Semi-Empirical Model for Predicting Surface Coal Mine Drill Respirable Dust Emissions

Abstract

Over exposure to airborne respirable crystalline silica dust can cause serious or fatal respiratory disease and mine worker exposure to silica dust continues to be an ongoing occupational health concern. Exposures of surface coal mine rock drillers to respirable crystalline silica are of particular concern. MSHA dust exposure data from 1985–1992 showed that the percentage of the highwall drill dust samples (Designated Work Position, DWP) having greater than 5 percent silica and exceeding the 100 µg/m 3 silica limit were 81 percent and 77 percent, respectively. Although a recent analysis of the MSHA data from 1996–2000 shows that the percentage of the DWP drill dust samples exceeding the permissible exposure limit has dropped to 31 percent, MSHA data still suggests that over exposure to silica dust is an ongoing surface coal mine dust problem for the highwall drill operator. On surface coal mine drills, bailing airflow flushes out the drill hole by removing the cuttings from the hole. Conveyor belting material is typically used to fabricate a shroud around the drill deck in an effort to contain the drill dust so that it can be captured by a collector. Dust leakage from the drill shroud is usually the worst dust source problem on most drills. The focus of this work is drill shroud dust leakage and the relationships of various drilling parameters on this leakage. Experimental data was obtained and used in combination with dimensional analysis to establish these relationships. In general, it is found that airborne respirable dust concentrations vary in a direct relationship with shroud leakage area and in an inverse relationship with drill deck cross-sectional area and shroud height.