CANNED AIR

[The Grim Sleeper]

well is one that can be found and stored easily and you not need mask because you inhale directly from the can and the cure the suffocation fast

This exists. I won't spoil it here, because apparently it is not common knowledge, but there exists a chem that restores O2 damage. It can be cooked at any chem-dispencer+heat source, can be found randomly (very rarely though) in lockers, and there are garuantied at least 6 pills of it on every station.