three distinct sources of radiation are                   Wall-barrier factors were calculated for a
brought together in a functional notation, producing           detector positioned between two plane walls of in-
the most sophisticated engineering procedure for               finite height and width, with a semi-lnflnlte plane
fallout-shielding analysis yet produced.                       source on each side as lndlcated in Figure 6, but
                                                               since the hypothetical structure configuration was
   (a) Assumptions. A number of assumptions                    that of a right circular cyllncler, the Decessity of
were necessary in the development of the OCD                   using these barrier factors in a system involving
Engineering Method, just as assumptions are neces-             cyllndrlcal geometry constitutes a serious logical
sary in the development of almost every analytical             defect in the entire approach. However, the dlffer-
method, whether it be for the analysis of rigid                ences in barrier effect may be quite ln81gnlflcant
frames or now in open channels. The important                  and, until such time as barrier factors for the cylin-
consideration is their magnitude and logic.                    drical coDflguration are calculated, those for plane
                                                               walls must suffice.
   (1) General. The fact that the whole engineering
method was originally developed for a structure in
an infinite field of contamination is a basic assump-
tion. Corrections for finite fields, which were a
later development, are based on the assumption
that rad1at1on scattered in the wall barrier must
be treated cI1fferently from skysbine and direct
radiation. This is because the non-wall-scattered
radiation-skyshine and direct-received in the                   e::~==-::q~       !. Xa PI'
structure is dependent on the solid-angle fraction                                                                        loplf
subtended at the detector by the source area, since
most radiation travels directly from source to de-
tector. Wall-scattered radiation, on the other hand,
is dependent on the solid-angle fraction subtended                                                                         I
by the source area at the mid-point of the wall and
                                                                                                               - ._ .. _---*-..
                                                                                                   Xo· X, +Xa + x.
the solid-angle fraction subtended by the wall at the                   (a)                              (b)
detector. In essence, the barrier factor for wall-                                                   SCHEMATIZEO
                                                                      ACTUAL
scattered rad1at1on is dependent on this source
geometry.                                                      Figure 4. Roof eouroe aasumpt1ou.


                                                         110

                                                                                              Digitized by   Google
    (b) Geometry factors                                                (Ui) The geometry factor for walls of inter-
      The shape factor E provides a sort of com-                             mediate mass thickness, taken to be a
pensation for this conflict of geometries and is                             weighted ratio of thin-wall geometry fac-
based on the assumption that the dose rate from a                            tor to thick-Wall geometry factor, with
straight wall varies as cosine ¢, where ¢ is the                             Sw, the scatter fraction, as the weighting
                                                                             factor. This scatter fraction is the frac-
azimuthal angle.
      The E for two walls of inWne length and height                         tion of the total radiation emerging from a
approaches 1.0 because of the extreme eccentricity,                          wall that has been scattered by the wall.
                                                                       (b) Advantages and disadvantages. It is said that
whereas for a square structure, E = J2, for an
                                                                   art and science have their meeting point in method.
eccentricity equal to unity.
                                                                   There is little doubt that development of the engineer-
      The question that arises here is: how neces-
                                                                   ing method from Spencer's basic calculations has
sary is it to have a varying shape factor? Since the
                                                                   been a real work of art. Its two outstanding features
angular distribution is only an assumption, and since
                                                                   are: (a) it is a very comprehensive method, in that
the majority of buildings have eccentricities in the
                                                                   almost any fallout-shielding situation can be ana-
range 0.25 to 0.75, then perhaps a constant value of
                                                                   lyzed, and (b) it would appear to be the most accurate
E around 1.3, or slightly larger, may be justified.
                                                                   method yet developed.
Certainly any reduction in the number of variables
                                                                      Justification for the assumptions and the degree
used in the engineering method would be welcomed,
                                                                   of precision will depend upon experimental confir-
particularly by those involved at the nuts-and-bolts
                                                                   mation, but unless a detailed analysis is made of all
end.
                                                                   the experiments completed to date, it will be ex-
      As a brief recapitulation, barrier factors de-
                                                                   tremely difficult to determine just how the engineer-
pend only on the mass, while geometry factors de-
                                                                   ing method should be modified.
pend primarily on solid-angle fraction and only
                                                                       Now that we have accounted for all the merits of
slightly on mass thickness.
                                                                   the method, what little shortcomings does it have
      There are two or three assumptions involving
                                                                   that might tend to demoralize even the most ambi-
the directional distribution of emergent wall-
scattered radiation that may be of interest. These                 tious of fallout-shelter analysts? The most signW-
                                                                   cant one is the shear drudgery with which an analyst
are:
                                                                   must contend when endeavoring to analyze even a
         (i) The angular distribution of emergent wall-            slightly complex structure. Although it is necessary
             scattered radiation for thick walls (much             to strive to perfect any art, the question is whether
             greater than 40 psf) is the same as that for          the effort necessary in finding the protection factor
             air-scattered radiation for walls of zero             of a relatively simple structure is justified in a sys-
             mass thickness.                                       tem where protection factors can be predicted only
        (U) The detector response for radiation emer-              to within a factor of 2, when, by using one of the
             gent from thick wiills is' file same from             simplified methods, one may achieve results that
             above the detector plane as that from below,          are perhaps 20 to 30 per cent less preCise, when
             provided the solid angles are equal.                  considering fairly Simple structures.
                                                                               10
                                                                                1
                                                                                II
                                                                                3
                                                                                I
                                                                                                   1\

                                                                                1                   \ \.
                                                                                1
                                                                                II                        "-
      ~             ~
                          I
                          I
                                                                                3
                                                                                I

                                                                               10
                                                                                          /
                                                                                            /              "'
                          I                                                     1        ./
             .. .         I                                                     III-
        I " ~' I                                                                3
           Ih I                               •
        I
              1           I
                              .
                                               ,   ....
                                              ' lJ·· .. ..
                                                                                I


  • •...t.:t;fj •• •                                                           10


                              .
                                               ~
                                                                                1
+ + I\,;:    .-::,.,..                                                          II
       '"   ~.      ...                                                         3
                                                                                I

            (a)                   (b)                                          ler
                                                                                    WI          HORIZON          DOWN
Figure 5. Ground source assumptions.                               FIgure 6. Wall scatter assumptiou.


                                                             III
                                                                                                        Digitized by   Google
    The answer is that detailed analysis of the com-             the skyshine effect for the full upper solid angle,
ponent parts of a structure cannot really be satis-              that is, the directional response is calculated for
factorily accomplished by the simpler methods, most              Wu in Figure 7.
of which are only Simplified versions of the engineer-              (2) Height parameter for barrier factor. In cal-
ing method. However, if an approximation of the                  culating barrier factors for walls in multi-story
protection factor of a structure is all that is desired,         buildings, a height appropriate to the particular
anyone of the less tedious methods will suffice. It              wall was used. When selecting a barrier factor for
18 unfair, of course, to criticize a method of analysis          the contribution through the walls of the story above
without consideration of its original purpose. Each              the detector, the height to the mid-point of the wall
of the methods mentioned has its place in shielding              was taken, and similarly for the barriers of other
analysis.                                                        factors.
    The other major feature of this method that tends               This means that three different barrier factors
to demoralize the beginner is functional notation.               were required even though the mass thickness might
The student eventually gets used to this, but it tends           be the same, which is a sophistication certainly not
to retard the learning process.                                  warranted by the system. In the new procedure the
                                                                 wall-barrier factor for each of the three floors
    (c) Recent changes. A few minor changes in the
                                                                 under consideration is determined using the height,
procedure of the engineering method have been made               H, of the detector. Should the wall-mass thicknesses
recently. These involve the skyshine response, the               of each floor vary substantially, three separate
height parameter of wall-barrier factors, and some               barrier factors will still be required. Figure 8
of the charts.                                                   shows a typical sample of a multi-story building
                                                                 whose walls have a mass thickness of 80 psf and
    (1) Skyshine. Of the three types of sources en-              heights as shown.
countered in fallout-shielding analysis, skyshine is                The individual barrier factors and the contribu-
usually the least Significant and accounts for about             tions from ground sources calculated by PM 100-1
10 per cent of the open-field dose. Two non-wall-                for each of the stories are given in Table 2.
scattered components included in the skyshine cal-
culation are air-scattered radiation and ceiling                    It can be seen that the change in contribution is
albedo.                                                          insignificant to the final result, primarily because
   Although skyshine usually has a secondary effect,             contributions from stories above and below the de-
there are certain situations in which the ceiling-               tector story constitute less than 10 per cent of the
albedo component may become relatively significant.              total contribution received at the detector.
A structure in a built-up area with a large overhead
mass and substantial walls is one of these cases.                                             TABLE 2
Because of close mutual shielding, the air-scattered
radiation is virtually negligible.                                       Individual Barrier Factors and Contributions
    Because most of the air-scattered radiation                          from Ground Sources Calculated by PM 100-1
originates from sources about 500 feet away, the
procedure followed in the Engineering Method for                                                       Ground          Ground
the situation illustrated in Figure 7 was to consider                                               Contribution     Contribution
the effective sky shine response as zero. This may               Story    Be <He, H, 1Iu)   Be(H)   Be (Hu, H,Hl)    Using Be(H)
be true for all practical purposes for the air-scat-
                                                                   2          0.1           0.088       .0022            .0020
tered component, but the backscatter from the wall                 3          0.088         0.088       .0287            .0287
of the adjacent building and ceiling albedo are defi-              4          0.076         0.088       .0006            .0007
nitely not zero. The current procedure considers




                                                                                                                    ,,
                                                                                               ,                     ,
                                                                                               ~-------------       .
Figure 7. Scysh1ne.                                                                   Figure 8. Multistory building.


                                                           112

                                                                                                    Digitized by   Google
   <d) Comment. There appears to be a definite                were no barrier. Figure 9 is a graph of the con-
need for further examination of some aspects of the           tribution through an aperture compared with the
Engineering Method, principally for the purposes of           contributions through walls of various mass thick-
removing some of the tedium of the operations in-             ness, but having the same area and the same loca-
volved and for improving its precision. One may say           tion relative to detector and source.
that the shielding problem bas been bracketed-with                (c) Comments. One excellent feature of nomo-
Spencer's monograph on one side and simpUfied                 grams is that the effect of a change in one of the
methods of analysis on' the other; and with the Engi-         parameters can be seen very readily by pivoting a
neering Method constituting almost a target round-            straight edge on the nomogram. They are extremely
but the operation cannot be considered really effec-          useful in preliminary design.
tive without proper adjustment to the mean point of               The aperture procedures adopted in the Nomo-
impact.                                                       graphic Guide yield results comparable to those
                                                              achieved by the Engineering Method for wall-mass-
   OCD Nomographic Guide. The shielding chapters              thickness values up to about 120 psf; above this the
of OCD document NP-10-2, Guide for Architects and             results begin to diverge somewhat, where more de-
Engineers, dated May 1960, were revised in 1963 by            tailed analYSis of the aperture contributions may be
Dr. Manual Suarez and Mrs. Jean Ravenscroft and               required.
resulted in the Simpl1f1ed Method of Shielding                    When treating basement areas, the area of the
Analysis. Its principal feature is that the charts            building, which is normally one of the parameters
used in the Architects and Engineers Guide have               in Simplified methods, is not used, since the varia-
been replaced with a series of nomograms or                   tion in geometry shielding effect between areas of
parallel-alignment charts that are much easier                400 sq ft and 14,000 sq ft is relatively insignificant.
to read and that produce consistent results.                  Geometry factors computed by the Engineering
    Its purpose is the same as that of the shielding          Method for a range of areas show Uttle change, at
chapters of the Architects and Engineers Guide;               least not sufficient to warrant inclusion of an addi-
i.e., to provide architects and engineers with an             tional parameter. The figures shown in Table 3 are
approximate method of shielding analysis for shelter          contributions calculated using geometry factors and
planning.                                                     a wall-mass thickness of 60 psf as a basis.

  <a) Assumptions. In developing this method, it                 Equivalent building method. This is a method of
was assumed that:                                             analysis based on the assumption that any complex
   1. all buildings are square in plan,                       shielding situation can be reduced to an equivalent,
   2. the roof is replaced by a circular disc equal           soUd-wall' single-story structure problem. It is a
in area to the horizontal projection of the roof,             Simplified approach utiUzing charts developed from
   3. for ground-floor areas, the detector is 3 feet          the solutions of many shielding problems analyzed
above ground level and centrally located,
   4. for below-ground areas, the detector is 5 feet
below the level of the ground floor and centrally                   0.13        40 PSI'"
located.
                                                                    012
   The mutual-shielding correction nomogram was
prepared from experimental data obtained using a                    0.11        50 PSF
steel model of a six-story building. The experiment                 0.10
was one of a series carried out by Technical                                    60 PSF
Operations Research, Inc., for the Office of Civil             G.C 0.09 APERTURES
Defense.
                                                                    0.08
   (b) Procedures. Apart from the use of nomo-
grams instead of charts or tables, the most radical                 0.07
departure from common practices involves the                        0.06
aperture approach when the detector is at or below
s1ll1evel. When the wall-mass thickness i~ equal to                 0.05
or less than 50 psf, the effect of the apertures can
                                                                    0.04
be ignored. The reason for this is that with wall
barriers of mass thickness ranging between about                    0.03+---.--~--.--~~--.--~--.--.......-
50 psf and 60 psf the wall-scattered radiation that                        o   0.1   0.2 0.3   0.4 0.5   0.6   0.7   0.8 0.9
would reach the detector from a given wall area                                                  W
approximately equals the skyshine radiation that              Figure 9. Contribution through an aperture oompared with
would be received through the same area if there              that through walls of various mass thicknesses.


                                                        113

                                                                                                Digitized by   Google
by the Eng1neeriDg Method, and obviates the neces-                    The procedure is developed on the principle that
sity of dealing with directional responses and solid-               every shielding problem must fall within one or
angle fractions.                                                    more of sJx zones illustrated in Figure 10.
   Commander J.C. LeDoux of the United States
Navy was the moving force behind its development.
The first printing became available early in 1963.

   (a) Assumptions.' Engineering Method assump-
tions apply equally to the Equivalent Building Method,                                              ZONE 2

but there are two additional assumptions that should
be mentioned. These are:
   1. all calculations are based on the premise that
                                                                              ZONE 3                ZONE 4A
the building is square,
   2. the detector is assumed to be at s111 height
for the purpose of calculating aperture contributions.
    The system revolves around a series of
                                                                              ZONE 48                ZONE !I
protection-factor charts that quickly show the rela-
                                                                    Figure 10. Possible shie1d1ng problems.
tive mass thicknesses of wall and roof required for
a given PF. In developing the system, it was found
that other parameters, such as apertures, limited
strips of contamination and height, produced defi-                      (a) Assumptions. This method involves some
nite patterns of variation in the protection factor.                manipulations of the directional responses for air-
It was poSSible, therefore, to establish correction                 scattered and wall-scattered radiation. The result-
factors to allow for the presence of apertures,                     ant procedure is relatively simple and removes a
finite areas of contamination, aDd for variations in                large percentage of the sources of human error
the height of the detector above the contaminated                   inherent in other methods. Tbe main assumption
plane.                                                              is that for certain ranges of Situations, a standard
                                                                    wall concept can be adopted; i.e., variations of
   (b) Advantages and disadvantages. The Equiva-                    certain parameters produce relatively insignificant
lent Building Method provides a means of rapldly                    changes in the results. This removes the necessity
estimating PF and also a convenient method for                      of considering every parameter for given situations,
the preliminary design of fallout shelters, which is                thus reducing the work involved.
tremendously useful in planning and determining
rough costs for budgeting purposes.                                    (b) Method. A system of composite rather tban
                                                                    separate directiorial responses has been adopted,
   A shielding method. In the summer of 1964, the                   which again reduces work. The procedure does not
Emergency Measures Organization of Canada asked                     involve the handling of those directional responses
Dr. Manuel Suarez to develop a procedure for the                    that were used only to develop data for charts and
analysis of structures against fallout radiation,                   tables. A typical geometrical expression is given
based on the OCD Engineering Method and Spencer's                   for Zone 4a, that is, for that portion of the wall
monograph with at least the same degree of pre-                     above the detector plane on the detector story:
cision as the Engineering Method, but using a
straightforward algebraic notation.                                 Gg   =(BwE + .26) Gs
                                                                         where Gs is the wall-scattered directional re-
                                                                         sponse given in the Engineering Manual and Bw
                                                                         and E the scatter fraction and shape factor
                           TABLE 3                                       respectively, also as given in the Engineering
                                                                         Manual.
  Mass                      Ground ContribuUon                         In essence, the combined air-scattered and wall-
Thickness       Area              Area           Area               scattered radiation is given in terms of the direc-
  (psf)       625 sq.ft.       2,500 sq.ft.   10,000 sq.ft.         tional response for wall-scattered radiation.
                                                                       One of the expressions for ground contribution is
   50           .0226            .0335           .0381              given below merely to illustrate the type of expres-
  100           .0088            .0127           .0143              sion used. It is for the zone usually having the most
  150           .0030            .0043           .0048
  200           .0012            .0017           .0019
                                                                    significant. contribution: Zone 4b-below detector
                                                                    plane.


