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Infectious disease


During the coronavirus pandemic, hospitals have taken unprecedented steps to disinfect N95 face masks

With protective equipment in short supply, health-care facilities are decontaminating and reusing items designed to be disposable

by Kerri Jansen
April 27, 2020


Photo of face masks on wire shelving inside Battelle decontamination unit.
Credit: Courtesy of Battelle
A decontamination system developed by Battelle uses hydrogen peroxide vapor to treat thousands of face masks at one time.

In March, health-care facilities in the US began preparing for a predicted avalanche of cases of COVID-19, the respiratory disease caused by the novel coronavirus. Hospital officials scrutinized their existing supplies of items like gloves and face masks and tracked usage to help forecast their future needs.

Many pieces of personal protective equipment (PPE) like N95 masks, the tightly fitted respirators designed to filter at least 95% of small infectious particles, are cheap and readily available from distributors, so under normal circumstances hospitals have little need to keep large supplies on hand. But, last month, in the midst of a global pandemic, formerly reliable distribution channels had dried up. Leaders at OhioHealth, which operates 12 hospitals in central Ohio, estimated that their existing supplies of N95 masks could be expended in a matter of weeks if they could not secure new shipments, according to Chris Clinton, who oversees the network’s supply chain operations. The team immediately began focusing efforts on conserving supplies and communicating with staff about the new measures.

Laurie Hommema, a family medicine doctor and OhioHealth’s medical director of provider and associate well-being, was one of the people attending those meetings in March. She thought ahead a couple weeks when she was scheduled to begin patient rounds with a group of residents.

“My mind went to the worst-case scenario where I’d be seeing tens of COVID patients every day, potentially without the right personal protective equipment,” she says. “You just worry about how significant of a disease this is and you bringing that home.”

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At home that evening, she mentioned these concerns to her husband, Kevin Hommema, an engineer at the research and development organization Battelle, where Laurie also used to work as a microbiologist. It would turn out to be a fortuitous conversation.

“I mentioned I was nervous,” Laurie Hommema says. “I made the statement that I’m afraid I’m not going to have an N95 at that time. And he simply said, ‘Well, why don’t you guys just decontaminate those masks?’ ”

N95 masks are designed to be used once and then discarded. But Kevin Hommema remembered research that a colleague had done in response to the 2009 H1N1 influenza pandemic to evaluate the efficacy of using hydrogen peroxide vapor to decontaminate N95 masks in the event of a PPE shortage. The team had found that such a system could be used to disinfect masks multiple times without damaging their performance. Perhaps such a system could be implemented at OhioHealth.

The Hommemas worked quickly to set up meetings with OhioHealth and Battelle leadership. Together, the organizations sorted out logistics as Battelle scientists hurried to scale up the disinfection technology, outfitting shipping containers with equipment that could process thousands of masks at a time.

Photo of several large boxes marked "biohazard" waiting to be processed at decontamination site.
Credit: Courtesy of Battelle
Boxes containing contaminated PPE await treatment at a Battelle-operated decontamination site.

On March 28, the US Food and Drug Administration, which assesses the safety of medical products, issued its first emergency use authorization (EUA) for a mask decontamination technology to Battelle’s Critical Care Decontamination System. Then, in April, the US federal government awarded Battelle a contract to fund the system’s deployment to 60 locations throughout the US, including sites in Seattle, Boston, Chicago, and near New York City. As of April 27, Battelle had processed tens of thousands of masks, including more than 30,000 for the OhioHealth network.

The decontamination process established in Ohio is just one example of an unprecedented effort to respond to shortages of N95 masks and other PPE during the novel coronavirus pandemic by finding ways to use disposable equipment more than once. Although such practices are not approved for standard care, the US Centers for Disease Control and Prevention notes that mask decontamination “may be necessary” when PPE supplies are severely constrained during a crisis. A handful of other technologies have now joined Battelle’s system on the FDA’s list of EUAs. And across the country, health-care facilities are establishing their own protocols, many relying on well-known disinfection methods like ultraviolet light and heat, as scientists work to understand such methods’ effectiveness and their long-term effects on equipment performance.

