Validating N95 Respirator Decontamination Methods

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Researchers at Mass General Brigham have been investigating mask decontamination methods to address the global N95 respirator shortage brought on by the COVID-19 pandemic. After a vigorous and peer-reviewed process, scientists at Massachusetts General Hospital have confirmed the efficacy of a hydrogen peroxide vapor sterilization system to decontaminate N95 respirators.

"When you intubate someone with COVID-19, there's a lot of aerosolized virus particles in the room. You have to have proper PPE (personal protective equipment) to protect yourself. N95 masks are critical in protecting frontline workers," says Orhun Muratoglu, PhD, director of Mass General's Harris Orthopaedics Laboratory and Technology Implementation Research Center (TIRC).

On where the project stands now, Dr. Muratoglu says, "We have been able to decontaminate over 60,000 masks—some went through three or four decontamination cycles. We also established post-decontamination surveillance to continue to monitor the filtration and fit of the masks. So far, we're up to four cycles with mask function staying in great shape."

Scientific Collaboration to Develop Decontamination Investigations

When the Mass General Brigham Center for COVID Innovation was established in March, new advances to reduce COVID-19 infections and protect frontline clinical staff were the first priorities. Leaders created the Reuse Working Group to investigate ways to optimize PPE supplies and asked Dr. Muratoglu to lead it because of his experience in orthopedic implants.

Dr. Muratoglu first examined 3D printing masks, which he compares with his experience developing joint implants.

"We do a lot of implant work, which involves designing and 3D printing them," he says. "The concept was similar: You design the mask and 3D print it. But when we started looking into it, we realized it would not be possible to print masks for thousands while ensuring they perform like real N95 masks in an expedited time horizon."

Dr. Muratoglu's team pivoted and began gathering information about how manufacturers produce N95 respirators, how they function and how to decontaminate them without compromising filtration efficiency.

"We had over 100 scientists around the country join our daily Zoom calls. For about two months, we met every day, exchanged ideas and data, and decided what the next experiments would be."

Assessing Decontamination Method Efficacy

Investigators in the Reuse Working Group established that successful sterilization would require neutralization of the SARS-CoV-2 virus while maintaining fit and filtration efficiency. Fit tests involve:

1. Putting the mask on the subject and covering the subject's head with a large hood
2. Spraying aerosolized saccharin
3. Moving the subject's head in all directions

The N95 respirator fits properly if saccharin particles are not able to reach the mouth and nose.

"This common test determines what mask fits your face the best," says Dr. Muratoglu. "While there are different companies, designs and sizes, everyone gets fitted to a certain type of mask, and you always use that one."

To validate filtration efficiency, Dr. Muratoglu's team enlisted an independent Ohio laboratory to calculate the measurements.

Exploring Different Decontamination Methods

Dr. Muratoglu's experience with hip and knee implant materials first led them to explore lessons learned from polyethylene sterilization.

"We've been playing with the molecular structure of this material using ionizing radiation like electron beam and gamma radiation. Those methods are also used to sterilize implants, so we started there."

The team looked at methods including electron beam radiation and ethylene oxide gas. The radiation caused loss of filtration efficiency, while ethylene oxide gas was too difficult to scale for the estimated 20,000 masks that needed to be sterilized weekly and was also extremely toxic, requiring additional aeration after sterilization.

Hydrogen Peroxide Vapor Decontamination Emerges

In the discussions with scientists around the country, hydrogen peroxide vapor came to the fore as a potentially safe and effective way to decontaminate N95 masks without compromising function. To test the method, investigators connected with a local orthopedic company that had just installed a hydrogen peroxide vapor sterilization system.

"We put the masks through multiple cycles and then looked at the filtration efficiency," says Dr. Muratoglu. "The results were great. The masks were sterilized, and there was no change in filtration efficiency."

Tests after five sterilization cycles also resulted in an uncompromised fit, and the hydrogen peroxide vapor had lower toxicity than other methods because it became water and oxygen out of containment. With the method validated, investigators needed to demonstrate that hydrogen peroxide gas would kill SARS-CoV-2.

"It killed bacteria," he says, "but we had no idea if COVID-19 would actually survive this exposure."

To access SARS-CoV-2, the Reuse Working Group partnered with the Boston University National Emerging Infectious Diseases Laboratories (NEIDL), a biosafety level 4 facility. The NEIDL team had access to the virus and other materials vital to investigating the efficacy of hydrogen peroxide vapor.

"The virus has to enter a permissive cell. It then replicates itself, and you quantify the viral plaques that are formed," says Dr. Muratoglu. "After three- to four-hour treatments with hydrogen peroxide vapor, we found that nothing grew, so we knew that it was working really well."

Filtration efficiency and fit testing confirmed the effectiveness of the method, and Dr. Muratoglu's team determined they could decontaminate approximately 2,000 masks in one cycle.

"We could do five or six of these rounds a day, and within a week, probably decontaminate all the N95 masks needed for Mass General Brigham staff, he says"

A Key Partnership Increases N95 Respirator Decontamination Capacity

Sterilization capacity increased with the addition of a decontamination container produced by Battelle. They had been working on a hydrogen peroxide vapor unit to decontaminate N95 respirators as well.

"They had also done the viral plaque experiments and demonstrated that nothing grows after exposure to hydrogen peroxide gas," Dr. Muratoglu relates. "Because we had done our homework, Battelle's data only confirmed our findings. That's when we decided to bring one of their decontamination machines to Boston."

Mass General Brigham identified a suitable location nearby to convert into a hydrogen peroxide decontamination center.

"Within 10 days, the facility was fully operational," says Dr. Muratoglu. "The system can do 80,000 masks in one day. Battelle also contracted with more than 300 other Massachusetts hospitals and now decontaminate the majority of N95 masks in the state."

While peer-reviewed data supports mask decontamination for up to 10 cycles, Mass General Brigham has limited their sterilization protocol to five cycles.

"You can subject these masks to this gas 20 times and they will survive," he says. "But if you're wearing them for eight hours, doing hard work and getting them wet with your sweat, the masks eventually will lose their form and that could compromise the fit function."

Although the surge of COVID-19 patients is slowing in Massachusetts, the need for N95 respirators remains. In addition to treating COVID-19 patients, clinicians will also use these masks during elective surgeries and in other clinical settings.

Helping Others Deploy Sterilization Methods

Mass General Brigham Center for COVID Innovation researchers are dedicated to sharing their methods and findings in the U.S. and around the world. A recent webinar educated clinicians from more than 50 countries on N95 function and decontamination.

"These were mostly for low-resource areas. Our position was if they had access to hydrogen peroxide gas, here's how to do it. But most didn't. In those cases, we showed them alternatives including moist heat and a UVC germicidal light source," Dr. Muratoglu says. "Before our webinars, a lot of places were trying to do their own decontamination using other techniques. After, many started following our recommendations."

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