An Investigation to Assess the Cause of Accident due to Flyrock in an Opencast Coal Mine: A Case Study

The paper deals with the investigation carried out to find out the possible reason of the flyrock incident causing fatality of one person at Bhurkunda ‘Á’ Colliery of Central Coalfields Limited (CCL). The flying fragment travelled up to 280 m from the blasting source causing the accidental death. The blasts were conducted in overburden rock strata consisting of medium grained sandstone and shale. The blasthole diameter used in the blast was 160 mm, and the average hole depth was 6.0 m. Site mixed emulsion (SME) explosive was used in the blast, and explosive charge per hole was 50.00 kg. Non-electric initiation systems were used for in-hole explosive and surface hole-to-hole initiations. The design parameters used in the blast were thoroughly analyzed using blast simulation software to check any anomaly in the blast design viz. sequence of hole firing, success rate of burden movement, maximum charge per delay fired within 8 ms windows, etc. The different flyrock fragments prediction models were used to assess the maximum possible travel distance of the flying in the blast. A synonymous blast was also conducted in the mines to replicate the blast where flyrock accident occurred. All the blasting events were recorded and monitored using a digital video camera. The simulation results of the blast showed the success rate of burden relief more than 80% with sufficient delay intervals for the rock movement during the blast. The maximum possible travel distance of flying fragments based on different flyrock prediction models was 227 m. In the synonymous blast, only vertical throws of the flying fragments up to 70 m (approximate) height were observed. It was difficult to find out the exact cause of flyrock incident. However, based on the detailed investigation, it was concluded that the possible cause of flying fragments travelling up to a distance of 280 m could be due to the presence of a weak zone in the rock strata. © 2020, The Author(s).