                                                              114

                                                                                               Digitized by    Google
GC4b =WE x Fgx FS x Fh                                             in the elimination of lengthy repetitive calculations.
                                                                   Results are almost completely consistent and have
   When apertures are present in this zone, the                    the same general degree of precision as those given
above expression is modified sUghtly and looks                     by the Engineering Method.
like this:                                                             As this method has not been thoroughly tested,
                                                                   its fiex1biUty and convenience in design work have

This partl represents
contrlbutiQn through
                            T
GC4b = WE.Fg (1':'Ap) + OE.Pa         Fs·Fh
                                       stiadow and
                                       height factors
                                                                   yet to be established, but, for analysis of structures,
                                                                   it is generally quicker and less trying than any other
                                                                   method having the same degree of precision. In
wall portion                 This represents                       addition, the soul-searing frustration of soUd-angle
                             contribution through                  fractions and directional responses has been
                             the apertures                         removed.
                                                                       In developing charts and tables, analytical expres-
where WE is the wall effect, using mass thickness                  sions derived by fitting functions to the main charts
exterior wall, Me.                                                 in Spencer'. monograph were used. Although some
Fg     is the geometry factor USing the square                     small error may be introduced by this operation, it
       normality ratio SN.                                         enables the computations to be simplified, produces
                2z
                                                                   consistent results, and is particularly suited to com-
       (SN =   JA"   where z is vertical distance                  puter operation. Any error resulting from this
                                                                   function fitting is probably relatively small compared
       DP to detector floor, A is area of building)                with chart-drafting errors.
       is percentage of aperture computed as area
       of apertures in that part of wall under con-
       sideration divided by the area of that part of              A Look at Survey Methods
       the wall.
OE     is the opening effect.                                         ODM Survey Method. The Office of Defense
                                                                   MobUization produced a draft manual of Shielding
Pa     is percentage apertures computed as total                   analysis in September 1957, prepared by Dhein and
       horizontal aperture length divided by length                Shapiro, aDd called A Method of Evaluating the
       of wall.                                                    Protection Afforded by Buildings against Fallout
Fs     is the floor shadow factor.                                 Radiation. Although one of the earliest manuals in
                                                                   this field, it illustrated techniques for assessing
using Me' H (height of detector above contaminated                 buildings of other than rectangular shape and for
      plane) and SN (calculate SN same way as for                  determining contributions to detectors located at the
      F g' but use z from DP to bottom of aperture)                corners of a building as well as centered ones. The
Fh     is the height correction factor.                            procedure was based on a table look-up system as
                                                                   opposed to charts. Wall-mass thicknesses were
   The results of an example calculated by this                    transposed into equivalent thickness of concrete
method and the Engineering Method are given below                  values for which a table of shielding factors had
for comparison purposes.                                           been prepared. These shielding factors appear to
                                                                   have been based on simple exponential attenuation,
                                                                   that is, they do not appear to include any build-up
                     Comparison of Results
                                                                   factor.
                          Engineering                 A               Apart from this, the ODM method is very similar
Component                    Method                 Method         in principle to that of the OCDM Guide, except that
                                                                   the latter is based principally on data developed by
Aperture.                    .13200                 •13680         the National Bureau of standards uDder Spencer .
Wall                         .01573                 .01633            In the comparison of results given toward the
Reduction                                                          eDd of this paper, it is interesting to note that the
                             .14773                 .15313         contribution through the wall calculated by the ODM
 Factor
                                                                   Survey Method is very close to that calculated by
                                                                   the Engineering Manual Method.

    (c) Advantages and disadvantages. The main                        OCDM AE Guide and EMO Manual No.1. A pre-
characteristic of this method is its relative sim-                 liminary draft of the OCDM "Guide" developed
plicity. The various parameters are sufficiently                   principally from the draft Engineering Method by
separated to enable a change to be made in any one                 Neal FitzSimons, was completed by the end of 1958,
of them without affecting the others, which results                while the EMO Manual No.1, An Engineer Looks at


                                                             115

                                                                                             Digitized by   Google
Fallout Shelter, was written during 1961 by Lieu-                The calculation routines from which the program
tenant Colonel J. W. Balley. The latter manual is             was written are given on EMO Form 17 illustrated
only an improved version of the OCDM "Guide" of               in EMO Manual No.1.
May 1960, adopting the same method and using the
same charts with minor variations.                               General Electric Fallout-Shelter-Evaluation
   Ground-contribution charts were developed by               Program. The New York State Civil Defense Com-
adopting fixed detector heights and a fixed story             mission decided that it would be extremely useful,
height. For example, with a fixed story height of             convenient, and economical to have a computer
10 ft and the detector located 5 ft below the base-           program that would not only analyze structures but
ment ceiling, contributions can be calculated for             also specify design factors for proposed fallout
variations of area and wall-barrier mass thickness.           shelters within existing structures. As a result,
   In calculating upper-story contributions from              the General Electric Company was asked to develop
ground sources, it is assumed that the detector is            such a program based on the OCD Manual, DeSign
located on the ground floor and then a height cor-            and Review of structures for Protection from
rection is applied. This height correction is the             Fallout Gamma Radiation.
ratio between the dose received at a detector for                Examination of the now chart indicates that this
various heights above an infinite field of contami-           program is fairly comprehensive. Calculation rou-
nation to that received at a detector in the standard         tines include off-centered detector locations as well
unprotected position.                                         as centered ones and, in the design phase, a series
    This method is an extremely Simplified one and            of shelter designs is prepared by the computer in
is therefore not very precise, but it serves its              terms of the various combinations of roof and wall-
purpose in that it enables one to estimate the rela-          mass thicknesses, from which an appropriate design
tive protection in various areas of buildings that            may be selected.
may be used as shelter.                                          The program was written in 1963 in machine
                                                              language for the GE 225 computer by the Schenectady
                                                              Information Processing Center of General Electric,
Computer Methods                                              under the direction of the Research and Develop-
                                                              ment Section of the New York State Civil Defense
   Introduction. It was inevitable that fallout-              Commission.
shielding analysis methods would be adapted for
use in computers because of the time involved in                  U. S. National Fallout-Shelter-Survey Method.
carrying out such calculations by hand. Programs              With congressional approval for a national fallout-
for at least six different methods of fallout-protec-         shelter survey, the National Bureau of Standards,
tion analysis have been developed since the spring            in September 1961, was asked to write a high-speed
of 1961, ranging from the simplest of methods to              computer program for a simplified method of shield-
the sophisticated OCD Engineering Method.                     ing analysis based on the methods shown in Fallout
                                                              Shelter Surveys: Guide for Architects and Engineers,
   DPW Survey Method 1961. Early in 1961, the                 published in 1960.
Department of Public Works of Canada surveyed all                 By the spring of 1962, the program was opera-
federal buildings to determine existing protection            tional. It was written in symbolic language for the
factors and the number of shelter spaces that could           IBM 7090 and utilized a film optical sensing device
be made available. The engineer charged with the              for input data, which required a mark-sense type
responsibility for survey operations and processing           of data-collection sheet, referred to as a FOSDIC
in the Ontario region asked the Ontario Department            form.
of Highways if they would be interested in develop-               In preparing calculation routines for this pro-
ing a computer program for calculation of fallout-            gram, consideration was given to all possible shield-
protection factors. The DHO undertood the work                ing situations, and consequently some modification
and developed a simple program for the IBM 650                of the method given in the Guide was required.
based on the shielding method given in EMO Manual             Because of the preponderance of finite contaminated
No.1, An Engineer Looks at Fallout. The main                  strips in built-up areas, a more detailed correction
restrictive feature of this program is that only              was included for this effect, which depended upon
ground-floor and basement areas can be assessed.              the mid-point height of the wall above the contami-
The object of the program was to reduce the cost              nated plane, and the limits of the finite strip.
of manual PF calculation of federal buildings in                  The relationship between the height, H, and the
Ontario. Since the terms of reference called for the          distance, D, is given by the expression:
assessment of basement areas only, there was no
requirement, at that time, for a more sophisticated
program.


                                                        116

                                                                                        Digitized by   Google
  where H is height in feet from contaminated
  plane to mid-point of detector story wall, and
  D is distance from wall to outer limit of
  contaminated strip.
This is derived from the solid-angle fraction for a
circular area,
                                                              Figure 12. NeIghboring roof contributIon.
w=l·cose
   Another important modification concerned the
height correction. In the case of finite strips less             Computer analysis for protective structures.
than 300 ft in width, height correction is not con-           Development of a series of electronic-computer
sidered because absorption is insignificant. The              programs for the complete engineering analysis of
height correction was applied only when fields                structures considering multiple effects of INclear
of contamination exceeded 300 ft. In addition, the            weapons is well advanced in the U. S. Office of Civil
change of wall attenuation with height was included           Defense. The CAPS-2 program, AnalysiS of struc-
in the height-correction factor.                              tures for Fallout Gamma Radiation Shielding, was
   Aperture corrections were applied only if the              in preliminary draft form in January 1964, at which
detector lay above all contaminated planes on any             time it was being prepared for field testing . It was
particular side, but they were not applied if the             developed and written for OCD by Praeger-Kavanagh-
detector happened to be below the sill. In other              Waterbury, Engineers-Architects, with Charles
words, no aperture correction was made if the                 Eisenhauer of the National Bureau of standards as
window sill was 3 ft or more above the floor.                 consultant, and is based on the methods of analysis
    The calculation of contributions from neighboring         given in PM 100-1, Design and Review of structures
roofs was included in the program because it was              for Protection from Fallout Gamma Radiation.
felt that there would be many occasions when such                The purpose of this program is to faciUtate rapid
contributions might be significant. Many cases arose          evaluation of fallout-protection factors of structures
in which it was necessary to divide a building having         for any detector location and to indicate the various
a complicated shape into a series of simple rectan-           shielding elements required, together with identifi-
gular shapes by passing vertical planes through the           cation of those areas where shielding would be most
building. (See Figure 11.)                                    effective. It is written in Fortran computer language
                                                              and utilizes a comprehensive table-look-up arrange-
                                                              ment and also incorporates the facility for calculat-
         ~                        ~
                                  ~~
                                                              ing reduction factors for any eccentric detector
                                                              location, taking into consideration all interior parti-
    ~J7                                                       tions . No mutual shielding is considered beyond 300
 VIEWA
                                       VIEW A
                                                              feet.
Figure ll. NeIghboring roof contribution.                        Rapid AnalYSis of Home Shelters (RAHS)*. The
                                                              necessity of providing a convenient service to home-
                                                              owners for the assessment of fallout protection in
   Many roofs are not simply plane surfaces, and              their homes resulted in development of the RAHS
the frequency of setbacks was sufficient to Justify           system by the Office of Civil Defense. It requires
the inclusion of a solution for this problem.                 that only six questions be answered by the home-
   The treatment of roofs of varying elevations is            owner concerning certain dimensions and the type
adequately dealt with in the OCD Engineering Manual,          of construction by marking appropriate, pre-printed
and will therefore not be discussed here. However,            answers on the RAHS card (see Figure 13) . The
the roof area must be divided into separate tasks             results are printed out on a card (see Figure 14),
before this approach can be used, and a special               and include protection factors for the following
routine was included in the program for this pur-             locations:
pose. The setback situation shown in Figure 12
would be split up as indicated on the right, thus                a. basement center
requiring the calculation of four separate contribu-             b. basement side having the highest PF
tions, which would be performed by the appropriate               c. basement corner having the highest PF
part of the roof-contribution-calculation routine.
   Those interested in the calculation routines
adopted should refer to NBS Report 7539 by Spencer            *Name changed to ''Evaluation of Fallout Protection in
and Eisenhauer.                                                Homes" (EFPH).



                                                        117

                                                                                            Digitized by   Google
    Residential structures without basements can be                                                                                        It is interesting to note that the U. S. Office of
accepted, but the printout will merely indicate that                                                                                    Civil Defense is now planning to implement the
the protection factor at the center of the Door is                                                                                      RAHS system on a national basis, which will no
less than 10.                                                                                                                           doubt contribute considerably to national prepared-
    Upon receipt of input data, the computer selects                                                                                    ness against the possible hazard of radioactive
a solution appropriate to the input data from a table                                                                                   fallout.
of approximately 1,400 solutions, which represent
almost every combination of answers to the ques-                                                                                            EMO Survey Method. In selecting the survey
tions given on the RAftS card. These solutions                                                                                          method of computing protection factors for the
were developed using the methods given in OCD                                                                                           Alberta Fallout Protection Survey 1964, careful
PM 100-1, Design and Review of Structures for                                                                                           consideration was given to utilizing the U. S. com-
Protection from Fallout Gamma Radiation. A com-                                                                                         puter program, which had been offered to the
parison between results of experiment!! .conducted                                                                                      Canadian government, but, because of our own
on residential structures using a cobalt-60 source                                                                                      particular requirements, it was felt that a new
and those calculated by RAftS shows extremely                                                                                           program should be written. The calculaUon rou-
realistic agreement, considering the simplicity                                                                                         tines were based on methods given in the OCD
of input requirements. Results of analysis by the                                                                                       Nomographic GuIde, but modified somewhat to
Engineering Method show very good correlation                                                                                           take into consideration setbacks and contaminated
with MHS results.                                                                                                                       planes for various ranges of height and width.
    With calculated protection factors arranged in                                                                                          Perhaps the most Significant difference between
tabular form, programming was designed for the                                                                                          the two programs mentioned is not the shielding-
IBM 1401 to select and printout the three protec-                                                                                       analysis method, but in the fact that the EMO pro-
tion factors for any combination of answers to the                                                                                      gram utilizes analytical expressiOns for different
six questions. In addition the computer maintains                                                                                       contributions rather than a table-look-up system,
statistics on input and results by geographical                                                                                         although, in certain cases, tables of values were
area. The question-and-answer card is a standard                                                                                        prepared for convenience. These expressions were
ADP card designed to facilitate input into the com-                                                                                     developed by Dr. Manual Suarez by fitting functions
puter. Its reverse side is in pre ..paid postcard form.                                                                                 to the appropriate charts in NBS Monograph 42 and
    After processing, a special package is returned                                                                                     the Engineering Manual.
to the householder, including information on the                                                                                            The expressions used are:
protection factors for the locations previously men-
                                                                                                                                               Roof Contribution
 tioned, a glossary of terms, a new shelter design,
 and various items of useful literature.                                                                                                       log Rt   =-0.OO938Xo -   0.38 log Xc,
                                                                                                                                               Ground Contribution - aboveground areas
                                                                                                                                               log Rt   =0.818 -
                                            RA~S
                                                                                                                                                                   O.OlO5Xe - 1/3 log A
                                                                                                                                               Ground Contribution - belowground areas
                                        !lOME SWELTER ANAL't'SIS CARD

                                                                        ---
                                                                ,)11-:....  "01-1........             ~"       ~
                                                                                                                                               log Rf   =-1.186 -   0.0089   CXe + Xi) -   0.0186Xa'


              .------                                           :'-.... :t'.-\.."'.:.........
                                                                J" ,~"' •••"
                                                                • ""~\......",,,,".'" .;'.~ 1C"1~.1~
                                                                f:,.:r-.·~..,<NN ..
                                                                .:0......, t,:' . . . . .
                                                                      w~......
                                                                     =r ......   ~
                                                                                  r:..



                                                                     .1- ........,...,:.'
                                                                                                  I

                                                                                          IC ...... loW ......

                                                                                            \:I~w ~ ..


                                                                                         :;.'"' .'..,
                                                                                       i"""'" "'""
                                                                                          ~
                                                                                                      :




                                                                                                      '

                                                                                             It "" ,"'~
                                                                                                ~      It.' II» .... 11).•
                                                                                                4.' .. ~ "' ",,\"
                                                                     _"..,.""" . . . ,...........,.•""rA·
                                                                                                          I




                                                                                                              ....
                                                                                                                                               where Xo is the total overhead mass thickness
                                                                                                                                                        Xe is the exterior wall-mass thickness
                                                                                                                                                        Xi is the interior wall-mass thickness
               : ...... f· . . .
                                                                                                                                                        Xa' is the basement ceiling-mass
Figure 13. Home shelter analysis instructions.                                                                                                             thickness
                                                                                                                                                        A is the floor area of the building.
                                                                                                                                            It should be emphasized that in the case of roof
                 OFFlCt OF CiviL OtfLNSt HOME. SHtLTtR tvALUATI.".                                                                      contribution the reduction factor is not obtained
                                                                                                                                        direcUy by substituting in the expression the value
                                                                                                                                        of leo. A set sequence is necessary, and the expres-
                                                                                                                                        sion is used according to that for detector response
                                                                                                                                        for a circular area given in Spencer's monograph,
   .)'1,
   to !ty.:,'n
           tllllltU. I(U
   "'"ILAlJlLPI1IA                 PA       19l~1
                                                    IIt.U   t(I","UM IJF BAUMt,..'                                           90

                                                                                     • StL C1.DSiAK'

                                                                                                                                        DIDo   =L(X) -    L   (I~W) ,
Figure 14. Home shelter analysis results.



