The air purification and oxygen renewal systems are based on the requirements of 44 men during 72 hours total submergence.  For air purification, a total of 315 canisters, each capable of absorbing 400 liters of CO2, are provided.  For oxygen renewal a total of 13 flasks, each containing 50 liters of oxygen under 160 atmospheres (2275 p.s.i.) pressure, are installed.  44 sets of emergency breathing apparatus are carried on board.

I hope this helps in some small way.

Scott