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The percentage of oxygen in cabin air..
  • A
    will reduce during a rapid decompression.
  • B
    is the same as at sea level.
  • C
    is proportional to the cabin pressure.
  • D
    varies with cabin altitude.

Composition of the Atmosphere

The atmosphere contains about 21% of oxygen. The other gases in the air are nitrogen, about 78%, and small amounts of carbon dioxide, water vapour and the rare gases such as argon. These volume percentages for each gases remain constant to about 70 000 ft - well within the altitudes at which conventional aircraft operate.

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