Every bang is not the same

Related Topics:| Quarry Wear Parts Industry | NewsFlash |

Every bang is not the same

Extracted from The Star, 11^th April 2000

In Horizontal blasting, the explosive charge is inserted into holes drilled horizontally into the rock face. This method produces large boulders that need subsequent reblasting to reduce their size – creating more noise, dust and vibration. This method of blasting also creates large and ugly “faces” that are one of the main causes of public complaints about quarries.

Vertical blasting (where vertical holes are drilled) is more controlled, allowing a precise area to blasted; the method ensures that up to 95% of the rock material shatters into the right size straightaway.

Typically, not more than 30% of the rock material in horizontal blasting is the right size at first blast.

Vertical blasting can only be conducted if there is a bench for the operator to work on. Creating the bench, though, is a costly undertaking as it requires the creation of a road and a working platform on the generally steep limestone hills.

Thus, it is hardly surprising that many existing small quarries – that were approved when environment awareness was non-existent or in its infancy – still rely on horizontal blasting.

Fortunately, benching is now a requirement for new quarries; the requirement is also gradually being imposed on existing quarries that do not use the method.

Generally, regulations governing blasting activities are pretty strict in Malaysia. The allowable noise level limit in the northern part of Peninsular Malaysia is 124 db(L). Vibration limits are between 3.5mm and 5mm per second – this is stricter than Australian limits, says Perak Mines Department director Abdul Rahman Mohd Rafek.

Nowadays, shot firers (people who set off the charges are called) use electrical initiation to time each individual small blast so that the (sine) waves from the explosions cancel each other out to a large degree and, hence, reduce the amount of vibration.

Quarries in Perak are pretty good at keeping to these limits; they have a compliance rate of 90%, says Rahman. Occasional incidents of noise and vibration topping the limits are usually due to cavities in the hills (especially in limestone hills) that cause deviations in the drill holes; this can then lead to explosions that cause more vibration than intended, he explains.

As for dust, he says that more dust is generated from crushing activities rather than blasting.

“In fact, most of the dust from blasting does not go far because it is mostly coarse and will settle within minutes.”

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