Exposure to cosmic radiation of British Airways flying crew on by wuyunyi

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Occupational and Environmental Medicine 1996;53:495-498                                                                         495


SHORT REPORTS


                            Exposure to cosmic radiation of British Airways
                            flying crew on ultralonghaul routes
                            M Bagshaw, D Irvine, D M Davies



                            Abstract                                               The earth is exposed to natural radiation
                            British Airways has carried out radiation           from terrestrial and extra-terrestrial sources,
                            monitoring in Concorde for more than 20             the extra-terrestrial sources being referred to
                            years and has used a heuristic model                as cosmic radiation.
                            based on data quoted by the National                   Galactic cosmic radiation originates from
                            Aeronautics and Space Administration                outside the solar system and produces a
                            (NASA) to model radiation exposure in               steady, reasonably predictable, low intensity
                            all longhaul fleets. From these data it has         flux of high energy charged particles, neu-
                            been calculated that no flight deck crew            trons, photons, and neutrinos which are gener-
                            would exceed the control level of 6 mSvly           ated when the primary protons and a particles
                            currently under consideration by regula-            interact with constituents of the earth's atmos-
                            tory authorities, which is three tenths of          phere. The primary and secondary radiation
                            the occupational dose limit of 20 mSv/y             thus produced in the atmosphere is referred to
                            recommended by the International                    as galactic cosmic radiation. There is about an
                            Commission on Radiological Protection               11 year cycle in the intensity of galactic radia-
                            (ICRP). The model suggested that less               tion reaching the earth's atmosphere, with the
                            than 4% of cabin crew based in Tokyo fly-           intensity being inversely related to solar activity.
                            ing only between London and Japan could             The last solar maximum was in 1991 and the
                            reach or exceed the 6 mSv/y level, based            next minimum during 1996/97, with an antici-
                            on a predicted effective dose rate of 7             pated 20% difference in dose rates based on
                            uSv/h. To validate this calculation a sam-          the results of measurements included in a
                            pling measurement programme was car-                recent review paper.'
                            ried out on nine round trips flown by a                A second source of cosmic radiation is the
                            Boeing 747-400 between London and                   release of charged particles from the sun but
                            Tokyo. The radiation field was measured             these are of lower energy and generally con-
                            with dosimeters used for routine personal           tribute little to the atmospheric radiation.
                            monitoring (thermoluminescence dosi-                However, occasionally the numbers and ener-
                            meters (TLDs) and polyallyldiglycol                 gies of ejected solar particles become signifi-
                            carbonate neutron dosimeters). The limi-            cant and this occurs during periods of solar
                            tations of the methodology are acknowl-             flare. A significant solar flare occurred in
                            edged, but the results indicate that the            February 1956 when the dose equivalent rate
                            effective dose rate was 6 pSv/h which is            at 10 km (about 33 000 ft) was around 10
                            consistent with the predicted effective             mSv/h. Since 1956, there have been six
                            dose rate of 7 ,uSv/h. This result, which is        recorded significant solar events in which the
                            in accordance with other reported studies           intensity of the solar radiation rose substan-
                            indicates that it is unlikely that any of the       tially above that of galactic radiation,3 but
                            cabin crew based in Tokyo exceeded the 6            there is no known instance of the Concorde
                            mSv/y level. In accordance with "as low             supersonic transport aircraft (SST) emergency
                            as reasonably achievable" principles                flightplan, which is triggered at 0-5 mSv/h,
                            British Airways will continue to monitor            being activated when the aircraft was flying
                            flying crew routes and hours flown to               during these events.4
British Airways Health      ensure compliance.                                     To follow "as low as reasonably achievable"
Services, Speedbird                                                             principles this would involve, subject to air
House, PO Box 10,
Heathrow Airport,           (Occup Environ Med 1996;53:495-498)                 traffic control approval, Concorde's immedi-
Hounslow, Middlesex                                                             ate descent to a lower altitude.
M Bagshaw                                                                          Protection from radiation is provided by the
D Irvine                    Keywords: cosmic radiation; flying crew; longhaul
D M Davies                  flights
                                                                                geomagnetic field and the attenuating effect of
Correspondance   to:
                                                                                the earth's atmosphere. Geomagnetic shield-
Dr M Bagshaw, Aviation                                                          ing decreases with increasing geomagnetic lati-
Medical Services, British   Cosmic radiation was first observed in 1912 by      tude, radiation levels over the polar regions at
Airways Health Services,
Speedbird House, PO Box     the Austrian physicist and balloonist, VF           typical subsonic cruising altitudes of 12 km
10, Heathrow Airport,
Hounslow, Middlesex         Hess, since when research has continued to          (about 39 000 ft) being about twice those over
TW6 2JA.                    develop knowledge and understanding of the          the equator at the same altitudes.
Accepted 21 February 1996   earth's radiation field.                               The cosmic radiation dose also increases
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496                                                                                        Bagshaw, Irvine, Davies

