NIOSH air filtration rating



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 classifications, NIOSH, under 42 CFR 84, partially defers to American National Standard ANSI K13.1-1973, and others, for matters such as chemical cartridge color classification. All classifications assume that the respirator is properly fitted.

NIOSH ratings trademark
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).

30 CFR 11
Prior to the approval of 42 CFR Part 84, MSHA and NIOSH approved respirators under 30 CFR Part 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.

NIOSH was concerned about users choosing inappropriate respirators, like confusion over choosing 'dust/mist' or 'dust/fume/mist' 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.

42 CFR 84


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.). 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. Class-100 filters can block asbestos. For N type filters, a 200 mg load of NaCl is used, with and 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. P100 filters, under 42 CFR part 84, are the only filters permitted to be magenta in color. HE (high-efficiency) labeled filters 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. Particles with a size both less than and greater than 0.3 μm may be filtered at an efficiency greater than 99.97%. 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.

Chemical Cartridge Classifications
42 CFR 84 Subsection L describes seven types of chemical cartridge respirators with maximum use concentrations and penetration, noting that colors and markings are definitively based off of ANSI K13.1-1973. A TB guide, published by NIOSH in 1999, describes 13 combinations of contaminants with unique color markings. The definitive guide from ANSI, who, since the passage of 42 CFR 84 in 1995, has published a 2001 revision of K13.1-1973, named Z88.7-2001, describes 14 combinations of contaminants with unique color markings, based on 13 out of the 28 NIOSH Protection Designations. The ANSI standard also notes that these classifications do not apply in aviation or military respirators.

A comparison table below details the NIOSH protection designations, 42 CFR 84, the Navy/Marine Field Manual, the NIOSH TB guide, and whether they match up with the groups of NIOSH protection designations, per color, in the 42 CFR 84-declared ANSI K13.1-1973 revision ANSI Z88.7-2001, for each type of chemical cartridge is described below. Note that, while the 2001 revision to ANSI K13.1-1973 provides exact colors under the Munsell Color System, colors and combinations outside the public domain, as well as cartridge/canister designation, have been omitted to facilitate this fair use comparison:

For particulate respirators, while NIOSH designates P100 as filter cartridges that can use the "magenta" color, ANSI designates P100 as "purple", a color which can be seen on some P100 filter cartridges. In addition, the 2001 revision to ANSI K13.1-1973 provides exclusive colors to be used for non-P100 cartridge filters, in two categories: oil-resistant (remaining R- and P- NIOSH ratings), and non-oil resistant (all N-ratings).

Table of TC/BM Approval Schedules
NIOSH is the current regulator of all the respirators in this schedule, under 42 CFR Part 84.

'BM' stands for the US Bureau of Mines, the historical regulator of respirators in the United States.

TC-21C respirator approval numbers for negative-pressure particulate respirators have three digits, in the form: TC-21C-###, while TC-84A respirator approval numbers have four digits, in the form: TC-84A-####. 42 CFR 84 did not change regulation regarding powered-air purifying particulate respirators, so have continued under TC-21C approval, with four digits, in the form TC-21C-####.

NIOSH rating limitations
NIOSH air filtration ratings do not test the fit of a respirator. Fit testing is required by OSHA for employers.

Similar standards
A few other jurisdictions use standards similar to the NIOSH scheme to classify mechanical filter respirators. They include:
 * China (GB 2626-2019): Similar testing requirements and grades. Has "KN" and "KP" resistance levels, 90/95/99. Has additional EU-like rules on leakage.
 * Mexico (NOM-116-2009): Same grades.
 * South Korea (KMOEL - 2017-64): EU grades, KF 80/94/99 for second/first/special