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What is the minimum pressure the human body can handle?

  1. Jun 19, 2010 #1
    .....assuming very slow adaptation is possible. How low can one go?

    And something else: if you're at very low pressure, water or blood would boil at RT (pressure is lower than the vapor pressure of water). Would this mean a relatively innocent cut wound would make you lose a lot of blood?:surprised

    The person is allowed to use breathing equipment, like a diver, but not a pressure-suit or anything similar.
     
    Last edited: Jun 19, 2010
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  3. Jun 19, 2010 #2

    mgb_phys

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    Long term anything below about 0.15atm pure O2 means you aren't going to live

    Short term nothing is actually going to kill you, except by removing all the O2 from your system
     
  4. Jun 19, 2010 #3

    Andy Resnick

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    People have been exposed to vacuum in explosive decompression tests:

    http://www.geoffreylandis.com/vacuum.html (about 1/2 way down).

    There's a video I've seen of the 1966 test, it's actually kind of boring to watch.

    Chronically, people can live up to about 15,000 feet altitude:

    http://news.nationalgeographic.com/news/2004/02/0224_040225_evolution.html

    And their bodies have undergone significant adaptation. The article states that death from hypoxia occurs around 25,000 feet in altitude, corresponding to about 282 mmHg (37.6 kPa)- atmospheric pressure is 101 kPa and 760 mmHg. Assuming 20% of the air is O2, the partial pressure at 15,000 feet agrees well with mgb_phys: those folks are living right at the edge of existence.
     
    Last edited by a moderator: Apr 25, 2017
  5. Jun 19, 2010 #4
    Just to clarify, I'm not talking about the threshold of being able to draw too little oxygen. I'll edit the first post.

    Let's say the person is allowed to use breathing equipment. But no space suit or anything similar that manually retains a high pressure.
     
  6. Jun 19, 2010 #5
    Thanks a lot for that link!

    Those kind of sites are what I love about the Internet. Unique knowledge being shared for non-commercial reasons. Unfortunately, these kind of pages are more and more hard to find as search machines first list E-bay and all kind of commercially related sites. Back to the topic now...
     
  7. Jun 19, 2010 #6

    mgb_phys

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    Lowest pressure is about 0.15atm with breathing apparatus, that's the lowest partial pressure of O2 you need and you can't breathe with breathing apparatus if the outside pressure is less
     
  8. Jun 19, 2010 #7
    What is the reason you can't breath with apparatus when the outside pressure is less than 0.15atm? And would that (hypoxia) be the cause of death in such a situation, or are do other lethal effects take place?
     
  9. Jun 20, 2010 #8
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  10. May 10, 2012 #9

    DHF

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    .15 is the triple point of O2. I am not sure what the exact effect a zero pressure environment would have on O2 but if you are looking at such low pressures you are facing a vacuum, and in a vacuum you would be exposed to extremely cold temperatures its possible that without a pressurized environment the 02 would convert to ice at those temperatures .

    However at such temperatures breathing would be the least of your problems. with nothing more then a breathing mask on, exposed to a vacuum you would freeze to death very quickly.

    Don
     
    Last edited: May 10, 2012
  11. May 10, 2012 #10
    No you don't freeze to death, because despite the low temperature (i'm not even sure if it has to be cold in a near vacuum) there is no matter to exchange heat with, so your body temperature will stay the same.
     
  12. May 10, 2012 #11

    A.T.

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    You loose heat trough radiation.
     
  13. May 10, 2012 #12

    russ_watters

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    ...but the reason you can't breathe is because your lungs would burst if the pressure differential is too high, even if you were strong enough to exhale.
     
  14. May 10, 2012 #13
    You generate heat inside your body as well...
     
  15. May 11, 2012 #14
    I could see that in space, but on the earth? With your surroundings being similar temperature?
     
  16. May 11, 2012 #15
    You'd still radiate heat. You are, right now. The matter surrounding you radiates heat too, and there is a balance of the heat absorbed and radiated by you, and this forms a dynamic equilibrium. When you're in vacuum, there is no 'matter' to radiate heat so that you can absorb it. Your heat is just radiated out, without you getting anything back.

