nected to non-portable tanks within the pres- 

 sure hull filled with compressed oxygen. 

 Both the portable or non-portable systems 

 offer the advantages of being simple to oper- 

 ate, reliable and relatively inexpensive. Eye 

 protection is afforded by face masks. The 

 disadvantage to the open-circuit system is 

 that the exhaled gasses may build up cabin 

 pressure to a point where decompression be- 

 comes a consideration. 



Closed-Circuit Breathing: 



In a closed-circuit system the occupants 

 inhale from a breathing bag and exhale each 

 breath back to the breathing bag through a 

 purifying cannister. Closed-circuit systems 

 consist fundamentally of an oxygen supply, 

 regulator, gas metering device, breathing 

 bag, mouthpiece or mask, carbon dioxide ab- 

 sorption cannister and breathing hose. Two 



systems used in submersibles are the West- 

 inghouse Corp.'s Min-0'Lung (Fig. 14.10) and 

 The Mine Safety Appliance's U.S. Navy 

 Mark II. Both use 100 percent oxygen and 

 are lightweight and simple to use. In addi- 

 tion to these advantages, the closed-circuit 

 system does not increase cabin pressure be- 

 cause the used air is recirculated back into 

 the system. A disadvantage, however, lies in 

 the toxicity of oxygen under pressure. 

 Though the submersible's cabin pressure is 

 generally held at atmospheric, a doubling of 

 this pressure (29.4 psia) allows less than 40 

 minutes of breathing before the danger of 

 toxicity occurs. In most submersibles the 

 pressure-toxicity potential level is unlikely 

 to be reached because the vehicle will be at 

 or near atmospheric pressure and, with the 

 donning of the closed-circuit system there is 

 no further introduction of gasses (pressure) 



Fig 14 10 The Westinghouse Min-O'Lung (left) and Drager (right) emergency breathing systems Both have about 5 hours endurance (Westinghouse Corp.) 



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