Engineering Controls Database

Best Practices for Dust Control in Coal Mining – Surface Mines – Enclosed Cabs

Problem:	Respirable dust exposure has long been known to be a serious health threat to workers in many industries. In coal mining, overexposure to respirable coal mine dust can lead to coal workers’ pneumoconiosis (CWP). CWP is a lung disease that can be disabling and fatal in its most severe form. In addition, miners can be exposed to high levels of respirable silica dust, which can cause silicosis, another disabling and/or fatal lung disease. Exposure to coal mine dust may also increases a miner’s risk of developing chronic bronchitis, chronic obstructive pulmonary disease, and pathologic emphysema. Once contracted, there is no cure for CWP or silicosis. The goal, therefore, is to limit worker exposure to respirable dust to prevent development of these diseases.
What this means to you:	U.S. mine workers continue to be at risk of exposure to excessive levels of silica dust. The percentage of Mine Safety and Health Administration (MSHA) dust samples during 2004–2008 that exceeded the applicable or reduced respirable dust standard because of the presence of silica were: 12% for sand and gravel mines, 13% for stone mines, 18% for nonmetal mines, 21% for metal operations, and 11% for coal mines [MSHA 2009]. At surface mining operations, occupations most frequently exceeding the applicable respirable dust standard are usually operators of mechanized equipment such as drills, bulldozers, scrapers, front-end loaders, haul trucks, and crushers.
Description of control:	Enclosed cab filtration systems are one of the mainstay engineering controls for reducing mobile equipment operators’ exposure to airborne dust at surface mines. Enclosed cabs with heating, ventilation, and air conditioning (HVAC) systems are typically integrated into the drills and mobile equipment to protect the operator from the outside environment. Air filtration is often part of the HVAC system as an engineering control for airborne dusts. Surface mining dust surveys conducted by NIOSH on drills and bulldozers have shown that enclosed cabs can effectively control the operator’s dust exposure, but cab performance can vary [Organiscak and Page 1999]. The enclosed cab protection factors (outside ÷ inside dust concentrations) measured on rotary drills ranged from 2.5 to 84, and those measured on bulldozers ranged from 0 to 45. NIOSH also conducted field studies of upgrading older equipment cabs to improve their dust control effectiveness. These studies involved retrofitting older enclosed cabs with air-conditioning, heating, and air filtration systems to show the effectiveness of upgrading older mine equipment cabs. During these retrofits, any reasonably repairable cracks, gaps, or openings were sealed with silicone and closed cell foam tape. Varying degrees of enclosure integrity were achieved. For example, the protection factor (outside ÷ inside dust concentrations) for rotary drills ranged from 2.8 to 89.3. The following is a summary of the key performance factors found in NIOSH controlled laboratory experiments for effective enclosed cab dust filtration systems: Ensure good cab enclosure integrity to achieve positive pressurization against wind penetration into the enclosure. Significant improvements in cab protection factors were achieved in the field studies when cab pressures exceeded 0.01 inch water gauge (in w.g.). This corresponded to wind velocity equivalents (an indicator of cab wind velocity resistance) greater than 4.5 miles per hour (mph). The cab enclosures with greater than 0.01 in w.g. pressure were of close-fitted construction, and their integrity could be readily improved by sealing cab enclosure cracks, gaps, or openings with silicone and closed cell foam tape. Use high-efficiency respirable dust filters on the intake air supply into the cab. Filter efficiency performance specifications used in the field were 95% or greater on respirable-sized dusts [Chekan and Colinet 2003; Cecala et al. 2003, 2005; Organiscak et al. 2003a]. Laboratory experiments showed an order of magnitude increase in cab protection factors when using a 99% efficient filter versus a 38% efficient filter on respirable-sized particles [NIOSH 2007]. Use an efficient respirable dust recirculation filter. All of the cab field demonstrations used recirculation filters that were 95% efficient or better in removing respirable-sized dusts [Chekan and Colinet 2003; Cecala et al. 2003, 2005; Organiscak et al. 2003a]. Laboratory experiments showed an order of magnitude increase in cab