(32bo) Steam Explosion: The Case for Process Safety in Molten Metal Processes

A catastrophic steam explosion occurred after an unexpected power loss at an aluminum billet casting facility. An employee was monitoring the flow of molten aluminum into a traveling casting system during the continuous casting of aluminum billets. A power outage occurred during the casting operation, which caused a loss of electronic controls and monitoring. Fail safe cooling water systems activated, and the operator initiated manual actions to stop the feed of molten metal to the casting system and to dump residual molten metal. The molten metal dump introduced molten aluminum into a water-filled drain pan. The resulting steam explosion destroyed the facility and caused serious injuries to nearby workers.

This manuscript will provide background and technical analysis of molten metal steam explosions to educate the reader on the hazards. This case study will discuss root cause analysis of the explosion and contrast the causes against risk-based process safety elements. One underlying root cause of the explosion was the inadequate management of change of systems and process equipment over several years. These changes included modifications to cooling water and molten metal containment systems to address the accumulation and clearing of fugitive metal over time, which compromised the barrier designed to prevent water from entering the drain pan. They also included fundamental changes to the control and monitoring systems’ hardware, logic, backup power, orientation, and location in the casting area. The manuscript will also analyze the human factors aspects that led to the operators’ decisions to dump molten metal: hazard complacency, understanding and response to alarms, and separation of people from hazards. We will conclude with lessons learned and suggestions for evaluating hazards, improving personnel’s awareness of hazards, and managing changes to unique process systems.