Study: Heating N95 Masks Could Disinfect for Reuse

Heating N95 respiratory masks to 185 degrees Fahrenheit for 20 minutes may be the safest and most reliable way to reuse the masks, researchers found in a recently released study.¹ The ability to sanitize and reuse personal protective equipment (PPE) such as masks, gowns, and face shields has become particularly important as the coronavirus disease 2019 (COVID-19) pandemic has resulted in ongoing PPE shortages.

PPE and appropriate infection control training are vital to keep health care workers safe, according to the researchers from Oregon Health and Science University.²

An evidence review of 64 studies related to rates of infection among health care workers exposed to COVID-19, Severe Acute Respiratory Syndrome (SARS), or Middle Eastern Respiratory Syndrome (MERS), indicated that providing PPE is not enough. Training workers on how to properly use the equipment is vital to ensuring their safety.²

The investigators also found that front-line exposures, such as involvement in intubations, direct contact with infected patients, or contact with bodily secretions, resulted in increased risk of infection. There is also a significant impact on mental health among workers exposed to the virus without proper PPE, including high rates of depression, anxiety, and psychological stress.²

“Infection control training is important,” said senior author Roger Chou, MD, in a statement. “It’s not just about providing the equipment but helping health care workers understand how they need to use it. Training and education were consistently associated with decreased risk of infection.”²

Providing that equipment has been a challenge, however, with one survey finding that 42% of respondents characterized the disruption in supplies of surgical-type medical masks as either “major” or “moderate.”³ In an effort to better understand techniques for disinfecting N95 masks, a team of researchers tested several strategies.

According to the authors, N95 masks contain a layer of polypropylene fibers that are electrostatically charged in order to form a porous, breathable fabric while still catching smaller particles. The CDC has recommended several possible techniques for disinfecting the masks, including heating, ultraviolet (UV) radiation, and bleach treatments, but the study authors noted that none of these options have been extensively tested, especially for multiple rounds of disinfectant.¹

The authors examined pieces of the fabric used to make N95 masks and compared various disinfecting methods. First, spraying the fabric with an ethanol or chlorine bleach solution drastically reduced the filtration efficiency, from about 96% to 56% after only 1 treatment with ethanol. With the chlorine bleach treatment, the efficiency dropped from 96% to 56%.¹

They found that a single steam treatment did maintain the filtration, but 5 treatments declined the mask’s efficiency. UV radiation, on the other hand, allowed up to 20 cycles of disinfection, but administering the precise dose of UV to kill the virus without damaging the materials could be challenging.¹

Finally, they found that heating the masks at 185°F for 20 minutes allowed the fabric to be treated 50 times without the loss of efficiency.¹

While this was a relatively small study, ongoing research combined with strengthened supply chains could help to alleviate some fears of health care workers caring for patients without proper PPE.¹

“Most people understand it’s a high priority to protect our nurses and doctors,” Chou said. “In addition to the impact that COVID-19 would have on infected health care workers, they can pose a transmission risk. Plus, they can’t work if they become infected, and maintaining health care capacity throughout the pandemic is important.”¹

REFERENCES

• Liao L, Xiao W, Zhao M, et al. Can N95 Respirators Be Reused after Disinfection? How Many Times? American Chemical Society Nano; May 5, 2020. https://pubs.acs.org/doi/full/10.1021/acsnano.0c03597. Accessed May 12, 2020.
• PPE, plus training, lowers risk of COVID-19 for health care workers [news release]. Oregon Health and Science University; May 5, 2020. https://news.ohsu.edu/2020/05/05/ppe-plus-infection-control-training-lowers-risk-of-covid-19-among-health-care-workers. Accessed May 12, 2020.
• Murphy J. ASHP Survey Finds Severe Supply Disruption in Medical Masks. Pharmacy Times; April 8, 2020. https://www.pharmacytimes.com/news/ashp-survey-finds-severe-supply-disruption-in-medical-masks. Accessed May 12, 2020.