358 



LOADING UP 



" free air," constructional engineers are afraid to put their men 

 under more than -|- 3-5 atmospheres. Bulhon has been salved 

 from ships lying 171 feet below the surface. The divers in this case 

 stayed below for only 20 minutes at a time and took 20 minutes to 

 ascend. Even then some of them were stricken with paralysis. 

 Greenwood endured compression to 7 atmospheres (= 210 feet of 

 sea water), but took over 2 hours to decompress. These long 

 periods of decompression which seem necessary for safety, put 

 the men in charge in an awkward dilemma wdien, on account of 

 some mishap, it is necessary to bring men at once to the surface. 



From Table LVI. it will be seen that the diver is brought to 

 the surface from the bottom in stages. These stages are 3 metres 

 apart, and the time spent at each one depends on the duration of 

 his stay on the bottom. This method of decompression by stages 

 depends on the empirical fact that no untoward results arise from 

 even a rapid decompression of 1 atmosphere or less. 



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 LVI 

 A Portion of a Diving Table used by Naval Divers 



Haldane and his collaborators liave 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 1 atmosphere (1-25 atmospheres to be exact) to 

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

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

 8 atmospheres, these workers advise a rapid decompression 

 to 4 atmospheres, and after a pause to 2 atmospheres, and, after 



