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N95 respirator

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An N95 respirator[1] is a filtering facepiece respirator or elastomeric filter that meets the U.S. National Institute for Occupational Safety and Health (NIOSH) N95 classification of air filtration, meaning that it filters at least 95% of airborne particles that have a mass median aerodynamic diameter of 0.3 micrometers[2] under 42 CFR Part 84, effective July 10, 1995.[3] This standard does not require that the respirator be resistant to oil; two other standards, R95 and P95, add that requirement. The N95 type is the most common filtering facepiece respirator.[4] It is an example of a mechanical filter respirator, which provides protection against particulates but not against gases or vapors.[5] An authentic N95 respirator is marked with the text "NIOSH" or the NIOSH logo, the filter class ("N95"), and, for most filtering facepiece respirators (respirators with non-replaceable filters), a "TC" approval number of the form 84A-####, the approval number. All N95 respirators, regardless of type, must be listed on the NIOSH Certified Equipment List (CEL)[6] or the NIOSH Trusted-Source page,[7] and it must have headbands instead of ear loops.[8]

Examples of N95 Respirators
A 3M 1860 filtering facepiece respirator with fluid resistance
Surgical N95 respirators for use in health care are both approved by NIOSH (as a respirator) and cleared by FDA (as a fluid resistant surgical mask)
Moldex Elastomeric Respirator with N95 filter circled
An elastomeric respirator with N95 filters installed. Note the lack of a TC number; TC numbers are absent on elastomeric respirators.
Thoroughly check the NIOSH Certified Equipment List, and compare the look and feel to known good respirators to verify that a suspect respirator is a NIOSH-approved N95.[9]

N95 respirators are considered similar to other respirators regulated under non-U.S. jurisdictions, but slightly different criteria are used to certify their performance, such as the filter efficiency, test agent and flow rate, and permissible pressure drop. For example, FFP2 respirators of the European Union are required to meet at least 94% filtration, and KN95 respirators of China are expected to meet at least 95% filtration.[10] However, NIOSH found that some products labeled "KN95" failed to meet these standards, some of them filtering out as little as one percent.[11] Both the U.S. Food and Drug Administration and Health Canada require such KN95 products failing to meet the filtration standards to be re-labeled as "face masks" instead of "respirators",[12][13] when being sold in the U.S. and Canada.

The N95 respirator is commonly made of a fine mesh of synthetic polymer fibers, specifically a nonwoven polypropylene fabric.[14] It is produced by melt blowing and forms the inner filtration layer that filters out hazardous particles.[15]

The N95 is a trademark of the United States Department of Health and Human Services. It is illegal in the United States to use the term "N95" without the approval of NIOSH.[9]


Early US Respirator Standards[edit]

A memorial for the workers of the Hawks Nest Tunnel who died of silicosis

Prior to the 1970s, respirator standards were under the purview of the US Bureau of Mines. 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.[16] 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.[17]

The Federal Coal Mine Health and Safety Act establishing MESA (later MSHA),[18] the Occupational Safety and Health Act of 1970, establishing NIOSH,[19] as well as other regulations established around the time, reshuffled regulatory authority for respirators, but nonetheless continued the use of USBM-era regulations.[17]

42 CFR Part 84[edit]

Respirator guidelines for TB were created by NIOSH as a result of the HIV/AIDS-induced outbreak in US hospitals (PDF)
An image of a the cover of the United States CFR. For Part 84, go to page 501.
N95 standard development is documented in the Federal Register, and the Code of Federal Regulations

TB Outbreak During the HIV Epidemic[edit]

While discussions for overhauling existing respirator regulations had been discussed since the late 1980s,[20] in 1992, the multidrug-resistant tuberculosis task force within the CDC was tasked with reducing the incidences of hospital acquired TB infections. TB infections had traditionally occurred mainly in underserved groups and areas, as well as the very young and elderly, but regardless, usually had around a 10% chance of turning into an active TB infection in a given person's lifetime. However, HIV/AIDS, (where the outbreak in the US was in full force at the time) was noted to be one of the strongest factors for TB activation, since most TB outbreaks and mortalities reported at the time involved healthcare workers and patients infected with HIV. Respiratory protection and the performance of respirators were emphasized in the 1994 guidelines to controlling TB, which, at the time, were limited to respirators equipped with HEPA filters.[a][21]

