A three-member team from the Chemical Safety & Hazard Investigation Board (CSB) will investigate an explosion and fire that killed two workers at a Pennsylvania zinc-refining facility on July 22. That accident occurred as zinc was being purified and separated from other metals in a high-temperature distillation process at Horsehead Holding Co., in Monaca, Pa., 35 miles north of Pittsburgh. At this time, CSB has not determined the source of the explosion and fire that killed the workers, who died from smoke inhalation, but so far interest has focused on a loss of containment that allowed zinc to enter the distillation column’s combustion chamber or combustion gases to enter the distillation column, either of which could have led to a fire. The technology used in the Pennsylvania plant goes back to the 1940s and ’50s, according to CSB investigators, who have found references to two similar accidents that occurred in Europe, killing 11 workers. CSB’s root-cause investigation will examine industry-wide zinc purification technologies as well as possible process alternatives for Horsehead.