# How long would it take to die in an N2/O2-rich atmosphere with super-high pressure? **URL:** \ **Category:** Factual Questions\ **Created:** [September 15, 2008, 2:11am UTC](https://boards.straightdope.com/t/how-long-would-it-take-to-die-in-an-n2-o2-rich-atmosphere-with-super-high-pressure/463647 "2008-09-15T02:11:41Z")\ **Posts on this page:** 17\ **Page:** 1
**Author:** ![Hostile\_Dialect](https://avatars.discourse-cdn.com/v4/letter/h/e495f1/32.png) [@Hostile\_Dialect](https://boards.straightdope.com/u/Hostile_Dialect)\ **Post date:** [September 15, 2008, 2:11am UTC](https://boards.straightdope.com/t/how-long-would-it-take-to-die-in-an-n2-o2-rich-atmosphere-with-super-high-pressure/463647/1 "2008-09-15T02:11:41Z")
It is my understanding that ultra-high atmospheric pressure (say, 2.5 atm) could kill you, regardless of the actual makeup of the atmosphere. My question is this: assuming the chemical makeup of the atmosphere is abundantly healthy for human respiratory systems–let’s say it’s richer in the stuff we need, like nitrogen and oxygen, than the Earth’s atmosphere, but not _too_ rich, if there is such a thing, and there’s nothing in the atmosphere that would hurt us in and of itself–and the atmospheric pressure is two and a half times that of Earth, (a) would it kill you, (b) how would it kill you, exactly, and © how long would it take to kill you upon exposure? Let’s assume you’re breathing normally without any kind of air supply, respirator, or anything else that would extend your survival. ETA: Also, assume perfect health in every other regard. ---
**Author:** ![Apollyon](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/apollyon/32/4238_2.png) [@Apollyon](https://boards.straightdope.com/u/Apollyon)\ **Post date:** [September 15, 2008, 2:46am UTC](https://boards.straightdope.com/t/how-long-would-it-take-to-die-in-an-n2-o2-rich-atmosphere-with-super-high-pressure/463647/2 "2008-09-15T02:46:37Z")
> [@Hostile\_Dialect](#): > > …ultra-high atmospheric pressure (say, 2.5 atm) could kill you… > > (a) would it kill you, > (b) how would it kill you, exactly, and > (c) how long would it take to kill you upon exposure? > > Let’s assume you’re breathing normally without any kind of air supply, respirator, or anything else that would extend your survival. At 2.5 atmospheres the oxygen in a standard 21% mix would be up to a little over 0.5 bar, and there would be issues with [oxygen toxicity](http://en.wikipedia.org/wiki/Oxygen_toxicity). > [@Wiki](#): > > The risk of … adult respiratory distress syndrome in adults, begins to increase with exposure for over 16 hours to oxygen partial pressures of 0.5 bar (50 kPa) or more… Usually several days of exposure without “oxygen breaks” are needed to cause severe lung damage. ---
**Author:** ![Rick](https://avatars.discourse-cdn.com/v4/letter/r/9f8e36/32.png) [@Rick](https://boards.straightdope.com/u/Rick)\ **Post date:** [September 15, 2008, 3:02am UTC](https://boards.straightdope.com/t/how-long-would-it-take-to-die-in-an-n2-o2-rich-atmosphere-with-super-high-pressure/463647/3 "2008-09-15T03:02:15Z")
IIRC from my SCUBA training 33 feet = 2 atm. So 2.5 atm is for sure inside of what a sport SCUBA diver encounters. Would it kill you? No ---
**Author:** ![toadspittle](https://avatars.discourse-cdn.com/v4/letter/t/c0e974/32.png) [@toadspittle](https://boards.straightdope.com/u/toadspittle)\ **Post date:** [September 15, 2008, 3:06am UTC](https://boards.straightdope.com/t/how-long-would-it-take-to-die-in-an-n2-o2-rich-atmosphere-with-super-high-pressure/463647/4 "2008-09-15T03:06:42Z")
> [@Hostile\_Dialect](#): > > let’s say it’s richer in the stuff we need, like nitrogen and oxygen, We don’t NEED to breathe nitrogen; there just happens to be a lot of it around here. ---