                                                                                                                                  118

                                                                                                                                                                        Digitized by   Google
    where each of the above two terms is represented                be achieved in a manner that requires less effort
    individually by the log Rf expression. In one case,             and time.
    only the barrier-mass thickness is considered; in                  One of the common weaknesses of shelter-design
    the second case the geometry is considered in terms             methods is the lack of entrance-design techniques,
    of X so that it can be substituted in the log Rt ex-            which is particularly noticeable with Simplified
    pression. Subtracting the two results gives the roof            methods of analysis. Ensuring that an entrance
    contribution. More details of the application of these          contains two right-angle turns can hardly be con-
    analytical expressions and the calculation routines             sidered a design technique, but rather only a very
    are given in EMO Fallout Protection Survey Report               rough rule of thumb. Considerable experimental
    No.1, Calculation of Protection Factors for the                 work on gamma radiation streaming through ducts
    Pilot Survey of Fallout Protection in the Province              has been carried out by Chilton, LeDoux, and many
    of Alberta.                                                     others. As a result, the data on which the methods
        Corrections for apertures were included to cover            for designing ducts and entrances have been im-
    situations where detectors were either above or be-             proved. The OCD Engineering Method is suffiCiently
    low sill level. In the case of detectors above sill,            comprehensive to carry out detailed entrance de-
    the contribution through apertures was determined               sign, but a separate document dealing only with
    using the perimeter ratio P a technique as opposed              entrance-design techniques would find a welcome
    to the percentage-aperture-area method. The re-                 spot on any fallout-shelter analyst's bookshelf.
    sults would be correct, however, only for situations               In reviewing the state of the art, one very
    in which the windows approached full wall height.               important question arises: What degree of confi-
    Results would be slightly less correct and somewhat             dence can the analyst have in the present system?
    conservative for windows of lesser length. The re-              The inconsistency of results presented by the
    quirement for a special correction for apertures                variety of methods certainly does not promote a
    with sills below detectors was perhaps more appar-              feeling of well-being. The fact that the correct
    ent than real, since the number of structures sur-              answer for most situations is unknown has an
    veyed in the Alberta Survey that had sills below the            undermining effect, because it is extremely diffi-
    detector constituted only a small percentage of the             cult to estimate errors without a yardstick. Certain
    total.                                                          of the errors inherent in the development of meth-
       A simple design facility was included in the pro-            ods, together with experimental comparisons, in-
    gram, more as an experiment than anything else, to              dicate that calculations may be accurate within a
    determine the additional mass thickness required to             factor of 2; and so one's first impression is usually
    be applied to one 01' more walls of a structure in              that the system is not very precise.
    order to raise its protection-factor category to the                Before making a judgment, one should compare
    next higher order. Its usefulness is rather l1m1ted             the factors of safety used in most current struc-
    in that it does not indicate overhead mass-thickness            tural design.· The design factors incorporated in
    requirements, which in many cases may be more                   reinforced-concrete work and structural steelwork
    economical than extra wall-mass thickness. In                   usually vary between 2 and 4 and actual safety fac-
    addition, this information is only useful in con-               tors may be as high as 10 and as low as 1. Some
    nection with determination of rough planning costs.             structures that have been tested to destruction have
        Since the Canadian government is embarking on               actually failed below design strength. When com-
    the first phase of a national fallout-protection survey         paring these factors of safety with those obtained
    in the summer of 1965, it is hoped this design facil-           in shielding-analysis work, the picture is not as
    ity will be improved so that it will produce the most           depressing as it may appear at first glance, and,
    economical balance between wall and overhead mass-              considering that this art is only eight years old, it
    thickness requirements for raising protection fac-              has moved ahead in ten-league boots. However, in
    tors of likely shelter areas to 100.                            addition to proving or disproving the assumptions,
    So What?                                                        the present procedures and techniques need to be
r                                                                   streamlined and manipulated so that they are much
    The foregoing has been but a brief look at some of              more convenient to use.
    the methods of fallout-shielding analysis, most of
    which are current. With such a wide variety it is               Comparison of Results
    inevitable that a fairly wide range of answers to the
    same problem will occur. With six different people              The typical building shown above was selected to
    calculating a solution to the same problem, the                 compare results calculated by the different meth-
    probability that any two of the answers will be the             ods mentioned in this paper. It should be empha-
    same is quite small. There is an urgent require-                sized, however, that the compariSOns given in
    ment, therefore, for the development of current                 Table 4 are definitely aot conclusive, since it is
    methods to the stage where consistent results can               possible to select specific situations that correlate

                                                              119
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reduction factors closely and others that show
major discrepancy.




                        TABLE 4
                                                                         Given
                Comparison of Results                                    ---..s thickness of walla, Me = 80 pst
                                                                            Mass thickness of floors, Yf'"' 70 pst
                       Wall Contribution                                    Mass thickness of roof, Kr = 70 pst
                      Side Sides T tal        Roof    Total                 Height of sills above floor, 3 It
     Method            C    A+B+C 0           Cont.    RF                   Perimeter ratio of apertures, P s = .80
                                                                           Aperture area percentap, A... = .37
OCD Engineering                                                             No s1pjf1cant interior partitt'ona
 Manual               .0046   .0567   .0613   .0014   .0627                 Mutual shielding on side C, Wc - 100'
British Bebeme 1963   .0114   .0879   .0993   .0014   .1007                                              Az1 = .147
ODM &lrvey Method     .0070   .0403   .0473   .0004   .0477                                              A S2 = .353
OCDM AE Guide         .0025   .0317   .0342   .0015   .0357
EMO Manual No.1       .0025   .0317   .0342   .0015   .0357              Required
OCD Nomographic                                                            Reduction factor at tile center of 3rd story.
 Guide                .0011   .0314   .0325 .0018     .0343
Canadian Manual       .0040   .0283   .0323 .0015     .0338         Figure 15. Building used in comparing results from
                                                                    different methods of calculation.




                                                              120

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                            ICHIBAN: THE DOSIMETRY PROGRAM
                             FOR NUCLEAR BOMB SURVIVORS OF
                                 HIROSHIMA AND NAGASAKI

                                               John Auxier
                                       Oak Ridge National Laboratory


Soon after the nuclear bombings of Hiroshima and                 Data from Operation Teapot indicated the possi-
Nagasaki in August 1945, U.S. military medical               bility of a definitive description of radiation fields
teams entered the cities,(l) In 1947, a permanent            from the Hiroshima and Nagasaki bombs. Conse-
medical survey-research organization, the Atomic             quently, early in 1956, a survey team, including
Bomb Casualty Commission (ABCC), was established.            members from the LASL, the Medical College of
Since that time, there bas been a comprehensive              Virginia, the Atomic Energy Commission (Division
program for documenting and analyzing the effects            of Biology and Medicine), and the ORNL, visited the
of nuclear weapons radiation on the survivors of the         ABCC in Hiroshima and Nagasaki with the objective
bombings and their offspring.                                of determiniog the feasibility of a dosimetry study.
   Duriog "Operation Teapot" at the Nevada Test              After reviewiog records and examiniog typical
Site (NTS) in 1955, the Health Physics Division of           shielding configurations, the survey group recom-
the Qak Ridge National Laboratory (ORNL), in                 mended that a dosimetry program be initiated. Due
collaboration with the Los Alamos Scientific Labo-           to the high structural uniformity of Japanese
ratory (LASL), conducted a series of experiments             dwelling-type structures, and the large number of
that provided significantly increased understanding          Survivors exposed in such buildings, emphasis was
of weapons-radiation fields. Gamma-radiation                 to be placed on persons so exposed.
dosimetry utilized tetrachloroethylene chemical
doSimeters, (2) and the neutron nux and dose distri-
butions were measured with threshold detectors.(3,4)
The dose-distance relationship, D(R), for fast neu-



                                                                       \
trons and gamma radiation was shown to be(5,6)
        G e(-R/L)
D(R) = 0 2
             R
for distances greater than about ODe relaxation                               \r
length, where Go is a function of the yield and
design of the weapon, and L is the relaxation length
for the type radiation considered. For a particular
                                                                                  \.
detonation

L=-L
    Po
     P   0

where P is the air density and Po and Lo are the
values for these factors at an air density of 1.29
                                                                                      \ \.
                                                                                                      \
g/Uter. Gamma-radiation exposure and neutron
nux and dose, both as functions of distance, are
shown for a typical detonation in Figures 1 and 2,
respectively. It was also shown that, for distances
greater than L .... 1, the neutron spectrum was
approximately constant; i.e., an equilibrium spec-                        SLANT flAME R IN HUNIJIBS at' YAROS
trum was obtained. (See Figure 2.) These data have                      GAMMA AIR DOSE        VI   SLANT RANGE
been discussed in detail by Ritchie and Hurst. (7)           Figure 1. Gamma air dose versus slant 1'8Ilp.


                                                       121
                                                                                            Digitized by   Google
   As a result of the survey group's recommenda-               the omission of thin glass and paper doors and
tions, a program was established in the Health                 windows. In addition, 120 collimation devices were
Physics Division of the ORNL, which is sponsored               constructed to permit measurement of angular dis-
by the Civil Effects Branch of the Division of Biology         tribution of the radiation field incident on a point
and Medicine, U.S.A.E.C., and is designated as                 detector in an open field. Seventy of these colli-
Ichiban.                                                       mators were for gamma-radiation measurements,
    The problem was divided into three parts: 1)               and 50 for neutron measurements. See Figures 3
documentation of the location of the survivor at the           and 4.
instant the bomb exploded; 2) establishment of air-                Data from Operation Plumbbob indicated that
dose curves; 3) shielding factors for the houses.               radiation-dose distribution in Japanese houses might
Work on the first part of the problem, undertaken              be generally related to identifiable parameters such
with the ABCC, has called for time rather than                  as house size, orientation, mutual shielding, prox-
research. The second part of the problem was                   imity of walls and windows, etc. The basic program
further subdivided into 1) determination, during                extended air-dose data and provided a descrJption of
weapons tests, of the shape of curves and 2) the
normalization of these curves to the radiation yield
of the subject weapons. From the beginning, the
problem of normalization was expected to be the
most difficult.
   A pilot study of neutron and gamma-radiation
dose distributions in Japanese houses was con-
ducted during Operation Plumbbob at the Nevada
Test Site (NTS) in 1957. A larger and more funda-
mental study of dose distributions in air was also
carried out for several weapons at this time.(8)
From materials imported from Japan, two replicas
of typical Japanese residences were constructed at
NTS, varying only from detailed specifications by



                                     LEGEND:                                              _~--WATER
                                        o Pu FLUX
                                        ~ All FLUX
                                        •   Hp FLUX
                                        ,   U    FLUX
                                        a s      FLUX
                                        , III
                                                               Figure 3. Neutron collimator.




                                                                                ,,----WATER/
      o                 10                  20
            SLANT RANGE R IN HUNDREDS OF YARDS
      NEUTRON AIR DOSE   a   FLUX VI SLANT RANGE
Figure 2. Neutron air dose aDd nux versus slant range.         Figure 4. Gamma collimator.


                                                         122
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angular distrlbution of radiation, especially for fast         and gamma-ray testing were concerned. Wood
neutrons. The greatest uncertainties in the air-dose           framing used in Japan fitted well with cement-
distribution involved the gamma radiation. See                 asbestos board substitution. Consequently, use of
Figures 5 and 6.
   Upon completion of the analysis of data from
Operation Plumbbob, a summary of all dOSimetry
information applicable to the survivors was pre-                            30-      2O·      100          00     1O·   20°       3QO

pared and transmitted to the shielding group in
ABCC. Designated T57D, this tentative dosimetry                 4O·                                                                     40°
information served as a guide for establishment of
techniques for determining dose values from the
shielding histories of the exposed individuals; it                 50-                                                                  50°
also provided an estimate of dose that supplanted
the use of distance and the correlative factor for                                                                                      60°
                                                                600
observed responses. Air-dose curves, seen in
Figures 7 and 8, were provided by York, (9) based                                                                                       70°
                                                                   70°
on all weapons data available to him. The large
uncertainties or probable errors in the curves are                 800                                                                  80°
indicated by dotted lines.                                      go-                                                                     90°
   After Operation Plumbbob, laboratory studies of
the shielding coefficients of Japanese and domestic            100°                                                                     100-
building materials were conducted. Cement-asbestos              11O-                                                                    110°
board, commercially available in large sheets, was
found to be a Suitable substitute for the clay, oyster         Figure 6. Angular distrfblltion of gamma-ray dose at
shells, and seaweed wall plaster and for the mud               1000 yards from a typical nuclear weapon of normal size.
and tile roofs of Japanese homes, as far as neutron



                                                                                                     NEUTRON AND GAMMA
                                                                                                     DOSE IN HIROSHIYA




                                                               :
                                                               & 2

                                                               ~ 10
                                                                                    FIRST COU.ISION
                                                                                    NEUTRON DOSE --~




                                                                    2




                                                                    2

                                                                   ~IL-_-L_ _~-~--~-~~~~-~.
                                                                        o     500      tOOO         1500        2000
                                                                                     HORIZONTA~   DtSTANC€ F _ GROIH) ZERO ,,.,

Figure 5.                                                      Figure 7. Dose versus horizontal distance from ground
yards.                                                         zero.


                                                         123
                                                                                                       Digitized by     Google
radiation analogs of Japanese houses for all further
field experiments were planned.
    Late in 1958 a weapons test series, Operation
Hardtack II, was conducted at NTS, and further work
was directed to the dose distributions in Japanese
houses, e.g., radiation analogs constructed of
cement-asbestos board in wood framing typical of
Japan. Emphasis was placed on determination of
the dose distributions as a function of house size,
orientation, and position relative to its neighbor.
Seven houses were constructed and, due to the
durability of the wall board and to other fortuitous
events, six could be repaired and used three times;
the seventh was used twice. One array of houses is
shown in Figure 9.
    Data available after Operation Hardtack II, (10)
made it possible to compute the neutron dose at any                                     Figure 9. Array of houses. Operation Hardtack   n.   1958.
point in a large number of typical configurations of
Japanese houses. The neutron data were generally
satisfactory, though some refinements in the angular                                    neutron shields used with the chemical dosimeters
distribution at small angles were needed. Nonethe-                                      of lithium, which was depleted in lithium-6.
less the neutron program was in an advanced stage.                                         Consequently, it was decided to make a definitive
When compared with earlier results, however, dis-                                       study of neutron- and gamma-radiation fields at
crepancies in gamma-radiation data became appar-                                        large distances from a point fission source. The
ent. These discrepancies were attributed, at the                                        ORNL Health Physics Research Reactor (HPRR)
time, to the inadvertent substitution in the thermal                                    (Figure 10) was suspended on a hoist car that was
                                                                                        mounted on a 1,527-ft-high tower at NTS (Figure 11).
                                                                                        Designated Operation BREN, the experiments were
                                                                                        conducted during the spring and early summer of
                                  NEUTRON AKJ GAIMoIA
                                   DOSE IN NAGASAKI
                                                                                        1962.(11,12) Major objectives of Operation BREN
                                                                                        included analyzation of energy, angular, and spatial
                                                                                        distributions of neutrons and gamma radiation from
                                                                                        the HPRR. A cobalt-60 source of a nominal 1,200
                                                                                        curies was substituted for the reactor upon comple-
                                                                                        tion of reactor studies. Measurements of spatial
                                                                                        distributions of dose extended to radiation analogs
                                                                                        of Japanese houses. Dose distributions were deter-
                                                                                        mined as a function of house Size, orientation, and
                                                                                        position relative to other houses. All measurements
                                                                                        were made with sensitive laboratory-type instru-
                                                                                        ments and only spectral measurements for gamma
                                                                                        rays from the fission source were considered to be
                                                                                        marginal. With maximum reactor power (for con-
                                                                                        tinuous operation) and the most sensitive instru-
                                                                                        ments, it appeared unlikely that the desired accuracy
                                                                                        could be attained. Although considerable information
                                                                                        concerning the spectrum was obtained, the number
                                                                                        and distance range of these measurements were
                                                                                        limited.
                                                                                            However, all other phases were highly success-
  !)
                                                                                        ful. Gamma-dose distributions in the houses were
                                                                                        similar to those found during Operation Hardtack,
                                                                                        but they were consistent and reproducible. A small
  2
                                                                                        Japanese house and a transite house of identical
 ~tL-      __- L____L -__     ~   ____    ~~~         ____     ~      __   ~
                                                                                        size were found to yield identical distributions.
       o     ~      tOOO       t~        2000       2500       3000        3500
                                                                                        These data, combined with those from later labora-
                  HORIZONTAL DISTANCE , _ OIIOUIiD ZERO (,-01.
Figure 8. Dose versus horizontal distance from ground                                   tory experiments, confirmed the hypothesis that
zero.                                                                                   neutron interactions with the major house elements

                                                                                  124

                                                                                                                    Digitized by   Google
and build-up from scattering of the high-energy                 shielding hiStory of the case in question. For gamma
gamma rays (from neutron interactions in the air)               radiation,
resulted in the observed gamma distributions. The
net attenuation of gamma radiation was found to be              Shielded Dose A A -Gl A -~ A G
small; frequenUy there was a net increase in gamma-               Air Dose = 1 + 2e   + Se + 4 3
radiation dose at points inside the house.                                     + A5G4 + AsG5 + A7 G6
   In addition to improved shielding information for
houses, Significant contributions were made to the              is used; at the 50 per cent confidence level, the
description and understanding of radiation fields               shielding factor is accurate to within less than
from nuclear weapons and other intense radiation
sources which occur at great distances. Of special
Significance are data on the effect of air-ground
interfaces.(13,14)
   By early 1964, final equations that technicians
can use were developed for computing shielding
factors for Japanese houses. For neutrons, the
expreSSion,

Shielded Dose    -G1
  Air Dose = Ale     + A2~ + A3 GS + A4G4
                              -G6           -G7
               + A5G5 + A6e         + A7e         +ASGS+A9,
yields a shielding factor accurate to within : 6 per
cent at the 50 per cent confidence level. The con-
stants Ai have all been determined. Geometric
factors 0i are physical dimensions taken from the




Figure 10. ORNL health physics research reactor for
Operation BREN.                                                 Figure 11. Tower for Operation BREN.


