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Humans in a vaccum?

  1. Aug 31, 2006 #1
    The wiki entry stated that the blood will boil if we were to be put in a vacuum. But boiling is defined as liquid turned into a gas. That is usually associated with an increase in temperture. The temperture inside a vacuum is lower than when in 1atm (due to less particle collisions) so why should the blood boil? Is it due to blood atoms being able to more freely move but where do they get the energy that allows them to do that?

    Or is it that blood has a vapour pressure (which is an indirect measure of how stable the chemical bonds are within the molecule and also dependent on the temperture of the environment) of say 0.5atm so it needs to be in an enviornment of 0.5atm to keep it in a liquid state. if the surrounding pressure is lower than 0.5atm than liquid blood will turn to gas because there is not enough force keeping them in the liquid form anymore. Alternatively if the temperture in the environment is increased, than the vapour pressure will decrease to a point where it might be less than the surrounding pressure, in which case it will boil. But it is the former point which is what the article is getting at?

    I have used terms in physics which I do not fully understand so please correct me if need be.
     
    Last edited: Aug 31, 2006
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  3. Aug 31, 2006 #2

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  4. Aug 31, 2006 #3

    russ_watters

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    Well, the what your blood does in a vacuum aside, I think you just figured out for yourself what it really means to "boil". Any decent high school physics lab will put a cup of water in a vacuum chamber and boil it at room temperature as a demonstration.
     
  5. Aug 31, 2006 #4
    If we are talking about blood contained in the body it will not start to boil in a vacuum. The body itself creates enough pressure on the blood to prevent that. There was an article I read where an astronaut training in a near vacuum chamber had some kind of malfunction in his suit, and was exposed to the vacuum. He did say that he could feel the saliva in his mouth start to boil before he passed out from lack of oxygen. He wasn't harmed in any way though, and his blood never boiled.

    The body may experience some slight expansion too, but nothing like the scenes in space odesy or total recall where the eyes explode and such.
     
  6. Aug 31, 2006 #5

    russ_watters

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  7. Aug 31, 2006 #6
    It should also feel much cooler (i.e. 50K) in a vaccum shouldn't it? But it wouldn't make sense to say he would freeze (i.e. his atoms turning into solids) to death since things are boiling up. So would it mean that the decrease in temperture has no effect on his body because of the low pressure (and so is keeping the atoms in the body from locking together and things balance out or the outgassing may even takeover to the point where the 'cold' wouldn't harm him but the 'boiling' might). But he will feel the cold wouldn't he? Would the cold feel harm him in any way. Physically, it wouldn't so how about psychologically?
     
    Last edited: Aug 31, 2006
  8. Aug 31, 2006 #7
    Conduction heat transfer and convection heat transfer do not occur in vacuum because there is no matter for the heat energy to transfer to. Radiation cooling DOES occur in space, but very slowly.

    The result is your body does not lose much temperature in space because there is no matter surrounding your body! Some temp will be lost as heat is transferred from your body by radiation cooling, but not too much.

    However, the pressure difference between the inside of your body and the outside is huge. liquids boil when their vapor pressures equal the atmospheric pressure. Well, the vapor pressures of your blood and saliva much more easily equal the atmospheric pressure in space, and therefore will boil even at body temp. However, as pointed out above, this process takes some time. The saliva in your mouth will begin to evaporate and the oxygen in your lungs will escape. Before anything else happens to you you will pass out from oxygen deprivation.
     
  9. Aug 31, 2006 #8
    just curious.
    say you breathed in a heap right before entering a vaccuum. would your lungs expand enough to cause bodily damage? because i would assume that something in your chest (particularly your lungs =p) would burst, leading to death. because i cant remember where i heard it but apparently if you exhale a heap before entering a vaccumm you would survive a little longer than if you were holding a huge breath.
     
  10. Aug 31, 2006 #9
    Yes holding your breath could result in a number of different over expansion injurys. Read Evo's post in the link Russ provided, it sums it up pretty well.

    The blood won't boil because of the pressure exerted by the rest of the body. Then only reason the saliva would boil is because it is directly exposed to the vacuum. It sounds like you are trying to say that blood inside the body will boil, and I just don't think that's true.
     
