Do N95 masks protect you from 95% of particles?

Short Answer:

An N95 mask will protect you from 95% or more non-oil based particles ONLY IF the mask fits you.

Long Answer:

In the USA, N95 masks are regulated by the National Institute for Occupational Health and Safety (NIOSH). NIOSH tests respiratory protection devices and assigns them a class based on the amount of filtration they provide from particles (95%, 99%, 100%) and the ability of the filter to reduce oil (N = not resistant to oil, R = partially resistant, P = oil proof). However, NIOSH is not guaranteeing that the face mask will fit you or any single individual. Each person has a unique face shape, which changes how masks fit. While one model of N95 mask might fit you, another model, even from the same manufacturer, might not fit. If the mask does not fit, it may not offer you high levels of protection. Without a proper fit, a NIOSH approved N95 mask might only protect you from a smaller percentage of particles - for example 50% rather than 95%.


Healthcare Design Group

Department of Engineering

Univeristy of Cambridge

© 2020