Okay so just had to share this moment...

I encountered some border patrol agents in a Zoltan sector and things escalated to a fight, which would normally be okay except that they landed three crew members onto my ship. I only had three at the time and 2 of them were Engi with their 50% combat penalty. They landed in my air lock and in the room next to it so I had the bright idea of openning my air lock and trying to destroy them through a lack of oxygen. I openned up a few doors and followed their path, which as it happened took them to my oxygen supply centre. They destroyed that then came after my shields, where I had all three of my crew ready to fight them. The lack of oxygen had brought them all down to about 60% health and thanks to the fact that the Engi ship comes equipped with auto-healing in all rooms my guys won. The problem was now that I was down to about 30% oxygen on ship, and had to move through some 0% oxygen rooms to get to my oxygen supply so that I could repair it. I also didn't have time to heal because then my guys would have died. I sent one out to fix it but he was too injured from the fight so he didn't get very far before he was down to about 10% health, so I moved him into a 'safe' room that still had some oxygen. Then I rushed both my human and my Engi to the oxygen room. The Engi one died and only my human pilot survived with about 10% health remaining. The oxygen was so low that it was hurting them, but the system came online just in time to help give them enough air to survive.

So basically from now on I'm going to consider getting air lock doors, which would have made my plan work much better. I also bought a system repair droid son afterwards.