Evaluating the use of a field-based silica monitoring approach with dust from copper mines

Abstract

Monitoring worker exposure to respirable crystalline silica in dusty environments is an important part of a proactive health and safety program. This is the case for surface copper mines in Arizona and New Mexico. The spatial and temporal variability of respirable dust and crystalline silica concentrations in those mines, coupled with the time lapse in obtaining crystalline silica analysis results from accredited laboratories, present a challenge for an effective exposure monitoring approach and the resulting intervention strategies. The National Institute for Occupational Safety and Health (NIOSH) is developing a novel approach to be used at a mine site for the quantification of crystalline silica in respirable dust samples collected with traditional sampling techniques. The non-destructive analysis is carried out using a portable Fourier transform infrared spectroscopy (FTIR) unit. In this study, respirable dust samples were collected over two visits to each of five copper mines, for a total of 10 datasets. The silica in each respirable dust sample was estimated by analyzing the sample with the portable FTIR unit. The quality of the estimation was assessed using the results of the NIOSH 7500 method on the same samples. The confounding effect of other minerals present in the respirable dust in the mines was also assessed, and two quantification approaches were investigated to address it: a sector-specific and a mine-specific approach. The results showed that the sector-specific approach is not effective due to the high variability of relative composition of the minerals among mines. For this approach the combined average relative difference was -13% (-17.6%, -8.9% CI). When using the mine-specific quantification approach, the average relative difference was as low as 2.8% (-3.7%, 9.3% CI); however, this approach was still affected by the variable relative composition of the minerals in the dust in each mine. The use of a multivariate approach on the analysis of each sample was proposed as the next step to achieve consistent low relative differences. This study demonstrates the potential of using a portable FTIR for estimation of crystalline silica in respirable dust samples for in-field exposure monitoring.

Direct infrared spectroscopy for the size-independent identification and quantification of respirable particles relative mass in mine dusts

“…The exposure of mine workers to crystalline particles in the respirable size regime is a global problem in occupational health and safety at surface and underground mining operations [1][2][3][4][5]. For inhaled particles, from which 50% can penetrate the larynx (i.e., thoracic particles, 10 μm) and especially those size regimes from which 50% of the mass fraction may enter unciliated airways (i.e., respirable particles, 4 μm), infield online monitoring of the composition and concentration is needed for the assessment of hazards and intervention [2,6]. The focus of recent studies is especially targeted to respirable crystalline silica (alpha quartz), which is known to cause a variety of lung diseases including chronic obstructive Published in the topical collection Advances in Direct Optical Detection with guest editors Antje J. Baeumner, Günter Gauglitz, and Jiri Homola.…”

“…Mine Safety and Health Administration (MSHA). The National Institute for Occupational Safety and Health (NIOSH) introduced a recommended exposure limit (REL) of 50 μg/m 3 as a time-weighted average for up to 10 h per day during a week of 40 work hours [2,13].…”

“…A commonly adopted standard method for the quantification of crystalline silica is the NIOSH 7500 XRD analysis [2]. At least in part, real-time methods based on light scattering can be used but are restricted to the presence of particles and cannot differentiate the type of dust particles and their composition for quantifying their hazardous potential [19].…”

“…The first successful results on the in-field quantification via the NIOSH direct-on-filter (DoF) method combined with portable FTIR spectrometers have proven to be of comparable quality to the NIOSH 7500 method [21]. In that study, mine dust particles were directly collected onto PVC filters by the respirable samplers [2,22]. The DoF method combined with the FTIR technique is included in ISO 19087:2018 by the International Organization for Standardization [23].…”

“…Those effects are most effectively addressed by single variable data evaluation strategies, as shown via a direct calibration approach for coal and non-coal mine dust using partial least squares regression (PLSR) [1,22]. Most recent studies by Cauda et al [2] confronted the problem of confounding variables with a sector-specific and a mine-specific approach.…”