Abstract: At approximately 5:00 p.m. on October 29, 1991, the cast house day crew used the #10 pendulum crane to suspend a rotor over the #5 casting furnace sniff box for pre-heating before insertion into the sniff box. At 5:00 p.m., the relief crew. including Employees #1, #5, and #7, completed a drop in DC #1. While Employees #1 and #5 took a break, Employee #7 made a drop in DC #2. When Employees #1 and #5 returned, Employee #5 attempted to move the #10 pendulum crane from the east end of the furnace to the west end to pull logs at DC #1. The crane alarms were used. When the crane moved west 18 in., the rotor snagged sniff box #5's overhead gas lines, causing several pipes, including a chlorine gas line, to rupture. The employees were overexposed to chlorine gas in a number of situations: attempting to repair the damage without donning SCBA; removing the SCBA when they thought they were in clear air; bringing extra SCBA into the contaminated zone; continuing the job in the contaminated area because it was critical; or being unaware of the chlorine gas cloud. Employee #1 escaped through the west exit ramp when he smelled the chlorine gas, but returned through the same route with a boxed SCBA for Employee #3, the mechanic. Employee #1 held his breath as he approached #5CF. When he was out of air, he inhaled on the east side of #5CF, but the air flow was west to east and he was in a gas cloud. Employee #1 was hospitalized. Not wearing SCBA or any type of respirator, Employee #2 , the foreman, attempted to disconnect the gas hoses to the damaged rotor air base of #5CF, but suffered overexposure before he could complete the task. Employee #3, a mechanic, was called to the scene. His SCBA ran out while he was on top of #5CF so he went to the east side of the operations floor near an opened SCBA box. Employee #3 lifted the mask, but suffered overexposure. Employee #7 continued to monitor the drop in DC #2 by filling his lungs at the south door and running to the furnace area while holding his breath. Employee #7 made four to five trips before Employee #4, who was wearing SCBA, arrived to watch. Completing the job was critical because of an explosion hazard. Employee #6 was working east of the cast house, which is an area within a larger building, and saw the commotion. She did not stop her task until escaping employees told her to leave. No chlorine monitoring equipment or alarm system was available.