What Are N95 Masks?
The N95 respirator is considered the gold standard of face coverings in the medical world, and even in the construction industry. These face coverings diverge from surgical masks in that the edges are designed to fit snugly to your face.
The U.S. Food and Drug Administration (FDA) defines N95 respirators as a "protective device designed to achieve a very close facial fit and very efficient filtration of airborne particles." The Centers for Disease Control and Prevention (CDC), however, still doesn't recommend the general public wear them. But that's only in order to reserve supplies for health care workers and medical first responders—not because the masks are ineffective.
How Do N95 Masks Work?
N95s filter out at least 95 percent of very small particles that are about 0.3 microns in size, according to the CDC. But this is the particle size for which the masks are least efficient. In fact, N95s are better at filtering out particles that are either larger or smaller than 0.3 microns.
These masks can filter about 99.8 percent of particles with a diameter of about 0.1 microns, according to a February 2017 study published in the Journal of Occupational and Environmental Hygiene. As an April 2020 review published in the journal eLife notes, SARS-CoV-2, the virus that causes COVID-19, is an enveloped virus with about a 0.1 micron diameter, so N95s are particularly suited to our current pandemic.
Why are N95s so efficient at filtering out the smaller particles?
It has something to do with "Brownian motion," or a phenomenon that causes particles smaller than 0.3 microns to move in a haphazard, zig-zagging motion. This makes it more likely for the particles to get caught inside the fibers of the N95. Plus, the masks use electrostatic absorption, which means that rather than passing through the fiber, the particles are trapped.
"Although these particles are smaller than the pores, they can be pulled over by the charged fibers and get stuck," Jiaxing Huang, a materials scientist at Northwestern University, told USA Today. "When the charges are dissipated during usage or storage, the capability of stopping virus-sized particles diminishes. This is the main reason of not recommending the reuse of N95 masks."
In an extensive review of various face masks published last September in the journal Science Advances, researchers from Duke University found N95 masks were most effective in filtering out particles. Those masks had a droplet transmission rate of less than 0.1 percent. However, this is with the caveat that N95s don't necessarily protect others around you.
"The performance of the valved N95 mask is likely affected by the exhalation valve, which opens for strong outwards airflow," the Duke scientists say. "While the valve does not compromise the protection of the wearer, it can decrease the protection of persons surrounding the wearer. In comparison, the performance of the fitted, non-valved N95 mask was far superior."
There are also various types of N95 respirators, so make sure the one you're using is rated for the performance you want. Some masks are defined as surgical, while others aren't. Some aren't fluid-resistant. All N95 masks should protect you from airborne particles, though, according to 3M, the manufacturer of most N95s in the U.S.
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