On June 3, 1993, an explosion occurred at the Mediterranea refinery, in Milazzo, Sicily. Seven people died and eighteen people were injured with burns. An explosion in the accumulation tank 27V-16 involved bot-oil circuits subserving the refining units Topping 3, Topping 4, and HDT-RC. The explosion was caused by a sudden overpressure in the 27V-16 tank, probably as a result of the sudden vaporization of a small quantity of water. Shortcomings in the process design and in the management were at the origin of the accident, in particular: Some process choices undertaken a couple of years before the accident, such as the use of gas oil from a Topping column in place of diathermic oil and the use of a combustible gas in place of nitrogen. Some operational mistakes in the 13F-2 oven conduction and the failure (or inadequacy or exclusion) of control systems or automatic and manual safety devices. A detailed Fault Tree connects the process, design and management shortcomings identified. (c) 2005 American Institute of Chemical Engineers Process Saf Prog 25: 21-32, 2006.