Some scientists and health officials anticipated the possibility of needing to decontaminate and reuse PPE, especially after the world’s experience with the H1N1 pandemic in 2009.

“We’ve known for some time that there could be shortages,” says Brian Heimbuch of Applied Research Associates (ARA), who leads research to evaluate methods of mask decontamination. Years ago, Heimbuch says, such research was not always taken very seriously. For some, it was hard to see the value in trying to extend the use of disposable items like face masks—effectively reprocessing garbage.

The company recently summarized their and others’ findings on decontamination methods in a literature review. Heimbuch notes that an effective decontamination process will deactivate pathogens without significantly weakening the mask’s performance, and also be safe for the wearer.

Although scientists are still learning about the biology of SARS-CoV-2, the virus responsible for COVID-19, they do know it is one of the easiest types of viruses to kill on surfaces. The virus relies on a protective lipid coating, which common disinfectants such as hydrogen peroxide and bleach can easily breach.

“We had absolutely no doubts” that a hydrogen peroxide vapor treatment would deactivate SARS-CoV-2, says Battelle’s Kevin Hommema, who notes that his team uses hydrogen peroxide vapor to decontaminate equipment in their lab where they study biological agents. For example, Battelle says they can decontaminate respirators with hydrogen peroxide and destroy Geobacillus stearothermophilus, a hardy bacterial spore. The company reports that its researchers have validated that the hydrogen peroxide system deactivates SARS-CoV-2 on masks as well.

Hydrogen peroxide vapor was among four readily available decontamination methods recently evaluated by a group of researchers, which included scientists at the National Institute of Allergy and Infectious Diseases (NIAID). The researchers also tested UV light, a 70% ethanol solution, and heating at 70 ºC. They published their results in a preprint that has not yet been peer-reviewed (medRxiv 2020, DOI: 10.1101/2020.04.11.20062018).

Photo of gloved hands separating layers of an N95 masks to reveal inner filtration layer.
Credit: Courtesy of 4C Air
N95 face masks contain multiple layers of materials.

The team found that all four methods decimated the amount of viable virus particles on samples of N95 filter fabric. Hydrogen peroxide vapor worked the fastest, requiring only 10 minutes of contact time under their experimental conditions. (The authors note that disinfection time will vary depending on the degree of virus contamination.) They found that UV radiation and 70 ºC dry heat were effective after at least 60 min.

Results from the ethanol treatment, though, highlighted a potential pitfall in decontaminating N95 masks: Some disinfectants degrade the performance of the mask’s filtration media. The group found sharp drops in filtration efficiency after two or more treatments with ethanol. And it’s not the only disinfectant to have this effect.

“We know alcohol ruins the respirators, ARA’s Brian Heimbuch says. He also notes that quaternary ammonium compounds, which are common disinfectants, can destroy the filtration material.

SEM image showing cross section of three layers of a face masks.
Credit: Courtesy of 4C Air
N95 face masks contain a dense filtration layer sandwiched between outer coverings, as seen in this scanning electron microscopy image.

Yi Cui, a nanomaterials researcher at Stanford University, thinks these methods cause problems because liquids and vapors can damage an important but invisible feature of N95 masks: electrostatic charge.

The part of an N95 mask that does the heavy lifting of particle filtration is a mat of microfibers, typically polypropylene. The fibers crisscross and overlap, forming a dense thicket that’s easy to breathe through but hard for virus-containing particles to navigate. Those fibers are electrostatically charged to help trap the particles.

In a recent, not yet peer-reviewed preprint, Cui and colleagues at Stanford and 4C Air, an air filtration start-up company he cofounded, reported the results of tests of the impact of several disinfection methods on N95 filtration performance (medRxiv 2020, DOI: 10.1101/2020.04.01.20050443). The group’s treatments with steam, bleach, and alcohol caused dramatic drops in filtration efficiency. But the treatments did not change the amount of air moving through the masks, suggesting to Cui that the methods did not change the physical structure of the fibers. Instead, he thinks that the liquid and vapor treatments reduce the material’s electrostatic charge.

