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Researchers at Lawrence Livermore National Laboratory have discovered a method to decontaminate N95 respirator masks without compromising their facial fit and ability to filter airborne particles.
The scientists determined that heating the N95 respirators up to 75 degrees Celsius (167 degrees Fahrenheit) for 30 minutes deactivates a surrogate coronavirus, lab officials said in a statement.
According to the lab, this temperature can be easily achieved in hospitals and field settings, allowing for the N95s to be reused once decontaminated. The heat treatment can be applied at least 10 times on an N95 respirator without degrading its fit.
“These results suggest that thermal inactivation of coronaviruses is a potentially rapid and widely deployable method to reuse N95 respirators in emergency situations where reusing the respirators is necessary and sterilization is unavailable,” said LLNL electrical engineer Travis Massey, who is the lead author of the Annals of Works Exposures and Health where the research appears.
N95 respirators are protective devices that filter airborne particles. The “N95” designation means that the respirator blocks at least 95% of very small (0.3 micrometers or larger) test particles, according to the lab.
They are typically used a single time in health care settings because the respirators can be contaminated when treating infected patients, thereby posing a risk to caregivers who continue wearing a contaminated device, as well as other patients treated by the provider.
“In March of 2020 the world turned upside down,” said LLNL material scientist Sal Baxamusa, a senior author on the paper. He added that at that time, lab researchers began discussing and exploring how they could help.
“I think we clearly recognized that health care workers were going to be on the frontlines and the question was whether there was any technology development that could be done to help support them,” he said.
After a team formed and started getting together virtually to brainstorm, Baxamusa said they identified a knowledge gap about N95 respirators and recognized that at the height of the pandemic, there was going to be a shortage of them in the health care environment, largely because they are designed to be used only once.
Other studies have determined that most viruses can be inactivated with some modest temperature (about 70-75 degrees Celsius), but according to Baxamusa, what other people had not looked at was whether that temperature could kill viruses that had been deposited onto a filter, like with N95 respirators.
In the testing experiment, the team used a mouse coronavirus that does not cause disease in humans as a surrogate for SARS-CoV-2 (the novel coronavirus).
The team enlisted two volunteers who were briefly fitted a new, unused N95 to their faces and noses to simulate a first-time use. The 3M Model 8210 N95s were used for all the heat treatment tests. The model is one of the most widely recognizable, is used in the industry and is available in one size as it was designed to seal effectively against most human faces, lab officials said.
“By checking the viral activity before and after temperature treatment, we found that, yes, the virus is inactivated even when it’s dried on a filter as opposed to sitting in a vial — which is what most other studies had done up to that point,” Baxamusa said.
“The other thing we found was that at those temperatures and those times, 75 degrees Celsius for 30 minutes, the mask can be re-worn and it still fits properly. It seems like a little thing but, incredibly, nobody really knew the answer to that,” he added.
Other Livermore researchers involved in the study include Monica Borucki, Samuel Paik, Kyle Fuhrer, Mihail Bora, Staci Kane and Razi-ul Haque. The research was funded by internal LLNL grants.
“It was exciting for me that this team sort of formed organically amongst staff at the laboratory and everybody sort of rallied together in the very early days of the pandemic — which seems like a lifetime ago now — but I think back to the uncertainty and the fear that was going on at the time and it was pretty remarkable that folks were able to rally around and get this project done,” Baxamusa said.
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