Abstract: Two employees of an electric power generation plant were clearing a grinder within a slag removal tank unit. After attempts to clear the grinder by mechanical means failed, the unit was shut down, flushed of water, and a porthole was opened for entry to the grinder area. After attempts to reach a stuck metal piece failed, Employee #1 squeezed himself through the porthole up to his waist. At the same time, a water pump that provided flow-by water failed and shut down. The water that was being pushed by the pump through the piping system out to a pond now began backfilling into the slag removal unit. Employee #1, inside the unit, was stuck under water. The other employee, plus another walking by, could not pull the stuck employee free before he drowned.