Urgent Research Shows Face Masks Can Be Safely Reused by Pandemic Medical Workers

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AMHERST, Mass. – Medical face masks, which have fallen into short supply during the COVID-19 pandemic, endangering both frontline health care workers and their patients, may be safely reused after sterilization, according to initial results from urgent research conducted this week by a University of Massachusetts Amherst environmental health scientist.

Richard Peltier, a School of Public Health and Health Sciences professor, partnered with Dr. Brian Hollenbeck, chief of infectious disease at New England Baptist Hospital in Boston, to test in his lab whether used N95 face masks were still effective at blocking infectious particles after sterilization.

This critical research aimed to address the worldwide shortage of N95 masks caused by the COVID-19 pandemic. “As environmental health scientists, we are always looking for opportunities to improve public health,” Peltier says. “These results show that there is no real difference in filtration between a new mask and one that has been sterilized.”

N95 face masks are worn over the mouth and nose, and capture particulates in the air. They are designed to be worn once and then discarded. When new, they are very effective at protecting a person from particulates, including droplets that carry infectious agents like COVID-19.

“While these are ordinarily disposable protective devices for medical workers, these are not ordinary times,” Peltier says, “and this science shows that sterilized face masks will protect our health care providers who are working under extraordinary conditions.”

Peltier used state-of-the-art pollution instruments and a mannequin head wearing a face mask to measure whether microscopic particles can pass through the mask after it’s sterilized.

Peltier carried out the testing in a small chamber, in which he affixed the masks to a mannequin that had a small pipe extending from its mouth. The chamber was flooded with pollution, and air was collected through the mask as if the mannequin were breathing inside a room filled with pollutants.

The air was delivered to analyzers that used lasers to both count and estimate the size of millions of microscopic particles. Peltier switched between measuring the air from the chamber and the air from behind the mask to calculate how many particles passed through each mask type. He tested both a new mask, as well as one that had been sterilized with hydrogen peroxide.

While there was concern that sterilization might substantially degrade the filter material, causing it to function improperly, this turned out not to be the case. “They work just as well after sterilization,” Peltier says.

Ordinarily, Peltier would repeat the test dozens of times, but the hospital in Boston could not spare additional masks, which, once tested, were unusable. “We are no longer under ordinary circumstances and we have to improvise as best we can,” Peltier says.

Because the particulates blocked by the face mask are retained by the mask, they must be sterilized if not thrown away. “A used mask could have COVID-19 on it, so reusing it without sterilization poses a danger to the wearer or to another patient,” Peltier explains.