Dr. THOMAS K. W. NG, M.B., B.S., D.P.H., D.I.H., LL.B.
                   Department   of Community   Medicine, University   of Hong Kong.

        With years of planning and negotiation, the mass transit system of Hong Kong is now
under construction. For the first time, work in compressed air is being carried out on large
scale in Hong Kong and ways and means have to be sought for the prevention and treatment
of decompression sickness.
        Compressed air is required to keep away the water on tunnelling through the previous
layer of the earth so as to provide a comparatively dry environment for working (Diagram 1).
The pressure of compressed air required depends upon the depth of the tunnel and the porosity
of the stratum. For the latter, the civil engineering industry is experimenting at the moment to
treat the soil with chemicals in order to reduce its porosity, thus lowering the pressure of com-
pressed air required and reducing the hazard to the workers.
        Decompression sickness was scheduled as an occupational disease in Hong Kong under
the Workmen’s Compensation (Amendment) Ordinance 1965. So far, no one has claimed
workmen’s compensation for this particular occupational disease,but this may not necessarily be
SOin future if no stringent measuresof prevention are imposed. Again, this is a notifiable occupa-
tional disease in Hong Kong under the Factories and Industrial Undertakings (Notification of
Occupational Diseases) Regulations 1965.
       The Factories and Industrial Undertakings (Work in Compressed Air) Regulations 1975
are made by the Commissioner of Labour under Section 7 of the Factories and Industrial Under-
takings Ordinance 1955. The law is not specially made for the mass transit system, but its
construction hastens the coming into being this piece of occupational health and safety legislation.
        The objective of this paper is to introduce these special regulations for the prevention
and treatment of decompression sickness to the medical profession in Hong Kong. Moreover,
these regulations bring forward an innovation -the appointed doctors, and it is hoped that this
paper may be helpful to those who intend to be appointed.

                                 DECOMPRESSION SICKNESS
         Decompression sickness is a disease known by many names such as caisson disease,
compressed air illness, pulmonary barotrauma, “bends”, diver’s paralysis, and aeroembolism of
aviators. Decompression sickness is the most appropriate term as it indicates that the cause of
this disease is due to improper decompression. A decompression is improper in the sense that
insufficient time has been allowed for the compressed air absorbed in the blood or tissue fluids
to come out of the body without forming gas bubbles inside the body. How these bubbles are
formed and related to the disease are still not clearly known and research is being carried out by
                                     THE BULLETIN           OF THE HONG        KONG     MEDICAL   ASSOCIATION            VOL.       27,       1975

the Department of Surgery, University of Newcastle to demonstrate the presence as well as the
effects of these bubbles on experimental animals (1) and men (2).

       This disease has both an acute and a chronic manifestation. Though workers with an
acute stage are more likely to develop the clinical picture of the chronic stage years later, it is
now known that quite a number of workers with chronic decompression sickness have never
experienced the acute stage before (3). Because of that, the decompression tables used in the
past have been reconsidered and new tables are computed to replace them (4).

     -----                                          ----                                                   -                    ----

     ---                                                         p--v-                                                                         ---

             ---                                            --                      -         Porous             -              -                    -          _         -     _
                                                       --------                                                                                                -
     ----                                                   ----------
     --                --                              -----                                                                        --_I
     ---                        -                          --                     --          Stratum                -                    -                -             -          -
     ----                                                   --                 ---                                          v-v-
      --                    -                                                                     -            Pressurised                               tunnel           _

     Lock          attendant                -          -                 -     -          -                                                          -              --
             -w                         -                   -        Man     lock             -         -Miners                        at Working                        face

                                    Diagram 1. Tunnel Construction Using Compressed Air.

       The acute stage is again divided into Type I and Type II; the former being common and
with no constitutional upset whilst the latter being rare but serious or even fatal (5).

