I am wondering if on an otherwise Earth-like planet the atmosphere pressure were constantly 2Atm at the sea level, how would a human body behave if we landed there? Suppose the air composition would be quite similar to our (like 25% oxygen, 73% nitrogen, water vapur etc.). Would our blood pressure raise or remain stable? Would our lungs function with more ease or with greater difficulty? The ability to move, work, act etc. - would they change? Would it influence our senses (hearing, seeing, etc.)? Would we be tired more easily or on the contrary less easily (having more oxygen)? Could we sleep better or worse? In general, how would we adapt? Would it influence our ability to survive - make our life longer or shorter? Thanks for any answer!

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    $\begingroup$ 2 atmospheres in analogous to scuba diving in 30 feet of water. Not deep enough for nitrogen saturation to be a problem. $\endgroup$ Jan 24, 2021 at 20:23
  • $\begingroup$ Thank you for a quick answer. Unfortunately I have no idea about scuba diving, have never done it. 30 feet that's approximately only 9 meters deep. Not much. Yet, I guesss, if you are in a scuba in the water however, all the other factors of your environment change, not only the pressure. You are in the water, not air, so your skin is constantly wet, your vision and audition are impared, your temperature (homeostatis) functions differently etc. I have read en.wikipedia.org/wiki/Human_physiology_of_underwater_diving, that's not what I mean. $\endgroup$ Jan 24, 2021 at 20:46
  • $\begingroup$ And of course you cannot be diving for 365days 24h a day. $\endgroup$ Jan 24, 2021 at 20:53
  • $\begingroup$ Divers don't need to be diving to be in pressure environments. There are underwater habitats that are maintained at the water pressure to facilitate 'moon pools'. People live perfectly ordinarily inside these. In most cases these use various heliox mixtures due to depth, but regular atmospheric air is good enough for about 2 atmospheres (10 meters), at 3 atm (20m) the nitrogen becomes narcotic. So for regular air the limit is somewhere between 2 and 3 atmospheres. Unfortunately I don't have suitable references at hand to make this proper answer. $\endgroup$
    – tylisirn
    Jan 24, 2021 at 21:54
  • $\begingroup$ The underwater habitats, that's a great idea to research. Thanks for the idea, even if without precise referewnces. $\endgroup$ Jan 26, 2021 at 20:24

2 Answers 2


My answer here: https://worldbuilding.stackexchange.com/questions/194650/what-would-be-the-effects-of-changing-the-composition-of-air-in-order-to-increas/194689#194689[1]

quotes research on the atmosphereic requirements of humans, specifically Habitable Planets for Man Stephen H. Dole, 1964, 2007, which has an online edition.


On page 15 Dole states that the normal atmospheric pressure of oxygen at sea level on Earth is about 149 millimeters of Mercury. The overall sea level atmospheric pressure is 29.92 inches of Mercury, or 759.968 millimeters of Mercury. Twice the sea level atmospheric pressure on Earth should be about 1,519.936 millimeters of mercury.

On page 19 Dole says:

To summarize, then, the atmosphere of a habitable planet must contain oxygen with an inspired partial pressure of between 60 and 400 millimeters of mercury and carbon dioxide with a partial pressure roughly between 0.05 and 7 millimeters of mercury. In addiiton, the partial pressures of the inert gases must be below certain specified limits and other toxic gases must not be present in more than trace amounts. Some nitrogen must be present so that nitrogen in combined form can find its way into plants.

Twice the sea level atmospheric pressure of oxygen would be about 298 milititers of oxygen, which Dole considered within the safe limits.

If a planet has an atmopsheric pressure of 1,519.936 millimeters of mercury which is entirely a substance which is not oxygen, humans would suffocate without oxygen.

But pressure of 1,519.936 millimeters of mercury is within the non toxic limits of such inert gases as argon, nitrogen, neon, and helium. A human would not suffer toxicity in atmospheres containing 1,519.936 milimeters pressure if it was composed of any of those gases, though humans would suffocate unless sufficient oxygen was also in the atmosphere. So if any of those elements was in an atmsophere of 1,519.936 millimeters of pressure and with the same percentage as Earth's atmosphere, it would not be toxic.

In Earth's atmosphere nitrogren and oxygen are the main components totalling almost 99 percent. And argon, neon, helium and krypton are in such low concentrations that doubling their concentration in an atmosphere twice as dense should still be far below their toxic levels.

The main concern with doubling the density of Earth's atmosphere would be doubling the pressure of carbon dioxide, methane, and water vapor.

The scale height of Earth's atmopshere is the height at which its density decreases by 2.718, and is 8.5 kilometers. So a mine extending 8.5 kilometers below sea level would have an atmosphereic denisty 2.718 times that at sea level, consdierably more than twice sea level.

The deepest mine in the world, the Mponeng Gold Mine in South Africa, extends 4.0 kilometers or 2.5 miles deep, though mine depth is measured from the surrounding elevation,not from sea level.

Reverse altitude sickness can happen when mumans move from a haigh altitude to a low altitude. Thus you might want to research reverse altitude sickness and find out whether it wo uld bother humans born in a region with twice the atmospheric pressure of Earth.

  • $\begingroup$ Inches and millimeters, must have been an international team. $\endgroup$ Jan 24, 2021 at 22:08
  • $\begingroup$ The surface elevation of Mponeng is 1565 m above sea level, so at it's deepest it's only 2435 m below sea level. $\endgroup$
    – user81881
    Jan 25, 2021 at 2:12
  • $\begingroup$ I am not sure if I have understood everything, partos of your explanation seem to me a bit cryptic, and the link to Dole gives the 404 ERROR, yet you have given me sothing to think about. E.g. it would be nice to know and consider the toxic limits of other gases. I have never heard about "reverse altitude sickkness", high mountain dwellers like Tibetans, Bolivians and Peruvians, seem to adapt more easily to life in the lowlands, than reverse, e.g. the Chinese who were resettled to Tibet, or Westerners trying to live in Machu Picchu, yet I will search for it. Thank you $\endgroup$ Jan 26, 2021 at 20:20
  • $\begingroup$ Researching the conditions in open mines, would also be great. Thanks $\endgroup$ Jan 26, 2021 at 20:21
  • $\begingroup$ A new link for Dole is rand.org/pubs/commercial_books/CB179-1.html and for another booklet by him and Asimov rand.org/pubs/commercial_books/CB183-1.html, both donloadable for free. Thank you for the reference. $\endgroup$ Jan 26, 2021 at 20:28

With question of atmospheric composition and pressure percentages are less important than the partial pressures of the various gases in the system. If I recall correctly the research I did for another question about atmospheric composition indicated that half an atmosphere partial pressure of oxygen would be a 1 on the "martini's per hour" scale used to measure gas intoxication, not immediately harmful but cumulatively quite damaging. I think the Carbon Dioxide and Nitrogen of an atmosphere twice as dense but with the same gas percentages would be bad news too but you'd have to check that.

  • $\begingroup$ Having reread after some time I can find that the link to Dole needs to be only slightly corrected, removing the [1][2] after the .pdf and one can download the report. I will read it now. $\endgroup$ Sep 6, 2022 at 17:08

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