How Long Can You Survive Without A Spacesuit?

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by Mark Aragona

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.”

Theory: Your blood and other bodily fluids start to boil.

Not quite true. Most of the blood in your body isn’t exposed to space, but fluids outside of your body or close to the surface (sweat, saliva, the blood in your skin’s capillaries) will start to boil away. This was experienced by a test subject in NASA’s Johnson Space Center who was accidentally exposed to near vacuum conditions during a test run and lost consciousness. Upon waking, he reported that his last coherent memory was the saliva on his tongue starting to boil.

Theory: You’ll be exposed to radiation.

True. Without an atmosphere or space suit to protect you, you’ll be exposed to all sorts of radiation: infrared, ultraviolet, cosmic, you name it. If you aren’t close to a star or a similar source, this may not pose an immediate problem. On the other hand, direct exposure to solar radiation will give you a bad case of sunburn, perhaps cancer later on.

In short, death by hypothermia or explosive decompression is unlikely; the quickest way to die in space is still asphyxiation. Here’s a timeline approximating what the effects would look like:

00:00-00:10 – Victim would still be conscious and able to act, perhaps to save himself.

00:10-00:15 – Minor injuries start to occur. Victim starts losing his ability to think. As oxygen starts to leave the body, blindness sets in and the victim’s nose and tongue start to freeze, making communication difficult.

00:15-00:20 – Victim loses consciousness from lack of oxygen.

00:30-1:00 – Saliva starts to boil due to lack of air pressure. Skin and other tissues expand as a result. Blood pressure starts to drop.

01:00-02:00 – Blood pressure continues to fall and the heart eventually stops beating. Beyond this point, the brain suffers irreparable damage.

Surviving in space without a suit can be measured in minutes, not seconds, and two minutes may be long enough to rescue and treat a victim of exposure before any permanent damage is done. After weeks of intensive care, they may even make a full recovery. Just goes to show how resilient the human body is, even when subjected to the harshest of environments.


  1. Pingback: Practical Tips And A New Review | Digital Science Fiction

  2. Very nice summary. Thanks! I learned things I may indeed use in upcoming stories.

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