Fear Of Blasting At Mines

Of all the activities that affect the relationship between mines and the communities in which they operate, none is more problematic than blasting. Many people have an almost instinctive fear of blasting and as a result they are opposed to mining in their communities, regardless of the benefits a mine may bring. As in many other situations, their fear usually arises from a lack of knowledge and that is perfectly understandable; after all, very few people have ever had an opportunity to even see a mine blast. Nevertheless, it is unfortunate.

A great deal is known today about blasting in mines and its effects on the surrounding environment. Essentially, the process involves the sudden release of a controlled amount of explosive energy inside a hole that has been drilled at the mine. The release of that energy is designed to separate a given quantity of material from its surrounding geologic structure, fragment it into manageable sizes, and drop the fragments in a pile on the floor of the mine where further processing of the material can take place. Mine blasts are similar to the practice seen on television when a building is imploded to expedite its demolition.

When a blast occurs, a very large portion of the energy that is released is absorbed in separating the material from its geologic structure. The small amount of remaining energy travels in waves through the ground, as well as through the air. These waves can be measured relatively easily. For ground waves, two common measurement criteria are a wave's length and "peak particle velocity"; that is, the intensity of the movement experienced by a particle of earth at a specific distance from the blast site as a result of the wave passing through. Air waves are usually measured by the amount of their "overpressure".

The effect of waves following a blast is somewhat analogous to what happens when a rock is dropped into a body of still water. Ripples radiate outward from the point of impact, gradually diminishing in size. Unlike ripples traveling through water, however, which are large enough to be seen, ground waves resulting from blasts are very small. The displacement of the earth that occurs as they pass through is generally less than a few thousandths of an inch. Yet that is enough movement to cause people relatively close to the blast site to feel a slight tremor for a moment or two.

Extensive research has been conducted by government and industry to understand the effects of the ground and air waves on persons and property near mines. Until it was eliminated by budget cuts, the United States Bureau of Mines was the leading force in calculating the likely results that such waves produce when they impact homes and buildings at different distances from the blast site. The work of the Bureau generally has been considered the benchmark in the field and the limits imposed on blasting by many states are based on its recommendations.

Since the effects of ground and air waves are now well understood, it would seem to be an easy step to conclude that the effects of blasting should not be a source of controversy. Experienced mining companies know the safe limits within which they can blast. And it can be determined with relative certainty if a blast actually caused a problem to a neighboring home or other building. Nevertheless, the fear surrounding blasting continues in the minds of many people. If they can feel their home shake following a blast, a number will remain convinced their home is being damaged.

Experience has shown that the answer to this dilemma for mining companies lies first and foremost in being perceived as trustworthy. When companies are trusted by their neighbors, they can help them begin to understand blasting. Companies can place seismographs at a neighbor's home and explain the measurements which are recorded. And they can show through independent studies that based on those measurements no harm to houses could have resulted. Not everyone will accept a mining company's explanation about blasting, of course, but many will begin to accept the explanation when they begin to believe what they are being told and understand that their fears have been misplaced.