If you have a door placed with no foundation duplicates climb though and down to the next tile without opening the door. This I have confirmed for the manual airlock door, still require to look at the other two doors. As well as not opening the door, there is no gas that can pass through.
I was going to make a room corantine with slime inside and accedently made a duplicant remove the tile I had under the door. Soon relized as my duplicants walked through that the door was not beeing used and no contaminated oxygen would get out