Dust Control Handbook for Industrial Minerals Mining and Processing

contains a piston which delivers hammer blows to the drill column or the drill bit, dependingupon the location of the drill (top hammer or down-the-hole hammer), eliminating the need forthe high down-pressures required in rotary drilling.Typical holes can be any size up to 15 inches in diameter, with the larger hole diameterscommonly produced using rotary drill bits. Generally, these holes are oriented vertically,although some operations do use angled holes in their blast design, and the holes are drilled in apattern where they are aligned in rows. The type of drilling equipment can range from smallsurface crawler rigs to truck-mounted drills to large track-mounted drill rigs, as seen inFigure 3.1.Dust control methods for surface drilling use wet drilling or dry drilling with dust collectionsystems. There are variations to these methods due to the operating environment of the surfacedrilling operation and the type of equipment used, but generally the principles of dust controlpresented in this chapter are applicable to all types of surface drilling; including small crawler,truck-mounted, and large track-mounted drills.Wet DrillingFigure 3.1. Illustrations depicting a small surface crawler drill rig,a truck-mounted drill rig, and a large track-mounted drill rig, respectively.The best method for dust control in surface drilling is to use wet drilling techniques. Wet drillinginjects water along with the air to flush the cuttings out of the hole as shown in Figure 3.2.Testing has shown that this technique can provide dust control efficiencies up to 96 percent[USBM 1987].Water injection requires monitoring by the drill operator to efficiently control dust. The amountof water required for dust control is not large. Typical water flow rates in wet drilling systemsgenerally range from 0.1 to 2.0 gpm, but this varies based on the drill type, geology, andmoisture level of the material being drilled. For example, testing at a surface mine site showed80 Drilling and Blasting