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tion of the effect of particle size on DM and DFM filter leakage. Also refer to Figures VI through X presented later in this evaluation.
  The linear air velocity through a filter, which is function of volumetric flow rate and filtering area, can have a substantial effect on filter leakage values. In general, leakage increases as air velocity increases through the filtering material. That is, as volumetric flow rate increases and filtering area decreases.
  Prior to the late 1980s, most researchers performed filter-leakage studies at volumetric flow rates of about 16 to 50 liters per minute per filter (L/min/filter). Generally, this was done because 32 L/min is the volumetric flow rate for non-powered respirators tested against silica dust, silica mist, and lead fume under the requirements of 30 CFR Part 11.^[1] That is, a test flow rate of 16 L/min/filter when two filters are used on a respirator and 32 L/min/filter when only a single filter is used. However, for DOP tests conducted on HEPA filters, Part 11 requires substantially higher volumetric flow rates of 85 L/min/mask (42.5 L/min/filter for 2-filter masks). As a historical note, 32 liters/min/mask was the flow rate used in U.S. Public Health Service tests respirator-performance tests conducted over 60 years ago. This flow rate was stated to be "the rate of breathing by a man doing vigorous work."222 However, at that time the Bureau of Mines evaluated the maximum per- missible resistance of gas masks at a flow rate of 85 liter/min. 223 NIOSH still uses the same flow rate today for the same resistance test. 224 221 Thus for comparing the potential for excessive filter leakage of Part 11-certified filters against that of any new Part 84-certified filters, leakage data obtained at volu- metric flow rates nearest to 85 L/min/mask are the most relevant. If leakage data 218(...continued) 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. 250-307 219 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 Rate, Am. Ind. Hyg. Assoc. J., 50(5):257-264 (1989).

22/Katz, S. H., E. G. Meiter, and F. H. Gibson: Efficiencies of Painters' Respirators Filtering Lead Paint, Benzol and Vitreous Enamel Sprays, Public Health Bulletin No. 177, Treasury Department, U.S. Public Health Service (June 1928). 222Tbid., p. 7. 123 Bureau of Mines: Schedule 14A, Procedure for Establishing a List of Permissible Gas Masks (August 25, 1923).

22430 CFR 11.102-1.