Caisson Disease at the New High Level Bridge

Papers.] BOYCOTT ON CAISSON DISEASE. 231

(Paper No. 3609.) ‘‘ Caisson-Disease at the New High-Level Bridge, Newcastle-on-Tyne.” By GEORGEWALTER MORGAN BOYCOTT. THE explanation of the cause of caisson-disease which is now generally accepted is that first put forward by Professor Raneaux in 1861, and known as the “ Air-emboli” theory. This theory was experimentally confbmed by the French physiologist, Mr. Paul Bert, in 1879 ; and others who have investigated the same subject are, on the Continent, Drs. Heller, Mager and Von Schrotter, whose results were published in 1898 ; and in Great Britain Drs. Leonard Hill and Macleod, whose results were published in 1903. The conclusions arrived at by these experimenters may be briefly summarized as follows :- (l) The blood-gases increase under pressure according to the law of Henry and Dalton. (2) On rapid decompression, gas-bubbles escape, arresting circula- tion and causing pressure on the nerves and tissue. (3) On re-compression, these gas-bubbles go again into solution. (4) The varying gravity of the symptoms is due to the varying seat of the air-bubbles. The law of Henry and Dalton is not, however, obeyed exactly, nor is it obeyed equally by all the gases present in the air. Time is required for the blood to become fully saturated;thus foremen, lock-tenders, and others whose duties necessitate their spending a comparatively short time under pressure, rarely suffer. Also, when the pressure is high, the number of cases of illness can be kept within reasonable limits by reducing the length of the shift. At Barmouth Viaduct, 1902, where the pressure reached was 46 lbs. per square inch above atmospheric pressure, the hours worked in each shift were l&hour at a time, twice a day. Under these conditions the cases of illness were, if anything, less severe and proportionately fewer than at Newcastle, where the pressure was 30 lbs. per square

inch and a nominal12-hour shift, with two breaks, was worked. With regard to the increase of the blood-gases under pressure, Mr. Paul Bert found that atincreased pressures the oxygen in theblood is increased only to a small extent ; the carbonic acid is notincreased to any appreciable extent ; and the nitrogen is increased more than eitherthe oxygen or the ca.rbonic acid. Drs. Leonard Hilland Macleod obtained similar results. The beneficial effect of re-compression has long been known, and at the ForthBridge men suffering from cc bends ’’ were in the habit of spending their Saturday afternoons and Sundays in the ordinary lock or working-chamber. At a tunnel under the Hudson River a special medical lock was introduced by Mr. Moir. Inthis lock cases were subjected to compressed air, which was then allowed to leak out slowly. As a result of the use of this lock, and also of a larger supply of air per man, the death-rate, which had been 25 per cent. per annum, was reduced to l$ per cent. per annum. It is necessary after re-compression that the subsequent decompression should be extremely slow, 30 minutes to 1 hour being allowed for a pressure of 30 lbs. per square inch, in order that the surplus air-gases may escape without again forming into bubbles. At Newcastle, the three caissons which were sunk for the founda- tions of the New High-Level Bridge were 113 feet in length from nose to nose of the cut-water, and 35 feet in width. The working- chamber was 9 feet in height, on an average, and access to it was obtained by means of three shafts, each of which was divided into two portions, one for men and the other for materials. The air was pumped into locks which were fixed at the top of the shaft, passed down the shafts and escaped under the cutting-edge. Escape-valves were provided for the purposes of ventilation, but were used only during the concreting of the working-chamber, since for the rest of the time the air found its way out freely under the cutting-edge. Air was pumped simultaneously into two shafts, of which the centre shaft was always one. Thenumber of men continuously under pressure varied between thirty and thirty-sixon each shift, and free air was delivered at the rate of about 1,400 cubic feet per man per hour. Two 12-hour shifts were worked, andin pressures upto 22 lbs. per square inch the men had only the usual 9 hour for break- fastand 1 hour for dinner allowed to men working outside. At pressures exceeding 22 lbs. per square inch, each meal-interval was increased by fr hour, and in addition a very liberal allowance was made for locking-in and locking-out, so that the actual time spent under pressure each day was 9h to 10 hours at the lower pressures :wl 8$ hours at the higher pressures. The maximum air-pressure

