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, 2. AIR-PURIFYING RESPIRATORS <br />These respirators generally consist of a flexible facepiece to <br />which filter cartridges are attached, or a filter canister is <br />connected by a hose. Half-face systems are available for use where <br />the air contaminants involved do not pose an eye irritation <br />problems, and/or where chemical splash is not a hazard. Full-face <br />systems are available for use when eye and face protection is also <br />required. <br />Air-purifying systems can ro be used in situations where: <br />(a) there is/may be a def iciency of oxygen (i.e., less than <br />19.5$), <br />(b) contaminant concentrations are unknown or are <br />"Immediately Dangerous to Life of Health" (IDLH)1, <br />(c) the contaminants involved have poor warning properties2, <br />(d) the contaminants present exceed the approved protection <br />limits for the cartridge or canister to be used. <br />In general, a HEPA filter element should be used in conditions <br />where hazardous dust or fume conditions exist. <br />Cartridges/canisters with appropriate sorbents should be employed <br />for use in environments where organic vapors, acid gas vapors, <br />and/or specific chemical contaminants are present. <br />3. POWER-ASSISTED AIR-PiTRIFYING RESPIRATORS <br />Air-purifying respirators which incorporate a blower to pass <br />contaminated air through the filter media are available. The <br />blower reduces breathing effort required by the wearer, and thus <br />can reduce respirator-use fatigue. The blower also results in some <br />level of positive pressure inside the respirator mask/facepiece, <br />which reduces the risk of face seal leakage. <br />The primary disadvantage to this type of system is that the <br />constant flow of contaminated air through the filter media results <br />in shortened cartridge/canister useful service life (i.e., the <br />media becomes saturated more quickly than a non-power assisted <br />respirator). <br />