SEM image of mask filtration fabric.
Credit: Courtesy of 4C Air
In many N95 face masks, a mat of polypropylene nanofibers does the heavy lifting of particle filtration.

Cui’s studies found dry heat to be a promising treatment, a key advantage being that it is widely accessible. A 30 min treatment at between 65 and 90 ºC didn’t significantly degrade the performance of filter materials, his team reported, even with varying humidity. Such temperatures can be achieved with readily available equipment, such as the blanket warming ovens used in hospitals.

The NIAID study, which put masks through three rounds of disinfection, reported some loss of filtration performance in masks heated multiple times to 70 ºC. The masks treated with hydrogen peroxide vapor and UV light maintained acceptable performance after the 3 cycles. A technical bulletin circulated by 3M, which manufactures N95 masks, notes that ionizing radiation, high temperatures, autoclave, or steam can all reduce filter performance for its masks.

But disinfection methods can also damage other materials in these masks, such as the elastic straps and nose clips that ensure a tight fit around a user’s face. As part of the NIAID study, after running the disinfection procedures on clean masks, volunteers wore the masks for 2 hours before the next cycle. The group reported that the UV and heat-treated respirators began showing fit and seal problems after 3 decontaminations, while the vaporized hydrogen peroxide–treated masks made it through 3 cycles without failing.

The NIAID scientists concluded that vaporized hydrogen peroxide treatments exhibit the best combination of rapid virus inactivation of SARS-CoV-2 and preservation of performance, under their experimental conditions. But the method carries safety concerns. The levels of hydrogen peroxide vapor needed to disinfect masks would be toxic if inhaled, so careful engineering controls are needed to make sure operators and mask users are not exposed to unsafe conditions. (This is also a concern for treatment with ethylene oxide, a carcinogen, as any remaining residues could be inhaled by the wearer.) Battelle monitors hydrogen peroxide levels within the decontamination units to determine when operators can collect treated masks safely and workers sample masks after processing to ensure the hydrogen peroxide has been removed from the mask materials. And the company operates centralized decontamination sites, staffed by trained workers, rather than installing systems at hospitals.

Battelle, OhioHealth, and other health organizations have established a protocol for collecting, shipping, and disinfecting masks. At a hospital, health-care workers discard used masks in large hampers. Workers trained in sterile processing collect and bag the masks, then send them to Battelle’s processing site. For OhioHealth hospitals, that’s only about a 30 min drive away. Clinton says the OhioHealth network has been sending out about 2,000 to 3,000 pieces of PPE per day, mostly masks.

At the processing site, workers unpack the masks and position them on wire shelving in shipping containers. Then, a solution of 35% hydrogen peroxide is flash-vaporized and pumped into the containers. In addition to circulating in the air, the hydrogen peroxide vapor condenses on the masks and any other surfaces, such as viewing windows.

“They will basically just get fogged up like you’re taking a shower,” Kevin Hommema says. “That gives you a very nice visual that, yes, we are achieving our desired conditions in there.”

Operators maintain a high concentration of hydrogen peroxide in the chamber for 2.5 h, after which the hydrogen peroxide is allowed to decompose into water and oxygen, which can take another few hours depending on environmental conditions.

During the process, workers mark each mask to track the number of disinfection cycles it’s been through and discard any soiled or damaged masks. After working through some initial hiccups, Battelle now needs to discard less than 10% of masks from OhioHealth, Clinton says. “It effectively stretches your inventory by multiples,” he says, noting that by late March the organization was reaching 4 to 5 cycles on some masks. Battelle’s EUA authorizes it to decontaminate masks up to 20 times.

Photo of wires holding clothespins next to UV light tower.
Credit: Nebraska Medicine
At Nebraska Medicine, masks are clipped to wires before being irradiated by UV light.

