Is prolonged use of passenger masks recommended above 25,000 ft?

The recommended guidance regarding the use of passenger masks at altitudes above 25,000 feet leverages the physiological effects of high altitude on the human body. Normally, supplemental oxygen is provided in the cabin to protect against hypoxia due to reduced atmospheric pressure.

When cabin pressure drops and oxygen levels become insufficient, passenger masks are deployed as a safety measure. However, prolonged use of these masks, particularly above 25,000 feet, is generally not recommended for several reasons. Firstly, the oxygen provided is intended to be used in emergencies or during temporary cabin depressurization events rather than as a continuous supply. Long-term reliance on passenger masks can lead to complications and discomfort, such as hyperoxia (excess oxygen in the body) and physiological stress.

In standard operating procedures, the masks are designed for temporary use until the aircraft descends to a safer altitude where cabin pressure can be restored or where supplemental oxygen is no longer necessary. This is why the recommendation is against prolonged use of passenger masks in scenarios where the situation is not critically urgent, emphasizing their intended purpose in emergencies over extended periods.