I'm designing a world with earthlike gravity where the human colonists are intended to live on top of a gigantic shield volcano as tall as Mount Everest. What would the pressure be at the bottom? Would it be too dense for humans to breathe?
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3$\begingroup$ I'm not going to vote to close, but I am going to downvote. A reasonable estimate is found with a 10-second google search. Current pressure on Everest: 4.89 psi. Sea level: 14.69 psi. Basic algebra: 4.89/14.69 = 14.69/X. X = 44.13 psi. P.S. your title question is very different from your body text question (how uninhabitable...), which is too broad. $\endgroup$– JBHFeb 10, 2019 at 23:10
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1$\begingroup$ It would probably be habitable. Big pressure changes are terrible for the human body, but over time it would be 100% plausible for them to slowly migrate down the mountain and adapt to the higher pressure. Usually the problem occurs if you change pressure too fast. Also as JBH mentioned, which question are you asking? the one in the Title or the one in the Body. Please bold it. $\endgroup$– ShadowzeeFeb 10, 2019 at 23:48
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2$\begingroup$ @JBH I'm pretty sure atmospheric pressure doesn't follow a linear curve. $\endgroup$– 0something0Feb 11, 2019 at 1:03
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1$\begingroup$ Deepak Chaudhary, do you know what the atmospheric pressure of Venus is? $\endgroup$– David JohnstonFeb 11, 2019 at 4:47
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1$\begingroup$ @Rekesoft, the downvote button rollover begins, "This question does not show any research effort...." the purpose of this (and all other Stack Exchange sites) is not to be your personal research assistant. Curiously, your accepted answer varies from my rapid estimation by only 6% and my comment was posted before you edited your question. We don't require users to have the knowledge to answer their own questions, but we do expect them to demonstrate that they've made an effort to figure it out first. $\endgroup$– JBHFeb 11, 2019 at 16:36
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2 Answers
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There are online calculators for that.
However, if you assume the same density and radius of Earth, then you can simply increase the pressure by a fixed factor. The factor must be so that pressure at 8800 m (currently about 31% of normal) becomes 1 bar. Which means that it is 1/0.31 = 3.22. Multiply the pressure at sea level by that factor and you get the new sea level pressure - 3.22 bar.
As for survivability, you have that - barely. At 3.21 bar you're skirting nitrogen narcosis (symptoms: Mild impairment of performance of unpracticed tasks, Mildly impaired reasoning, Mild euphoria possible)
However, you can start with a lower pressure at height (perhaps two thirds of normal), which is easily survivable - you have that in La Paz, Bolivia - and gets you about 2 atmospheres at sea level, also survivable with next to no symptoms.
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This website has an atmospheric pressure calculator. Since we are assuming that everything about the planet is the same except for the modified atmosphere, plugging in -8000 meters for altitude gives me 2.39 bars of pressure.
But is it survivable?
This chart from Atomic Rockets tells me maybe. At 2.39 bars or 34.66 pounds per square inch (what the chart uses), we skirt the edge of oxygen toxicity and nitrogen narcosis.
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$\begingroup$ @Brythan yeah read the left side as bars and not atmospheres (EDIT: I didn't. what am I even doing?). Will update. $\endgroup$ Feb 11, 2019 at 2:57
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1$\begingroup$ As I read that graph, 2.9 bar isn't all that close to nitrogen narcosis -- but anyway, oxygen toxicity will kill you a lot faster than nitrogen narcosis -- and still takes a while. Didn't they used to run hyperbaric oxygenation chambers above 3 bar? $\endgroup$ Feb 11, 2019 at 17:21