Since the outbreak of the COVID-19 pandemic, N95 face masks have been in short supply. Health care workers, in particular, desperately need these masks to protect themselves from the respiratory droplets of infected patients. But because of the shortage, many have to wear the same mask repeatedly.
Now, researchers have tested several methods for disinfecting N95 materials, finding that heating them preserves their filtration efficiency for 50 cycles of disinfection. N95 masks contain a layer of "melt-blown" polypropylene fibres that form a porous, breathable network. To help capture smaller particles that could slip through the holes, the fibres are electrostatically charged.
The US Centres for Disease Control and Prevention 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. 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.
In this study, instead of analysing N95 masks – which should be reserved for health care workers – the researchers examined pieces of the melt-blown 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.
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% to 56% (ethanol) or 73% (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. For example, heating at 185 F for 20 minutes allowed the fabric to be treated 50 times without loss of filtration efficiency. But frequently donning and removing N95 masks could affect fit, which also impacts performance, the researchers point out.
Abstract
The coronavirus disease 2019 (COVID-19) pandemic has led to a major shortage of N95 respirators, which are essential for protecting healthcare professionals and the general public who may come into contact with the virus. Thus, it is essential to determine how we can reuse respirators and other personal protective equipment in these urgent times. We investigated multiple commonly used disinfection schemes on media with particle filtration efficiency of 95%. Heating was recently found to inactivate the virus in solution within 5 min at 70 °C and is among the most scalable, user-friendly methods for viral disinfection. We found that heat (≤85 °C) under various humidities (≤100% relative humidity, RH) was the most promising, nondestructive method for the preservation of filtration properties in meltblown fabrics as well as N95-grade respirators. At 85 °C, 30% RH, we were able to perform 50 cycles of heat treatment without significant changes in the filtration efficiency. At low humidity or dry conditions, temperatures up to 100 °C were not found to alter the filtration efficiency significantly within 20 cycles of treatment. Ultraviolet (UV) irradiation was a secondary choice, which was able to withstand 10 cycles of treatment and showed small degradation by 20 cycles. However, UV can potentially impact the material strength and subsequent sealing of respirators. Finally, treatments involving liquids and vapors require caution, as steam, alcohol, and household bleach all may lead to degradation of the filtration efficiency, leaving the user vulnerable to the viral aerosols.
Authors
Lei Liao, Wang Xiao, Mervin Zhao, Xuanze Yu, Haotian Wang, Qiqi Wang, Steven Chu, Yi Cui
[link url="https://www.acs.org/content/acs/en/pressroom/newsreleases/2020/may/heating-could-be-best-way-to-disinfect-n95-masks-for-reuse.html"]American Chemical Society material[/link]
[link url="https://pubs.acs.org/doi/10.1021/acsnano.0c03597"]ACS Nano abstract[/link]