# What range of atmospheric pressure can a human survive in?



## MazterCBlazter (Sep 13, 2008)

*.*

.


----------



## lookitsmarc (Feb 2, 2008)

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


----------



## EvanPitts (Mar 9, 2007)

MazterCBlazter said:


> 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.



> 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.



> 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.



> 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.


----------



## lookitsmarc (Feb 2, 2008)

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?


----------



## Gerbill (Jul 1, 2003)

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.


----------



## chas_m (Dec 2, 2007)

MazterCBlazter said:


> 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.


----------



## Sonal (Oct 2, 2003)

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.


----------



## MazterCBlazter (Sep 13, 2008)

.


----------



## MazterCBlazter (Sep 13, 2008)

.


----------



## Gerbill (Jul 1, 2003)

MazterCBlazter said:


> 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


----------



## MazterCBlazter (Sep 13, 2008)

.


----------



## EvanPitts (Mar 9, 2007)

MazterCBlazter said:


> What?
> 
> You wouldn't freeze or explode?


Actually not, at least in short time frames. Since a vacuum is mostly devoid of gas, the convection of heat from say, a human, would be very slow. Any cooling effect comes from "outgassing", where a human (or whatever) is converted from solid into gas by virtue of the vacuum. Cooling is a very real problem in space, and thought it is extremely cold (perhaps a few kelvin at most), there is just no way to convect heat away from an object rapidly.

By the same means, objects will not "explode", but will undergo either sublimination from solid to gas, or evaporation from liquid to gas, under high vacuum. This outgassing is not a rapid effect, as comets like Halley's have been outgassing in a most spectacular fashion for eons.

If a human was subjected to vacuum (like the 1x10^-5 torr found in Earth orbit), death would be caused by the rapid boiling of bodily fluids and their loss into space, mostly through the lungs. Just as the boiling point of water is lower at high altitudes, it is even lower in a vacuum. Then what is left, the "solids", would slowly outgas into space, with the skin hardening into what would look like a seared tissue paper, light but woodlike. The body itself would exist only until it outgassed, or was eroded away by spurious ionic oxygen and from ionic hydrogen driven by the solar flux. Luckily, death would be very fast indeed, but no explosions or rapid freezing.


----------



## Kazak (Jan 19, 2004)

Inquiring minds want to know why you're interested in this, MCB . . .


----------



## MazterCBlazter (Sep 13, 2008)

.


----------



## bryanc (Jan 16, 2004)

MazterCBlazter said:


> When I was a fisherman, when some fish were hauled up from the depths, they blew up. Others came up in perfect condition.


Fish have swim bladders (gas-filled compartments that they use to maintain neutral buoyancy). In some species, the swim bladder is connected to the esophagus, so they can 'burp' excess pressure out of their bladders when ascending rapidly. Fish that live in deep water, and which never venture near the surface don't have this connection, so their swim bladders will burst if they're brought to the surface.


----------



## Kazak (Jan 19, 2004)

Thanks for the detailed response, MCB. I was sort of hoping you had a stunt planned. Nothing wrong with learning for the sake of learning, though.


----------



## EvanPitts (Mar 9, 2007)

MazterCBlazter said:


> I want to know the range of life's adaptability, especially for humans. If out of necessity can we build cities to live in the depths of the oceans under pressure for example.


Sure, some people have even posited that at some point, we could actually build floating cities for Jupiter - designed to float around in the zone of atmosphere where the pressure is the same as ours, and the temperatures at that level are also within our zone. Of course, I have no idea what we would do there, though some belief it may be profitable to harvest the isotope Helium 3, which is fairly rare on Earth.

Living in the ocean on Earth is a possibility as well, especially if we were to harvest minerals from the ocean floor, like Manganese nodules and such. The limiting factors are the costs, satisfactory materials that can handle stresses, and the amount of risk one is prepared to put people at. Considering that people live in LA, right on top of a fault line - I think the risk is the smallest factor, while costs versus profits is the overwhelming factor.



> When I was a fisherman, when some fish were hauled up from the depths, they blew up. Others came up in perfect condition.


That's the gases coming out of the tissues, unable to escape. Many creatures from the deep bottom simply fall apart or go limp.



> A planet somewhere in the future with a thin atmosphere (Mars), can we live in it?


If Mars had oxygen, and enough air pressure, we could live there. We need oxygen, it is part of our metabolic process. Of course, there are forms of life that do not need oxygen, and are even poisoned by oxygen - so those kinds of life could exist on Mars, if they can adapt to scrounging energy out of some kind of Carbon Dioxide trade. The main limit with Mars is the thin, low pressure atmosphere that leads to liquids quickly boiling into gas - and with the exception of some devolved lifeforms on Earth, we know of no form of life that can exist in the solid form. Mars also lacks a magnetosphere, so it is hit by the full brunt of solar radiation, like UV - stuff that is blocked by our magnetosphere as well as the ozone layers and Van Allen belts...

Of course, there is the possibility of a Silicon based lifeforms - it's not just Star Trek hockum - but Silicon is in the same family in the periodic table as Carbon, and hence, shares many chemical properties, so given the right circumstances and method of energy supply.



> If Venus could be cooled down, can we adapt to its pressures?


Venus has a pressure that is 90 times that of Earth - which would be beyond even the most exotic pressures of 1000 psi that humans could endure. The problem with Venus would be the "rain", which is sulphuric acid. Cooling down the atmosphere would mean that the "rain" would actually reach the ground - instead of the current state of it boiling back up 25 miles above the ground. It would be one hellish place, with lakes and rivers of acid dissolving everything in it's path...



> How about other living things like plants and animals?


Those things we simply do not know. The life we find on Earth, or at least know of right now, would not survive for long in these other enviroments. Of course, the big unknown is whether life can exist under the ices of some of the moons, like Europa, or can take advantage of the hydrocarbons present on Titan. But then, we do not know if life exists in our own Lake Vostok, in Antarctica - which would have similar conditions to that of Europa. We do know of bacteria that exist in a hydrocarbon systems, and there are even some theories that oil on Earth is not actually from fossils, but is being produced by a variety of rock eating bacteria. Exobiology will be the most exciting discovery ever - proof that we are not alone in the universe; but a Holy Grail that we are not even close to yet.


----------

