N95 masks sterilisation

Scarce N95 Masks Can Be Safely Disinfected With Steam

By Linda Carroll

April 24, 2020


(Reuters Health) – As the number of COVID-19 cases explodes around the world and PPEs become increasingly scarce, the need to disinfect and reuse disposable N95 masks becomes an important option, according to Texas researchers who show in a letter published in Infection Control & Hospital Epidemiology that the masks can be safely disinfected with steam.

“Steam sterilization is probably one of the safest ways to sterilize them,” said study coauthor Firas Zabaneh, director of system infection prevention and control at Houston Methodist Sugarland Hospital. “You’re not using any chemicals or anything that could alter the makeup or structure of the mask. And that’s why we thought of steam.”

It’s estimated that the U.S. will need 3.5 billion N95 masks for healthcare workers during the pandemic and currently only 1% of that number exist, Zabaneh and his colleagues note.

“In countries where equipment shortages have progressed, healthcare workers are currently being infected with COVID-19 at three times the rate of the general population,” they write. “Thus, it is essential to create a protocol for sanitizing masks without reducing efficacy.”

The design of the N95 mask, while effectively protecting wearers from infection, presents challenges when it comes to disinfection, Zabaneh and his colleagues explain. Other research has shown that washing with water decreases mask performance by 21% and sanitizing with alcohol reduces performance by 37% and results in mask shrinkage.

Studies of disinfection with UV radiation found the integrity of the masks was compromised in 90% of cases, the researchers write. And sanitation with bleach or ethylene oxide can leave a residue that creates a risk for wearers.

That is why the researchers decided to investigate the use of steam sterilization. They performed their tests using the Steris Amsco Evolution HC1500 PreVac Steam Sterilizer autoclave, with the masks packed in paper-plastic sterilization peel pouches. The masks were photographed and fit-tested prior to and after steaming.

The researchers test sterilized a number of models and brands of N95 masks using five volunteers for fit-testing to account for differences between faces. “Two (masks) in particular withstood the treatment well: the 3M 1870 and the 3M1870+,” Zabaneh said, adding that, in general, steam sterilization could be done twice without affecting the fit of the masks.

While another method, sterilization with hydrogen peroxide, can be repeated more times, you can’t count on the chemical always being available, Zabaneh said. So, it’s good to have steam sterilization as a backup method.

Currently there are no shortages of N95 masks at Zabaneh’s hospital. But that could change at any time with the growing pandemic, he said.

In Pittsburgh, however, healthcare workers are already having to come up with solutions to shortages of N95 masks.

“While the masks aren’t designed to be used more than once, shortages have forced us to ask how we can be less wasteful,” said Dr. Graham Snyder, medical director of infection prevention and hospital epidemiology at UPMC in Pittsburgh. “We started with limiting the number of healthcare workers going into rooms to what is needed for patient care. We extended use by wearing the same mask all day.”

Even with those measures there are still supply problems, Dr. Snyder said. “And that’s why we are looking into how we can disinfect the masks so they can last even longer,” he said.

“There have been a handful of methods explored: UV, hydrogen peroxide, ethylene oxide,” Dr. Snyder said. “And this paper is looking at steam sterilization.”

The steam method has advantages, Dr. Snyder said. “Generally it’s widely available; it’s easy and it’s not noxious.”

What hasn’t been established yet for the N95 mask is the temperature and duration of steam, Dr. Snyder said. When the manufacturers set that, steam sterilization can be used, he added.

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