I have a generic question about the usage of n95/99 or higher filtration respirators in high-altitude flights. With current pandemic situation we see many government/airlines are enforcing the use of mask in-flight. Now, although the cabin is usually pressurized to 8000ft when cruising, ambient O2 concentration inside the cabin stays below normal [1,2]. As per the datasheet of 3m n95 respirator - "Do not use in atmosphere containing less than 19.5% oxygen."

Does the use of respirator in-flight, along with low ambient O2 level, pose possible dangers of hypoxia? Or any other serious illness?


  1. Aldrette JA, Aldrette LE. Oxygen concentrations in commercial aircraft flights. South Med J. 1983;76(1):12‐14.
  2. Humphreys, S., Deyermond, R., Bali, I., Stevenson, M., & Fee, J. P. H. The effect of high altitude commercial air travel on oxygen saturation. Anaesthesia. 2005; 60(5), 458-460.
  • You need a link to prove that oxygen percentages drop in a pressurised cabin. This seems rather unlikely. Jun 8, 2020 at 6:41
  • barometric pressure x 0.209 (atmospheric fraction of O2) = atmospheric Po2. At sea level, 760 x 0.209 = 159 mm Hg. While at 8000ft, 564 mm Hg x 0.209 = 118 mm Hg. With less driving pressure it is similar to lower O2 concentration. Anyhow I have added some references above. Jun 8, 2020 at 7:38
  • Oxygen pressure drops but the percentage you said also drops. What is it replaced by? Jun 8, 2020 at 21:34
  • 4
    The relative mix of gasses in air does not change with altitude. Only the pressure changes, so the N95 datasheet's warning doesn't appear to be relevant.
    – Carey Gregory
    Jun 9, 2020 at 1:19
  • Yeah, they feed in stored air to help pressurize the compartments. Jun 9, 2020 at 3:56


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