Science
Related: About this forumSteven Chu and Yi Cui: Can N95 Respirators Be Reused after Disinfection? How Many Times?
The paper to which I will refer is co-authored by President Obama's first Secretary of Energy (the best Secretary of Energy, by the way), Nobel Laureate Steven Chu and Dr. Yi Cui, who is among the most cited authors in Materials Science.
This is the paper: Can N95 Respirators Be Reused after Disinfection? How Many Times? (Lei Liao, Wang Xiao, Mervin Zhao , Xuanze Yu, Haotian Wang, Qiqi Wang, Steven Chu, and Yi Cui* ACS Nano 2020, 14, 5, 63486356.
The paper is fully open sourced, and anyone can read it. It's not overly technical, but has a few words that might strike a non-technical person as obscure, like say, "triboelectric," which means "rubbing together to generate static charges, something most everyone has done.
Some excerpts:
...The N95 grade is determined by the CDCs National Institute of Occupational Safety and Health (NIOSH) (document 42 CFR Part 84), which designates a minimum filtration efficiency of 95% for 0.3 μm (aerodynamic mass mean diameter) of sodium chloride aerosols. In addition to N95, there are N99 and N100 standards, which correspond to filtration efficiencies of 99% and 99.97%, respectively. For oil-based aerosols (DOP), NIOSH also has created grades R and P (with filtration efficiencies 9599.97%). Elsewhere around the globe, the equivalent filtration grades to N95 are FFP2 (European Union), KN95 (China), DS/DL2 (Japan), and KF94 (South Korea). Although the actual SARS-CoV-2 virus is ca. 150 nm,(18) commonly found N95 respirators can offer protection against particles as small as 80 nm with 95% filtration efficiency (initial testing, not loaded).(19) With the actual viral aerosols in the ∼1 μm range, the N95 FFRs filtration efficiency should be sufficient for personal protection...
...The COVID-19 pandemic has led to a significant shortage of N95 FFRs,(25) especially among healthcare providers. Although the virus will eventually become inactive on the mask surface and it is unlikely to penetrate fully to the users intake side, a recent study shows that 72 h were required for the concentration of SARS-CoV-1 and SARS-CoV-2 viruses on plastic surfaces (40% RH and 2123 °C) to be reduced by 3 orders of magnitude (from 103.7 to 100.6 TCID50 per mL of medium).(26) Assuming a similar longevity on FFR surfaces, it is important to develop procedures for the safe and frequent reuse of FFRs without reducing the filtration efficiency. The CDC has recommended many disinfection or sterilization methods, typically involving chemical, radiative, or temperature treatments.(27) In brief, the mechanisms of disinfection or sterilization of bacteria and viruses include protein denaturation (alcohols, heat), DNA/RNA disruption (UV, peroxides, oxidizers), and cellular disruption (phenolics, chlorides, aldehydes). Although none of these methods have been extensively evaluated for SARS-CoV-2 inactivation specifically, we tested methods that can be easily deployed within a hospital setting, and possibly accessible for the general population, with relatively high throughput for FFR reuse...
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I will skip my usual long winded commentary. Again, it's open sourced.
The paper is worth a look in my view.
DonaldsRump
(7,715 posts)It's nearly 90 degrees in the Bay Area this week, and I turn the mask both ways to face the sun. I usually go several days before wearing the mask again. I am hoping, perhaps naively, that this is enough.
eppur_se_muova
(36,289 posts)NNadir
(33,545 posts)I just took a quick look on Google Scholar. There are hundreds of patents and papers on the subject apparently in just the last few years.
It is pretty cool, I think. Maybe air filters should include capacitors. Maybe they do, I don't know.