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Wikipedia lists the atmospheric pressure of Mars to be about 600 pascals, or just 0.6% of Earth's atmosphere. I'm wondering, can anyone shed any light on what that means, in practical terms?

Specifically, I'm looking for what might happen if a habitat on the surface of Mars, pressurized for Human occupants, got a leak. Not huge, like opening a door, but something along the lines of a bullet hole in the wall or a small meteorite impact.

Would that kind of pressure difference lead to an explosive decompression, or just the equivalent of a strong wind blowing out the hole? If they were outfitted with oxygen face-masks like Everest climbers, would the occupants be able to survive for long, or is that pressure quickly lethal? There are so many images of depressurization in space, that I'm having a hard time visualizing an accurate picture of depressurization into the Martian atmosphere.

Thanks in advance for any insight you have! This is my first question here, but I've already fallen in love with this particular Stack site.

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  • $\begingroup$ See space.stackexchange.com/questions/57563/… for a detailed answer, Spoiler alert: the vapor pressure of water (not the partial pressure of oxygen) puts a lower limit on survivable pressure. $\endgroup$
    – Woody
    Commented Oct 11 at 21:53

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Whether or not a decompression will be explosive depends on the size of the hole and the shape and material of the wall it's made in. In terms of human factors, 600 Pa is not very different from a vacuum. To give a comparison, it is equivalent to an altitude of about 34 km -- compare that with Mt. Everest's 8.8 km.

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  • $\begingroup$ Yet on Mt Everest people can stay and breath (with training), and with oxygen supply will feel totally well. $\endgroup$
    – Anixx
    Commented Jan 17, 2014 at 2:37
  • $\begingroup$ It's not really a question of oxygen per se. The atmospheric pressure at Everest's altitude is about 33.7 kPa, that is, more than 56 times the atmospheric pressure on Mars. Your primary obstacle to survival would be a severe case of the bends, as well as tissue swelling and loss of circulation. You would need to find a way also to get at least about 20 kPa of oxygen to your lungs. That pressure differential could cause pretty significant problems. $\endgroup$
    – Tristan
    Commented Jan 17, 2014 at 19:17
  • $\begingroup$ @Tristan: Would the bends be a problem if the person was acclimated to breathing a gas mixture with an inert filler other than nitrogen? $\endgroup$
    – supercat
    Commented Oct 29, 2014 at 21:25
  • $\begingroup$ The bends are problem if you use nitrogen for the gas mixture, but also if you use helium. Hydrogen is not possible, xenon is to expensive and also narcotic. But the bends may be avoided by breathing pure oxygen at a pressure of some 20 to 30 kPa. $\endgroup$
    – Uwe
    Commented Nov 23, 2016 at 15:46
  • $\begingroup$ @Anixx The peak of Mt Everest is not a place to stay. If you stay in the death zone above 8000m too long, your life is at risk, see en.wikipedia.org/wiki/… An astronaut died there en.wikipedia.org/wiki/Karl_Gordon_Henize $\endgroup$
    – Uwe
    Commented Sep 11, 2017 at 14:10
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Even with the most generous assumptions, a certain minimum partial pressure of Oxygen is needed to keep someone alive. Formally, I believe this is Hypoxia. There's obviously a certain range that we can tolerate.

Mount Everest has about 7 kPa of Oxygen partial pressure, and this is almost universally deadly. However, the total air pressure is still around 33.7 kPa. That means that we can up the partial pressure of Oxygen by increasing its ratio compared to other gases. This is effectively what Oxygen tanks do.

Mars is different, because its atmospheric pressure is lower than even our minimum required partial pressure of Oxygen. You are correct that the habitat will eventually reach equilibrium with the outside, so gas will only transfer through diffusion around the hole after that. But even if you completely saturated the habitat with Oxygen, this would not be sufficient for a person to survive.

For places with sufficient pressure, you can make due with a suit that isn't a pressure suit and tanks. Unfortunately, the Martian atmosphere is too thin, by over an order of magnitude.

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  • $\begingroup$ Yet it is not clear whether one can stay on Mars with non-pressure suit and hermetic oxygen helm/mask. $\endgroup$
    – Anixx
    Commented Jan 17, 2014 at 2:41
  • $\begingroup$ You can't, at least, and not stay alive. Mars' atmosphere is (well) beneath the en.wikipedia.org/wiki/Armstrong_limit, the point where external fluids (but not blood) will boil away. At best, it would be very painful, and result in essentially whole body edemas...shortly after exposure, I imagine that the fluids inside you (not being pressure sealed) would boil away, leaving you an utterly dry respiratory and digestive system, stem to stern. $\endgroup$
    – Chris B. Behrens
    Commented Nov 8, 2016 at 18:19

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