Respirator Explained

A respirator is a device designed to protect the wearer from inhaling hazardous atmospheres including lead fumes, vapours, gases and particulate matter such as dusts and airborne pathogens such as viruses. There are two main categories of respirators: the air-purifying respirator, in which respirable air is obtained by filtering a contaminated atmosphere, and the air-supplied respirator, in which an alternate supply of breathable air is delivered. Within each category, different techniques are employed to reduce or eliminate noxious airborne contaminants.

Air-purifying respirators range from relatively inexpensive, single-use, disposable face masks, known as filtering facepiece respirators, reusable models with replaceable cartridges called elastomeric respirators, to Powered air-purifying respirators (PAPR), which use a pump or fan to constantly move air through a filter and supply purified air into a mask, helmet or hood.

History

Earliest records to 19th century

The history of protective respiratory equipment can be traced back as far as the first century, when Pliny the Elder (–79) described using animal bladder skins to protect workers in Roman mines from red lead oxide dust.[1] In the 16th century, Leonardo da Vinci suggested that a finely woven cloth dipped in water could protect sailors from a toxic weapon made of powder that he had designed.[2]

Alexander von Humboldt introduced a primitive respirator in 1799 when he worked as a mining engineer in Prussia.[3]

Julius Jeffreys first used the word "respirator" as a mask in 1836.[4]

In 1848, the first US patent for an air-purifying respirator was granted to Lewis P. Haslett[5] for his 'Haslett's Lung Protector,' which filtered dust from the air using one-way clapper valves and a filter made of moistened wool or a similar porous substance.[6] Hutson Hurd patented a cup-shaped mask in 1879 which became widespread in industrial use.[7]

Inventors in Europe included John Stenhouse, a Scottish chemist, who investigated the power of charcoal in its various forms, to capture and hold large volumes of gas. He built one of the first respirators able to remove toxic gases from the air, paving the way for activated charcoal to become the most widely used filter for respirators.[8] Irish physicist John Tyndall took Stenhouse's mask, added a filter of cotton wool saturated with lime, glycerin, and charcoal, and in 1871 invented a 'fireman's respirator', a hood that filtered smoke and gas from air, which he exhibited at a meeting of the Royal Society in London in 1874.[9] Also in 1874, Samuel Barton patented a device that 'permitted respiration in places where the atmosphere is charged with noxious gases, or vapors, smoke, or other impurities.'[10] [11]

In the late 19th century, Miles Philips began using a "mundebinde" ("mouth bandage") of sterilized cloth which he refined by adapting a chloroform mask with two layers of cotton mull.[12]

20th century

United States

In the 1970s, the successor to the United States Bureau of Mines and NIOSH developed standards for single-use respirators, and the first single-use respirator was developed by 3M and approved in 1972.[13] 3M used a melt blowing process that it had developed decades prior and used in products such as ready-made ribbon bows and bra cups; its use in a wide array of products had been pioneered by designer Sara Little Turnbull.[14]

1990s

21st century

2020

China normally makes 10 million masks per day, about half of the world production. During the COVID-19 pandemic, 2,500 factories were converted to produce 116 million daily.[15]

During the COVID-19 pandemic, people in the United States, and in a lot of countries in the world, were urged to make their own cloth masks due to the widespread shortage of commercial masks.[16]

2024

See also: 2020–2024 H5N1 outbreak.

Summary of modern respirators

All respirators have some type of facepiece held to the wearer's head with straps, a cloth harness, or some other method. Facepieces come in many different styles and sizes to accommodate all types of face shapes.

A full facepiece covers the mouth, nose and eyes and if sealed, is sealed round the perimeter of the face. Unsealed versions may be used when air is supplied at a rate which prevents ambient gas from reaching the nose or mouth during inhalation.

Respirators can have half-face forms that cover the bottom half of the face including the nose and mouth, and full-face forms that cover the entire face. Half-face respirators are only effective in environments where the contaminants are not toxic to the eyes or facial area.

An escape respirator may have no component that would normally be described as a mask, and may use a bite-grip mouthpiece and nose clip instead. Alternatively, an escape respirator could be a time-limited self-contained breathing apparatus.

For hazardous environments, like confined spaces, atmosphere-supplying respirators, like SCBAs, should be used.

A wide range of industries use respirators including healthcare & pharmaceuticals, defense & public safety services (defense, firefighting & law enforcement), oil and gas industries, manufacturing (automotive, chemical, metal fabrication, food and beverage, wood working, paper and pulp), mining, construction, agriculture and forestry, cement production, power generation, painting, shipbuilding, and the textile industry.[17]

Respirators require user training in order to provide proper protection.

Use

User seal check

Each time a wearer dons a respirator, they must perform a seal check to be sure that they have an airtight seal to the face so that air does not leak around the edges of the respirator. (PAPR respirators may not require this because they don't necessarily seal to the face.) This check is different than the periodic fit test that is performed by specially trained personnel using testing equipment. Filtering facepiece respirators are typically checked by cupping the hands over the facepiece while exhaling (positive pressure check) or inhaling (negative pressure check) and observing any air leakage around the facepiece. Elastomeric respirators are checked in a similar manner, except the wearer blocks the airways through the inlet valves (negative pressure check) or exhalation valves (positive pressure check) while observing the flexing of the respirator or air leakage. Manufacturers have different methods for performing seal checks and wearers should consult the specific instructions for the model of respirator they are wearing. Some models of respirators or filter cartridges have special buttons or other mechanisms built into them to facilitate seal checks.[18]

Contrast with surgical mask

Surgical N95

Respirator selection

Air-purifying respirators are respirators that draw in the surrounding air and purify it before it is breathed (unlike air-supplying respirators, which are sealed systems, with no air intake, like those used underwater). Air-purifying respirators filter particulates, gases, and vapors from the air, and may be negative-pressure respirators driven by the wearer's inhalation and exhalation, or positive-pressure units such as powered air-purifying respirators (PAPRs).

