Abstract: Employees #1 and #2 and a supervisor were cleaning a cupola at the end of their shift. They had drained the hot metal out of the cupola and had shut off the gas heater and air blower before attaching a chain to a pin holding the bottom doors. Employee #2 was waiting outside the building with a water hose to spray the hot material after it dropped out of the cupola. The supervisor stepped behind an interior wall before the material was dropped. Employee #1 hooked the chain to a Bobcat approximately 20 ft from the cupola and pulled the pin on a signal from the supervisor. As soon as the doors opened, there was an explosion. The supervisor and Employee #1 were knocked down by the force of the blast. Employee #1 suffered a sprained back and soot inhalation. Employee #2 was struck by parts blown from the building and sustained burns on his head and face. When this report was filed, no causal factors had been established.