L. M. RYAN Medical Examiner, New York Foundation Company. Under conditions as they exist in New York at present employment in compressed air is not such a dangerous occupation as it was a few years ago. As improvements have been made in equipment for lessening the laborious part of the work and for overcoming the difficult problems of engineering, so has there been a great advance toward bettering the conditions under which the men are working. Chief among the altered conditions which have lessened the dangers of loss of life from caisson disease are: (1) physical examination of all employees; (2) shortening the hours of labor; (3) hospital locks, in charge of qualified attendants, where victims of the "bends" can be immediately recompressed; (4). lengthening the time of decompression in coming from work; (5) substitution of electricity for candlelight; and (6) a greater tendency on the part of the men to sobriety. I am speaking now with reference to the work of sinking caissons for foundations of buildings, and particularly of the compressedair work during the last five years in connection with many of the large buildings in lower Manhattan. Caissons or large vertical boxes are sunk to rock or hardpan, as necessity may demand. As the earth is excavated from underneath and inside the boxes the caisson settles, so that when rock or hardpan is reached we have a hollow vertical cylinder, or a miniature tunnel, leading from the surface of the ground to a solid support. For a building which extends over a large area a great many of these caissons have to be sunk. In the case of the municipal building of New York, for example, one hundred and six caissons were sunk to a depth of one hundred and twelve feet below water level and one hundred and thirty-five feet below the street level. These boxes or caissons are sunk in groups of three, four, five, or six, so that a force of from one hundred to one hundred and fifty men, or even as many as five hundred men, are employed at one time. The air is pumped from air compressors to the caissons and the pressure varies ac cording to the depth of sinking, so that at the same moment we may have one caisson, which is nearing its destination, having a pressure of as much as forty-five or forty-six pounds and another one, just being begun, having a pressure of only two or three pounds. In caisson work we have a few difficulties to be dealt with that are not met in tunnel work, but in the main the problem is the The percentage of cases of compressed-air disease in my experience has been lower on foundation work than in tunnel work, in spite of the fact that under most circumstances employees in caissons are working under more disadvantageous conditions than tunnel workers. The reason for this is, I think, that in tunnel work, up to the present time, for the same pressure the men have worked longer hours. In caisson work our main difficulty in the past has been in lengthening the time of decompression on exit from work. One reason for this is that, on account of the comparatively small size of the lock used in this work and through which all employees must pass, it is a much greater mechanical problem to diminish the pressure gradually. I mean that, comparing two locks, one large and the other small, with an equal pressure of air on them, if you release the same amount of air from each through the same sized valve, the pressure in the small lock will drop much more quickly than in the large one. Another reason is that the lock used on the caisson, in contrast with tunnel work, is not permanently placed, as it must be lowered with the caisson. The necessity for the frequent removal of locks leaves a greater margin of chances for leaks to occur from time to time, and from a leaky lock it is almost impossible to release the air slowly. In addition, the cramped position that the air worker must assume while sitting in the bucket during decompression differs from the comparative comfort with which he issues from a tunnel lock. Another feature of caisson work that has to be reckoned with is the environment of a busy city, as compared with the location of a tunnel plant which is usually in a more secluded section. In the former case the force of men, like the pressure of the air, is constantly changing; in the latter the tendency is more for the force to be a steady one, for the men have a pressure to work in that is pretty nearly constant and is not accompanied with the same degree of uncertainty. In considering the problem of how to care for the men, the two factors that are of the utmost importance are: (1) the rejection for work of all physically unfit; and (2) slow decompression in coming from work. The only death that has occurred in any of the work of which I have had charge during the last five years was due to a pressure of only twelve pounds of air where a man had gone to work without having been examined. Post-mortem examination showed that he had had a dilated heart which ruptured from the strain of a fairly rapid decompression. Very few cases of caisson disease occur in a pressure less than twenty pounds. In the examination of the men it should be borne in mind that it is an extraordinary occupation in an extraordinary atmosphere, and only extraordinary men should be employed. They should be physically above the average, between the ages of twenty-one and forty, of slender build, non-alcoholic, and with absolutely sound heart and lungs. Any variation from normal, even in rate or regularity of the heart, should be enough to reject a man. No man with symptoms of any organic disease should be passed. The fight for slower decompression has not been with the contractors so much as with the employees themselves, and I do not believe that the reason is so much the desire on the part of the men to get away from their work quickly as it is a spirit of bravado that prevails with nearly all. There is a certain contempt developed for the air, the result of familiarity. As they say, they can "eat air". Reason and a few painful lessons, however, have diminished this spirit to a great extent and, by the placing of responsible men in the position of lock-tender, we have been able to regulate the time to much better advantage. Nearly all cases are caused by too rapid decompression, and my experience has been that where the decompression has been slow no serious case has ever resulted. It is my belief that if a sufficiently long time were taken for decompression we would never have a fatal case in an otherwise healthy man. The time that should be taken for proper and scientific decompression depends directly on the amount of air that is dissolved by the blood under pressure. And the amount of air dissolved by the blood is determined by (1) the length of time spent in the air, (2) the number of pounds of pressure, and (3) the amount of exercise undertaken in the air. A lock-tender may go rapidly in and out of very high pressure with no ill effects, IN SINKING FOUNDATIONS FOR SKYSCRAPING BUILDINGS MEN Go Down AIR CHAMBERS OR CAISSONS THE AIR PRESSURE IS FREQUENTLY MORE THAN THREE TIMES THE NORMAL |