Dry heat sterilization as a method to recycle N95 respirator masks: The importance of fit.

John G Yuen,Kenneth R Shroyer,Amy C Marshilok,Kim Kisslinger,Kenneth J Takeuchi,Sruthi Babu,Glen Itzkowitz,Chavis A Stackhouse,Daniel A Knopf,Shan Yan,Esther S Takeuchi,David C Bock,Jeronimo Cello,Lei Wang,David Thanassi,Peter Todd Benziger

doi:10.1371/journal.pone.0257963

Abstract

In times of crisis, including the current COVID-19 pandemic, the supply chain of filtering facepiece respirators, such as N95 respirators, are disrupted. To combat shortages of N95 respirators, many institutions were forced to decontaminate and reuse respirators. While several reports have evaluated the impact on filtration as a measurement of preservation of respirator function after decontamination, the equally important fact of maintaining proper fit to the users' face has been understudied. In the current study, we demonstrate the complete inactivation of SARS-CoV-2 and preservation of fit test performance of N95 respirators following treatment with dry heat. We apply scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDS), X-ray diffraction (XRD) measurements, Raman spectroscopy, and contact angle measurements to analyze filter material changes as a consequence of different decontamination treatments. We further compared the integrity of the respirator after autoclaving versus dry heat treatment via quantitative fit testing and found that autoclaving, but not dry heat, causes the fit of the respirator onto the users face to fail, thereby rendering the decontaminated respirator unusable. Our findings highlight the importance to account for both efficacy of disinfection and mask fit when reprocessing respirators to for clinical redeployment.

Highlights

After incubating the N95 respirators at 80 ̊C for 60 minutes, 1 x 103 PFU of viable virus was recovered from the respirator, demonstrating a 2-log reduction of virus as compared to samples that were kept at room temperature
Quantitative fit testing was performed on four models of N95 respirators after autoclaving or dry heat incubation at either 100 ̊C for 30 minutes or 80 ̊C for 60 minutes
-7.83 -1.11 -1.04 -7.22 0.00 -0.02 0.00 -0.48 0.00 0.00 0.00 -0.56 offers guidance, based on an institutions’ burn rate and crisis capacity strategies, whether N95 respirators are recommended for reuse and what methods for decontamination are authorized

Summary

Introduction

Both the CDC and other organizations including 3M, a major respirator manufacturer, have frequently cited ultraviolet germicidal irradiation, vaporous hydrogen peroxide, and moist heat as recommended methods for decontamination of FFRs [7,8,9,10] These methods, often call for specific equipment that may prove difficult to obtain and/or difficult to implement in many healthcare facilities and in the general public. While several reports have evaluated the impact on filtration as a measurement of preservation of respirator function after decontamination [16], the important fact of maintaining proper fit to the wearer’s face has been understudied Per both the National Institute for Occupational Safety and Health Part 84 Title 42 of the Code of Federal Regulations (NIOSH 42 CFR 84) and the FDA, respirators must be assessed for filter performance, and fit, i.e., the sealant performance between mask on the individual’s face. Our findings highlight the importance to account for both efficacy of disinfection and mask fit when reprocessing respirators to for clinical redeployment

Materials and methods

Measurement Procedure

Results

Discussion