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[insert obligatory statement of my lack of knowledge in physics]

Alright, so we have all seen the movies where someone gets blasted out of the airlock on their starship, or their suit decompresses while on a space walk. The poor schmoe usually either decompresses so violently that blood is oozing out of every orifice in their body, or they freeze instantly.

From this I have two questions:

  1. Would the decompression really be that violent?
    1. Clearly the drastic difference in pressure from a normal "earth" like environment to space would be bad, but would it be that devastating.
    2. I vaguely remember that standard atmospheric pressure was something like 15 psi, which doesn't seem like enough to mess you up that bad.
  2. Would you actually freeze instantly in space?
    1. Heat, or lack thereof is a measure of internal energy, but in a vacuum there wouldn't be anything to have internal energy, so does space even have a temperature?
    2. Wouldn't some form of matter have to be present in order to cool off? If there were no matter besides yourself and a few stray particles here and there, it seems like it would take a very long time to cool off.
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5 Answers 5

up vote 3 down vote accepted

What you see depicted in SF movies is nonsense:

http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/970603.html

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I realize that... which is why I posed the question here. –  Josh Jan 16 '11 at 20:37
    
Yes, that's how I understood your question. The link gives all the answers. –  Johannes Jan 16 '11 at 20:39
    
That's a pretty cool link. I'd be interested to know some of the physics behind it... –  Josh Jan 16 '11 at 20:44
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The answer to your second question (how would you cool-off in empty space?) is thermal radiation. According to The Stefan–Boltzmann law, the power emitted by a black body is directly proportional to its area A and to the fourth power of its absolute temperature: P = sigma A T^4. With Stefan-Boltzmann's constant sigma = 5.67 10^-8 W m^-2 K^-4 it follows that a human being (A = 2 m^2, T = 310 K) would lose energy at a rate of about 1 kW. At his rate lack of oxygen would kill you much sooner than undercooling. (This simple calculation assumes a worst case, i.e. Human=Black body / no sunshine) –  Johannes Jan 16 '11 at 23:51
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An answer with nothing but a link in it is not a very good answer. At the very least, provide a summary. –  endolith May 23 '11 at 19:08
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I saw a video last year of a person testing a pressure suit in a vacuum chamber. This occurred back in 1966. The video has been removed unfortunately. What happened is a pressure hose detached and the air pressure ran out of his suit. He actually stood up conscious for about 30 seconds, but then passed out. He fell off of a stage, which frankly looked painful. The crew outside repressurized the chamber and within a minute the guy was alert and stood up. According to this man he could feel the saliva in his mouth start to boil as if he were drinking a soft drink. Otherwise there were no ill effects.

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Wow, now I feel grateful that my experiments are not as scary. Do you have any more information about this event, I would have guessed that he dies pretty fast as water boils violently in a vacuum chamber. –  Alexander Nov 18 '11 at 2:04
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Most of what is shown in sci-fi on this is believed to be false. You do not freeze to death and your blood does not boil.

Provided you do not try to hold your breath there are not likely to any ill effects for at least 30 seconds or so. If you do try to hold your breath as the de-pressurisation takes place you can suffer a "burst lung" i.e. an embolism, just as a diver would if he holds his breath during an ascent from depth.

After some time in space the lack of oxygen will be the most damaging. A few minutes will lead to death.

I found this answer at http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/970603.html where you can find a lot more details.

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remember some SF story (I think it was something by Clarke) where a large number of people go into space for a brief period without a proper suit because they have to quickly evacuate a spaceship harmed in battle. They have a kind of space war veteran explaining them that the usual stories are bogus, and how they can make it across to the rescue vessel (it's just some hundred metres). It's very much in accordance with that article. –  Hanno Fietz Jan 3 '13 at 21:58
    
Also, this is what Johannes' answer should have looked like. Just sayin. –  Hanno Fietz Jan 3 '13 at 21:59
    
Unless you're near a hot object, you will eventually freeze, but it takes hours for all your body heat to radiate away. –  endolith Jul 13 '13 at 6:04
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Your circulatory system puts enough extra pressure on your blood to keep it from boiling in a vacuum, and space itself doesn't conduct heat, so all the heating/cooling would be due to radiation or evaporation.

I think your exposed skin would swell, and fluids would evaporate and dry out your tongue, throat, and lungs, and your eardrums might burst, which would be painful. If you tried to move around you might risk overheating, since there's no way to cool yourself.

On the other hand, there's a chance your sweat-glands might still work, since they cool with evaporation.

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If you remember the infamous teenage date malady, the hicky. I think you'd see something like that as the blood would begin to ooze through your skin. But, I think this effect takes several minutes, so you'd already have died from lack of Oxygen.

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Joseph Kittinger the man who parachuted from space had a leak in his pressure suit glove which he said gave him a very impressive hickey - his hand swelled to twice it's normal size –  Martin Beckett Apr 1 '11 at 16:50
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