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| Air curtain being tested on roof bolter |
Background
The results of MSHA compliance sampling indicate that roof bolter operators are exposed to some of the highest silica dust levels measured in underground coal mines. From 2000 through 2004, MSHA inspectors collected and analyzed over 4000 samples for silica. Of these, 14% exceeded the permissible exposure limit. Past research by NIOSH has found that significant silica exposure can result when a roof bolter must work downwind of a continuous miner. With the increase of continuous miner supersections, bolter operators are being required to work downwind of con-tinuous miners more frequently. Conse-quently, control technologies are needed that can reduce roof bolter operators’ exposures to dust when working in the return airstream of a continuous miner.
NIOSH researchers developed a system that filters approximately 250 ft3/m of ventilation air and transports it through flexible tubing to an air curtain mounted on the underside of an operator’s canopy during installation of roof bolts. The air curtain contains baffling material that distributes the clean air evenly down over the operator. Laboratory tests were conducted to evaluate the effectiveness of the air curtain under differing operating conditions. Results showed that the dust levels were reduced under the curtain by approximately 60% for the mean air velocities commonly found in roof bolter entries. An underground evaluation was also completed recently to evaluate air curtain performance in an operating mine. Mine results demonstrated the proof-of-concept and the potential for this control technology.
Potential Outcome
The leading roof bolter manufacturer in the United States has expressed an interest in furthering the development of this technology. After a joint meeting among NIOSH, MSHA, the mine operator, and the bolter manufacturer, it was agreed that NIOSH, the mine operator, and the bolter manufacturer would continue this research to refine and improve the air curtain with the goal of reaching commercialization. Successful imple-mentation of this technology will result in a significant reduction in exposures to respir-able dust and silica among roof bolter operators, particularly when they are forced to work downwind of continuous miners. Field tests of this system should be completed in early 2007, with a bolter manufacturer offering the technology on its equipment by 2008.