A 6:30 pm., a reaction vessel explosion and fire injured four people at a detergent alkylate plant. The chemical (alkyl benzene) was manufactured by mixing powdered aluminum chloride (the catalyst) with liquid hydrocarbons, chlorinated hydrocarbons, and benzene. About 3 months prior to the incident, the facility changed its process technology : aluminium chloride was substituted by powdered aluminium that should combine with hydrogen chloride to form the necessary aluminium chloride. Shortly after the plant switched to the new process, the reactor became fouled with a sludge-like catalyst residue.

When the process was shut down for maintenance, the operators were unable to empty the liquid that remained in the reactor. Sludge had settled in the vessel, plugging the bottom outlet nozzle. Unsuccessful attempts were made to clear the nozzle (by injecting high-pressure nitrogen, flushing with oil…). A sample of the remaining sludge was extracted and given to a plant chemist, who was asked for advice on dissolving the remaining sludge.

Although reactivity testing showed the reaction of the sludge with water yielding a white gas (hydrochloric acid) and generating heat, the chemist advised using water to clear the sludge, with a 1:8 ratio in order to absorb the heat generated.

Due to poor communication between process supervisor and day-shift supervisor, and between day- and night-shifts supervisors, the night shift supervisor instructed an operator to add continuous steam to the reactor (instead of a short injection). The reactor vessel exploded minutes after the operator started to inject the steam.

There were no fatalities, but 2 employees and one contractor received first- and second-degree burns (the wear of fire-resistant work clothing provided protection) and Another contractor injured his back when he fell. Property damage was estimated at $13 million.

The US CSB investigated the case and emphasized the importance of systematically managing changes. The changes in catalysts should have been studied and would have showed that the higher density material overtaxed the mixing capability of the agitator and allowed aluminium to settle and accumulate in the bottom of the reactor. The plan devised by the chemist and the engineer for dissolving the sludge also posed hazards and would have required precise execution. Furthermore, the temperature-sensing device did not accurately indicate the process temperature because it was located in a stagnant pipeline between the reactor and another vessel. The chemist and the engineer relied on misleading temperature indications when they noted the stabilization of the reactor temperature before leaving for the day. Finally, the absence of written instructions increased the likelihood of miscommunication between the two shift supervisors, which led to the unsafe application of steam in the reactor vessel.