**Author:** ![Santo\_Rugger](https://avatars.discourse-cdn.com/v4/letter/s/e95f7d/32.png) [@Santo\_Rugger](https://boards.straightdope.com/u/Santo_Rugger)\ **Post date:** [September 15, 2008, 3:10am UTC](https://boards.straightdope.com/t/how-long-would-it-take-to-die-in-an-n2-o2-rich-atmosphere-with-super-high-pressure/463647/5 "2008-09-15T03:10:34Z")
> [@Apollyon](#): > > At 2.5 atmospheres the oxygen in a standard 21% mix would be up to a little over 0.5 bar, and there would be issues with [oxygen toxicity](http://en.wikipedia.org/wiki/Oxygen_toxicity). The way I understand the OP, it stipulates that we can tune down the mix to prevent that from happening. Sorry I can’t be of more help, all my research on the matter has been with overpressures. ---
**Author:** ![Hostile\_Dialect](https://avatars.discourse-cdn.com/v4/letter/h/e495f1/32.png) [@Hostile\_Dialect](https://boards.straightdope.com/u/Hostile_Dialect)\ **Post date:** [September 15, 2008, 3:23am UTC](https://boards.straightdope.com/t/how-long-would-it-take-to-die-in-an-n2-o2-rich-atmosphere-with-super-high-pressure/463647/6 "2008-09-15T03:23:45Z")
Interesting, thanks! ---
**Author:** ![Hostile\_Dialect](https://avatars.discourse-cdn.com/v4/letter/h/e495f1/32.png) [@Hostile\_Dialect](https://boards.straightdope.com/u/Hostile_Dialect)\ **Post date:** [September 15, 2008, 3:25am UTC](https://boards.straightdope.com/t/how-long-would-it-take-to-die-in-an-n2-o2-rich-atmosphere-with-super-high-pressure/463647/7 "2008-09-15T03:25:57Z")
> [@Santo\_Rugger](#): > > The way I understand the OP, it stipulates that we can tune down the mix to prevent that from happening. > > Sorry I can’t be of more help, all my research on the matter has been with overpressures. Actually, no, I was assuming that there was as much or more oxygen as in our atmosphere. > [@Rick](#): > > IIRC from my SCUBA training 33 feet = 2 atm. So 2.5 atm is for sure inside of what a sport SCUBA diver encounters Sure, but you’re not breathing in that atmosphere down there. At least, I hope not :eek: ---
**Author:** ![Santo\_Rugger](https://avatars.discourse-cdn.com/v4/letter/s/e95f7d/32.png) [@Santo\_Rugger](https://boards.straightdope.com/u/Santo_Rugger)\ **Post date:** [September 15, 2008, 3:34am UTC](https://boards.straightdope.com/t/how-long-would-it-take-to-die-in-an-n2-o2-rich-atmosphere-with-super-high-pressure/463647/8 "2008-09-15T03:34:01Z")
> [@Hostile\_Dialect](#): > > Actually, no, I was assuming that there was as much or more oxygen as in our atmosphere. “Abundantly healthy” and “richer in the things we need” are mutually exclusive. You could have as much oxygen, but it’d have to be as much absolutely, not as much by volume. > [@Hostile\_Dialect](#): > > Sure, but you’re not breathing in that atmosphere down there. At least, I hope not :eek: I don’t know much about SCUBA diving, but I’m pretty sure if your regulator wasn’t turned up to nearly the pressure of the water, the hydrostatic force would crush your lungs. I’d be pretty similar to an overpressure, I believe. Those start to get deadly around 4 psi. ---
**Author:** ![Rick](https://avatars.discourse-cdn.com/v4/letter/r/9f8e36/32.png) [@Rick](https://boards.straightdope.com/u/Rick)\ **Post date:** [September 15, 2008, 3:48am UTC](https://boards.straightdope.com/t/how-long-would-it-take-to-die-in-an-n2-o2-rich-atmosphere-with-super-high-pressure/463647/9 "2008-09-15T03:48:01Z")
> [@Hostile\_Dialect](#): > > Actually, no, I was assuming that there was as much or more oxygen as in our atmosphere. > > Sure, but you’re not breathing in that atmosphere down there. At least, I hope not :eek: Of course you are breathing at whatever the surrounding pressure is. That is why you have a regulator that compensates for ambient pressure. If you were at two atm with an air supply at 1 atm, you would not be able to inflate your lungs. Pressure in and of itself does not kill. Oxygen can be come toxic if in too high a concentration at greater pressures, and Nitrogen can lead to disorientation (Martini’s law says that each 50 feet of depth = 1 dry martini on an empty stomach) but these problems can be minimized via the use of mixed gasses. The largest problem with high pressures is decompression so that you don’t get the bends on the way back up. ---
