[3][4] It is important that they deliver good air; contaminants (which may also be introduced by faulty operation of the machinery) can be dangerous.

SAR users therefore often carry a small backup air tank (called an auxiliary escape cylinder[4]).

Constant-flow respirators supply a steady stream of air, some of which escapes from the wearer end unbreathed.

SARs without an auxiliary SCBA may also be used in conditions where an air-purifying respirator may be used, and have the benefit of a higher range of assigned protection factors (APF).

For substances hazardous to the eyes, a respirator equipped with a full facepiece, helmet, or hood is recommended.