The engineering controls that relate to blasting near communities revolve around the reduction of the strength of the sources of vibration and airblast, the breakup of the blast energy into small pulses, and the improvement of confinement such that the energy will not be released to the environment. The best strategy is always to optimize the blast design rather than fixing the effects of the blast afterward.
In the first place, blasters can minimize the maximum instantaneous charge and charge per delay by using small hole charges, smaller bench height, decking the charge, and minimizing the simultaneous blast holes. These practices contribute to a reduction in the peak particle velocity and help prevent vibration from reaching community limits. Some of the controls associated with this practice involve burden and spacing considerations.
Secondly, delay timing is an important control mechanism for vibrations as well as air blasts. The use of electronic detonators and millisecond delays timed in a manner to spread out energy reduces constructive interference of blast waves and thus the level of vibration as much as 69.7%, according to one research study. In terms of engineering controls, practice guidelines point out the importance of delay timing as it influences air blast by producing superimposing of pressure waves if not done properly.
Third, stemming and burden are very important engineering controls for noise as well as overpressure. Stemming helps keep explosive gases within the blasthole for a duration needed for fracturing rock rather than releasing into the atmosphere, whereas sufficient burden helps avoid blowout and prevent overpressure. When there is inadequate burden or geological fractures are present, the operator should decrease powder factor and increase the length of stemming.
Fourth, the process involves the use of either deck loading, air-decking, water decking, or presplitting to reduce vibration transmission and enhance energy distribution. Decking breaks down the explosive load into smaller loads, thus reducing the amount of energy per delay and resulting in reduced vibration. It has been observed that both the air-decking and water-sealing of explosives have been helpful in reducing vibrations in the adjoining structures.
Fifth, operators ensure proper geometrical orientation and initiation to achieve controlled vibration transmission by controlling energy dissipation direction. This is achieved by initiating the process in another direction apart from the current one. It also involves utilizing one to two free faces and proper sequencing. This is particularly important in areas with nearby settlements since geology, topography, and geometric orientation will determine the distance over which noise and vibrations travel.
In summary, engineering measures are best applied when used along with monitoring and seasonal/condition-specific timing of blasts. Seismic and air blast monitoring ensures that maximum particle velocity and air overpressure remain within allowable limits, while blasting activities should not be carried out during temperature inversion periods or strong wind blowing towards homes and other areas where noise amplification is likely. Ideally, any blasting program that ensures minimal impact should consider all the above aspects, among others.
