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?


1 Answer 1


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.

  • 3
    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. Commented Mar 21, 2012 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
    Commented Mar 22, 2012 at 1:31
  • @JohnRhoades A positive pressure difference is different from a negative pressure difference. Commented Jul 31, 2012 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. Commented Jul 31, 2012 at 20:21

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