MODEL RELEASED. Supplying oxygen on airliner. Crewmember on a commercial aircraft holding an oxygen mask to the face of a passenger who has passed out due to lack of oxygen (anoxia). Oxygen masks are dropped if the passenger compartment becomes depressurised. The decreased air pressure at high altitudes means there is not enough oxygen available. It is important to don masks rapidly because one of the first symptoms of anoxia is impaired judgement. At 3000 metres, passengers without masks would experience symptoms such as tiredness, dizziness and nausea. Above 6000 metres, they would rapidly lose consciousness.