Hypoxia - An invisible enemy..!!
Operating at high altitude without adequate understanding, training or equipment protection can be dangerous.
One of the first encounters with the dangers of high altitude flight was reported in 1862 and this marked for the first time the risk of low ambient pressure.
symptoms,like loss of visual and hearing capability, paralysis of arms and legs, and finally, unconsciousness occurred.
The concentration of oxygen in the atmosphere is constant at 20.95% at altitudes up to 100,000ft, As altitude increases above sea level the partial pressure of the Oxygen decreases with the decrease in total atmospheric pressure.
The partial pressure of oxygen at 40,000ft is reduced to 39mbar only, which is far too inadequate to support human metabolism.
The hypoxia effects of a quick cabin depressurization:
During a quick depressurization the partial pressure of oxygen in the lungs/alveolae reduces rapidly with the effect of reverse diffusion. This means that once the oxygen partial pressure in the alveolae has
reached a level that is below the level in the blood, the blood oxygen
moves out of the body back into the ambient air.
The FAA initiated a Special Certification Review (SCR) on pressurization systems.
The SCR recommends that the aircraft flight manual (for aircraft certified for flights above 25,000ft) require in the emergency procedures the donning of oxygen masks as the first crew action after a cabin altitude warning.
The only effective means of protection is the quick donning of oxygen masks as the first action - before troubleshooting!
Any delay in donning a mask will significantly increase the risk of losing consciousness before cabin pressure is regained.