According to the NIOSH Respirator Selection Logic, air-purifying respirators are recommended for concentrations of hazardous particulates or gases that are greater than the relevant occupational exposure limit but less than the immediately dangerous to life or health level and the manufacturer's maximum use concentration, subject to the respirator having a sufficient assigned protection factor. For substances hazardous to the eyes, a respirator equipped with a full facepiece, helmet, or hood is recommended. Air-purifying respirators are not effective during firefighting, in oxygen-deficient atmosphere, or in an unknown atmosphere; in these situations a self-contained breathing apparatus is recommended instead.[19]

Types of Filtration

Mechanical filter

Main Article: Mechanical filter respirator (and regulatory ratings)

Mechanical filters remove contaminants from air in several ways: interception when particles following a line of flow in the airstream come within one radius of a fiber and adhere to it; impaction, when larger particles unable to follow the curving contours of the airstream are forced to embed in one of the fibers directly; this increases with diminishing fiber separation and higher air flow velocity; by diffusion, where gas molecules collide with the smallest particles, especially those below 100 nm in diameter, which are thereby impeded and delayed in their path through the filter, increasing the probability that particles will be stopped by either of the previous two mechanisms; and by using an electrostatic charge that attracts and holds particles on the filter surface.

There are many different filtration standards that vary by jurisdiction. In the United States, the National Institute for Occupational Safety and Health defines the categories of particulate filters according to their NIOSH air filtration rating. The most common of these are the N95 respirator, which filters at least 95% of airborne particles but is not resistant to oil.

Other categories filter 99% or 99.97% of particles, or have varying degrees of resistance to oil.[20]

In the European Union, European standard EN 143 defines the 'P' classes of particle filters that can be attached to a face mask, while European standard EN 149 defines classes of "filtering half masks" or "filtering facepieces", usually called FFP masks.[21]

According to 3M, the filtering media in respirators made according to the following standards are similar to U.S. N95 or European FFP2 respirators, however, the construction of the respirators themselves, such as providing a proper seal to the face, varies considerably. (For example, US NIOSH-approved respirators never include earloops because they don't provide enough support to establish a reliable, airtight seal.) Standards for respirator filtration the Chinese KN95, Australian / New Zealand P2, Korean 1st Class also referred to as KF94, and Japanese DS.[22]

Chemical cartridge

See main article: Respirator cartridge.

Chemical cartridge respirators use a cartridge to remove gases, volatile organic compounds (VOCs), and other vapors from breathing air by adsorption, absorption, or chemisorption. A typical organic vapor respirator cartridge is a metal or plastic case containing from 25 to 40 grams of sorption media such as activated charcoal or certain resins. The service life of the cartridge varies based, among other variables, on the carbon weight and molecular weight of the vapor and the cartridge media, the concentration of vapor in the atmosphere, the relative humidity of the atmosphere, and the breathing rate of the respirator wearer. When filter cartridges become saturated or particulate accumulation within them begins to restrict air flow, they must be changed.[23]

If the concentration of harmful gases is immediately dangerous to life or health, in workplaces covered by the Occupational Safety and Health Act the US Occupational Safety and Health Administration specifies the use of air-supplied respirators except when intended solely for escape during emergencies.[24] NIOSH also discourages their use under such conditions.[25]

Air-purifying respirators

Powered air-purifying respirators

Atmosphere-supplying respirators

These respirators do not purify the ambient air, but supply breathing gas from another source. The three types are the self contained breathing apparatus, in which a compressed air cylinder is worn by the wearer; the supplied air respirators, where a hose supplies air from a stationary source; and combination supplied-air respirators, with a emergency backup tank.[26]

Supplied air respirator

Escape respirators

Self-contained breathing apparatus

Self-rescue device

Disadvantages

Hierarchy of Controls point of view

The Hierarchy of Controls, noted as part of the Prevention Through Design initiative started by NIOSH with other standards bodies, is a set of guidelines emphasizing building in safety during design, as opposed to ad-hoc solutions like PPE, with multiple entities providing guidelines on how to implement safety during development[27] outside of NIOSH-approved respirators. US Government entities currently and formerly involved in the regulation of respirators follow the Hierarchy of Controls, including OSHA and MSHA.[28]

However, some HOC implementations, notably MSHA's, have been criticized for allowing mining operators to skirt engineering control noncompliance by requiring miners to wear respirators instead if the permissible exposure limit (PEL) is exceeded, without work stoppages, breaking the hierarchy of engineering controls. Another concern was fraud related to the inability to scrutinize engineering controls,[29] [30] unlike NIOSH-approved respirators, like the N95, which can be fit tested by anyone, are subject to the scrutiny of NIOSH, and are trademarked and protected under US federal law.[31]

