PAPR (powered air-purifying respirator) systems filter ambient air and deliver safe, breathing air to employees. A battery-powered blower in PAPR systems circulates ambient air via a HEPA filter into the facepiece. PAPR respirators can be worn for longer lengths of time than SCBA (self-contained breathing apparatus) systems that employ air canisters because they filter ambient air. PAPR systems should only be used in non-IDLH situations (immediately dangerous to life and health).