Mild hypoxia and the use of oxygen in flight

Hypoxia in aviation remains a major hazard. It may be caused by ascent while breathing air, failure of oxygen supply or loss of cabin pressurisation. Malfunction of equipment or its improper use accounted for the majority of hypoxic incidents in one 10-year military study. Symptoms of hypoxia depend on rate of ascent, temperature, and individual variation, as well as altitude. Dyspnoea, lack of coordination and reduction in capacity for skilled performance precede the gross changes which occur at altitudes of over 4572 m (15,000 ft) and lead ultimately to unconsciousness. Studies have shown a significant decrease in psychomotor task ability at altitudes as low as 2438 m (8000 ft). Developments in aircraft oxygen systems are discussed and the importance of adequate crew instruction on hypoxia and their aircraft oxygen equipment is stressed.