To quickly address the HEPA-only[a] respirator requirement for TB controls, stemming from the lack of biological protection in the existing 30 CFR Part 11 standards (which were mainly designed for miners), NIOSH aimed to have the proposed 42 CFR rule changes finished by the end of 1994. The proposal at the time would drop the HEPA classification for non-powered respirators, and add three respirator types, at the time called Type A, B and C, with filtration efficiencies of greater than or equal to 99.97%, 99%, and 95% respectively,[20] with Type C corresponding to the current N95 standard.

According to NIOSH, all the new respirator types proposed in 42 CFR Part 84, including Type C (later N95), would meet the CDC's requirement for protection against TB, and would provide avenues for cheaper NIOSH-approved respirators without the need for HEPA[a] or NIOSH class-100 filters.[20]

After the passage of 42 CFR 84, a 1999 NIOSH guide for health care administrators noted that respirators selected for TB prevention under 42 CFR would likely be N95 respirators.[22]

Approval of Part 84 and Replacement of 30 CFR 11[edit]

Historically, respirators in the US had generally been approved by MESA/MSHA/NIOSH under federal regulation 30 CFR Part 11. On July 10, 1995, in response to respirators exhibiting "low initial efficiency levels," new 42 CFR Part 84 standards, including the N95 standard, were enforced under a three-year transition period,[3] ending on July 1, 1998. The standard for N95 respirators includes, but is not limited to, a filtration of at least 95% under a 200 milligram test load of sodium chloride. Standards and specifications are also subject to change.[23]

Once 42 CFR Part 84 was in effect, MSHA, under a proposed rule change to 30 CFR 11, 70, and 71, would withdraw from the approval process of rated respirators (outside of respirators used for mining).[20]


When mandated by United States employers[edit]

Infographic on three key factors required for a respirator to be effective
For men, certain beards can worsen fit.
Guidance for performing a user seal check, which is required every time a respirator is put on

Fit testing is a critical component to a respiratory protection program whenever workers use tight-fitting respirators. OSHA (US) requires an initial respirator fit test to identify the right model, style, and size respirator for each worker; as well, as annual fit tests. Additionally, tight-fitting respirators, including the N95, require a user seal check each time one is put on. Facial hair at the sealing area of the respirator will cause it to leak.[24]

Before use of a respirator can be mandated by an employer, OSHA regulations require a medical evaluation.[25] In the United States medical evaluation is required once, prior to initial fit testing and use, although it may need to be repeated if any adverse signs or symptoms are observed.[26] Correct use of the respirator decreases the chances of airborne contamination by viruses.[27]

For persons who are medically disqualified from negative-pressure respirators, or who cannot pass a fit test due to facial hair or other reasons, a powered air-purifying respirator is a possible alternative.[28][29]

In industry[edit]

N95 respirators are also designed for industrial use in sectors such as mining and construction.[30] They have also been shown to be effective as protection against engineered nanoparticles.[31]: 12–14 [32][33]

According to the NIOSH Respirator Selection Logic, respirators with filters in the N, R, and P series are recommended for concentrations of hazardous particulates 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.[34][35]

N series respirators, including the N95 respirator, are only effective in the absence of oil particles, such as lubricants, cutting fluids, or glycerine. For substances hazardous to the eyes, a respirator equipped with a full facepiece, helmet, or hood is recommended. They 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. They are not effective against hazardous gases or vapors, for which a cartridge respirator is recommended.[35]

In industrial settings where infectious disease exposure is not a concern, users can wear and reuse a filtering facepiece respirator until it is damaged, soiled, or causing noticeably increased breathing resistance, unless there is a manufacturer-specified duration of use. However, in laboratories at biosafety level 2 and higher, respirators are recommended to be discarded as hazardous waste after a single use.[36]

