DECOMPRESSION RATE 



273 



An atmosphere or 760 mm. of mercury is equal to a pressure 

 of 1 kg. per sq. cm. or to about 3 metres of sea water. Even with 

 this more rapid means of attaining normal pressure, the diver is 

 limited either to a very short stay under water or to a tedious 

 waiting at various levels. 



TABLE XLVIII, 



A PORTION OF A DIVING TABLE USED BY NAVAL DIVERS. 



Haldane and his collaborators have very fully investigated 

 this question. They argue that, as the volume of gas in solution 

 is constant no matter what is the pressure, and as it has been 

 proved to be perfectly safe to decompress rapidly from a plus 

 pressure of one atmosphere (1-25 atmospheres to be exact) to 

 normal, then it must be equally safe to decompress rapidly to half 

 pressure for any value. For example, if the total pressure were 

 eight atmospheres, these workers advise a rapid decompression 

 to four atmospheres, and after a pause to two atmospheres, and, 

 after a pause, more slowly to normal pressure. The principle 

 underlying this plan is that the discharge of nitrogen from the 

 start of decompression is at the maximum rate consistent with 

 safety. The rate of discharge, of course, depends on the gradient 

 of pressure between venous blood and alveolar air. This gradient 

 is kept as steep as possible, and there is, therefore, a maximum 

 elimination by the lungs. 



18 



