Ground vibrations, air over-pressure, fly-rock, generation of fines and dust, blasting fumes, damage to remaining rock and in some cases leaching of chemicals in the blast holes and polluting ground water are some of the undesirable impacts associated with blasting which collectively affect the surrounding environment adversely.
- Management of environmental impact of any blast depends on the following:
- Blast design – this is in the operator’s control.
- Design to ensure safety and compliance with regulatory limits and standards
- Identification of significant factors having impact
- Geology, not under operators control but can be taken into account
- Weather, not under operators control and cannot easily be taken into account.
- Effective implementation of the blast design
- Accurate measurements and assessment before, during and after blast.
- Blast and vibration records which can be retrieved, assessed and analysed.
It is possible to manage impacts of blasting operations by effective implementation of the design and the ability to evaluate the effect of any minor variations from the blast design that may become necessary to achieve a practical outcome to achieve desired goals. Most problems arising from blasting are related to the response of people to the operation. These complaints are often connected with the fear of structural damage despite the fact that vibration levels are usually way below those likely to cause even cosmetic damage.
Control Strategies for Environmental Impact
Essentially, the energy released by the explosives is useful for fragmentation, displacement and movement of broken rock whereas wasteful part of energy causes so many other impacts such as ground vibration, airblast and flyrock. A blast with poor fragmentation is likely to have a higher than expected environmental impact. The key therefore is the effective blast design and proper implementation for both efficient blasting and environmental impact control.Blast Design
A good, efficient blast design optimises fragmentation and movement whilst keeping environmental impact to a minimum. Conventional blasting techniques being adopted in India are leading to both uneconomic operations and sometime closure of mines. Blasts in surface mines are small sized, resulting in frequent blasting, poorer fragmentation and involving more manpower. Often environmental consequences of blasting such as vibrations, noise, flyrock and dust are causing hardships to mining industry. This is impacting mining industry in a big way. In India, often huge amount of compensation is paid for relocation of villages located in close vicinity of mines. However, due to improper control on the ground vibrations, airblast and flyrock, relocation does not reduce complaints and results in poor image of mining. However, trend abroad is to carryout large blasts thus reduce the frequency of blasts while controlling all the impacts which may result in complaints for ground and air vibrations, fly rock and dust hazard.
Blast Auditing
Good blast design is worthless if it is not implemented and an audit system helps to ensure the continuity of the process. Pre-blast monitoring should also be done cautiously to check deviation in the values of design parameters from the actual ones. All details like hole position, hole depths, nature and condition of holes, type and quantity of explosives; initiation system, sequence and delay timings are to be recorded. Prior to the introduction of new methods & technologies as working tools in mines, it was not possible to directly measure inaccessible locations on rock faces. With the introduction of laser profiler and blast hole logger, on-site collection and analysis of information related to blast geometry is possible.
Public relations
Studies have shown that initiating a good programme of public relations is the most effective way of reducing complaints about blasting. Programme content related to blasting activities could include notification of blasting, signals, direct notification, monitoring at nearby properties, education about the blasting process and environmental impact.
Blast Information Record
In India, monitoring and assessing blasting results is still in a qualitative form and is performed manually. Blast related data are recorded in the form of hard copy and often insufficient data are recorded.
TrainingTraining allows company employees to have confidence in their ability to use the system effectively to help achieve the two things blasters crave – efficient, productive blasts and, the most valuable commodity of all, peace of mind. If scientifically designed blasts are properly executed then all hazards could be controlled and efficiency could be improved.
ConclusionsThe challenge before the mining industry is to make changes in the presently used blasting technology. These involve detailed blast preparations, design of blasts according to conditions and desired results, proper execution of blasts and then monitoring of the performance during and after the blasts to optimise the results. All these need use of new tools to improve blasting technology. The developments in the areas of planning and design of blasts, drill monitoring, drill hole deviation, laser profiling systems, tools for monitoring during and after the blasts are needed. The innovative practices in the area of drilling, new bulk loading of explosives, performance measurement and the evaluation of blast outcome and productivity need to be adopted. Blast information need to be available online for easy retrieval and analysis. Indigenous computer aided design and analysis tools must become available for predicting and mitigating blasting hazards such as ground vibrations and airblast. Risk analysis and risk management steps need to be implemented. A mechanism is needed for professional training in this skilled technology.