An Empirical Equation for Rapid Validation of the Performance of Commercial N95 Equivalent Respirators

Abstract

The COVID-19 pandemic has underscored the importance of wearing effective facepiece filtering respirators (FFRs) to reduce infection and disease transmission. One of the reasons causing the widespread prevalence was found to be the failure of N95-Equivalent FFRs (N95-EFs), i.e., efficiency <<95 %, during the pandemic. To investigate the reasons causing the ineffectiveness of commercial N95-EFs, this study measured the efficiency of several dozens of commercially available N95-EFs following standard testing protocols. The specifications of the N95-EF including fiber diameter, solidity and surface potential of the main layer media of N95-EFs were also determined. We provide a simple method for manufacturers to quickly screen the efficiencies of their N95-EF products before distributing them to the market. We found that the failures of N95-EF are majorly attributed to overprediction of the efficiency due to i) missing neutralization of challenging particles, ii) too small or oversize of challenging particles, and iii) particle detectors with large sizing limits (>500 nm). Based on the pressure drop, respirator area, and surface potential of the N95-EFs, an empirical equation is developed to fast screen and help design effective N95-EFs.