Abstract: Two employees were using jackhammers to break up a 240-square-meter, 150-millimeter-thick concrete pad located in the center of a round condominium. The building was 13 stories high with an open center. Tenants used the pad to drive through the center of the building, unload, and check into the condominium. A switchgear room was located on the north side of the building. A 7200-volt underground power line supplied the switchgear room, which served as the electrical supply for the building. The three phase conductors ran from the switchgear to a fuse cabinet. A three-phase transformer fed the fire pump room located on the south side of the building, approximately 18.3 meters away. The three-phase line had been installed in the concrete pad approximately 4 years earlier. The conductors ran in 51-millimeter-diameter Schedule 40 rigid polyvinyl chloride conduit, and concrete had been poured around the conduit. Miss Utility marked the location of the underground power line, and the employees were aware of where it was. The employees had used the jackhammers to break the concrete near the line and were using hammers to break the concrete from around the conduit. However, a 1.8-meter by 6.1-meter pad was located under the existing pad, and the employees had difficulty breaking a 1.8-meter section of concrete with the hammers. One of the employees used a jackhammer to break the concrete over the conduit. The jackhammer slipped and the employee lost his balance. He fell to the ground, and the jackhammer broke through the concrete and conduit and contacted the three-phase line. The bit of the jackhammer cut all three AWG #2 stranded copper conductors and causing an electrical fault. The ensuing electric arc burned the employee who had been using the jackhammer. The electrical fault also damaged the control cabinet in the fire pump room. The injured employee was treated at a hospital for burns to his face and released the same day.