Hypoxia

Hypoxia is a condition where the body does not receive adequate oxygen. In aviation, hypoxia is a critical hazard at high altitudes where atmospheric pressure (and thus oxygen partial pressure) decreases.

Effects by altitude (without supplemental oxygen):

• 10,000-12,000 ft: Impaired night vision, subtle judgment degradation
• 12,000-15,000 ft: Impaired judgment, coordination, and memory
• 15,000-20,000 ft: Serious impairment, Time of Useful Consciousness (TUC) 20-30 minutes
• Above 25,000 ft: TUC 3-5 minutes
• Above 40,000 ft: TUC 15-20 seconds

This is why cabin pressurization, supplemental oxygen systems, and oxygen masks are critical safety equipment.