# 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 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.

## 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).

## Early NIOSH/USBM classifications
### 30 CFR 14 Schedule 21

Prior to the 1970s, respirator standards were under the purview of the US Bureau of Mines (USBM). An example of an early respirator standard, Type A, established in 1926, was intended to protect against mechanically generated dusts produced in mines. These standards were intended to obviate miner deaths, noted to have reached 3,243 by 1907. However, prior to the Hawks Nest Tunnel Disaster, these standards were merely advisory, as the USBM had no enforcement power at the time. After the disaster, an explicit approval program was established in 1934, along with the introduction of combination Type A/B/C respirator ratings, corresponding to Dusts/Fumes/Mists respectively, with Type D blocking all three, under 30 CFR 14 Schedule 21.

### 30 CFR 11

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 and asbestos-related diseases.
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.
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.
(OBSOLETE) 30 CFR 11 efficiency levels :
| Particulate | Respirator approval | Maximum dust penetration | Minimum efficiency level | Permitted for TB | Permitted for asbestos |
| 158.4 mg silica 7.92 m$^3$ (280 cu ft) air | Single-use Dust/Mist filters | 1.8 mg | 98.86% | No | No |
| 158.4 mg, usually silica 7.92 m$^3$ (280 cu ft) air | Replaceable Dust/Mist filters | 1.5 mg | 99.05% | No | No |
| 0.3 micron DOP 0.05 mg per cubic meter air for particles | HEPA (includes Dust/Mist approval) | N/A | 99.97% | Yes | Yes |

## Transition

On July 10, 1995, in response to respirators exhibiting "low initial efficiency levels", new 42 CFR 84 standards, including the N95 standard, were enforced under a three-year transition period, ending on July 10, 1998. The standard for N95 respirators includes, but is not limited to, a filtration of at least 95% under a 0.3 micrometer 200 milligram test load of sodium chloride. Standards and specifications are also subject to change.

## Current classifications
### 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.
NIOSH particulate respirator class minimum efficiency levels :
| Particulate | Respirator class | Minimum efficiency level | Permitted for TB | Permitted for asbestos |
| NaCl (N) or DOP (R,P) | N95, R95, P95 | 95% | Yes | No |
| NaCl (N) or DOP (R,P) | N99, R99, P99 | 99% | Yes | No |
| NaCl (N) or DOP (R,P) | N100, R100, P100 | 99.97% | Yes | Yes |
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 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. 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. 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.

#### 2020 powered air-purifying respirator update

42 CFR 84, from 1995 to 2020, copies 30 CFR 11 rules for PAPRs.
The following table lists the air flow requirements for NIOSH-approved PAPRs under Part 84.175. Tight-fitting PAPRs may be fit tested with the facepiece unpowered and in negative-pressure (under 29 CFR 1910.134) while loose-fitting PAPR fit test protocols have not been changed from 30 CFR 11.
Part 84 air flow requirements :
| Facepiece | Air flow in liters/minute |
| Tight-fitting | 115 |
| Loose-fitting | 170 |
The following table lists the ratings for particulate ratings for Part 84 PAPRs. PAPR100 ratings were added in 2020.
NIOSH particulate classes for powered air-purifying respirators :
| Particulate | Respirator class | Minimum efficiency level | Permitted for TB | Permitted for asbestos |
| 0.3 micron DOP | HEPA or HE | 99.97% | Yes | Yes |
| 0.075 to 1.86 micron NaCl | PAPR100-N | 99.97% | Rating discontinued | Not yet defined |
| 0.075 to 1.86 micron DOP | PAPR100-P | 99.97% | Rating discontinued | Not yet defined |
PAPR100-N is not designed to filter oil particulates, and the official color-coding for all three respirator types is magenta.

