What range of atmospheric pressure can a human survive in? - ehMac.ca
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Old Jul 20th, 2009, 03:06 PM   #1
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Old Jul 20th, 2009, 03:42 PM   #2
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Here is a good graph that describes the tolerances of humans to different pressures, and how long they can be tolerated.

Actually, its source site has a lot of interesting figures (including tolerances to acceleration, temperature, drinking water, radiation, stress...).

Note that there usually around 21% oxygen in the air at sea level. Some interesting facts from this graph are...

- Breathing pure oxygen at sea level is safe for only about a day
- Assuming your air supply is sea level air, you could survive under 100 ft of water
- Surviving on top of Mount Everest without an air supply is credible, although outside the safe zone
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Old Jul 20th, 2009, 04:07 PM   #3
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At the altitude of Mt. Everest, people have claimed to climb it without oxygen. Were the claims true?
It is possible, just possible, though there can be many long term effects. Many people have troubles above 10,000 feet, which is not even near the level of an Everest Base Camp. The top of Everest is right on the edge, low air pressure and scanty oxygen levels. Of course, another problem is the lack of carbon dioxide, because without CO2 accumulation in the lungs, the body doesn't know to breathe harder, so people because even more deprived of oxygen. People can survive at such altitudes without bottled oxygen but many people will end up with long term damage, and in later years, even Edmund Hilary had to limit time at high altitude because he would end up passing out.

The body can more accommodate higher pressures, to an extent - the problem with high pressures is that it forces nitrogen gas into the blood, where the body does nothing with it. Of course, the gas does no harm until depressurization, when the gas forms bubbles that form embolisms and cause "the bends" - which is kind of like a stroke but with gas bubbles that won't dislodge rather than blood clots. Deep sea divers use exotic mixtures to compensate - like breathing an Oxygen-Helium mix, where the helium is much less prone to forming gas bubbles.

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At great depths, humans can live under pressures much higher than sea level. Sea level is 14 psi right?
About 14.7 psi, plus or minus a bit depending on local conditions. Human life is adapted to a small band of pressures and conditions, so anything outside our normal range requires special equipment or specific adaptation.

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I am aware that Strength athletes have increases in muscular strength at higher atmospheric pressure. Endurance athletes do well with altitude training.
Higher pressures help force oxygen into the lungs, increasing the amount of oxygen in the system when any "strength" is needed - since "strength" is an anerobic activity where the muscles mostly burn up their existing reserves, then restore later.

Endurance, on the other hand, reaps the benefit of stressing the body at higher altitudes, so that specific adaptations are made to handle oxygen more effectively, since these are aerobic activities. When the athlete returns to normal altitudes, they have more oxygen to uptake in a body that is used to less - and thus, it is like blood doping, but without adding extra blood - which is fairly dangerous because it can raise the blood pressure far too high.

At one time it was thought that alpine people had more blood on their system, but their adaptation is that they have the same amount of hemoglobin, but larger lung capacity coupled with slightly higher levels of blood plasma, which keeps things moving without causing clotting in the lungs.

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I was watching some interesting stuff on Astronomy and I think Mars has a 2 PSI atmosphere. Can human and other life adapt to that, and areas of atmospheric and gravitation levels much higher than Earth?
Mars has much lower atmospheric pressure, less than 1/100th of the pressure on Earth, and it is composed primarily of Carbon Dioxide. We would not be able to breath in the air on Mars at all, and at those "pressures", any attempt would lead to the boiling out of all bodily fluids in quick manner. We would have to have a way of creating a pressurized environment with an oxygen atmosphere of some sort. Mars also has a negligible magnetophere, so solar radiation is a very real problem, with doses that prolonged exposure would lead to the development of cancer, radiation sickness and such. Not to mention the extreme cold, with average temperatures below -100C, while a warm, balmy summer day in the middle of an equatorial desert barely pushes above 0C. The lower gravity would lead to humans loosing lower body strength, but larger chests, as lungs would tend to expand in the low gravity. Astronauts have similar problems when they are in space for long missions.

Life on other worlds would be adapted to their environments - and we have not found any environment similar to our own - the only place we know life can exist. It doesn't mean it can't or doesn't exist though. On our own world, we know of organisms that exist in all sorts of crazy environments, from bacteria that lives inside rocks tens of miles below the surface, creatures that exist in the extreme pressures and darkness of the ocean bottom, stuff that can live in the saltiest possible lakes, spiders that live near the South Pole, tardigrades that can exist in extreme levels of radiation without damage, etc. We just can't say - but we know that humans can only exist in a small band of environments.

If say, Mars was colonized, I would expect that humans that live there would evolve into different species - and would end up not being able to return to Earth after evolving because of the crushing gravity of this world compared to the much smaller gravity of Mars.
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Old Jul 20th, 2009, 04:11 PM   #4
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I wonder if we ever did find a human-friendly planet, would it be more efficient to figure out how to get there (we would presumably need either a currently non-existing propulsion system or the ability to put humans in suspended animation, or both), or should we just try to terraform Mars?
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Old Jul 20th, 2009, 07:35 PM   #5
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Depends on how long you need to survive - you can actually survive briefly in complete vacuum - long enough to transfer from one airlock to another, for example.
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Old Jul 20th, 2009, 07:52 PM   #6
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Quote:
Originally Posted by MazterCBlazter View Post
At the altitude of Mt. Everest, people have claimed to climb it without oxygen. Were the claims true?
Stephen Colbert just interviewed such a fellow on a recent episode -- I can't link directly to it, but go to ComedyNetwork.ca, Colbert Report, Interviews A-Z and look up Ed Viesturs (under "V" of course) or just watch the whole show from July 2nd.

Viesturs (I hope I'm spelling his name correctly) has documented himself climbing Everest several times, with and without oxygen. He said in the interview (among many other things) that the experience is definitely different with and without supplemental oxygen.

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Old Jul 20th, 2009, 11:55 PM   #7
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It also depends on how long you give yourself to acclimatize, and how you go about acclimatizing.

The Andean people in Peru seem to do just fine. The area I visited was between 3,000m - 5,000m above sea level, and the locals live and farm there without problem. Meanwhile, us tourists were all feeling the altitude to varying degrees. All of us got headaches when we reached 5,000m, though we'd driven up from 2000m withing just a few hours. Taking time to acclimatize properly, though, and we'd likely be fine.

Any cardiovascular activity is more tiring at high altitude because the air is thinner... the first day up, we were all getting winded climbing a flight of stairs, and most of us were at a reasonable level of fitness.

Diving and then going for a plane ride the next day is a problem because you are not giving yourself enough time to acclimatize.... how high or low an altitude you can live at is a different question from how quickly you can go from one altitude to the next.
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Old Jul 21st, 2009, 02:24 AM   #8
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Old Jul 21st, 2009, 02:31 AM   #9
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Old Jul 21st, 2009, 05:29 PM   #10
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What?

You wouldn't freeze or explode?
Not immediately. If you just had to stroll a few steps from one airlock to another one on the Moon's surface, you would likely be OK. Don't trip!

Explosive Decompression and Vacuum Exposure
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