Talk:The Ark/@comment-24946020-20160506023044/@comment-150.135.161.168-20170928205216

When they mean air they mean  Oxygen. Once they use that axygen it turns in CO2 or in some cases such as one oxygen is running low CO which is pisonous to humans hence people getting sick from lack of Oxygen. So the air presure will pretty much stay the same since the Oxygen molecules will be replaced by the same amount of CO2 or CO molecules.