Respirator non-compliance

With regards to people complying with requirements to wear respirators, various papers note high respirator non-compliance across industries,[32] [33] with a survey noting non-compliance was due in large part due to discomfort from temperature increases along the face, and a large amount of respondents also noting the social unacceptability of provided N95 respirators during the survey.[34] For reasons like mishandling, ill-fitting respirators and lack of training, the Hierarchy of Controls dictates respirators be evaluated last while other controls exist and are working. Alternative controls like hazard elimination, administrative controls, and engineering controls like ventilation are less likely to fail due to user discomfort or error.[35] [36]

A U.S. Department of Labor study[37] showed that in almost 40 thousand American enterprises, the requirements for the correct use of respirators are not always met. Experts note that in practice it is difficult to achieve elimination of occupational morbidity with the help of respirators:

Beards

Certain types of facial hair can reduce fit to a significant degree. For this reason, there are facial hair guidelines for respirator users.[38] This is another example of potential respirator non-compliance.

Counterfeiting, modification, and revocation of regulated respirators

Another disadvantage of respirators is that the onus is on the respirator user to determine if their respirator is counterfeit or has had its certification revoked. Customers and employers can inadvertently purchase non-OEM parts for a NIOSH-approved respirator which void the NIOSH approval and violate OSHA laws, in addition to potentially compromising the fit of the respirator.[39] This is another example of respirator mishandling under the Hierarchy of Controls.

Issues with fit testing

If respirators must be used, under 29 CFR 1910.134, OSHA requires respirator users to conduct a respirator fit test, with a safety factor of 10 to offset lower fit during real world use.[40] However, NIOSH notes the large amount of time required for fit testing has been a point of contention for employers.[41]

Other opinions concern the change in performance of respirators in use compared to when fit testing, and compared to engineering control alternatives:

Issues with respirator design

Extended use of certain negative-pressure respirators can result in higher levels of carbon dioxide from dead space and breathing resistance (pressure drop) which can impact functioning and sometimes can exceed the PEL.[42] [43] [44] This effect was significantly reduced with powered air purifying respirators.[45] Certain respirator designs, especially those with head straps, can also lead to headaches,[46] dermatitis and acne.[47]

Complaints have been leveled at early LANL NIOSH fit test panels (which included primarily military personnel) as being unrepresentative of the broader American populace.[48] However, later fit test panels, based on a NIOSH facial survey conducted in 2003, were able to reach 95% representation of working US population surveyed.[49] Despite these developments, 42 CFR 84, the US regulation NIOSH follows for respirator approval, allows for respirators that don't follow the NIOSH fit test panel provided that: more than one facepiece size is provided, and no chemical cartridges are made available.[50]

Issues with lack of regulation

Respirators designed to non-US standards may not be subject to as much or any scrutiny:

Some jurisdictions allow for respirator filtration ratings lower than 95%, respirators which are not rated to prevent respiratory infection, asbestos, or other dangerous occupational hazards. These respirators are sometimes known as dust masks for their almost exclusive approval only against dust nuisances:

In the US, NIOSH noted that under standards predating the N95, 'Dust/Mist' rated respirators could not prevent the spread of TB.[53]

Regulation

The choice and use of respirators in developed countries is regulated by national legislation. To ensure that employers choose respirators correctly, and perform high-quality respiratory protection programs, various guides and textbooks have been developed:

For standard filter classes used in respirators, see Mechanical filter (respirator)#Filtration standards.

See also

Further reading

External links

cdc.gov/niosh. Respirator manufacturer approvals for NIOSH-certified air-purifying respirator with CBRN Protections (CBRN APR). This link covers APR and Air-Purifying Escape Respirators (APER) certified by the NIOSH's National Personal Protective Technology Laboratory (NPPTL), Pittsburgh, PA, to CBRN protection NIOSH standards. CBRN APR are tight-fitting, full-face respirators with approved accessories and protect the user breathing zone by relying on user negative pressure, fit testing and user seal checks to filter less than Immediately Dangerous to Life and Health (IDLH) concentrations of hazardous respiratory compounds and particulates through NIOSH CBRN Cap 1, Cap 2 or Cap 3 canisters for CBRN APR- or CBRN 15- or CBRN 30-rated APER.

cdc.gov/niosh. Respirator manufacturer approvals for NIOSH-certified powered air-purifying respirator with CBRN Protections (CBRN PAPR-loose fitting or tight fitting)

