Which best describes a pressure-demand oxygen system?

• A. A continuous-flow oxygen system.
• B. A demand oxygen system that supplies 100 percent oxygen at sufficient pressure above the altitude where normal breathing is adequate.
• C. A venturi-driven ambient-air system.
• D. A system that provides oxygen only during icing conditions.

Answer: (B)

The main idea is that a pressure-demand oxygen system delivers oxygen only when you inhale, and it does so under pressure so the gas can reach your lungs even when ambient air is thin. This setup provides 100 percent oxygen at a pressure above the surrounding air, which is crucial at altitudes where normal breathing can’t supply enough oxygen. Because oxygen is released only on inhalation, it’s used efficiently and you’re protected from wasted gas. In contrast, a continuous-flow system would supply oxygen constantly, regardless of inhalation, which wastes oxygen and isn’t optimized for each breath. A venturi-driven ambient-air system relies on ambient air entrainment and isn’t delivering pressurized, pure oxygen on demand. The notion of supplying oxygen only during icing conditions isn’t related to how the system delivers oxygen.