The oxygen requirements only come into play when you fly depressurized. The reason that passengers aren’t on oxygen when you are flying pressurized at 30,000 feet (probably 5-7,000 ft pressure altitude inside the plane) is that the air they are pressurizing (thin, high altitude air) is still the same ratio of nitrogen/oxygen/CO2 even though there are smaller amounts of each.

The FAAs requirement of people being on supplemental oxygen only matters in non-pressurized flight, like small Cessnas and pressurized aircraft experience a depressurization emergency.

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