Notes and References

  1. Naturalis_Historia/Liber_XXXIII#XL. la.
  2. Web site: 11 September 2001 . Women in the US Military – History of Gas Masks . https://web.archive.org/web/20110512042523/http://chnm.gmu.edu/courses/rr/s01/cw/students/leeann/historyandcollections/collections/photopages/phesgasmasks.html . 12 May 2011 . 18 April 2010 . Chnm.gmu.edu.
  3. Web site: Ueber die unterirdischen Gasarten und die Mittel ihren Nachtheil zu vermindern. WorldAtlas. 1799. en. 2020-03-27. Humboldt. Alexander von.
  4. David Zuck. 1990. Julius Jeffreys: Pioneer of humidification. Proceedings of the History of Anaesthesia Society. 8b. 70–80. 16 August 2020. 4 November 2021. https://web.archive.org/web/20211104215545/http://kora.matrix.msu.edu/files/21/120/15-78-188-22-1990-Zuck-JeffreysResp.pdf. live.
  5. Book: Christianson, Scott. Fatal Airs: The Deadly History and Apocalyptic Future of Lethal Gases that Threaten Our World. ABC-CLIO. 2010. 9780313385520. Scott Christianson.
  6. US . 6529A . patent . Lung Protector . 1849-06-12 . 1849-06-12 . Lewis P. Haslett .
  7. Improvement in inhaler and respirator. 1879-08-26.
  8. Book: Britain, Royal Institution of Great. Notices of the Proceedings at the Meetings of the Members of the Royal Institution, with Abstracts of the Discourses. 53. 1858. W. Nicol, Printer to the Royal Institution. en.
  9. Tyndall. John. 1873. On Some Recent Experiments with a Fireman's Respirator. Proceedings of the Royal Society of London. 22. 359–361. 112853. 1873RSPS...22R.359T. 0370-1662.
  10. Web site: Gas Mask Development (1926). 67.225.133.110. 2020-03-27. 27 February 2021. https://web.archive.org/web/20210227141330/http://67.225.133.110/~gbpprorg/invention/development.html. live.
  11. US . 148868A . patent . Respirator . 1874-03-24 . 1874-03-24 . Samuel Barton .
  12. Lowry . H. C. . Some Landmarks in Surgical Technique . The Ulster Medical Journal . 1947 . 16 . 2 . 102–113 . 18898288 . 2479244 .
  13. Web site: The untold origin story of the N95 mask. Fast Company and Mansueto Ventures, LLC. 9 April 2020. 19 May 2020. https://web.archive.org/web/20200519041831/https://www.fastcompany.com/90479846/the-untold-origin-story-of-the-n95-mask. live.
  14. Web site: Ask Why: Sara Little Turnbull. Rees. Paula. Eisenbach. Larry. 2020. Design Museum Foundation. 2020-04-01. mdy-all. 20 July 2020. https://web.archive.org/web/20200720125822/https://designmuseumfoundation.org/ask-why/. live.
  15. Web site: World Depends on China for Face Masks But Can Country Deliver?. Xie. John. 19 March 2020. www.voanews.com. Voice of America. en. live. https://web.archive.org/web/20200321094219/https://www.voanews.com/science-health/coronavirus-outbreak/world-depends-china-face-masks-can-country-deliver. 21 March 2020.
  16. Web site: Dwyer . Colin . April 3, 2020 . CDC Now Recommends Americans Consider Wearing Cloth Face Coverings In Public . .
  17. Web site: Respirator use and practices. U.S. Bureau of Labour Statistics. 29 March 2020. 17 October 2020. https://web.archive.org/web/20201017155428/https://www.bls.gov/iif/oshwc/osh/os/osnr0014.txt. live.
  18. Web site: Filtering out Confusion: Frequently Asked Questions about Respiratory Protection, User Seal Check (2018) . NIOSH . 8 December 2021.
  19. NIOSH respirator selection logic. Bollinger. Nancy. 2004-10-01. U.S. National Institute for Occupational Safety and Health. 5–16. en-us. 10.26616/NIOSHPUB2005100. 2020-04-20. free. 15 July 2020. https://web.archive.org/web/20200715045859/https://www.cdc.gov/niosh/docs/2005-100/default.html. live.
  20. Metzler . R . Szalajda . J . NIOSH Fact Sheet: NIOSH Approval Labels - Key Information to Protect Yourself . DHHS (NIOSH) Publication No. 2011-179 . 2011 . 0343-6993 . 10 September 2017 . 20 July 2018 . https://web.archive.org/web/20180720182756/https://www.cdc.gov/niosh/docs/2011-179/pdfs/2011-179.pdf . live .
  21. Web site: A Guide to Respiratory Protective Equipment . hsa.ie . 12 July 2024 . 30 June 2024 . https://web.archive.org/web/20240630012837/https://www.hsa.ie/eng/Publications_and_Forms/Publications/Chemical_and_Hazardous_Substances/Respiratory%20Protective%20Equipment.pdf . live .
  22. Web site: Technical Bulletin: Comparison of FFP2, KN95, and N95 and Other Filtering Facepiece Respirator Classes. January 2020. 3M Personal Safety Division. 3 April 2020. 14 April 2020. https://web.archive.org/web/20200414004708/https://multimedia.3m.com/mws/media/1791500O/comparison-ffp2-kn95-n95-filtering-facepiece-respirator-classes-tb.pdf. live.
  23. [:File:Methods for the timely replacement of cartridges in respirators.pdf|The document describes the methods used previously and currently used to perform the timely replacement of cartridges in air purifying respirators.]
