Originally Posted by
InkUnderNails
Good info. One question. Is the atmosphere in an aircraft at altitude and .75 atm the same O2 ratio as "normal" air or do they add O2?
The same. They're not going to haul around tanks of O2 without a good reason to--it's quite a fire danger. (Yeah, oxygen doesn't burn. Things burn *VERY* vigorously in pure oxygen, though!)