# What are the ranges a human can survive AND breathe in?

I am writing a space sci-fi short story series, and I am trying to figure out what the range in pressure a human can survive AND breathe. I am trying to find the lowest, safest air pressure a human can breathe in where the oxygen isn't leaving the blood. The atmosphere is the same as Earth's.

• This may have already been answered in this site. I recall some discussion in posts and comments about the minimum pressure for a pure oxygen environment, oxygen toxicity, scuba diving, etc., but you haven't mentioned the composition of the atmosphere in your question. Are you asking about a standard composition with something like 21% oxygen and just a loss of pressure, or an enhanced oxygen atmosphere at lower total pressure.
– uhoh
Apr 24, 2018 at 2:41
• The minimum pressure depends on the gas mixture. For pure oxygen it is much lower than for air with only 21 % oxygen.
– Uwe
Apr 24, 2018 at 8:30
• Also you must describe how long the guy must survive in that conditions: 1 minute, 1 hour, 1 year?
– jean
Apr 24, 2018 at 10:51
• @Norm, The pressure in an EVA suit can be less than that if the gas is pure oxygen. Apr 24, 2018 at 20:05
• 4 psi of pure O2 is used in the US Shuttle/Station suits. space.stackexchange.com/questions/13331/… Apr 28, 2018 at 22:20