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The question has implicitely a lot of variables attached to it:

  • volume of the room
  • activity
  • how closed the room is
  • size of the person (I'm 168cm long and 64 kg heavy)

That could probably be turned into some formula and I am interested in scientific insights.

But at the end of the day my question is actually of very practical nature. I have a small room - about 1m x 2m x 2.5m = 5m3 - and I would like to use it as super-quiet place for meditation, reading etc. - hence calm activities, no excessive moving around. To improve sound proofness I'll probably also increase the sealing of the door and there is no ventilation - no air exchange.

Now if I close the door - how long can I expect to stay there without the air quality deteriorating to a level where my mental processes start to be impaired by it?

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Since you are considering to meditate in the room, without any excess of activity, you can consider the average resting O2 consumption, which is C = 3.5 mL/(min.kg) [1].

If we ignore the volume of your body, initially the room is filled with VO2(t0) = 0.21 * 5 = 1.05 m3 of O2.

With you breathing in the room, you can consider the volume of O2 in the room as a function of the time: VO2(t) = VO2(t0) - C * M * t where M is your weight in kg, and where C is converted to m3/(min.kg).

An oxygen defficient atmosphere is an atmosphere for which oxigen content is below 19.5 % of the volume [2]. An oxygen defficient atmosphere can be dangerous for your health. So in your case you need to find the value of t for which VO2(t) becomes inferior to the threshold Th = 0.195 * 5 = 0.975 m3.

So the maximum time you can spend in your room would be: tmax = (VO2(t0) - Th)/(C * M) = 335 min = 5 h 36 min

Of course, this value is a bit surestimated, and you should leave the room before that time.

[1] M. Kwan, J. Woo & T. Kwok (2004) The standard oxygen consumption value equivalent to one metabolic equivalent (3.5 ml/min/kg) is not appropriate for elderly people, International Journal of Food Sciences and Nutrition, 55:3, 179-182, DOI:10.1080/09637480410001725201

[2] https://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=STANDARDS&p_id=12716

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    $\begingroup$ There is another problem: The rising concentration of CO2. If the volume of it get over 10 Volume% in the air, this is dangerous. $\endgroup$
    – Chris ♦
    Nov 4, 2016 at 13:40
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    $\begingroup$ @Chris During respiration 1 mol of CO2 is produced for 1 mol of O2 consumed. Both gas being at the same pressure, we can consider that C is also the average CO2 production. $\endgroup$
    – Flo
    Nov 4, 2016 at 13:53
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    $\begingroup$ Not because the volume is getting bigger - CO2 in large concentrations is a problem for breathing. $\endgroup$
    – Chris ♦
    Nov 4, 2016 at 13:57
  • $\begingroup$ @Chris Sorry I involuntarly send the comment above before it was finished. So, CO2 production is also a function of the time: VCO2(t) = C * M * t (initial amount of CO2 can be ignored). So VCO2 gets above 10% of the volume for t'max = Th(CO2)/(C*M) = 37h12min. t'max being superior than tmax, the first limitation is O2 depletion. $\endgroup$
    – Flo
    Nov 4, 2016 at 13:57
  • $\begingroup$ @Flo Can you check your citations for dangerous CO2 and O2 concentrations? 19.5% might be OSHA's suggestion for a safe environment, but the more severe effects of O2 require much lower concentrations; CO2 on the other hand can cause mental confusion well before 10%. That said, the estimation in the original answer is still reasonable and should provide a decent safety margin given the assumptions made. $\endgroup$
    – Bryan Krause ♦
    Nov 4, 2016 at 16:35
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The average untrained healthy male will have a VO2 max of approximately 35–40 mL/(kg·min). [1]

So even if we take minimum value, your consumption in a minute is 35x64 = 2.24Liters. But NOT all O2 is consumed since about 16% is exhaled along with 5% CO2.

So, Oxygen will get 50% by around 4 hours and I highly doubt if even 50% Oxygen is enough to breathe properly, you will feel suffocation much earlier. [2]

[1] Guyton, A.; Hall, J.E. (2011). "Textbook of Medical Physiology, 12th Ed.". pp. 1035–1036. [2] https://www.princeton.edu/%7Eoa/safety/altitude.html

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