N95 face masks have been in short supply since the COVID-19 pandemic broke out. In particular, health-care staff urgently need these masks to shield themselves from contaminated patients’ respiratory droplets. But many have to wear the same mask repeatedly, because of the shortage. Researchers have now tested several methods to disinfect N95 masks. On April 15, Robert Fischer, Ph.D., with the Hamilton, Montana National Institute of Allergy and Infectious Diseases, and colleagues posted the findings on a preprint server. The paper is not peer-reviewed yet.
Fischer and colleagues evaluated four methods optimized for one-time decontamination of the masks: UV radiation (260 – 285 nm); 70 ° C dry heat; 70% ethanol spray; and VHP. For each method, the researchers compared the rate at which SARS-CoV-2 on N95 filter fabric is detected to that on stainless steel. The researchers treated intact, clean masks with the same decontamination process to assess reliability over three uses, and evaluated performance through quantitative fit testing.
All four methods removed detectable SARS-CoV-2 virus from the fabric test samples, though the decontamination time required varied. VHP was the fastest, taking 10 minutes to complete. It took about 60 minutes each to get dry heat and UV light. Ethanol required a medium amount of time. Rocky Mountain Laboratory volunteers wore the masks for 2 hours to test fit and seal.
Results showed that masks decontaminated with ethanol spray did not work effectively after decontamination and did not suggest using the process. UV and VHP decontaminated masks can be used up to three times and can work properly. Masks decontaminated with dry heat could be employed twice before declining function.
However, the greatest possible care should be taken to disinfect N95 masks and ensure that the N95 respirator functions properly after each decontamination using readily available qualitative fit testing tools, and to ensure that treatments are performed for sufficient time to achieve the desired risk reduction.
