There's some merit to this. The hatch not opening from the inside means that even if they did manage to reach the surface of the ocean, if they didn't find the

There's some merit to this. The hatch not opening from the inside means that even if they did manage to reach the surface of the ocean, if they didn't find their way back to either their own mothership or something else capable of opening the hatch from the outside they still would have died due to lack of oxygen when the oxygen ran out.