This filter is designed to remove 100% of dust and aerosols (including oils). Filters do not remove gases or vapors. End of service life for filters is normally determined by the increase in breathing resistance sensed by the user. When it becomes difficult to breathe comfortably, the filters should be replaced. All particulate filters are NIOSH approved, meet 42 CFR 84 requirements, when used with 3M™ air-purifying respirators. 502 is the retainer used for #2091 filters. 2 filters per pack. Sold by the pack.