                                                          125

                                                                                        Digitized by   Google
about 6 per cent. The constants Ai and the geo-                and Nagasaki weapons must yet be accomplished; at
metrical parameters Gi are different for each of               least one calculational and two experimeDtal studies
these equations. Confidence limits are based on a              are underway, and success for at least two of these
comparison with approximately 600 datum points                 studies is expected soon.
from weapons tests and Operation BREN.
   The remaining problem is the normalization of
air-dose distributions to.the radiation yield of the
                                                               References
Hiroshima and Nagasaki bombs. An analysis of
early post-bombing studies of neutron activation                1. CaDnan, R.K., News Repo~ NattoD&l Academy of
by Japanese scientists yielded no useful information;              Sciences-NatioD&l Research Council, ,!!, No.1 (1962).
apparenUy samples were collected without sufficient
                                                                2. S1go1off, S.C., Nucleonics, !!, No. 10, 54 (1956).
regard for their precise location at the time of deto-
natioD. Later studies of steel samples were llWe                3. Hurst, G.S. et al., Review Scientific Instruments. 27,
better. In early 1963, a group at the Japanese                     153 (1956).
National Institute of Radiological Sciences headed              4. Reinhardt,P.W. and F.J. Davis, Health Physics,       b
by T. Hashizumi commenced an activation study in                   169 (1958).
collaboration with the Ichllian doSimetry group. In             5. S. Glasstone (ed.), The Effects of Nuclear Weapons,
these studies only samples of steel that were                      U.S. Atomic Energy COmmission (1962).
several centimeters deep in concrete at the tops
of buildings and had not been disturbed are being               6. Harris, P.S. !!.!:!.-' ITR-1167 (Classified), U.S. Atomic
                                                                   Energy Commission (1955).
analyzed. The HPRR is being used in calibration
studies. Similar studies are concerned with                     7. RItchie, R.H. and G.s. Burst, Health Physics,   b 390
                                                                   (1959).
radiation-induced thermoluminescence in Japanese
roof tiles.(l5)                                                 8. Burst, G.S. !!. al., WT-1504 (Classified), U.s. Atomic
   Ideally, the method of normalization would be to                Energy Commission (1958).
refire exact duplicates of the Japanese weapons                 9. York, E.N., in communication from II. Morgan, Armed
under like environmental conditions. However, as                   Forces ~ial Weapons Center, to G.s. Burst, oak
testing in the atmosphere is unlikely, it may be                   RIdge NattoD&l Laboratory, ORNL CF-57-11-144
desirable to make radiation leakage measurements                   (1957).
from underground tests. In addition, it is possible            10. Auxier, J.A., J.S. Cheka, and F.W. Sanders, WT-1725
to calculate the yield of weapons, and a collaborative             (Classified), U.s. Atomic Energy Commission (1961).
program between LASL and ORNL is directed toward
                                                               11. Auxier, J.A., F.W. Sanders, F.F. Haywood, J.H.
making these calculations. However, their accuracy                 Tborngate. and J.s. Cheka, Technical Concept -
is probably not better than about 30 to 50 per cent.               Operation BREN, USAEC Report CEX-62.01 (1962).
All these methods are being explored, as each is
independently useful for other problems.                       12. Sanders, F.W., F.F: Haywood, M.I. Lundin, L.W.
                                                                   GUIey, J.S. Cheka, and D.R. Ward, Operation Plan and
   In summary, shielding factors for Japanese                      Hazards Report - Oeration BREN, USAEC Report
dwellings can now be computed and simple empiri-                   CEX-62.02 (1962).
cal formulae are being generated to simplify these
computations. Spatial and angular distributions of             13. Auxier, J.A., F.F. Haywood, and L.W. GWey, General
                                                                   Correlative Studies - Operation BREN, USAEC Report
dose are well defined, and spectral distributions are              CEX-62.03 (1963).
crudely known. It now appears feasible, with some
further study, to calculate dose distributions in              14. Haywood, F.F., ~tial Dose Distribution in AIr-Qver-
many of the more heavily shielded configurations.                  GroUDd Geometry, Health Phys., 10 (in press).
Normalization of air-dose curves to the Hiroshima              15. Higash1mura, T. et al., Science, 139, 1284 (1963).




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FIRE-SAFE SHELTER DESIGN

  Gordon Shorter, Chairman




                             Digitized by   Google
                                  FIRE-SAFE SHELTER DESIGN

                                            John G. Degenkol b
                                          Los Angeles, Cal ifornia

Introduction                                                       Last, and least effective, were private cellar
                                                               shelters. It should be remembered that German
The specific objective of a shelter is to provide a            dwellings in buUt-up areas were four or five stories
place of protection: a refuge. After seeing some               high and bad masonry walls, wood floors, wood roof
existing shelters and proposals for new ones, there            and cellings, at best, of a brick arch type. This
is serious doubt as to the degree to which they will           construction is quite different from that prevalent
attain that objective. They may be structurally safe,          in residential areas in the United States. It may be
but hardly fire-safe.                                          well to point out that there is even a difference in
                                                               basic attitudes toward fire prevention. Europ88n
                                                               countries tend to fix responsibility, moral and fi-
Past Shelter Experience                                        nancial, upon the owner of the property where an un-
                                                               friendly fire originates. In the United States this is
Perhaps a review of the history of air raid shelters           not so. Rather, there is a feeling of compassion and
would be useful. During World War D shelters were              sympathy for the one whose property was destroyed
designed to provide protection against high-explosive          even though it may have been the result of his own
and incendiary bombs. They were designed to pro-               neglect or carelessness.
vide protection for approximately three to ten hours               When Hamburg was bombed, it was a city pre-
at a time. Today, since radiation protection is also           pared for attack as a result of previous raids and
required, design should be based on an anticipated             fire-fighting experiences. (3) Even so, the city was
continued use of as much as two weeks,(1) During               overwhelmed by the immensity of the attack, the
that period the shelter will have to provide all that          fire, and the devastation. The fire reached its
is necessary for survival, including air, heat and             greatest height io.Jess than one hour, possibly in
moisture removal, water, food, sleeping and sani-              only 20 minutes. {'
tary facUities, emergency power sources, medical                   Despite the fact that there was no threat of radio-
service, etc. But, probably above all, it should be            active fallout, there was need for interconnection
fire-safe.                                                     of shelters when they were of less formidable con-
   The safest shelter thus far designed is the bunker          struction than bunkers. Emergency exits and an
type. Of heavy reinforced concrete construction,               evacuation plan were needed. Evacuation had to be
well compartmented and with large capacity and                 done at precisely the right moment. Emergency exits
complete living facUities, it was designed to with-            had to terminate a reasonable distance from the shel-
stand direct hits by high-explosive bombs.                     ter to assure that one would at least be clear of pUed
   Next safest were tunnel shelters and trench shel-           debris and superheated rubble. WhUe this could be
ters, though comparatively few tunnel shelters were            done by interconnection of shelters, the matter of
built. They were made up of shafts dug into a bill;            properly separation of shelters was important. A
with possibly 20 to 50 ft of the bill remaining above          wall breached or a door opened too soon could allow
the shelter. They had reinforced concrete ceilings,            admission of toxic gases and searing heat, and could
walls, and floors; and were well outfitted with living         result in the death of all occupants.
facilities. (2) Trench shelters were partly below                 Data on deaths occurring in shelters during World
ground and usually bad a 1-3-ft-tbick concrete slab            War D sbow that the development and presence of
roof with dirt pUed on top. Such shelters bad sparse           carbon monoxide and carbon dioxide was a major
accommodations since they were usually long,                   problem. It remains with us today. Another problem
narrow (6 ft wide, 7 ft high) structures.                      anticipated is excessive heat within the shelter.
   Next were communal cellar shelters, which were              According to the Hamburg Police President's report,
converted for shelter purposes. These were nor-                "The heat round these buUdings was more than human
mally in business districts and were seldom found              beings could stand. Nevertheless, in no instance
in outlying residential neighborhoods.                         either in bunkers or surface shelters did shelterees


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come to any harm from the heat, nor had they to               during an emergency period of two weeks is 35 u
leave the buildings prematurely." This statement              effective temperature. The maximum endurable tem-
may contradict itself when consideration is given to          perature during an emergency of at least two weeks
the appearances of those found dead in the shelters,          is 85 0 effective temperature. Each person requires
even though a vast number of persons survived.                approximately three cubic feet of fresh air per min-
Recent information, which will be discussed later,            ute to insure safe levels of oxygen and carbon dioxide.
also belies the accuracy of the above statement as            Incoming air should be filtered through an indicating
applied to today's problem.                                   carbon dioxide absorbent. If the changing color of
   Complete research projects provide us with some            the absorbent indicates the presence of carbon di-
basis for establishing criteria that may be used in           oxide, the intake system should be shut down; if an
designing safe shelters. However, so that there are           internal recirculation system is present, it should
no misunderstandings, we must establish our area              be used. A sensor-alarm should be used to detect
of concern. It is understood that a 20-mt bomb will           dangerous amounts of carbon dioxide if outside air
affect an area of 800 square miles. Within this area,         is to be introduced into the shelter.
blast pressure is expected to be no lower than 2 psi              A method of maintaining carbon dioxide concen-
or an overpressure of 288 Ibs per sq ft. We must be           tration in the neighborhood of 1 per cent, and pref-
concerned with people within this area and hope that          erably less" is needed if there is to be prolonged
most will be in safe shelters. From the tenor of              exposure'<6, The Mechanics Research Division of
some research projects, it seems that protection is           the General American Transportation Corporation
envisioned only for persons outside this basic area.          did research on environmental control systems for
                                                              closed shelters(7) assuming a carbon-dioxide produc-
                                                              tion rate of 0.85 cu ft per person. It was concluded
Criteria for Fire-Safe Shelters                               that at least 8 Ibs of Baralyme should be used for
                                                              each shelter occupant for each 24-hour period. The
There are several basic requirements that must be             cost per person per 24-hour period would range from
met if a fire-safe shelter is to be constructed.              $4.38 to $7.20. Baralyme proved to be the best of
    Design must be predicated upon a prospective              three solid absorbents: lithium hydroxide (anhydrous),
two-week period of occupancy.                                 Baralyme, and soda lime.
    Construction must be such that the shelter would              "The most probable reason that would compel
not collapse even if the remainder of the building            closed operation of a shelter and consequent use of
fell upon it.                                                 an internal life support system is the presence of hot,
    Walls must be of sufficient thickness or low heat         toxic gases resulting from proximate fires."(7)
conductivity to maintain low temperatures even after              Clearly, oxygen will have to be provided for shel-
extreme exposure.                                             ters. Oxygen content of the air should ideally be
    The shelter must be made gas-tight or have a              maintained at 20 per cent; however, as little as 12
slight positive air pressure. This means that many,           per cent will sustain human life. Assuming oxy....sen
if not most, of our existing shelters are in need of          consumption per person at one cu ft per hr,(5-7} it
correction. Ordinary fire doors with conventional             can be provided at a cost of about $4.70 per person
clearances are not gas-tight. A further disadvantage          for smaller shelters (100-man) or at about $4.15 per
of such fire doors is that those of hollow metal con-         person in larger shelters (l,OOO-man) per 24-hour
struction transmit heat very readily and to a high            closure period. The safest, most reliable, easiest
degree.                                                       handled method of prOviding oxygen would probably
    An adequate air-conditioning system will probably         be by means of either chlorate candles or high pres-
be needed-particularly for major shelters. Proper             sure cylinders: In shelters for less than five persons,
precautions must be taken so that radioactive fallout         chlorate candles are recommended. The study pro-
will not be introduced into the shelter. Emergency            gram indicated that present equipment for dispens-
power will have to be provided to keep air-condition-         ing oxygen from large, high-pressure storage bottles
ing and certain other facilities operating. Natural           is both too expensive and too complicated for use
ventilation openings may be of benefit if they extend         except by trained personnel who should be found in
to a location from which safe air can be brought into         larger shelters.
the shelter. This means that inlets will have to be               The development or build-up of carbon monoxide
clear of burning debris, carbon monoxide-loaded air,          must be controlled. In World War n it was estab-
or air filled with smoke, obnoxious odors, and                lished that carbon monoxide was one of the principal
radioactivity .                                               killers of shelter inhabitants. It is probably still the
    One Office of Civil Defense Study(5) determined           greatest single hazard. If there is 0.16 per cent of
that the optimum temperature at 60 per cent relative          carbon monoxide in inhaled air, headache, dizziness,
humidity is 68-72 0 F for healthy people at rest and          and nausea will develop in approximately 20 minutes.
properly clothed. The lowest endurable temperature             Collapse, unconsciousness and possible death will