Some industrial N95 series respirators have an exhaust valve to improve comfort, making exhalation easier, reducing leakage on exhalation and steaming-up of glasses. Research has indicated that wearing a valved N95 respirator does provide some source control to prevent the spread of diseases like COVID-19 when worn by asymptomatic infected users, at a level similar to that of a surgical or cloth facemask, although it is not equivalent to the performance of unvalved respirators. [37] The same study found that "[m]odifications [such as the use of an electrocardiogram pad or surgical tape secured over the valve from the inside of the FFR] [...] can further reduce particle emissions."[37]

In healthcare[edit]

A U.S. Navy sailor wearing a surgical N95 respirator

Respirators used in healthcare are traditionally a specific variant called a surgical respirator, which is both approved by NIOSH as a respirator and cleared by the Food and Drug Administration as a medical device similar to a surgical mask.[38] These may also be labeled "Surgical N95", "medical respirators", or "healthcare respirators".[39] The difference lies in the extra fluid-resistant layer outside, typically colored blue.[40]

In the United States, the Occupational Safety and Health Administration (OSHA) requires healthcare workers who are expected to perform patient activities with those suspected or confirmed to be infected with COVID-19 to wear respiratory protection, such as an N95 respirator.[24] The CDC recommends the use of respirators with at least N95 certification to protect the wearer from inhalation of infectious particles including Mycobacterium tuberculosis, avian influenza, severe acute respiratory syndrome (SARS), pandemic influenza, and Ebola.[41]

Unlike a respirator, a surgical mask is designed to provide barrier protection against droplets and does not have an air-tight seal and thus does not protect its wearer against airborne particles such as virus material to the same extent.[24]

Use during shortages[edit]

During crisis situations where there is a shortage of N95 respirators, such as the COVID-19 pandemic, the U.S. Centers for Disease Control and Prevention (CDC) has recommended strategies for optimizing their use in healthcare settings.[42] N95 respirators can be used beyond their manufacturer-designated shelf life, although components such as the straps and nose bridge material may degrade, making it particularly important that the wearer perform the expected seal check.[42][43] N95 respirators can be reused a limited number of times after being removed, as long as they have not been used during aerosol-generating procedures and are not contaminated with patients' bodily fluids, because this increases the risk of surface contamination with pathogens. The respirator manufacturer may recommend a maximum number of donnings or uses; if no manufacturer guidance is available, preliminary data suggests limiting to five uses per device.[42][44] Respirators approved under standards used in other countries and are similar to NIOSH-approved N95 respirators—including FFP2 and FFP3 respirators regulated by the European Union—can be used.[42]

According to NIOSH, respirators may still be used in crisis situations if standard respirator fit testing is not available, as a respirator will still provide better protection than a surgical mask or no mask. In this case, best practices for getting a good face seal include trying different models or sizes, using a mirror or asking a colleague to check that the respirator is touching the face, and doing multiple user seal checks.[24]

Given that the global supply of personal protective equipment (PPE) may be insufficient during a pandemic, in 2020, the World Health Organization recommended minimizing the need for PPE through telemedicine; physical barriers such as clear windows; allowing only those involved in direct care to enter a room with a COVID-19 patient; using only the PPE necessary for the specific task; continuing use of the same respirator without removing it while caring for multiple patients with the same diagnosis; monitoring and coordinating the PPE supply chain; and discouraging the use of masks for asymptomatic individuals.[45]

When it is no longer possible for all healthcare workers to wear N95 respirators when caring for a COVID-19 patient, CDC recommends that respirators be prioritized for workers performing aerosol-generating procedures on symptomatic persons, and those within three feet of an unmasked symptomatic person. Under these conditions, masking of symptomatic patients with at least a surgical mask and maintaining distance from the patient are particularly important to reduce the risk of transmission. When no respirators are left, workers who are at higher risk for severe illness may be excluded from caring for patients, and workers who have clinically recovered from COVID-19 may be preferred to care for patients. Portable fans with HEPA filters may also be used to increase ventilation in isolation rooms when surgical masks are being used in place of respirators. A high-quality HEPA filter can trap 99.97% of dust particles that are 0.3 microns in diameter.[46] If neither respirators nor surgical masks are available, as a last resort, it may be necessary for healthcare workers to use masks that have never been evaluated or approved by NIOSH or homemade masks, such as cloth face masks, although caution should be exercised when considering this option.[42]


