What is the published time of useful consciousness at 25,000 feet?

At an altitude of 25,000 feet, the time of useful consciousness refers to the duration that a person can maintain effective cognitive function before the lack of oxygen begins to impair their ability to think clearly and respond. The correct range, which is 3-5 minutes, is based on physiological studies regarding the effects of hypoxia—the decreased availability of oxygen at high altitudes.

At 25,000 feet, a person is exposed to a significant drop in atmospheric pressure, which leads to a reduction in the partial pressure of oxygen in the air and subsequently in the bloodstream. Depending on individual health factors and level of acclimatization, most individuals can remain conscious and perform basic functions for a brief period, but beyond this timeframe, the onset of hypoxia can result in confusion, disorientation, and loss of consciousness.

Understanding these effects is crucial for pilots and aviation personnel, as proper precautions such as supplemental oxygen are necessary when operating at higher altitudes to ensure safety and operational effectiveness. The other ranges provided do not accurately reflect the physiological responses to decreased oxygen availability at 25,000 feet, as timeframes such as 1-2 minutes or less would be representative of much higher altitudes, and greater than 20 minutes would apply to conditions