WORK UNDER PRESSURE AND IN GREAT HEAT 389 



These considerations led us to introduce a new method — 

 that of decompression in graduated stages. The principle of 

 this method is that the diver or worker in compressed air is 

 brought rapidly to half the absolute pressure (or a little further 

 if his tissues are not saturated), stopped there for a time, then 

 decompressed a little further after sufficient time has elapsed to 

 allow the maximum nitrogen pressure in his tissues to become 

 not more than twice the nitrogen pressure of the air at the lower 

 stage. He is then brought on by further stages on the same 

 principle until he reaches atmospheric pressure. For the 

 difference between the stages a pressure of o'3 atmosphere 

 was selected, corresponding to 10 ft. (or 3 metres) of sea water. 

 The diver's progress is, of course, controlled by signal from 

 surface, according to the indications of the pressure-gauge on 

 the pump. The proper stoppages, after stays at different 

 depths and for different periods of time, have been carefully 

 calculated and put into the form of a table, which is now in 

 use in the British Navy. A portion of this table is shown 

 in Table V. 



TABLE V 



Portion of Diving Table for British Navy 



For ordinary diving work the table limits the stay on the 

 bottom in such a way that the diver can come up safely within 

 half an hour. This is desirable for many reasons : after pro- 

 longed stays on the bottom at great depths the time required 

 for safe decompression, even by the stage method, is far too 

 long ; and with uniform decompression many hours would 

 certainly be needed at the greatest depths. 



^ Ordinary limit of time. 



