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Sudden pressure drop: a killer

A Mandala Airlines Boeing 747 has crashed minutes after take-off in a residential part of Medan, Indonesia. While the cause of this crash is not yet known, many questions are being asked on the reasons for the series of recent commercial airline crashes.

A sudden drop in cabin pressure, although almost never the cause of aircraft crashes, can result in complications during a flight. Health24 investigates.

Why are low air pressure levels so dangerous?
The usual flying altitude for commercial aeroplanes is between 10 600 and 11 200 m above sea level. The higher you go, the more the atmospheric pressure drops. In other words, the air is 'thinner': there are fewer air molecules present in a given volume of air. Inside the aeroplane, air pressure is kept at a level that is tolerable for the human body - much higher than the air pressure outside the aircraft at these heights.

Cabin pressure can be lost through air leaks in doors or windows. The larger the leak, the faster air pressure levels in the aircraft will drop. The decreasing air pressure outside the body causes the air trapped inside the organs to expand. Serious internal ruptures can occur, and cause problems such as collapsed lungs, inflated intestines, burst eardrums and even loss of eyesight.

Decreased air pressure also means that the amount of oxygen in the air is decreased. As the level of oxygen in the blood drops, passengers will experience symptoms such as light-headedness and confusion, and eventually loss of consciousness.

Another factor at these high altitudes is very low temperature - often below freezing - which puts the human body under further stress and can cause severe hypothermia (abnormally low body temperature).

Gradual depressurisation can be rectified
In situations where the air pressure decrease is gradual, it is fairly straightforward to avoid the negative effects. Very few pressure leaks are deadly. In a situation where the leak becomes severe, the pilot would instruct passengers and crew to put on oxygen masks and he/she would fly at a lower altitude.

If a plane had been flying at 10 600 m, it would take over one and a half minutes to get to 3 000 m. The pilot only had 60 seconds to get to a lower altitude level before everyone would have lost consciousness.

(Matthew Louw, Health24, September 2005)

Read more:
Tips for healthy flying

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