Blast pattern dust control is the use of chemical dust palliatives to control dust generated from drilled blasthole patterns for the benefit of safety and health of workers and local communities. It is important to control dust at its source hence GRT formulates polymeric blast pattern dust control palliatives that eliminate dust harnessing the power of chemistry and particle size. What is a blast pattern? It is the geometry of the drill holes laid out of a bench or the real pattern after drilling at the bottom of a bench. Also, the geometry of the drill holes at the face of a drift or tunnel including the burden and the spacing distance and their relationship to each other. Blasting is a chemical-physical-mechanical process including the initiation (firing) of explosives for the purposes of breaking materials such as coal, ore at mines, mineral stone at quarries. Blasting can also be used to move materials, splitting off rock blocks for building purposes, demolishing building and constructions or generating seismic waves. Blasting environmental impacts include dust and dust explosions which have different particle sizes. These different dust particles are harmful to workers and nearby communities to areas where blasting is taking place. Dust kills. It is never an issue of a little bit of dust, the main issue is dealing with complacent approaches that lead to loss of life due to exposure to dust in its different forms. GRT evaluates in this article open pit and underground blast patterns, blast pattern dust generation and blast pattern dust control.
Open pit and underground blast patterns – differences and similarities.
Bench blasting is the common technique used for open-pit mines. It is a blasting technique in a vertical or sub-vertical hole or a row of holes towards a free vertical surface. More than one row of holes can be blasted in the same round. A time delay in the detonation between the rows creates new free surfaces for each row. In underground mining there are three methods involved and these are short-hole blasting, long-hole bench blasting and ring drilling and blasting methods. Short-hole blasting is usually limited to drilling rounds of 1.2 m to 5.0 m length and hole diameters of up to 43 mm. Long-hole bench blasting is like bench blasting in open pits, using long holes drilled downward either parallel to each other or in slight rings to cover the stope area. Initiation of the blast is with a booster down the hole. In ring drilling and blasting, series of sub level drill drifts are developed in the ore body. The drill pattern is designed to cover off the extent of the ore in the stope. The blasting will cause the ore to swell by 30% and this must be allowed for when blasting otherwise the blast may freeze.
Regular symmetrical or irregular arrays are used for blasting. To break any irregular areas at the edge of a regular array, the blast holes may be distributed irregularly. The standard blast patterns are of three major types namely:
In staggered pattern, the alignments are diagonal. The first-row blast holes and third row blast holes are in alignments. The drill holes may be vertical, inclined or horizontal. In open cast mines, both vertical and inclined holes parallel to the bench face is practiced. The positioning of the blasthole is very important. The required burden is always adjacent to the vertical blast hole to remove excessive burden further to the left of the required burden. In an inclined blast hole, which has an excessive inclination there are risks and hazards associated with bursting at the bottom leading to the rest of the burden coming down as a big block. This might necessitate secondary blasting. The location and design of the blasthole may produce air blast which can lead to failure in blast operations resulting in loss of explosives. The row of the blastholes may be single or multiple which then leads to single row and multi-row blasting patterns. In single row blasting, the fragmentation will be low, and the explosive consumption may be more than in multi-row blasting. Hence the multi-row blasting pattern is better and mostly preferred.
Blast pattern dust generation – sources of dust
The explosive is often located in drill holes in rock, but sometimes such as in boulder blasting, it may be located on the surface of the rock mass. Compared with placing the charge in a borehole, surface charges require a specific charge up to 10 times in excess, but typically 3 times for correct placing of an appropriate lay-on charge. Dust is generated regardless of the blasting pattern design, but it is important to understand what different blast patterns yield with regards to fragmentation. In the multi-row blasting design, the mass moves vertically upwards. In the box-cut design the area to be fragmented is not a square. A valley-like excavation is aimed at in the design with the fragmented mass falling back within the trapezium. In the corner-cut design also known as the echelon design the fragmented mass will fall back on the cut bench itself. These blast designs are preferred for different rock materials. The alternate delay pattern is used for softer rocks. The consecutive shot delay pattern is used for rocks with medium hardness. Whilst the short delay firing with a cut is used for hard rocks. Dust comes from the fragmentation processes of the rock. As the cycle of retrieving rock materials continues dust also is generated from crushing and separation of the burden into smaller fragments. Transportation of the rock material also generates a lot of dust particles with vehicular movement contributing to the dust generation as well. It is very important to consider the drill to blast to product cycle from a dust generation perspective. Any stage in the dust generation cycle should be approach with intent to eliminate dust at its source a discussion with tackle in dealing with dust at its source in the next section.
Blast pattern dust control – dealing with dust at its source
Prevention of dust generation from hazardous piles of drill cuttings produced by drill and blast activities is non-negotiable. Dust should be dealt with at its source. It is important to work diligently to protect workers and communities from fine respirable dusts which result in lung diseases such silicosis and lung cancer. GRT prioritises the following through the applications of its specialised technology in the form of GRT: DC Binder to drill pattern dust control:
Learn more about GRT DC Binder for blast pattern dust control a new flagship product that protects your crew from dust generated in key industries such as mining, quarrying and exploration drilling and blasting.
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REFERENCES
Petrosyan, M.I. 1994. Rock Breakage By Blasting. Taylor & Francis Group.
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