An accessible method for screening aerosol filtration identifies poor-performing commercial masks and respirators

Abstract

Background The COVID-19 pandemic has presented an acute shortage of regulation-tested masks. Many of the alternatives available to hospitals have not been certified, leaving uncertainty about their ability to properly protect healthcare workers from SARS-CoV-2 transmission. Objective For situations where regulatory methods are not accessible, we present experimental methods to evaluate mask filtration and breathability quickly via cost-effective approaches (e.g.,~$2000 USD) that could be replicated in communities of need without extensive infrastructure. We demonstrate the need for screening by evaluating an existing diverse inventory of masks/respirators from a local hospital. Methods Two experimental approaches are presented to examine both aerosol filtration and flow impedance (i.e., breathability). For one of the approaches ("quick assessment"), screening for appropriate filtration could be performed under 10 min per mask, on average. Mask fit tests were conducted in tandem but are not the focus of this study. Results Tests conducted of 47 nonregulation masks reveal variable performance. A number of commercially available masks in hospital inventories perform similarly to N95 masks for aerosol filtration of 0.2 μm and above, but there is a range of masks with relatively lower filtration efficiencies (e.g., <90%) and a subset with poorer filtration (e.g., <70%). All masks functioned acceptably for breathability, and impedance was not correlated with filtration efficiency. Significance With simplified tests, organizations with mask/respirator shortages and uncertain inventories can make informed decisions about use and procurement.

Risk compensation and face mask mandates during the COVID-19 pandemic

“…The airborne nature of SARS-CoV-2 suggests masks could reduce spread 1 , and a growing body of evidence supports that high rates of mask use in the general population reduces overall virus transmission [2][3][4] , despite the lack of any randomized control studies to definitively demonstrate that masks reduce transmission of SARS-CoV-2 4 . Yet, mask quality matters 2,5 , which implies the benefits of face masks depend on correct usage. This latter point highlights that masks are a behavioral intervention, so how they are worn and how they affect other behaviors is as important as the physical attributes of the mask.…”

“…Most recommendations are for cloth masks and non-medical masks because of concerns that the opportunity cost of masks might be high, given the scarcity of masks for medical personnel 7,8 . Evidence suggests cloth masks are less effective than N95 respirators 2,5 . A more insidious cost exists if individuals substitute mask wearing for other protective behaviors, risk compensation.…”

Aerosol Transmission of SARS-CoV-2: Physical Principles and Implications

“…A fairly wide range of multilayer filters (125)(126)(127) and even some combinations of natural fibers (121,126) seem to give worthwhile filtration of aerosol-size particles in practice. Even single cloth layers that do not capture aerosols reduce the range of exhaled air (119,122,128), Rapid screens for filtration efficiency are available (129,130). There is no support for the argument that aerosol transmission makes masks useless (120).…”

Non-woven materials for cloth-based face masks inserts: relationship between material properties and sub-micron aerosol filtration

“…The methodology for the aerosol filtration efficiency testing was adapted from that proposed by Schilling et al 41 for screening filtration properties of face masks. We chose to use NaCl as the test aerosol, as it has been widely used in regulatory testing of face masks.…”