       A worker with acute Type I decompression illness has pain in one or more of his limbs
but he does not feel or look ill. The pains may commence at any time from the final stages of
decompression to 12 hours after decompression. The intensity of the pain may be agonising
(bends) or slight (niggles).
                        AN   INTRODUCTION    TO THE HONG   KONG   FACTORIES    AND   INDUSTRIAL    97
                              UNDERTAKINGS    (WORK   IN COMPRESSED   AIR)    REGULATIONS

       A patient with acute Type II decompression sickness usually feels and appears ill.         The
presentation varies greatly and may take up any one or a combination of the following:-
       1.   loss of consciousness,
       2    collapse, with signs and symptoms of shock,
       3.   giddiness (the staggers),
       4.   difficult breathing (tightness of chest or chokes'),
       5.   visual symptoms (‘flashes of light’ or spots before the eyes),
       6.   headache,
       7.   stomach pains, with or without vomiting,
       8.   weakness or paralysis of limbs,
       9.   tingling or numbness of limbs.
        Chronic decompression sickness can take up at least three forms. The neurological and
psychiatric forms, including paralysis, are not very common. The serious problem of the osseous
form, known as aseptic necrosis of bone, is brought into light by careful analysis of the records
of the past compressed air projects in the United Kingdom by the Decompression SicknessPanel
of the Medical Research Council (6) and becomes at present the focus of attention. It affects
chiefly the heads of humerus and femur as well as the lower end of femur and the upper end of
tibia. The Decompression Sickness Panel adopts the following classification of bone necrosis in
compressed air workers (7) :-
       A.   Juxta -   Articular     Lesions
       1.   Dense areas, with intact articular cortex.
       2.   Spherical segmental opacities.
       3.   Linear opacity.
       4.   Structural failures :
            (a) Translucent subcortical band.
            (b) Collapse of articular cortex.
            (c) Sequestration of cortex.
       5.   Osteoarthritis.
       B.   Head, Neck and Shaft Lesions
       1.   Dense areas.
       2.   Irregular calcified areas.
       3.   Translucent areas and cysts.
       4.   Endosteal thickening.

        Symptoms in asceptic necrosis of bone do not usually develop until there is collapse of the
necrotic juxta-articular bone. In a review of over 600 bone lesions in compressed air workers,
the only joints found to become secondarily affected with degenerative arthritis are the shoulder
and the hip, giving rise to crippling conditions (8).

        Decompression sickness is such a hazardous occupational diseasethat the best method of
control is prevention. The law lays down the method of decompression (Third Schedule), the
provision of man-locks or decompression chambers (Regulations 8 & 9), the duties of the lock
attendants (Regulations 10 & 11), and the requirement of routine medical examinations
(Regulations 24, 26 & 28).
98                   THE BULLETIN   OF THE   HONG    KONG   MEDICAL   ASSOCIATION   VOL.   27,   1975

        The reference decompression tables for Hong Kong are those computed by H. V.
Hempleman for the Medical Code of Practice for Work in Compressed Air (9). These are also
known as the Blackpool Tables because they were first tried in a civil engineering project in that
place. It is claimed that these tables represent a compromise between practicability and
theoretical ideals.
        Two important factors are taken into consideration in the computation of decompression
tables. The first one is the absolute pressure of the working environment and the second one is
the duration of the working shift. For the first one, Haldane believed in 1908 that it was
quite safe to reduce the absolute pressure rapidly to half (10) and this permitted reduction ratio
of 2 has been followed for years. Now, it has been demonstrated that such a ratio is in fact too
high for safe decompression and the Blackpool Tables are calculated with permitted reduction
ratios varying from 1.9 for the low gauge pressure to 1.6 for the high gauge pressure (9).
        Evidence also shows that for short exposure times it is possible to go safely to great
pressures, whereas for long exposure times only relatively low pressures are safe. But for work
in compressed air, it is uneconomical for workers to do split shifts, and so, most workers work
an 8-hour shift whilst there are three shifts of workers per day. Thus, the decompression table
that is in frequent use is the one for exposure period from 4 hours to 8 hours. A copy of this
table is given below for information and reference:-

                             Decompression Table for Exposure Period
                                         From 4 Hours to 8 Hours

