Engineering Controls Database
Best Practices for Dust Control in Metal/Nonmetal Mining –
Controlling Respirable Silica at Surface Mines – Controlling Haulage Road Dust
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Respirable crystalline silica dust exposure has long been known to be a serious health threat to workers in many industries and occupations. Workers with high exposure to crystalline silica include miners, sandblasters, tunnel workers, silica millers, quarry workers, foundry workers, and ceramics and glass workers Overexposure to respirable crystalline silica dust can has been associated with development of silicosis, lung cancer, pulmonary tuberculosis, and airways disease. The International Agency for Research on Cancer (IARC) reviewed the published experimental and epidemiologic studies of cancer in animals and workers exposed to respirable crystalline silica and concluded that there was sufficient evidence to classify silica as a human carcinogen [IARC 1997]. Silicosis is also a fibrosing disease of the lungs caused by the inhalation, retention, and pulmonary reaction to the crystalline silica. When silicosis becomes symptomatic, the primary symptom is usually dyspnea (difficult or labored breathing and/or shortness of breath), first noted with activity or exercise and later, as the functional reserve of the lung is also lost, at rest. Once contracted, there is no cure for silicosis. The goal, therefore, is to limit worker exposure to respirable dust to prevent development of these diseases. |
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Silica refers to the chemical compound silicon dioxide (SiO2), which occurs in a crystalline or noncrystalline (amorphous) form [NIOSH 2002]. Silica is a common component of rocks. Ore goes through a number of crushing, grinding, cleaning, drying, and product-sizing sequences as it is mined and processed into a marketable commodity. Because these operations are highly mechanized, they are able to process high tonnages of ore and generate high levels of silica. Surface mining operations present dynamic and highly variable silica dust sources. Most of the dust generated at surface mines is produced by mobile earth-moving equipment such as drills, bulldozers, trucks, and front-end loaders excavating silica-bearing rock and minerals. Four practical areas of engineering controls designed to mitigate exposure of surface mine workers to all airborne dusts, including silica, are controlling dust on unpaved haulage roads, enclosed cab filtration systems, drill dust collection systems, and controlling dust at the primary hopper dump. Off-road haul trucks used in the mining industry typically contribute most of the dust emissions at a mine site. Although most of the airborne dust generated from unpaved haulage roads is nonrespirable, up to 20% is in the respirable size range [Organiscak and Reed 2004]. Given their mobility, trucks have the potential for exposing downwind mine workers to respirable dust, as well as other truck drivers traveling on the haul road. |
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The most common method of haul road dust control is surface wetting with plain water, but others include adding hygroscopic salts, surfactants, soil cements, bitumens, and films (polymers) to the road surface [NIOSH 2003; USBM 1987]. Figure 1 shows the effectiveness of road wetting with water on airborne respirable dust generation measured next to an unpaved haul road [Organiscak and Reed 2004]. The road was wetted in the morning and dried out in the afternoon. Although the road treatment methods have been shown to be very effective, their application generally involves continual maintenance due to road degradation from traffic, dry climatic conditions, and material spillage on the road. Road dust generation can be inevitable at times during the mining operation, until controls are applied. NIOSH has recently studied the size characteristics, concentrations, and spatial variation of airborne dust generated along unpaved mine haulage roads to examine the potential human health and safety impacts of this dust source and is examining other avenues of truck dust mitigation. Techniques for controlling haulage road dust are summarized below. Methods for Controlling Haulage Road Dust Exposures • Treatment of unpaved road surfaces. Figure 1 shows the effectiveness of road wetting on respirable dust next to the road and an example of the time frame of effectiveness [Organiscak and Reed 2004]. A number of factors, including quantity of traffic on the road, humidity, and cloudiness, can impact the length of protection afforded by wetting with water. Other haulage road treatments, such as hygroscopic salts, surfactants, soil cements, bitumens, and films (polymers), can extend the time of effectiveness between treatments to up to several weeks [NIOSH 2003; USBM 1987].  • Increase distance between vehicles traveling the haul road. Airborne dust concentrations generated from haulage roads rapidly decreased and approached ambient air dust levels 100 feet from the road [Organiscak and Reed 2004]. This road dust dissipation and dilution occurrence provides administrative and mine planning controls to reduce worker dust exposure. The distance placed between trucks not following within 20 seconds of each other can result in a 41–52% reduction in airborne respirable dust exposure to the following truck [Reed and Organiscak 2006]. Finally, road layout and traffic patterns that can be economically incorporated into the mine plan could also isolate the haul road dust sources from other workers [Organiscak and Reed 2004]. |
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NIOSH [2010]. Information circular 9517. Best practices for dust control in metal/nonmetal mining. Morgantown, WV: U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, DHHS (NIOSH) Publication No. 2010-132. IARC [1997]. IARC monographs on the evaluation of carcinogenic risks to humans: silica, some silicates, coal dust and para-aramid fibrils. Vol 68. Lyon, France: World Health Organization, International Agency for Research on Cancer. NIOSH [2002]. NIOSH hazard review: health effects of occupational exposure to respirable crystalline silica. Cincinnati, OH: U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, DHHS (NIOSH) Publication No. 2002-129. NIOSH [2003]. Handbook for dust control in mining. By Kissell, FN. Cincinnati, OH: U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, DHHS (NIOSH) Publication No. 2003147. Organiscak JA, Reed WR [2004]. Characteristics of fugitive dust generated from unpaved mine haulage roads. International Journal of Surface Mining, Reclamation, & Environment, Vol. 18, No. 4, pp. 236–252. Reed WR, Organiscak JA [2006]. The evaluation of dust exposure to truck drivers following the lead haul truck. In: SME Transactions 2005, Vol. 318. Littleton, CO: Society for Mining, Metallurgy and Exploration, Inc., pp. 147–153. USBM [1987]. Fugitive dust control for haulage roads and tailing basins. By Olson KS, Veith DL. Washington, DC: U.S. Department of the Interior, U.S. Bureau of Mines, RI 9069. |
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dust control metal/nonmetal mining mineral mining miners surface mines |