I'm on the Oil update Alpha branch.
(Mechanized) airlocks destroy large amounts of Oxygen every time they operate. This is a large problem, I'm losing a lot Oxygen this way.
See screenshot of low pressure area created by airlock destroying air. After dupes going through it a few times, the refrigerator room will be in nearly vacuum.
Build small room, close it with airlock - Enter gas overlay - Send a dupe through airlock a few times