Flyrock danger zone demarcation in opencast mines: a risk based approach

Flyrock, a rock fragment thrown to an excessive distance, is a random event and an ongoing problem in opencast bench blasting. Existing criteria for a ‘Flyrock Danger Zone’ are rigid, such that blasting may not be permitted where there are structures within about 100 m. A statistical approach to the problem is proposed and new concepts of Factor of Safety, Threat Levels and Flyrock Risk have been introduced in order to elucidate risk classes for different geo-mining conditions. The new criteria allow the mining engineer to work out the confidence level of the blasting practice in terms probabilities and risk. The approach is unique, with the emphasis on the categories of blasting and degree of risk that a blasting engineer can afford without sacrificing production and at the same time controlling the travel distance of the flyrock. The proposed dynamic danger zone gives the engineer flexibility to adjust blasting operations to take account of safety requirements and production demands.