Assessment of the Qualitative Fit Test and Quantitative Single-Pass Filtration Efficiency of Disposable N95 Masks Following Gamma Irradiation | Critical Care Medicine | JAMA Network Open | JAMA Network
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Figure.  Single-Pass Filtration Efficiency of N95 Masks That Underwent Gamma Irradiation
Single-Pass Filtration Efficiency of N95 Masks That Underwent Gamma Irradiation

Box plots show data from a given particulate size for N95 masks that received 0, 1, 10, and 50 kGy gamma radiation doses from a cobalt-60 source. Tops and bottoms of boxes denote 75th and 25th percentiles, respectively. Lines within boxes denote medians. Circles denote outliers. Error bars were calculated by 6 observations of the upstream and downstream particle concentration.

Table.  Single-Pass Filtration Efficiencies for Ambient Particles of Irradiated N95 Masks
Single-Pass Filtration Efficiencies for Ambient Particles of Irradiated N95 Masks
1.
Feng  S, Shen  C, Xia  N, Song  W, Fan  M, Cowling  BJ.  Rational use of face masks in the COVID-19 pandemic.   Lancet Respir Med. Published online March 20, 2020. doi:10.1016/S2213-2600(20)30134-XPubMedGoogle Scholar
2.
Bauchner  H, Fontanarosa  PB, Livingston  EH.  Conserving supply of personal protective equipment: a call for ideas.   JAMA. Published online March 20, 2020. doi:10.1001/jama.2020.4770PubMedGoogle Scholar
3.
Viscusi  DJ, Bergman  MS, Eimer  BC, Shaffer  RE.  Evaluation of five decontamination methods for filtering facepiece respirators.   Ann Occup Hyg. 2009;53(8):815-827.PubMedGoogle Scholar
4.
Feldmann  F, Shupert  WL, Haddock  E, Twardoski  B, Feldmann  H.  Gamma irradiation as an effective method for inactivation of emerging viral pathogens.   Am J Trop Med Hyg. 2019;100(5):1275-1277. doi:10.4269/ajtmh.18-0937PubMedGoogle ScholarCrossref
5.
Sullivan  R, Fassolitis  AC, Larkin  EP, Read  RB  Jr, Peeler  JT.  Inactivation of thirty viruses by gamma radiation.   Appl Microbiol. 1971;22(1):61-65. doi:10.1128/AEM.22.1.61-65.1971PubMedGoogle ScholarCrossref
6.
Harrell  CR, Djonov  V, Fellabaum  C, Volarevic  V.  Risks of using sterilization by gamma radiation: the other side of the coin.   Int J Med Sci. 2018;15(3):274-279. doi:10.7150/ijms.22644PubMedGoogle ScholarCrossref
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    Research Letter
    Occupational Health
    May 26, 2020

    Assessment of the Qualitative Fit Test and Quantitative Single-Pass Filtration Efficiency of Disposable N95 Masks Following Gamma Irradiation

    Author Affiliations
    • 1Harvard-MIT Division of Health Sciences and Technology, Boston, Massachusetts
    • 2Department of Building Science, Tsinghua University, Beijing, China
    • 3Department of Nuclear Science and Engineering, Massachusetts Institute of Technology, Cambridge
    • 4Division of Neuroradiology, Massachusetts General Hospital, Boston
    JAMA Netw Open. 2020;3(5):e209961. doi:10.1001/jamanetworkopen.2020.9961
    Introduction

    The coronavirus disease 2019 pandemic has led to a dramatic shortage of masks and other personal protective equipment in hospitals around the globe. One component of personal protective equipment, the disposable N95 face mask, is in particular demand.1,2 To alleviate a shortage of N95 masks, many methods to resterilize them have been proposed and studied.3 Any method for resterilizing masks must not degrade the filtration efficiency of the mask.

