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Accidental ‘happy hypoxic’ deaths are not uncommon and there is a number of situations that can bring them about. One example is the sudden drop in oxygen level that occurs when an aeroplane depressurizes at high altitude. This can lead to a rapid loss of consciousness and the death of all those on board.
When the plane depressurizes, passengers still breathe easily. The problem is that there is little oxygen in the inhaled air. Because of the large volume of air within the plane, there is no build up of carbon dioxide. It is not uncommon for planes that have suddenly depressurized to travel on autopilot until they run out of fuel; well after everyone on board has died. Witnesses (from planes sent to investigate) say that it appears as though everyone is sleeping peacefully.
When a person exhales fully, then pulls down an Exit bag that is pre-filled with an inert gas and takes a deep breath, the person’s lungs will be filled with a gas in which there is very little oxygen. The blood passing the lungs on the way to the brain will have no oxygen to transport, and consciousness will be rapidly lost. This loss of consciousness will occur quickly, within one or two breaths. If there is no intervention, death will occur within 5 to 10 minutes. It is the lack of oxygen in the inhaled gas that causes death, not the characteristics of the particular inert gas used.
For the process to work, it is important that the air (with 21% oxygen) in the lungs can be quickly and fully replaced with the inert gas in the Exit bag. With good lung function (and practice) this can be achieved with a single exhale/ inhale cycle.