**Author:** ![Apollyon](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/apollyon/32/4238_2.png) [@Apollyon](https://boards.straightdope.com/u/Apollyon)\ **Post date:** [September 15, 2008, 4:48am UTC](https://boards.straightdope.com/t/how-long-would-it-take-to-die-in-an-n2-o2-rich-atmosphere-with-super-high-pressure/463647/10 "2008-09-15T04:48:12Z")
> [@Rick](#): > > Oxygen can be come toxic if in too high a concentration at greater pressures, and Nitrogen can lead to disorientation…but these problems can be minimized via the use of mixed gasses. I find the fascinating diving gases to be the “bottom mix” ones that you can’t breathe at sea-level, due to their lowered O2 content (to avoid oxygen toxicity at the partial pressures encountered at depth). ---
**Author:** ![A\_shameful\_cracka](https://avatars.discourse-cdn.com/v4/letter/a/ebca7d/32.png) [@A\_shameful\_cracka](https://boards.straightdope.com/u/A_shameful_cracka)\ **Post date:** [September 15, 2008, 5:44am UTC](https://boards.straightdope.com/t/how-long-would-it-take-to-die-in-an-n2-o2-rich-atmosphere-with-super-high-pressure/463647/11 "2008-09-15T05:44:02Z")
> [@Apollyon](#): > > I find the fascinating diving gases to be the “bottom mix” ones that you can’t breathe at sea-level, due to their lowered O2 content (to avoid oxygen toxicity at the partial pressures encountered at depth). Like heliox. Typically 90% or more helium with the remainder oxygen. Used in deep sea diving because nitrogen at those pressures would essentially poison you, but helium is safe. ---
**Author:** ![Sunspace](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/sunspace/32/1250_2.png) [@Sunspace](https://boards.straightdope.com/u/Sunspace)\ **Post date:** [September 15, 2008, 6:32am UTC](https://boards.straightdope.com/t/how-long-would-it-take-to-die-in-an-n2-o2-rich-atmosphere-with-super-high-pressure/463647/12 "2008-09-15T06:32:06Z")
> [@A\_shameful\_cracka](#): > > Like heliox. Typically 90% or more helium with the remainder oxygen. Used in deep sea diving because nitrogen at those pressures would essentially poison you, but helium is safe. I was just wondering, how high a pressure we could survive if the relative pressures of the oxygen and carbon dioxide were cranked back to maintain appropriate absolute partial pressures, and assuming that pressures were equalised inside and outside the body. Nitrogen poisons you at high pressures? How? If we went with helium and oxygen, could we increase the pressure until we were basically breathing liquid? ---
**Author:** ![Hostile\_Dialect](https://avatars.discourse-cdn.com/v4/letter/h/e495f1/32.png) [@Hostile\_Dialect](https://boards.straightdope.com/u/Hostile_Dialect)\ **Post date:** [September 15, 2008, 8:44pm UTC](https://boards.straightdope.com/t/how-long-would-it-take-to-die-in-an-n2-o2-rich-atmosphere-with-super-high-pressure/463647/13 "2008-09-15T20:44:37Z")
I don’t know about “basically”, but literally breathing liquid would probably be a fast track to lung failure. ---
**Author:** ![mlees](https://avatars.discourse-cdn.com/v4/letter/m/ba8739/32.png) [@mlees](https://boards.straightdope.com/u/mlees)\ **Post date:** [September 15, 2008, 9:22pm UTC](https://boards.straightdope.com/t/how-long-would-it-take-to-die-in-an-n2-o2-rich-atmosphere-with-super-high-pressure/463647/14 "2008-09-15T21:22:08Z")
At what pressure does actual physical damage (tearing?) start appearing in the lung tissues? ---
**Author:** ![Apollyon](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/apollyon/32/4238_2.png) [@Apollyon](https://boards.straightdope.com/u/Apollyon)\ **Post date:** [September 15, 2008, 9:52pm UTC](https://boards.straightdope.com/t/how-long-would-it-take-to-die-in-an-n2-o2-rich-atmosphere-with-super-high-pressure/463647/15 "2008-09-15T21:52:20Z")
> [@Sunspace](#): > > Nitrogen poisons you at high pressures? How? An excellent question. My dive instructor said that the mechanism wasn’t really understood, but that at sufficient partial pressure even gases that were inert at sea-level had odd effects. The Wikipedia article on [nitrogen narcosis](http://en.wikipedia.org/wiki/Nitrogen_narcosis) gives “inert