Abstract: An electric utility employee was cleaning ash out of a boiler. He was on a regularly scheduled job rotation from another plant where he conducted similar work. The operation involved sucking the ash out of the bottom of the boiler through a hopper box with a water pressure line (sluice line) below, creating a venturi vacuum effect. The hopper had two relief points. The first one was an open vent from the hopper to the boiler, but this vent had been plugged for over a month. The other was a relief valve that was inoperable because its sensor had been turned off somehow. Apparently, the discharge valve in the sluice line was not completely open (or the line was plugged) when the flow valve was opened, and water pressure from the sluice line backed up. This pressurized the hopper, and the door (the weakest link) blew off, hitting the employee in the head and chest area and throwing him about a meter or two. He died of injuries sustained in the accident.