Abstract: On August 12, 1993, Employees #1 through #5 at the Penzoil refinery were attempting to remove a thick layer of crust from inside the potassium hydroxide treater. The employees attempted to melt the crust with hot water from the bottom of vessel, instead of from the top as had been done before. The hot water converted to steam in the void space under the crust and created enough pressure to blow the crust out of the top of the vessel. The caustic material blew into the air and rained down onto the employees and equipment. Employees #1 through #5 suffered first- and second-degree burns. Two of the five employees were kept overnight in the hospital for observation, and the other three were released after several hours.