  24. OSHA standard 29 CFR 1910.134 "Respiratory Protection"
  25. Book: Bollinger, Nancy. NIOSH Respirator Selection Logic. DHHS (NIOSH) Publication No. 2005-100. 2004. National Institute for Occupational Safety and Health. Cincinnati, Ohio. 32. etal. 10.26616/NIOSHPUB2005100. 10 September 2017. 23 June 2017. https://web.archive.org/web/20170623115207/https://www.cdc.gov/niosh/docs/2005-100/. live.
  26. Web site: Respirator Selection: Air-purifying vs. Atmosphere-supplying Respirators. U.S. Occupational Safety and Health Administration. 2020-04-09. 17 April 2020. https://web.archive.org/web/20200417114028/https://www.osha.gov/SLTC/etools/respiratory/respirator_selection_airvsatmos_resp.html. live.
  27. Web site: The State of the National Initiative on Prevention through Design. May 2014. NIOSH. 3 June 2024. 3 June 2024. https://web.archive.org/web/20240603035524/https://www.cdc.gov/niosh/docs/2014-123/pdfs/2014-123_v2.pdf. live.
  28. Web site: Summary of Key MSHA Requirements for a Respiratory Protection Program. 3 June 2024. 16 June 2024. https://web.archive.org/web/20240616204739/https://www.uaf.edu/mapts/tools/15_Respiratory_Program_Requirements.pdf. live.
  29. Web site: RE: Lowering Miners' Exposure to Respirable Crystalline Silica and Improving Respiratory Protection (RIN 1219-AB36). 11 September 2023.
  30. Web site: MSHA's proposed rule on silica has 'shortcomings,' lawmakers say. 21 September 2023. 3 June 2024. 5 June 2024. https://web.archive.org/web/20240605172058/https://www.safetyandhealthmagazine.com/articles/24515-mshas-proposed-rule-on-silica-has-shortcomings-lawmakers-say. live.
  31. Web site: Counterfeit Respirators / Misrepresentation of NIOSH Approval. 23 May 2024 . NIOSH.
  32. Factors influencing respirator use at work in respiratory patients . 10.1093/occmed/kqr132 . 2011 . Fukakusa . J. . Rosenblat . J. . Jang . B. . Ribeiro . M. . Kudla . I. . Tarlo . S. M. . Occupational Medicine . 61 . 8 . 576–582 . 21968940 .
  33. Web site: Use, failure, and non-compliance of respiratory personal protective equipment and risk of upper respiratory tract infections—A longitudinal repeated measurement study during the COVID-19 pandemic among healthcare workers in Denmark . 10.1093/annweh/wxae008 . 2024 . Biering . Karin . Kinnerup . Martin . Cramer . Christine . Dalbøge . Annett . Toft Würtz . Else . Lund Würtz . Anne Mette . Kolstad . Henrik Albert . Schlünssen . Vivi . Meulengracht Flachs . Esben . Nielsen . Kent J. . Annals of Work Exposures and Health . 68 . 4 . 376–386 . 38373246 .
  34. Health care workers' views about respirator use and features that should be included in the next generation of respirators . 10.1016/j.ajic.2009.09.005 . 2010 . Baig . Aliya S. . Knapp . Caprice . Eagan . Aaron E. . Radonovich . Lewis J. . American Journal of Infection Control . 38 . 1 . 18–25 . 20036443 . 7132692 .
  35. Web site: The Hierarchy of Controls, Part Four: Personal Protective Equipment. Simplified Safety. 3 June 2024. 3 June 2024. https://web.archive.org/web/20240603031949/https://simplifiedsafety.com/blog/the-hierarchy-of-controls-part-four-personal-protective-equipment/. live.
  36. Web site: Personal Protective Equipment (PPE): Protect the Worker with PPE. 5 May 2023. NIOSH. 3 June 2024. 3 June 2024. https://web.archive.org/web/20240603031949/https://www.cdc.gov/niosh/learning/safetyculturehc/module-3/7.html. live.
  37. Book: U.S. Department of Labor, Bureau of Labor Statistics. Respirator Usage in Private Sector Firms, 2001. U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health. Morgantown, WV. 273. 22 January 2019. 1 November 2017. https://web.archive.org/web/20171101172745/https://www.cdc.gov/niosh/docs/respsurv/pdfs/respsurv2001.pdf. live.
  38. Web site: To Beard or not to Beard? That's a good Question!. 2 November 2017. NIOSH. 27 February 2020. 18 March 2020. https://web.archive.org/web/20200318034249/https://blogs.cdc.gov/niosh-science-blog/2017/11/02/noshave/. live.
  39. Web site: Transcript for the OSHA Training Video Entitled Counterfeit & Altered Respirators: The Importance of Checking for NIOSH Certification. January 2012. US Department of Labor, OSHA. 3 June 2024. 3 June 2024. https://web.archive.org/web/20240603060828/https://www.osha.gov/video/respiratory-protection/niosh/transcript. live.
  40. Web site: MAJOR REQUIREMENTS OF OSHA'S RESPIRATORY PROTECTION STANDARD 29 CFR 1910.134. United States Department of Labor, OSHA. 3 June 2024. 27 January 2024. https://web.archive.org/web/20240127222116/https://www.osha.gov/sites/default/files/training-library_major_requirements.pdf. live.
