Systematic experimental comparison of particle filtration efficiency test methods for commercial respirators and face masks

TL;DR

This study systematically compares different standardized test methods for evaluating the filtration efficiency of respirators, masks, and face coverings, revealing how test conditions influence measured performance and aiding cross-standard product comparison.

Contribution

It provides an experimental analysis of how various test parameters affect filtration efficiency measurements across multiple certification standards.

Findings

Filtration efficiency is most sensitive to face velocity and particle charge.

Using charged aerosols and lower face velocities can overestimate efficiency by about 10%.

Environmental conditioning affects filtration efficiency differently across samples.

Abstract

Respirators, medical masks, and barrier face coverings all filter airborne particles using similar physical principles. However, they are tested for certification using a variety of standardized test methods, creating challenges for the comparison of differently certified products. We have performed systematic experiments to quantify and understand the differences between standardized test methods for N95 respirators (NIOSH TEB-APR-STP-0059 under US 42 CFR 84), medical face masks (ASTM F2299/F2100), and COVID-19-related barrier face coverings (ASTM F3502-21). Our experiments demonstrate the role of face velocity, particle properties (mean size, size variability, electric charge, density, and shape), measurement techniques, and environmental preconditioning. The measured filtration efficiency was most sensitive to changes in face velocity and particle charge. Relative to the NIOSH method, users of the ASTM F2299/F2100 method have commonly used non-neutralized (highly charged) aerosols as well as smaller face velocities, each of which may result in approximately 10% higher measured filtration efficiencies. In the NIOSH method, environmental conditioning at elevated humidity increased filtration efficiency in some commercial samples while decreasing it in others, indicating that measurement should be performed both with and without conditioning. More generally, our results provide an experimental basis for the comparison of respirators certified under various international methods, including FFP2, KN95, P2, Korea 1st Class, and DS2.