What would happen to you if you stepped into space without a spacesuit?

On a space station orbiting Saturn, a man inside a punctured spacesuit swells to monstrous proportions and explodes ( See the movie 'Outland'). On Mars, the eyes of a man exposed to the near-vacuum of the martian atmosphere, pop out of his head and dangle by their optic nerves on the sides of his face (See the movie 'Total Recall'). Enroute to jupiter on the Discovery spacecraft, Astronaut Dave Bowman space walks for 15 seconds with no helmet, and in no apparent pain, succeeds in reentering the Discovery through an open hatch ( See the movie,'2001:A Space Odyssey'). Fortunately, only in science fiction stories do humans ever come into direct contact with the vacuum of space, but these contacts are often portrayed as having horrific consequences.

To experience the vacuum is to die, but not quite in the grisly manner portrayed in the movies Total Recall and Outland. The truth of the matter seems to be closer to what Stanley Kubrik had in mind in 2001: A Space Odyssey.

According to the 1966 edition of the McGraw/Hill Encyclopedia of Space, when animals are subjected to explosive decompression to a vacuum-like state, they do not suddenly balloon-up or have their eyes pop out of their heads. It is, in fact, virtually impossible to compress or expand organic tissues in this way. Instead, death arises from the response of the free gasses trapped within the tissues.

If decompression takes 1/2 second or longer, even lung tissue remains intact. When the ambient pressure falls below 47 mm of mercury (similar to the pressure at the surface of Mars), the water inside all tissues passes into a vapor state beginning at the skin surface. This causes the collapse of surface cells and the loss of huge amounts of body heat via evaporation. After six seconds, the process of cell collapse involves the heart and lungs causing circulatory interruption, followed by acute anoxia, convulsions and the relaxation of the bowel muscles. After 15 seconds, mental confusion sets-in, and after 20 seconds you become unconscious. You can survive this for about 80 seconds if a pressure higher than about 47 mm mercury is then reestablished, otherwise, you turn into freeze-dried dead meat on a stick.

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