Abstract: On June 6, 2008, an electrical utility worker employed by Commonwealth Edison Company, was in a 6-ft by 6-ft underground electrical vault, which was 5-ft-deep. As he was working in the electrical vault, an explosion occurred, and he received second- and third-degree electrical burns to 75 percent of his body. A Commonwealth Edison Company internal investigation determined that a 12-kv feeder cable (Y3040) faulted, while a three man crew was preparing to replace it with another 12-kv feeder cable (Y3080). The utility worker was wearing flame resistant coveralls. At the time of the explosion, he was standing with the upper portion of his body outside the manhole opening, which placed him directly in the path of the escaping explosive gases. The worker died from his injuries.