One of my first jobs with the Victorian Government as an inspector of mines and quarries was to investigate a fly rock incident, where a quarry production shot resulted in fly rock that landed in a schoolyard more than a kilometre away from the shot.
It was fortunate there were no children playing in the schoolyard at the time. The shotfirer lost his licence and blasting at the quarry was suspended until the quarry owner carried out a review of its blasting practices and could demonstrate that blasting could be undertaken safely.
Fly rock, lack of blast area security, premature blasts and misfires are the four major causes of injuries and fatalities from blasting in open cut mines and quarries. Significant progress has been made in the reduction of serious injuries and fatalities resulting from the use of explosives in mines and quarries in Australia.
Blasting regulations across all jurisdictions that reference the Australian Standard AS 2187.2 Explosives – Storage and Use and the requirement for a competent and licensed shotfirer, who must ensure workers and the public are safe by ensuring appropriate exclusion zones and blasting shelters are in place, have helped reduce injuries and fatalities in our industry.
Blast management plans developed in accordance with AS 2187.2 are now mandated by the regulations and provide quarry and mine owners with a structured approach to assess all the risks to workers, community and infrastructure and to devise appropriate controls to eliminate or reduce those risks as reasonably practicable.
More recently, quarries and mines close to houses, along with regulators, have been kept busy responding to complaints from the community that blasting is causing damage to their homes. Approvals of residential developments near existing quarries are contributing to the increased number of complaints.
The common response from our industry, that the ground vibration and air blast levels measured at their property are within the limits specified in approvals, will not alleviate the concerns of householders that cracks in plaster or brickwork are attributed to blasting.
Another quarry I was involved with as an inspector of mines and quarries had to continually review its blast designs to manage residential encroachment on the substantial buffer zone that was in place when the quarry commenced operations. Residential development in some areas got to within 50m of the quarry boundary.
Even though the quarry operator complied with the ground vibration and air blast limits, blasting complaints escalated when a community action group was formed. The common theme of the complaints was that the quarry blasting was responsible for the cracking that occurred inside and outside residents’ homes.
The community accepted that blasting at the quarry was not contributing to the cracking of their homes after the local council building surveyor inspected all houses near the quarry and mapped and carried out an analysis of the cracking, which was attributed to reactive clays and other structural defects.
Safe use of blasting explosives with acceptable environmental impacts can be achieved with the development of blast management plans by quarry and mine owners, and by employing and supporting licensed and competent shotfirers in charge of the blasting.