Compressed Air Work And Diving 1909

4 COMPRESSED AIR WORK. orclinary circumstances, and a man who cannot compiess comfortably at this rate should be rejected for compressed air work. Sometimes, when a worker is suffering from a cold, considerable cliscomfort is experiencecl during compression. Under these circumstances a longer time may be required, and a man with a bacl cokl should not attempt to pass through thc air-lock with others. Ifa man experiences any pain he should turn back, and similarly a diver should reascencl to the surface. Air Supply.—It has been found (Haldane and Priestley, Journal of Physiology, vol. 32) that the partial pressure of CO2 in the lung air is about 5.6 pei cent, of an atmosphere, and remains constant whatever the pressure of the air breathed may be. Thus at two atmospheres absolute pressure the percentage of CO2 in the lung air will be = 2.8 per cent., and at three atmos- pheres 1.9 per cent. And since the percentage of 3 CO.> in the air breathed must not be allowed to rise above that normal to the lung air, it follows that when the air supply, with the diver’s head just below water, is the minimum required, it must be increased with the depth. Thus a diver who will require at atmospheric pressure a minimum of about 1.5 cub. ft. of free air per minute, at a depth of 33 ft., or two atmospheres’ absolute pressure, will want 3 cub. ft. of free air per minute, and at 66 ft. 4.5 cub. ft. of free air per minute. Or, to put it another way, starting with a minimum supply at atmospheric pressure, the volume of air, measured at the given pressure, supplied him must remain constant whatever the pressure. In caisson or tunnel work the supply should be at