MODEL RELEASED. Airliner oxygen masks. Passengers on a commercial passenger jet about to put on oxygen masks. The oxygen masks are dropped if the passenger compartment becomes depressurised. The flow of oxygen is started by pulling the mask downwards before it is put on. At high altitudes, the low air pressure means that there is not enough oxygen available, leading to altitude hypoxia. At 3000 metres, passengers without masks would slowly begin to feel unwell, with symptoms such as tiredness, dizziness, nausea and impaired judgement. Above 6000 metres, they would rapidly lose consciousness.