Coal Age

SEP2014

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d a t i o n s t o M S H A b a s e d o n O M S H R ' s s c i e n t i f i c r e s e a r c h . Together, MSHA and NIOSH work to keep coal mining as safe as possible. The UBB explosion in West Virginia killed 29 miners. Upon investigation, the agency determined one of factors in the severity of the explosion was that the mine was not applying a sufficient amount of rock dust. A closer examination of the MSHA final investigation report revealed that the rock dust found in the mine did not meet both the total incombustible content and the sizing requirements of 30 CFR § 75.2. Based on MSHA's UBB investigation, it was determined that there was almost no rock dust in the tailgate entry of the longwall. Had there been rock dust present in sufficient quantities in this area, MSHA believes that the UBB methane explosion would not have propagated into the resulting coal dust explosion. In September 2010, MSHA published an emergency tempo- rary standard (ETS) for rock dust, revising the existing standard 30 CFR § 75.403 by requiring mine operators to increase the total incombustible content (TIC) of the combined coal dust, rock dust and other dust from 65% to 80% in all accessible areas of underground bituminous coal mines, and an additional 0.4% for each 0.1% of methane where methane is present in any ven- tilating current. This ETS became law on June 21, 2011. MSHA and NIOSH subsequently embarked on a project to better educate themselves on rock dust, obtaining nearly 400 samples of rock dust across the country to test for compliance to 30 CRF § 75.2. In a population of 393 rock dust samples, which were collected by MSHA personnel from 278 under- ground coal mines, 47% were found to contain less than the minimum sizing specification of 70% passing through a 200- mesh sieve (see Figure 1). Non-compliant rock dust was found at 51% of the mines sampled. These results indicated to both MSHA and NIOSH that several rock dust suppliers were using rock dust as a possible outlet for undesirable materials. In October 2011, NIOSH issued Hazard ID 16 (HID 16) on Non-Conforming Rock Dust, stating that rock dust not con- forming to the requirements in 30 CFR § 75.2 for particle size and caking properties was being used in U.S. underground coal mines. The announcement identified two concerns with the rock dust being used today; first, rock dust may not meet the sizing requirements, and second, it may form an undesirable "cake" when wetted and dried. NIOSH recommended that mine operators test their supply of rock dust to assure it met 30 CFR § 75.2 and that rock dust suppliers should provide docu- mented assurance to their customers that their rock dust met 3 0 C F R § 7 5 . 2 . T h e a g e n c y s u b s e q u e n t l y i s s u e d P r o g r a m Information Bulletin No. P11-50 on October 27, 2011, essential- ly repeating the recommendations by NIOSH found in HID 16. In HID 16, NIOSH highlighted that the requirement for "the particles [of rock dust] of which, when wetted and dried, will not cohere to form a cake, which will not be dispersed into separate particles by a light blast of air" was not being met by current commercially available rock dust. That is, the rock dust was "caking" upon exposure to water, then drying, and could not be dispersed by a light blast of air. NIOSH consid- ered this a major problem as the rock dust needs to be readily r o c k d u s t i n g c o n t i n u e d September 2014 www.coalage.com 41

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