N95 masks have become one of the most coveted pieces of personal protective equipment (PPE) during the COVID-19 pandemic; however, the mechanism by which these masks capture particles has very little to do with the gaps between mask fibers (ie, the N95 doesn’t work like a strainer).
Instead, N95s filter large and small microscopic particles using a layer of fibers arranged to maximize the chance of contacting these particles. Weak, short-range electrostatic forces (Van der Waals) help these particles “stick” to fibers. Depending on the size of the particle, some are more likely to travel in straight lines (their inertial path) and others through Brownian motion (scattered, haphazard motion due to redirection from encountering air molecules).
But what about medium-sized microscopic particles? Electrostatic attraction due to an electric field present in the N95 helps create dipole-dipole interactions to capture these particles. In fact, the “95” in N95 refers to the percentage of medium-sized aerosolized particles that the mask effectively captures. This electric field is why N95s cannot simply be washed with soapy water or bleach.
Remember, the most important determinant of an N95’s performance is its seal on your face! Make sure you get fit-tested, shave those beards, etc.
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