No, pilots don't always breathe pure oxygen. The oxygen system in aircraft delivers a blend of oxygen and air, adjusting the ratio based on altitude.
Altitude and Oxygen Mixture
At lower altitudes, the air contains sufficient oxygen. However, as altitude increases, air pressure drops, reducing the available oxygen. To compensate for this, the oxygen system increases the oxygen concentration in the air supplied to the pilot.
- Lower altitudes: A mixture of oxygen and air is provided.
- Higher altitudes: A higher concentration of oxygen is mixed with the air, eventually reaching a 100% oxygen supply at extremely high altitudes. This is crucial to prevent hypoxia (lack of oxygen).
Several sources confirm this: one states that at higher altitudes, "a 100% mixture of oxygen is supplied," while another clarifies that most regulators provide "zero percent cylinder oxygen and 100 percent cabin air at cabin altitudes," adjusting the mixture as needed.
Specific Aircraft and Missions
The need for pure oxygen depends on the aircraft and mission profile. U-2 pilots, for example, breathe pure oxygen for extended periods due to their high-altitude flights. This pre-breathing of pure oxygen also helps purge nitrogen from their bodies, improving performance at high altitudes. However, this is not the norm for all pilots.
Some sources highlight the use of liquid oxygen (LOX) for pilots at high altitudes, further emphasizing the variable oxygen supply depending on operational needs.
Health Considerations
While pure oxygen is essential at high altitudes to prevent hypoxia, prolonged exposure to 100% oxygen at sea-level pressure can pose health risks. Breathing 100% oxygen for short durations (1-2 hours) is generally considered safe, but longer periods can be harmful.