         with altitude such that the dose equivalent at        Subsonic longhaul flights
         18 km (about 59 000 ft) is roughly twice that         Subsonic longhaul flights (greater than six
         at 12 km (about 39 000 ft).                           hours) normally operate at an altitude in the
                                                               region of 12 km (about 39 000 ft) where
                                                               atmospheric shielding is predicted to give
         Radiological protection                               about half the cosmic radiation dose rate of
         The International Commission on Radiological          that at 18 km (about 59 000 ft) at a similar lat-
         Protection (ICRP) has published recommenda-           itude. However, the dose of cosmic radiation
         tions5 which take account of new biological           at polar latitudes is about twice that at the
         information and approaches to the setting of          equator at a given altitude. A dose rate
         safety standards. It has also now recommended         received from a transatlantic Concorde flight,
         that exposure of crew to cosmic radiation in jet      in the region of 10 piSv/h, can therefore be
         aircraft should be considered part of occupa-         thought of as an upper limit for the worst case
         tional exposure, which implies radiological sur-      transpolar subsonic flight.
         veillance of flying crew. The recommended                The introduction of the Boeing 747-400
         mean principal whole body limits on effective         aircraft has led to the development of ultra-
         dose are (over five years) 20 mSv/y for workers       longhaul flights of up to 16 hours duration,
         (which would include flying crew) and 1 mSv/y         some of which are trans-polar or trans-
         for the public. There is the additional recom-        Siberian, where geomagnetic and atmospheric
         mendation that equivalent dose to the foetus          shielding are less than for routes at lower lati-
         should not exceed 1 mSv during the declared           tudes.
         term of pregnancy.                                       Other longhaul flights are trans-equatorial
            The equivalent dose in an organ or tissue is       or east-west at near equatorial latitudes.
         the mean absorbed dose modified by the radia-            Two crews are normally carried on the
         tion weighting factor, based on the type and          ultralonghaul flights so that each crew works
         quality of the external radiation field. The effec-   half the flying hours, but of course they take
         tive dose is the sum of organ or tissue equivalent    their rest on board the aircraft. They are thus
         doses each weighted by a factor which takes           exposed to cosmic radiation during both their
         account of the probability of a particular effect.    working and non-working hours but are con-
         Quality factors are also modifying factors            sidered to be on duty during the whole flight,
         applied to absorbed dose to take account of the       their permitted flying hours being limited
         type and quality of the radiation field. They are,    accordingly. British Airways flight deck crew
         however, different in concept to the radiation        flying mixed longhaul and ultralonghaul flights
         weighting factors. The result of modifying            fly up to 600 hours a year.
         absorbed dose with quality factors is termed             It should be noted that flight time is defined
         dose equivalent.                                      as being from the time the aircraft first moves
            Since the recent ICRP recommendations,5            under its own power until it ceases to move at
         the values of effective dose for neutrons are         the end of the flight. The result is that a person
         about 50% greater than the previous recom-            is in fact only at high altitude for a proportion
         mended values of the limit for the cosmic radia-      of the recorded flying hours.
         tion fields.                                             With the introduction of ultralonghaul
            In accordance with standard radiological con-      flights between Japan and London flying the
         trol practice, the United Kingdom National            polar and trans-Siberian routes, British
         Radiological Protection Board (NRPB) recom-           Airways has been using cabin crew based in
         mends that there should be a systematic assess-       Tokyo who fly only these ultralonghaul sec-
         ment of the individual dose of those workers          tors, but may fly up to 900 hours a year.
         considered likely to receive an effective dose of        With a heuristic model based on data
         more than 6 mSv/y.6                                   quoted by the National Aeronautics and Space
                                                               Administration (NASA),' that provides a con-
                                                               servative estimate of dose equivalent based on
         Supersonic transport (SST) flights                    proposed values of quality factors,9 which
         The Concorde SST entered service with British         accounts for time at cruising altitude, time
         Airways and Air France in 1969 and was                taken to achieve this altitude, and a stepwise
         designed to fly at the unprecedented commer-          function change for effect of latitude, a sample
         cial operating altitude of around 18 km (about        of flight deck and cabin crew was examined
         59 000 ft). Concern for potential hazards to the      across all fleets to determine likely exposure.
         occupants such as exposure to cosmic radiation        The arithmetic means of most of the annual
         led to monitoring equipment for ionising radia-       dose equivalent rates varied between 2 and 4
         tion being installed in all Concorde aircraft.        mSv/y, and were directly correlated with num-
         Many data have been derived from this, includ-        ber of hours flown. The only exception was a
         ing more than 20 years experience of the radio-       mean of just below 6 mSv/y for the cabin crew
         logical environment.4 7                               based in Tokyo. It was thought appropriate to
            Most of the SST routes are transatlantic           study this group more closely with known
         between latitudes N70 degrees and N40 degrees,        schedules and flight hours to describe the
         with additional sectors between N40 degrees           likely distribution of exposure estimates.
         and N25 degrees in the eastern United States;            A total of 145 cabin crew were assessed for
         there are occasional charter flights in higher        the 12 months of 1992, during which the
         northern latitudes. Data from these flights indi-     London-Osaka route supplemented the
         cate that the radiation exposure of Concorde fly-     London-Tokyo route. Across the whole data
         ing crew is unlikely to exceed 6 mSv/y.4 7            set the calculated dose equivalent rate was
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Exposure to cosmic radiation ofBritish Airways flying crew on ultralonghaul routes                                                497

