Robert J. Timko

Sampling Results of the Improved SKC Diesel Particulate Matter Cassette

Diesel particulate matter (DPM) samples from underground metal/nonmetal mines are collected on quartz fiber filters and measured for carbon content using National Institute of Occupational Safety and Health Method 5040. If size-selective samplers are not used to collect DPM in the presence of carbonaceous ore dust, both the ore dust and DPM will collect on the quartz filters, causing the carbon attributed to DPM to be artificially high. Because the DPM particle size is much smaller than that of mechanically generated mine dust aerosols, it can be separated from the larger mine dust aerosol by a single-stage impactor. The SKC DPM cassette is a single-stage impactor designed to collect only DPM aerosols in the presence of carbonaceous mine ore aerosols, which are commonly found in underground nonmetal mines. However, there is limited data on how efficiently the SKC DPM cassette can collect DPM in the presence of ore dust. In this study we investigated the ability of the SKC DPM cassette to collect DPM while segregating ore dust from the sample. We found that the SKC DPM cassette accurately collected DPM. In the presence of carbon-based ore aerosols having an average concentration of 8 mg/m 3 , no ore dust was detected on SKC DPM cassette filters. We did discover a problem: the surface areas of the DPM deposits on SKC DPM cassettes, manufactured prior to August 2002, were inconsistent. To correct this problem, SKC modified the cassette. The new cassette produced, with 99% confidence, a range of DPM deposit areas between 8.05 and 8.28 cm 2 , a difference of less than 3%.

Differential Pressure Response of 25-mm-Diameter Glass Fiber Filters Challenged with Coal and Limestone Dust Mixtures

This article summarizes results of research conducted by the National Institute for Occupational Safety and Health (NIOSH) at its Pittsburgh Research Laboratory. The objective of this work was to determine the correlation between the mass (M) of respirable coal and limestone dusts collected on 25-mm-diameter glass fiber filters mounted in cassettes and the increase in differential pressure (deltaP) that develops across the filters when drawing at constant air flow. Test aerosols were generated inside a laboratory dust chamber using various coal dusts, limestone dust, and mixes of the two. Dusts with different particle size distributions were deposited on the filters by sampling from the chamber through cyclone preclassifiers at different flow rates. Results show that the relationship between differential pressure increase (cm water) and dust mass (mg) is linear and can be approximated by the equation deltaP = KM. The K values (slopes) range from 1.14 to 1.64, depending on the parent coal of the samples. The influence of particle size distribution was also found. The overall K value for all the data summarized in this article is 1.35, with R2 = 0.84 for the summary equation. When calibrated for individual work sites, or other circumstances where great variability in dust characteristics is avoided, the relationship between collected dust mass and increase in differential pressure may provide an exploitable principle for measurement of respirable dust concentrations.