Explosions that killed five employees at a central Illinois chemical plant in 2004 were caused by a worker mistakenly opening a valve on a high-temperature processing unit, a federal agency said Tuesday.
The U.S. Chemical Safety and Hazard Investigation Board said the plant owner, Formosa Plastics Corporation U.S.A., should have recognized that such an accident could occur because of similar previous incidents.
Formosa spokesman Rob Thibault said the company had already addressed some of the board's concerns and is working on others.
Both Formosa and investigators said the employee who opened the valve apparently was confused about which of the plant's 24 chemical reactors he was supposed to clean. The reactors use 120-degree heat and high pressure for the process of making polyvinyl chloride, or PVC.
The blast also injured seven workers, led to the closure of the plant and forced the temporary evacuation of 150 people who lived nearby.
Formosa agreed in 2005 to pay $300,000 in fines.