Engineering Controls Database
Best Practices for Dust Control in Metal/Nonmetal Mining –
Underground Drilling 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. |
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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; consequently, mine workers are potentially exposed to silica dust when rock is drilled. Wet drilling has been shown to be effective in controlling dust and is commonly found on face drills or jumbo drills. Regular maintenance, as recommended by the drill manufacturers, should be completed to ensure proper operation and maximized protection of these systems. Dry hole drills, where water is not used to suppress dust, are commonly used on downhole drills in preparation for shooting benches. Silica dust is generated by compressed air (bailing airflow) flushing the drill cuttings from the hole. Dry dust collection systems, incorporated into the drilling machine by the original equipment manufacturers, tend to be the most common type of dust control. Ninety percent of dust emissions with this type of system are attributed to drill deck shroud leakage, drill stem bushing leakage, and dust collector dump discharge. |
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The following procedures should be used to reduce crystalline silica dust during drilling: Minimize silica dust generation and reduce levels in the ambient mine air by using the following recommended drill operating parameters: (a) maintain a tight drill deck shroud enclosure with the ground, (b) maintain a collector-to-bailing airflow ratio of at least 3:1, (c) install a shroud on the collector dump discharge that extends close to the ground, and (d) maintain the dust collector as specified by the manufacturer [NIOSH 1998, 2005; Reed et al. 2004]. Use booster fans to improve local ventilation. Booster fans should be used to improve local ventilation and remove dust from the drill site when drilling benches in areas where ventilation provided by the main mine fan is not adequately diluting and transporting dust. Studies have shown that diesel-powered propeller fans, because of their mobility and entry coverage, have favorable ventilation characteristics for this application [Chekan et al. 2006; NIOSH 2003a]. To protect drill operators from dust that escapes the controls discussed above, enclosed cabs should be used on drills and should be properly equipped with an upgraded filtration and pressurization system. |
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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. Chekan GJ, Colinet JF, Grau RH III [2006]. Impact of fan type for reducing respirable dust in an underground limestone crushing facility. In: Proceedings of the 11th North American/Ninth U.S. Ventilation Symposium, University Park, PA, June 5–7, pp. 203–210. 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 [1998]. New shroud design controls silica dust from surface mine and construction blast hole drills. By Page SJ, Organiscak JA, Flesch JP, Hagedorn RT. 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. 98-150. 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 [2003a]. Dust control in stone mines. By Kissell FN, Chekan GJ. 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. 57–72. |
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drilling metal/nonmetal mining miners mining stone mining underground mines |