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May 16, 2020
An N95 mask or N95 respirator is a particulate-filtering facepiece respirator that meets the N95 standard of the U.S. National Institute for Occupational Safety and Health (NIOSH) air filtration rating, meaning that it filters at least 95% of airborne particles, while not resistant to oil like the P95. It is the most common particulate-filtering facepiece respirator. This kind of respirator protects against particulates, but not gases or vapors.
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.
The N95 mask requires a fine mesh of synthetic polymer fibers, also known as nonwoven polypropylene fabric, which is produced through a highly specialized process called melt blowing that forms the inner filtration layer that filters out hazardous particles.
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. Unlike a respirator, a surgical mask does not have an air-tight seal and thus does not protect its wearer against airborne particles such as virus material.
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 N95s, require a user seal check each time one is put on.
Use during shortages
Under serious outbreak conditions in which respirator supplies are severely limited, workers should work with their employer to choose the respirator that fits best, as, even without fit testing, a respirator will provide better protection than a surgical mask or no mask. In this case, best practices include trying different models or sizes to get a good face seal, checking manufacturer training videos and literature on proper donning and doffing, doing a user seal check several times, and checking the fit in a mirror or asking a colleague to look to be sure the respirator is touching the face.
During crisis situations where there is a shortage of N95 respirators, such as the 2019–20 coronavirus pandemic, the U.S. Centers for Disease Control and Prevention (CDC) has recommended strategies for optimizing their use in healthcare settings. N95 respirators can be used beyond their manufacturer-designated shelf life, although components such as the straps and nose bridge material may degrade, which can affect the quality of the fit and seal, making it particularly important that the wearer perform the expected seal check. 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. 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 to ensure an adequate safety margin.
When it is no longer possible for all healthcare workers to wear N95 respirators when caring for a COVID-19 patient, respirators should 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 facemasks, though caution should be exercised when considering this option.
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.
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. 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. Battelle received an Emergency Use Authorization from the U.S. Food and Drug Administration to sterilize N95 masks. OSHA does not currently have any standards for disinfecting N95 masks. 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.