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Abstract
Fit factor is the ratio of the particle concentration outside (Cout) to the inside (Cin) of the respirator and assumes that filter penetration is negligible. For Class-95 respirators, concerns were raised that filter penetration could bias fit test measurements. The TSI N95-Companion was designed to overcome this limitation by measuring only 40–60 nm size particles. Recent research has shown that particles in this size range are the most penetrating for respirators containing electrostic filter media. The goal of this study was to better understand the performance of the N95-Companion by assessing the impact of filter penetration and by comparing Cout/Cin ratios measured by other aerosol instruments (nano-Differential Mobility Analyzer/Ultrafine Condensation Particle Counter (nano-DMA/UCPC) and the TSI PortaCount Plus) using N95 filtering facepiece respirators sealed to a manikin and with intentionally created leaks. Results confirmed that 40–60 nm-diameter size room air particles were most penetrating for the respirators tested. A nonlinear relationship was found between the N95-Companion-measured Cout/Cin ratios and the other instruments at the sealed condition and at the small leak sizes because the N95-Companion measures only charged particles that are preferentially captured by the electrostic filter media, while the other instrument configurations also measure uncharged particles, which are captured less efficiently. The Cout/Cin ratios from the N95-Companion for experiments conducted under sealed condition suggest that filter penetration of negatively charged 40–60 nm size particles was less than 0.05%. Thus, the N95-Companion measured Cout/Cin ratios are due primarily to particle penetration through leakage, not through filter media, while the Cout/Cin ratios for the PortaCount, nano-DMA/UCPC, and UCPC result from a combination of face seal leakage and filter penetration.
ACKNOWLEDGMENTS
The authors acknowledge NIOSH colleagues Ziqing Zhuang, Roland BerryAnn, William Newcomb, and Christopher Coffey for their critical review of the manuscript and suggestions. This research work was supported by NIOSH funding-CAN #927 Z1NT.
Mention of commercial product or trade name does not constitute endorsement by the National Institute for Occupational Safety and Health. The findings and conclusions of this report are those of the authors and do not necessarily represent the views of the National Institute for Occupational Safety and Health.