An N95 mask is a respirator that has been certified by the U.S. National Institute for Occupational Safety and Health (NIOSH) to achieve a filtration efficiency of at least 95% against non‑oil‑based particulates.
The N95 respirator is one of nine types of particulate‑filtering respirators certified by NIOSH (the National Institute for Occupational Safety and Health). The “N” designation indicates that the mask is intended to protect against non‑oil‑based particles, such as viruses, bacteria, and dust; the “95” rating means that, under the test conditions specified by the standard, the mask achieves a filtration efficiency of at least 95%. N95 respirators provide effective protection against airborne particulates.
Why can N95 masks be worn during the novel coronavirus pandemic?
1. The novel coronavirus requires a host to spread; once it leaves the body of its host—whether an animal or a human—it will die within a short period. However, the virus can be transmitted through contact—for example, via contaminated hands—and through respiratory droplets. Among these, droplets produced when coughing, speaking, or sneezing are the primary means of transmission. If a person carrying the novel coronavirus sneezes in a confined space—such as a train or an airplane—the expelled droplets can easily be inhaled by another individual, leading to potential infection. Therefore, wearing a mask is essential for protection.
2. Since viruses and their transmission vectors (droplets) also exist in particulate form, and their particle diameters are relatively small, the filtration mechanism of an N95 mask relies on its high-performance filter material to capture these fine particles. The standard test method uses particles with an aerodynamic diameter of 0.3 micrometers—this size represents the most challenging particle diameter to filter, based on known normal distributions. In addition, N95 masks must meet stringent requirements for facial fit. Therefore, when worn correctly, an N95 mask can reduce exposure to airborne pathogenic microorganisms and effectively prevent viral entry through the respiratory tract. However, wearers should also take precautions to protect their hands, eyes, and other body parts to avoid infection via alternative routes.
How often should an N95‑rated mask be replaced?
Under normal circumstances, when used outdoors—in public places such as subways, buses, supermarkets, and shopping malls—N95‑level masks should be replaced every 4 to 6 hours. However, in areas affected by the novel coronavirus outbreak, it is recommended to replace N95‑level masks every 2 hours.
