Specifications include, but are not limited to: The SR 500 system is a belt mounted Powered Air-Purifying Respirator (PAPR) with tight fitting face pieces, loose fitting respirators or loose fitting hoods that protects against particulates, gases and vapors, or a combination. It is designed to be used in oxygen sufficient and non-immediately dangerous to life and health (IDLH) environments. The SR 500 PAPR system functions as an alternative to Air Purifying Respirators (APR) in all situations for which these are recommended. This applies particularly to work that is hard, warm or of long-duration. The filtered air is supplied through a breathing hose to the tight fitting face piece, loose fitting respirators or loose fitting hoods. The above-atmospheric pressure then generated prevents pollutants from the surroundings from penetrating into the breathing zone.