                               8 uSv/h. This is considered to represent a con-      to correct the results of thermoluminescence
                               servative upper limit for the effective dose.On      measurements from the thermoluminescence
                               the basis of this value, as many as 60% of the       dosimeters for the difference in response effi-
                               group would exceed 6 mSv/y. The percentage           ciencies to different types of radiation and to
                               exceeding 6 mSv/y would, however, reduce to          determine the relation of tissue dose equivalent
                               less than 4% if the effective dose rate of 7 ,uSv/h  to other quantities. However, from a considera-
                               (a reduction of about 10%) were used. In accor-      tion of kerma factors and stopping power ratios
                               dance with good radiological protection prac-        for the dosimeter, detector material, and for tis-
                               tice, a study was made of actual doses received      sue, and based on the flat depth-dose distribu-
                               to enable the predictions to be validated.           tion in tissue for the non-neutron component,'0
                                  Work is ongoing to improve the understanding      the measured value of tissue dose for a caesium-
                               of the radiation field and the NRPB is working       137 photon calibration is considered to be a
                               closely with other European laboratories in          good estimate, within 10%-20% of effective
                               defining appropriate quantitative measurement        dose for the non-neutron component.
                               procedures. None the less, it was considered            The neutron component of the radiation field
                               that there is sufficient understanding to enable a   was measured by a polyallyldiglycol carbonate
                               preliminary survey to be performed.                  (PADC, also known as CR39) dosimeter. This
                                                                                    responds to neutrons of all energies above about
                                                                                    100 keV (and also to thermal and epithermal
                               Aim                                                  neutrons) and its response characteristics are
                               The aim of this study was to measure the cos- known up to 70 MeV. The PADC dosimeter
                               mic radiation field encountered throughout the responds also to high energy protons. On the
                               London Heathrow-Tokyo Narita route flown by assumption of an isotropic neutron field and for
                               the Boeing 747-400 to give a guide to the valid- representative neutron spectra, the neutron flu-
                               ity of the predicted radiation dose received by ence calculated from the response of the track
                               cabin crew based in Tokyo.                           detectors may be converted to an estimated
                                                                                    value of effective dose. Because of the assump-
                                                                                    tions made and incomplete knowledge of both
                               Equipment                                            detector response characteristics and the radia-
                               Galactic cosmic radiation can be measured tion field, there is a correspondingly greater
                               actively or passively. Many detectors measure uncertainty, estimated at around 30%, in the
                               only one type of radiation accurately and usually value of effective dose for the neutron compo-
                               for only a limited energy range, but they may nent.
                               show some sensitivity to other types of radia-          Notwithstanding the limitations, based on
                               tion.                                                advice from NRPB, it was considered that
                                  An active, or direct reading, instrument dis- a combination of thermoluminescence dose-
                               plays the appropriate readings immediately or meters and PADC dosimeters was appropriate
                               after a short delay, whereas passive, or integrat- for use in this validation study.
                               ing, instruments need to be evaluated in a labo-
                               ratory after the flight. Active dosimetry can be
                               based on Geiger-Muller counters (y radiation), Method
                               ionisation chambers (y radiation), moderated Packs were prepared and supplied by the NRPB
                               boron trifluoride counters (neutrons), scintilla- consisting of sealed plastic bags containing two
                               tion counters (yradiation or neutrons), or tissue PADC neutron and two thermoluminescence
                               equivalent proportional counters (for mixed dosimeters suitable for installation in a British
                               radiation fields) which can be set up to indicate Airways Boeing 747-400 aircraft.
                               both actual dose and dose equivalent.                   Suitably labelled packs were installed on verti-
                                  The calibration and instrumentation are rela- cal surfaces on the flight deck, in the wardrobes
                               tively complex and a suitable tissue equivalent of the upper deck, the first class area, the club
                               proportional counter instrument was not readily (business) area, the world traveller (economy)
                               available for use on this trial. Other forms of area, and in the cabin crew rest area. They were
                               active instrumentation such as y and neutron secured by tape, situated away from strong heat
                               dosimeters can be difficult to interpret because sources, and left undisturbed in situ for the
                               of the complexity of the radiation spectrum, duration of the study.
                               including energetic charged particles.                  Also a pack was put on the ground at London
                                   It was considered that active dosimetry was Heathrow Airport and another at Tokyo Narita
                               not appropriate for this study.                      Airport, remaining at these sites for the duration
                                   Passive dosimeters have the advantage of of the measurement programme.
                               being small, light, and robust and are readily          Nine return flights were made between
                               available. Compared with active dosimeters, London and Tokyo, departing between 11 May
                               they are relatively much less sensitive. However, 1993 and 2 June 1993.
                               this can be overcome by increasing the exposure         The dosimeters from the aircraft and from
                               time.                                                 the ground stations were returned to the NRPB
                                   Standard thermoluminescence dosimeters on 8 June 1993 and processing was completed
                               respond to x and yradiation and also to charged within three days.
                               particles (electrons, protons, muons, etc) and
                                can give a good estimate of tissue dose equiva-
                                lent for the non-neutron components of the cos- Results
                                mic radiation field at aviation altitudes. A fuller Eighteen non-stop sectors were recorded
                                understanding of the radiation field is required between London Heathrow and Tokyo Narita
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498                                                                                                       Bagshaw, Irvine, Davies