    This quality improvement study examines cobalt-60 gamma irradiation as a method of N95 mask sterilization. Viral inactivation of severe acute respiratory syndrome coronavirus has been reported at radiation doses of 10 kGy at most, with other studies supporting a radiation dose of 5 kGy for many types of viruses.4,5

    Gamma irradiation has certain logistical advantages over other sterilization methods but there is a concern that radiation may damage the mask by cross-linking polymers within it and make them brittle. Ionizing radiation can disrupt the electrostatic charge distribution in the electret material of the mask and reduce its filtration efficiency against submicron particles.6

    Methods

    This study was performed as part of hospital operations and infection control and, as per Massachusetts General Hospital policy, did not require institutional review board approval. This study follows the Standards for Quality Improvement Reporting Excellence (SQUIRE) reporting guideline.

    A set of 3M 8210, 1805, and 9105 masks were irradiated using a cobalt-60 irradiator (GammaCell 220 E; Atomic Energy of Canada) at the Massachusetts Institute of Technology. Three masks of each type received 0 kGy (control), 1 kGy, 10 kGy, and 50 kGy of approximately 1.3 MeV gamma radiation from the source, at a dose rate of 2.2 kGy per hour.

    The control (0 kGy) and 3 sets of irradiated masks (1, 10, and 50 kGy) were subjected to the Occupational Safety and Health Administration Gerson Qualitative Fit Test 50 (saccharin apparatus) by 1 of the authors (M.S.) and a Partners Healthcare physician in a blinded fashion. Another set of control and irradiated masks were tested for their particulate single-pass filtration efficiency. These masks were inserted into a specialized air duct, and ambient particulate matter was driven through the duct and the mask. The pressure differentials and flow velocities are shown in the Table. Three different particle sizes—0.3, 0.5, and 1 μm—were tested, and the single-pass filtration efficiency was measured using an optical particle counter (Aerotrak 9306; TSI Inc). The measurement system, which was not calibrated for N95 mask certification, was only used to assess the relative changes in the filtration efficiency.

    Statistical analyses were performed using R statistical software version 3.6.3 (R Project for Statistical Computing) with the level of significance set at P < .05. All tests were 2-sided. A linear mixed effects model was performed to assess the effects of dose (untreated, 1 kGy, 10 kGy, and 50 kGy) on the filtration efficiency of particles of 3 different sizes (0.3 μm, 0.5 μm, and 1 μm) using 2 masks per condition with 2 mask types (9105 and 8210). A Tukey honestly significant difference test was performed for the post-hoc analysis. Because of a lack of availability at the time of testing, we had to substitute the 1805 for the 9105 masks at 1 kGy. Data analysis was performed in April 2020.

    Results

    Nine of 9 of the tested control and irradiated masks, when donned properly, passed the qualitative fit test. Single-pass filtration data are shown in the Table and in the Figure. There was statistically significant degradation of filtration efficiency for all treated masks. For example, for 1 of the 9105 masks, mean (SD) filtration efficiency for 0.3-μm particles decreased from 85.9% (3.9%) at 0 kGy to 28.3% (1.1%) at 10 kGy, and for 1 of the 8210 masks, mean (SD) filtration efficiency for 0.3-μm particles decreased from 88.1% (1.9%) to 30.8% (0.8%) at 1 kGy (for particle size, F = 59.0002; for radiation dose, F = 75.6986; P < .001 for both). However, there was no difference in filtration efficiency between the masks irradiated at1 kGy (mean [SE] estimate, 42.275 [3.542]), 10 kGy (mean [SE] estimate, 44.258 [23.542]), or 50 kGy (mean [SE] estimate, 44.117 [3.542]). For example, for 1 of the 8210 masks, the mean (SD) filtration efficiency for 0.3-μm particles was 26.2% (1.4%) at 1 kGy, 23.3% (1.6%) at 10 kGy, and 29.6% (1.0%) at 50 kGy. The filtration efficiency for 1-μm particles was greater than that for 0.5-μm particles (mean [SE] estimate, 23.125 [3.068]; z = 7.538; P < .001) which, in turn, was greater than that for 0.3-μm particles (mean [SE] estimate, 9.219 [3.068]; z = 3.005; P = .007).

