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between different brands of the same filter type.^[1] These leakage functions can be considered to be leakage bands, ranges, or distributions that are a function of each (contaminant size, volumetric flow rate, filter lot) combination, rather than a single leakage value for each combination of (contaminant size, volumetric flow rate). Additionally, these functions can be characterized as "narrow band" or "wide band" functions, depending on how narrow or wide a range of contaminant sizes the substantial filter leakage occurs over. Refer to leakage functions reported by Hinds and Kraske, 212 Liu and Fardi, 213 or Stevens and Moyer 214 to gain an appreciation of dif- ferent leakage functions. Also refer to Figures VI through IX presented later in this evaluation. Regarding the effect of particle size on filter leakage, contaminant count diameters between about 0.05 and 0.5 μm generally produce the highest leakage values for DM and DFM filters (some authors report a size range of about 0.1 to 0.4 μm). Particle count diameters smaller or larger than this range generally produce considerably lower leakage results. If a median diameter for a size distribution is reported, then leakage values must be evaluated on the basis of count median diameter (CMD), not mass median diameter (MMD) or mass median aerodynamic diameter (MMAD). 215 If either one of the latter two is reported, it should be converted to a count median diameter. Typically a CMD is at least one fifth to one tenth the size of the corres- ponding MMD or MMAD, depending on the geometric standard deviation of the con- taminant size distribution. 216 Refer to multiple particle-size results reported by Hinds and Kraske, 217 Liu and Fardi, 218 or Stevens and Moyer 219 to gain an apprecia-

21Tbid., Figures 5 and 6. 21Liu, B. Y. H. and B. Fardi: A Fundamental Study of Respiratory Air Filtration, Final Report for NIOSH Grant # R01 OH01485-01A1, University of Minnesota, Particle Technology Laboratory Publica- tion No. 680, Minneapolis, Minnesota (September 1988), Chapter 6-Experimental Results, pp. 250-307 214 Stevens, G.A. and E. S. Moyer: "Worst Case" Aerosol Testing Parameters: 1. Sodium Chloride and Dioctyl Phthalate Aerosol Filter Efficiency as a Function of Particle Size and Flow Rata, Am. Ind. Hyg. Assoc J., 50(5):257-264 (1989). 215 The count median diameter (CMD) is defined as the contaminant size for which half the total num- ber of contaminant particles are larger and half are smaller. In contrast, the mass median aerodynamic diameter (MMAD) is defined as the aerodynamic diameter for which half the total mass of particles is contributed by particles larger than the MMAD and half by particles smaller than the MMAD. 21 Hinds, W. C.: Aerosol Technology, John Wiley & Sons, New York (1982), p. 93, Figure 4.16. 217 Hinds, W. C. and G. Kraske: Performance of Dust Respirators with Facial Seal Leaks: 1. Exper-

imental, Am. Ind. Hyg. Assoc. J., 48(10):836–841 (1987), Figures 5 and 6.