### Chemical cartridge and canister classifications

Under 42 CFR 84, chemical cartridges and gas mask canisters are defined separately. Use of the TC-14G canister schedule or the TC-23C chemical cartridge schedule for a given respirator depends on whether "acid gas" is a designated contaminant, which is designated for gas mask canisters only, or if the manufacturer is obligated to list all designated contaminants supported by a given chemical cartridge.
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 on 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 that details the NIOSH protection designations, 42 CFR 84, the Navy/Marine Field Manual, the NIOSH TB guide, and whether they match up with the (42 CFR 84-declared ANSI K13.1-1973 revision) ANSI Z88.7-2001 colors, 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:
Respirator/Filter type designation and color comparison :
| NIOSH protection designations | NIOSH protection abbreviation | 42 CFR 84 max use concentration | Penetration allowed by 42 CFR 84 | Efficiency level | 1999 NIOSH TB Guide color | Correlated with Z88.7-2001 (K13.1-1973 revision)? |
| Acid gas (gas mask only) | AG | N/A | N/A | N/A | White | Yes, for canisters only |
| Ammonia | AM | 300 ppm | 50 ppm | 83.3% | Green | Yes |
| Chlorine dioxide | CD | N/A | N/A | N/A | N/A | In standard as combination |
| Chlorine | CL | 10 ppm | 5 ppm | 50% | White with 1/2" yellow stripe | No stripe, but within designation color |
| Chloroacetophenone | CN | N/A | N/A | N/A | N/A | N/A |
| Carbon monoxide | CO | N/A | N/A | N/A | Blue | Yes |
| Chlorobenzylidene malononitrile | CS | N/A | N/A | N/A | N/A | N/A |
| Ethylene oxide | EO | N/A | N/A | N/A | N/A | N/A |
| Formaldehyde | FM | N/A | N/A | N/A | N/A | N/A |
| Hydrogen chloride | HC | 50 ppm | 5 ppm | 90% | N/A | In standard as combination |
| Hydrogen fluoride | HF | N/A | N/A | N/A | N/A | In standard as combination |
| Hydrogen cyanide | HN | N/A | N/A | N/A | White, with 1/2" green stripe | No stripe, wrong color, actual color for unlisted combinations |
| Hydrogen sulfide | HS | N/A | N/A | N/A | N/A | In standard as combination (escape only) |
| Methylamine | MA | 100 ppm | 10 ppm | 90% | N/A | In standard with ammonia |
| Mercury vapor | MV | N/A | N/A | N/A | N/A | N/A |
| Nitrogen dioxide | ND | N/A | N/A | N/A | N/A | N/A |
| Organic Vapor | OV | 1000 ppm or lower | 5 ppm | Depends | Black | Yes |
| Phosphine | PH | N/A | N/A | N/A | N/A | N/A |
| Sulfur dioxide | SD | 50 ppm | 5 ppm | 90% | N/A | In standard as combination |
| Vinyl chloride | VC | 10 ppm | 1 ppm | 90% | N/A | NIOSH designation does not exist, may use unlisted combination color |
| Toluene diisocyanate | TDI | N/A | N/A | N/A | N/A | N/A |
| Demand (SCBA) | DE | Non-air-purifying respirators (Atmosphere-supplying respirators) | Non-air-purifying respirators (Atmosphere-supplying respirators) | Non-air-purifying respirators (Atmosphere-supplying respirators) | Non-air-purifying respirators (Atmosphere-supplying respirators) | Non-air-purifying respirators (Atmosphere-supplying respirators) |
| Pressure Demand (SCBA) | PD | Non-air-purifying respirators (Atmosphere-supplying respirators) | Non-air-purifying respirators (Atmosphere-supplying respirators) | Non-air-purifying respirators (Atmosphere-supplying respirators) | Non-air-purifying respirators (Atmosphere-supplying respirators) | Non-air-purifying respirators (Atmosphere-supplying respirators) |
| Supplied-air (Air-line) | SA | Non-air-purifying respirators (Atmosphere-supplying respirators) | Non-air-purifying respirators (Atmosphere-supplying respirators) | Non-air-purifying respirators (Atmosphere-supplying respirators) | Non-air-purifying respirators (Atmosphere-supplying respirators) | Non-air-purifying respirators (Atmosphere-supplying respirators) |
| Supplied-air Abrasive Blast | SB | Non-air-purifying respirators (Atmosphere-supplying respirators) | Non-air-purifying respirators (Atmosphere-supplying respirators) | Non-air-purifying respirators (Atmosphere-supplying respirators) | Non-air-purifying respirators (Atmosphere-supplying respirators) | Non-air-purifying respirators (Atmosphere-supplying respirators) |
| Self-Contained (SCBA) | SC | Non-air-purifying respirators (Atmosphere-supplying respirators) | Non-air-purifying respirators (Atmosphere-supplying respirators) | Non-air-purifying respirators (Atmosphere-supplying respirators) | Non-air-purifying respirators (Atmosphere-supplying respirators) | Non-air-purifying respirators (Atmosphere-supplying respirators) |
| Escape (SCBA) | ESC | Non-air-purifying respirators (Atmosphere-supplying respirators) | Non-air-purifying respirators (Atmosphere-supplying respirators) | Non-air-purifying respirators (Atmosphere-supplying respirators) | Non-air-purifying respirators (Atmosphere-supplying respirators) | Non-air-purifying respirators (Atmosphere-supplying respirators) |
Respirator combination designation and color comparison :
| | NIOSH protection abbreviation | Color | Correlated with Z88.7-2001 (K13.1-1973 revision)? |
| 1999 NIOSH TB Guide combinations | Any of above chemicals/ Particulates | Gray stripe | Wrong color, no stripe |
| 1999 NIOSH TB Guide combinations | HN/Chloropicrin | Yellow with 1/2" blue stripe | NIOSH designation does not exist, no stripe, wrong color, actual color for unlisted combinations |
| 1999 NIOSH TB Guide combinations | Radionuclides | Purple/Magenta | Yes, under 30 CFR 11 HEPA |
| 1999 NIOSH TB Guide combinations | AG/HN/CL/OV/AM/CO/ Chloropicrin/ radionuclides/ particulate | Red with 1/2" gray stripe | No stripe needed, combination more than required for color (AG/OV/AM/CO) |
| 1999 NIOSH TB Guide combinations | AG/AM | Green with 1/2" white stripe | No stripe, wrong color, actual color for unlisted combinations |
| 1999 NIOSH TB Guide combinations | AG/OV | Yellow | Yes, for canisters only |
| 1999 NIOSH TB Guide combinations | AG/OV/AM | Brown | Yes, for canisters only |
| Navy/Marine Field Manual combinations | "Acid Gases": CL/CD/HS/HC/SD/HF | White | Combination more than required for color (CL/HC/SD) |
| Navy/Marine Field Manual combinations | "Organic Vapors": Xylene/Toluene | Brown | Within designation color, but wrong color if exclusive |
| Navy/Marine Field Manual combinations | "Basic gases": AM/MA | Green | Yes |
| Navy/Marine Field Manual combinations | FM | Tan | Within designation color, but actual color for unlisted combinations |
| Navy/Marine Field Manual combinations | MV | Orange | NIOSH designation does not exist, wrong color, actual color for unlisted combinations |
| Navy/Marine Field Manual combinations | HEPA | Purple | Yes |
* 1 2 3 4 5 See the NIOSH pocket guide for additional respirator use guidelines. Breakthrough concentration times can be calculated through the NIOSH MultiVapor tool, or OSHA math models.
* ↑ For brevity, only combinations that are different from the TB guide are listed.
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).
By definition, ANSI Z88.2-2015 considers N100, R100, P100, and HE as HEPA filters.

