Disposable N95 Masks Pass Qualitative Fit-Test But Have Decreased Filtration Efficiency after Cobalt-60 Gamma Irradiation

Abstract

The current COVID-19 pandemic has led to a dramatic shortage of masks and other personal protective equipment (PPE) in hospitals around the globe [1]. One component of PPE that is in particular demand are disposable N95 face masks. To alleviate this, many methods of N95 mask sterilization have been studied and proposed with the hope of being able to safely reuse masks [2]. Two major considerations must be made when re-sterilizing masks: (1) the sterilization method effectively kills pathogens, penetrating into the fibers of the mask, and (2) the method does not degrade the operational integrity of the N95 filters.We studied Cobalt-60 ( 60 Co) gamma irradiation as a method of effective sterilization without inducing mask degradation. Significant literature exists supporting the use of gamma radiation as a sterilization method, with viral inactivation of SARS-CoV reported at doses of at most 10 kGy [3], with other studies supporting 5 kGy for many types of viruses [4]. However, concerns have been raised about the radiation damaging the fiber material within the mask, specifically by causing cross-linking of polymers, leading to cracking and degradation during fitting and/or deployment [5,6].A set of 3M 8210 and 9105 masks were irradiated using MIT's 60 Co irradiator. Three masks of each type received 0 kiloGray (kGy), 10 kGy and 50 kGy of approximately 1.3 MeV gamma radiation from the circular cobalt sources, at a dose rate of 2.2kGy per hour.Following this sterilization procedure, the irradiated masks passed a OSHA Gerson Qualitative Fit Test QLFT 50 (saccharin apparatus) [7] when donned correctly, performed at the Brigham and Women's Hospital, in a blinded study repeated in triplicate. However, the masks' filtration of 0.3 µm particles was significantly degraded, even at 10 kGy.These results suggest against gamma, and possibly all ionizing radiation, as a method of disposable N95 sterilization. Even more importantly, they argue against using the qualitative fit test alone to assess mask integrity.

The role of environmental factors to transmission of SARS-CoV-2 (COVID-19)

“…The most available type is the N95 mask, which according to studies can be sterilized and reused by hydrogen peroxide, gamma rays from CO60, UV rays, dry and wet heat, and ethylene oxide. In the meantime, the use of radiation is preferable to other methods (Card et al 2020;Cramer et al 2020;Kenney et al 2020). Gamma CO60 with a dose of 10 KG can sterilize the N95 mask used in SARS-COV environments, and kill the virus (Feldmann et al 2019).…”

Analysis of SteraMist ionized hydrogen peroxide technology in the sterilization of N95 respirators and other PPE: a quality improvement study

“…The possibility that disposable N95 masks could be sterilized and reused was raised 15 years ago as a strategy to address shortages arising from medical emergencies, [3][4][5] but with the exception of a single FDA-funded study by the Battelle Memorial Institute, 6 little subsequent research was performed on the topic. Recently, in response to acute N95 mask shortages, multiple strategies for mask sterilization have been proposed and studied, including exposure to ultraviolet (UV) germicidal irradiation, vaporized hydrogen peroxide, moist heat, ethylene oxide, and gamma irradiation [7][8][9][10][11][12][13][14] . In this study, we evaluate a recently developed technology, ionized hydrogen peroxide (iHP), as a method for sterilizing N95 masks and other PPE.…”

Effect of gamma sterilization on filtering efficiency of various respiratory face-masks

“…(Kumar et al, 2015 andLei et al, 2020). All above sterilisation method having advantages and disadvantages from one than others (Avilash et. al., 2020 andJuan et al, 2020).…”