The sodium chlorate candle, or emergency oxygen generator.
A device which when triggered burns and produces a source of oxygen, which when filtered is breathable. It's an irreversible reaction, with modern units having a burn time of 10-20 minutes, used currently in aviation as one of a few possible sources for the passenger emergency oxygen system on aircraft.
If we were to implement this into the game, I have a few ideas we could choose from:
-emergency O2 supply: acts as a large O2 tank for people stood on the tiles directly next to it, if they attach their masks to it. Possibly have two per department or one per major room stored in an emergency closet or even the wardrobes in some areas, people who want to use it right click it, instead of a set pressure contained, it could provide for a set time from ignition?
-room refiller: used as a generator by atmos techs to help speed up the filling process for a room, at this point we could reason that the candle is assembled so as to have a nitrogen source (N2 tank that is replaceable?) and then mixes into air mix as it comes out of the nozzle.