Six other workers suffered less serious injuries in the blast late Friday, which demolished 50 to 75 percent of the Formosa Plastics Plant and rattled the windows and walls of houses well over a mile away.
``I'm not a war veteran, but that is the loudest explosion I've ever heard in my life,'' said Illiopolis Mayor Allen Brickey, who lives less than two miles from the plant.
Dozens of firefighters Saturday night were still working to put out fires at the plant, about 25 miles east of Springfield. Officials said they didn't expect the fires to be out until Sunday.
Workers were mixing vinyl chloride and vinyl acetate when an explosion occurred, followed by one or two subsequent blasts, Sangamon County Sheriff Neil Williamson said. Eighteen workers were in the plant at the time.
Four injured workers were admitted to Springfield's Memorial Medical Center. Hospital spokesman Ed McDowall said two were in critical condition, one was in serious condition and one was in fair condition. Four others were treated for smoke inhalation at other hospitals.
Sangamon County Coroner Susan Boone identified those killed as Joseph Machalek, 50, Larry Graves, 47, and Linda Hancock, 56, all of Decatur, and Glenn Lyman, 49, of Cornland.
Illiopolis' roughly 1,000 residents were evacuated after the explosion because of hazardous fumes created by burning chemicals. Evacuees were sheltered in malls, stores and hotels. All but about 30 residents were allowed back home by Saturday afternoon.
When vinyl chloride burns it emits hydrochloric acid, said Rich D'Elia, a battalion chief with the Springfield Fire Department who was the incident commander on the scene. He added, however, that preliminary tests indicated the air was safe to breathe.
Plant manager Roe Vadas said the cause of the explosion was unknown. Investigators from the U.S. Chemical Safety and Hazard Investigation Board and the plant's corporate parent, Formosa Plastics Corp. U.S.A., were traveling to the scene.
The plant, with about 135 workers, makes PVC resins that are used in vinyl flooring, traffic cones and carpet backing, said Rob Thibault, a spokesman for the plant's corporate parent.
A 20-mile section of Interstate 72 was closed for about six hours after the explosion, said Patti Thompson, a spokeswoman with the Illinois Emergency Management Agency.