         airports. The mean sector flying time was 11 5 and Tokyo Narita represents the worst case for
         hours, with 10 hours spent above an altitude of cosmic radiation exposure for British Airways
         10 km (about 33 000 ft).                                    longhaul flying crew, particularly the cabin
           The latitudes varied between N39 degrees                  crew based in Narita who fly this route regu-
         and N66 degrees, with a mean time above N50                 larly. Prediction of the radiation exposure of
         degrees on each sector of 10 hours.                         this group showed that 60% had yearly dose
           Ground level background radiation was mea-                rates in the order of 6 mSv based on an upper
         sured at Heathrow and Narita airports as 0 07     limit effective dose rate of 8 /uSv/h, but less than
         puSv/h.                                           4% for an estimated effective rate of 7 ,uSv/h.
            Analysis of the thermoluminescence dosi-       Although well within the dose limit of 20
         meters gave a value, rounded up, for inflight x, y,
                                                           mSv/y, a suggested control limit of exposure of 6
         and charged particle components of 3 /uSv/h.      mSv/y above which individual assessment of
            The inflight neutron component measured        dose and dose recording would be required,
         by the PADC dosimeters also gave a rounded may be set, and this would conform with existing
         up value of 3 #uSv/h.                             British Airways practice.
            The mean effective dose rate was calculated       The effective dose rate of 6.uSv/h estimated
         to be around 6 #uSv/h (with an uncertainty of from measurements is, however, consistent
         about 20%) giving an effective dose for the with the conservatively calculated value of 7
         return London-Tokyo flight in the region of ,uSv/h, and although subject to a degree of
         120 jsSv.                                         uncertainty, indicates that it is unlikely that any
            No significant variation in dose rate between of the cabin crew based in Tokyo, who repre-
         the dosimeter locations on the aircraft was sent the group most at risk, will exceed 6
         found.                                            mSv/y.
                                                              No British Airways flight deck crew members
                                                           approach the ICRP recommended control level
         Discussion                                        or dose limit.
         Interpretation of these data requires some We acknowledge the advice and technical assistance given by
         caution as further work is necessary to take bet- Dr D T Bartlett of the National Radiological Protection Board,
         ter account of the characteristics of Chilton, Didcot, Oxfordshire.
         the radiation field and the most appropriate       1 Bartlett DT, McAulay IR, Schrewe UJ, Schnuer K, Menzel
         quantity to be measured. This is being                 HG, Bottollier-Depois J-F, et al. Dosimetry for occupa-
                                                                tional exposure to cosmic radiation, presented at the 8th sym-
         considered by the NRPB and other European              posium on neutron dosimetiy, Paris, 13-17 November 1995.
         laboratories. None the less, this study has pro- 2 Foelsche ofAircraft safety in high altitude air traffic.
                                                                         T. Radiation
                                                                Journal
         duced results which are consistent with 3 Friedberg W, Snyder1977;14:1226-33. Radiation exposure of
                                                                                      L, Faulkner DN.
         the values of exposure to radiation predicted by       air carrier crewmembers ii. Washington: Department of
                                                                Transport, 1992. (Final report DOT/FAA/AM-92/2.)
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         agreement with similar investigations per-                       the impact of new ICRP recommendations on commercial
                                                                          aviation. Radiation Protection Dosimetry 1993;48:121-4.
         formed in the United States," Germany,'2 13                  5 International Commission on Radiological Protection,