Disposable filtering facepiece respirators such as N95 respirators are not approved for routine decontamination and reuse as standard of care. However, their decontamination and reuse may need to be considered as a crisis capacity strategy to ensure continued availability.[47][48]

There have been efforts to evaluate cleaning methods for respirators in emergency shortages, although there is concern that this may reduce filter performance, or affect mask fit by deforming the mask.[49][50][51] Duke University researchers have published a method for cleaning N95 respirators without damaging them using vaporized hydrogen peroxide to allow reuse for a limited number of times.[52][53][54] Battelle received an Emergency Use Authorization from the U.S. Food and Drug Administration for its technology used to sterilize N95 respirators.[55][56]

OSHA does not currently have any standards for disinfecting N95 respirators.[50] NIOSH recommends that during shortages N95 respirators may be used up to five times without cleaning them, as long as aerosol-generating procedures are not performed, and respirators are not contaminated with patients' bodily fluids. Contamination can be reduced by wearing a cleanable face shield over an N95 respirator, as well as using clean gloves when donning and seal-checking a used N95 respirator and discarding the gloves immediately after.[44] According to CDC, ultraviolet germicidal irradiation, vaporous hydrogen peroxide and moist heat showed the most promise as potential methods to decontaminate N95 respirators and other filtering facepiece respirators.[47]

Contrast with surgical mask[edit]

A table listing the attributes of surgical masks and N95 respirators in eight categories
An infographic on the difference between surgical masks and N95 respirators

A surgical mask is a loose-fitting, disposable device that creates a physical barrier between the mouth and nose of the wearer and potential contaminants in the immediate environment. If worn properly, a surgical mask is meant to help block large-particle droplets, splashes, sprays, or splatter that may contain viruses and bacteria. Surgical masks may also help reduce exposure of the wearer's saliva and respiratory secretions to others.[57]

A surgical mask, by design, does not filter or block very small (aerosolized) particles in the air that may be transmitted by coughs, sneezes, talking loudly, singing, or certain medical procedures. Surgical masks also do not provide complete protection from germs and other contaminants because of the loose fit between the surface of the face mask and the face.[57] Collection efficiency of surgical mask filters can range from less than 10% to nearly 90% for different manufacturers’ masks when measured using the test parameters for NIOSH certification. However, a study found that even for surgical masks with "good" filters, 80–100% of subjects failed an OSHA-accepted qualitative fit test, and a quantitative test showed 12–25% leakage.[58]

A CDC study found that in indoor public settings, always wearing a respirator was associated with an 83% lower likelihood of testing positive for SARS-CoV-2 (Covid-19), as compared to a 66% reduction when using surgical masks and 56% for cloth.[59]

History During Pandemics[edit]

HIV/AIDS and Tuberculosis Epidemic[edit]

Under a rule proposed by OSHA, this sign would be paired with the words No Admittance Without Wearing a Type N95 or More Protective Respirator near where TB is present[60]

While NIOSH was busy finishing 42 CFR 84 respirator regulations (including the N95), other agencies and groups were advocating for new standards for the prevention of TB. In 1992, the Labor Coalition to Fight TB in the Workplace started lobbying OSHA to create advisories and formal rules to protect workers from TB. The group was especially concerned about the rise of multidrug-resistant tuberculosis, which would require more rigorous standards to mitigate, especially since they felt that the 1990 CDC guidelines for TB were not being properly followed. The CDC eventually revised and released new TB guidelines in 1994, and in 1995 and 1996, meetings started to be held between OSHA and various stakeholders for a new TB standard, borrowing heavily from the CDC's work.[61][60]

In 1997, OSHA proposed new rule changes for industries affected by the spread of tuberculosis, like hospitals, where many patients infected with TB were also infected with HIV. The proposed rule would require signage that includes a STOP sign, with red background, white symbols, and a set of words warning people to wear "N95 or more protective" respirators (under 42 CFR 84) near isolation rooms where TB infection is likely. Additional notices could be added at the discretion of an employer, so long as it did not contradict the required wording.[60]

