Running out of Air.

Like you Biomechanic, I look at the films with a very discerning eye. I have also wondered why they would remove their suit helmets. Why David would stick his bare hand in the ampule and extract that biological material, why he isn't wearing full isolation gear when exposing the ship to a potential BIOHAZARD. Unless.....nobody is there watching him, droids are always following their own secret agenda's though right?

I've seen speculation that: They're all wearing their helmets, then the mo-hawk guy gets hit by the acid (destroying his helmet) yet he can still breathe, so the rest of the crew remove theirs.

Well maybe he doesn't have bio-gear on because he's a robot but still yes not smart and could be significant. Don't touch alien matter!