An Accessible Method for Screening Aerosol Filtration Identifies Poor-Performing Commercial Masks and Respirators
32 Pages Posted: 14 May 2020
Date Written: April 28, 2020
Background: The COVID-19 pandemic has presented an acute need for masks, specifically N95 respirators to be used by healthcare workers contacting COVID-19 patients and medical masks to be used by the public. The shortage of regulation NIOSH-tested masks make it necessary to find alternatives to protect frontline healthcare workers. Many of the available alternatives have not been NIOSH-certified or tested in the United States, leaving room for question as to whether they are performing at a level that is protecting the wearer from SARS-CoV-2 transmission. In addition, currently there are many counterfeit N95 and other masks being produced and sold as authentic products. It has become critical to be able to test these masks from non-traditional suppliers as well as the many masks that are being donated to hospitals at this time in order to ensure the safety of healthcare workers.
Methods: For situations where regulatory methods are not accessible, we present an experimental setup and screening method to evaluate mask filtration and breathability quickly via a cost-effective approach that could be replicated in communities of need without the extensive research infrastructure necessary for regulation mask tests. The experimental approaches presented here examined both mask aerosol filtration performance and mask flow impedance to ensure breathability, and mask fit tests were conducted in tandem but are not the focus of this study.
Findings: Tests conducted of 28 non-regulation masks using this setup reveal that a number of commercially- available masks in hospital inventories perform similarly to N95 masks for aerosol filtration of 0.2 μm and above. There are also a range of masks with relatively-weaker filtration efficiencies. Yet, a subset of commercially-available masks have poor filtration performance relative to N95 or similar masks at typical breathing velocities. All masks functioned acceptably with regards to breathability (i.e. flow impedance) and impedance was not correlated with filtration efficiency.
Interpretation: With a small set of simplified tests, organizations with critical personal protective equipment (PPE) shortages and uncertainties about their mask/respirator inventories can quickly evaluate the efficacy of their masks relative to N95-regulation masks to make informed decisions about which PPE to use and future procurement. This is essential since the results of this study use an actual diverse inventory of masks/respirators from a hospital network and show significant variability in their performance for filtering airborne aerosols that could contain SARS-CoV-2 and a subset of masks that would not be acceptable for frontline workers.
Note: Funding: Yale University, U.S. EPA, NSF.
Conflict of Interest: D.R.G. has externally-funded projects on low-cost air quality monitoring technology (EPA, HKF Technology), which Yale has licensed to HKF Technology. The remaining authors declare no conflict of interest.
Keywords: COVID-19, Personal Protective Equipment, Respirators, Masks, Aerosol Filtration, N95, SARS-CoV-2
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