    Discussion

    This study has limitations. The test we used to assess filtration efficiency is not approved by the National Institute for Occupational Safety and Health, and particulate matter smaller than 0.3 μm was not examined. The number and type of masks studied was limited by the current supply shortage. However, these findings suggest that a qualitative fit test alone is unable to fully assess mask integrity and that at the doses required for sterilization, gamma radiation degrades the filtration efficiency of N95 masks.

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    Article Information

    Accepted for Publication: April 28, 2020.

    Published: May 26, 2020. doi:10.1001/jamanetworkopen.2020.9961

    Open Access: This is an open access article distributed under the terms of the CC-BY License. © 2020 Cramer A et al. JAMA Network Open.

    Corresponding Author: Avilash Cramer, MS, Harvard-MIT Division of Health Sciences and Technology, 149 13th St, Room 2.406, Charlestown, MA 02129 (avilash@mit.edu).

    Author Contributions: Mr Cramer and Dr Short had full access to all the data in the study and take responsibility for the integrity of the data and the accuracy of the data analysis.

    Concept and design: Cramer, Gupta, Short.

    Acquisition, analysis, or interpretation of data: Cramer, Tian, Galanek, Lamere, Li, Short.

    Drafting of the manuscript: Cramer, Galanek, Gupta, Short.

    Critical revision of the manuscript for important intellectual content: Cramer, Tian, Lamere, Li, Gupta, Short.

    Statistical analysis: Cramer, Tian.

    Administrative, technical, or material support: Tian, Lamere, Li, Gupta, Short.

    Supervision: Li, Gupta, Short.

    Conflict of Interest Disclosures: None reported.

    Additional Contributions: Sherry H. Yu, MD (Brigham and Women’s Hospital) assisted with the qualitative fit test. Jinhan Mo, PhD, (Tsinghua University) contributed to the design of the filtration testing apparatus. They were not compensated for their time. The PanFab Consortium and the MIT Nuclear Science and Engineering Department helped connect us with appropriate resources.

    References
    1.
    Feng  S, Shen  C, Xia  N, Song  W, Fan  M, Cowling  BJ.  Rational use of face masks in the COVID-19 pandemic.   Lancet Respir Med. Published online March 20, 2020. doi:10.1016/S2213-2600(20)30134-XPubMedGoogle Scholar
    2.
    Bauchner  H, Fontanarosa  PB, Livingston  EH.  Conserving supply of personal protective equipment: a call for ideas.   JAMA. Published online March 20, 2020. doi:10.1001/jama.2020.4770PubMedGoogle Scholar
    3.
    Viscusi  DJ, Bergman  MS, Eimer  BC, Shaffer  RE.  Evaluation of five decontamination methods for filtering facepiece respirators.   Ann Occup Hyg. 2009;53(8):815-827.PubMedGoogle Scholar
    4.
    Feldmann  F, Shupert  WL, Haddock  E, Twardoski  B, Feldmann  H.  Gamma irradiation as an effective method for inactivation of emerging viral pathogens.   Am J Trop Med Hyg. 2019;100(5):1275-1277. doi:10.4269/ajtmh.18-0937PubMedGoogle ScholarCrossref
    5.
    Sullivan  R, Fassolitis  AC, Larkin  EP, Read  RB  Jr, Peeler  JT.  Inactivation of thirty viruses by gamma radiation.   Appl Microbiol. 1971;22(1):61-65. doi:10.1128/AEM.22.1.61-65.1971PubMedGoogle ScholarCrossref
    6.
    Harrell  CR, Djonov  V, Fellabaum  C, Volarevic  V.  Risks of using sterilization by gamma radiation: the other side of the coin.   Int J Med Sci. 2018;15(3):274-279. doi:10.7150/ijms.22644PubMedGoogle ScholarCrossref
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