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result within two bours.(5) The U.S. Navy found it             locked so that access will not be possible during the
necessary to develop atmosphere-control equipment              time when portable ext1ngu1shers might be effective.
for submarines. (8) Hydrogen from battery recharg-            Furthermore, portable extinguishers, unless of the
ing was burned off and, simultaneously, carbon mon-           proper type, will not work for a variety of materials
oxide was removed. This equipment, together with              nor wUl they handle fires of considerable SiZe.
carbon beds, solved the carbon-monoxide problem.                  The blast follows soon after the thermal pulse.
    Moisture control is a problem in that high humid-         At that time public-utility facilities would be de-
ity creates unbearable living conditions. It is im-           stroyed, gas mains ruptured, electrical and water
portant from the standpoint of morale, comfort, and           lines broken, and arcing would occur. As a result,
health. The use of previously mentioned equipment             buildings would be made vulnerable to fire.
in larger shelters is probably the best answer to                 A 20-mt bomb would provide apprOximately a 2-
this problem. In smaller shelters the use of desic-           psi overpressure at a distance of 80,000 feet from
cants is probably beat. Calcium chloride would cost           ground zero. This results in an area of approxi-
about $.32 per person per 24-hour period. Despite             mately 800 square miles within which buildings
high capacity and low cost it has the disadvantage            would be damaged, e.g., windows would be blown in
that, as moisture is absorbed, a solution is formed,          completely, doors blown loose from their hinges,
possibly creating a disposal problem,(8) Sodium               beams cracked, and building deflection would occur.
hydroxide or potasSium hydroxide would cost some-             It would be quite likely that gas, electriC, and water
what more. They have no advantage over calcium                lines would be broken and that fires would develop.
chloride save that they also absorb carbon dioxide.           We are concerned for the lives and safety from fire
   Odor removal is another consideration. Atmos-              of those within that extensive area.
phere-control equipment will help in this area.                   If sufficient warning were given, the public would,
   Sanitary facilities, food preparation, sleeping            hopefully, be in shelters and thus not be available to
facilities, medical aid, and emergency power are              extinguish the myriad of small incipient fires scat-
other factors that must be considered if a shelter            tered throughout the area. Following the shock wave,
is to be occupied for a number of days.                       but before the arrival of radioactive fallout, there
                                                              might be a period in which self-help would be pos-
                                                              sible. However, due to major damage, it is unlikely
Comments Concerning an Attack                                 that the immediate blast area would be such that its
                                                              built-in or pre-arranged fire-fighting facilities
It seems that some researchers feel that an attack            would be usable. Fire suppression and rescue groups
would come when buildingB are completely occupied             might have to come in from surrounding areas where
and that incipient fires wUl all be controllable within       there would be lesser damage.
a few minutes. (9) In disagreement, it may be pointed             People within the central damage area would have
out that, obviously, all buildings cannot be completely       to be in shelters and would have to plan on remaining
occupied at the same time. Since it is not known              for a considerable number of days. Because of radio-
when an attack might come, people cannot be con-              active fallout they would not be able to fight fires in
stantly ready to perform self-help. The researcher'S          the buildings above the shelter.
approach seems to overlook the fact that ours is a
heterogeneous community with varied types of build-
ing construction, occupancy, economy, and use. There          Comments Concerning Relative Fire Vulnerability
is considerable intermixing of residential, commer-
cial, and industrial buildingB.                               A survey established three supposed levels of build-
   In the event of attack, it seems reasonable to             ing fire performance to identify the relative fire
assume that a multiplicity of fires will be erupting          vulnerability of shelter buildings.
over an extensive area. Some will be in homes,                   The first level, "fire-limiting buildings," includes
some in multi-family buildings such as apartments             those buildings in which fire will be confined to the
or hotels, and others in industrial plants where fires        floor of origin even without suppression activity.
can develop with extreme rapidity due to the nature              The second level, "suppression-dependent build-
of equipment and inventories. The Hamburg fires               ings," includes those buildings in which the structure
attest to the fact that fires can develop to conflagra-       cannot satisfactorily resist a spreading fire, but
tion proportions within 20 to 60 minutes. It is not at        where it is reasonable to assume that all inCipient
all unlikely, and in fact quite probable, that fires will     fires can be located and extinguished before they
occur Simultaneously in more than one part of a               present a danger to shelter occupants.
building. People cannot be in two places at once.                The third level, "untenable buildings," includes
Thus, while one fire is being fought, another may             those buildings in which incipient fires can be ex-
develop unchecked. When persons are absent from               pected to develop rapidly to a magnitude such that
a room or building, the premises will probably be             they cannot be controlled through use of portable


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equipment by the occupants.                                    poses, for clean-up, or for preparation, as was the
    It is my contention that there are practically no          case in Hamburg.
buildings of the "fire-limiting" type. Present-day                 As one who is more experienced in practical
building construction, with its extensive use of glass,        matters and the interplay of one factor with another,
inadequate protection of vertical shafts, dependence           it appears that much research work now being done is
on sprinklers (which would no longer be operable),             based on questionable assumptions. The researcher
and the combustibility of contents, makes the possi-           has oversimplified the problem and tried to work
bility of any established fire being confined to the           with only one factor while ignoring all others. For
floor of origin quite remote. An excellent example             example, much work has been done with respect to
is a Dallas, Texas, department store fire that oc-             fire-spread danger from radiated heat, without
curred shortly before Christmas, 1964. It actually             simultaneously conSidering convection, which is the
makes little difference whether this type of building          real problem in fire-spread. Fire-spread researcb
exists or not. This is because, as a building burns,           cannot be limited to a study of radiation. Isolation of
the heat rises and the downward spread is limited to           factors or problems is justified only to a limited
that resulting from collapse. As long as the shelter           degree. The entire problem-not a simple facet-must
stands up, damage to the building above is compara-            be considered. Another example of questionable
tively immaterial.                                             assumptions is a research study that continues to
    It is my contention that in the event of nuclear           credit automatic fire sprinklers as a means of pro-
attack where blast and fire are factors, shelterees            tection of buildings after nuclear attack.(9) It seems
would not be able to move through the building in              most apparent that sprinklers would be ineffectual
time to control or extinguish all inCipient fires be-          because there would be no water supply. The system
fore it became necessary for them to return to the             will be ineffectual even with its own conventional
shelter to avoid radioactive fallout.                          elevated supply tank (if it survives the blast), be-
    Persons would have to return to a completely               cause it was designed to handle only one or two fires
sealed, highly fire- resistant shelter designed to             at a time-not a multiplicity of fires throughout the
provide a refuge for 10 to 14 days. The shelter                structure.
would need its own air supply, and a means of re-                  The complexity of the problem of fires would
moving carbon dioxide, mOisture, and surplus heat.             exist over an 800-square-mile area. Beyond that
It would need to be equipped with adequate food and            area the problem would be more simplified-com-
water, sanitary facilities, self-contained communi-            parable to a typical peace-time conflagration. A
cations, fire equipment for fires that might develop           solution would be enormously expensive if it were
within the shelter, etc. It would require alternate,           put into effect. What would have to be done is clear.
thoroughly protected escape routes to remote                       The situation may be localized, but in some areas
locations.                                                     shelters have been designated only on the basis of
    It has been conSidered a fundamental fact that a           structural qualities. Fire-safety aspects have not
shelter will have to be located at the very lowest             been considered. In fact, in one case, the fire depart-
point in a building-most likely a basement or sub-             ment went to court to have a hotel closed as an innate
basement. But conSidering the height of high-rise              fire hazard. The strongest counter-argument was
buildings, narrowness of stairs, inadequacy of                 that one of the major shelters for the downtown area
elevators, etc., it is quite unlikely that all occupants       was located in the basement. Among other factors,
of a building would reach a basement shelter. To be            the basement in question had open stairways to the
fire-safe, it would have be structurally so sound that,        main-floor lobby, wooden partitions, a boiler room
even though the building were completely burned out,           unseparated from the remainder of the building, no
the shelter would not collapse from the weight of              sprinklers, and extensive storage of combustibles.
falling debris. It would have to be so heat- resistant             A recent edition of a magazine that reports on
that the extensive burning debris would not be trans-           municipal problems referred to a civil-defense" pro-
mitted into the shelter. With such a structure we               gram that is apparently being implemented in eight
need not be overly concerned with the structure                areas of the United States. Newly constructed build-
above or with neighboring structures.                          ings were to incorporate shelters in their design.
Conclusions                                                    When a check was made of one of these so-called
                                                               shelters, it was found that virtually nothing had been
It is my opinion that events of World War 0, such as           done to make it qualify as a shelter other than making
Hamburg and Hiroshima, are but a prelude. Judging              it structurally acceptable and stocking it with water
from what has been written and said, we can expect             and food. Water, gas, sewage, compressed gases,
a nuclear attack to be at least as destructive, if not         and other pipe lines for servicing the building were
much more so, and with added complications of                  exposed and vulnerable. There were no explosion-
radioactive fallout. The hours or days between raids           proof or gas-tight doors, no independent air supply.
could not be used for fire-fighting, for rescue pur-           It was, in other words, a pseudo-shelter.


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   It is my observation that our present shelters are                   J.n. Jeff, Environmental Control Systems for Closed
not designed to be fire-safe and fall short of the term                 Underground Shelters. OCD-OS-62-56. Prepared by
"shelter" where nuclear attack Is concerned.                            MRD Division of General AmerioaD. Transportation
                                                                        Corp., April 1963.
                                                                   6.   Schaefer, K.E., A Concept of Triple Tolera.nce Baaed
References                                                              on Chronic C02 Toxicity Studies.
1.   Yaglou, C.P., Environmental Engineering in Protective         7.   Charan1an. T.R. and J.D. Jeff, Experimental Evalua-
     Shelters. National Academy of Sciences Protective                  tion of Environmental Control Systems for Closed
     structures Symposium, 1960.                                        Shelters. OCD-PS-64-6 of July 1964. MRD Division
                                                                        of General American Transportation Corp., July 1964.
2.   Earp, Kathleen F., Deaths from Fire in Large Scale
     Air Attack.                                                   8.   Gates, A.S., Submarine Atmosphere Control Problems
                                                                        aDd Methods. Reported in Proceedings-Environmental
3.   Report by the Police President on the Large Scale
                                                                        Engineering in Protective Structures, National
     Balds on Bamburg.
                                                                        Research Counoll, 1960.
4.   Broido, A., SUrviving Fire Effects of Nuclear
                                                                   9.   Smith, J.B., E.W. Cousins, and R.M. Newman, Fire
     Detonations.
                                                                        Hazard to Fallout Shelter Occupants: A Class1fioation
5.   Cbaran1an, T.R., A.J. Gluckert, R.G. Barne, and                    Guide, April 1964.




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                                FIREPROOF SHEL TERS WITH
                              SECURED VENTILATING SYSTEMS

                                              Hermann Leutz
                                Federal Ministry for Housing, Urbanization,
                                           and Land Planning
                                       Federal Republ ic of Germany


Tbe decision as to the degree of usefulness of sbelter      German specifications require that the sbelter room
rooms depends, among otber things, on wbetber or            enclosures and air-locks be bigbly fire- resistant as
not a climate in wbicb human beings can endure is           protection against area conflagrations. Closures of
provided throughout their stay in the shelter without       air locks and the emergency exits must be fire-
any impairment to their health. The most decisive           resistant. In basement shelters 0.6 meter of
factors in this case are the ambient temperature of         concrete is required for the protective shell.
sbelter-room air, of the interior surfaces, and the             In addition to natural and protective ventila-
condition of shelter-room air combined with mix-            tion, rooms of reinforced sbelters are required to
tures of water vapor, carbon dioxide, poisonous and         have equipment for normal ventilation with a capacity
odorous substances.                                         of at least 150 liters per person per minute or 300
    Specifications for German home shelters require         liters per min per square meter of net floor areas.
that ceilings, outer walls, and air-locks of the basic      Tbe combined ducting for both normal and protective
fallout shelters be very fire-resistant to protect          ventilation must be protected from air blast by an
against individual fires resulting from collapse of         automatic closure between the intake and the sand-
buildings. Sbelter doors must also be fire-resistant.       filter room.
In the case of shelters located in basements, 0.3
meter of concrete is required for tbe protective            Fire Characteristics of Protective Slabs
shell.                                                      Subject to Large-Scale Fires
    There are three requirements for basic sbelter
ventilating systems. First, in order to make a longer       Fire effects sbould be studied in particular to obtain
period of occupancy possible, shelter rooms must be         an over-all picture of the ambient condition of shel-
provided with natural ventilation as well as equip-         ter rooms.
ment for protective ventilation which assure bearable           In considering these problems, we begin with the
conditions. Second, natural ventilation should permit       assumption that a sbelter area wbicb offers a definite
changing of air ten times per hour; this can be             degree of protection is built in the basement of a
achieved by opening the entrance door and clOSing           multistory building. Sbould a catastropbe cause the
lids to the filtering area. And third, sand filter          building above to collapse, combustible parts could
ventilating equipment should be constructed so that         ignite, burn or smolder. Considerable but undeter-
external air can be sucked in, processed so that it         mined amounts of energy would be released in the
is breathable, and then forced out. Sand filters must       debris, wbicb places a particular strain on ceilings
be constructed as beat cushions (arithmetic value:          of the sbelter room located below. Flames from
external temperature 200 u C for five hours) and must       burning surfaces may coalesce in heavily built-up
prevent the penetration of radioactive dust, as well        areas. Tbe temperature in the debris and the dura-
as cbemical and biological agents. Tbe equipment            tion of the fire's effects will be greater in this case
must be able to provide at least 30 liters of air per       than in that of single fires. It is theoretically diffi-
person per min, or 60 liters of air per min per sq Pl-      cult to determine tbe magnitude and duration of tem-
of net floor area. In protective ventilation, provision     peratures in the refuse dump and on the ceiling of
must be made for up to eigbt bours of uninterrupted         the sbelter area. Too wide fluctuations are possible
operation per week. An overpressure of from 15 to           in tbe combustible content of the debris and the com-
20 mm of Hg must be available inside the sbelter.           bustion rate of the fire. Even the type of ignition
    In the case of reinforced sbelter S3 (blast-            must be considered. However, based on the assump-
resistant shelters of about 45-psi overpressures),          tion that there are 30 kilograms of wood per sq m of


                                                      134
                                                                                     Digitized by   Google
floor area, temperatures ranging from 400° - 700°C                        sides of the slabs. This is due to the fact that the
were found to be possible.                                                mathematical model assumes an infinite homogeneous
   It can be assumed, from both the experiences of                        slab with sections equal in thickness to the slab
World War n and fire experts, that a temperature of                       thicknesses. The temperature in the shelter area
from 300 to 400"'C exists for a period of about five                      should be approximately the same as the temperature
or six hours on a shelter roof slab. After the limited                    of the underside of the slab.
amount of combustible materials present in modern                             It is likewise shown that the critical temperature
homes has burned, the temperature gradually                               for humans (50°C) is reached within two or three
lessens. In this case we have a situation in which                        hours in the case of a reinforced concrete slab 20
hot fire gases flow upward at such speed that cold                        cm thick. Such a slab should be consistent with that
air is immediately sucked under them. Although                            expected for normal basement ceilings when a floor
fire-gas temperatures of over 1,2000C can occur                           made of concrete or similar material is added.
when fires last for over five to six hours, the as-                           For a reinforced concrete slab 30 cm thick, such
sumption of a temperature of 400°C on the roof slab                       as that used in basic shelter construction, the criti-
is sufficient for theoretical purposes.                                   cal temperature is reached within five to seven hours.
   Experiments have been carried out on the heat                              Results are much more satisfactory for slabs
permeability of reinforced concrete slabs of various                      40 cm and 60 cm thick, as is indicated in the diagram.
thicknesses for temperatures between 400 and                                  An accurate investigation is required in order to
1,0000C. Results are to be taken only as approxi-                         ascertain whether a 4O-cm slab should be considered
mate evaluations since experiments had to be carried                      adequate for reinforced (83) shelters.
out based on idealized assumptions.                                           Large-scale investigations have been proposed to
    Figure 2 shows the heat conductivity of various                       obtain more accurate conclUSions concerning tem-
slab thicknesses. The variables are slab thickness,                       peratures and duration occurring in burning debris.
time, and actual temperature. Temperatures ob-                                Under like conditions, a 40-cm slab will reach
tained in this manner give, to some extent, informa-                      the critical temperature in a period approximately
tion concerning temperature conditions on the under-                      four times as long as for a 20-cm slab; for a 60-cm




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Figure L The Hamburg fire    of July 27-28.1943.

                                                                    135
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slab about 15 times as long.                                                                                   dangers. When designing ventilating systems, the
   It must be pointed out here that heat-transmission                                                          entire range of internal dangers must be considered.
times can be greatly lengthened in the case of thinner                                                         These are the dangers which develop as a result of
slabs by improvements in the form of insulation be-                                                            crowding many persons in an area deprived of fresh
tween the shelter roof and the first-floor slab.                                                               air for long periods of time.
   Finally, it should be pointed out that blast closures                                                          It can be said that external dangers determine the
should be sealed against hot-air infiltration.                                                                 design of ventilating systems, while internal dangers
                                                                                                               determine equipment size requirements. External
Requirements for Shelter-Ventilating Equipment                                                                 dangers determine the design of the filter system;
                                                                                                               internal dangers determine the deSign of the supply
Shelter-ventilation equipment must provide protec-                                                             system.
tion against external dangers. The task of ventilating                                                            Oxygen intake, carbon dioxide release, heat pro-
equipment is, however, not limited to these external                                                           duction, and the release of water vapor can be esti-
                                                                                                               mated accurately enough for the design of reliable
                                                                                                               ventilating systems.
                                                                                                                  Table 1 shows average figures which are the
                  /'--Fii..o.m--.. . . .
                                                                                                               result of a large number of shelter investigations
  1200
              {             _T~'\                                                                              concerning heat, oxygen, and carbon dioxide exchange
~ooo          I                 (F~l         \
                                                                                                               between humans and surroundlng air.
ireoo         ,
              I
              ,
                                                 \
                                                     \
                                                         \                                                        In determining the air supply rate it is necessary
~eoo I        I                                          \
                                                             \                                                 to ascertain which of the above figures influence
~400
     ,                 PIobcIbIe T_ _ 01 EapoMd. />.                                                           shelter habitability most significantly. An essential
              I                                                  ~.,
                                                                                                               factor is the carbon dioxide content of the shelter
...200        ,
              I                                                  " ,            ~                              air during the stay. The effects of various percent-
          I       . . . . . - of ~ F«e 01 CeIIftg Slab-~"'_
                                                                                                               ages of carbon diOxide on shelterees are shown in
                     2345618.                                                          12   13      14
                       TIoIE IN HOURS
                                                                                                               the figures given below:
                                                                              Qlm Slab ("""'.26.5
                                                                               at_33 .....1
                                                                                                                 Up to 2 .5%      No effects
Figure 1a. Temperatures of the name. and exposed and
unexposed faces of ceiling slab of reinforced concrete.                                                                3   %      Somewhat increased rate of
thickness 0.3 m and 0.6 m.                                                                                                        breathing



  T                                                              T    = Temperature an Underside of Slab
COC J                                                            To   • Temperature Difference between HI;her Effective Temperature and Oullet Temperature (20·C)
                                                                 d    = Slab Thickness
  75                                                              t   = Time In Hours
                                                                  a   = Coefficient of Conductivity (here, 0.0025)




         0.25                                                          1.00


                                                                                                                                                     tCh J
Figure 2. Heat conductivity of various                            ~cknesses            of reinforced-concrete slabs.

