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Researchers found a way to clean N95 masks for reuse — in a common electric cooker

Researchers out of University of Illinois at Urbana-Champaign show household electric cookers can be used to decontaminate N95 respirators for reuse. (Video: Global Food and Water Safety/University of Illinois at Urbana-Champaign)
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The request for help reached Thanh H. Nguyen in March, just as the novel coronavirus had begun to ravage the United States, overwhelming hospitals with scores of infectious patients. Could Nguyen, a professor of civil and environmental engineering at the University of Illinois at Urbana-Champaign, and her colleagues assist local health-care providers with shortages of critical personal protective equipment?

“One thing they mentioned right at the very beginning is the N95 respirator mask, because that is a crucial, essential piece of PPE,” Nguyen said. “They already told us that the price has been really high, it’s hard to get, they have to recycle instead. They don’t know how to do it safely.”

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So Nguyen and Vishal Verma, an assistant professor in the same department, got to work examining various technologies and chemicals. But it wasn’t long before another question emerged: What about people who can’t access lab-grade materials and machinery?

The pair didn’t have to go farther than their kitchens to find an answer.

“It just happened that both Vishal and myself and a number of our students are Asian, and we cook rice every night,” Nguyen said. “We said like, ‘Oh, maybe some type of electric cooker might work.’ ”

She swiftly dispatched one of her students to Walmart with specific instructions. “Look for something at Walmart anyone can buy,” she said. “Something easy; they just hit the button.”

The student came back with a Farberware multifunction pressure cooker that cost about $50.

In a recently published study, Nguyen and Verma detailed how the dry heat produced by such electric cookers (rice cookers or multicookers such as Instant Pots) may be an effective way of decontaminating medical-grade N95 masks. Using the rice preset on the Farberware cooker and N95 respirators from 3M, a major manufacturer of the protective coverings, the researchers found that 50-minute treatments without pressure at a temperature of 212 degrees Fahrenheit left the masks thoroughly cleaned without compromising fit or filtration efficiency.

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“The N95 can be reused using a very simple method,” said Nguyen, whose research focuses on pathogen transmission and control. “We are not testing exhaustively every device out there, everything, but we want to show that this concept works. Then people can use the idea and apply to other things.”

The study — published in Environmental Science & Technology Letters, a peer-reviewed journal — joins a growing body of research that has emerged during the pandemic that evaluates the efficacy of kitchen appliances as a sanitation tool. In February, a team from Chung Shan Medical University in Taiwan found that dry-steaming surgical masks in a rice cooker for several minutes had a sterilizing effect, the Taipei Times reported. Taiwan’s health minister later demonstrated the technique at a Central Epidemic Command Center news conference. More recently, scientists in Ohio suggested in April that steaming masks in rice cookers could also be effective — a finding that aligns with guidance from the Centers for Disease Control and Prevention on reusing N95 respirators, which lists “moist heat” as a promising method of decontamination.

Nguyen said the work she and Verma have done doesn’t contradict past research but rather builds upon it.

“Our study is comprehensive in the sense that we’re not only worried about the inactivation of pathogens,” she said, adding that the researchers also focused on preserving the mask’s effectiveness.

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To guide their experiments, the researchers turned to 3M’s suggestions for reusing its respirators, which draw on recommendations from the CDC and other federal agencies, according to the study. The company states that an effective decontamination technique must inactivate the target virus without negatively affecting the mask’s fit and filtration ability or leaving behind a residue from dangerous chemicals.

Masks being tested were contaminated with four different common viruses, including one that is in the same family as the virus that causes the disease covid-19, Nguyen said. The virus was added to an artificial saliva solution, which was then applied to various parts of the mask before it was placed into the cooker. The study recommends using a towel or some other barrier to protect the mask so it does not touch the appliance’s inner walls or heating element.

After the 50-minute cooking cycle, each virus tested was inactivated by at least 99.9 percent, which is the level required by the Food and Drug Administration, the study said. An infrared thermometer was used to monitor the surface temperature of the masks during each cycle, Nguyen said.

Then the masks went through an additional series of tests to assess whether cooking them had compromised their function. Verma said the tests were done in accordance with protocol developed by the National Institute for Occupational Safety and Health.

“After 20 cycles of the dry-heat treatment, we didn’t see any significant difference in the filtration efficiency of the respirator,” said Verma, who studies aerosols. He added that the masks, which also passed a fit test, still functioned at above 95 percent efficiency.

Sara L. Zimmer, an associate professor of biomedical sciences at the University of Minnesota Medical School, praised the researchers for thinking of an alternative method that could help people without access to sophisticated technology. But she cautioned against thinking of the cooker as “a magical cleaner.”

Masks are “still going to have skin oils, sweat, other materials” on them, said Zimmer, who is affiliated with the university’s Duluth campus and not involved in the research. “The study’s authors didn’t look at what are the other factors that are going to be happening at the same time you’re using these masks, besides maybe acquiring a viral load, that could be problematic over time.”

Sanjay Maggirwar, a professor of microbiology, immunology and tropical medicine at George Washington University, said the study was “very well done.”

“It’s very carefully done and very useful in current days,” said Maggirwar, who was also not part of the study. “Scientifically, a very sound paper.”

But before people start throwing masks into their electric multicookers or rushing out to buy the appliances, Nguyen emphasized that the findings are based on tests done with one type of cooker and a specific brand of N95 mask. If people want to try to replicate the test at home, Nguyen only recommends doing so if the same materials can be used.

“That would be low risk,” she said. “Extending it to other devices, other masks and everything else, that would need more study.”

The researchers also discouraged people from disinfecting masks in the same appliance they are using to prepare food, according to the study’s FAQ page.

Still, Nguyen touted her team’s results.

“We looked for a method that is easy to use, not expensive, not involving chemicals,” she said. “As long as you make sure you don’t have moisture, as long as you can measure temperature and keep the same exposure time, it is very likely to work.”