Downloaded by [ UNIVERSITY OF IOWA LIBRARIES] on [11/09/16]. Copyright © ICE Publishing, all rights reserved. Papers.] NEW HIGH-LEVEL BRIDGE, NEWCASTLE-ON-TYKE. 233 reached was a little more than 30 lbs. per square inch, and decompression was effected at the rateof 5 lbs. per square inch per minute. This rate was very strictly enforced. Locking-in iwas done at the same rate, but no definite rule was laid down and many of the men were in the habit of going in very rapidly. For persons who can easily inflate their Eustachian tubes, or who are not suffering from a cold and who do not for other reasons experience any pain or in- convenience during the locking-in process, there is no danger in this beingrapid. All men hadto be examined by the doctor before starting to work under air-pressure, and any mm found to be un- sound were rejected. It has been very generally held that the number of cases of illness varies as the percentage of carbonic acid present in the air. On the other hand, experiments on animals have shown that the increase of carbonic acid in solution in the blood under pressure is very small. It was therefore decided at Newcastle to take daily readings, during the sinking of one of the caissons, of the percentage of carbonic acid present in the air of the working-chamber, in order to ascertain whether any relation existed between the number of cases of illness andthe percentage of carbonic acid. Samples of air were taken daily by the Author, one sample being taken a few feet south of the centre shaft and the othernear that one of the two end shafts down which no air was being pumped. The percentage of carbonic acid present in each sample was obtained by means of theHaldane mrbonic-acid a.ppartus.The fluctuations inthe percentage of carbonic acid present in the samples taken near the centre shaft are shown inthe diagram (Fig. 1). The percentage present inthe samples taken near the end shaft was usually slightly higher. The high peaks in the fist and third weeks were due to the air-engine not pumping to its full capacity. Duringthe concreting of the working-chamber, on account of the freelime present in thecement, the percentage of carbonic acid fell rather below the point to which it fell duringthe week-ends when no work was being done. In order to supplement the more serious cases which would be reported to the doctor, and which would be too few to give any satisfactory results,a book was keptin which the foremen were requested to enterany cases,however trivial, which might come totheir notice. These cases have been plotted in Fig. 1 ;a case is shown by a hatchedsquare on theday on which it occurred. Thus on 27th October there were five cases. It will be seen that the cases are fairly evenly distributed, and that there isno marked increase when the percentage of carbonic acid is high. Indeed, the most serious caes, one in which B man was pardyzed, and another in which n

Downloaded by [ UNIVERSITY OF IOWA LIBRARIES] on [11/09/16]. Copyright © ICE Publishing, all rights reserved. 234 BOYCOTT ON CAISSON-DISEASE AT THE [Selected man lost S& shifts, occurred on 22nd and 24th October respec- tively, when the per- centages of carbonic acid were rather below the normal. Of the cases plotted, four only were of sufficient gravityto come under official medical supervision. On account of the form in which these figures are given, the Author has not been able to compare alto- gether accurately Dr. Snell’scases atthe Blackwall Tunnel, taken from his book on compressed-air illness, with those at Newcastle. The results of such com- parisons as he has been able to make, however, show that the cases of illness at Newcastle were neither more nume- rous nor of greater severity than those at the Blackwall Tunnel. The carbonic acid present in the working-chamber at Newcastle, as will be seen from the diagram (Fig. l),was on an average about twenty parts in ten thousand, whilst at

