What happens with a Pressure demand supplied air respiratory protection?

In pressure demand supplied air respiratory protection, the system is designed to provide a continuous flow of breathable air while maintaining a positive pressure in the mask or helmet. This means that air is supplied continuously, but the flow rate responds to the user's breathing pattern. When the wearer breathes in, air flows at an adequate rate, and when breathing stops, the system reduces the airflow to prevent unnecessary waste of air while still maintaining the positive pressure to protect against contaminants.

By contrast, the other choices outline characteristics that do not accurately describe a pressure demand system. Continuous air flow is a core element of this type of respiratory protection, as it ensures that a consistent and safe environment is maintained for the user, particularly in hazardous areas with potential airborne contaminants.