Deposition Uniformity of Coal Dust on Filters and Its Effect on the Accuracy of FTIR Analyses for Silica

Abstract

Miners are exposed to silica-bearing dust which can lead to silicosis, a potentially fatal lung disease. Currently, airborne silica is measured by collecting filter samples and sending them to a laboratory for analysis. Since this may take weeks, a field method is needed to inform decisions aimed at reducing exposures. This study investigates a field-portable Fourier transform infrared (FTIR) method for end-of-shift (EOS) measurement of silica on filter samples. Since the method entails localized analyses, spatial uniformity of dust deposition can affect accuracy and repeatability. The study, therefore, assesses the influence of radial deposition uniformity on the accuracy of the method. Using laboratory-generated Minusil and coal dusts and three different types of sampling systems, multiple sets of filter samples were prepared. All samples were collected in pairs to create parallel sets for training and validation. Silica was measured by FTIR at nine locations across the face of each filter and the data analyzed using a multiple regression analysis technique that compared various models for predicting silica mass on the filters using different numbers of "analysis shots." It was shown that deposition uniformity is independent of particle type (kaolin vs. silica), which suggests the role of aerodynamic separation is negligible. Results also reflected the correlation between the location and number of shots versus the predictive accuracy of the models. The coefficient of variation (CV) for the models when predicting mass of validation samples was 4%-51% depending on the number of points analyzed and the type of sampler used, which affected the uniformity of radial deposition on the filters. It was shown that using a single shot at the center of the filter yielded The authors would like to thank Joe Archer and Jeanne Zimmer for their invaluable assistance and attention to detail in preparing the many filter samples required for this study.Address correspondence to Arthur L. Miller, National Institute for Occupational Safety and Health, Spokane Research Lab, 315 E. Montgomery Ave., Spokane, WA 99207, USA. E-mail: ALMiller@cdc.gov predictivity adequate for a field method, (93% return, CV approximately 15%) for samples collected with 3-piece cassettes.

Aerosol Emission Monitoring and Assessment of Potential Exposure to Multi-walled Carbon Nanotubes in the Manufacture of Polymer Nanocomposites

“…Closed face sampling at a flow rate of 4 L/min was conducted for the TSP sampling. Such sampling conditions may have resulted in an uneven deposit on the filter (Miller et al, 2013), invalidating the assumption made that the ~1.5 cm 2 punch analyzed was representative of the entire filter. As a result, reported TSP concentrations for OC-EC may be overestimated.…”

Respirable size-selective sampler for end-of-shift quartz measurement: Development and performance

“…7 The chamber, with a hexagonal cross section is 2.44 m high with an inside diameter of 1.19 m. The dust was introduced at the top of the chamber and thoroughly mixed in this region by the energy of an air jet entering at the side of the chamber. From this mixing area, the dust flows downward through a 10-cm thick honeycomb structure where turbulence in the air is reduced, providing a low velocity downward flow through the test section portion of the chamber.…”

“…Deposition profiles of respirable coal dust, with sample-to-sample variation, changed slightly as filter loading increased when samples were collected with 10-mm nylon cyclones. 7 Different deposition profiles of coal dust were also found on filters from different sampling cassettes (2-piece, 3-piece, MSA cassette) collected with 10-mm nylon cyclone. 7 The deposition profiles generated by various low-flow and high-flow rate samplers were also investigated with respirable metal mine dust.…”

“…7 Different deposition profiles of coal dust were also found on filters from different sampling cassettes (2-piece, 3-piece, MSA cassette) collected with 10-mm nylon cyclone. 7 The deposition profiles generated by various low-flow and high-flow rate samplers were also investigated with respirable metal mine dust. 8 Most of the samplers employ 37-mm filters, and filters are usually removed from filter cassettes for EoS quartz measurements.…”

Direct-on-Filter α-Quartz Estimation in Respirable Coal Mine Dust Using Transmission Fourier Transform Infrared Spectrometry and Partial Least Squares Regression

“…14 Specifically, preliminary investigations using a limited set of laboratory-prepared samples concluded that RCS determination using DoF IR analysis for lab-generated coal dusts is not substantially impacted by current sampling equipment and methodologies. 14,15 …”