         Sweden, '4 France, 'I5 Czechoslovakia,'6 and                     publication 60. Annals of the ICRP 1991;21:1-3.
                                                                      6 Document of the National Radiological Protection Board.
         Japan,'7 18 and reviewed by the European Radia-                  Chilton, Oxford: NRPB 1993,4.
         tion Dosimetry Group (EURODOS).1                            7 Preston FS. Eight years of Concorde operations: medical
                                                                         aspects. R Soc Med 1985;78:193.
            The heuristic model with a dose equivalent               8 Transport methods and interactions for space radiations.
         level of 8 puSv/h is overly conservative in implying            Springfield, VA: NASA Technical Information Service,
                                                                          1991. (NASA Ref Publ 1257, December 1991.)
         that as many as 60% of the cabin crew based in              9 The quality factor in radiation protection. International
         Tokyo could exceed 6 mSv/y if the effective                     Commission on Radiation Units and Measurements Report
                                                                         No 40, 1986. Bethesda, MD: ICRU, 1986.
         dose were the same. For the experimentally                 10 O'Brien K, Friedburg W. Atmospheric cosmic rays at
         determined effective dose rate of 6 ,uSv/h none                 aircraft altitudes. Environment International 1994;20:
                                                                         645-63.
         of this potentially high risk group would exceed           11 Friedberg W, Faulkner DN, Snyder L, Darden EB Jr,
         the 6 mSv/y level where roster restrictions                     O'Brien K. Galactic cosmic radiation exposure and asso-
                                                                         ciated health risks for air carrier crew members. Aviat
         would have to be contemplated.                                  Space Environ Med 1989;60:1 104-8.
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                                                                         Final report GSFIBGIDLH research project. Germany:
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         be satisfied that the existing monitoring proce-           13 Schuhmacher H, Schrewe UJ. Dose equivalent measurements
                                                                         on board civil aircraft. Braunschweig, Germany: 1993.
         dure, based on duration, altitude, and latitude                 (Report PTB-Bericht N-13.)
         of flight using our heuristic model, is a good             14 Lindborg L, Karlberg J, Elfhag T. Legislation and dose equiv-
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         approximation for immediate practical pur-                      Swedish Radiation Protection Institute, 1991. (SSI
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                                                                    15 Nguyen VD, Lebaron-Jacobs L, Bouisset P, Kerlau G, Itie
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                                                                         aboard French airliners. In: Proceedings of the 40th
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                                                                    16 Spurny F, Obraz 0, Pernicka F, Votockova I, Turek K.
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                                                                    18 Kaji M, Fujitaka K, Sekiya T, Asukata I, Ohkoshi H,
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                                                                         tion dose equivalent on board aeroplanes to/from Japan:
         The direct flight between London Heathrow                       2nd report. Aviat Space Environ Med 1995;66:487.
                    Downloaded from oem.bmj.com on August 1, 2012 - Published by group.bmj.com




                                  Exposure to cosmic radiation of British
                                  Airways flying crew on ultralonghaul routes.
                                  M Bagshaw, D Irvine and D M Davies

                                  Occup Environ Med 1996 53: 495-498
                                  doi: 10.1136/oem.53.7.495


                                  Updated information and services can be found at:
                                  http://oem.bmj.com/content/53/7/495




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