The NIOSH air filtration rating is the U.S. National Institute for Occupational Safety and Health (NIOSH)'s classification of filtering respirators. The ratings describe the ability of the device to protect the wearer from solid and liquid particulates in the air. The certification and approval process for respiratory protective devices is governed by Part 84 of Title 42 of the Code of Federal Regulations (42 CFR 84). Respiratory protective devices so classified include air-purifying respirators (APR) such as filtering facepiece respirators and chemical protective cartridges that have incorporated particulate filter elements.
The NIOSH-provided classifications only cover the filtration of particles or aerosols, not the air-purifying respirator's ability to remove chemical gasses and vapors from air, which is regulated under 42 CFR 84 Subpart L. For chemical cartridge classifications, NIOSH, under 42 CFR 84, partially defers to American National Standard ANSI K13.1-1973. All classifications assume that the respirator is properly fitted.
It is illegal in the United States to use filtration terms coined under 42 CFR 84, or mark masks with the word "NIOSH" without the approval of NIOSH. Information about approved respirators can be found in the NIOSH certified equipment list (CEL).
Early NIOSH/USBM classifications
Prior to the approval of 42 CFR 84, MSHA and NIOSH approved respirators under 30 CFR 11. Non-powered respirator filters were classified based on their design against a contaminant, including substances like Dusts, Fumes, Mists, radionuclides, and asbestos. Dust/Mist was usually tested with silica, and Fume was usually tested with lead fume. The most popular respirator filters were often referred to as DM (Dust/Mist) or DFM (Dust/Fume/Mist) in CDC and NIOSH literature as shorthand. Non-powered filters were also classified under the HEPA specification, if applicable.
Only 30 CFR 11 HEPA filters were permitted by NIOSH for the prevention of tuberculosis[C3] and asbestos-related diseases.[CF1]
NIOSH was concerned about users choosing inappropriate respirators, like confusion over choosing DM or DFM respirators with regards to particle penetration, so proposed Part 84 rules in 1994 dropped the contaminant/HEPA classification for most respirators in favor of three specifications, Type A, B and C, each representing filtration of 99.97%, 99%, and 95% respectively, with Type A proposed to be used in place of HEPA for non-powered respirators.[C1]
In 1973, the Los Alamos National Laboratory (LANL) recommended NIOSH use NaCl aerosol to test DM and DFM filters. Results from those tests showed significant leakage, with efficiency levels measured at around 75% to 90%. LANL noted that lead fume would plug the tested filters, increasing the apparent filtration efficiency of the filter.
Under the current revision of Part 84 established in 1995, NIOSH established nine classifications of approved particulate filtering respirators based on a combination of the respirator series and efficiency level. The first part of the filter's classification indicates the series using the letters N, R, or P to indicate the filter's resistance to filtration efficiency degradation when exposed to oil-based or oil-like aerosols (e.g., lubricants, cutting fluids, glycerine, etc.).[CF2][N2] Definitions and intended use for each series is indicated below.
N for not resistant to oil. Used when oil particulates are not present. Tested using sodium chloride particles.
R for resistant to oil. Used when oil particulates are present and the filter is disposed of after one shift. Tested using dioctyl phthalate (DOP) oil particles.
P for oil-proof. Used when oil particulates are present and the filter is re-used for more than one shift. Tested with DOP oil particles.
The second value indicates the minimum efficiency level of the filter. When tested according to the protocol established by NIOSH each filter classification must demonstrate the minimum efficiency level indicated below.
All respirator types are permitted for TB.[C1] Class-100 filters can block asbestos.[CF1][S2] For N type filters, a 200 mg load of NaCl is used, with an undefined service time. For R type filters, a 200 mg of DOP is used, with a defined service time of "one work shift". For P type filters, an indefinite amount of DOP is used until filtration efficiency stabilizes.[N2] P100 filters, under 42 CFR part 84, are the only filters permitted to be magenta in color.
HE (high-efficiency) labeled filters (described in the subsection) are only provided for powered air-purifying respirators. HE-marked filters are 99.97% efficient against 0.3 micron particles and are oil-proof.
Since filters are tested against the by definition most penetrating particle size of 0.3 μm, an APR with a P100 classification would be at least 99.97% efficient at removing particles of this size.[N2] Particles with a size both less than and greater than 0.3 μm may be filtered at an efficiency greater than 99.97%.[N2] However, this may not always be the case, as the most penetrating particle size for N95s was measured to be below 0.1 μm, as opposed to the predicted size of between 0.1 and 0.3 μm.
2020 powered air-purifying respirator update
Chemical cartridge and canister classifications