                                                                                                         136
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                      TABLE 1                                       An essential factor in determining the air supply
                                                                 rate in shelters is heat and water vapor release by
  Buman ExcbaDge of Beat, Oxygen, and Carbon Dioxide             the occupants. It should be added that an air intake
              with tbe SurroUDding Air                           rate of 30 liters/person/min. does not suffice for
                                                                 carrying away excess heat to the outside air. Com-
Beat Emission       Exchange             Exchange During
 at 22.5°C         While Sleeping        Normal Periods
                                                                 putations and investigations indicate that massive
                                             of Quiet            concrete slabs, such as shelter ceilings, walls and
                                                                 floors, contribute greatly to solving this problem.
Dry                62 kcal/hr            72 kcal/hr              This contribution is baSed on their great heat stor-
Humid              25 kcal/hr            3Okcal/hr               age capacity and good degree of conductivity which
 Total             87kcal/hr            102 kcal/hr              comes as a result of reinforcement.
Water vapor                                                         In the case of protective ventilation, uninterrupted
 emission          42 g/hr               50 g/hr                 operation of up to 24 hours should be possible when
CO2 exhaled        0.2 liters/min        0.3 liters/min
                                                                 needed. The protective ventilation system can be in
02 iDhaled         0.24 literS/min       0.36 literS/min
                                                                 continuous operation for the entire period during
                                                                 which outside air is unbreathable because of the
                                                                 presence of radioactive fallout, overheating, con-
                                                                 taminants, etc. Eight hours after deposition begins
                                                                 there should be no serious contamination in the air.
        4     %    Minor discomforts such as                        Ground combat substances, such as mustard gas,
                   headaches, buzzing in the ears,               do not evaporate within eight hours. It is, however,
                   and palpitations of the heart                 probable that the majority of such substances will
         5.5%      Considerable increase in rate of              fade to such a degree that they are no longer danger-
                   breathing                                     ous. Dangerous outside air temperatures are also
                                                                 not expected eight hours following area conflagra-
   about 8.5%      Unconsciousness                               tions and firestorms. If necessary, ventilation could
   above 10.5%     Death                                         be shut off for several hours.
                                                                    In .the case of high-grade shelters, proviSions
    From the above figures it follows that during                have been made for normal as well as natural ventila-
normal conditions maximum CO2 content of about                   tion systems, in order to provide breathable air
2 per cent is indicated, while during time of danger             throughout the necessary shelter occupancy.
the limit is about 5 per cent. Shelters would have to               With this type of ventilation, use of special filters
be evacuated when CO2 content reached 7.5 per cent.              with high resistance to flow is not necessary. Air
   In addition to the amount of CO2 exhaled, an im-              supply rates which are to be circulated throughout
portant cause for the increase in carbon dioxide con-            the structure can therefore be increased. German
tent is the amount of air space available per person.            specifications therefore prescribe an air flow of
If we assume that the normal amount of CO2 exhaled               150 liters/person/min or 300 liters/min/m2 of
in shelters is 0.3 liters per person per minute, and             usable ground surface. This corresponds to the five-
make allowances for per person air space availa-                 fold increase in the protective ventilation air flow.
bility, we obtain the following maximum hours of                 These air supply rates are sufficient to considerably
occupancy with ~ at 5 per cent and without                       improve conditions of occupancy.
ventilation:
Air space per                        Maximum hours of
   person                               occupancy                Protective Measures Against External Dangers
                                     about 2.5 hours
                                                                 Shelters should offer protection against the effects
                                     about 5 hours               of both atomic and conventional weapons. This in-
                                                                 cludes protection against initial shock waves, high
                                     about 7.5 hours
                                                                 temperatures, atomic radiation, and bacteriological
   In especially dangerous situations, for instance              contamination or chemical poisoning of the outSide
carbon monoxide in the outside air, it would be pos-             air. Thus, the construction of the ventilating system,
sible to hermetically seal the shelter from outside              above all the connections with outside air, must be
air for several hours.                                           arranged such that provision is made for secure
    From computations and subsequent investigations,             operation even in the event of one or more of these
it was determined that 20 liters of air per person               dangers. It is required that all clOSing devices
per minute is sufficient to maintain shelter CO2                 leading to the outside are at least as safe as the
content well under the 2 per cent limit.                         design and function of the shelter require.


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      -
    Investigations carried out toward the end of the          substances. Tests have shown fiiters to be effective
Second World War with make-shift, coarse-sand                 against chemical war gases in concentrations that
filters showed that sand of appropriate granulation           seem possible in the event of attack.
provided excellent filtration against combat sub-
stances then known. When new planning·of protective              Coarse-sand filters against radioactive dusts.
measures was instituted after the war, these inves-           Radioactive substances suspended in the air-even
tigations were resumed and a thorough study was               the most minute dust particles-were filtered out up
carried out on the protection capability of coarse-           to 99.95 per cent. This figure suggests that filters
sand filters against modern weapons.                          would be sufficiently effective when used against
    The following aspects of coarse-sand filters              radioactive dusts.
were shown to be especially important:
                                                                  Application and filter arrangement. Primary sand
   Coarse-sand filters as pressure cushions. A                filters are the only type currently prescribed in
coarse-sand filter layer shows only slight resistance         German specifications. The amount of sand required
to slowly moving air masses, but with air shock               always depends on the amount of air which is to pass
waves and their high kinetic energy, however, resist-         through it. Thus, a protective ventilation system
ance is so great that the shock wave is effectively           with a capacity of 0.75 m3 per min sufficient for 25
absorbed by the filter.                                       persons, contains a primary sand filter with a sand
                                                              volume of 1.5 m3 . The height of the layer is 1 m.
    Coarse-sand filters as heat cushions. Heat-
cushioning effects of sand filters have been thoroughly          Types of sand. The most appropriate types of
investigated. A comparison of the storage capability          sand are crushed basaltic sands with stable grain
of large masses of sand for possible heat (brought in         size of 1-3 mm and crushed sand up to 1 mm. Flow
by air passing through it) shows that large amounts           reSistance to the air passage must be between 30 mm
of heat were effectively absorbed. In addition, be-           and 35 mm of mercury.
cause of sand's .great storage capacity, changes in
temperature caused by the weather were cushioned
even when they were of long duration.
    In order to check the effectiveness of the sand
filter as a heat cushion, outside air heated to 200°C         Summary
was passed through the filter. During a 14-hour
period the temperature of the air reaching the                In fireproof shelters, provision must be made for
shelter area slowly rose from 17"C to a maximum               the prevention of dangerous heating which can lead
of only 22°C.                                                 to a situation similar to that in an oven. This danger
    In field tests involving about 50 persons, differ-        can be prevented by means of sufficient thickness of
ences in temperature of up to 20°C were compen-               the protective shell and by securing entrances with
sated for in such a manner that, during the week-long         fireproof closures.
investigation, a change in temperature could not be               Ventilating systems must be suitable for the siZe
measured.                                                     of the shelter area and must be constructed such
                                                              that both external and internal dangers are con-
    Coarse-sand filters as water cushions. A coarse-          trolled and that provision is made for tolerable air
sand filter is virtually insensitive to water condensed       conditions within the shelter. Oxygen reserves for
from air passing through it, since the mass of this           family shelters would usually not be necessary.
water, in relation to the amount of sand in the filter,       Even in firestorm areas survival appears possible
is inSignificant.                                             fOf those in fireproof shelters with secured ventilat-
                                                              ing systems built according to present German
   Coarse- sand filters against chemical warfare              specifications.




                                                        138
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                          FIRE-SAFE SHELTER DESIGN-SWEDISH VIEWS

                                                    GOsta Smitt
                                                Stockholm, Sweden


As a background to our efforts to provide fire-safe            Protection is afforded in both residential and work
shelter designs, I will begin with a short survey of           areas.
the types and locations of public shelters being built            Conditions in central areas of our largest towns
in Sweden.                                                     have forced us to construct shelters of far greater
    Most shelters belong to a group called" standard           protective value than could be provided by standard
shelters," which are built by house owners in the              shelters. These superior "rockfirm shelters" are
basements of new buildings. They can withstand                 either built in rock or are designed as bunkers in
loads up to 15 psi as well as secondary effects from           concrete. Combinations of these two types of con-
conventional bombs. Most are located in newly built            struction are also used. They are capable of with-
suburbs of our cities. Currently the total capacity            standing 150 psi from long-duration pressure waves
of this type shelter is sufficient to accommodate              as well as direct hits from the size bomb that can
over 50 per cent of the inhabitants of those regions.          be most effectively used in mass attacks. Currently




             --.._....




           ~   ,,,-'1'"




    -111111!-                                       I~:~l
                                                1!TI1
                                                               (MEllO UIT IlNCl
                                                                                              SANDflll£ll
                                                                                               SECTION




                          fNfllG EJIT DETAILS



   Figure 1. Plan of staDdard shelter.


                                                         139

                                                                                         Digitized by   Google
ten such shelters are being built and a ten-year                Shelter location is also chosen with regard to fire
program of shelter investment bas been provided              risks in building areas both above and in the base-
for.                                                         ment. Shelter conditions can deteriorate to such an
    According to Swedish civil defense laws, each            extent that they must be evacuated. There are,
homeowner is required to provide simple radiation            therefore, at least two protected emergency exits;
shielding, generally within basements. Because of            basement walls to adjacent buildings are broken
this, almost every home will have some form of               through in case usual exits are found to be insuffi-
protection against radiation in the event of war. To         cient. The possibilities of escape to the outside are,
varying degrees they also will be protected from             on the whole, considered fairly good even if the blast
fire hazards, since the fire hazard is considered in         breaks floor slabs and basement walls around the
conjunction with others in the coming public direc-          shelter, since passageways can develop between large
tions on the subject.                                        pieces of building debris within the basements.
    One assumption for standard shelters is that they           Special directions are given showing location of
will be located in areas with good town planning,            combustibles near the shelter roof or walls. A mini-
where modern buildings have separations between              mum distance of at least 50 feet from the shelter is
units. U this requirement is met, the risk of mass           required for normal oil-storage tanks.
fires is practically eliminated. Such general require-          In modern houses, concrete floor slabs very
ments are important to shelters of this type as they         effectively isolate a fire's downward effects. U
provide protection for large areas.                          main building elements are intact, fire load on the
    Buildings where standard shelters are constructed        shelter roof is limited to the combustible material
comply with regulations for fire protection, which           on the floor above. For residential buildings, the
means that all floor slabs and supports are built of         fire load is estimated at 20 - 70 kg/m2 (4 - 14Ib/ft2),
fireproof material, primarily concrete. SpecifiC             for commercial and industrial buildings from about
demands are made upon staircase construction with            100 up to 200 kg/m2 (20 - 40 lb/ft2). Under such
regard to load capacity, stability, and fire resistance.     circumstances we can assume an adequate supply
Direct connections between basements and staircases          of air and complete combustion of the fire-load
are not permitted. Special smoke outlets for the             material.
staircases must be arranged in the roof.




                                    "'!U!!!   'p-




Figure 2. Rook shelters.

                                                       140
                                                                                      Digitized by   Google
Figure 3. Plan of town.



   In the event the building has collapsed above the           With present lmowledge serving as a guide, it is
shelter, the fire-load situation is more favorable,         possible to estimate rate of temperature and heat
as combustible material will be trapped between             flow through shelter enclosures when such criteria
heavy, broken, but still continuous, concrete elements.     as fire loads with lmown calorie content, rate of
Fire in such debris develops slowly, with incomplete        combustion in enclosed fire cells of certain dimen-
combustion lessening direct fire risks. These fires         sions and material are given.
may, however, be a source of carbon monoxide and               As an example, we have studied the conditions for
heavy smoke.                                                a standard shelter of medium size located in a house:
    The thermal properties of building materials
within the temperature ranges of fire have been             1 kC&lImh"C
studied, but many fundamental questions are still
                                                              1,4
unanswered. The coefficient of thermal conductivity
of concrete is bighly dependent on temperature and            1,2
~ecreases with temp!rature increases.                                     CONCRETE (GRANIT      BALLAST MATERIAL)
    Another problem is that the material structure is
transformed, which complicates efforts to produce
methods of calculating heat flow through shelter
roofs and walls. Concrete has considerable heat
inertia [CC = specific heat coeff. kcal/kgjOCC =
0.230, 6 =weight by unit of volume, kg/m3 =2,3000J
and is subjected to uneven temperature distribution
accompanied by stresses which are amplified by               0.2
vaporization of enclosed water. Basic studies on the
theoretical determination of temperature develop-            o
ment in constructions subjected to fire are being               o 200 tIIJ 600 D) 0)()
made at the Technical University in Stockholm.              Figure 4. Thermal conductivity of concrete.

                                                      141


                                                                                        Digitized by   Google
   Size:                                                                                                                  •• ~ ~-CCIII1INT"'"

                                                                                                                                                                             ---
                                                                                                         TIW              III • fOTIL AlE LOID _

   ---gO persons at 0.75 m2/person (8.2 ft 2/person)                                                      ec        -- ••• Q.OK,.,...,. ....1111 ....
                                                                                                                    AUA.'.~M..ua ...
                                                                                                                                                                       _ _ c:aa

   Fire loads:
                                                                                                                                                              ............
      Case A, above the shelter roof 70 kg/m2
               (14Ib/ft2)
      Case B, adjacent to the shelter roof 30 kg/m 2
               (6Ib/ft2)
   Fire cell material:
      Case A, 1-1/2 stone brick tiers, floor 20 cm
              concrete, window area 2 x 2.25 m 2
      Case B, Floor, walls, floor of concrete,
              window area 2 x 1.0 m2
   Assumptions:                                                                                          Figure 6. Temperatures in fire cells.
     Ample air supply, a constant combustion rate,
     no personnel or ventilation.
   Temperature development in the fire cells is
shown in Figure 5. The fire above the shelter roof
lasted about 3 hours, creating maximum tempera-
tures in the cell of 1,200°C, followed by a rather
long cooling period of more than 10 hours.                                                                                                                                              101-
                                                                                                                                                                                        IOIWNTUIIIII

   The fire in the basement adjacent to the shelter
wall was of lesser proportions. It lasted about an
hour and a half; maximum temperature in the cell
was 800°C; and it was followed by a cooling period
of some length.




  SECTION       /     ...................
  ---/                                      '-,                 ~LT   A.
                                                  "-           FIRE     ABCYE    THE    SHELTER
                                                               ROOF.


                tC"4 CONCII.E1                     II")
                                                           F1RECF.U.. 70 kG • ,~2 (14 LB 1FT 2 )
                                              . 11         ...OMB. MMERIAL (WOOD)
                                                           M • 1)6')0 I(c, \ 12400 LB)
                                                                                                         Figure 7a. Temperature development, Case A.

25 CM   -:,            ZOCM (I)')                 r--      WINDCW AREA 4,5 M2,
(10')               SHELTER




                       10 "4




        f.-t-....---=-II-f
                                                               A~T    1'.
                                                               FIRE IN BASEMf::T
                                                               CLOSE TO SHELTER         WALL
                                                                                                         'C


                                                                                                               -
                                                                                                               •
                                                                                                               -
                                                                                                                                    UI




                                                                                                                                                        --
                                                                                                                                                        .aM
                                                                                                                                                                                  101-
                                                                                                                                                                                  101 WNTUIIIII




  4M                 BASEMENT
                                                                                                         110   IlOO

        ~ir   ~~~~~~- f'.,
                      I
                                 25001(10')            .
                                                                 M = 1200 KG 12700 La )
                                                            '. , N:'~;JOW AR,El. 2101 2                        100

                    SHELTER
                    200 M 3
               (7000 FT3 )
                                                                                                         110
                                                                                                               -   IlOO


                                                                                                          10   IlOO


                                                                                                               110



                                                                                                              ••
                                                                                                                                                              -   10         ..     •      ..     •   l1li.

