Abstract

Dust containing crystalline silica is common in mining environments in the U.S. and around the world. The exposure to respirable crystalline silica remains an important occupational issue and it can lead to the development of silicosis and other respiratory diseases. Little has been done with regard to the characterization of the crystalline silica content of specific particle sizes of mine-generated dust. Such characterization could improve monitoring techniques and control technologies for crystalline silica, decreasing worker exposure to silica and preventing future incidence of silicosis. Three gold mine dust samples were aerosolized in a laboratory chamber. Particle size-specific samples were collected for gravimetric analysis and for quantification of silica using the Microorifice Uniform Deposit Impactor (MOUDI). Dust size distributions were characterized via aerodynamic and scanning mobility particle sizers (APS, SMPS) and gravimetrically via the MOUDI. Silica size distributions were constructed using gravimetric data from the MOUDI and proportional silica content corresponding to each size range of particles collected by the MOUDI, as determined via X-ray diffraction and infrared spectroscopic quantification of silica. Results indicate that silica does not comprise a uniform proportion of total dust across all particle sizes and that the size distributions of a given dust and its silica component are similar but not equivalent. Additional research characterizing the silica content of dusts from a variety of mine types and other occupational environments is necessary in order to ascertain trends that could be beneficial in developing better monitoring and control strategies.

Highlights

  • IntroductionExposure to respirable crystalline silica (hereafter silica) is an important concern, in surface and underground mining

  • In occupational environments, exposure to respirable crystalline silica is an important concern, in surface and underground mining

  • Particle mass size distributions determined from inversion of gravimetric data collected using the Microorifice Uniform Deposit Impactor (MOUDI) indicated a mass median diameter (MMD) of 5.17 μm for Alaska, 3.92 μm for South Africa, and 3.88 μm for Nevada dusts

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Summary

Introduction

Exposure to respirable crystalline silica (hereafter silica) is an important concern, in surface and underground mining. The current Mine Safety and Health Administration (MSHA) rule for the mining industry remains an 8-hour TWA concentration of 100 μg m−3, controlled indirectly by reducing the respirable dust standard (30 CFR 56.5001; 30 CFR 57.5001; 30 CFR 70.101; 30 CFR 71.101). While enforcement of such regulatory limits on the mass of silica that workers may be exposed to has resulted in a decrease in the occurrence of silicosis, its incidence has been recently documented in workers aged 15–44 (Bang et al, 2015; Mazurek et al, 2015), indicating that the current workforce continues to be exposed to dusts capable of inducing silicosis. The percent silica (by mass) in such dusts has been observed to be quite variable, ranging from less than 1% to over 30%, depending on the type of mining operation (Cauda et al, 2013)

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