At what altitude is prolonged use of passenger oxygen masks not recommended?

Prolonged use of passenger oxygen masks is generally not recommended above 25,000 feet above ground level (AGL) due to physiological considerations related to the body's response to high altitudes. At this altitude, the effects of hypoxia—reduced oxygen availability—begin to significantly impact passengers, leading to symptoms like impaired cognitive function, fatigue, and decreased performance.

Using oxygen masks beyond this threshold is intended to ensure safety; however, the quality and amount of oxygen supplied can become less efficient over prolonged durations. This makes it critical to avoid extended use at this altitude unless absolutely necessary. Additionally, the likelihood of experiencing discomfort and potential health issues increases as altitude goes up, making 25,000 feet the critical point where caution becomes increasingly important.

The selection of this specific altitude is informed by safety guidelines established by aviation authorities that address the physiological effects of altitude on unacclimated individuals, reinforcing the importance of managing oxygen levels effectively in an aircraft environment.