The screenshot attached almost tells the whole story. I boarded a dupe with an atmo suit to a ship and didn't remove the suit because pressure was too high and I didn't want them to get "popped eardrums". I thought "well just by breathing they will lower the oxygen pressure and then I can remove the suit": but pressure never dropped.
This duplicant has lived off NO OXYGEN for dozens of cycles, oxygen pressure remains the same 4 kg/tile as before, no new carbon dioxide, nothing.
- Board a dupe to a ship that has some oxygen in it.
- Let oxygen in the suit run out, and do not unequip the suit.
- Let the dupe breath every time they run out of oxygen. They won't actually consume any oxygen. Look at the stats table, it says "inhlaing 0 Kg/O2, exhaling 0 Kg/02"