Principles and practice for SARS-CoV-2 decontamination of N95 masks with UV-C

Abstract

A mainstay of personal protective equipment during the coronavirus disease 2019 pandemic is the N95 filtering facepiece respirator. N95 respirators are commonly used to protect healthcare workers from respiratory pathogens, including the novel coronavirus severe acute respiratory syndrome coronavirus 2, and are increasingly employed by other frontline workers and the general public. Under routine circumstances, these masks are disposable, single-use items, but extended use and reuse practices have been broadly enacted to alleviate critical supply shortages during the coronavirus disease 2019 pandemic. Although extended-time single use presents a low risk of pathogen transfer, repeated donning and doffing of potentially contaminated masks presents increased risk of pathogen transfer. Therefore, efficient and safe decontamination methods for N95 masks are needed to reduce the risk of reuse and mitigate local supply shortages. Here, we review the available literature concerning use of germicidal ultraviolet-C (UV-C) light to decontaminate N95 masks. We propose a practical method for repeated point-of-use decontamination using commercially available UV-C cross-linker boxes from molecular biology laboratories to expose each side of the mask to 800-1200 mJ/cm 2 of UV-C. We measure the dose that penetrated to the interior of the respirators and model the potential germicidal action on coronaviruses. Our experimental results, in combination with modeled data, suggest that such a UV-C treatment cycle should induce a >3-log-order reduction in viral bioburden on the surface of the respirators and a 2-log-order reduction throughout the interior. We find that a dose 50-fold greater does not impair filtration or fit of 3M 8210 N95 masks, indicating that decontamination can be performed repeatedly. As such, UV-C germicidal irradiation is a practical strategy for small-scale point-of-use decontamination of N95s.

Decontamination of High-Efficiency Mask Filters From Respiratory Pathogens Including SARS-CoV-2 by Non-thermal Plasma

“…As expected, both techniques maintained the filtration efficiency of the filters ( Table 1 ), and exposure to UVC was also efficient in inactivating all respiratory pathogens tested ( Figures 2 , 3 and Supplementary Table S1). This confirms that irradiation techniques can be regarded as methods of choice, as concluded by a number of studies ( Derraik et al, 2020 ; Boškoski et al, 2020 ; Su-Velez et al, 2020 ; Huber et al, 2021 ). However, a drawback for broad applicability of gamma irradiation is the requirement of expensive equipment and expert operating personnel.…”

Decontamination Methods of N95 Respirators Contaminated with SARS-CoV-2

“…(D) light microscope images of the four layers, with a lower row at four-fold higher magnification (3M model 8210). Adapted from [18] with permission.…”

“…(A) Environmental interface; (B) user interface; (C) from left to right: inner layer (shell), middle layers (filter 2 and filter 1), and outer layer (coverweb);(D) light microscope images of the four layers, with a lower row at four-fold higher magnification (3M model 8210). Adapted from[18] with permission.…”

Ultraviolet-C Irradiation, Heat, and Storage as Potential Methods of Inactivating SARS-CoV-2 and Bacterial Pathogens on Filtering Facepiece Respirators

“…Ultraviolet germicidal irradiation (UVGI, 250 to 280 nm) is a portion of the UV-C spectrum (200 to 280 nm) frequently generated using low-pressure mercury lamps emitting at 253.7 nm [21]. Although the dose (or fluence) required to inactivate bacteria and viruses has been studied over the years [21], the current COVID-19 pandemic has reignited the need to develop cost-effective procedures to decontaminate surfaces and materials using UV-C [22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40]. In the case of SARS-CoV-2, UV-C doses ranging from 16.9 mJ/cm 2 in cell culture [41] to 1500 mJ/cm 2 on FFR [42] are reportedly required to fully inactivate virus replication.…”