WorkSafe Tasmania recently issued a safety alert to warn shotfirers and others who handle explosives about the risks associated with flyrock following several incidents involving flyrock in Tasmania.

Flyrock is created when pieces of rock are thrown from the blast site by the force generated by the explosives. It’s commonly created when the force used is more than what’s needed to fragment the rock and displace the muckpile.

Situations that can cause flyrock include inadequate burden, particularly of front-row holes, inadequate or ineffective stemming, and firing drop cuts, oversized boulders or toes.

Flyrock can travel a considerable distance from the blast site, and can cause death, serious injury and property damage, according to the alert, which said shotfirers and others who handle explosives must take all reasonable precautions and care to achieve an acceptable level of risk when carrying out blasting.

The measures to control the risk of flyrock injuring a person or damaging property are well known. “They include attempting to prevent flyrock from being created through appropriate blast design, loading and stemming, and removing people from the designated area around the blast where any flyrock may land,” said the alert, which added that typical control measures include:

•  ensuring that the blast design (including the hole diameter and depth, burden and spacing, explosives type and quantity and the initiation sequence) are suitable for the rock being blasted, taking into account the presence of geological structures
•  adjusting the loading of any front row (or other) holes which are found to have a reduced burden due to overbreak, hole deviation and other cause
•  ensuring that blastholes are charged and stemmed in accordance with the design, and making appropriate adjustments if voids are intersected to prevent overcharging
•  designating an appropriate exclusion zone around the blast, with an appropriate factor of safety and withdrawing everyone from this area while blasting is taking place
•  in some situations (such as when carrying out the blasting of construction sites or road cuttings near houses, roads or other public places), additional precautions may be required to protect members of the public from flyrock. “You may need to fire the blast in smaller sections using blast mats to contain any potential flyrock, or to close off selected areas to the public while blasting is carried out. In these cases, it is critical that the shotfirer closely monitor the controls being used, to ensure they are fit for purpose and are being used as intended,” the alert said.