Reused and Expired N95 Masks Retain Their Effectiveness

Dentistry Today


Reused N95 masks, sterilized N95 masks, and N95 masks that are very out of date retain their effectiveness at protecting healthcare workers from COVID-19 infection, according to the University of North Carolina (UNC).

To assess mask fitted filtration effectiveness, Emily Sickbert-Bennett, PhD, director of infection prevention at UNC Medical Center and her colleagues turned to her father, William Bennett, PhD, professor of medicine and leader of the Mucociliary Clearance and Aerosol Research Laboratory at the UNC Center for Environmental Medicine, Asthma, and Lung Biology.

“I told him we had two types of masks—used, sterilized and expired N95 masks—and we needed to know whether they would offer safe and effective protection, in case we needed our healthcare coworkers to use them,” said Sickbert-Bennett. “And he said it would be possible for his lab to test them and give us data upon which to base our decision-making.”

Thanks to a cooperative agreement with the Environmental Protection Agency (EPA) Human Studies Facility on the UNC-Chapel Hill campus, where Bennett’s labs reside, Bennett worked with assistant professor Phillip Clapp, PhD, research associate Kirby Zeman, PhD, and EPA research scientist James Samet, PhD.

Together, the researchers measured the fraction of submicron particles that penetrate into the breathing space of subjects wearing a mask while performing a series of tasks simulating conditions such as speech and movement during a work shift. The tests provided quantitative data so the researchers could rank the best respiratory protection options.

The researchers found that certain N95 masks as rated by the National Institute of Occupational Safety and Health Administration (NIOSH) provide greater than 95% effectiveness at keeping the wearer from inhaling very small airborne particles that may carry SARS-CoV-2, and they retain their effectiveness many years beyond their expiration dates.

These NIOSH-rated masks also can be sterilized with hydrogen peroxide or ethylene oxide without compromising their efficiency. Plus, their fitted filtration procedures showed that surgical masks with ties were about 70% effective at filtering their inhaled particles, while surgical masks with ear loops were about 40% effective.

“One of the keys to protection is how snug a mask fits. An N95 mask that forms a tight seal offers the optimal infection prevention. However, evidence from previous studies suggests that even the surgical masks with less than 95% efficiency are effective in preventing acquisition of epidemic coronaviruses,” said Clapp, who was co-first author on the study.

“Our hierarchy of mask supplies essentially amounts to always using the safest option on the shelf, especially for those healthcare workers caring for COVID-19 patients,” said Sickbert-Bennett, who also was co-first author on the study. “We start with products of our usual make and model, then follow with CDC-FDA-NIOSH approved products.”

“To date, UNC Health has maintained adequate supplies of NIOSH-approved PPE,” said Sickbert-Bennett. “We feel confident we can maintain protection of the UNC Health workers with the variety of face masks and respirators tested as part of this JAMA-published study.”

The study was published by JAMA Internal Medicine.

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