1906.] on Compressed Air ami its Physiological Effects. 373 



The Prevention of Compressed Air Illness. 



Bert, from his experiments on animals, conclnded that all troul)le 

 could be avoided by extending the decompression period to 30 minutes 

 for 2-3 atm., 60 minutes for 3-4 atm. 



This ruling of Bert has never been carried out at anv of the 

 English or American works, a minute or two (at most 15 minutes) 

 being the usual period allowed for " leaking out." V. Schrotter, 

 from his experiments, concluded that 20 minutes per atm. was a safe 

 period, and I have found this to be uniformly safe for a large number 

 of animals which I had exposed to saturation for some hours at a 

 time. 



On the Continent the decompression period has been made nearer 

 to that demanded by Bert, and yet severe and even fatal cases have 

 not been avoided. Thus at the Limf jord works two deaths occurred, 

 the pressure being +3*5 atm., and the decompression period 

 45 minutes. At Cubsac there were sixteen severe cases and three 

 deaths, the pressure being + 2 to + 3 atm., and the decompression 

 period 25-30 minutes ; at Nussdorf two deaths, the pressure being 

 + 2'3 atm., and decompression period 25-30 minutes. 



In discussing these cases we are uncertain whether the men 

 obeyed the rules, or were in truth more rapidly decompressed. Snell 

 suggests the men disobeyed the rules at Blackwall. The decompres- 

 sion rate, too, may not have been uniform. It is especially of impor- 

 tance not to hurry the last atmosphere, because any gas free in the 

 blood doubles its volume on dropping from 2 to 1 atm. (Haldane). 

 This is just the period which the men might think it safe to hurry. 

 I think it important that all parts of the body should be moved 

 in turn and often during decompression, so as to drive the blood 

 back to the heart, and increase the rate of circulation and depth of 

 respiration. 



Can Work Safely be Extended to Greater Depths ? 



In caisson works the sickness has been so great at the higher 

 pressures that no engineer has dared to use more than -f- 3 • 5 atm. 

 (115 ft.). Divers do more than this ; the best pearlers and sponge 

 divers reach 140 ft. Lambert salved 100,000/. at a depth of 160 ft. 

 Erostabe salved bullion at 171 ft. These men stayed but 20 minutes 

 below at a time, and took 20 minutes to ascend. Lambert was 

 stricken slightly with paralysis after his last ascent, when he had 

 stayed down longer looking for the last box of gold. 



Hersent experimentally compressed a workman to just over 6 atm. 

 (76 'S lb.) for 1 hour, giving him 2 hours 25 minutes for decom- 

 pression. No ill result followed. I have been compressed to the same 

 pressure, while my colleague, Mr. Greenwood, has reached a pressure 

 of over 7 atm. (92 lb.), corresponding to a depth of 210 ft. 



