Slate asked NASA researchers if it is possible to survive in space without a spacesuit. The surprising answer: “Yes, for a very short time.”
The principle functions of a spacesuit are to create a pressurized, oxygenated atmosphere for astronauts, and to protect them from ultraviolet rays and extreme temperatures. Without it, a spacewalker would asphyxiate from the lack of breathable air and suffer from ebullism, in which a reduction in pressure causes the boiling point of bodily fluids to decrease below the body’s normal temperature. Since it takes a bit of time for these things to kill you, it’s possible to make it through a very quick stint in outer space.
At most, an astronaut without a suit would last about 15 seconds before losing conciousness from lack of oxygen.
You can read the full article here. There is also an interesting post about this on NASA’s Goddard Space Flight Center website:
How would the unprotected human body react to the vacuum of outer space? Would it inflate to bursting? or would it not? or would just the interior gases hyperinflate?…
answer:
You do not explode and your blood does not boil because of the containing effect of your skin and circulatory system. You do not instantly freeze because, although the space environment is typically very cold, heat does not transfer away from a body quickly. Loss of consciousness occurs only after the body has depleted the supply of oxygen in the blood. If your skin is exposed to direct sunlight without any protection from its intense ultraviolet radiation, you can get a very bad sunburn.
The full Goddard post has some interesting stories about past testing accidents involving loss of pressure.