  41. Web site: New NIOSH Study Supports the OSHA Annual Fit Testing Requirements for Filtering Facepiece Respirators. NIOSH. 5 January 2016. Ziqing. Zhuang. Michael. Bergman. Jaclyn. Krah.
  42. Mean values for several models. For example, IDLH for CO2 = 4%, but filtering facepiese "AOSafety Pleats Plus" provided concentration up to 5.8%. According to the paper the model was discontinued from manufacturing and had its NIOSH approval withdrawn. (It is also no longer on the CEL, TC-84A-2630 and TC-84A-4320. Former approval by the FDA, while other discontinued models are still on the CEL) Source: E.J. Sinkule, J.B. Powell, F.L. Goss . Evaluation of N95 respirator use with a surgical mask cover: effects on breathing resistance and inhaled carbon dioxide . Annals of Occupational Hygiene . 2013 . 57 . 3 . 384–398 . 10.1093/annhyg/mes068 . 23108786 . Oxford University Press . en . 2398-7308 . free .
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  45. 10.1186/s12879-021-06056-0 . free . Carbon dioxide increases with face masks but remains below short-term NIOSH limits . 2021 . Rhee . Michelle S. M. . Lindquist . Carin D. . Silvestrini . Matthew T. . Chan . Amanda C. . Ong . Jonathan J. Y. . Sharma . Vijay K. . BMC Infectious Diseases . 21 . 1 . 354 . 33858372 . 8049746 .
  46. Headache Related to PPE Use during the COVID-19 Pandemic . 10.1007/s11916-021-00968-x . 2021 . Ong . Jonathan J. Y. . Chan . Amanda C. Y. . Bharatendu . Chandra . Teoh . Hock Luen . Chan . Yee Cheun . Sharma . Vijay K. . Current Pain and Headache Reports . 25 . 8 . 53 . 34129112 . 8203491 .
  47. Chris C.I. Foo, Anthony T.J. Goon, Yung-Hian Leow, Chee-Leok Goh . Adverse skin reactions to personal protective equipment against severe acute respiratory syndrome – a descriptive study in Singapore . Contact Dermatitis . 2006 . 55 . 5 . 291–294 . 10.1111/j.1600-0536.2006.00953.x . John Wiley & Sons . 17026695 . 7162267 . en . 0105-1873. free .
  48. Web site: Determination of Sample Size and Passing Criteria for Fit Test Panels. 3 June 2024. 8 August 2023. https://web.archive.org/web/20230808002256/https://www.cdc.gov/niosh/docket/archive/pdfs/NIOSH-137/0137-081809-DraftNIOSHReport.pdf. live.
  49. New Respirator Fit Test Panels Representing the Current U.S. Civilian Work Force . 10.1080/15459620701497538 . 2007 . Zhuang . Ziqing . Bradtmiller . Bruce . Shaffer . Ronald E. . Journal of Occupational and Environmental Hygiene . 4 . 9 . 647–659 . 17613722 .
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  51. Web site: 国家标准|Gb 2626-2019 . 3 June 2024 . 3 June 2024 . https://web.archive.org/web/20240603192044/https://openstd.samr.gov.cn/bzgk/gb/newGbInfo?hcno=16D8935B45AD7AE40228801B7FADFC6C . live .
  52. Web site: Protection levels: FFP1 masks, FFP2 masks, FFP3 masks. Moldex Europe. 3 June 2024. 2 June 2024. https://web.archive.org/web/20240602194300/https://www.moldex-europe.com/en/moldex-good-to-know/protection-levels-ffp1-masks-ffp2-masks-ffp3-masks/. live.
  53. Web site: DEPARTMENT OF HEALTH AND HUMAN SERVICES Centers for Disease Control and Prevention Guidelines for Preventing the Transmission of Mycobacterium Tuberculosis in Health-Care Facilities, 1994. US Federal Register. 2024-05-08. 8 June 2024. https://web.archive.org/web/20240608020741/https://archives.federalregister.gov/issue_slice/1994/10/28/54237-54364.pdf. live.
  54. Book: Nancy J. Bollinger, Robert H. Schutz. etal. NIOSH Guide to Industrial Respiratory Protection. 10 June 2018. DHHS (NIOSH) Publication No 87-116. 1987. National Institute for Occupational Safety and Health. Cincinnati, Ohio. 305. 10.26616/NIOSHPUB87116. 23 November 2017. https://web.archive.org/web/20171123081757/https://www.cdc.gov/niosh/docs/87-116/. live.
  55. Book: Nancy Bollinger. etal. NIOSH Respirator Selection Logic. 10 June 2018. DHHS (NIOSH) Publication No 2005-100. 2004. National Institute for Occupational Safety and Health. Cincinnati, Ohio. 32. 10.26616/NIOSHPUB2005100. 23 June 2017. https://web.archive.org/web/20170623115207/https://www.cdc.gov/niosh/docs/2005-100/. live.
  56. Book: Linda Rosenstock. etal. TB Respiratory Protection Program In Health Care Facilities - Administrator's Guide. 10 June 2018. DHHS (NIOSH) Publication No 99-143. 1999. National Institute for Occupational Safety and Health. Cincinnati, Ohio. 120. 10.26616/NIOSHPUB99143. 2 April 2020. https://web.archive.org/web/20200402011920/https://www.cdc.gov/niosh/docs/99-143/. live.
  57. Book: Kathleen Kincade, Garnet Cooke, Kaci Buhl . Respiratory Protection Guide. Requirements for Employers of Pesticide Handlers . Pesticide Educational Resources Collaborative (PERC) . 2017 . Janet Fults . Worker Protection Standard (WPS) . California . 48 . etal . 10 June 2018 . https://web.archive.org/web/20210322031631/https://cdnjs.cloudflare.com/ajax/libs/mark.js/8.11.1/jquery.mark.min.js . 22 March 2021 . live. PDF Wiki