gas narcosis” as an alternate term and says: > [@Wikipedia](#): > > Its precise mechanism is not well understood, but it appears to be a direct effect of nitrogen dissolving into nerve membranes and causing temporary disruption in nerve transmissions. While the effect was first observed with nitrogen (in air), other gases including argon, krypton, and hydrogen also cause very similar effects under higher than atmospheric pressure… The noble gases argon, krypton, and xenon are more anesthetic than nitrogen at a given pressure, and xenon has so much anesthetic activity that it is actually a usable anaesthetic at 80% concentration and normal atmospheric pressure. So not going diving with xenon would seem to be in order. 🙂 Helium isn’t mentioned there, and this scuba-doc article on partial pressures ([pdf](http://www.scuba-doc.com/ppPhysics.pdf)) states that “Helium lacks this anesthetic property and is used in place of N2 as the diluent for O2 in deep diving”. > [@](#): > > If we went with helium and oxygen, could we increase the pressure until we were basically breathing liquid? I suspect at the pressures you’d need, and despite humans being mostly incompressible water, we’d be just water and some red paste. Lower pressure [liquid breathing](http://en.wikipedia.org/wiki/Liquid_breathing) is possible however, if still experimental. (There’s also a dramatization of it in [The Abyss](http://www.imdb.com/title/tt0096754/)). ---
**Author:** ![intention](https://avatars.discourse-cdn.com/v4/letter/i/e95f7d/32.png) [@intention](https://boards.straightdope.com/u/intention)\ **Post date:** [September 15, 2008, 11:01pm UTC](https://boards.straightdope.com/t/how-long-would-it-take-to-die-in-an-n2-o2-rich-atmosphere-with-super-high-pressure/463647/16 "2008-09-15T23:01:31Z")
As a sport diver, a very occasional commercial diver, and a volunteer at the local recompression chamber, I can assure you the “2.5 atmospheres” is a long way from “super-high pressure”. It translates to only about 42’ of water depth, and people dive to that depth and breathe compressed air at that pressure all of the time. In fact, divers are recompressed to well above that pressure if they suffer the bends, in order to cure them. Oxygen toxicity does become a problem at higher pressures, but only above something like (IIRC) fifteen atmospheres pressure. In any case, it’s at a pressure equivalent to diving deeper than a couple of hundred feet, which is about 14 atmospheres. w. ---
**Author:** ![flex727](https://avatars.discourse-cdn.com/v4/letter/f/258eb7/32.png) [@flex727](https://boards.straightdope.com/u/flex727)\ **Post date:** [September 16, 2008, 6:57pm UTC](https://boards.straightdope.com/t/how-long-would-it-take-to-die-in-an-n2-o2-rich-atmosphere-with-super-high-pressure/463647/17 "2008-09-16T18:57:33Z")
> [@mlees](#): > > At what pressure does actual physical damage (tearing?) start appearing in the lung tissues? My understanding, based SCUBA diving training classes, is that the lung aveoli can handle about 2 psi of pressure differential. Once that is exceeded, embolism and likely death will result. This is why divers are trained to maintain an open airway at all times and to never hold one’s breath while diving. Previous posts (including the OP) fail to understand that absolute pressure is of little consequence in this discussion. Very high pressure has no ill effects (strictly from the pressure itself) as long as all pressures are equalized. High pressure can cause oxygen toxicity or various kinds of narcosis if the air mixture is not handled properly. High pressure can also cause embolisms and/or DCS (the bends) when the pressure is released too quickly or improperly. I don’t know what the absolute upper limit is to the handling of high pressure when all proper precautions are taken, but there does seem to be some sort of nervous system impact when the pressure is increased enough, regardless of all currently known precautions. There is an interesting fictional treatment of some aspects of this issue near the end of the movie The Abyss.