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Articles by M. Harper
Total Records ( 2 ) for M. Harper
  E. G Lee , J Nelson , P. J Hintz , G Joy , M. E Andrew and M. Harper

The performance of two thoracic samplers, the GK2.69 cyclone and the CATHIA-T sampler, and the GK3.51 cyclone was investigated in the field against the standard cowled sampler (current NIOSH 7400 method) to determine the effect of thoracic sampling. The CATHIA-T sampler and the GK2.69 cyclone were operated at 7 and 1.6 l min–1, respectively. The GK3.51 sampler is related to the GK2.69 cyclone, but designed to give a thoracic cut at a flow rate of 3.2 l min–1. A total of 136 area samples were obtained from a tremolitic talc processing mill and 148 area samples were obtained within a quarry in which metamorphosed volcanic rocks were being crushed for construction stone. Sample slides were prepared using the dimethyl formamide/Euparal technique and relocatable cover slips. NIOSH 7400 ‘A’ counting rules were used to examine fibers. Additionally, counters were asked to record the number of fibers where a fiber meets the ‘A’ rules and is wider than 3-µm physical diameter in order to estimate the proportion of extra-thoracic fibers. A few slides from each sampler type were randomly selected and fiber widths for those fibers satisfying the counting rules were measured to determine median width ratios of each thoracic sampler to the cowled sampler. Overall, the combined results of this study and the previous study by the same authors (Lee et al., 2008) showed lower fiber concentrations for the CATHIA-T sampler and higher concentrations for the GK2.69 cyclone and the GK3.51 cyclone compared to the standard cowled sampler. The proportion of extra-thoracic fibers (>3-µm physical diameter) on the filters collected with each type of thoracic samplers was comparable to the proportion of such fibers collected with the cowled sampler. The most consistent result over this study and our previous study is that both cyclones gave higher fiber concentrations than the CATHIA-T sampler. However, the estimated width ratios of each cyclone type to the cowled sampler were similar to or equal to 1 indicating no separation of fiber bundles due to cyclone effects. An inverse relationship between the fiber concentration ratios of each thoracic sampler type to the cowled sampler and the relative sample loading rate compared to the cowled sampler was observed. The difference in fiber concentration ratios might be a function of sample loading rather than an effect of thoracic size selection. Therefore, it is not recommended that any of these samplers be used to replace the cowled sampler in measurements intended for comparison with limit values arising from risk assessments developed from cowled sampler measurements without considering this possible effect.

  T Lee , S. W Kim , W. P Chisholm , J Slaven and M. Harper

The American Conference of Governmental Industrial hygienists (ACGIH) lowered the threshold limit value (TLV) for respirable crystalline silica (RCS) exposure from 0.05 to 0.025 mg m–3 in 2006. For a working environment with an airborne dust concentration near this lowered TLV, the sample collected with current standard respirable aerosol samplers might not provide enough RCS for quantitative analysis. Adopting high flow rate sampling devices for respirable dust containing silica may provide a sufficient amount of RCS to be above the limit of quantification even for samples collected for less than full shift. The performances of three high flow rate respirable samplers (CIP10-R, GK2.69, and FSP10) have been evaluated in this study. Eleven different sizes of monodisperse aerosols of ammonium fluorescein were generated with a vibrating orifice aerosol generator in a calm air chamber in order to determine the sampling efficiency of each sampler. Aluminum oxide particles generated by a fluidized bed aerosol generator were used to test (i) the uniformity of a modified calm air chamber, (ii) the effect of loading on the sampling efficiency, and (iii) the performance of dust collection compared to lower flow rate cyclones in common use in the USA (10-mm nylon and Higgins–Dewell cyclones). The coefficient of variation for eight simultaneous samples in the modified calm air chamber ranged from 1.9 to 6.1% for triplicate measures of three different aerosols. The 50% cutoff size (50dae) of the high flow rate samplers operated at the flow rates recommended by manufacturers were determined as 4.7, 4.1, and 4.8 µm for CIP10-R, GK2.69, and FSP10, respectively. The mass concentration ratio of the high flow rate samplers to the low flow rate cyclones decreased with decreasing mass median aerodynamic diameter (MMAD) and high flow rate samplers collected more dust than low flow rate samplers by a range of 2–11 times based on gravimetric analysis. Dust loading inside the high flow rate samplers does not appear to affect the particle separation in either FSP10 or GK2.69. The high flow rate samplers overestimated compared to the International Standards Organization/Comité Européen de Normalisation/ACGIH respirable convention [up to 40% at large MMAD (27.5 µm)] and could provide overestimated exposure data with the current flow rates. However, both cyclones appeared to be able to provide relatively unbiased assessments of RCS when their flow rates were adjusted.

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