Evaluation of the performance of the N95 companion: effects of filter penetration and comparison with other aerosol instruments.
Rengasamy S; Eimer BC; Shaffer RE
J Occup Environ Hyg 2012 Jul; 9(7):417-426
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 nmdiameter 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.
Respirators; Respiratory-equipment; Air-purifying-respirators; Personal-protective-equipment; Equipment-reliability; Filters; Filtration; Particulates; Measurement-equipment; Anthropometry; Performance-capability; Leak-prevention; Face-masks; Particle-counters;
Author Keywords: face seal leakage; filter penetration; fit testing; N95-Companion; N95 filtering facepiece respirators; PortaCount Plus
Samy Rengasamy, National Institute for Occupational Safety and Health, National Personal Protective Technology Laboratory, 626 Cochrans Mill Road, P.O.Box 18070, Pittsburgh, PA 15236
Journal of Occupational and Environmental Hygiene