At approximately 2:30 p.m. on March 2, 2011, six workers were employed as milling or planing machine operators at a corn and flour milling facility in Lincoln, NE. A chlorine leak was detected in the chlorine room, so the milling superintendent and a miller/operator entered the chlorine storage room and closed a manual valve on a manifold. The facility was evacuated, and members of the local fire department and a hazmat team responded. The expanding cloud of chlorine gas seeped from the storage area on the east side of the facility. It entered the negative pressure mill and surrounding outside area. Employees working in the immediate area and in the mill were exposed. Employees were also exposed as they were evacuating their work areas. Seven employees were transported to three local hospitals. Six of the employees were treated and released without needing hospitalization. One employee remained hospitalized overnight. One additional employee was treated on the scene by fire department paramedics. Only the seven employees who were transported to the hospitals were mentioned in the narrative. Because some 8,000 lbs. of chlorine were at the facility, the site was subject to process safety management standards. It was later determined that a vacuum regulator in the chlorine process piping system had ruptured.