Is my planet's atmosphere livable for humans?

Question

My planet has a atmospheric pressure of 1.4 atm. The gases that make up the atmosphere are 79% nitrogen, 18.6% oxygen, 1.4% argon, 0.5% water vapor, 0.3% xenon, 0.02% CO2, 0.01% krypton, 0.17% other trace gases. Would this atmospheric composition be livable?

Answer 1

18.6% of 1.4 atmospheres (which I am assuming is your sea level pressure) is ~.26 atmospheres. 21% of our Earth's 1 atmosphere is ~.21 atmospheres. Therefore, the partial pressure of oxygen on this planet is actually higher than the partial pressure of oxygen in the Earth's atmosphere — you get more oxygen per breath than you do on Earth, because each breath forces more oxygen into your lungs.

In terms of other gasses, it's not an issue either.

• 0.1% more water vapor than the Earth is a non-issue.
• It has orders of magnitude more xenon and krypton in the atmosphere than the Earth, but this too is a non-issue; it takes much higher ratios of noble gasses to oxygen to be an issue, and this is orders of magnitude less than that. Perhaps there will be a freak incident or two involving xenon or krypton which pools at very low (sub-sea level) elevation and suffocates an explorer or two who walks into the "puddle".
• Half the carbon dioxide in the atmosphere compared to Earth is probably better for humans. It will pose a problem for plants but they will probably survive at percentages over 0.01%.
• No idea what the trace gasses are, but they probably can't be that bad.

However, the big issue here is that the human chest wall can only withstand about 80 mmHg static overpressure (static overpressure = a constant pressure greater than 1 atmosphere) within the lungs, which is about 0.105 atmosphere — about 0.3 atmospheres short of this planet's atmosphere. Similarly, a human can only breathe out with ~88mmHg of pressure. You will want one or a combination of three things:

• Some kind of reverse-SCUBA apparatus pressure valve which takes in 1.4-atmosphere air, decompresses it to 1 atmosphere, then lets the human breathe it, then repressurizes the exhalations so they can be pushed out.
• Genetic/surgical/cybernetic augmentation to reinforce humans against the higher pressure.
• Living at higher altitudes where the pressure is lower.

Otherwise, the air pressure is high enough that they will suffocate — not because they can't breathe oxygen in, but because they can't breathe carbon dioxide out against 1.4 atmospheres of pressure.