Use of Event Tree Analysis to Optimize Electrical Accident Countermeasure Systems for Metal/Non-Metal Mines

Four hundred and five electrical accidents which occurred in the metal/non-metal mining industry over three years were studied in detail to determine what "countermeasures" could have been used to prevent their occurrence. A total of 23 individual countermeasures were proposed. A detailed event tree was constructed to describe the circumstances leading up to electrical accidents, and each accident was located on the tree. The countermeasures were then visualized as preventing certain types of accidents by inhibiting the flow of events along certain branches or sub-branches of the tree. In this way the impact of each countermeasure could be visualized clearly, as well as any overlap between countermesures. The tree was then used to build countermeasure systems employing two or more countermeasures simultaneously. Optimum systems were developed by implementing first those countermeasures which had the greatest potential to prevent accidents (based on the accident data used). Additional countermeasures were added to each system as the next-most- effective countermeasure not yet implemented, and so on. A running total of accidents prevented was maintained as additional countermeasures were added. Along with the accident prevention benefits, the cost to the mining industry to implement each successive countermeasure in the systems was estimated. The final result is a cost-benefit curve for electrical accident countermeasures. The work demonstrated that large improvements in the benefit-cost ratio can be made by a judicious choice of countermeasures. It also showed that the concept of accident event flow inhibition on the event tree is a valuable analytical tool.