Abstract: An employee was breaking concrete in a 4-foot-deep excavation. He thought he was breaking up concrete protecting a sewer line. In fact, he was working on a concrete slab protecting a 34-kilovolt underground power line. The employee's pneumatic hammer penetrated the shield of one of the cables, creating an electrical fault. The ensuing electric arc burned the employee on his face and chest and caused internal burns on his lungs and trachea. He was hospitalized for his injuries. The contractor had requested that the location of underground facilities be marked in the southwest corner of the intersection where the employee had been working. The marking was completed before the work was started. However, the employee was working at the southeast corner of the intersection, where the underground facilities had not been marked. No marking had been requested for that area.