Explosive Decompression

Decompression is defined as the inability of the airplane's pressurization

system to maintain its designed pressure differential. This can be caused

by a malfunction in the pressurization system or structural damage to the

airplane. Physiologically, decompression's fall into two categories; they

are:



Explosive Decompression - Explosive decompression is defined as a

change in cabin pressure faster than the lungs can decompress;

therefore, it is possible that lung damage may occur. Normally, the

time required to release air from the lungs without restrictions,

such as masks, is 0.2 seconds. Most authorities consider any

decompression that occurs in less than 0.5 seconds as explosive and

potentially dangerous.

Rapid Decompression - Rapid decompression is defined as a change in

cabin pressure where the lungs can decompress faster than the cabin;

therefore, there is no likelihood of lung damage. During an explosive

decompression, there may be noise, and for a split second, one may

feel dazed. The cabin air will fill with fog, dust, or flying debris.

Fog occurs due to the rapid drop in temperature and the change of

relative humidity. Normally, the ears clear automatically. Air will

rush from the mouth and nose due to the escape of air from the lungs,

and may be noticed by some individuals.



The primary danger of decompression is hypoxia. Unless proper utilization

of oxygen equipment is accomplished quickly, unconsciousness may occur in a

very short time. The period of useful consciousness is considerably

shortened when a person is subjected to a rapid decompression. This is due

to the rapid reduction of pressure on the body—oxygen in the lungs is

exhaled rapidly. This in effect reduces the partial pressure of oxygen in

the blood and therefore reduces the pilot's effective performance time by

one-third to one-fourth its normal time. For this reason, the oxygen mask

should be worn when flying at very high altitudes (35,000 feet or higher).

It is recommended that the crew members select the 100 percent oxygen

setting on the oxygen regulator at high altitude if the airplane is

equipped with a demand or pressure demand oxygen system.



Another hazard is being tossed or blown out of the airplane if near an

opening. For this reason, individuals near openings should wear safety

harnesses or seat belts at all times when the airplane is pressurized and

they are seated.



Another potential hazard during high altitude decompression is the

possibility of evolved gas decompression sicknesses. Exposure to wind

blasts and extremely cold temperatures are other hazards one might have to

face.



Rapid descent from altitude is necessary if these problems are to be

minimized. Automatic visual and aural warning systems are included in the

equipment of all pressurized airplanes.