OSHA withdrew the proposal in 2003, owing to commenters and reviewers pointing to a likely overstating of risk, declining rates of TB in the years following the proposal, as well as compliance without a rule by OSHA.[62]

SARS Pandemic[edit]

A lab worker wearing an N95 respirator during the SARS outbreak

In 2003, in response to the SARS outbreak, the United States CDC advised healthcare workers to wear N95 respirators.[63] Despite this advice, a patient who had traveled from Ontario exposed six healthcare workers in Pennsylvania following contact tracing by the CDC, though fitted N95 respirators were worn at a hospital upon suspicion of SARS.[64]

Following the SARS outbreak in the US, US Senate hearings started to be held proposing the Strategic National Stockpile start stocking PPE and N95 respirators in the event of another SARS outbreak. It was noted at the time that there were few N95 respirator manufacturers, potentially exacerbating a shortage in a crisis.[65]

Meanwhile, in Canada, discussions with Ontario EMS and New York Department of Health in 2004 noted that infected emergency medical personnel failed to properly use N95 respirators.[66] According to Ontario SARS commission final report, this was likely due to confusion over infectious disease control, confusion over respirator procedures, and the insinuation by various infection control practitioners that N95 respirators were not necessary. However, the report concludes, from laws preceding SARS, healthcare workers were obligated to wear N95 respirators throughout the outbreak, despite suggestions to the contrary.[67]

Ultimately, a paper published in the New England Journal of Medicine concluded that universal use of N95 respirators, as well as additional infection control measures, ended the SARS outbreak in Ontario.[68]

2007 CDC/HICPAC Infection Control Guidelines[edit]

In 2007, HICPAC published an updated set of guidelines for precautions to be taken in healthcare facilities, called the 2007 Guideline for Isolation Precautions: Preventing Transmission of Infectious Agents in Healthcare Settings, which includes "barrier precautions", "standard precautions", and "airborne precautions". "Airborne precautions" cover "infectious agents" like tuberculosis and SARS-CoV, which mandate the use of N95 respirators.[69]

H1N1 Swine Flu Pandemic[edit]

In May of 2009, in response to the H1N1 swine flu outbreak, the CDC authorized the release of N95 respirators from the Strategic National Stockpile, and the waiving of certain quality controls on certain models of newly manufactured N95 respirators, provided they were documented "for use during the swine flu emergency".[70] Initially, the CDC's interim guide for H1N1 recommended N95 respirators for the prevention of H1N1, but stopped short of recommending respirators for groups not deemed "at increased risk of severe illness from influenza", except for occupational use in healthcare.[71] NIOSH also emphasized the differences in fit between an N95 respirator and a surgical mask for prevention against the flu.[72] For those in the general public wishing to wear N95 respirators, properly wearing a N95 was noted to be difficult, but the tendency for people to distance themselves from those wearing masks complimented the six-foot social distancing rules at the time.[73]

H1N1 Respirator/Mask Randomized Control Trials[edit]

Around the time of the H1N1 pandemic, randomized control trial studies of masks started being done, comparing surgical masks and N95 respirators with the tendency for medical staff to be infected by the flu. One paper concluded that N95s were better than surgical masks, but its results were later called into question.[74] Another paper found that protection provided by an N95 respirator compared similarly to a surgical mask, but the study did not control health care personnel potentially being exposed outside, without respirators, via the community.[75]

After the 2009 H1N1 flu season, the CDC issued guidelines recommending surgical masks instead, after complaints were leveled by various groups on the effectiveness of surgical masks compared to N95 respirators, along with complaints about comfort. The new recommendations were met with approval by groups like the Society for Healthcare Epidemiology of America.[76]

COVID-19 Pandemic[edit]

A Hospital Corpsman wearing a Surgical N95 during the initial months of the COVID-19 pandemic

During the COVID-19 pandemic, the mask and respirator market rapidly grew, along with counterfeit respirators.[77] NIOSH, on behalf of the Department of Health and Human Services, filed a trademark application on June 17, 2020 for various 42 CFR 84 trademarks, including the N95, allowing NIOSH to enforce rules on counterfeit masks outside of rules defined in 42 CFR 84.[78][8] The trademarks were registered in 2022.[79]

