Dust Control Handbook for Industrial Minerals Mining and Processing

unsubstantiated due to the inconsistent drilling rates (ranging from -24.9 to +57.5 percent) andthe dependency upon drilling circumstances [USBM 1943].External Water SpraysExternal water sprays, depicted in Figure 3.19, have been used in the past, but when dry drillingthey only produced dust reductions up to 25 percent compared with dry drilling alone—i.e.,drilling without the use of any water [USBM 1921]. In an attempt to improve dust reductions, anexternal water spray device, a ring which contained spray holes on the inside diameter for dustcontrol during dry drilling, was developed and tested. This device was slipped over the drill steeland sprayed water on the drill steel outside of the hole. It produced dust reductions that werevariable, ranging from 75 to 88 percent, over dry drilling [USBM 1939]. Shrouding of thedrilling area was tested through the addition of a rubber shroud mounted at the area at the end ofthe boom to surround the external spray and drill bit. It was shown to improve dust reduction to53 percent [USBM 1982a]. Although these devices were an improvement over external watersprays, results showed that these devices along with external water sprays could not be used toreplace wet drilling and maintain proper dust control during drilling operations. They could beused to enhance dust control in conjunction with wet drilling.Figure 3.19. Drill boom showing external water sprays directed onto the drill steel.RESPIRABLE DUST CONTROL FOR BLASTINGBlasting is a controlled operation which generally occurs intermittently at mining operations andis used to fragment the rock being mined. This is an important step in industrial mineralproduction as it is required to break up the mineral product, and the effectiveness of blasting may100 Drilling and Blasting