Still other health-care facilities across the US are using other decontamination methods and setting up on-site systems. For example, the 800-plus-bed Nebraska Medicine network is using shortwave ultraviolet light to irradiate rooms full of masks all at once. According to documentation of the protocol, workers use clothespins to hang the masks on wires that span the length of a room, flanked by two UV light towers. The lights are activated remotely and monitored to ensure the desired exposure is achieved, after which the masks are placed in clean bags and returned to the original wearer. Workers can process 2,000 masks per day using the system.


ARA’s Heimbuch notes that due to the safety risks of exposure to shortwave light, such systems are best implemented by professionals who are experienced with the technology. And because exposure may not be uniform throughout the treatment space, it’s critical to calibrate the dose and duration of irradiation so that each mask gets sufficient exposure.

“It’s not as simple as shining a light on it,” he says.

Smaller-scale UV light systems have proved an accessible option for facilities that lack the resources or need to process huge numbers of masks. At a fire station in Oakland County, Michigan, around 96 workers are using a toaster oven–sized UV unit to stretch their supplies of N95 masks, according to Geoff Lassers, a firefighter and paramedic. Lassers also works as quality improvement coordinator at the Oakland County Medical Control Authority, where he’s involved with securing supplies, including PPE.

Photo of a tabletop UV light box.
Credit: Geoffrey Lassers
At a fire station in Oakland County, Michigan, emergency personnel use a small UV light unit to disinfect face masks.

Under normal circumstances, paramedics have rarely needed to use N95 masks, Lassers says. Now, he and his colleagues are wearing N95 masks for every call, along with goggles and gloves. As the pandemic started, he says that he and his colleagues started to wonder how long they could wear individual pieces of PPE.

The station’s UV unit can fit 2 to 3 masks at one time. After each call, Lassers lets his N95 mask and goggles sit in the box for about 10 min. Although he’s able to get a new mask any time he feels it’s necessary, he typically reuses a mask for 10 to 20 calls, disinfecting in between, he says.

For Lasser’s station, the availability of UV disinfection has helped reduce the guessing game that can occur with limited supplies.

“We know people are going to obviously ask the question, “Okay, so I just went on a call, I’m pretty sure that guy had COVID-19. And even if he didn’t, I’ve kind of played it that way. Do I throw [the mask] out? Or do I reuse it? And so that’s going to start a million questions for people.”

Back in Ohio, Laurie Hommema, as OhioHealth’s advocate for employee well-being, also knows the importance of health-care professionals being able to have confidence in their safety.

“When you’re worried about either getting the disease or taking the disease to your loved ones, that actually puts a psychological barrier in between you and the type of care that you can provide and what you feel that you can provide,” she says. “It puts people in a really difficult position of providing the care that they want to, versus the care that they feel that they can actually do safely.” She says the decontamination protocol was welcomed eagerly by staff members.

“We were really surprised because we prepared for people to be completely skeptical,” she says. “And 99% of the responses were, ‘Thank goodness!’ Everyone was so thankful because it was top of mind. Overall the response was really positive.”

OhioHealth is now working with Battelle to evaluate whether other PPE items can be effectively decontaminated using hydrogen peroxide vapor. Although the system’s authorization for use does not extend past the end of the pandemic, Clinton said he expects that an increased focus on waste and reuse will remain even after the urgent need has passed.

ARA’s Heimbuch agrees, suggesting that manufacturers may put more resources into developing reusable alternatives to traditionally disposable items, as there may now be more demand for such technologies.

“I would expect to see a huge emphasis on developing sustainable technologies,” Heimbuch says. “If we don’t make changes now, we will have the same problem when the next pandemic hits.”


This story was revised on May 7, 2020, to correct a reference to “the 800-plus-bed University of Nebraska Medical Center.” In fact, UNMC is a partner of the Nebraska Medicine network, which has 800-plus beds across two hospitals.


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