NIOSH air filtration rating

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A filtering facepiece N95 dust mask
Half-face air-purifying respirator with combination P100 particulate filter (magenta) and organic vapor (black) cartridge
A firefighter wearing an N95 dust mask

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 dust and liquid droplets 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).[1] Respiratory protective devices so classified include air-purifying respirators (APR) such as filtering facepiece respirators (dust masks) and chemical protective cartridges that have incorporated particulate filter elements.

The 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 more information see Cartridge (respirator). The classifications assume that the respirator is properly fitted.[2]

NIOSH classifications[edit]

NIOSH has currently 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 aerosols (e.g., lubricants, cutting fluids, glycerine, etc.).[1][3][4] Definitions and intended use for each series is indicated below.[5]

  • N for Not resistant to oil. Used when oil particulates are not present.
  • R for Resistant to oil. Used when oil particulates are present and the filter is disposed of after one shift.
  • P for oil Proof. Used when oil particulates are present and the filter is re-used for more than one shift.

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[1]



Efficiency Level

N95, R95, P95 95%
N99, R99, P99 99%
N100, R100, P100 99.97%

Since filters are tested against the 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.[4] Particles with a size both less than and greater than 0.3 μm are filtered at an efficiency greater than 99.97%.[6] Although it is counter-intuitive that particle sizes of less than 0.3 μm are filtered with a greater efficiency, the forces which have the greatest impact on the effectiveness of filtration (aerosol impaction, interception, and diffusion) are weakest at this size for filters tested by NIOSH.[7] A filter's collection efficiency for particle sizes other than those for which it is least efficient is indicated by the filter's efficiency curve.

Classic collection efficiency curve with filter collection mechanisms

See also[edit]


  1. ^ a b c "42 CFR Part 84 - Approval of Respiratory Protective Devices". United States Government Publishing Office. 6 February 2020. Retrieved 9 February 2020.
  2. ^ "To Beard or not to Beard? That's a good Question!". NIOSH Science Blog. CDC. 2 November 2017. Retrieved 27 February 2020.
  3. ^ "Respirator Trusted-Source Information Section 1: NIOSH-Approved Respirators". The National Personal Protective Technology Laboratory (NPPTL). Centers for Disease Control and Prevention. 29 January 2018. Retrieved 9 February 2020.
  4. ^ a b "NIOSH Guide to the Selection and Use of Particulate Respirators". The National Institute for Occupational Safety and Health (NIOSH). Centers for Disease Control and Prevention. 6 June 2014 [January 1996]. Retrieved 9 February 2020.
  5. ^ "OSHA Technical Manual Section 8VII: Chapter 2 Respiratory Protection Appendix 2-4". OSHA (TED 01-00-015 ed.). Retrieved 9 February 2020.
  6. ^ "NIOSH Guide to the Selection and Use of Particulate Respirators Appendix E: Commonly Asked Questions and Answers About Part 84 Respirators". The National Institute for Occupational Safety and Health (NIOSH). Centers for Disease Control and Prevention. 6 June 2014. Retrieved 9 February 2020.
  7. ^ Guidance for Filtration and Air-Cleaning Systems to Protect Building Environments from Airborne Chemical, Biological, or Radiological Attacks (PDF). Cincinnati, OH: National Institute for Occupational Safety and Health. April 2003. pp. 8–12. Retrieved 9 February 2020.