Abstract: On July 16, 1999, new underground oxygen, propane, and water lines were being installed. The new lines run west to east in the yard. A north to south line was installed a few years ago. The new west to east line was tied into the existing north south line. Approximately 100 ft of linear lines were laid but not covered by soil. They were preparing to test the first work station on the new west to east line and a welding torch was connected by welding hoses to a header. Welding hoses for oxygen and propane were ran from the master shutoff valves at the welding lines to the header. An employee tried to light the torch but it would not stay lit. The oxygen and propane hoses from the shutoff valves were reversed and were switched to the correct lines. The propane and oxygen hoses were bled out at the header from the shutoff valves to clean the hoses. However, the hoses from the welding torch were not bled and when they attempted to light the welding torch again an explosion occurred. Employee #1's foot at the ankle was amputated, Employee #2's lower leg was amputated, and Employee #3's lower arm was amputated. All three employees were hospitalized.