Evaluating portable infrared spectrometers for measuring the silica content of coal dust

Abstract

Miners face a variety of respiratory hazards while on the job, including exposure to silica dust which can lead to silicosis, a potentially fatal lung disease. Currently, field-collected filter samples of silica are sent for laboratory analysis and the results take weeks to be reported. Since the mining workplace is constantly moving into new and often different geological strata with changing silica levels, more timely data on silica levels in mining workplaces could help reduce exposures. Improvements in infrared (IR) spectroscopy open the prospect for end-of-shift silica measurements at mine sites. Two field-portable IR spectrometers were evaluated for their ability to quantify the mass of silica on filter samples loaded with known amounts of either silica or silica-bearing coal dust (silica content ranging from 10-200 µg/ filter). Analyses included a scheme to correct for the presence of kaolin, which is a confounder for IR analysis of silica. IR measurements of the samples were compared to parallel measurements derived using the laboratory-based U.S. Mine Safety and Health Administration P7 analytical method. Linear correlations between Fourier transform infrared (FTIR) and P7 data yielded slopes in the range of 0.90-0.97 with minimal bias. Data from a variable filter array spectrometer did not correlate as well, mainly due to poor wavelength resolution compared to the FTIR instrument. This work has shown that FTIR spectrometry has the potential to reasonably estimate the silica exposure of miners if employed in an end-of-shift method.

Evaluation of Laser-Induced Breakdown Spectroscopy (LIBS) for Measurement of Silica on Filter Samples of Coal Dust

“…Therefore, NIOSH is evaluating field-portable technologies capable of end-of-shift (EOS) or near-realtime quantification of silica in coal dust samples. 8 This paper evaluates the use of laserinduced breakdown spectroscopy (LIBS) for that purpose.…”

“…3 There are currently no known therapies that reduce the mortality rate of people affected with silicosis, but a simple line of defense against the disease is to monitor the amount of silica dust in the air and limit worker exposure. 5 While silicosis is easily preventable in principle, it still persists, 6,7 motivating NIOSH to investigate potential new monitoring approaches including Fourier transform infrared (FT-IR) spectroscopy, 8,9 and in the current study, LIBS.…”

“…For coal dusts with a higher mass fraction of silica, the regulated limit in units of mg/m 3 is calculated as 10 divided by the percentage of silica. 8,12 To measure exposure to coal dust, NIOSH developed and certified a direct reading monitor. 13,14 This personal dust monitor (PDM) successfully aided miners in reducing their exposure to coal dust by making changes to their work activities and implementing dust control practices based on the continuous reading provided by the device.…”

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

“…The limitations of such field-portable methods are that they are usually less sensitive than laboratory methods and are also not capable of analyzing the entire amount of material on the filter, but rather depend on localized measurements or "shots" that include only a small portion of the filter area (Chen et al 2010;Miller et al 2012). It is desirable that a potential EOS method produces results that are as close to the laboratory method as possible, while keeping the analytical method simple and easy to use in the field.…”

“…It has recently been shown that a field-portable FTIR spectrometer could be used for relatively accurate analysis of filter samples, with potential for use as an end-of-shift (EOS) method (Miller et al 2012). The limitations of such field-portable methods are that they are usually less sensitive than laboratory methods and are also not capable of analyzing the entire amount of material on the filter, but rather depend on localized measurements or "shots" that include only a small portion of the filter area (Chen et al 2010;Miller et al 2012).…”