Tests of multiple commonly used disinfection schemes on media with particle filtration efficiency of 95% found that heat (≤ 85°C)—under various levels of humidity (≤ 100% relative humidity)—was the most promising, nondestructive method for the preservation of filtration properties in meltblown fabrics, as well as N95-grade respirators. This data, published in ASC Nano, also found that ultraviolet (UV) irradiation was a potential secondary choice.

The coronavirus disease 2019 (COVID-19) pandemic has led to major shortages of personal protective equipment and N95 respirators. To deal with supply concerns, it is necessary to determine how these items may be safely reused.  Investigators tested methods for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) inactivation that can be easily deployed within hospital settings, and that may be accessible for the general population, with relatively high throughput for filtering facepiece respirators reuse.

Heating has been shown to inactivate SARS-CoV-2 in solution within 5 minutes at 70 °C and is among the most scalable, user-friendly methods for viral disinfection. Investigators found that temperatures of < 85°C in relative humidity levels of < 100% was the most promising method. At 85°C and 30% relative humidity, investigators could preform 50 cycles of treatment without significant changes to filtration efficiency. Temperatures of 100°C did not alter filtration efficiency significantly within 20 cycles at low humidity or dry conditions. At temperatures of ≤85 °C, humidity did crucially affect the filtration properties, as filtering facepiece respirators tested at a near 100% relative humidity at 85 °C were unaffected. However, as steam results in a decrease in efficiency, the humidity should be kept low if approaching 100 °C.

Tests with UV irradiation showed the tested materials could withstand 10 cycles and showed small degradation by 20 cycles. Importantly though, UV can affect material strength and subsequent sealing of respirators. It was also shown that liquid and vapor treatments require caution as steam, alcohol, and household bleach can all degrade filtration efficiency.


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Investigators stressed that, “although these methods were not tested on [filtering facepiece respirators] that have been exposed to SARS-CoV-2, these methods use disinfection precedents set by either SARS-CoV or recent data based on inactivation of SARS-CoV-2 in solution.”

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Based on their data investigators concluded, “commonly deployable methods, heating (dry or in the presence humidity) <100 °C can preserve the filtration characteristics of a pristine N95 respirator.” They also cautioned that the use of steam requires caution as the treatments seem to be suitable but prolonged treatment may leave users unprotected. Finally, they advised against liquid contact to clean respirators. For example, alcohol solutions or chlorine-based solutions, and soaps will lead to the degradation in the static charge that is required for filtering facepiece respirators to meet the N95 standard.

Reference

Liao L, Xiao W, Zhao M, et al. Can N95 respirators be reused after disinfection? How many times? [published online May 5 2020] ACS Nano. doi:10.1021/acsnano.0c03597.