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I was once given a question in the popular quiz-show game, You Don't Know Jack, that went something like:

You find yourself suddenly ejected into space. Which of these gruesome things happens first?

  1. Your blood would boil
  2. Your eyes would explode
  3. You'd freeze to death
  4. You'd suffocate

The answer was 1. (followed shortly by 2.), because the drop in pressure reduces the boiling-point of the blood. They are usually pretty good about checking their facts, so I trusted this as a fact, until today.

On this thread, the top-rated comment states that this isn't true, and gives a plausable-sounding explanation for why.

So, which is it?

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The order of these seems highly dependent on where you are in space. For example, close to the sun, you would definitely boil and not freeze, and presumably your eyes would explode from the boiling water inside them. – Brendan Long Mar 20 '12 at 3:15
See also this question on the Astronomy site. – Keith Thompson Mar 20 '12 at 21:49
Have a look at and QI - What Happens if You Get Sucked into a Vacuum? (YouTube). Both provide some actual real life knowledge (but not that much). – Martin Scharrer Mar 20 '12 at 21:59
sudden decompression on aircraft: "The FAA (in its Advisory Circular 61-107A) provides a helpful chart showing just how long crewmembers are able to perform flight duties with an insufficient supply of oxygen. In an aircraft at 22,000 feet, passengers and crew would have 5 minutes of “useful consciousness” after rapid decompression. But at 43,000 feet, the time drops to a mere 5 seconds, hardly long enough to don an oxygen mask. " from – Paul Apr 16 '12 at 8:37
up vote 33 down vote accepted

One of the slashdot comments points to a NASA article originally from 1997 which tells you not to hold your breath and then says in summary,

theory predicts -- and animal experiments confirm -- that otherwise, exposure to vacuum causes no immediate injury. You do not explode. Your blood does not boil. You do not freeze. You do not instantly lose consciousness. Various minor problems (sunburn, possibly "the bends", certainly some [mild, reversible, painless] swelling of skin and underlying tissue) start after ten seconds or so. At some point you lose consciousness from lack of oxygen. Injuries accumulate. After perhaps one or two minutes, you're dying. The limits are not really known.

and then describes a test subject accidentally exposed to a near vacuum in a vacuum chamber in 1965 who remained conscious for about 14 seconds, until oxygen-deprived blood went from the lungs to the brain. After repressurisation, the subject reported that his last conscious memory was of the water on his tongue beginning to boil.

The answer therefore seems to be 4. You may also be affected by other common pressure effects such as the bends and ear tube issues.

Your blood does not boil because your skin maintains pressure.

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Since people may be interested in some of the reasons behind this: There's a major misconception that the vacuum of space is somehow infinite. That doesn't really make sense. What space has is zero (or nearly zero) pressure. All that really matters mechanically is the pressure DIFFERENCE. Divers go deep enough to experience a pressure difference of several atmospheres. By contrast, empty space has a pressure difference of one atmosphere. It's in the other direction, but it's still not a big difference. As for surface fluids "boiling": it's better to think of them as quickly evaporating. – John Rhoades Mar 21 '12 at 16:21
At some point you lose consciousness from lack of oxygen am I missing something, or he was just being captain obvious? – ajax333221 Mar 22 '12 at 1:31
@JohnRhoades A positive pressure difference is different from a negative pressure difference. – DJClayworth Jul 31 '12 at 14:16
@DJClayworth Not really. That's like saying negative velocity is different than positive velocity. The only real difference is perspective and situation. A negative pressure doesn't "do" anything differently than a positive one, it's just the same from the other side. That being said, if what you meant is that the human body can handle a couple extra atmospheres of pressures better than it can handle one less, then yeah, I think that's probably true. – John Rhoades Jul 31 '12 at 20:21

if you do the math pressure times volume divided by temperature = pressure2 times volume2 divided by temperature2, or pv/t = p2v2/t2 wich is 1atm * approximately 5 liters/approximately 30c = 0 * 5liters (liquids are incompressible) wich is 0/unknown temp. simplified 5/30 = 0/x now solve for x , multiply both sides by x and get 5/30 * x = 0 therefore x = 0 your blood will freeze but you would asphyxiate before the transfer of heat could occur

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Some of the information contained in this post requires additional references. Please edit to add citations to reliable sources that support the assertions made here. Unsourced material may be disputed or deleted.

Welcome to Skeptics! This is a theoretical answer to a practical question. We expect answers to be base on fact. You must provide some references to support your claims. In practice you provide no empirical proof that any of the formulas in your answer are appropriate to use in this context. – Sklivvz Jul 31 '12 at 6:50

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