Abstract: On June 27, 1991, a reactor vessel cracked, allowing nitrobenzene and paraminophenol to mix with coolant water. The contaminated water was atomized in a cooling tower, releasing nitrobenzene into the air. Nitrobenzene odors were detected off site and emergency services such as the Falls Fire Department and the Raleigh Hazardous Materials Team responded. Mallinckrodt was not aware of the air release until the Falls Fire Department arrived on the scene. The source of the release was identified as being the cooling tower for the #205 Pap plant. When the cooling tower was shut down, liquid in the system flowed into the tower and overflowed a sump. About 200 gallons of fluid, contaminated with 2,000 ppm of nitrobenzene, was spilled into a ditch. A total of about 130 pounds of nitrobenzene was released. Employees of Mallinckrodt and Reno Eddins Contracting Company engaged in emergency response and cleanup operations on the plant site. No employees of any employer involved in the incident were made ill or injured. There were no injuries or illnesses in the surrounding community.