  58. Web site: Respiratory Protection eTool. Occupational Safety and Health Administration. 1998. OSHA. en, es. 10 June 2018. Washington, DC. 22 March 2021. https://web.archive.org/web/20210322031609/https://www.osha.gov/SLTC/etools/respiratory/index.html. live.
  59. Book: Hilda L. Solis. etal. Small Entity Compliance Guide for the Respiratory Protection Standard. 10 June 2018. OSHA 3384-09. 2011. Occupational Safety and Health Administration, U.S. Department of Labor. Washington, DC. 124. 22 March 2021. https://web.archive.org/web/20210322031609/https://www.osha.gov/dte/librarymaterials_library.html#respiratoryprotection. live. PDF Wiki
  60. Book: OSHA . Hospital Respiratory Protection Program Toolkit . Occupational Safety and Health Administration, U.S. Department of Labor . 2015 . OSHA 3767. Resources for Respirator Program Administrators . Washington, DC . 96 . etal . 10 June 2018 . https://web.archive.org/web/20210322031610/https://www.osha.gov/SLTC/respiratoryprotection/guidance.html . 22 March 2021 . live. PDF Wiki
  61. Book: J. Edgar Geddie. A Guide to Respiratory Protection. 10 June 2018. 2. Industry Guide 44. 2012. Occupational Safety and Health Division, N.C. Department of Labor. Raleigh, North Carolina. 54. 22 March 2021. https://web.archive.org/web/20210322031637/https://www.labor.nc.gov/safety-and-health/occupational-safety-and-health/occupational-safety-and-health-topic-pages/respiratory-protection#learn-more. live.
  62. Book: Patricia Young, Phillip Fehrenbacher & Mark Peterson . Breathe Right! Oregon OSHA's guide to developing a respiratory protection program for small-business owners and managers . Oregon OSHA Standards and Technical Resources Section, Oregon Occupational Safety and Health . 2014 . Publications: Guides 440-3330 . Salem, Oregon . 44 . 10 June 2018 . https://web.archive.org/web/20210322031612/https://osha.oregon.gov/Pages/topics/respiratory-protection.aspx . 22 March 2021 . live. PDF Wiki
  63. Book: Patricia Young & Mark Peterson. Air you breathe: Oregon OSHA's respiratory protection guide for agricultural employers. 10 June 2018. Publications: Guides 440-3654. 2016. Oregon OSHA Standards and Technical Resources Section, Oregon Occupational Safety and Health. Salem, Oregon. 32. 22 March 2021. https://web.archive.org/web/20210322031612/https://osha.oregon.gov/Pages/topics/respiratory-protection.aspx. live.
  64. Book: Oregon OSHA. Oregon OSHA Technical Manual. https://osha.oregon.gov/rules/Pages/tech-manual.aspx. 10 June 2018. Rules. 2014. Oregon OSHA. Salem, Oregon. 38. Section VIII / Chapter 2: Respiratory Protection. 22 March 2021. https://web.archive.org/web/20210322031618/https://osha.oregon.gov/rules/Pages/tech-manual.aspx. live. PDF Wiki
  65. Book: Cal/OSHA Consultation Service, Research and Education Unit, Division of Occupational Safety and Health, California Department of Industrial Relations. Respiratory Protection in the Workplace. A Practical Guide for Small-Business Employers. 10 June 2018. 3. 2017. California Department of Industrial Relations. Santa Ana, California. 51. 22 March 2021. https://web.archive.org/web/20210322031639/https://www.dir.ca.gov/dosh/PubOrder.asp. live. PDF
  66. Book: K. Paul Steinmeyer . etal . Manual of Respiratory Protection Against Airborne Radioactive Material . 2001 . Office of Nuclear Reactor Regulation, U.S. Nuclear Regulatory Commission . Washington, DC . 166 . NUREG/CR-0041, Revision 1 . 10 June 2018 . 22 March 2021 . https://web.archive.org/web/20210322031619/https://www.nrc.gov/reading-rm/doc-collections/nuregs/contract/cr0041/index.html . live . PDF Wiki
  67. Book: Gary P. Noonan, Herbert L. Linn, Laurence D. Reed . etal . Susan V. Vogt . A guide to respiratory protection for the asbestos abatement industry . 1986 . Environmental Protection Agency (EPA) & National Institute for Occupational Safety and Health (NIOSH) . Washington, DC . 173 . NIOSH IA 85-06; EPA DW 75932235-01-1 . 10 June 2018 . 22 March 2021 . https://web.archive.org/web/20210322031623/https://www.wbdg.org/ffc/epa/criteria/epa-560opts86001 . live .
  68. Book: Jaime Lara, Mireille Vennes . Guide pratique de protection respiratoire . 2002 . Institut de recherche Robert-Sauve en sante et en securite du travail (IRSST), Commission de la sante et de la securite du travail du Quebec . Montreal, Quebec (Canada) . 978-2-550-37465-7 . 56 . 1 . Projet de recherche: 0098-0660 . 10 June 2018 . fr . 12 June 2018 . https://web.archive.org/web/20180612142520/http://www.irsst.qc.ca/publications-et-outils/publication/i/862/n/guide-pratique-de-protection-respiratoire-r-319/redirected/1 . live .

