Near the end of the movie, where HAL locks Dave out of the ship, Dave has to explode himself into the emergency air-lock area without a helmet. It has no air. The plan works, but it takes about 15 seconds for him to close the door and fill the room with air. By that time, if you understand that in space without a full suit, your blood will boil, then evaporate, your eyeballs will pop out, your head will cave in, and guts will explode. This doesn't happen, Dave is also holding his breath, which wouldn't work in real life, you would still die.