Application of Factor of Safety Concept for Evaluation of Flyrock risk in some Limestone Mines

Flyrock is the unwanted throw of rock fragments to excessive distances in opencast blasting. The incidence is relative in nature incorporating the distance of objects of concern like structures within and outside the mine, equipment within the mine & near the blast and persons within and off the mine. Several attempts to predict and define flyrock made worldwide could not address the problem since the phenomenon is not a regular feature in blasting. This probabilistic nature of flyrock allows for risk calculation. CIMFR, India developed a Factor of Safety based risk criterion (10, 14) for evaluation of throw/flyrock in opencast mines that incorporates all the above in terms of distance and allowable limit of throw – which in turn determines the risk. The criterion provides the blaster a tool for mathematical evaluation of flyrock risk in terms of a Factor of Safety and threat ratio (defined for the 1st time), thereby enhancing confidence when basting. The method is easy to use and has been applied to several mines in India and the results are significant. This paper details the evolution of the concept and its application in there limestone mines of India and the results obtained. The application of the method for defining a flexible danger zone is also discussed