    Maximum                          Prescribed number of minutes to stay
 working pressure                      in each stage pressure (lb/in”g)                                        Total time
     (Lb/in8g)                                   (see Note 2)                                                  (minutes)
  (see Note 1)    28                                                                                          (see Note 3)
                                    24          20             16            12             8            4
     14 to    16                                                                                         15         15
     '16 to   18                                                                                         30         30
     18 to    20                                                                                         45         45
     20 to    22                                                                            5            55         60
     22 to    24                                                                           15            60         75
     24 to    26                                                                           30            60         90
     26 to    28                                                              5            35            60        100
     28 to    30                                                             10            45            60        115
     30 to    32                                                             20            45            60        125
     32 to    34                                                5            30            45            65        145
     34 to    36                                               10            35            45            70        160
     36 to    38                                               20            35            45            80        180
     38 to    40                                     5         25            40            50            85        205
     40 to    42                                    10         30            40            50            90        220
     42 to    44                     5              15         30            40            55           100        245
     44 to    46                     5              20         35            40            60           110        270
     46 to    48                    10              25         35            45            65           120        300
     48 to    50        5           10              30         40            45            70           130        330
                           AN   INTRODUCTION    TO THE HONG   KONG   FACTORIES    AND   INDUSTRIAL
                                 UNDERTAKINGS    (WORK   IN COMPRESSED    AIR)   REGULATIONS

1.   Where alternative  decompression           procedures    are given     (e.g. 46 lb/in”)         the longer decompression
     procedure should be followed.
2.   Decompress      between stages at a rate of 5 1b/in2 per minute.
3.   Not including    time between stages.

       Seldom for work in compressed air will the pressure exceed 50 1b/in.2 Under that
working pressure, it takes almost 6 hours for decompression when the shift is over. On the
other hand, decompression by stages is not required if the working pressure is below 14 lb/in2
gauge, irrespective of the length of the shift.
        A decompression chamber or man-lock must be of adequate internal dimensions, prc-
viding a space of 45 cubic feet per person. As decompression sometimes may take hours, the
workers must be ensured as comfortable an environment as possible inside the chamber. The
decompression chamber must be designed in such a manner that efficient means of communica-
tion are available between the lock attendant outside and the workers inside. Moreover, these
workers must be able to see the clock used by the lock attendant and to know the pressure
they are experiencing at any particular moment during decompression.
        Decanting is a type of decompression whereby the workers in the decompressionchamber
(usually a very small one called blister lock due to lack of space underneath the surface of the
ground) are rapidly decompressed to atmospheric pressure and then transferred to a decant lock
(on the surface of the ground) for recompression followed by proper decompression. This is a
hazardous procedure and is to be discouraged.
        A lock attendant not only controls the pressure inside the decompression chamber and
keeps records accordingly, but also screens workers and visitors that they possess proper
authorisation to enter work in compressed air and records accurately and fully the details of
each exposure of each person on the Lock Attendant’s Register. Before he is posted to the job,
he must attend a recognised course of training designed to familiarise him with the problems
associated with compression, decompression, decompressionsickness and the keeping of records.
       Routine medical examination is required to ensure that only fit persons are permitted to
worker in compressed air and to detect any early deviation from health among the workers.
Every person must undergo a medical examination before being employed in, or exposed to,
compressed air. The following conditions are absolute disqualifications suggestedby the Decom-
pression Sickness Panel :-
          1.   chronic catarrh of the upper air passages,in particular recurrent sinus infection.
          2.   chronic suppurative otitis media.
          3.   inability to ‘clear the ears’.
          4.   chronic lung disease past or present, bronchial asthma, bronchiectasis, history of
          5.   peptic ulcer.
          6.   hernia.
          7.   heart disease.
          8.   hypertension.
          9.   diabetes.
         10.   epilepsy.
         11.   disease of central nervous system.
         12.   gross obesity.
         13.   bone disease.
100                        THE BULLETIN   OF THE   HONG   KONG   MEDICAL   ASSOCIATION   VOL.   27,   1975

        Medical examination has to be repeated every 3 months for workers employed at pressures
not exceeding 14 lb/in2, and every 4 weeks for workers employed at pressures equal to or above
14 lb/in”. Moreover, a worker suffering from a cold in the head, chest infection, sore throat
or earache should not work in compressed air. Workers suffering from these conditions or any
other illness or injury necessitating absence from work for more than 3 days must undergo
another medical examination for fitness before returning to work in compressed air.
      Radiographic examination of the major joints is required within 4 weeks of employment
in compressed air exceeding 14 lb/in2 and has to be repeated at intervals of 6 months.

