I have a small group of astronauts in a damaged vessel, adrift for days with a non-functional environmental system/scrubbers. Ambient oxygen levels are low, but they have some emergency tanks of compressed air (say several hours' worth) around the cabin/from their spacesuits.

My question:

  • How long, and at what oxygen levels, could they conceivably survive before rescue without severe brain damage setting in from prolonged hypoxia
  • What steps would they take to try and extend their survival while awaiting rescue
  • What would they experience during that time (ie. if they're blacking out and experiencing muscle weakness, is it realistic that they experience that over the course of days?)

I assume they'd try to seal any leaks and keep physical activity to an absolute minimum until rescue. Ideally for, plot reasons, I'd like them to stay alive and adrift for several days but I'm not sure how much I'm stretching what's feasible without serious medical repercussions. (I will say - it's fine if some of the crew get injured, but I do need at least one person to walk out of this experience only emotionally scathed)

Edit - Based on Comments:

In order for the 4 crew members to survive up to 3 days, what is the minimum volume of Air/Oxygen that my crew need to survive but it also be a dire situation with a very real possibility of Death.

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    $\begingroup$ Need more info - specifically the internal volume of air that they started with. $\endgroup$ Apr 17, 2023 at 0:36
  • $\begingroup$ Good question - I have it basically that the hab of their spaceship (typical crew complement 8-10) has been damaged and started to vent, and they've sealed themselves off into a compartment of the ship. So let's assume it was at a normal ambient level like 20% to start with and that they managed to seal themselves off pretty quickly. The hab area is pretty small and close-quarters, but long-term living - similar to a modern-day submarine. The volume of the area I'm still toying around with -- but I'm thinking 3-4 crew members, probably holing up in the mess hall $\endgroup$
    – bird
    Apr 17, 2023 at 0:50
  • $\begingroup$ as it is currently, the question is unanswerable. I would be looking at the Kursk Tragedy as a yard stick (although IIRC - they had CO2 Scrubbers which pro-longed their survival until they got one wet) - but to give a hard science answer (which is what you've asked for) at best we need to know an internal volume - then we can use that to get a percentage of Oxygen, then it's just a bunch of maths to work out rate of consumption and then time. $\endgroup$ Apr 17, 2023 at 1:04
  • $\begingroup$ ok, let's change the parameters of the question then: how much space do i need for 3-4 people to survive an event like this, for several days, and not die $\endgroup$
    – bird
    Apr 17, 2023 at 1:16
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    $\begingroup$ Unless there is something to remove CO2 from the air, they will die from CO2 poisoning rather than O2 deficit. (CO2 level of 4% is immediately dangerous, O2 levels from 20% to 16% is very "meh!"). $\endgroup$ Apr 17, 2023 at 10:07

1 Answer 1


Okay - based on your comments:

Using these parametres

11,000 Litres per day for an Average adult. That's 11 m3 of Air. Times 4, that's 44 m3, times 2-3 days that's 132 m3 of Air that is breathed. It's also consuming 0.55m3 of Oxygen per day.

Now, Standard air is 21% Oxygen, using levels from here:


OSHA upper limit for Oxygen deficient environment is below 19%, Mental impairment is at around 10-15% and 6% is a death sentence.

So for your story - you essentially want your environment to be sitting at around 10-15% oxygen on the last day before their rescue.

Using some very quick back-of-the-envelope maths, going from 20% to 15% oxygen in the atmosphere is the difference between 12* 0.55 = 6.6m3. 6.6 m3 * 4 is 26.4 (this is to get the starting amount of Oxygen), using a 20% atmosphere multiple that by 5 is 132 m3 - which is what we started out with (not sure if that's intended - but there you go) - which is your total internal volume that by day 3 - they are starting to get mental impairment and be in real jeopardy.

  • $\begingroup$ And they be dead from CO2 poisoning a coupe of hours before they get rescued. About 4% CO2 is real bad, 5% is probably lethal. You (more or less) exchange O2 for CO2 by breathing. So the critical point is reached at roughly 17% O2 (which is low but still OK) if you start with 21%. Better to start with a slightly lower O2 level which is still perfectly OK for humans (18% or so) and drop to 4% lower (14%). $\endgroup$
    – Tonny
    Apr 17, 2023 at 13:45
  • $\begingroup$ @Tonny then I guess the scrubbers are working, just not the oxygen! or have them stuff a hairdryer with lithium hydroxide or something :) $\endgroup$
    – user253751
    Apr 17, 2023 at 14:56
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    $\begingroup$ What is in your first aid box? If you have a small crew, it may be possible to put badly injured people into 'suspended animation' or at least some very low metabolism rate so they all survive until you get back to somewhere there is better support. This is has been done already but the means would not fit in a first-aid box. But it is not unreasonable to guess that this may be standard in the future. If you have four crew, put three into deep sleep. $\endgroup$ Apr 17, 2023 at 20:02
  • $\begingroup$ @RichardKirk --- I think you could expand this comment into a very interesting answer! $\endgroup$
    – elemtilas
    Apr 18, 2023 at 1:45
  • $\begingroup$ Agreed - as I said in my answer, I did some back-of-the-envelope maths, so if anyone has a more substantial answer - then even better. $\endgroup$ Apr 18, 2023 at 2:43

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