How Effective are Re-used Surgical Masks and N95 Respirators?

by | Sep 1, 2020 | 2020, COVID-19

Written by Joyce Smith, BS. This study tests the effectiveness and safety of hospital disinfection of reused masks and N95 respirators.

Our global pandemic has resulted in an extraordinary short supply of disposable surgical and N95 respiratory masks that has led to the medical community’s re-use of these devices. While generally considered disposable and unsafe for re-use, the US Centers for Disease Control and Prevention made and exception to their “decontamination and re-use policy” and allowed “as a crisis capacity strategy” 1 the disinfection and re-use of masks to improve the personal protection equipment shortage and ensure an adequate supply for hospital staff. Thus on March 3, 2020, an Emergency Use Authorization 2 allowed for the decontamination of disposable masks. FFR filter sterilization treatments such as ultraviolet germicidal irradiation, plasma sterilization, microwave oven irradiation, and bleach treatment have all been studied, yet other available methods that inactivate viruses and bacteria on FFR filters such as autoclaving and 70% alcohol, commonly used in hospitals during the COVID-19 pandemic, have not been tested for their performance and integrity.

In this study 3 Grinshpun and team, using autoclaving or a 70% alcohol treatment, tested two brands of NIOSH-certified N95 respirators and two types of surgical masks (Lsp M-301 with low and 3M-1818 with high filtration capability) for their filter collection efficiencies. Masks and respirators were autoclaved before soiled and replicated in triplicate in 5 different soil and sterilization cycles to simulate and compare the efficiency of unused equipment to that of re-used equipment for 5 days.  The alcohol treatment method involved soaking the respirators and surgical masks in a 70% ethanol for two hours, then drying the devices before re-use. As in the autoclaving procedure, different soil and treatment cycles were repeated up to 5 times to simulate the reusage that might occur in an actual hospital setting.

Neither sterilization in an autoclave nor ethanol treatment caused visible damage to the surgical masks. While the unused 3M1818 mask (with high filtration capability) performed well when treated with alcohol; autoclaving reduced its ability to efficiently trap particles. The ability was further reduced by repeated autoclaving especially when the filter was soiled with protein. While both mask filters lost their ability to trap smaller particles, the re-used, most decontaminated, and most autoclaved 3M-1818 filter was still able to trap > 82% of MPPS at 30 L/min and > 70% at 85L/min. The surgical mask, Lsp M-301, which had an initial relatively inefficient ability to trap particles, did not perform as well and significantly dropped its ability to trap particles the size of the coronavirus from 70% to 50%.

The M95 FFR filters performed much better. As with the surgical masks but to a much lesser degree, autoclaving decreased the respirator filter’s ability to trap particles with the highest difference observed for the filters that were soiled and autoclaved five times. However, performing at significantly greater efficiency than the 3M1818 mask filter, even the smallest particles that penetrated the filter were trapped at 99.1% at 30 L/min and 97.1% at 85 L/min, making it capable of capturing the coronavirus (5x larger in size than the small particles).

N95 respirators and some surgical masks rely on fibers that have an electrostatic charge that allows them to capture small particles and protect the wearer. The moist heat of autoclaving, and more so the alcohol treatment, weakened this electrostatic charge 4,5. Three of the tested devices, the 3M 1818 surgical mask and the two N95 respirators had electret filters that accounted for their reduced filter collection efficiency. A study limitation is its focus on filter performance and not on fit.  After autoclaving, some N95 FFRs had damaged nose pads and seals around the nose clip and loss of strap elasticity due to heat which made the devices non-reusable. Regardless of repeated treatments (autoclaving or alcohol), the major damage inflicted on the performance ability of the masks and respirators occurred after the first test.

These results highlight the limitations of hospital re-use of masks and respirators that have been autoclaved and alcohol treated and recommend a reassessment of strategies used by hospitals to decontaminate and re-use their masks and N95 respirators.

Source: Grinshpun, Sergey A., Michael Yermakov, and Marat Khodoun. “Autoclave sterilization and ethanol treatment of re-used surgical masks and N95 respirators during COVID-19: impact on their performance and integrity.” Journal of Hospital Infection (2020).

© 2020 The Healthcare Infection Society. Published by Elsevier Ltd. All rights reserved.

Posted September 1, 2020.

Joyce Smith, BS, is a degreed laboratory technologist. She received her bachelor of arts with a major in Chemistry and a minor in Biology from  the University of Saskatchewan and her internship through the University of Saskatchewan College of Medicine and the Royal University Hospital in Saskatoon, Saskatchewan. She currently resides in Bloomingdale, IL.

References:

  1. CDC. Implementing Filtering Facepiece Respirator (FFR) Reuse, Including Reuse after Decontamination, When There Are Known Shortages of N95 Respirators. 2020; https://www.cdc.gov/coronavirus/2019-ncov/hcp/ppe-strategy/decontamination-reuse-respirators.html. Accessed August 24, 2020.
  2. FDA. Emergency Use Authorization. 2020; https://www.fda.gov/emergency-preparedness-and-response/mcm-legal-regulatory-and-policy-framework/emergency-use-authorization. Accessed August 24, 2020.
  3. Grinshpun SA, Yermakov M, Khodoun M. Autoclave sterilization and ethanol treatment of re-used surgical masks and N95 respirators during COVID-19: impact on their performance and integrity. The Journal of hospital infection. 2020;105(4):608-614.
  4. Martin SB, Jr., Moyer ES. Electrostatic respirator filter media: filter efficiency and most penetrating particle size effects. Applied occupational and environmental hygiene. 2000;15(8):609-617.
  5. Bałazy A, Toivola M, Adhikari A, Sivasubramani SK, Reponen T, Grinshpun SA. Do N95 respirators provide 95% protection level against airborne viruses, and how adequate are surgical masks? Am J Infect Control. 2006;34(2):51-57.