Rice University Creates Effective Recipe To Decontaminate Disposable COVID Facemasks at Home

Rice University graduate students Faye Yap, left, and Zhen Liu characterize a mask monster. Researchers from Rice and the Medical Department at the University of Texas, Galveston, have established a framework for properly sanitizing disposable masks. They found that heating a mask in a 160 degrees Fahrenheit oven for five minutes kills more than 99.9% of viruses tested, including SARS-CoV-2. Credit: Jeff Fitlow/Rice University

Proper heating of PPE kills 99.9% of SARS-CoV-2 virus without breaking down any material.

Here’s the recipe to sanitize a disposable face mask: Heat it in an oven at 160 degrees Fahrenheit for five minutes. You can use your own oven.

Science now confirms that, according to Rice University engineers who, through extensive experimentation and modeling, have determined that proper heating will eliminate the virus that causes COVID-19 from a standard disposable surgical mask without affecting the mask itself.

The work of mechanical engineer Daniel Preston of Rice’s George R. Brown School of Engineering, Rice graduate student Faye Yap and collaborators at the University of Texas Medical Branch (UTMB), Galveston, shows that masks can be disinfected and reused multiple times before being used. to be interrupted.

Best of all, heating to 70 degrees Celsius (about 160 F) killed more than 99.9% of the SARS-CoV-2 and other viruses they tested and met FDA guidelines for decontamination. That bodes well for adapting the protocol to deal with future outbreaks where personal protective equipment (PPE) is expensive.

The research is detailed in the Journal of Hazardous Materials.

Rice University graduate students Faye Yap, left, and Zhen Liu characterize a mask monster. Researchers from Rice and the Medical Department at the University of Texas, Galveston, have established a framework for properly sanitizing disposable masks. They found that heating a mask in a 160 degrees Fahrenheit oven for five minutes kills more than 99.9% of viruses tested, including SARS-CoV-2. Credit: Jeff Fitlow/Rice University

The paper is the third in a series in response to the COVID-19 pandemic and is supported by a National Science Foundation Rapid Response Research grant. The first paper in August 2020 suggested that a thermal approach to decontamination would be viable. The second paper, published in May, compared the effects of ambient temperature ranges on the virus in different locations in the US.

The current study introduces a modeling framework that researchers can use to determine how much heat a person needs, and for how long, to kill a particular virus. Preston pointed out that the framework applies not only to airborne viruses such as SARS-CoV-2, but also to viruses that live on surfaces and are transmitted primarily by touch.

In describing their strategy, study authors Yap and Preston detailed decontamination methods that have been tried, but only work to a certain extent: exposure to ultraviolet light, because it doesn’t reach into folds or crevices common with masks; steam, as it can affect the structure of a mask; or chemical disinfectants that can leave harmful residues and also affect the material.

“In general, ultraviolet light has been shown to be quite effective, especially for flat or smooth surfaces,” said Preston, an assistant professor of mechanical engineering. “There is a lot of good work to be done, but not everyone has access to UV, and heat overcomes the problems caused by crevices or folds in fabrics.”

When Preston realized that little had been done to create a modeling framework for decontaminating personal protective equipment, he decided his lab was right for the job, along with collaborators in Galveston who performed most of the heating experiments.

“We really haven’t found anything in the literature that clearly describes the effect of temperature on virus decontamination,” he recalls. “At least nothing that can be applied to the pandemic. That got us in on it even before we applied for the grant.

Researchers from Rice University and the University of Texas Medical Branch, Galveston, inoculated standard surgical masks with droplets containing active viruses to determine the best method of disinfecting masks with dry heat. Credit: Jeff Fitlow/Rice University

“Ultimately, what we hypothesized and have now shown to be true is that the thermal inactivation of the virus can be easily explained by a combination of two fundamental relationships,” he said. “One of these is the Arrhenius equation, which relates reaction parameters to temperature. And the other is the rate law, which uses those reaction parameters to tell you how fast a reaction is taking place. In this case, the response is to inactivate the virus itself.”

It’s important to make sure the mask heats up, Yap said. Because masks are thin, that’s not as much of a problem as disinfecting larger objects, a topic of future research by the Preston lab. Heating to 70°C should work equally well for cloth masks, as long as all layers reach the required temperature for a full five minutes.

She noted that if the heat is too high, the polymer fibers that make up most masks will melt, as they saw in microscope images of their samples. “At about 125°C, the (middle) filter layer in the mask starts to deform and at 160°C it melts,” Yap said. “There’s a thin line when you start approaching the melting point of the material.”

But where the decontamination protocol does work, it works very well. “If you can heat up the whole mass to the right temperature, 70 degrees C, you’ll still be incapacitating the viruses within five minutes,” Yap said. Even heating masks to the right temperature for up to 30 minutes didn’t significantly affect them, she said.

While COVID-19 is hopefully on the way out in the West, Preston said a shortage of personal protective equipment remains a problem in many parts of the world. A simple and effective method of disinfecting masks can help many. However, the ability to reuse masks isn’t all it takes to stay safe during a pandemic.

“I’m not arguing that thermal inactivation of viruses stabilized on surfaces will be the main contributor to preventing the spread of COVID-19,” he said. “Viruses will still spread through aerosolized droplets passed from one person to another. Masks can prevent that and decontamination is a secondary precaution to limit spread.”

Reference: “Efficacy and Self-Similarity of SARS-CoV-2 Thermal Decontamination” by Te Faye Yap, Jason C. Hsu, Zhen Liu, Kempaiah Rayavara, Vivian Tat, Chien-Te, K. Tseng, and Daniel J. Preston, 7 Nov 2021, Journal of Hazardous Materials.
DOI: 10.116/j.jhazmat.2021.127709

Jason Hsu of UTMB is co-lead author of the article. Co-authors are Rice graduate student Zhen Liu and research scientist Kempaiah Rayavara, graduate student Vivian Tat and Chien-Te Tseng, a professor of microbiology and immunology, at UTMB.

National Science Foundation grants 2030023 and 2030117 supported the research.