During the current COVID-19 pandemic, the use of N95 respirators—not for use by the general public—has been advised to reduce and prevent the user's exposure to airborne contaminants. Guidance issued by the US Centers for Disease Control and Prevention (CDC) says that N95 respirators are critical supplies that are to be reserved for health care workers and other medical first responders.
Since N95 respirators are short in supply, health care workers may have to wear the same mask repeatedly. After trying and testing out various methods for disinfecting N95 materials, a team of researchers have found that heating them preserves their filtration efficiency for 50 cycles of disinfection.
N95 masks—designed to filter smaller contaminants compared to the average surgical mask— contain a layer of "meltblown" polypropylene fibers that form a porous, breathable network. To help capture smaller particles that could slip through the holes, the fibers are electrostatically charged.
The CDC has recommended several methods for disinfecting N95 masks, such as heating, ultraviolet (UV) radiation and bleach treatment, but so far they have not been tested extensively, especially for multiple rounds of disinfection.
In their study, Yi Cui and colleagues wanted to compare five of the methods that could reasonably be used within a hospital setting to see how mask materials hold up to repeated disinfections.
Instead of analysing N95 masks, the researchers examined pieces of the meltblown fabric used to make these masks. They treated the material with a particular disinfectant and compared its ability to filter aerosol particles (resembling respiratory droplets, but lacking coronavirus) before and after disinfection.
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The team found that spraying the fabric with an ethanol or chlorine bleach solution drastically reduced the filtration efficiency after only one treatment, from about 96 per cent to 56 per cent (ethanol) or 73 per cent (bleach).
A single steam treatment maintained filtration, but five steam treatments led to a sharp decline in efficiency.
UV radiation allowed up to 20 cycles of disinfection; however, administering the exact dose of UV that kills the virus without damaging mask materials could be problematic, the researchers note.
The best disinfection method appeared to be heating. Heating at 85 degree Celsius for 20 minutes allowed the fabric to be treated 50 times without loss of filtration efficiency.
The study, published in the American Chemical Society’s ACS Nano, warns that frequently donning and removing N95 masks could affect fit, which also impacts performance.
