Surviving the vacuum

[aegisknight]

So I was talking with someone a week or so ago, and he said "would you really be able to just run around without a helmet like that?"

and of course I said no, you'd die instantly.

Well, I was wrong. I was reading a bunch of stuff today, and it turns out that our hero's behavior on the Moon without a suit was surprisingly fairly realistic.

A human can survive somewhere between 10 and 30 seconds out in a vacuum without any serious problems (that we know of). This is because of several reasons:

1. It is really, really cold in the vacuum of space (just a few degrees above absolute zero), and so most people assume you would basically freeze instantly. However, because there is very little matter to actually carry that heat energy away (since the heat of your skin in the winter is transferred to the very cold air molecules, heating the air around you while making you cold) you actually lose your heat relatively slowly. You would die of other things long before you were freeze-dried to death.

2. Rapid depresurization would kill you. While this also has its merits, it would not happen very quickly, and you certainly wouldn't explode. You would get very sick if out for more than a few seconds, but it would be similar to a diver who came up from the ocean's depths too quickly; you would get depressurization sickness due to your inards getting mixed up. But if you breathe out while in the vacuum (as our heros do while talking) it wouldn't be quite as bad.

3. Your blood will boil. This isn't as well known, but still fairly well documented. If you try to boil water at higher altitudes with less air pressure, it takes less and less time for it to just start boiling. If there is no pressure, it will boil instantly. So with your blood in vacuum, it would boil instantly, and everything would be terrible. However, thanks to your skin and circulatory system, your blood is actually quite well contained and pressurized itself, so you still have several seconds of being totally fine before it sinks in.

So while it is unrealistic to do the little manuever where you run into an airlock and back out again to get a breath of air, the act of running across the lunar surface from one airlock to another without protection isn't a stretch of the imagination.

[piepwns]

Huh. Interesting analysis. [brains] for you

[Tom852]

Well, I have a really hard time to believe that, but it seems to be true

I am just wondering. I have heard once somewhere, that we always keep about 1 liter air in our lungs, even if max breathed out. And that is, that all the tubes in there don't get together and clotty. Now I wonder, if a vacuum doesn't suck out all of your air out of your lungs instantly and leading to this cause...

[aegisknight]

it wouldn't suck anything out, but if you left your mouth open air would escape due to differences in pressures.

[Tom852]

I'm not sure... Just thinking about the nose path, the air can take. Plus the pressure might just blow your mouth open - like vacuums can blow up balloons?

[aegisknight]

it can't, your mouth muscles are stronger than the vacuum. Its not like a vacuum cleaner which is actively sucking, it is just very low pressure that causes your body to expand.

Holding your breath provides a sufficient seal from too much air escaping (although you want a bit to leave to prevent your lungs from bursting).

Vacuums can blow up balloons because the rubber of a ballon is much, much weaker than your flesh in terms of resisting changes in pressure, which entirely why balloons inflate as easily as they do

[MysteryMachineX]

Interesting. Good post.

[Blamco177]

I swear, I thought I saw a post on this a while ago.....

Still, even if I'm imagining things, this was a great post. I always questioned the temperature aspect of being in space without the suit.