What is the primary function of a pressure-demand oxygen system?

A pressure-demand oxygen system is designed primarily to provide supplemental oxygen to individuals, especially at high altitudes, where atmospheric pressure drops and the availability of breathable oxygen decreases. The system operates by delivering oxygen at pressures higher than atmospheric pressure during inhalation. This ensures that the oxygen is effectively pushed into the lungs and that the user receives adequate oxygen even in a low-pressure environment.

This type of system is especially critical in aviation and high-altitude activities, as it allows pilots and passengers to maintain cognitive functioning and physical performance in conditions where normal breathing would be insufficient. The higher pressure of the supplied oxygen helps overcome the lower density of the ambient air at altitude.

Other options describe functionalities that do not align with the intended use of a pressure-demand oxygen system. For instance, supplying oxygen only during exhalation would not meet the need for adequate oxygen intake during inhalation. Providing oxygen at atmospheric pressure would not be effective at high altitudes where supplemental pressure is needed. Storing oxygen in a liquid state is a different process involved in oxygen storage systems, not directly related to how pressure-demand systems function during use.