Jon C. Volkwein

Determining the Spatial Variability of Personal Sampler Inlet Locations

This article examines the spatial variability of dust concentrations within a coal miners breathing zone and the impact of sampling location at the cap lamp, nose, and lapel. Tests were conducted in the National Institute for Safety and Health Pittsburgh Research Laboratory full-scale, continuous miner gallery using three prototype personal dust monitors (PDM). The dust masses detected by the PDMs were used to calculate the percentage difference of dust mass between the cap lamp and the nose and between the lapel and the nose. The calculated percentage differences of the masses ranged from plus 12% to minus 25%. Breathing zone tests were also conducted in four underground coal mines using the torso of a mannequin to simulate a miner. Coal mine dust was sampled with multi-cyclone sampling cans mounted directly in front of the mannequin near the cap lamp, nose, and lapel. These four coal mine tests found that the spatial variability of dust levels and imprecision of the current personal sampler is a greater influence than the sampler location within the breathing zone. However, a one-sample t-test of this data did find that the overall mean value of the cap lamp/nose ratio was not significantly different than 1 (p-value = 0.21). However, when applied to the overall mean value of the lapel/nose ratio there was a significant difference from 1 (p-value < .0001). This finding is important because the lapel has always been the sampling location for coal mine dust samples. But these results suggest that the cap location is slightly more indicative of what is breathed through the nose area.

Analysis of sampling line bias on respirable mass measurement.

This study investigated the bias introduced by an inlet sampling line on a respirable mass monitor. The 1.5-m electrically conductive, flexible sampling line conducts aerosol at a flow rate of 2.2 Lpm from a helmet-mounted inlet to a waist-mounted sensor for mass concentration measurement. Particulate transport was modeled for each section of the sampling line and considered the effects of diffusion, gravitational settling, and inertial impaction. An estimate of respirable mass concentration measured with the sampling line was determined by integrating assumed workplace aerosols with the transport curves. The bias introduced by the sampling line was then calculated by dividing the difference between the respirable mass concentration with and without the sampling line by that without the sampling line. For the current sampling line, in which the inner diameter is 4.83 mm, bias was calculated as -0.3 percent, -2.4 percent, -4.6 percent, and -6.7 percent for four test aerosols with mass median aerodynamic diameters of 0.6 microm, 4 microm, 12 microm, and 30 microm, respectively. Optimization studies suggest that increasing the sampling line with a larger inner diameter by a factor of 1.25 to 1.75 will minimize bias to below -3.0 percent. An experimental study confirmed that bias due to the presence of the sampling line is small.

Particulate Penetration of Porous Foam Used as a Low Flow Rate Respirable Dust Size Classifier

Porous foam has been used as a material for classification of particulate matter into various size fractions. The penetration characteristics of a nominal 90 pores per inch porous foam were studied at various flow rates, face velocities, and foam plug diameters and compared to the aerosol penetration of a 10 mm Dorr Oliver cyclone operated at 1.7 L/min. Poly-dispersed triethanolamine spheres were classified through porous foam plugs and the resulting penetration was determined using an aerodynamic particle sizer. Results showed that for a given plug diameter, as face velocity increased from 26 to 39 cm/sec, the 50 percent cut point decreased from 4.5 to 3.8 microns. Furthermore, as the diameter of the plug increased from 4 to 12 mm, the 50 percent cut points were similar to other plug diameters at equivalent face velocities. The best match to the 1.7 L/min cyclone penetration characteristics occurred at a flow rate of 250 ml/min through a 25 mm by 4 mm diameter section of 90 pore per inch foam. Because of the need to provide short-term or real-time estimates of worker respirable dust exposure, porous foam may be a viable classification media for a low flow rate, disposable respirable dust sampler for use in the coal mining industry.

A revised conversion factor relating respirable dust concentrations measured by 10 mm Dorr-Oliver nylon cyclones operated at 1.7 and 2.0 L min−1

Accurate measurement of workplace respirable dust concentration is an essential step in eliminating lung disease in any occupational setting. In the United States (U.S.) coal mining industry, this measurement process has relied upon a personal sampler that includes a 10 mm Dorr-Oliver (DO) nylon cyclone operated at a flow rate of 2.0 L min(-1) to collect a respirable dust sample. Dust concentrations measured with this sampler are multiplied by 1.38, which was empirically derived, to convert them to measurements approximating the United Kingdom British Medical Research Council (BMRC) definition of respirable dust upon which the health effects of coal mine dust are based. The International Organization for Standardization (ISO) subsequently refined the respirable dust definition and the U.S. National Institute for Occupational Safety and Health (NIOSH) 1995 Criteria for a Recommended Standard presented a conversion multiplier of 0.857 to apply to the 2.0 L min(-1) DO (in addition to the1.38 multiplier) to obtain equivalent ISO concentrations, as approximated by the 1.7 L min(-1) DO. However, the conversion multiplier 0.857 was derived indirectly from a limited size distribution data set rather than a direct comparison of the DO samplers. The present analysis focuses on providing a more accurate conversion multiplier derived from direct comparisons of the 2.0 L min(-1) (with 1.38 BMRC equivalency multiplier) and 1.7 L min(-1) DO cyclones. A weighted linear regression analysis of this database suggests that a more accurate estimate of the conversion multiplier is 0.815.

Laboratory Evaluation of Pressure Differential-Based Respirable Dust Detector Tube

Assessment of exposure to occupational dusts is a first step in reducing exposures to harmful dust concentrations. A new type of respirable dust sampler was developed and compared side-by-side to personal gravimetric samplers in the laboratory. The new sampler correlates filter back pressure with mass accumulation to provide mid-shift- and end-of-shift determinations of cumulative exposure. The sampler uses a small low flow rate pump to draw dust through a small detector tube that contains a porous urethane foam respirable classification section and glass fiber filter that collects respirable dust. Six different coal dusts were aerosolized in a laboratory dust chamber and a total of 119 triplicate observations were obtained. For individual coal types, the correlation coefficients were between 0.87 and 0.97. The precision of the two methods was similar, with the percent relative standard deviation of the personal samplers of 12 percent and the new detector method of 14 percent. For all coal types tested th data were best described by a power function where delta P = 1.43 mass (0.85), with a correlation coefficient of 0.73. The method becomes more accurate at higher dust loadings such that all laboratory data with mass loadings greater than an equivalent concentration of 2 mg/m3 fall within +/- 25 percent of the power function. Assessment of the method under field conditions is in progress.

Field Measurement Of Diesel Particulate Matter Emissions

A primary means to reduce environmental levels of diesel particulate matter (DPM) exposure to miners is to reduce the amount of DPM emission from the engine. A quick and economic method to estimate engine particulate emission levels has been developed. The method relies on the measurement of pressure increase across a filter element that is briefly used to collect a DPM sample directly from the engine exhaust. The method has been refined with the inclusion of an annular aqueous denuder to the tube which permits dry filter samples to be obtained without addition of dilution air. Tailpipe filter samples may then be directly collected in hot and water-supersaturated exhaust gas flows from water bath-cooled coal mine engines without the need for dilution air. Measurement of a differential pressure (DP) increase with time has been related to the mass of elemental carbon (EC) on the filter. Results for laboratory and field measurements of the method showed agreement between DP increase and EC collected on the filter with R(2) values >0.86. The relative standard deviation from replicate samples of DP and EC was 0.16 and 0.11, respectively. The method may also have applications beyond mining, where qualitative evaluation of engine emissions is desirable to determine if engine or control technology maintenance may be required.