What is the time of useful consciousness at 40,000 feet?

At an altitude of 40,000 feet, the time of useful consciousness is approximately 18 seconds. This period refers to the amount of time a person can effectively think and perform useful tasks after exposure to hypoxia, which occurs due to a lack of oxygen at high altitudes. At this altitude, the atmospheric pressure decreases significantly, leading to reduced availability of oxygen for the body.

After losing cabin pressure or in situations where supplemental oxygen is not provided, a pilot or individual has around 18 seconds to react appropriately before cognitive function begins to deteriorate. This timeframe is critical in aviation contexts since it emphasizes the importance of having emergency oxygen systems onboard and the need for pilots to recognize the onset of hypoxia quickly.

The other timeframes listed, while they may represent various scenarios at different altitudes, do not accurately reflect the established understanding of time of useful consciousness specifically at 40,000 feet.