A new website spearheaded by researchers at Stanford University is helping hospitals and first responders across the globe to decontaminate the gear they rely on for protection against the coronavirus.
The research literature clearinghouse, N95Decon.org, is overseen by a team of 60 scientists and engineers, students and clinicians from universities and the private sector and focuses on the reuse and decontamination of N95 masks.
The team wanted to help overwhelmed health workers find reliable, scientific information about the pros and cons of methods, should shortages of gear force them to make a choice between reusing masks or going without, the group stated in an April 1 announcement.
The team scoured hundreds of peer-reviewed publications and met online multiple times to assess the methods, members said.
The group has focused on three methods: heat and humidity; a specific wavelength of light called ultraviolet C (UVC); and hydrogen peroxide vapors. They didn't endorse any single method.
The group found no available data specifically on decontamination of COVID-19 on N95 masks for any of the methods. However, there is data regarding the methods on other coronaviruses that are similar to the one that causes COVID-19.
Hydrogen peroxide vapor and hydrogen peroxide gas plasma
Perhaps the most promising method, hydrogen peroxide vapor, has been proven to kill viruses and highly resistant bacterial spores on N95 masks. The process uses specialized equipment to aerosolize hydrogen peroxide, which permeates the layers of the mask without degrading the mask material.
Another method using hydrogen peroxide, known as hydrogen peroxide gas plasma — or the use of an "ionized" gas — has also been tested and found effective.
On March 29, the Food and Drug Administration approved a hydrogen peroxide vapor mechanical system on an emergency basis for use on N95 masks.
Duke has found the masks can be decontaminated and used more than 50 times without degrading, saving hospitals much needed protective gear that is in short supply, according to a press release.
The technology has been used in Duke's biocontainment laboratory for years.
"We had never considered needing it for something like face masks. But we've now proven that it works and will begin using the technology immediately in all three Duke Health hospitals," said Matthew Stiegel, director of the Occupational and Environmental Safety Office.
The N95Decon group found data that stated the vapor does not degrade 3M-brand 1860 N95 mask filters, straps nor the mask fit in tests of up to 20 decontamination and reuse cycles.
The review team noted that the vapor and plasma processes are distinct and use very different protocols. The systems are complex and dangerous and require trained personnel, the research review team noted.
According to research, at least 1 Joule — one watt of power radiated for one second — per square centimeter of ultraviolet C light (UVC) kills viruses that are similar to the SARS-CoV-2 virus on N95 masks. It also kills some bacteria spores. However, one concern with the method is that the light might not reach the inner layers on all masks.
Tests also found that straps on the masks might not be fully decontaminated, especially when parts of the mask cast shadows and block the UV rays. The remaining contamination on the mask would need to be wiped with disinfectant, the research literature found. Cosmetics and sunscreen on masks might also hinder decontamination.
The masks do keep their fit and filtering capabilities after up to 20 cycles of UV treatment. High doses of the light damaged straps and facepieces on some mask models, however.
Perhaps disappointing for do-it-yourselfers, consumer UV products are not recommended for the decontamination, the group noted.
The heat and humidity method
The N95Decon group did not find any experiments using heat to kill coronaviruses specifically on N95 masks. But coronaviruses that were put in a solution (not on masks) were killed when treated at 140 degrees to 167 degrees Fahrenheit for 30 minutes, according to the group's literature summary.
H1N1 and H5N1 influenza viruses, which are not coronaviruses but have also caused pandemics, are able to be killed at 150 degrees Fahrenheit for 30 minutes and at 85% humidity, tests showed. Repeated decontamination cycles could damage the fit of the mask and its ability to filter the viruses, however.
Different makes and models of masks might also respond differently to heat and humidity, the N95Decon group said. Heat did not kill all bacteria nor mold spores on the masks, they found.
The U.S. Centers for Disease Control and Prevention has released guidelines on the heat and humidity method, but it has not been validated for use by the U.S. Food and Drug Administration, the N95Decon group noted.
The process does have the advantage of being inexpensive and can be used in a number of easily available settings including ovens, warming cabinets and autoclaves, they noted. Use of home ovens is not recommended, however, because that would require bringing contaminated masks into homes.
Stanford University professors Steven Chu, of the Department of Physics, and Yi Cui, of the Department of Material Sciences and Engineering. Chu and Cui are collaborating with researchers from 4C Air Inc. of Sunnyvale on studies using hot air, ultraviolet light and steam to test the filtering effectiveness and degradation of N95 masks.
In a March 25 preliminary "commentary" report published online by the Stanford Medicine Anesthesia Informatics and Media Lab, they found the hot air, treated at 167 degrees Fahrenheit for 30 minutes, did not degrade masks when going through 20 decontamination cycles.
Masks treated with the UV light didn't degrade nor lose efficacy through 10 cycles of treatment, but steam-treated masks degraded to 85% efficiency after five treatment cycles and dropped to 80% after 10 cycles, they noted. The treatments were performed on masks contaminated with E. coli bacteria and not coronavirus, however.
The researchers stressed the research has not been peer reviewed, nor is it complete. They are continuing the study, which could be updated over a number of weeks.
Find comprehensive coverage on the Midpeninsula's response to the new coronavirus by Palo Alto Online, the Mountain View Voice and the Almanac here.