At 40,000 feet, what is the time of useful consciousness?

At an altitude of 40,000 feet, the time of useful consciousness is approximately 18 seconds. This is the period during which an individual can still make rational decisions and take action before incapacitation occurs due to hypoxia, which is the deficiency of oxygen reaching the tissues.

At this high altitude, the atmospheric pressure is significantly lower than at sea level, resulting in decreased partial pressure of oxygen, leading to reduced oxygen availability for bodily functions. After the initial 18-second period, a person may start to experience disorientation and loss of consciousness. This makes understanding altitude physiology crucial for pilots and others who may find themselves at high altitudes, emphasizing the importance of immediate corrective actions, such as deploying supplemental oxygen or descending to lower altitudes if hypoxia is suspected.