Inspection Detail

Inspection: 303588750 - 3m Company

Inspection Information - Office: San Bernardino Mining &Tunneling District Office

Investigation Summary

At approximately 1:14 a.m. on May 31, 2006, Employee #1, an electrician, was working on a 480 motor power circuit at the Crushing & Screening Motor Control Center. The screw driver he was using caused a phase to ground short resulting in a large electrical arc flash. While attempting to clear an electrical fault and tightening lugs on the Number 5 Rolls Crusher Feed Conveyor Circuit Breaker, the uninsulated screw driver caused a short when the tip of the screw driver was inadvertently inserted into a lug on the energized feed side of the breaker. The short was completed when shaft of the screw driver contacted the grounded metal frame of the circuit enclosure. The main circuit breaker (1,500 ampere rated) upstream from the electrician tripped out as a result of this short circuit. The electrician was hospitalized to treat burns to his face and hand and was then release on June 2, 2006. The electrician stated that he was talking to the plant operator via walkie talkie at the time of the arc flash and was not paying attention to the location of his screw driver. The electrician also stated that he had no intention of working on the energized side of the breaker but inadvertently placed the screw driver into the recessed lug on the energized side. The cause of this accident was the employee in attention to his work and a failure to test for the presence of voltage, as required by California Code of Regulations Title 8 - 2320.3 prior to starting work.

Keywords: BURN, ELECTRIC ARC, CIRCUIT BREAKER, CONVEYOR, FACE, HAND