                           TREATMENT               OF DECOMPRESSION SICKNESS
       The only treatment for acute decompression sickness is by means of recompression in a
medical lock followed by therapeutic decompression. Recompression in a medical lock also is the
only method to confirm the dianosis of acute Type II decompression sickness if the signs and
symptoms disappear after recompression.
       As acute Type II decompression sickness usually occurs within one hour after decom-
pression, the proprietor or contractor is required by law to provide and maintain for the use of
compressedair workers adequate and suitable facilities for remaining on the site for one hour
after decompression from pressure exceeding 14 lb/in2. (Regulation 15 (1) (c)).       Moreover,
these workers should wear labels indicating that they are compressedair workers and the address
of the medical lock they should be taken to if found unconscious (Regulation 33). A specimen
of a personal label used in the Trial Tunnel Project in Hong Kong in 1974 is given below for
illustration   (Diagram    2) :

                                          H.K. M.T.S. TRIAL TUNNELS
                                            CHARLES BRAND & SON
                                      (COMPRESSED AIR WORKER)
                                       IF THIS MAN IS FOUND ILL
                                    PLEASE SEND TO MEDICAL LOCK
                                            LAI CHI KOK SITE
                                  NEXT TO OLD LAI CHI KOK HOSPITAL
                                     CASTLE PEAK ROAD, KOWLOON
                                           TELEPHONE 3-721497
                          Diagram 2 -        Person Label Of Compressed Air Workers

        Whenever work in compressed air exceeding 14 lb/in2 is commenced, it is necessary to
notify the factory inspectorate, the Senior Industrial Health Officer, and the nearest police station
(Regulation 30) so as to ensure that the compressed air workers are sent to the correct place
for treatment.
         The law requires the provision of a suitable medical lock if the working pressure exceeds
 14 lb/in2 (Regulation 21) and it must be kept at all times ready for immediate use. Except
for the testing of men without previous experience of compressed air work and in certain emer-
gencies, the medical lock must be used only for therapeutic purpose. The medical lock must
have two compartments so that it can be entered while under pressure.
                        AN   INTRODUCTION    TO THE HONG   KONG   FACTORIES     AND   INDUSTRIAL   101
                              UNDERTAKINGS    (WORK   IN COMPRESSED   AIR)    REGULATIONS

        At least one medical lock has to be provided for 100 compressed air workers on a site.
It must be manned by a medical lock attendant who should be, preferably a registered nurse,
or minimally a person trained in first aid, and who should have completed a suitable course of
training in the medical aspects of compressed air work. He must be physically fit and willing
to go into compressed air at any working pressure. He works under the direction and supervision
of an appointed doctor.
        Therapeutic procedures for acute decompression sicknessare stated clearly in Appendix 8
of the Medical Code of Practice for Work in Compressed Air (9). The basic principles are
immediate recompression to working pressure, or a higher pressure if required, the maintenance
of the effective pressure for some time (at least 10 minutes for Type I and 30 minutes for Type
II) after all abnormal signs and symptoms have disappeared and then decompressioncarried out
very slowly and very carefully. This treatment may take a period of days, but it should be
continued as long as there is improvement, however slight. The patient should not be trans-
ferred to hospital, until it is certain that the residual symptoms are either not due to decom-
pression sickness or can no longer be improved by compression.
       Treatment for chronic decompressionsickness will not be mentioned here, as it is essentially
an orthopaedic problem for aseptic necrosis of the bone or even the neurological paralysis.

                                      THE APPOINTED DOCTORS

       One innovation of the Factories and Industrial Undertakings (Work in CompressedAir)
Regulations is the introduction of the concept of appointed doctors.
       When the maximum working pressure is likely to exceed 14 lb/in2, a doctor has to be
appointed by the contractor, usually on a full time basis, to supervise all medical matters which
may arise in connection with the work. The contractor has to notify the Commissioner for Labour
the name and address of the doctor appointed (Regulation 24). This appointed doctor must be
physically fit as he may have to go into the medical lock for the diagnosis and treatment of
workers suffering from acute decompression sickness whenever required. He conducts medical
examination of the workers and visitors for fitness to enter work in compressed air. He runs
the medical service on the construction sites. He supervises the working of the medical lock
attendants. He also supervises the keepers of the following records:-
         (i)   medical examination records of compressedair workers,
        (ii)   treatment records of compressed air workers suffering from decompression sickness
       (iii)   individual air records of each compressed air worker.
        A general practitioner can be a part-time appointed doctor if his duty is to conduct routine
medical examinations for those compressed air workers emproyed by employers other than the
contractors. His appointment has to be notified as well (Kegulations 25).
       Each compressed air worker carries a Compressed Air Health Register (Form 6) as
evidence that he is physically fit for work in compressed air. The appointed doctor signs the
Compressed Air Health Register after he has examined the worker and found him fit to work
in compressed air. The Compressed Air Health Register is a personal property of the worker
102                  THE BULLETIN   OF THE   HONG   KONG   MEDICAL   ASSOCIATION   VOL.   27,   1975

