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Heat, humidity combo effectively cleans N95 masks, researchers say

Researchers have been searching, since the COVID-19 pandemic started earlier this year, for methods of cleaning N95 and other facemasks while not degrading their ability to prevent spread of the coronavirus. Photo by Bill Greenblatt/UPI
Researchers have been searching, since the COVID-19 pandemic started earlier this year, for methods of cleaning N95 and other facemasks while not degrading their ability to prevent spread of the coronavirus. Photo by Bill Greenblatt/UPI | License Photo

Sept. 28 (UPI) -- All over the world, healthcare workers battling the ongoing COVID-19 pandemic are facing shortages of protective equipment, including N95 masks. As a result, hospitals are having to find ways to disinfect respirators for reuse.

New research suggests a simple combination of moderate heat and high relative humidity can disinfect N95 mask materials without hindering their ability to filter out virus particles.

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Unlike other disinfecting strategies, researchers suggest their novel mask treatment can be relatively easily automated and scaled-up.

"This is really an issue, so if you can find a way to recycle the masks a few dozen times, the shortage goes way down," senior study author Steven Chu said in a news release.

"You can imagine each doctor or nurse having their own personal collection of up to a dozen masks. The ability to decontaminate several of these masks while they are having a coffee break will lessen the chance that masks contaminated with COVID viruses would expose other patients," said Chu, a professor of molecular and cellular physiology at Stanford University.

Researchers have previously tested a variety of disinfecting strategies, including ultraviolet light, hydrogen peroxide vapors and chemical disinfectants. One study found a spin in the microwave can successfully sterilize used N95 masks.

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Unfortunately, each of these strategies has been shown to degrade the filtering abilities of respirators.

For the new study, published this month in the journal ACS Nano, researchers sprayed coronavirus virus-dosed fluids on pieces of meltblown fabric, the main filtering component in N95 masks.

After allowing the pieces of fabric to dry, researchers exposed them to temperatures from 25 to 95 degrees Celsius for up to 30 minutes with relative humidity up to 100 percent.

The higher scientists turned up the temperature, the less and less virus scientists were able to find on the treated fabric samples. But at the highest temperatures, researchers found the meltblown fabric pieces lost some of their filtering ability.

Tests revealed the sweet spot for decontamination and material integrity to be 85 degrees Celsius with 100 percent relatively humidity.

Researchers got similar results when they performed the same tests with the coronavirus responsible for the common cold and the chikungunya virus. The results showed the masks could be treated up to 20 times before they began to suffer declines in filtering performance.

Scientists say their disinfecting method should be adopted by hospitals and healthcare providers to relieve pressures on PPE supplies, adding that N95 mask reuse has environmental and economic benefits.

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"It's good all around," said Stanford professor Yi Cui.

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