Atmosphere and respiration · Question 10 of 12
At approximately what altitude is the air pressure in the standard atmosphere about half the sea-level value?
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Answer
- A At about 18 000 ft (5 500 m)
Explanation
In the ICAO standard atmosphere, the pressure halves from 1 013 hPa to about 500 hPa at around 5 500 m or 18 000 ft. The partial pressure of oxygen therefore also halves. How quickly oxygen deficiency takes effect also depends on exertion, health and duration.