Coal Age

JUL-AUG 2018

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14 July/August 2018 rock dust For more than 100 years now, underground coal operators have spread rock dust to pre- vent dust explosions in coal mines. After a series of explosions killed hundreds of min- ers in the early 1900s, researchers began to look for a way to reduce the explosive nature of coal dust underground. The idea was to place enough limestone on the floor, roof and rib, so that in the event of an igni- tion, the dust cloud kicked up by the fireball would be incapable of propagating an ex- plosion because of the inert limestone. Over time, acceptance and regulation led to today's practice of rock dusting un- derground. It has helped to greatly reduce the number and severity of coal dust ex- plosions, but most would agree there is room for improvement. Traditional dry dusting leads to hours of downtime. The application process is inconsistent and much of the rock dust ends up on the floor rather than the roof and ribs. During the last five years, several wet or foam-related systems have been devel- oped that apply rock dust uniformly. These products adhere well to the roof and rib. They are not, however, approved by the Mine Safety and Health Administration (MSHA) because they have not passed full- scale explosion testing. MSHA refers to these products as "effective temporary de- terrents" and mandated that, when miners use them, they apply dry dust on top of it to comply with the laws. That defeats the purpose of using the wet rock dust. These products cannot be tested in the U.S. because the U.S. no longer has a testing facility. When the U.S. Bureau of Mines (USBM) closed in 1996, the respon- sibility for full-scale explosion testing was passed along to the National Institute for Occupational Safety and Health (NIOSH). Researchers from NIOSH led the world with rock dust-related research at its Lake Lynn facilities, until it was closed in 2013, which was about the same time the foam products were entering the market. Without full-scale explosion testing, no one could know for sure how well these new products would perform, until now. Wright Concrete & Construction, a large rock-dust supplier based in south- ern West Virginia, recently made a huge The three photos above show coal-dust explosion tests conducted at the CSIR Explosion Research Facility at Kloppersbos, South Africa. The top photo is a successful test of Wright-Mix O2 ARD, where the fireball is extinguished before it reaches the coal dust in the second fuel zone. The middle photo shows the successful result of using traditional rock dust — coal dust in the second fuel zone rifles from the tube with no fireball. The bottom photo is the worst case scenario. Full-scale Testing Demonstrates That a New Mixture Performs as Well as Rock Dust Even though U.S. coal operators could benefit from the use of a new rock dusting product, regulators refuse to acknowledge the results by steve fiscor, editor

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