To my (admittedly limited) understanding a human being in outer space wouldn't last very long, mainly due to three factors:

  • the extreme cold
  • the intense radiation
  • and the vacuum of space

So if my understanding is correct, humans would die within seconds (if anyone could put an approximate number on this that would be great!).

What I want to know is that if a human being was exposed to space for half that time, would they suffer lasting and life threatening after effects?

In other words, is there any amount of exposure to space that wouldn't result in your imminent or eventual death?

Would exposure of just a hand kill you, or would you just lose that hand?

Would being exposed to space from inside a room with a single open door help much (I am assuming here the room would shield you from much of the radiation in space), or would the other two factors still kill you off?

Please feel free to correct my assumptions wherever I am wrong.

Many thanks for any help offered to my slightly morbid musings on space.


2 Answers 2


I will go deeper into the three factors you gave:

  • The extreme cold Well, not only cold, also heat. There's nothing that resists the hot sunwaves, so it can get hot. Temperature isn't much of a very direct problem, because space is almost vacuum, meaning that there is no matter to transfer the heat. If you forget about all the other factors, if you would stick out a hand in space, it'll not feel cold immediatly like you would feel if you enter a freezer. That's because there's no matter transferring the heat. So, your body temperature would slowly drain in forms of radiation. If your hand is in the sun in space however, it would warm up and you would burn your hand. The temperature in space varies from 2,7 K to 497 K.
  • The intense radiation It's not that intense. It damages your DNA over a long time, causing cancer. Not much of a direct problem, because vacuum or temperature would kill you instead.
  • The vacuum This is the biggest threat. You would die in several seconds because of it. Water starts boiling, you can't breathe air, all the gas molecules would be sucked out of the body... So does the oxygen. It takes about 10-15 seconds to reach the blood from your lungs to your brains, and if that happens you pass out. Several seconds more and you are dead.

Here's a video that explains all these things very well.

Now your questions: Exposing your hand would not kill you, nor would lose your hand, but if you are wearing a space suit the air would escape it's suit, resulting in vacuum in the suit and then you would die.

In a room with a door open will filter a very little part of radiation, but that doesn't matter because that's only usefull over a long time. Since the "door" is open means that the air will escape in a few milliseconds, which means you're in vacuum again. That would kill you.

And your "amount of exposure of space" question: I can't really give an answer to that because I don't see how you could give yourself that "amount of exposure". What I can give you is that people in the ISS have space exposure in forms of radiation, and they don't die. Radiation would give them an extra chance of cancer and other symptoms thought. There are some other effects, see other questions for more info on that.


Regarding the "intense radiation": The Earth's magnetic field does a good job of protecting low Earth orbit from radiation, so depending on where you are, that isn't a huge concern. Earth's atmosphere gives even more protection, of course, so e.g. cancer risk from cumulative exposure is a thing for ISS crew, but it's not an immediate or certain thing.


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