The protective performance of reusable cloth face masks, disposable procedure masks, KN95 masks and N95 respirators: Filtration and total inward leakage

  1. Scott Duncan
  2. Paul Bodurtha
  3. Syed Naqvi

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Abstract

Face coverings are a key component of preventive health measure strategies to mitigate the spread of respiratory illnesses. In this study five groups of masks were investigated that are of particular relevance to the SARS-CoV-2 pandemic: re-usable, fabric two-layer and multi-layer masks, disposable procedure/surgical masks, KN95 and N95 filtering facepiece respirators. Experimental work focussed on the particle penetration through mask materials as a function of particle diameter, and the total inward leakage protection performance of the mask system. Geometric mean fabric protection factors varied from 1.78 to 144.5 for the fabric two-layer and KN95 materials, corresponding to overall filtration efficiencies of 43.8% and 99.3% using a flow rate of 17 L/min, equivalent to a breathing expiration rate for a person in a sedentary or standing position conversing with another individual. Geometric mean total inward leakage protection factors for the 2-layer, multi-layer and procedure masks were <2.3, while 6.2 was achieved for the KN95 masks. The highest values were measured for the N95 group at 165.7. Mask performance is dominated by face seal leakage. Despite the additional filtering layers added to cloth masks, and the higher filtration efficiency of the materials used in disposable procedure and KN95 masks, the total inward leakage protection factor was only marginally improved. N95 FFRs were the only mask group investigated that provided not only high filtration efficiency but high total inward leakage protection, and remain the best option to protect individuals from exposure to aerosol in high risk settings. The Mask Quality Factor and total inward leakage performance are very useful to determine the best options for masking. However, it is highly recommended that testing is undertaken on prospective products, or guidance is sought from impartial authorities, to confirm they meet any implied standards.

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  1. Version published to 10.1371/journal.pone.0258191
  2. ScreenIT

    SciScore for 10.1101/2020.11.24.20237446: (What is this?)

    Please note, not all rigor criteria are appropriate for all manuscripts.

    Table 1: Rigor

    Institutional Review Board Statementnot detected.
    Randomizationnot detected.
    Blindingnot detected.
    Power Analysisnot detected.
    Sex as a biological variableA pool of eleven test subjects were recruited for this test from Defence Research and Development Canada (DRDC) Suffield Research Centre (Ralston, Canada) and were chosen based on obtaining a cross-section of both males and females, with a wide distribution of age, height and weight.

    Table 2: Resources

    No key resources detected.

    Results from OddPub: We did not detect open data. We also did not detect open code. Researchers are encouraged to share open data when possible (see Nature blog).

    Results from LimitationRecognizer: We detected the following sentences addressing limitations in the study:
    It also follows that there is an obvious synergistic effect where if everyone in group settings were to wear a face covering made from a high filtration efficiency material the aerosol concentration that individuals would be exposed to would be proportionally that much lower, and the limitations of the protective performance of face coverings less of an issue. Accordingly, effective attenuation of respiratory generated aerosol is paramount and the biggest gain collectively to reduce the level of aerosol exposure comes from the filtration efficiency of the material used in their construction. Haphazard implementation of PHM protocols, including wearing face coverings, has not been effective in eliminating the transmission of SARS-CoV-2. Unfortunately, collective acceptance and adherence to wearing face masks in public is not widespread in many jurisdictions. At the time of writing there have been numerous protests by certain factions of society demanding that governments withdraw mask wearing entirely. We certainly advocate mandatory wearing of face masks collectively in all public spaces to standardize the response to protective posture and address increased concerns round the potential airborne transmission of SARS-CoV-2. A recent study (72) found viable SARS-CoV-2 virus in the air up to 4.8 m from an infected individual. The genome sequence from the virus collected by air samplers was identical to that isolated from a nasopharyngeal swab taken from the infected individual. ...

    Results from TrialIdentifier: No clinical trial numbers were referenced.

    Results from Barzooka: We did not find any issues relating to the usage of bar graphs.

    Results from JetFighter: We did not find any issues relating to colormaps.

    Results from rtransparent:
    • Thank you for including a conflict of interest statement. Authors are encouraged to include this statement when submitting to a journal.
    • Thank you for including a funding statement. Authors are encouraged to include this statement when submitting to a journal.
    • No protocol registration statement was detected.

    About SciScore

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  3. Version published to 10.1101/2020.11.24.20237446v1 on medRxiv