and he hands it over to his employer for custody on taking up new employment (Regulation 27).
It expires if the worker does not subject himself to another medical examination when the time is
due (Regulation 29).
        Any doctor practising in Hong Kong is required by the Factories and Industrial Under-
takings (Notification of Occupational Diseases) Regulations to notify every case of decompression
sicknesshe comes acrossby a statutory form to the Director of Medical & Health Services. Failure
for doing so will render him liable to a fine of five hundred dollars.
       Preferably, the appointed doctor should have some experience in hyperbaric medicine or
have attended a course of training in the medical aspectsof work in compressed air. It is hoped
that as soon as medical locks are installed in some of the construction sites, training courses for
doctors in Hong Kong can be arranged. As a basic requirement, each appointed doctor should
possessa copy of Medical Code of Practice for Work in Compressed Air and a copy of the
Factories and Industrial Undertakings (Work in Compressed Air) Regulations.

        There are many approaches to health education. The Factories and Industrial Undertakings
 (Work in Compressed Air) Regulations make it compulsory for the proprietor or contractor to
supply to each person employed to work in compressed air for the first time a statutory leaflet
(Form 8) containing advice as to the precautions to be taken in connection with such work
(Regulation 32). A copy of this leaflet is included as Appendix 1 for reference. The law also
states that the contents of this leaflet should be explained verbally to the workers whenever
       The law specifically prohibits the consumption of alcohol whilst in compressed air as an
acute Type II decompression sickness patient may easily be mistaken as a drunkard. A person
under the influence of alcohol is not allowed to work in compressed air (Regulation 34).
       Finally, the frequent medical examinations required will make the compressed air workers
conscious and aware of their own state of health.

         This piece of occupational health and safety legislation prescribes in detail the measures
for the prevention and treatment of decompression sickness. We are fortunate in that we are
learning from other people’s experience so that we can have a more or less comprehensive
legislation from the beginning.
       Just becausewe acquire our knowledge of decompression sickness from elsewhere, we must
have prevision for review and research. Unfortunately, the suggestion to centralise all the com-
pression records as well as all the medical records in a Central Registry was not accepted. In
order to detect the early deviation from health, not only of the individual workers, but also the
working force as a whole, I hope all the appointed doctors will get together and form a Hong
Kong Decompression Sickness Research Panel.
      For years, there is a lack of strong emphasis on the practice of occupational health in
Hong Kong. The new legislation invites medical practitioners interested in this particular aspect
                           AN   INTRODUCTION    TO THE HONG   KONG   FACTORIES    AND   INDUSTRIAL
                                 UNDERTAKINGS    (WORK   IN COMPRESSED   AIR)    REGULATIONS

    of medical practice to become appointed doctors. Gradually, we hope to have a full occupational
    health service for Hong Kong as envisaged in the Medical White Paper produced by the Director
    of Medical And Health Services in 1974 (11).

           Lastly, this legislation protects only one type of worker from decompression sickness,
    namely, the compressed air worker. We have a number of divers in Hong Kong, employed in
    the docks, civil engineering industry, salvage work, Police Force, Fire Service, Preventive Service
    and recreational clubs. It is high time that we should have Diving Regulations as well.

                                                     APPENDIX I

           The Factories and Industrial         Undertakings (Work in Compressed Air) Regulations

    Advisory leaflet prescribed by the Commissioner for Labour for issue to


    for the purpose of Regulation 18 of the Factories and Industrial Undertakings (Work in
    Compressed Air) special Regulations, 1975.

                                               READ THESE RULES CAREFULLY
                                               MAKE SURE YOU UNDERSTAND THEM
                                               FOR YOUR OWN SAKE-FOLLOW THEM

    Compressed air workers sometimes get pains in their joints soon after leaving the workings.
    These pains are called “the bends”, “caisson sickness”, or just “pains”. They may occur in
    muscles and other parts of the body. They can almost always be avoided. Pain is sometimes
    felt in the ears or head during compression. This can be avoided too.

