In the movies, many terrible fates await those who end up in space without a spacesuit. Some instantly lose consciousness. Others are flash-frozen, or their blood boils. Messiest of all, they may explode!

Yet in the classic Stanley Kubrick film 2001: A Space Odyssey astronaut Dave Bowman had to brave the vacuum of space without a spacesuit in order to get back into the airlock. He succeeded, but would this really be possible? After all, there are good reasons for spacesuits to be pressurized, provide oxygen, get rid of carbon dioxide, and maintain a safe temperature.

Could you actually survive unprotected – and if so, for how long? Let's consider these movie scenarios.

How long could you stay conscious?
Maybe ten seconds, no more than fifteen. For that time you might be able to function, but then the oxygen in your blood would be used up. When your brain lacks oxygen you pass out.

Not surprisingly, no one has volunteered to test suitless survival in a vacuum. However in 1965, in what is now NASA's Johnson Space Center, there was an accident in a vacuum chamber during spacesuit tests.

Jim LeBlanc was testing a space suit when it lost pressure. He stayed conscious for 14 seconds. Fortunately, they were able to help him within a minute. In fact, when a doctor got to him, he was already conscious and said that he felt fine except that his ears hurt.

It may be time for a warning here. Please don't imagine that holding your breath would give you more time in a vacuum. This is one thing not to do. As the pressure drops, the gas in your lungs expands. This would cause fatal damage to your lungs if you stopped the air from being expelled. The best strategy would be to exhale before exiting the spacecraft.

Surely you would be instantly frozen?
No. The only way of losing heat in a vacuum is by radiation. Transferring heat by other means needs particles (atoms and molecules) and there aren't many of those in a vacuum. Remember: your thermos is a good insulator because of its vacuum layer.

Astronauts actually have more trouble keeping cool than keeping warm. They are insulated against low temperatures, but it's more important to get rid of the heat their bodies produce or the heat of the Sun. It would take a long time for your body to radiate away all its heat and freeze, because it isn't a very efficient radiator.

Would your blood boil?
No. It's true that as air pressure decreases liquids boil more readily, so they would boil away quite quickly in a vacuum. However your blood wouldn't be exposed to the vacuum because it's safely tucked away inside blood vessels that are inside your body.

Your skin might feel cool as the moisture on it evaporated. Also the moisture in your mouth and nose would boil away so their temperature would drop dramatically. Jim LeBlanc said that the last thing he remembered before losing consciousness was “I could feel the saliva on my tongue starting to bubble.”

Would you explode?
No. You've probably worked that out already.

Parts of your body would swell in the absence of a pressure suit, but your skin is really quite strong. It would contain the swelling, though there would probably be some bruising from tiny blood vessels being broken.

Could you survive unprotected in space?
Possibly. But for no more than a couple of minutes. Even so, you'd need help at hand – like Jim LeBlanc had. Or you'd need to be going from a vacuum into a pressurized area – like the hero of 2001. In these cases you might be none the worse for it.

However, there are other problems in space I haven't mentioned.

For example, without an atmosphere or other protection against the Sun's UV radiation, you could well end up with a nasty sunburn.

A more serious danger is what divers call “the bends”. The bends are caused by nitrogen gas forming gas bubbles when you're coming rapidly from a higher pressure to a much lower one. Depending on where the bubbles go, there may be no symptoms at all, but it can be extremely painful or even cause long-term damage.

Conclusion
I think that we can learn from this that the movies are only occasionally right, and that the human body is really quite marvelous. Also that we need to dress appropriately in space!

References:
Geoffrey A. Landis, “Human Exposure to Vacuum” http://www.geoffreylandis.com/vacuum.html
“Space Suit Testing” (Jim LeBlanc video) https://www.youtube.com/watch?feature=player_detailpage&v=KO8L9tKR4CY