An employee was using a hydraulic excavator with a hammer attachment to demolish part of a bridge. The excavator was on concrete ground and there was a gap where the debris from the demolition would fall between the vehicle and the bridge. The hammer attachment got caught in the concrete and pulled the excavator off the ledge, causing it to fall 6-8 feet to the concrete debris below. The operator sustained a left shoulder dislocation and a vertebral fracture.