Is the Current N95 Respirator Filtration Efficiency Test Sufficient for Evaluating Protection Against Submicrometer Particles Containing SARS-CoV-2?

This article has been Reviewed by the following groups

Read the full article See related articles

Abstract

The National Institute of Occupational Safety and Health procedure No. TEB-APR-STP-0059 recommend of measuring the respirator filtration efficiency using sodium chloride aerosol with count median diameter of 75 nm ± 20 nm and geometric standard deviation ≤1.86. This study showed that this method would overestimate the respirators’ ability to protect against submicrometer particles. In this study, we converted both mobility diameter and equivalent volume diameter to aerodynamic diameter for comparison. The results showed that one unqualified KN95 respirator (with the filtration efficiency of 72%±3% for ≥300 nm sodium chloride aerosol) still passed the test with a measured overall filtration efficiency of 98%±3%, due to its larger most penetrating particle size compared to the typical N95 respirator. In addition, after three cycle H 2 O 2 plasma vaporous sterilizations, the most penetrating particle size for the N95 grade respirators also shifted to 250 nm – 500 nm, in which size the particles carried the peak concentration of the SARS-CoV-2 in hospitals. This size shift caused the significant difference between the size specific (250 nm – 500 nm) filtration efficiency and overall filtration efficiency using the same NaCl test aerosol. For example, after three cycle H 2 O 2 plasma vaporous sterilizations, the size specific filtration efficiency of the N95 was 55%±2%, however, the measured overall filtration efficiency was still 86%±5%. The size Specific filtration efficiency of the KN95 was 69%±2%, but, the measured overall filtration efficiency was still 90%±3%. In order to protect health care personnel adequately, we recommend increasing the test aerosol size, and measuring the size specific filtration efficiency to evaluate the N95 alternatives (e.g. KN95), and the reuse of N95 level respirators. In addition, multi-cycle sterilization with ultraviolet germicidal irradiation appears to have fewer negative effects than H 2 O 2 .

Article activity feed

  1. SciScore for 10.1101/2020.05.14.20102327: (What is this?)

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

    Table 1: Rigor

    NIH rigor criteria are not applicable to paper type.

    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:
    Limitations include the small variety of respirator manufacturers and the limited numbers of samples (n=5) for each respirator and only two sterilization techniques evaluated. In addition, this study only evaluated the filtration efficiency after three sterilization cycles as this corresponds with guidance from the American College of Surgeons for H2O2 sterilization. The filter material might degrade further with more cycles, which should be investigated for UV treatment.

    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

    SciScore is an automated tool that is designed to assist expert reviewers by finding and presenting formulaic information scattered throughout a paper in a standard, easy to digest format. SciScore checks for the presence and correctness of RRIDs (research resource identifiers), and for rigor criteria such as sex and investigator blinding. For details on the theoretical underpinning of rigor criteria and the tools shown here, including references cited, please follow this link.