## Table of TC/BM approval schedules

NIOSH is the current regulator of all the respirators in this schedule, under 42 CFR 84. 'BM' stands for the US Bureau of Mines, the historical regulator of respirators in the United States.
Approval schedules :
| US Code | Gas mask (Canister) | Air-line | SCBA | Particulate | PAPR | Chemical Cartridge |
| BM | BM-14 | BM-19 | BM-13 | BM-21 | N/A | BM-23 |
| 30 CFR 11 | TC-14G | TC-19C | TC-13F | TC-21C | TC-21C | TC-23C |
| 42 CFR 84 (enacted) | TC-14G | TC-19C | TC-13F | TC-84A | TC-21C | TC-23C |
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 (until 2020) 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 Certified Equipment List

NPPTL is the designated publisher of the NIOSH Certified Equipment List, or CEL. The CEL is a public domain database that details the respirators currently approved by NIOSH, and is ordered separated based on type of respirator, which is designated with a schedule (e.g. TC-84A).

## NIOSH rating limitations

NIOSH air filtration ratings do not test the fit of a respirator. Fit testing is required by OSHA for employers when a hazard is present, and voluntary respirator use under Appendix D is not allowed due to the hazard. Rules for fit testing are also defined by ANSI Z88.2. Z88.2 notes that, in Canada, respirator care and fit testing are defined by CSA Z94.4.

## 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