Engineering Controls Database
Best Practices for Dust Control in Metal/Nonmetal Mining – Mucking Operations
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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. 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; consequently, mine workers are potentially exposed to silica dust when rock is cut, drilled, crushed, and transported. |
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| Hard rock mining requires drilling and shooting of faces to produce a “muck” which is loaded and hauled using different types of production vehicles depending on commodity and mining type. Production equipment is usually diesel-powered, and vehicle cabs may be either enclosed or open depending on commodity. For instance, limestone and granite mines generally use the room-and-pillar mining method, with entry widths ranging from 30 to 60 feet and entry heights on development ranging from 20 to 45 feet. Production equipment includes large front-end loaders and 50- to 100-ton capacity trucks with enclosed cabs. Gold and other metal operations may use sublevel caving, long-hole open stoping, or cut-and-fill methods with entries ranging from 15 to 20 feet wide and 12 to15 feet high. Open cab load-hauldump vehicles and muckers are commonly used in the above operations. Local ventilation and water application to the muck pile are the primary means of dust control during the loading and hauling cycle. | |
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In mucking operations, several dust control methods should be considered to lower airborne levels of silica dust: Establish an air circuit and keep fans as close to the loading area as possible. Dead-end entries and stopes are difficult to ventilate and they create conditions where exposure to silica dust is most prevalent. In stone mines, booster fans located in key locations are commonly used to improve local ventilation and provide a more direct and controlled volume of airflow. Using a combination of booster fans in both the blowing and exhaust mode will provide both turbulent air to dilute dust and an air circuit to sweep the face and remove airborne particulate. In metal operations, blowing and exhaust systems using ventilation tubing directed into the dead-entry are more applicable. A blowing system delivering 10,000 cfm and kept within 100 feet of the face is required to provide adequate dilution. For exhaust systems to effectively transport dust-laden air into return entries, the tubing needs to be kept within 10 feet of the dust source for adequate dust capture [NIOSH 2003b]. Figure 1 shows a typical fan set-up for ventilating a dead-end entry in a limestone mine.  Keep muck wet when loading. The amount of water applied to the muck pile will differ between commodities, depending on the acceptable amount of moisture allowed during processing. Keeping the muck wet to reduce airborne dust levels while loading is a widely accepted practice, and studies have shown it also reduces silica dust levels in gold mining [Chekan 2002]. Silica generation in stopes that had a wet muck was 28% less than that produced by a dry muck. Silica exposures for load-haul-dump (LHD) machine operators were impacted during the loading and dumping activities with wet muck, with 32% and 35% dust reductions, respectively. Control haul road dust. The most common method of controlling haul road dust is surface wetting with water, but other dust control methods include adding hygroscopic salts, surfactants (commonly referred to as wetting agents), soil cements, bitumens, or films (polymers) to the road surface [Organiscak and Reed 2004]. Haul road wetting with water trucks in stone mines has been demonstrated to be very effective when continual wetting is practiced. Wetting is primarily conducted on the main tram roads; however, other trucks and mine equipment using secondary tram roads can raise the silica levels in the mine atmosphere and have the potential for exposing other mine workers conducting tasks unrelated to the production cycle. NOTE: The above information is taken directly from the following publication: 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. |
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Chekan GJ, Colinet JF [2002]. Silica dust sources in underground limestone mines. In: Proceedings of the Thirty-Third Annual Institute on Mining Health, Safety and Research. Blacksburg, VA: Virginia Polytechnic Institute and State University, Department of Mining and Minerals Engineering, pp. 55–70. 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 [2003b]. Underground hard-rock dust control. By Kissell FN, Stachulak JS. In: Handbook for dust control in mining. Cincinnati, OH: U.S. Department of Health and Human Services, Centers for Disease Control, National Institute for Occupational Safety and Health, DHHS (NIOSH) Publication No. 2003-147, pp. 83–96. Organiscak JA, Reed WR [2004]. Characteristics of fugitive dust generated from unpaved mine haulage roads. Int J Surf Min Reclam Environ 18(4):236–252. Reed WR, Organiscak JA, Page SJ [2004]. New approach controls dust at the collector dump point. Eng Min J July:29–31. |
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blasting crushing drilling hauling loading metal/nonmetal mining mineral processing miners mining stone mining underground mines |
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| Keeping the muck wet to reduce airborne dust levels while loading is a widely accepted practice, and studies have shown it also reduces silica dust levels in gold mining [Chekan 2002]. Silica generation in stopes that had a wet muck was 28% less than that produced by a dry muck. Silica exposures for load-haul-dump (LHD) machine operators were impacted during the loading and dumping activities with wet muck, with 32% and 35% dust reductions, respectively. |