Utility of an Optical Particle Counting Instrument for Quantitative Respirator Fit Testing with N 95 Filtering Facepieces

urrently, the aerosol-based quantitative respirator fit testing is primarily conducted using a PortaCount® (TSI Inc., Shoreview, MN, USA), which utilizes a condensation particle counting (CPC) technique and measures particles in a size range of dp ~ 0.02 – 1 μm. A U.S. OSHA-accepted fit testing protocol or similar protocols approved by other countries’ regulatory agencies shall be followed. We recently investigated a new instrument, MT-05U (Sibata Scientific Technologies, Ltd., Tokyo, Japan) utilizing an optical particle counting (OPC) technique, dp ≥ 0.3 μm, for the quantitative fit testing of three types of respirators with highefficiency filters – the P100 filtering facepiece respirators (FFRs), and elastomeric halfand full-face respirators. Conducted with the PortaCount® as the reference instrument, good feasibility of the OPC method for fit testing of the above-mentioned types of respirators was demonstrated, according to the ANSI standard Z88.10-2010. The present effort is a follow-up study, in which the same fit testing instrument MT05U was evaluated utilizing the same approach for N95 FFRs via the PortaCount® N95-CompanionTM as the reference instrument. It was found that the new instrument could identify inadequate fits of all tested N95 FFRs with sensitivity (probability of identifying inadequate fits) of 1.00, exceeding the ANSI mandatory requirement of ≥ 0.95. The predictive value of a pass was 1.00 as well, exceeding the advisory criteria of ≥ 0.95. Additionally, the specificity and predictive value of a fail were 0.59 and 0.69, respectively, both exceeding the advisory criteria of ≥ 0.5. The value of the kappa statistic was 0.58 falling below the threshold of 0.7 (it is acknowledged though that the latter is optional as it is neither mandatory nor advised according to ANSI). In conclusion, the evaluated OPC-based fit tester could be successfully deployed as an alternative method for quantitative fit testing for N95 FFRs.