Global shortages during the COVID-19 pandemic[edit]

The Strategic National Stockpile had not been refilled following the H1N1 pandemic,[80] and by April of 2020, Department of Homeland Security officials reported that the supply of respirators and other PPE in the stockpile was nearly gone.[81] Respirators came to be in short supply and high demand during the COVID-19 pandemic, causing price gouging and hoarding, often leading to confiscation of masks.[82][83][84] Production of N95 respirators was limited due to constraints on the supply of nonwoven polypropylene fabric as well as the cessation of exports from China.[14][85]

Also in early April 2020, the United States federal government, invoking the DPA, ordered 3M to stop exporting N95 respirators to customers in Canada and Latin America, and to keep them within the U.S. instead. However, 3M refused, saying: "Ceasing all export of respirators produced in the United States would likely cause other countries to retaliate and do the same, as some have already done. If that were to occur, the net number of respirators being made available to the United States would actually decrease. That is the opposite of what we and the administration, on behalf of the American people, both seek."[86]

Dropping of Mask Mandates in Hospitals[edit]

By 2023, HICPAC noted that the Public Health Emergency in the United States had ended since May. Since medical centers have updated their policies,[87] concerns have about the CDC's lack of guidance with regards to what to do during times of high viral activity. Both changes have raised concerns that patients could be infected while visiting a hospital.[88] This can be especially risky for vulnerable visitors, like cancer patients, where an increase in deaths have been noted during Omicron waves.[89][90]

A continuing concern among hospitals, and some hospital staff, is the political controversy surrounding masks during the COVID-19 pandemic. Despite this, National Nurses United petitioned the CDC to mandate N95 respirators when updating the CDC/HICPAC's 2007 infection-control guidelines.[88]

Criticism of N95 RCTs and Other Controversial Studies[edit]

Following previous H1N1 randomized control trials comparing N95s and surgical masks, new RCTs were published. Major flaws were noted, including contraction of virus outside hospital, the lack of controls over time in hospital, and assumptions made about transmission via droplets instead of aerosols.[91]

In addition, in 2024, a paper published in the American Society for Microbiology Clinical Microbiology Reviews noted the harms of continued undue weight being placed on RCTs and other similarly flawed mask studies in a social and political context, as retracted papers continue to be circulated to justify certain masking behaviors and beliefs. One retracted JAMA paper[92] garnered a million views, while another retracted paper in Frontiers Public Health[93] continues to circulate across social media.[94]

H5N1 Outbreak[edit]

Among Dairy Workers[edit]

The CDC recommends farm workers wear PPE, including N95 or better respirators, when working with farm animals potentially infected with H5N1.[95][96] However, outbreaks of H5N1 have continued among dairy workers, likely due to workers' fear of retaliation by their employers, and reluctance by employers and state officials to allow CDC investigators into dairy farms.[97]

Selected patents[edit]

An image of two N95 Kimberly-Clark duckbill respirators.
The patent to this 'Duckbill' style respirator was assigned to Kimberly-Clark in the US until expiry in 2015.
  • US patent 3333585, Robert J Barghini, Walter M Westberg, Patrick H Carey Jr, "Cold weather face mask", published 1967-08-01, issued 1967-08-01, assigned to 3M Co 
  • US patent 3971373A, David L. Braun, "Particle-loaded microfiber sheet product and respirators made therefrom", published 1976-07-27, issued 1976-07-27, assigned to 3M Co 
  • US patent 4215682A, Donald A. Kubik & Charles I. Davis, "Melt-blown fibrous electrets", published 1980-08-05, issued 1980-08-05, assigned to 3M Co 
  • US patent 4536440A, Harvey J. Berg, "Molded fibrous filtration products", published 1985-08-20, issued 1985-08-20, assigned to 3M Co 
  • US patent 4807619, James F. Dyrud, Harvey J. Berg, Alice C. Murray, "Resilient shape-retaining fibrous filtration face mask", published 1989-02-28, issued 1989-02-28, assigned to 3M Co 
  • US patent 4850347, Martin R. Skov, "Face mask", published 1989-07-25, issued 1989-07-25, assigned to Moldex Metric Inc 
  • US patent 4856509, Jerome H. Lemelson, "Face mask and method", published 1989-08-15, issued 1989-08-15 
  • US patent 5307796A, Joseph P. Kronzer, Roger J. Stumo, James F. Dyrud, Harvey J. Berg, "Methods of forming fibrous filtration face masks", published 1994-05-03, issued 1994-05-03, assigned to 3M Co 
  • US patent 3985132A, Elvin L. Boyce & William Keith Robinson, "Filter mask", published 1976-10-12, issued 1976-10-12, assigned to Kimberly-Clark Worldwide Inc. and Alpha Pro Tech Inc.  Marketed by AlphaProTech as 'Magic Arch.'
  • US patent 4688566A, Elvin L. Boyce, "Filter mask", published 1987-04-25, issued 1987-04-25, assigned to Alpha Pro Tech Inc. 

