You can survive in space without a spacesuit for around 2 minutes, and the thing that kills you isn’t the change in pressure, it’s simply the lack of oxygen.
If you write space-based science fiction you may have to craft scenes where an unfortunate soul gets blown out into space without benefit of a protective suit. An accident—an explosion on deck, debris punching through the hull of a ship, a micrometeorite smashing through a helmet—can suddenly fling a character into a dark, hostile vacuum. How would it feel? What happens to an unprotected human body in space, and how long can an average person survive? As you can see, it’s far different from what’s seen in the movies.
Theory: You would freeze instantly. Seen in the films “Mission to Mars” and “Sunshine,” where some characters froze or developed frostbite upon leaving the airlock.
False. While outer space is cold (e.g. -100 degrees Celsius), and you definitely will feel it, freezing to death will be the least of your worries. In a vacuum, there is no medium to carry the heat away from your body. Assuming there aren’t any nearby heat sources (such as a star), your body will eventually cool down to the same temperature of space, but in a matter of hours, not minutes.
Theory: Holding your breath will help you stay alive. Seen in “2001: A Space Odyssey” when David Bowman enters an open airlock.
False. Due to the lack of atmospheric pressure, oxygen will be forcibly try to leave your body. You’ll feel an instant swelling in the lungs and intestines. To prevent your lungs from rupturing, you should actually blow the air out of your lungs within the first few seconds of exposure in space.
Theory: Your bodily organs, like your eyes, would inflate and explode.
Seen in “Total Recall” when Arnold Schwarzenegger’s helmet is smashed open, exposing him to the low atmospheric pressure on Mars.
False. Explosive decompression does not literally mean what it says. While you will experience bloating as the water in your body starts turning into vapor, it won’t result in a bloody mess. More likely, you will have severe bruising all over your body as capillaries break and blood spreads under your skin.
On the other hand, the reduced pressure may cause the nitrogen in your bloodstream to turn into bubbles, causing a terrible injury that divers call “the bends.”