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Tests show heating is the best way to disinfect N95 masks for reuse

Wendy Gould, R.N., inspects a N95 masks that have been sanitized in a special trailer at Saint Louis University Hospital in St. Louis on April 23. Photo by Bill Greenblatt/UPI
Wendy Gould, R.N., inspects a N95 masks that have been sanitized in a special trailer at Saint Louis University Hospital in St. Louis on April 23. Photo by Bill Greenblatt/UPI | License Photo

May 5 (UPI) -- Test results suggest N95 masks can be safely disinfected through heating 50 times before their filtration efficiency begins to decline.

With N95 masks still in short supply in many parts of the country. Doctors, nurses and other professionals on the front lines of the COVID-19 pandemic have been forced to reuse their masks.

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N95 masks feature a fine webbing of "meltblown" polypropylene fibers. The porous material is breathable but capable of capturing 95 percent of particles. Electrostatically charged fibers help wrangle those particles that slip through the pores.

Recommendations from the U.S. Center for Disease Control and Prevention suggest heating, ultraviolet radiation and bleach can all be used to disinfect N95 masks.

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However, when scientists at Stanford University and 4C Air, a startup company making air filters, tested the different methods, they found heating worked best.

When researchers sprayed ethanol or chlorine bleach solution on N95 masks, they found the respirators' filtration abilities suffered a swift drop off. Steam treatments worked fine as a one-off method, but after five steams, filtration efficiency declined. Masks treated with UV light began to suffer performance declines after 20 disinfecting cycles.

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For the heating method, scientists exposed N95 masks to a temperature of 185 degrees Fahrenheit for 20 minutes. The heating method successfully disinfected the test masks 50 times before scientists measured a decline in filtration efficiency.

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Scientists acknowledged that their tests results -- published Tuesday in the journal ACS Nano -- aren't the final word on the matter. The are other factors to consider, such as fit.

"Frequently donning and removing N95 masks could affect fit, which also impacts performance," researchers wrote in a news release.

Last month, the Pentagon awarded the Battelle Memorial Institute $415 million for the decontamination of used N95 respirator systems. Battelle deploys a concentrated, vapor phase hydrogen peroxide to decontaminate masks for reuse up 20 times.

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The latest research suggest there are more promising disinfectant methods than those deployed by Battelle.

"Treatments involving liquids and vapors require caution, as steam, alcohol, and household bleach all may lead to degradation of the filtration efficiency, leaving the user vulnerable to the viral aerosols," scientists wrote in their paper.

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