Blasting
The purpose of mine and quarry blasting is to fracture or fragment the rock mass to enable excavation. The mechanism of fracturing is beyond the scope of this summary, but it is important to understand that not all the energy produced when the explosive is detonated goes into breaking the rock. Some of it is “lost” in the form of heat, sound (causing noise), displacement (when this is excessive it causes flyrock) and ground shaking (causing vibrations). Blasting can therefore be seen to give rise to a number of unwanted and sometimes disturbing effects, but with modern technology and techniques, these impacts can be minimized.
Reducing the Environmental Effect of Aggregate Quarrying: Dust, Noise and Vibration contains additional information which can be referenced, and a comprehensive summary of recent research into the control of environmental effects of blasting. The key findings are now included in this section.
Vibrations
Vibrations transmitted through the ground (seismic waves) and pressure waves through the air (overpressure) shake buildings and people and may cause nuisance or, in extreme cases, damage. However, the air overpressure wave may arrive after the ground vibration by up to two seconds over a distance of 1km. The perception of both factors is likely to be stronger inside a building than outside.
Noise
Audible noise is the sound of the gasses venting from the blast area, and rocks collapsing into the muck pile. Noise is part of the pressure wave so it occurs at the same time as overpressure. It may be augmented by the rattling of windows, etc. which can be caused by the overpressure or by the structure shaking in response to the ground vibration event. Equipment is now available to determine whether noise caused by the structural response of a building is the result of ground vibration or air overpressure (the air blast). This needs to be identified if the effects are to be minimized.
Flyrock
Flyrock is the name given to fragments of rock propelled into the air by the explosions. This is clearly potentially dangerous to people and property both inside and outside the site, and therefore should more correctly be thought of as a health and safety issue, rather than an environmental matter.
Dust
Dust can be an issue on some sites, but as the blasting takes place within the excavation it is usually confined within the workings. Dust is discussed in more detail in another section.
Fumes
Fumes can occasionally be produced by the incomplete reaction of the explosive chemical. There are a variety of causes and is recognizable by the presence of orange fumes.
There are a significant number of publications covering the subject of blasting which are referred to through the text and listed in the reference section.