    2 edition: Book: Jaime Lara, Mireille Vennes . Guide pratique de protection respiratoire . 26 August 2013 . Institut de recherche Robert-Sauve en sante et en securite du travail (IRSST), Commission de la santé et de la sécurité du travail du Québec . Montreal, Quebec (Canada) . 978-2-550-40403-3 . 60 . 2 . DC 200-1635 2CORR . 10 June 2018 . fr . 22 August 2019 . https://web.archive.org/web/20190822135121/https://www.cnesst.gouv.qc.ca/publications/200/Pages/dc_200_1635.aspx . dead . ;

    online version: Web site: Jaime Lara, Mireille Vennes . Appareils de protection respiratoire . www.cnesst.gouv.qc.ca . Commission des normes, de l'equite, de la sante et de la securite du travail . 10 June 2018 . Quebec (Quebec, Canada) . fr . 2016 . 22 March 2021 . https://web.archive.org/web/20210322031624/https://reptox.cnesst.gouv.qc.ca/apruq/guide-reglementaire/Pages/000-table-des-matieres.aspx . dead .

  69. Web site: Jacques Lavoie, Maximilien Debia, Eve Neesham-Grenon, Genevieve Marchand, Yves Cloutier . A support tool for choosing respiratory protection against bioaerosols . www.irsst.qc.ca . Institut de recherche Robert-Sauve en sante et en securite du travail (IRSST) . 10 June 2018 . Montreal, Quebec (Canada) . 22 May 2015 . 7 May 2021 . https://web.archive.org/web/20210507040129/https://www.irsst.qc.ca/bioaerosol/Accueil.aspx?l=en . live . Publication no.: UT-024; Research Project: 0099-9230.
  70. Web site: Jacques Lavoie, Maximilien Debia, Eve Neesham-Grenon, Genevieve Marchand, Yves Cloutier . Un outil d'aide a la prise de decision pour choisir une protection respiratoire contre les bioaerosols . www.irsst.qc.ca . Institut de recherche Robert-Sauve en sante et en securite du travail (IRSST) . 10 June 2018 . Montreal, Quebec (Canada) . fr . 22 May 2015 . 7 May 2021 . https://web.archive.org/web/20210507040136/https://www.irsst.qc.ca/bioaerosol/Accueil.aspx?l=fr . live . N° de publication : UT-024; Projet de recherche: 0099-9230.
  71. Book: M. Gumon . Les appareils de protection respiratoire. Choix et utilisation . 2017 . Institut National de Recherche et de Securite (INRS) . Paris . 978-2-7389-2303-5 . 68 . 2 . ED 6106 . 10 June 2018 . fr . 7 May 2021 . https://web.archive.org/web/20210507040213/https://www.inrs.fr/media.html?refINRS=ED+6106 . live .
  72. Book: Spitzenverband der gewerblichen Berufsgenossenschaften und der Unfallversicherungsträger der öffentlichen Hand (DGUV) . BGR/GUV-R 190. Benutzung von Atemschutzgeräten . 2011 . Deutsche Gesetzliche Unfallversicherung e.V. (DGUV), Medienproduktion . Berlin . 174 . 10 June 2018 . de . 7 May 2021 . https://web.archive.org/web/20210507040141/https://publikationen.dguv.de/regelwerk/dguv-regeln/1011/benutzung-von-atemschutzgeraeten . live . PDF
  73. Book: The Health and Safety Executive . Respiratory protective equipment at work. A practical guide . 2013 . Crown . 978-0-71766-454-2 . 59 . 4 . HSG53 . 10 June 2018 . 9 August 2015 . https://web.archive.org/web/20150809032140/http://www.hse.gov.uk/pubns/books/hsg53.htm . live .
  74. Book: The UK Nuclear Industry Radiological Protection Coordination Group . Respiratory Protective Equipment . 2016 . IRPCG . London (UK) . 29 . Good Practice Guide . 10 June 2018 . 7 May 2021 . https://web.archive.org/web/20210507040136/https://www.nuclearinst.com/write/MediaUploads/SDF%20documents/IRPCG/RPE_Good_Practice_Guide_Issue_1.pdf . live .
  75. Book: The Health and Safety Authority . A Guide to Respiratory Protective Equipment . 2010 . HSA . Dublin (Ireland) . 978-1-84496-144-3 . 19 . HSA0362 . 10 June 2018 . 7 May 2021 . https://web.archive.org/web/20210507040143/https://www.hsa.ie/eng/Publications_and_Forms/Publications/Chemical_and_Hazardous_Substances/Respiratory_Protective_Equipment_.html . live . PDF
  76. Book: Occupational Safety and Health Service . A guide to respiratory protection . 1999 . NZ Department of Labour . Wellington (New Zealand) . 978-0-477-03625-2 . 51 . 8 . 10 June 2018 . 12 June 2018 . https://web.archive.org/web/20180612143214/https://worksafe.govt.nz/topic-and-industry/respiratory-protective-equipment/rpe-advice-for-workers/ . dead . PDF
  77. Book: Christian Albornoz, Hugo Cataldo . Guia para la seleccion y control de proteccion respiratoria . 2009 . Departamento de salud occupational, Instituto de Salud Publica de Chile . Santiago (Chile) . 40 . Guia tecnica . 10 June 2018 . es . 22 August 2019 . https://web.archive.org/web/20190822135111/http://www.ispch.cl/documento/13129/guia-de-seleccion-equipos-de-proteccion-respiratorias . dead . PDF
  78. Book: Instituto Nacional de Seguridad, Salud y Bienestar en el Trabajo (INSSBT) . Guia orientativa para la seleccion y utilizacion de protectores respiratorios . Instituto Nacional de Seguridad, Salud y Bienestar en el Trabajo (INSHT) . Madrid . 16 . Documentos tecnicos INSHT . 10 June 2018 . es . 24 April 2019 . https://web.archive.org/web/20190424044021/http://www.insht.es/portal/site/Epi/menuitem.0c9dc88588aacbc9a614c52a180311a0/?vgnextoid=7bfb791385e83310VgnVCM1000008130110aRCRD . live . PDF

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