Federal agencies Workplace exposures Respiratory protection Health Care Workers

OSHA updates FAQs to address particle sizes and N95s

Photo: Centers for Disease Control and Prevention

Washington — In an effort to dispel “incorrect claims” about the efficacy of N95 respirators to protect wearers against COVID-19 infection, OSHA has added a section on respirators and particle size to its series of answers to frequently asked questions on protecting workers from exposure to the coronavirus.

In an Oct. 19 press release, the agency states that it’s aware of the claims that N95 respirators don’t “capture particles as small as” SARS-CoV-2 – the coronavirus that causes COVID-19.

The “N95” classification means respirator filters remove at least 95% of “very small” particles (around 0.3 microns in diameter) from the air, OSHA explains, adding that some people have claimed incorrectly that the virus is about 0.1 microns in size. Further, when the virus becomes airborne via an infected person talking, coughing or sneezing, those particles contain more than the virus – they also include water or mucus. Those larger particles are too big to pass through an N95 respirator filter, while electrostatic charge attracts the particles to the fibers in the filter.

“In addition, the smallest particles constantly move around (called Brownian motion), and are very likely to hit a filter fiber and stick to it,” the agency states.

OSHA also explains why NIOSH uses 0.3-micron diameter as a standard and states that an N95 respirator is “more effective at filtering particles that are smaller or larger than 0.3 microns in size.”


The agency continues: “The N95 respirator filter, as is true for other NIOSH-approved respirators, is very effective at protecting people from the virus causing COVID-19. However, it is important for employers and workers to remember that the respirator only provides the expected protection when used correctly.”

Respirators, when required, must be used as part of a comprehensive, written respiratory protection program that meets OSHA’s Respiratory Protection Standard (1910.134), the agency notes. Those requirements include training, fit testing and medical evaluations.

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