SAFETY WORKS Paint & Pesticide Respirator Replacement Cartridges and Pre-FiltersThese cartridges and pre filters are approved by NIOSH (National Institute for Occupational Safety and Health) to the P95 OV category. The long life pre filters are approved to the NIOSH P95 Class, so they are at least 95% efficient against oil and non oil based contaminants, and are oil proof so they have no time use limitation. These cartridges include Pre Filter covers with narrow openings to retain the P95 pre filters on the cartridges, and to