Air purifying respirators with filters provide respiratory protection against aerosols by removing dusts, mists, fumes fibers and other particulates. 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. North offers an extensive line of replaceable filters that provide different levels of filtration efficiency. All particulate filters are NIOSH approved, meet 42 CFR 84 requirements, when used with North air-purifying respirators. 7531N95 is a complete N95 filter assembly consisting of 7506N95 filter, 7500-27 filter cover and 7500-15 filter holder. The 7500-15 filter holder holds 7506N95 N95 filter; requires 7500-27 filter cover. 7500-27 seal check/filter covers for 7506N95 filter. It can attach to the gas/vapor cartridge or for filter use only, requiring the 7500-15 filter holder.