The lack of a tank emergency pressure valve resulted in the death of one worker and the evacuation of 26 residents and a "shelter in place" warning for 1,500 others living near the D. D. Williamson & Co. chemical plant in Louisville. The Chemical Safety & Hazard Investigation Board, which is responsible for finding the causes of chemical accidents, presented this conclusion in a report released on March 12. An explosion occurred last April just after 2:00 AM, when an eight-foot-tall food-additive processing tank exploded, blowing its top 100 yards away. The tank shell struck an ammonia tank, releasing some 26,000 lb of ammonia gas in a water solution over five hours. The accident was clearly avoidable, the board investigators determined, and probably occurred when operators tried to open an air vent to release excess pressure. The vent was not sized for the tank, which had also been damaged in previous accidents, noted the board. More information is available at http://www.csb.gov.