protection factors when using an 85%–94.9% efficient filter compared to no recirculation filter [NIOSH 2007]. Laboratory testing also showed that when using a recirculation filter, the time for interior cab concentration to decrease and reach stability after the door had been opened and closed was cut by more than half. Use good housekeeping practices to minimize dust sources in the cab.Miners can carry dirt and mud into the cab on their boots. As this material dries, it can become entrained in the cab air, increasing the exposure of the worker. One method of suppressing dust entrainment from a soiled cab floor is to place a gritless (without sand added) sweeping compound on the floor during the working shift. Most commercial sweeping compounds have petroleum-based oils or wax added to the cellulose material. It must be noted, however, that people sensitized to petroleum distillates could have allergic reactions to these sweeping compounds if used in enclosed cabs. Non-petroleum-based sweeping compounds that use either a natural oil or chemical additive for dust adhesion [NIOSH 2001] are available and should be considered. It is also recommended to cover the floor with rubber matting instead of carpeting for easier cleaning. More frequent cleaning of heavily soiled floors by the operator may be a more straightforward alternative to using sweeping compounds to minimize this type of dust entrainment. Dust entrainment from the floor can be increased by heaters that blow across soiled cab floors. Dust levels were shown to increase from 0.03 to 0.26 milligram per cubic meter (mg/m3) by turning on a floor heater inside the cab [Cecala et al. 2005]. The floor heater was removed and cab heating was discharged down from the ceiling HVAC system, reducing dust entrainment in the cab during colder winter months. Keep doors closed during equipment operation. On one drill operation, the respirable dust concentrations inside the cab averaged 0.09 mg/m3 with the door closed and 0.81 mg/m3 when the door was briefly opened to add drill steels [Cecala et al. 2007]. Although this occurred after drilling stopped and the visible dust dissipated, opening the door, even briefly, produced a ninefold increase in respirable dust concentrations inside the cab during the many drill steel changes made over a working shift.
References:	NIOSH [2010]. Information circular 9517. Best practices for dust control in coal 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. 2010-110. Cecala AB, Organiscak JA, Heitbrink WA, Zimmer JA, Fisher T, Gresh RE, Ashley JD [2003]. Reducing enclosed cab drill operator’s respirable dust exposure at a surface coal operation using a retrofitted filtration and pressurization system. In: Yernberg WR, ed. Transactions of Society for Mining, Metallurgy, and Exploration, Inc. Vol. 314. Littleton, CO: Society for Mining, Metallurgy, and Exploration, Inc., pp. 31–36. Cecala AB, Organiscak JA, Zimmer JA, Heitbrink WA, Moyer ES, Schmitz M, Ahrenholtz E, Coppock CC, Andrews EH [2005]. Reducing enclosed cab drill operator’s respirable dust exposure with effective filtration and pressurization techniques. J Occup Environ Hyg 2(1):54–63. Cecala AB, Organiscak JA, Zimmer JA, Moredock D, Hillis M [2007]. Closing the door to dust when adding drill steels. Rock Prod 110(10):29–32. Chekan GJ, Colinet JF [2003]. Retrofit options for better dust control. Aggregates Manag 8(9):9–12. MSHA [2009]. Program Evaluation and Information Resources, Standardized Information System. Arlington, VA: U.S. Department of Labor, Mine Safety and Health Administration. NIOSH [2001]. Technology news 487: Sweeping compound application reduces dust from soiled floors within enclosed operator cabs. Pittsburgh, PA: U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health. NIOSH [2007]. Technology news 528: Recirculation filter is key to improving dust control in enclosed cabs. Pittsburgh, PA: 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. 2008–100. Organiscak JA, Page SJ [1999]. Field assessment of control techniques and long-term dust variability for surface coal mine rock drills and bulldozers. Int J Surf Min Reclam Env 13:165–172. Organiscak JA, Cecala AB, Thimons ED, Heitbrink WA, Schmitz M, Ahrenholtz E [2003a]. NIOSH/industry collaborative efforts show improved mining equipment cab dust protection. In: Yernberg WR, ed. Transactions of Society for Mining, Metallurgy, and Exploration, Inc. Vol. 314. Littleton, CO: Society for Mining, Metallurgy, and Exploration, Inc., pp. 145–152.
Keywords:	coal miners coal mining driller drilling mining surface mines surface mining