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Author: Mike Williams, Rice University

This is how to disinfect disposable masks: Heat them in an oven at 160 degrees Fahrenheit for five minutes. You can use your own oven.

According to engineers at Rice University, science has now proven this, and they have determined through extensive experiments and modeling that proper heating can eliminate the virus that causes COVID-19 from standard disposable surgical masks without reducing it. The quality of the mask itself. 

The work of Daniel Preston, a mechanical engineer at Rice University’s George R. Brown School of Engineering, Faye Yap, a Rice University graduate student, and a collaborator at the University of Texas Galveston Medical Branch (UTMB) showed that masks are degraded before they degrade. It can be purified and reused many times. 

Most importantly, heating to 70 degrees Celsius (approximately 160 degrees Fahrenheit) can kill more than 99.9% of SARS-CoV-2 and other viruses they tested, in line with the FDA's purification guidelines. This shows the prospect of adjusting the agreement to deal with personal protective equipment (PPE) in a very valuable future outbreak.

The research is described in detail in the "Journal of Hazardous Materials".

This paper is the third in a series of papers triggered by the COVID-19 pandemic and is supported by the National Science Foundation's Rapid Response Research Fund. The first paper in August 2020 showed that thermal decontamination is feasible. The second paper published in May of this year compared the effects of environmental temperature ranges in several places in the United States on viruses. 

The current research introduces a modeling framework that researchers can use to determine how much heat a person needs and how long it takes to kill a particular virus. Preston pointed out that the framework is not only applicable to airborne viruses such as SARS-CoV-2, but also to viruses that live on surfaces and are mainly spread by touch.

When describing their strategy, research authors Yap and Preston detailed the decontamination methods that have been tried but only work to a certain extent: exposure to ultraviolet light because it does not enter the folds or crevices common to masks; steam , Because it will damage the structure of the mask; or chemical disinfectants will leave harmful residues, and may also degrade materials.

"In general, UV light has proven to be very effective, especially for flat or smooth surfaces," said Preston, an assistant professor of mechanical engineering. "There is a lot of good work there, but not everyone is exposed to ultraviolet light. Heat can overcome the problems caused by fabric cracks or wrinkles."

When Preston realized that he had done little to create a modeling framework for purifying PPE, he thought his laboratory was suitable for the work, and Galveston’s collaborators performed most of the heating experiments.

He recalled: "We really didn't find anything in the literature that clearly described the effect of temperature on virus purification." "At least there is nothing that can be applied to the pandemic. This put us in a dilemma even before we applied for funding.

"Ultimately, we assumed and now found to be correct. The heat inactivation of the virus can be easily explained by a combination of two basic relationships," he said. "One of them is the Arrhenius equation, which relates reaction parameters to temperature. The other is the law of rate, which uses these reaction parameters to tell you how fast the reaction takes place. In this case, the reaction is the extinction of the virus. Life itself."

Yap said that it is important to ensure that the mask can be heated. Because the mask is so thin, it is not as important as decontaminating larger objects, which is the subject of future research in Preston Labs. A cloth mask heated to 70 degrees Celsius should be equally effective, as long as all layers reach the desired temperature for a full five minutes. 

She pointed out that if the heat is too high, the polymer fibers that make up most masks will melt, as they can see in the microscope images of the samples. "At about 125 degrees Celsius, the (middle) filter layer in the mask begins to deform and melts at 160 degrees Celsius," Yap said. "As you start to approach the melting point of the material, there is a thin line."

But where the purification protocol works, it works very well. "If you can heat the entire mass to the right temperature, 70 degrees Celsius, then you can still inactivate the virus in five minutes," Yap said. She said that even if the masks are heated to the proper temperature for up to 30 minutes, their performance will not be significantly reduced.

Although COVID-19 is expected to fade in the West, Preston said that the shortage of personal protective equipment is still a problem in many parts of the world. A simple and effective method of mask purification can help many people. However, the ability to reuse masks is not the entire and ultimate goal of maintaining safety during a pandemic.

"I don't want to claim that heat inactivation of the virus stabilized on the surface will be the main factor preventing the spread of COVID-19," he said. "The virus will still be spread through atomized droplets that spread from one person to another. Masks can prevent this from happening, and decontamination is a secondary preventive measure to limit transmission."

Jason Hsu of UTMB is the co-lead author of the paper. The co-authors are Rice University graduate student Liu Zhen and research scientist Kempaiah Rayavara, graduate student Vivian Tat and microbiology and immunology professor Chien-Te Tseng, at UTMB. Further exploration of Rice engineers' funding for research on temperature and coronavirus. More information: Te Faye Yap et al. The efficacy and self-similarity of SARS-CoV-2 thermal decontamination, Journal of Hazardous Materials (2021). DOI: 10.1016/j.jhazmat.2021.127709 Journal information: Journal of Hazardous Materials

Citation provided by Rice University: The laboratory details the conditions for disinfecting disposable masks (2021, November 12), retrieved on November 13, 2021, from https://phys.org/news/ 2021-11-lab-conditions-decontaminate-disposable-masks.html This file is protected by copyright. Except for any fair transaction for private learning or research purposes, no part may be copied without written permission. The content is for reference only.

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