So you're in an airlock, sans spacesuit, and in a few moments the outer hatch will open and ... well we've seen the films, and the TV shows: The moment that door opens you'll explode, or possibly flash freeze solid. Either way.. you're a gonner.
|Let's be clear: This. Doesn't. Happen.|
First, lets look at the 'you'll explode' idea: By itself that's not completely crazy - in fact there was a tragic, and very, very messy incident involving a group of deep sea divers going from nine atmospheres to one - but you're only going to get a one atmosphere drop, not nine*: You won't explode, because your organs and skin are too tough.
That doesn't mean the next bit will be any fun but it might just be survivable...
The airlock decompresses: Any air you're holding in will be pulled instantly out through your throat - so to avoid tissue damage vent everything gassy from yourself. And I mean everything: Any gasses in your stomach and bowels will also exit the premesis, carrying stomach and bowel contents with them at high speed.
So burp and fart as much as you can before that hatch pops, unless you're wearing brown trousers and like the taste of stomach acid.
All that means the only oxygen you'll have out there is what's already dissolved in your blood. If you're in really good shape you might get fifteen seconds of full consciousness, and maybe a few of total disorientation, before your pass out (link to NASA article on the subject). Maybe enough to save yourself**.
How will you do that, when you'll be floating in space? Actually... most airlocks decompress before the outer hatch opens. If the hatch does just 'blow' then, unless the airlock you're in is huge with a tiny door, the air will empty in much less than a second - not enough time for the gale to transfer much force to your body. Tying yourself to the handle of the inner hatch with your shirt should keep you anchored in place.
|Sorry, you can't really get rid of the xenomorphs that way either...|
So, you're in the airlock, the outer door is open and you've got eighteen seconds. But won't the cryogenic cold of space instantly freeze you solid?
|This also doesn't happen.|
Lucky you, no it wont: Space is a big nothingness - there's no conduction or convection to carry heat away, and you'll radiate heat no faster than you would on Earth.
Damn...this is getting both dull and smelly: You won't explode, be sucked into the void, or freeze. You may poo yourself. Will anything happen like in the movies?
Well...you'll swell up, although not so much you can't move. Some animals go temporarily blind but there're no reports I've found of that happening to humans. After your fifteen or so seconds you'll pass out - but that's not the point you die: Your heart will carry on beating for about three minutes: Animal experiments*** suggest you'll recover if you get repressurised before your heart stops.
What should you do once the hatch is open?
|Astronauts agree : Wearing a space suit is the key factor.|
- If you've gotten spaced by accident I'd thoroughly recommend just shutting the airlock hatch and pressing the re-pressurising control.
- If your airlock is broken you've got fifteen to twenty seconds to get out and reach another. Incidentally, Dave Bowman from the film 2001 pulls this off somwhat realistically, as he's hunted by HAL the insane computer.
- If you've been spaced deliberately, and your would-be assassin got his knowledge from movies.... I suggest just re-pressurising the airlock and kicking his teeth down his throat.
- If you're being spaced by someone who can override all the ships airlocks... then, frankly, I'm out of ideas. Float to the window nearest to them and use your last few seconds to shove your bum against it?
Above: Time it with a stopwatch - he actually would have pulled this off (as far as my research can tell)
On the whole I suggest putting ' get exposed to vacuum' on your list of things not to let happen. But, should you make that particular mistake^... Stay calm, brace up, be ready to shut that hatch and hit that re-pressurise control - you should make it.
* Even so, it won't be fun and it could be very messy in... other ways.
** I've heard it suggested that forcing yourself to hyperventillate and load your blood stream with O2 just beforte you exhale might help (although, as far as I know, that's never been tested). Slowing your heartbeat probably would, as it would slow the passage of de-oxygenated blood to your brain.
*** Yes that's a mean thing to do to an animal - please don't write to me telling me that, I never said I approved.
**** Unless the airlock is just for throwing people out of.
^ HOW have you managed to make that particular mistake?