Air purifying respirators filter ambient air through cartridges, canisters, or HEPA filters to remove gases, vapors, particulates, and aerosols before inhalation. Unlike SCBAs, APRs don't supply external oxygen suitable for oxygen-sufficient environments with known contaminants like chemicals, fumes, or dust. Types include half/full-facepiece respirators with replaceable cartridges (organic vapor, acid gas, multi-gas), disposable filtering facepieces (N95/P100), and powered air-purifying respirators (PAPRs) with battery blowers delivering positive-pressure filtered air through hoods or helmets for 99.97% particle filtration