I’m curious what it would feel like if an astronaut’s spacesuit ran out of air while they were on mars, vs taking the suit off?

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  • $\begingroup$ EVA space suits are pressured with pure oxygen to be more flexible. They can't run out of air thus. $\endgroup$
    – Uwe
    Jun 28, 2019 at 14:57
  • 2
    $\begingroup$ Are you asking about exposure to vacuum or carbon dioxide buildup? $\endgroup$
    – GdD
    Jun 28, 2019 at 15:32
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    $\begingroup$ Due to carbon dioxide buildup, I believe they'd just pass out. $\endgroup$ Jun 28, 2019 at 15:56
  • $\begingroup$ It takes a while for the air in the suit to have its oxygen depleted. It’s not immediate, more like at least 30 seconds -2 minutes before effects are noticed, depending on breathing rate. $\endgroup$ Jul 1, 2019 at 19:05

1 Answer 1


Eva suits use pure oxygen. This allows much lower pressure and hence a more flexible suit than using air would. Atmospheric pressure on mars is about 1% of earths, even with pure oxygen that is too low to survive.

So the big question is what does the suit do when it runs out of oxygen. I see two posibilities.

  1. The pressure in the suit remains the same, but replacement of CO2 with oxygen stops. The person will feel they are suffocating.
  2. The pressure in the suit drops as CO2 is removed but not replaced. I suspect in this case with a conventional suit the person will quietly pass out and die, with a "mechanical counterpressure" suit the person will find themselves unable to breathe because the mechanical counterpressure is no longer balanced.
  • 2
    $\begingroup$ "The pressure in the suit remains the same, but replacement of CO2 with oxygen stops" That happens when the CO2 scrubber is saturated but not when oxygen tank is empty. So this possibility is wrong. $\endgroup$
    – Uwe
    Jun 28, 2019 at 22:01

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