Abstract: On November 26, 2000, a four-member crew was cleaning out a vessel called a Lump Breaker. The Lump Breaker, located on the DAP-2 side of the fertilizer plant, is an enclosed space that has two access doors, one at the top of the space, and one at the bottom. The cleaning process requires two men to enter the chamber to remove lumps of material that have created a blockage to the flow of material through the chamber. Air hammers are used to loosen the material. Two men work out side of the chamber as attendants. The lumps of material are removed and discharged through an access door in the bottom. The floor opening is created by removing a 15-inch by 40-inch section of the metal floor. At the time of the accident, the employees had completed the cleaning process. As one employee exited the bottom door in the Lump Breaker, he closed the door and stepped back. He then fell through the opening in the floor of the supporting platform. The employee died from a concussion.