Fire due to welding operation

A fire started at the manhole of an inspection pit for underground pipes of a petroleum storage depot during a welding operation as part of maintenance work on the piping supplying a tank. The underground pipes were feeding eleven tanks in different conditions. At 11:15 a.m., a leak of premium-grade gasoline occurred, followed by a sudden flash. Site technicians attempted to extinguish the ensuing pool fire. The operator activated the internal emergency plan, issued the order to close all motorised valves and called for assistance from petroleum industry partners. At 14.00, emergency responders were still unsuccessful in suffocating the fire with sand. At 15:20 an explosion occurred which was caused by two acetylene cylinders used in the welding operation. Fed by an unknown source, the fire continued to rage for several hours despite firefighting interventions. Eventually, the foot valve on the adjacent gasoline tank was found open by the firefighters. After its closure, the fire receded Intervention efforts were substantial and the toll quite heavy; 15 firemen were burned during the accident: 2 of them were badly hurt, 5 seriously and 8 slightly. Apparently, the firemen suffered burn injuries due to a gust of wind and for the cylinders' explosion. The entry valve of the adjacent tank was left open for an unknown reason.

Important findings
• According to the site director, the piping should have been submerged in water during the onsite works and therefore was omitted from the valve closure checklist and control diagram.

Firefighters encountered myriad difficulties, in particular:
• The fire route to the tank was submerged under a layer of burning hydrocarbons;
• Fire water pipes burst under the weight of vehicles evacuating the zone;
• Lack of information about the source of the fire.

Lessons Learned
• The accident scenario was not included in the site’s risk assessment study. Fires initiated from welding operations are abundant in the literature.  A hazard assessment of tank maintenance operations should examine all possible ignition scenarios (what if?) associated with hot work.
• In order to prevent subsequent fires or explosions to occur, ignition sources, such as the acetylene cylinders should be removed from the area of emergency operation.
• Operators should provide accurate information on location of safety instrumentation to the emergency responders as soon as possible, especially if such devices can contribute to the fire or explosion.

Source: European commission