  11. Aug 31, 2006 #10
    You are right. The saliva will boil and the oxygen in your lungs will boil, but I do not believe the blood will boil, and if it did it would take a large amount of time. Keep in mind that it high vacuum conditions, even your skin may vaporize, as even flesh has a vapor pressure...and in vacuum conditions, this vapor pressure exceeds the atmospheric pressure, and I suppose eventually the blood will be expose and vaporize. But, as pointed out in the above post, it takes quite some time for this type of damage to occur, as the astronaut was exposed to high vacuum for 10 seconds and was not harmed.
     
  12. Aug 31, 2006 #11

    Danger

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    From stuff that I've seen in the past (ie: pre-PF), the effect is essentially mummification. Evo's post pretty much nailed it. One other possibility that is seldom considered, though, is severe toothache. If there are cavities, the pulp can expand and apply pressure to the nerves. Also, it's not a good idea to doff your suit if you have glaucoma. :surprised :biggrin:
     
  13. Sep 1, 2006 #12
    Your way of looking at heat and how temperture of the body does not drop is interesting.

    The vapour pressure of a liquid depends on the surrounding temperture? Increase in temperture -> Increase in vapour pressure
    At low temptures like 20C, vapour pressure of water is much lower than 1atm. But as temptures increase, vapour pressure increases to 1atm which corresponds to 100C and so water start evaoparating as the sorrounding pressure is unable to keep it contained as a liquid.
     
  14. Sep 1, 2006 #13

    LURCH

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    It should be noted that this boiling of water in the mouth would also be happeneing on the skin, and at the eyes. Boiling is a heat transfer process so cooling should actually be quite rapid. But, as has been stated before, not as rapid as the loss of consciousness due to O2 deprivation.
     
  15. Sep 1, 2006 #14
    How does this happen? What is being cooled and why is it rapid?
     
  16. Sep 1, 2006 #15
    Vapor pressure of a liquid (and even a solid...yes, solids have vapor pressures) does not depend on the surrounding temperature...it depends on the temperature of the of liquid or solid!When the vapor pressure of the liquid is equal to or greater than the pressure of the atmosphere then boiling will result.
     
  17. Sep 1, 2006 #16

    DaveC426913

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    Correct me if I'm wrong, but the moisture from the surfaces of your body (such as your eyes and mucous tissues) will vapourise (boil is a misleading word because it is hard not to think of lots of <I>heat</I>).

    This vapourization will draw heat from the body quite rapidly, just like evaporating sweat writ large. It is an endothermic process, meaning it will steal heat - the heat goes into the kinetic motion of the escaping water molecules.

    Lack of air notwithstanding, the effect experienced will still be that of extreme cold.
     
  18. Sep 1, 2006 #17

    DaveC426913

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    Pretty hard for a gas to boil...:biggrin:
     
  19. Sep 1, 2006 #18

    LURCH

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    As Dave said in the above post; boilimg is a cooling process. In fact, evaporative cooling is a very efficient method of cooling, maybe the most efficient. So heat form the body keeps the moisture on the skin warm anough to vaporize (in a vacuum, that is), and as this moisture turns to gas and escapes the body it takes heat with it. The skin should get cold very quickly, and the eyeballs might even freeze.

    But, as mentioned in earlier posts, loss of consciousness ocurred in the astronaut with the leaky suit in just 15 seconds. So you'd probably never have a chance to feel the real bite of the cold.
     
  20. Sep 2, 2006 #19
    And with the issue about taking a large intake of air and than going into a vaccum. The air in the lungs will expand because the surrounding pressure is much lower. The organs would want to expand as well wouldn't it? But the air will expand much more and so if there is a large amount of air in your lungs and you try to keep it there, you will fail because it forces itself out with large amounts of force due to less force inwards as when in 1atm. That is why your lungs will burst if you move from high to low pressure when holding in lots of air.
     
  21. Sep 2, 2006 #20

    But as pointed by others, the water molecules can just escape from the body and at a faster rate than normal since there are no surrounding atoms blocking it. These molecules contain energy and in this way, heat is lost from the body. Although it will be harder to measure this effect because at any point in space, not as large tempertures will be recorded because there is not as many collisions as when not in a vaccum. But the heat lost by the body should be more than when not in a vaccum. In this way the body should decrease in temperture by a lot.
     
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