N95 mask

An N95 mask or N95 respirator is a particulate-filtering facepiece respirator 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. This standard does not require that the respirator be resistant to oil; another standard, P95, adds that requirement. The N95 type is the most common particulate-filtering facepiece respirator.[1] It is an example of a mechanical filter respirator, which provides protection against particulates but not against gases or vapors.[2]

An N95 mask for industrial use
Surgical N95 respirators for use in health care are both approved by NIOSH and cleared by FDA

N95 respirators are considered functionally equivalent to certain respirators regulated under non-U.S. jurisdictions, such as FFP2 respirators of the European Union and KN95 respirators of China. However, slightly different criteria are used to certify their performance, such as the filter efficiency, test agent and flow rate, and permissible pressure drop.[3][4]

The N95 mask requires a fine mesh of synthetic polymer fibers, specifically a nonwoven polypropylene fabric.[5] It is produced by melt blowing and forms the inner filtration layer that filters out hazardous particles.[6]

Use
Infographic on three key factors required for a respirator to be effective – click to enlarge
Guidance for performing a user seal check, which is required every time a respirator is put on – click to enlarge

Fit testing is a critical component to a respiratory protection program whenever workers use tight-fitting respirators. OSHA 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.[7]

Respirators require a medical evaluation before use because they can make breathing more difficult. Some conditions that could prevent respirator use include heart conditions, lung disease, and psychological conditions such as claustrophobia.[8] 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.[9]

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.[10][11]

In industry

N95 respirators were originally designed for industrial use in sectors such as mining, construction, and painting.[12] They have also been shown to be effective as protection against engineered nanoparticles.[13]:12–14[14][15]

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.[16]

N series respirators, including the N95 mask, 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.[16]

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.[17]

Some industrial N95 series respirators have an exhaust valve to improve comfort, making exhalation easier, reducing leakage on exhalation and steaming-up of glasses. Such respirators are not suitable for source control of disease, such as COVID-19, when worn by asymptomatic, but possibly infected users, even if excess N95 respirators are available when healthcare needs are met. [18]

In healthcare
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.[19] These may also be labeled "Surgical N95", "medical respirators", or "healthcare respirators".[20][21] As part of the Families First Coronavirus Response Act, changes were made to liability and certification laws to allow industrial respirators to be used in healthcare settings, in response to shortages of respirators during the COVID-19 pandemic.[22]

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.[7] 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.[23]

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.[7]

Use during shortages

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.[4] 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.[4][24] 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, although 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.[4][25] Respirators can be used that are approved under standards used in other countries that are similar to NIOSH-approved N95 respirators, including FFP2 and FFP3 respirators regulated by the European Union.[4]

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.[7]

Given that the global supply of personal protective equipment (PPE) is insufficient during the pandemic, the World Health Organization recommends 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.[26]

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 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. 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.[4]

Decontamination

Disposable filtering facepiece respirators such as N95 masks 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.[27]

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.[28][29][30] 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.[31][32][33] Battelle received an Emergency Use Authorization from the U.S. Food and Drug Administration to sterilize N95 masks.[34][35]

OSHA does not currently have any standards for disinfecting N95 masks.[29] 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.[25] According to CDC, ultraviolet germicidal irradiation, vaporous hydrogen peroxide, and moist heat showed the most promise as potential methods to decontaminate N95 masks and other filtering facepiece respirators.[27]

Contrast with surgical mask
An infographic on the difference between surgical masks and N95 respirators – click to enlarge

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.[36]

A surgical mask, by design, does not filter or block very small particles in the air that may be transmitted by coughs, sneezes, 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.[36] 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.[37]

The U.S. Centers for Disease Control and Prevention recommends surgical masks in procedures where there can be an aerosol generation from the wearer, if small aerosols can produce a disease to the patient.[38]

History

N95 facemasks have several historical predecessors. One was a design for a cloth facemask by Lien-teh Wu, who was working for the Chinese Imperial Court in the fall of 1910 during the Manchurian plague outbreak.[39] It was the first that protected users from bacteria in empirical testing, and inspired masks used during the 1918 flu pandemic.[40] Another predecessor was gas masks developed during World War I, which were adapted for use by miners. They were reusable but bulky and uncomfortable due to their fiberglass filters and heavy rubber construction.[12][40]

In the 1970s, the Bureau of Mines and NIOSH developed standards for single-use respirators, and the first N95 respirator was developed by 3M and approved in 1972.[40] 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.[41]

Originally designed for industrial use; N95 masks became a healthcare standard subsequent to virus-blocking technology invented by University of Tennessee professor Peter Tsai,[42][43] and patented in 1995.[44] The anti-viral technology was first developed to prevent the spread of drug-resistant tuberculosis.[12][40] Following the onset of the COVID-19 pandemic, Tsai ended his retirement to help alleviate shortages related to the COVID-19 pandemic, by researching N95 mask decontamination.[42]

Many American companies stopped producing N95 masks in the 2000s due to litigation costs and foreign competition.[45]

COVID-19 pandemic
Main article: Face masks during the COVID-19 pandemic § N95 and FFP masks

On January 24th, Taiwan announced that it was imposing a temporary ban on the export of masks.[46] The masks 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.[47][48][49][50] Production of N95 masks was limited due to constraints on the supply of nonwoven polypropylene fabric (which is used as the primary filter) as well as the cessation of exports from China.[5][51] China controls 50% of global production of masks, and facing its own coronavirus epidemic, dedicated all its production for domestic use, only allowing exports through government-allocated humanitarian assistance.[5]

In Canada, the Quebec company AMD Medicom began making masks in 1997 through an agreement with United Medical Enterprises in Atlanta, Georgia. Medicom added factories in Shanghai in 2002, Yilan Taiwan in 2010 and France in 2011.[52] As the pandemic escalated, China, France and Taiwan either prohibited the export of masks, or requisitioned Medicom's output for local use.[53] The federal government of Canada came to an agreement with Medicom to buy millions of masks over the next ten years, leading to Medicom announcing plans to open a new factory in Montreal. Novo Textiles in British Columbia quickly acquired a surgical mask making machine, and announced plans to acquire an N95 making machine as well.[54]

In March 2020, President Donald Trump applied the Defense Production Act against the American company 3M that allows the Federal Emergency Management Agency to obtain as many N95 respirators as it needs from 3M.[55][56] In early April 2020, Berlin politician Andreas Geisel alleged that a shipment of 200,000 N95 masks that it had ordered from American producer 3M's China facility were intercepted in Bangkok and diverted to the United States. Berlin police president Barbara Slowik stated that she believed "this is related to the US government's export ban."[57] However, Berlin police later corrected themselves and confirmed that the shipment was not seized by U.S. authorities, but was said to have simply been bought at a better price, widely believed to be from a German dealer or China.[58][59]

Selected patents
  • 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

See also

References
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