Trygve Skjold

Investigation of an explosion in a gasoline purification plant

An explosion in an atmospheric storage tank initiated additional tank explosions and a pool fire at a tank facility in Norway. The tank farm had been operated as a purification plant for a petroleum product called coker gasoline. The process entailed extraction of malodorous sulfur containing components, in particular thiols (mercaptans). After several tanker loads of coker gasoline had been treated with a solution of sodium hydroxide and water, the efficiency of the sweetening process declined as precipitated waste accumulated in the tanks and the alkaline solution became increasingly saturated with impurities. The approach adopted for handling the accumulated waste included the addition of hydrochloric acid to neutralize the spent caustic. The explosion occurred when about 80% of the scheduled amount of acid had been added to the solution in the tank. There were no fatalities in the accident, but at least two people received medical treatment for injuries sustained during the course of events. The investigation concluded that the accident was caused by a chemical explosion in the tank. Several factors point toward thiols as the predominant constituents in the fuel–air mixture, but vapors from other volatile substances may also have played a decisive role. The ignition source was most likely a hot surface, resulting from adsorption of volatile organic compounds on activated carbon in the air filter and subsequent self‐heating and glowing combustion in the carbon bed. The article summarizes the main results from the accident investigation and lists various measures that can be taken to prevent similar accidents in the future.