Figure 5. Test of standard shelter.                                                                      Figure 7b. Temperature development, Case B.


                                                                                                   142

                                                                                                                                                         ~igitized by Google
    Heat flow througb the warm, inner roof area              Under sucb extreme conditions, air ducts must be
reacbes its maximum after 7 bours-l,600 kCal/m2/          kept sbut during the time in wbicb extensive fires
br (575 BTU/ft2/br) as does the temperature, 170°C.       beat air and mix it with bot gases and particles-an
    Sbelter inner-air temperature reacbes its maxi-       interval of 10-12 hours. Within the closed sbelter
mum of 120·C somewhat later-after 9 hours. Sucb           the air is cooled and dosed with oxygen, and carbon
temperature necessitates evacuation of the sbelter        dioxide is removed by a chalk filter.
within a few hours. Corresponding figures for the
basement fire are: maximum beat flow after 6.5
bours-630 kcal/m 2/br (225 BTU/ft2/br) maximum            Ventilation Standards
wall temperature after 6.5 bours-80 u C, and maxi-
mum air temperature after 9 hours-34°.                    Free ventilation rate-1.5 m 2/person, maximum 20
   If it is assumed that the shelter contains 90 per-                            m3/person/br (700 ftS /p/h)
sons, generating 100 kcal/person/hr (36 BTU/ft2/hr)       Free ventilation rate-0.5 m2/person, maximum 10
and is ventilated during summer by 7.5 m3/person/                                m3/person/br (350 ft3/p/ h)
hr (265 ft3 /person/hr), the maximum inner-air            Gas ventilation (minimum ventilation) 1.5 m3/per-
temperature rises approximately 5°C to 40°C in                                   son/br (53 ftS /p/b)
Case B.
    Recent studies on temperature-rise in standard
sbelters indicate that, even with a high ventilation
rate, maximum allowable temperature will be reached       Temperature Standards
in the event of a prolonged stay. Therefore, local
fire effects must be kept at a rather low level.          Maximum temperature and humidity- 28 u C, 80%
    Fire-protection potential within the central areas    Data for air purifying equipment (only inner air
of our largest cities has improved recently due to        circulation)
extensive reconstruction activities. Even in these
vulnerable central city areas, construction of            Oxygen supply at +20°C, 760 mm Hg-0.25 m3/person/
standard shelters of higher resistance capability-        hr (9 ft3/person/hr)
45 psi-has occurred.                                      Chalk supply, layer height 100 cm-0.2 Kg/person/
    Complete calculations regarding outer fire effects    hr (0.44 lb/person/hr)
on standard sbelters will be made to obtain informa-
tion about necessary equipment and maximum allow-         Chalk specific weight-0.8
able staying time under various conditions.               Heat exchange by CO2 absorption-23 kcal.person/
    Temperatures occurring in concrete sbelters can       hr (92 BTU/person/hr)
be so higb that they have considerable effect on the
sbelter's strength. Reinforcing steel of average          Air volume through absorber-I. 5 m3 /person/br
quality loses about 50 per cent of its strength at        (53 ft3/person/hr)
6OO°C-a temperature easily reacbed by other               Air temperature and bumidity after absorption-
parts exposed to direct fire. Tbe main decrease in        40°C, 97%
strength occurs during the first days of beating,
wben sbelters fulfill their most important functions.         Shelters of this type are considered to be com-
At present, theoretical-failure load calculations of      pletely protected against outer fire.
statically indeterminable constructions clue to fire          Fire risks inside the sbelter must be kept to a
influence are not being made. Recent studies of           minimum. Generation of hot smoke, carbon mon-
temperature and beat-flow through construction            oxide, and other gases must be avoided. Shelters
elements therefore could be used as the basis for         are provided with conventional fire-extinguishing
sucb work.                                                equipment and warning systems and are divided into
   Wben providing standard sbelters at oil refiner-       fireproof sections, which include the ventilation sys-
ies, storage facilities, and distribution plants, fire    tem. Special smoke outlets are required. They must
protection is of prime concern. Fire hazards neces-       be wide enough to allow smoke divers to pass through.
sitate location of sbelters at distances of more than     Fire-protection measures for shelters conform with
200 meters from, and at higber levels than, oU            general,fire regulations as shelters are used as
sources, in order to avoid surface oilflow. In ex-        garages, work shops, gymnastic halls, etc., during
treme cases, equipment for air purification within        peacetime.
closed space is also indicated.                              Macbine rooms and oU tanks are located in sucb
   Our rock sbelters are located near industrial          a way that they can be isolated in case of fire.
plants, whicb means that they often must protect
against area conflagrations. Air intakes and outlets         A control panel gives information concerning
are equipped with filters and well concealed, but are     engines and openings, and also contains fire indica-
unusable in fires of this type.                           tors from certain shelter points.

                                                    143
                                                                                   Digitized by   Google
                                  A",
                                    I




                       ,Jl

                       -i..._




                                                        I
                                                  A ... J

Figure 8. Rock shelter plan.




    Fires around the shelter as well as other weapons                In a rock shelter at Katarlnavagen, Stockholm,
effects limit the possibility of utilizing shelters fully         calculations based upon actual measurement have
if duration of continuous stay exceeds 24 hours.                  given the following results:


                                                                  Minimum ventilation

                                                                  Maximum 20,000 persons (0.5 m2 person) - 24 hours
                                                                          10,000 persons                 - 3 days
                                                                           9,000 persons                 - 7 days
                                                                           5,000 persons                 > 7 days

  .ta.




         .a..J        .a...   J
Figure 9. Rock shelter plan.                                      Figure 10. Rock shelter cross section.


                                                            144

                                                                                                Digitized by   Google
Maximum ventilation                                           to the conclusion that, because of costs, further
                                                              investments to avoid partial evacuation of such
          9,000 persons                    > 7 days           shelters under the worst circumstances are not
                                                              justified.
   Surrounding rock absorbs about 40 per cent of the             In conclusion, I would like to say that because
total heat generated, while the cooling plant absorbs         long shelter stays will most likely be necessary we
50 per cent and the ventilation air 10 per cent.              should make a more thorough examination of fire-
   The capacity of technical equipment, including             safe shelter-design principles and their influence
that for fire protection, thus determines the length-         on actual construction regulations.
of-stay limit of big public shelters. We have come




                                                        145
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                    FIRE-SAFE SHEL TER DESIGN-CANADIAN VIEWS

                                                Gordon Shorter
                                                Ottawa, Canada


Work that has been done toward improving the safety           time. Thus, it was decided that kerosene was suit-
of Canadian shelters with respect to fire hazards is          able on several counts, and consequently the investi-
inevitably related to current Canadian shelter policy.        gation of heating appliances was concentrated on
One phase of this has been to encourage homeowners            kerosene heaters.
to develop their own fallout protection. One study               Initial studies suggested that unvented appliances
concerning conditions within a fallout shelter located        could not be ruled out. In other words, small heating
in a house basement may be of interest.                       appliances might exhaust into the basement. The
    When the home-fallout-shelter program was first           investigation of appliances has been concerned with
initiated, the Emergency Measures Organization was            CO2 and CO production as well as with fire hazards.
concerned about environmental conditions that might           To date, the following four points have been
be experienced within a shelter and requested that a          established.
study of these conditions be undertaken by the                    First, certain kerosene-burning appliances ex-
Canadian National Research Council. In Canada,                perience a marked reduction in burning rate in an
much of the living accommodation is provided in the           enclosed space-with an increase in C02 and a de-
form of single-family dwellings; thus, basement fall-         crease in 02-and thus become self-limiting in the
out shelters can serve a real need. This is particu-          production of CO2 and probably also of CO.
larly true in rural areas where it is unlikely that              Second, a simple wick-type burner, drawing its
shelters would be subjected to blast or fire damage.          fuel from a reservoir below, by capillarity through
However, since the basement wall area of these                the wick, is inherently more safe than those having
basement shelters is one fourth to one half above             either a/predetermined constant fuel feed or a
ground, another problem arises in that heat must be           constant-level device. In the first case, the appli-
provided at certain times of the year to keep tem-            ance has a tendency to flood, with a consequent risk
peratures above 32°F. Concern was expressed that              of fuel spillage and fire. This is due to the decrease
heat-producing appliances and their fuel might pro-           in burning rate, which at times can be as much as
vide both fire and health hazards to occupants. Thus,         one fourth of the original rate, as CO2 increases
much of the study has been concerned with these               and 02 decreases in a confined space, while the fuel
hazards, and a number of fuels and heating appliances         supply is held constant. In the second case flooding
have been investigated. Suggested requirements                can also occur, as was found in England. With air
were that (a) the appliance be such that it could             velocities of 3-5 mph, hot productions of combustion
maintain a shelter temperature of 50°F for a period           blown against the fuel tank will cause flooding.
of two weekS, (b) the appliance be suitable for heat-            Third, catalytic heaters have two faults, although
ing food and drinks, (c) the appliance and its fuel be        they burn without flame. If the device is designed to
relatively fire-safe, and (d) since better lighting than      operate at a low temperature (below 400":r) it is not
that from dry batteries was desired, it be obtainable         suitable for cooking, and produces large amounts of
from simple lamps using the same fuel as the                  CO. If the operating temperature is raised, it is
appliance.                                                    possible to reduce CO but the advantage (safety) of
    Almost all conventional fuels produce about               low-temperature operation is lost.
20,000 BTU/lb. Therefore, 10 gals of kerosene                     Fourth, kerosene lamps may be used as ~/02
would be sufficient for two weeks if burnt at a maxi-         indicators; as C02 increases there is a marked
mum rate of about 5,000 BTU/hr. Kerosene is less              reduction in flame size.
hazardous than other liquid fuels for re-filling hot              Studies still going on are concerned with ventila-
appliances. In addition, it stores better: than gasoline,     tion of shelters and basements and the characteris-
which tends to form gum when stored for long periods.         tics of unvented appliances. Although studies related'
It was stated that gas cylinders would pose a hazard          to CO production have been completed, reports have
if stored indoors ready for use for long periods of           not yet been issued. As a result of studies to date,


                                                        146

                                                                                          Digitized   by,Google
the use of unvented wick-type kerosene-burning             basement fallout shelters, to forestall the use of
appliances cannot be ruled out for use in basement         less safe appliances that might be used if no
fallout shelters. It is considered advantageous to         recommendation were made.
recommend kerosene fuel and appliances for family




                                                     147

                                                                                      Digitized by   Google
Digitized by   Google
DESIGN PROCEDURES/BLAST

  Will iam J. Hall, Cha irman




                                Digitized by   Google
                         FOOTINGS FOR PROTECTIVE STRUCTURES
                                   Robert V. Whitman and Ulrich Luscher
                                   Massachusetts Institute of Technology
                                    (paper presented by R. V. Whitman)


Introduction                                                 structure such as a cylinder or a complete box
                                                             would probably be provided. ConsequenUy only the
Many buried structures, particularly arches and              air-induced ground shock has to be considered;
rectangular structures, can be supported on spread           direct-induced ground-shock effects can be neglected.
foundations, i.e., footings several feet in width and         Even then, the loading experienced by the structure
hence covering only a relatively small percentage             is quite complicated, and it is necessary to introduce
of the total area of the structure. The design of            some simplifications in order to understand the
these footings, on one hand, and the evaluation of           essential features of the problem.
the effects of footing design and footing motion on              The first of these simplifications is to ignore
the response of the structure as a whole, on the             components of the loading that are not symmetric
other, are integral parts of the over-all design of          about the vertical center-line. Such a simplification
such structures. This paper discusses both these             is permissible so long as there is sufficient depth of
aspects.                                                     cover over the structure.<l)
    Considerable research has been done in this field            The second simplification is to ignore wave-
in the last ten years or so by several organizations,        propagation effects, both within the soil and within
and much additional research is currently under way.         the structure. Thus reflections of stress waves by
Most of this work has concerned only the first part          the structure are not conSidered; such reflections
of the problem, i.e., the behavior of footings under         seldom have been observed in field tests. Moreover,
dynamically applied loadings. The appendix lists             one ignores the possibility that stress reaches the
completed studies and indicates roughly the range            level of the foundation by wave propagation through
of variables considered.                                     the structure before the stress wave in the soU
    Very little work has been done up to now on the          reaches this level. The possible errors introduced
second part of the problem, i.e., the effect of footing      by this Simplification are poorly understood at the
motion on the behavior of the supported structure.           present time. However, it seems reasonable that
It is generally recogniZed that footing motion should        these errors are negligible in the case of small
enhance arching within the soil over the structure,          personnel shelters of flexible construction.
just as any other effect that makes the structure                The third simplification concerns the forces that
more compliant than the surrounding soil enhances            affect the response of the footings. In this paper, we
arching. However, very little detailed quantitative          are concerned only with the footing motion relative
information exists in this area.                             to the free-field motion at the elevation of the foot-
    This paper synthesizes the available information         ings. It is assumed that this relative motion is
on the design of impulsively loaded footings and the         affected only by loads that reach the footings through
effect of footing response on the structure. Where           the structure itself. Actually the footings will re-
possible, ranges of uncertainty are indicated, and           ceive some secondary loads directly from the sur-
areas of needed further research are identified.             rounding soU, as shown in Figure 1. However, these
                                                             secondary loads will be negligible so long as the
                                                             area of the footings is small compared to the total
General Aspects of the Problem                               plan area of the buUding. The stresses in the soil
                                                             to the side of the footings must influence the level
Figure 1 shows a typical shallow-buried structure,           of stress within the pressure bulb of the footing;
in this case an arch, and indicates how it is envel-         however, this influence is ignored, partly because
oped by the effects of air-induced ground shock.             it seems that it should be small and partly because
Structures with spread foundations are found only            there is no actual information regarding this point.
in regions of relatively low to moderate design                  With these three Simplifications, it is possible
pressures, since under higher pressures a closed             to represent the behavior of the structure, founda-


                                                       151

                                                                                         Digitized by   Google
                                                                                carried by arching increased from 40 to 60 per cent
                                                                                upon narrowing footings from 2.4 to 1.2 in., because
                                                                                of the larger settlement undergone by the smaller
                                                                                footings.
                                                                                    This effect gives rise to a dilemma regarding the
                                                                                design of footings, which may readily be illustrated




            ~ ....
                                                                                by conSidering the case of static loading: decreasing
           /PtfJ                                      -                         the width of footings will decrease the stress reach-

            -
              - --
s..~ . .     ~
                                                                                ing the structure, but will increase the total motion
      ......                                                    ~               of the footings. The first of these trends is desira-
             " _-, ....   . ""         ,
                                          '---"
                                        ','--"                                  ble; the second may be undesirable. These trends are
                                                                                illustrated in Figure 3. Studies aimed at developing
           ~ .,."".                ."",.   .,                                   methods to determine the optimum footing width are
Figure 1. Envelopment of buried structure by air-iDduced
ground shook.
                                                                                being carried out at NCEL.

tion, and surrounding soil by the model shown in
Figure 2. This model can conveniently be used to
discuss two interrelated aspects of the problem of
                                                                                       ,  \
designing buried structures: the effect of footing                                        \
motion upon arching in the soil above the structure;                                      \
and the effect of the inertia of the structure and                                            \
overlying soil upon loading history for the footing.                                           \
                                                                                               \



                                                                                                                     --
                                                                                                   \
                                                                                                       \


                                                                                                            ......   --!!'L·".,.,r ------
                                                                                                                          -----
                                                                                      o                                       /hU..-Mg   -
                                                                                                           #IV/Dn! t#     FOOn""
                                                                                Figure 3. Effect of footing width upon arc bing and settle-
                                                                                ment: static loading.
                                 1l.1l1hi/,'fa . ,    ~               ,
                                 _ _ . , lOoN", . ". . .


