A Scalable Method of Applying Heat and Humidity for Decontamination of N95 Respirators During the COVID-19 Crisis

Loïc Anderegg; Cole Meisenhelder; Chiu Oan Ngooi; Lei Liao; Wang Xiao; Steven Chu; Yi Cui; John M Doyle

While N95 filtering facepiece respirators (FFRs) were made for single use operation, the ongoing COVID-19 pandemic has caused a shortage worldwide of these masks. COVID-19, caused by the SARS-CoV-2 virus, has been shown to be very contagious and spread through aerosolized droplets. These fine droplets can remain in the air, increasing the risk of contagion to those nearby [1, 2] . This is particularly risky to healthcare workers who work with Covid patients. In order for an N95 mask to be reused more safely, the mask should be decontaminated of SARS-CoV-2 while maintaining its filtration efficiency and fit factor [3, 4] . Currently, limited information is known about SARS-CoV-2 inactivation. The addition of moisture possibly plays a role in the inactivation of some viruses [5] [6] [7] . A study found viral inactivation in 70 o C for 5 minutes [8] while in a buffered solution. SARS-CoV-2 has also been shown to be inactivated at temperatures of 60-75 o C for 5-30 minutes in various liquid media [9] [10] [11] . Other enveloped viruses, such as H1N1 and H5N1 Influenza strains have been shown to be inactivated with moist heat at 65 o C and over 50% humidity [5] [6] [7] . These studies also found that dry heat alone was not enough to deactivate H1N1. While previous studies have looked at the effects of moist heat on N95 FFRs, these were done at substantially lower temperatures of 60-65 o C [5, 7, 12, 13] . We also note that recent CDC guidelines have indicated that moist heat is a reasonable method for reusing N95 FFRs. The resistance of Clostridium difficile (C. diff.) at elevated temperature and moisture was also studied and found temperatures Figure. 1 Figure 1 (a) Each N95 FFR (1) was placed into a plastic container with a paper towel (2) with 500 uL of water. Both the mask (3) and container (4) were labeled with a Sharpie black permanent ink marker, which would allow the mask to be identified by the correct healthcare worker and avoid cross contamination. (b) For testing purposes, the lid of each container was modified to have a temperature and humidity sensor (STH30).