Definition - What does Pressure-Demand Respirator mean?
A pressure-demand respirator is a type of respirator that pumps air into the facepiece only once the pressure inside the facepiece has been reduced (usually due to inhalation). It belongs to a category of respirators called positive-pressure respirators, which maintain a level of air pressure inside the mask higher than the ambient air pressure of the environment the mask is being used within.
Pressure-demand respirators may be either supplied air respirators (SARs) or self-contained breathing apparatuses (SCBAs). They are usually considered to offer the highest level of protection from exposure to hazardous environments such as those with a toxic atmosphere.
Safeopedia explains Pressure-Demand Respirator
Pressure-demand respirators provide an airtight seal around the facepiece, and the positive pressure within the facepiece helps prevent the accidental inspiration of contaminants in the event of a breach in the seal. Because air is only supplied to the facepiece when pressure in the mask decreases (e.g., due to breathing), pressure-demand systems are economical on gas. This makes them useful for situations in which a finite amount of air is available. The pressure within the mask remains above ambient levels during the reduction in pressure that occurs due to inhalation.
Occupational health and safety agencies prescribe the protective use of respirators for a variety of different occupational settings and as protection against a variety of different hazards. These include biohazards, chemical spills, waste contamination, low-oxygen and toxic-gas environments, and smoke particulates. The level of protection needed for work in a given environment depends on the potential exposures that are faced within that environment. Those considered to be “Immediately Dangerous to Life or Health” (IDLH) require the use of the most-protective types of respirators.
The protectiveness of a given type of respirator is described in terms of a numerical value called an “assigned protection factor” (APF). The APF of a given type of respirator can vary by jurisdiction; however, pressure-demand respirators typically have the highest APFs. A pressure-demand full-face SAR has an APF of 1,000, while a pressure-demand full-face or hooded SCBA has an APF of 10,000—the highest available rating.