'Duckbill' style[edit]

  • US patent 5322061A, Kevin K. Brunson, "Disposable Aerosol Mask", published 1994-06-21, issued 1998-06-02, assigned to Kimberly-Clark Worldwide Inc. 
  • US patent 5694925A, "Face mask with enhanced seal and method", published 1997-12-09, issued 1997-12-09, assigned to Kimberly-Clark Worldwide Inc. 

See also[edit]


  1. ^ a b c This refers to the MSHA's definition of 'HEPA' under 30 CFR Part 11 for respirators, which is 99.97% filtration of 0.3 micron DOP, not the EN 1822 or ISO 29463 definition of HEPA.


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  4. ^ "NIOSH-Approved N95 Particulate Filtering Facepiece Respirators - A Suppliers List". U.S. National Institute for Occupational Safety and Health. March 19, 2020. Retrieved March 27, 2020.
  5. ^ "Respirator Trusted-Source: Selection FAQs". U.S. National Institute for Occupational Safety and Health. March 12, 2020. Retrieved March 28, 2020.
  6. ^ "Certified Equipment List | NPPTL | NIOSH | CDC". www.cdc.gov. June 4, 2020.
  7. ^ "Respirator Trusted-Source Information | NPPTL | NIOSH | CDC". www.cdc.gov. August 3, 2020.
  8. ^ a b "Counterfeit Respirators / Misrepresentation of NIOSH-Approval". NIOSH, Centers of Disease Control and Prevention. Retrieved October 27, 2020.
  9. ^ a b "Counterfeit Respirators / Misrepresentation of NIOSH Approval". May 23, 2024.
  10. ^ "Comparison of FFP2, KN95, and N95 and Other Filtering Facepiece Respirator Classes" (PDF). 3M Technical Data Bulletin. January 1, 2020. Retrieved March 28, 2020.
  11. ^ "Health Canada issues recall of some KN95 masks made in China". Canadian Broadcasting Corporation. Retrieved October 25, 2020.
  12. ^ "Certain Filtering Facepiece Respirators from China May Not Provide Adequate Respiratory Protection - Letter to Health Care Providers". U.S. Food and Drug Administration. Retrieved October 25, 2020.
  13. ^ "Important safety information for certain respirator masks". Health Canada. Retrieved October 25, 2020.
  14. ^ a b Xie, John (March 19, 2020). "World Depends on China for Face Masks But Can Country Deliver?". Voice of America.
  15. ^ Feng, Emily (March 16, 2020). "COVID-19 Has Caused A Shortage Of Face Masks. But They're Surprisingly Hard To Make". Goats and Soda. NPR.
  16. ^ Howard W., Spencer. "The Historic and Cultural Importance of the HAWKS NEST TUNNEL DISASTER" (PDF). American Society of Safety Professionals.
  17. ^ a b Spelce, David; Rehak, Timothy R; Meltzer, Richard W; Johnson, James S (2019). "History of U.S. Respirator Approval (Continued) Particulate Respirators". J Int Soc Respir Prot. 36 (2): 37–55. PMC 7307331. PMID 32572305.
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