Dust control using a horizontally installed air-blocking shelf inside a drill shroud was shown to be effective by researchers at the National Institute for Occupational Safety and Health (NIOSH). However, when a medium-sized drilling machine lowers its mast, material deposited on the shelf can produce a significant dust cloud. To minimize this dust exposure hazard, researchers applied a 208-L (55-gallon) drum-sized ring, installing it concentrically with the drill stem under the deck table to act as a vertical air-blocking ring to control the drill dust leakage. Simultaneously, gravity force was utilized to minimize material buildup. Computer simulation was used in the evaluation. Three groups of ring heights were studied: short [5.1-cm (2-in), 7.6-cm (3-in), and 10.2-cm (4-in)], medium [15.2-cm (6-in), 30.5-cm (12-in), and 45.7-cm (18-in)], and long [61.0-cm (24-in) and 76.2-cm (30-in)]. The dust leakage was simulated using computational fluid dynamics (CFD) under the commonly encountered field conditions of a 2:1 dust-collector-to-bailing airflow ratio and a 5.1-cm (2-in) shroud-to-ground gap. Based on this simulation study, the vertical air-blocking ring with medium heights has the potential to effectively confine the dust inside the drill shroud. Other shorter or longer height rings may not be as effective in preventing dust leakage from the shroud. The results of this study can be used to guide future laboratory tests.
