Air pressure and air supply in submarine?

Question

How is the air pressure inside a submarine maintained at one atmosphere?

What does the crew breath inside the submarine? Do they breath the same air we breath?

Please state the sources. Thank you.

Answer 1

Air pressure is not necessarily maintained at one atomsphere.  It fluctuates depending on depth, if an air compressor is running, a weapon is launched, and the contents of the atmosphere.  As the air is breathed by 100-150 men the oxygen level in the boat goes down and CO2 level goes up.  

The CO2 is scrubbed from the air and pumped overboard.  The oxygen in the air is replenished by an oxygen generator which separates pure water into H2 and O2 via electolysis or via bleeding oxygen into the pressure hull from oxygen flasks.  

A lot of the time the submarine will come up to periscope depth for various evolutions, one of which can be to change out the atmosphere in the boat.  A snorkel mast is raised and a low pressure blower sucks in air from the outside and circulated throughout the boat.