Under the epidemic, N95 masks were extremely scarce, and the United States also began to find ways to disinfect and reuse them. On April 15, the National Institutes of Health (NIH) said that it has found three disinfection methods that can reuse N95 masks a limited number of times, namely hydrogen peroxide (VHP), dry heat at 70 degrees Celsius, and ultraviolet treatment.
Among them, vaporized hydrogen peroxide is the most effective disinfection method, because after only 10 minutes of treatment with it, the virus cannot be detected on the N95 filter cloth. Ultraviolet and dry heat methods can also be used to disinfect N95 masks, but the process takes at least 60 minutes.
The research was completed by the Rocky Mountain Laboratory (RML) affiliated with the American Institute of Allergy and Infectious Diseases (NIAID) in collaboration with the University of California, Los Angeles. The researchers tested the N95 filter cloth exposed to the new coronavirus with four disinfection methods. Test methods include vaporized hydrogen peroxide, dry heat at 70 degrees Celsius, ultraviolet light and 70% ethanol spray. The results showed that all four methods eliminated the detectable live virus from the N95 fabric test sample.
To test the durability of repeated use, the researchers then used the same method to deal with complete and clean masks. During the experiment, volunteers from the Rocky Mountain Laboratory were asked to wear a mask for two hours to determine whether the mask fits well and can be sealed on the face. The researchers used the same procedure to sterilize each mask three times.
They found that after two sterilization treatments, ethanol spray destroys the fit and seal integrity of the mask, so it is not recommended to disinfect N95 masks with ethanol spray. Masks sterilized with ultraviolet light and heat treatment have problems with fit and tightness after the third treatment, which shows that these two methods can be used to reuse the mask twice. The masks treated with vaporized hydrogen peroxide showed no problems after three treatments, indicating that they may be reused three times.
The National Institutes of Health emphasized that the research was conducted in a controlled laboratory environment and the results were published on the medical preprint platform MedRxiv.
The researchers reminded that before using a disinfected N95 mask, the fit and tightness of the mask should be checked.