At approximately 9:30 p.m. on June 30, 1993, Employee #1, a cleaning contractor, was cleaning up the “cut floor” at a beef facility in Council Bluffs, IA. The facility maintenance employees were removing an ammonia valve from the refrigerant line in the ceiling and had NOT locked or tagged out the isolation valves on the roof. The valve on the cut floor was removed and taken to the maintenance shop for alteration. The foreman gave workers their evening assignments, then went to the roof and OPENED the isolation valves, sending liquid ammonia through the lines and onto the cut floor.