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Haul road dust control.

Reed-WR; Organiscak-JA
Coal Age 2007 Oct; 112(10):34-37
This truck haulage dust study showed that primarily wind, distance, and road treatment conditions notably affected the dust concentrations at locations next to, 50 ft from, and 100 ft away from the unpaved haulage road. Airborne dust measured along the unpaved haul road showed that high concentrations of fugitive dust can be generated with these concentrations rapidly decreasing to nearly background levels within 100 ft of the road. Instantaneous respirable dust measurements illustrated that the trucks generate a real-time dust cloud that has a peak concentration with a time-related decay rate as the dust moves past the sampling locations. The respirable dust concentrations and peak levels were notably diminished as the dust cloud was transported, diluted, and diffused by the wind over the 100 ft distance from the road. Individual truck concentrations and peak levels measured next to the dry road surface test section were quite variable and dependent on wind conditions, particularly wind direction, with respect to reaching the sampling location. The vast majority of the fugitive airborne dust generated from unpaved and untreated haulage roads was non-respirable. At least 85% of the airborne dust sampled by impactors was larger than 10 microm (aerodynamic diameter size). Since the truck-generated dust appears to dilute and diffuse rapidly away from the road, the most susceptible persons for exposure are the truck workers themselves. Exposure is not as likely from their own truck, but from dust plumes of opposing truck traffic and when following behind trucks in the same direction. Other occupations that can be exposed to fugitive truck dust are the operators of shovels and frontend loaders that fill the trucks, and bulldozer and crusher operators who may be working in the close proximity to the dump, processing, and storage facilities. As surface mine facilities are dynamic operations exposed to changing weather conditions, day-to-day dust levels can be highly variable. However, there are many dust control practices for haul trucks available which can assist with maintaining worker exposures below mandated standards. These practices include reducing haul truck speed and maintaining safe following distances, watering haul roads, treating haul roads, and maintaining equipment cabs. Reducing the haul truck speed is the simplest control method. The reduction in dust is attributable to the lower amount of disturbance to the haul road at lower speeds. The results of the field study completed at the LQ and CP showed that the critical time period of maximum dust exposure when following a truck is from 0 to 20 seconds. Implementing a policy to ensure that trucks do not follow within 20 seconds of another truck can result in a 41%-52% reduction in airborne respirable dust exposure to the following truck. The use of water on haul roads is the most common dust control method used. As seen in Figure 1, watering the haul road on the test section in this study allowed instantaneous dust concentrations to remain below 2 mg/m3 for over three hours. Past research has shown that watering haul roads with a water truck once an hour has been shown to have a control efficiency of 40% for total suspended particulates (TSP). If watering is increased to once every half hour, the control efficiency for TSP increases to 55%. The control efficiency was defined as a comparison of the controlled (watered) emission rate to the uncontrolled emission rate. The EPA reported several test results of watering haul roads. The results ranged from a control efficiency of 74% for TSP for the three to four hours following the application of water at a rate of 2.08 L/m2 (0.46 gallons/yd2) to a control efficiency of 95% for TSP for 0.5 hours after the application of 0.59 L/m2 (0.13 gallons/yd2). Treating haul roads is generally completed through the application of chemicals, and requires a significant amount of road maintenance. In one study, control efficiencies were shown to be 95% for magnesium chloride and 70% for a petroleum derivative for controlling haul truck generated dust. Maintaining equipment cabs in good operating condition also reduces operator exposure to respirable dust. A study conducted on dozers and drills demonstrated that properly maintained cabs can attain dust reductions of 90% for drills and between 44% and 100% for dozers. The variations of the dust reductions for dozers were attributed to re-entrainment of internal cab dust. An additional study completed on haul trucks, which involved the retrofitting of a cab with a filtration/pressure air conditioning system to produce positive pressure in the cab, showed that properly maintained cabs can produce a potential 52% reduction of respirable dust. Characterizing the fugitive dust emissions from haul trucks at surface mine sites will help operators understand the effects of dust generated by haul trucks. This knowledge will also help in the understanding of dust exposure for equipment operators and mine personnel, which will provide mine operators additional insight as to how to effectively reduce dust.
Mining-industry; Surface-mining; Dust-control; Dust-analysis; Respirable-dust; Mine-workers; Truck-drivers; Particulate-dust
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Journal Article; Trade
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Coal Age