                                                ...--,.,...,.
                                                        ,
                                 mom,       ..,HA   f6tWins
                                   "''-
                                   ~                 ",.   .,..,.",
                                                                                   Inertia of structure and overlying soil. Because
                                                                                a buried structure supported on footings that bear
                                                                                upon soil is a relatively flexible system, the system
                                                                                will not respond immediately to an applied step load.
Figure 2. Schematic model for behavior of soU-structure
system.                                                                         Thus, even though the surface pressure has a rise-
                                                                                time of less than a millisecond, the load reaching
   Effect of footing motion upon arching. For buried                            the footing will have a significantly longer rise-rime,
structures, as for most conventional structures, mo-                            as illustrated in Figure 4.
tion due to footing displacement is of the same order                              This point has been illustrated in tests at NCEL
as, if not larger than, motion due to deformation of                            involving the blast loading of small buried arches. (2)
the structure. Thus footing settlement greatly in-                              The rise-time of the surface overpressure was 1 or
creases the effective compressibility of a buried                               2 millisec, but the rise-time of the load reaching the
structure, and so enhances the tendency for active                              footings was more like 5 or 6 millisec. Also, in
arching, i.e., development of shear stresses in the                             dynamic footing tests where the load was trans- •
soil that reduce the pressures acting on the struc-                             mitted to the footing through a column with consid-
ture in comparison with free-field pressures.                                   erable mass, it has repeatedly been observed that,
   Experimental evidence of this effect has been                                even when the load pulse at the top of the column
obtained at the U.S. Naval Civil Engineering Labora-                            was triangular, with a rise-time of very few milli-
tory (NCEL) by Allgood et al. (2) and by Gill and                               seconds, the load actually reaching the footing had
Allgood. (3) They demonstrated, in static tests on                              a rise-time in the tens of millisec.(4)
arches of 30-in. diameter with a 6-in. soil cover                                  The reason for this change is that the inertia of
over the crown, that the percentage of applied load                             the mass located between the applied load and the


                                                                          152

                                                                                                                       Digitized by   Google
footing is mobilized as this mass is accelerated to                                              and distortion within the soil under the footing and
follow the footing motion. In the case of the buried                                             by the degree to which a bearing capacity failure
structure, this mass is that of the structure plus all                                           develops. In the case of buried structures such as
or some part of the overlying soil.                                                              that in Figure 1, bearing capacity failures will occur
    The change in loading history will be further ex-                                            on the interior side of the footing, so that the be-
plored later in this paper, in connection with a dis-                                            ha vior is essentially that for a surface footing or a
cussion concerning the effect of the inertia of the                                              footing at very shallow depth.·
soil located below the footing.                                                                      Figures 5-8 show typical cu"es of peak load
                                                                                                 vs. peak displacement for surface footings, from
                                                                                                 dynamic loading tests involving load durations on the
Foundation Behavior                                                                              order of 40 to 300 millisec. The load shown here is
                                                                                                 that actually acting upon the bearing plate. These
The magnitude of the settlement under a dynamic                                                  curves have the shape generally encountered in static
load is determined by the amount of compression                                                  load tests, i.e., there is a yield point at a relatively
                                                                                                 small settlement, and thereafter the slope of the load-
                                                                                                 settlement curve decreases markedly. However, at

           .,  ~..".'                  Iood,..                                                   any given settlement, dynamic resistance clearly
                                                                                                 exceeds static resistance. The following subsections

               ,
               I

               I
                                                                                                 consider factors that contribute to the shape of these
                                                                                                 curves and to the magnitude of the resistance at any
                                                                                                 given displacement.
               I
               I
               I
                                                                 '"-'
Figure 4. Effect upon load pulse of inertia of structure                                         .Because the bearing pressure on the footing will greatly
aDd overlying soU.                                                                                exceed the free-field stress at the same elevation. a
                                                                                                  bearing capacity fallure with heave immediately adjacent
                                                                                                  to the footing will be a more critical problem than the


                             ..,-
                                                                                                  wide-spread bottom heave that sometimes occurs with
               tS , _ - - . NAU                                             I                     braced excavations.


     2S
                   .,,--~


                                                                                -
                                                                                Ie·


                                                                                                                   PLATa W".,,, AR6A 01" fU ..!
                                                                                                                           ON   SIJIf~;JK:a   _     $AND



     20                                                        •            /                             4r-------~------~---------~------_,
                                                        •/                                        Q
                                                                                                  ~
     15                               tll~/                                                       ...
                                   rI"?                                                           \c

                                                                                                  I
                            ~)~
                                                                     -,'"
                                                             ",,-'
      10
                        V                    -'
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                    ~                  /'"                                  I                     I
                                  4"                                        I
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                                -'!J

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           :                                                                                             II
                                                                                                              0
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                     z                                   8                            12


                   PEAK     /)IaPLAcEMENT          -i~.


                                                                                                 Nofw.: dt!".",ic , . . _    ,.,."", M;",gu,-. ""iHI •
1Wh: ~ Iood .... ~20;.' ..,;". ,jH-'-" of tI6ouI-                                                   ,.,..-"- ~ fI60cd     !I    .. ~ ~ •
     _ """U ids .".,. ~.,.....". 60 ,.;~                                                            ~ J.,..; All               . . . .. . " . .
Figure 5. Results of tests with sand at the University of                                        Figure 6. Results of tests with sand at the Waterways
IlUnois.                                                                                         Experiment station.


                                                                                           153
                                                                                                                                                  Digitized by   Google
   Inertia of soU below footing. If a footing is loaded
by impact, the inertia of soU below the footing un-                                                                       WESTests                    NeEL Testa
doubtedly affects the motion achieved by the foot-                           SOU                                          Sand aDd clay               Sand
ing.*'" However, several arguments can be used to                            Estimated cR                                 500 ft/sec                  500ft/sec
show that the inertial resistance of this soU is neg-                        to                                           12 msec                     6 msec
ligible for most practical problems.                                         B                                            8 inches                    1.2~s
   A first argument is based on the fact that the                            cRtO/B                                       9                           30
rise-time of the load applied to footings will typi-
cally be long compared to the time required for
stress-waves to traverse the pressure bulb of the
footing. For example, Carroll has suggested that                             A second argument concerns the effect of inertia
wave-propagation effects will not be important as                            in actual footing tests. In those tests that have in-
long as:(5)                                                                  cluded measurement of the acceleration given to a
c t                                                                          footing by a dynamic load, it has been possible to
~ ~3                                                                         show that the inertia of the soU below the footing
  B               '                                                          has negligible effect upon the peak resistance of the
where c R         =rod wave velocity =JE/p                                   soU. Figure 9 shows one such record. The actual
                                                                             resistance of the soil is shown by the curve labeled
         to       =time to maximum applied load =rise-time                   R. Making a generous assumption as to the mass of
         B = width of footing                                                the soU that moves with the footing, and multiplying
                                                                             this assumed mass by the measured acceleration,
         E = Young's modulus
         p       =    mass density.
                                                                             **Thts fact is of importance if a structure receives a
This condition has been met in the past small-scale                            sharp slap when the ground shock first reacbes the
footing tests with controlled-stress loading, as is                            structure, thus causing a stress pulse of high intensity
illustrated by the following table, which uses esti-                           but short duration to run through the structure at the
mated rod wave velocities and average results:                                 wave velocity of the structural material.



      240
                                                                                     ,,-.:.......                     ,...        -       ~       ft' • .... , . " . .
                                                                                             ,;...,.". " . - u I 40 ...,...___ '..t • ......,..
                                                                                             .,...."..MO~ .



                                                 . ...
                             V~
                        -                                                           .'~--~----'-----r---~--~



                      if ~
                       - -,/
                        I
                                  ~AN6EOF
                                  STATIC T6S15
                                                                                    I.   t----1----+--::::.,.,.:::;:




                 rI ,

                 '//
                  I
                        I
                            /'
                                 ,'"
                                                   IS-INCH DIA-
                                                  Mn"6RPl.ATE._
                                                  ONSUHMCE
                                                         DI=&ANP
                                                                                    • L-tf---?-"' ..........
                                                                                         n

                                                                                              /
                                                                                                  ".,

                                                                                                  ",'"
                                                                                                         ,
                                                                                                                    ...
                                                                                                             tfIN.:=--- f i r
                                                                                                              ...
                                                                                                                              ~
                                                                                                                                  ---
                                                                                                                                      STATIC 12$TS
                                                                                                                                           ----      ---




        o                                                   I
            II               I          2                          6




      He:    -t-""c ,...",.,..    ~ .,.,.",.,., MIll •                                       DlM~N$IONU!"                               I¥AK SlTTUMMiT
          " ..-.";,,. -.uf 10 . . . .- - . - . I . _frIfiM
           oF __I 1000 MiIIiH_M.                                                                                      Z/b
Figure 7. Results of tests with sand at the Naval Civil                      Figure 8. Results of tests with clay at the Waterways
Engineering Laboratory.                                                      Experiment station.



                                                                       154
                                                                                                                              Digitized by   Google
    gives a correction that is subtracted from R to give                     and especially the mass of the soil overlying the
!   the curve R'. Referring to the model of Figure 2,                        structure. Since the flexibility of the soil below the
    the resistance R is the resistance of the combina-
                            #                                                footing generally exceeds or is about equal to the
    tion of the three elements ktl' k f2 and b f"                            flexibility of the structure and to the flexibility of
       Except at early stages, this correction is· negli-                    the soil above the structure, the several masses
    gible. Moreover, at the time when R was a maximum                        shown in Figure 2 will tend to move together. Thus,
    the footing actually was decelerating. Hence the peak                    the effect of the mass of soil below the footing will
    R' exceeded the peak R. Thus, for this test, the fact                    be negligible.
    that the dynamic resistance exceeds the static resist-                      These several arguments presume that the mass
    ance cannot be explained by citing the inertia of the                    through which the load was applied in the small-scale
    soil: indeed, the peak soil resistance is somewhat                       tests provides a reasonable model for the masses in
    greater than the peak load applied to the footing.                       prototype situations. The tests at NCEL actually
    This same situation has existed in the majority of                       involved a model buried arch. In the tests at WES,
    the tests. In the few tests where the peak R' was                        the mass of the structure and overlying soil was
    less than the peak R, the difference was negligible                      represented by the mass of the loading piston. A
    in magnitude.                                                            brief analysis indicates that the mass in the WES
       A third argument concerns the effect of other                         tests was equivalent to about 4.5 feet of soil over-
    inertia forces. So long as the footings occupy only                      lying the structure and moving with the structure.*
    a small portion of the plan area of the structure,                       Such a depth should be present in most practical
    the mass of soil involved in the footing motion will                     prototype situations.
    generally be small compared to the other masses
    involved in the problem-the mass of the structure                           Time-dependent effects. The stress-strain prop-
                                                                             erties of soils unquestionably are time-dependent.
                                                                             The role of this effect may be illustrated in two
                                                                             different ways.
                                                                                First, the relationship between the maximum load
                                                                             applied to the footing and the maximum motion of the
                                                                             footing will be a function of the duration of the applied
                                                                             load (see Figure 10). Recent, as yet unpublished,
                                    Dtdrt ~ I'IES rHf 9-3                    tests at WES using a load-decay time of several
                                     (~         ..., , . . . , ttIH)         seconds have given a peak-load vs. peak-displace-
                                     IJ-;" . - . . , . " ."    cr.,          ment relation that was almost identical to the static
                                    c::..t-. ,....,. -"..                    load-settlement curve. Such a load-decay time is
                                          ...
                                    "...., ~,.-.-..
                                        116· :?,,,.. -.54 ,...
                                                                             characteristic of that for the air blast at large
                                                                             distances from a very large explOSion.
                                                                                In the case of clay soils the peak loads at some
                                                                             displacement for dynamic loadings (with durations on
                                                                             the order of 100 millisec) have been about 1. 7 times
                                                                             the load at this same displacement during static
                                                                             loadings. This factor is just about what might be
                                                                             expected on the basis of Shear-strength measure-
                        /                                                    ments at fast and slow rates of loading.(5)
                    /
       ·S
        I
                     ".,.".
                ;.....-....w...
                •


       1tD~_I-------+--~~~~~~~                                               *It bas been shown that mass is scaled as A3, where A is
       J .                                                                    the length soale factor. Thus, scaling from the 6-1nch
       ! !                                                                    square model footing with a 160-lb mass to a 4-ft square
                                                                              prototype footing, the structural mass scales up to 82,000

       fl   Il.o,t-----+----+---+t--I
                                                                              lb. If one assumes a contributory area of 12 ft sq (i.e.,
                                                                              the footing covers a ninth of the total area) and a unit
                                                                              weight of 130 lb/cu ft (an average between concrete and
                                                                              soU), a cooperating depth of 4.4 ft is required. This
            i                                       I
                                                    I
                                                    1                         depth may not always be avaUable, espec1ally if one con-
                                                                              siders that the surcharge soU is not rigidly connected to
                                                /                             the footing and may therefore not be fully active as in-
                                                                              ertia. On the other band, it bas also been shown that a
    Figure 9. Typioalload-settlement-time relations during                    limited change in mass did not exert auy appreciable
    dynamic loading test.                                                     influence on the maximum settlement. (4)


                                                                       155
                                                                                                            Digitized by   Google
   Dynamic load factors of 1.5 to 2, and even as                 been reported that rupture surfaces did not form      as
high as 3, have been observed during tests on sand.              a result of dynamic loadings. The differences be-
This result has been rather surprising, since the                tween the static and dynamic resistance of footings
strength of sand generally has been found to be                  have often been attributed to such differences in
more or less independent of strain rate.(6) There                failure mode.
are several possible explanations. There is some                     For impact loadings, the authors do not doubt
evidence to suggest that strain rate may have more               that there is a significant difference in the modes of
effect upon strength during plane strain than it does            deformation. The tests performed by Kerr perbap8
during triaxial compression. (7) Another possible                shed some light upon phenomena present In connec-
explanation is that the pressure in the pore air of              tion with such high-speed load1ngs,(l1)
the sand under the footings momentarily decreases                    For controlled-stress loadings with rise-times
during the rapid shearing action, thus temporarily               of 5 mWisec or longer, however, the authors have
raising effective stresses and hence shearing resist-            failed to find evidence of difference In modes of
ance. The causes of the apparent time effect with                failure. Regardless of the rate of loading, footings
sand deserve further study.                                      used for the test program have tended to move
   Next, it is pertinent to examine the load-displace-           straight down with but little tipping. When patterns
ment relation from a given test. Two examples are                of deformation within the soil around the footing are
given in Figure 11. Note that the peak displacement              compared at equal settlements, the patterns have
occurs after the peak load, especially in the case of            appeared to be similar regardless of the rate of
tests on sands. Since it has already been shown that             loadtng.(9)*
inertia of the soil did not introduce a significant time
effect, this pattern of behavior indicates that the
resistance of the soil (the sum of the springs and               Approaches to Design
dashpot of Figure 2) is time-dependent. In other
words, a dashpot (possibly with a non-linear be-                 Design must be done by a step-by-step procedure of
havior) is needed if the model is to correspond to               assuming footing dimensions, analyzing the situation,
observed behavior.                                               adjusting the dimenSions, etc. Two methods of anal-
   At the present time, there is very little basis               ysis may be used to determine the footing response.
upon which to select a dashpot constant. The best
data are for compression(8) and it appears that the                 Q,Jasi-static analysis. In the case of static load-
time scale of time-dependent effects is similar in               ing, two relationships are required In order to
compression and shear.                                           design the structure and its footing: one relating

   Mode of failure. Much has been written about the
differences between the modes of failure under dy-               *Jf patterns of deformation are compared at equal loads,
namic and static loadings'<9,10) For example, it has              the patterns are quite different for dynamic and slow
                                                                  loadlnp. However, the development of rupture surfaces
                                                                  must be associated with the magnitude of the strains
                                                                  rather than the stresses.




                                                                                                  UTTU""ENT

               PEAl< DloSPLACEMENT
Figure 10. Hypothesized effect of load duration upon             Figure 11. Typical load-settlement relations for dynami-
relation between peak load and peak displacement.                cally loaded footings.


                                                           156

                                                                                           Digitized by   Google
 movement of the structure to the degree of arching              static-loading tests, it is known that such tests
 over the structure, and a second relating movement              always involve some uncertainty. (13) In addition,
of the footing of a given size to the load carried by            there still is considerable uncertainty as to the
the footing. First an estimate is made of the seWe-              appropriate dynamic-load factor.* In short, with
ment of the footings. The amount of arching is then              the best procedure available today, the estimated
found from the first relationship, and the column                reSistance at a given displacement can easily be in
loads computed from the loads reaching the structure.            error by a factor of 2 or more.
Then a revised seWement estimate is made using                       For the full dynamic analysis, it is necessary to
the second relation, and the cycle is repeat~ until              asSign properties to springs and the dashpot repre-
the estimated and calculated settlements agree.                  senting the soil below the footings. ConSidering the
    This approach can also be used, at least approxi-            present state of knowledge, it would seem best to
mately, for problems involving dynamic loadings. It              forget about dashpot, and to use a dynamic displace-
is necessary to have a relationship between peak dy-             ment vs. load relation to describe the behavior of
namic load reaching the structure and peak movement              the springs. Procedures discussed in the previous
of the structure, and another relationship between               paragraph may be used to estimate this relation.
peak movement of the footing and peak load carried                   In view of these uncertainties as to the load-
by the footing. Since the mass of the structure will             settlement relation for actual footings, it is recom-
generally be much less than that of overlying soU,               mended that two analyses be made for each design.
the inertia of the structure may be neglected so that                One is used to determine loads for which the
peak load reaching the footing can be obtained directly          structure should be designed. For this analysis,
from peak load reaching the structure. Then analysis             one sh