(57b) Horsehead Corporation Zinc Explosion

A fatal explosion occurred on July 22^nd, 2010 at the Horsehead Corporation Zinc Refinery in Monaca, Pennsylvania. The accident resulted in the deaths of two workers and serious injury to a third. The United States Chemical Safety Board conducted a thorough investigation to determine the cause of the disaster and provide recommendations on how to prevent future accidents. From the investigation, it was determined that a cadmium distillation column, a process unit used to separate cadmium and other relatively low boiling impurities, exploded. It was determined that the sump, the structure through which the bottom product drained, became clogged; this resulted in liquid zinc flooding the distillation unit. The large accumulation of liquid led to the development of pressures and temperatures above the unit’s design specifications and ultimately the failure of the system. Though this was the physical initiating event of the actual accident process, many other factors played a role in causing the accident.

The design itself used for the distillation column, specifically the sump, had specifications that were determined to be hazardous in prior investigations across the globe. The company failed to address issues with the design even though multiple nonfatal explosions had occurred at the same facility in the years prior to the disaster. The facility considered such accidents as normal and never addressed the problem. If proper safety protocol had been followed and these near misses investigated, the 2010 explosion may have never occurred. The Horsehead facility also did not follow proper management of change (MOC) protocol in the construction of the cadmium distillation column, and it did not educate employees on how to identify and evaluate hazards while operating the process. All these factors led to the eventual explosion on July 22^nd, 2010.