the Blackwall Tunnel it was never allowed to rise above ten parts in ten thousand. The Author is of opinion, as the result of his observa- tions at Newcastle, that the importance of good ventilation has been much over-estimated, andthat the true preventive treatment of caisson-illness is slowdecompression. The locks at Newcastle, although roomy and convenient as compared with many types with which the Author has had experience, were yet not large enough to render a long stay in them other than exceedingly irksome. He is of opinion that on work on which any large number of men is likely to be employed under air-pressure, special roomy locks should be provided in which decompression might be carried on at some such rates as those suggested by Drs. Leonard Hill and Macleod, which are given in theAppendix. When this is impossible the rate of decompression should be made as low as practicable, and themen should be encouraged to rest for a while before going home at theend of the shift, in order that if attacked by “ bends ” they may be treated by re-compression in the medical lock. Serious cases of illness generally come on within 3 hour of leaving the air-lock. Less serious cases may come on some hours afterwards. In many cases at Newcastle men have gone home and straight tobed, to wake up later suffering from“bends.” TheAuthor noticed that cases rarely occurred during a meal-time but nearly always at the end of a shift. This is probably because the effect of thethree periods of theshift is cumulative ; that is, the gas absorbed during a portion of a shift is not entirely liberated during the 1 hour or 14 hour allowed for meals. It may also be that towards the end of the day the muscles are tired and therefore less elastic than at the commencement of work ; and under these circumstances the liberation of the gas would be more difficult. This has been given as the reason why quite young men or youths enjoy greater immunity from “bends ” than older men. The men employed at Newcastle were all comparatively young, the age of the oldest being about 42 years. There was therefore not much opportunity of observing that increased liability to illness which is generally held to exist amongst older men. With regard to another opinion generally held, that plethoric people are specially liable to illness, it may be mentioned that many of the men at Newcastle were stoutly built, and amongst these were two or three men whom the Author particularly noted as being peculiarly free from any form of caisson-illness. Men who have worked under pressure for long periods appear to be as likely to suffer from “bends ” as those who are new to the work. Of the two most serious cases which occurred at Newcastle, one was that of a man who had worked under pressure for the

Downloaded by [ UNIVERSITY OF IOWA LIBRARIES] on [11/09/16]. Copyright © ICE Publishing, all rights reserved. 236 EOPCOTT OX CAISSOS-DISE$SE AT THE [Selected contractorsfor many years. After working 3 or 4 weeks under pressure the men had a very sallow appearance but did not seem to be in any way unhealthy. Indeed, there wasless ill-health among the caisson-men than amongst the men working in the open air on otherparts of the works. At one timean outcry was raised by members of the firm’s sick-club that caisson-men should pay an increased weekly contribution on the ground that theywere specially liable to sickness. On investigation, however, it was found that the caisson-men were drawing proportionately less sick-pay than other members of the club ; and at a regatta held amongst the men in the summer of 1904, during the active sinking of one of the caissons, more than half of the events were won by men who had been working under pressure right up to theday of the regatta. A medical lockwas provided at Newcastle. It was formed by converting an old air-lock which had been in use on a previous contract, and WSLSfitted with a bunk, so that it accommodated one man lying down and another sitting. It was found to answer all require- ments.The Author is of opinion thatwith slowdecompression, such as is recommended by Drs. Leonard Hill and Macleod, proper medical supervision, and, when necessary, curative treatment in the medical lock, it would be possible, provided it were made compulsory for the men to rest afterleaving the air-lock, to carry on compressed- air work with comparative immunity from illness at higher pressures than the 46 lbs. to 50 lbs. per square inch which has usually been considered the limit in thiscountry. The New High Level Bridge contract has been executed by Mr. F. W. Davis, Assoc. M. Inst. C.E., acting for the Contractors, the Cleveland Bridge and Engineering Company, Limited, assisted by Mr. C. R. S. Kirkpatrick, ASSOC.M. Inst. C.E. The Author super- vised the caisson-work under their direction.

The Paper is accompanied by a diagram, from which the Figure in the text has been prepared ; and by the following Appendix.

[APPENDIX.

TARLEOB LEXGTHSOF SHIFTSAND DECOMPRESSIOX-PERIODSSUGGESTED AS SAFE BY DRS. LEONARLIHILL AXD MACLEOD.

Lbs. per Square Inch above Atmosphere.I Shift. I Decompression-Periud. 30 4 hours 30 minutes to 1 hour 45-60 4 hours 1 to 2 houra 75 I hour 1 to 2 hours 90-105 30 minutes to 1 hour 2 hours