Contamination of Stone Dust in the Personal Coal Dust Samples for Exposure Assessment in Underground Coal Mines.

The application of stone dust for coal dust explosion prevention has been practiced in South African coal mines in the 1970s. By late 1990s, improvements in its method application were resulted in new regulations on the application of stone dust to freshly exposed coal face areas came into effect in 1998. However, the implication of frequent stone dusting of freshly exposed coal faces has resulted in contamination of the personal and engineering dust samples meant for exposure assessment in mines. In a continued effort to identify and reduce the dust problem and informed exposure assessment in the coal mines, influence of stone dust on the personal coal dust exposure levels was determined. This was determined on the basis of the collected real-time personal dust data and the time study in the continuous miner (CM) section. From the data analyses of the three personal dust samples it is noted that, on average, 26.43% of the dust samples were contaminated with stone dust (mass basis), with an average exposure level of 12 mg/m3 for a period of just 12 minutes. The amount of stone dust in the sample appears to be small, but it must be noted that the actual exposure to stone dust at the waiting place is a significant underestimation of the exposure closer to the stone dust source. Similarly, fallout of stone dust analyses indicated that to avoid the influence of stone dust in the personal dust samples require no stone dusting during the shift, or at least 5 hours before the start of the morning shift. Problem is relevant to all underground coal mines and there are no easy solutions to the mine operators to overcome this unavoidable situation. However, there are efforts to develop alternate to dry spraying of stone dust, which is currently being trialed in South Africa and Australia. In the meantime, greater administrative control of stone dusting well before the start of the shift would alleviate the situation or documenting the stone dust contamination in dust sampling results so that personal dust samples submitted specifically to regulators were not contaminated with the stone dust, which could skew the exposure values towards non-compliance. [ABSTRACT FROM AUTHOR]