This filter is designed to remove a minimum of 95% of non-oil dust and aerosols. 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. 501 is the retainer used for 5N11 filters. 10 filters per box. Sold by the box.