    Edit : Also, vacuum has no temperature, since there are no molecules to vibrate.
     
  17. May 11, 2012 #16
    Perhaps you mean when you're in space? Just because you're in a vacuum doesn't mean there's no matter around you. Maybe not in direct contact with you, but surely the thick stainless steel walls which have to fully surround you (if you hope to create a vacuum on earth) count as matter, and they radiate just as much heat back to you as you radiate to them?
     
  18. May 11, 2012 #17
    Given a long enough interval for the attainment of equilibrium, yes, they would.
     
  19. May 26, 2012 #18
    This intrigued me and was running through my head. Alright: Suppose you didn't receive your oxygen through your lungs, but your blood was being circulated through a separate device, and you had no need to breathe (all crazy hypothetical stuff). Can the body survive just fine in a vacuum if given sufficient time to equalize? Is there a minimum pressure after which the human body cannot equalize anymore?

    Meaning: How much does pressure matter to the human body outside blood oxygenation needs?
     
  20. May 29, 2012 #19
    I have two concerns/hypotheses about this

    First

    Even if you didn't have to breathe and you could cover up your nose and mouth, think about all the openings into your body (ears, digestive tracts, eyes, etc... even your pores). I think that contained pressure in the body would strive to get into an equilibrium with the surrounding vacuum and the gasses/fluids in your body would be forced out.

    I think it would be similar to a fish that is adapted to pressure in the deepest trenches of the ocean. These creatures (depending on which) sometimes ooze out fluids and gasses when brought to the surface because they are used to such high pressure.

    There's a reason that vacuum chambers are sealed so tightly (to form a barrier that prevents equilibrium with the surroundings from happening). I doubt that our mere skin is a sufficient barrier.

    Second


    I think someone already mentioned this, but wouldn't the water and other liquids in our skin and our eyes evaporate? As the pressure decreases the boiling point should decrease as well.




    EDIT: Back to your meaning - I don't think it matters too much when breathing isn't an issue because naturally, we can't even reach pressures that would be considered close to a vacuum on earth. Ergo, we are not meant to float around in space so I think that our bodies (when breathing is not considered) may be well adapted for low pressures.
     
  21. May 30, 2012 #20

    Regarding the first point: Humans are frequently subjected to 8 bars of pressure in hyperbaric medicine, which means that, over a period of time, the human body can go from a pressure of 8 bars to 1 bar, a difference of 7 atmospheres. This happens very slowly. If this were to happen quickly, terrible things happen. The Byford Dolphin incident had divers living in a condition of 9 atmospheres just fine. The problem arose when there was an explosive decompression, which basically liquefied some of the bodies and rapidly filled the blood of the others with fat.

    But, anyway, humans can definitely handle pressure changes of many atmospheres, provided they are given enough time for the pressure in various pressure vessels in their bodies to equalize. Wouldn't a difference of one atmosphere (1 atm -> 0 atm) be even less harsh, if given the same amount of time to slowly depressurize? It's been stated here that the min. sustainable pressure is 0.15 atmospheres of pure oxygen, but this is with the breathing requirement in place. But, at that point, they have already depressurized 85% towards a vacuum.

    I envision being completely open, not worried about covering up any pores. Let all the air from all the pores evacuate themselves wherever possible. Whatever it is, it will *certainly* be much less of a pressure change to an animal than bringing those deep sea creatures up to the surface. Physically, the pressure change from 1 atm to a vacuum is ~1/500th that of from deep sea to 1 atm.


    Your second point is what I was thinking as well. I think the biggest challenge we'd face if "breathing" was taken care of in a vacuum would be drying out. The fluids in our eyes, nasal cavities, ears, etc, probably have some kind of water content which would want to become gaseous when subjected to a vacuum. The rest of our body is actually pretty good at holding in the water against the pressure. Our eyelids would drag across our eyes, the skin in our mouths would be as if we'd just woken up after mouth breathing all night. I can't imagine what a 100% dry nasal cavity would feel like...

    So, maybe the biggest challenge to being in a vacuum = dessication?
     
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