    Very rarely a more serious kind of “bends” may occur and the worker may even “pass out”
    suddenly. Immediate recompression is necessary. (This is why it is so important that you
    always wear the label you have been given in case you get the “bends” when you are away from
    the site.)

    A certain number of persons who work in compressed air develop, after a time, small areas of
    damage in some of their bones. If these affect the hip or shoulder joints arthritis may follow.
    Failure to obey these rules will increase the risk of bone damage.


    Do not try to work in compressed air if you have a cold, earache or a sore throat. If you
    have had any of these complaints, or if you have been off sick through illness or accident for
    more than three days, you must be re-examined by the Doctor before you go back into
    compressed air.


104                  THE   BULLETIN   OF THE   HONG   KONG   MEDICAL   ASSOCIATlON   VOL.   27,   1975

If the working pressure is over 14 lb. per square inch, you must be examined by the Doctor
at least once every four weeks.

The outside lock attendant has to keep a record of all persons who enter and leave the lock,
and also has to control all decompression. Always obey his instruction.


If you get an attack of “bends” get back to the site as quickly as you can and report to the
medical lock attendant who will arrange for treatment in the medical lock.

You must never drink alcohol in compressed air, and smoking is also forbidden.

If you have not worked in compressed air before you must not enter the lock unless an
experienced compressed air worker is with you.

If the rate of compression is not controlled by the outside lock attendant, the proprietor or con-
tractor may tell the leading man to take charge of the valves which let in the compressed air.
If you feel pain or discomfort, warn the leading man or outside lock attendant at once, and
compression will be stopped. If the pain does not go, pressure will be reduced slowly and you
will be let out of the lock.


Decompression is usually in two stages, the first quick and the second very slow, though other
methods can be allowed under the Regulations.

The outside lock attendant must control all decompressions. Do not try to interfere with his
control. You can get in touch with him by means of the speaking tube, the telephone or the
observation window.

Attacks of “bends” usually start within 11/2 hours of decompression. If the working pressure
is over 40 lb. per square inch you should stay near the medical lock for at least 11/2 hours. If
it is less than this you should stay near the medical lock for at least an hour.


                                                             LABOUR DEPARTMENT
                                                             HONG KONG.
                           AN   lNTRODUCTlON     TO THE HONG      KONG   FACTORIES    AND   INDUSTRIAL
                                 UNDERTAKINGS     (WORK   IN    COMPRESSED   AIR)    REGULATIONS


 (1)   Evans A., and Walder         D. N., Detection           of Circulating       Bubbles in Intact     Mammal,      Ultrasonics
       8:216, 1970.

 (2)   Evans A., Barnard E. E. P., and Walder D. N., Detection                          of Gas Bubbles in Man at Decom-
       pression, Aerospace Medicine 43:10, 1972.

 (3)   Walder D. N., Caisson Disease of Bone in Great Britain in “Proceedings of the Fourth                                  Inter-
       national Congress of Hyperbaric  Medicine”, Igaku Shoin Ltd., Tokyo, 1970.

 (4)   Medical Research Council Decompression Sickness Panel, Blackpool                            Trial Decompression     Tables,
       University of Newcastle, Newcastle, 1966.

 (5)   Golding F. C., Griffiths P. D., Hempleman H. V., Paton W. D. M., and Walder D. N., Decom-
       pression Sickness During Construction of Dartford Tunnel, British Journal of Industrial Medicine
       17:167, 1960.

 (6)   Medical Research Council Decompression Sickness Panel, Decompression                              Sickness    and Aseptic
       Necrosis of Bone, British Journal of Industrial Medicine 28:1, 1971.

 (7)   McCallum R. I., Tunnelling in Compressed Air                   and Bone Necrosis,           Transactions     of Society   of
       Occupational Medicine 22:2, 1972.

 (8)   Davidson    J. K. and Griffiths         P. D., Caisson Disease of Bone, X-ray                 Focus 10:2, 1970.

 (9)   Medical Research Council Decompression Sickness Panel, A Medical Code of Practice for Work
       in Compressed Air, Construction  Industry. Research and Information   Association, London,

(10)   Boycott    A. E., Damant G. C. C., and Haldane J. S., The Prevention                          of Compressed Air Illness.
       Journal    of Hygiene 8:342, 1908.

(11)   Medical and Health Department, Hong Kong Government, The Further Development                                    of Medical
       and Health Services in Hong Kong, Government Printer, Hong Kong, 1974.

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