"Damage at the plant was not as extensive as we originally thought," said Rob Thibault, manager of corporate communications for Formosa. "It's our intention to continue operating the plant after we get it restored."

An explosion ripped through the facility about 10:40 p.m. Friday. The cause of the explosion had not been determined Sunday.

Four Formosa employees were killed in the explosion, and three other employees remained hospitalized Sunday. A total of 18 employees were at work at the time of the blast.

Randy Hancock and Bradford Bradshaw, both of Decatur, were in critical condition at Memorial Medical Center, and Chris Havener of Decatur was in serious condition. Dan Lyons of Riverton was discharged Sunday from Memorial.

The employees killed in the explosion were identified Saturday by the Sangamon County coroner's office as: Joseph Machalek, 50, Larry Graves, 47, and Linda Hancock, 56, all of Decatur, and Glenn Lyman, 49, of Cornland.

Randy and Linda Hancock were husband and wife.

"A lot of the people injured and killed were our dear friends," said Roe Vadas, the plant manager. "It is a very emotional event for all of us."

Thibault said Sunday the main fire had been extinguished, but there was an area that was still smoldering. A specialized contractor is being brought in to demolish part of the warehouse so they would have better access to smoldering materials.

"The town air is safe, and the drinking water is safe," Thibault said. "We have captured virtually all the runoff from the fire."

The Sangamon County Sheriff's Office announced that its mobile command center was leaving the area about 3 p.m. Sunday, but deputies would remain in the area to keep roads near the plant blocked off.

"We will remain here as long as they need us," said Sgt. Joe Rath.

About the same time, the Springfield Fire Department, which had provided both manpower and hazardous materials equipment, was preparing to leave Illiopolis.

On Saturday, officials said air quality tests of a nearby residential area known as Kelsan Heights indicated that the air was safe, and residents of the neighborhood were allowed to return home.

Sunday evening, officials reduced the 1-mile evacuation radius to a half-mile, which allowed other people to return home.

Allen Brickey Jr., president of the Illiopolis Board of Trustees, said about a dozen houses that are in the half-mile radius. He added that so far, the residents of Illiopolis are handling things well.

"I've been extremely pleased with their calmness," Brickey said.

Officials with the American Red Cross said they helped find lodging for about 19 people Friday evening. They have volunteers in Illiopolis who have been supporting the rescue personnel, and mental health counselors are available to meet with family members of the plant employees.

"We have been doing mass feedings for the emergency personnel. We will continue to do that until the disaster is over," said Val Friedrich, director of community relations for the Illinois Capital Area Chapter of the American Red Cross.

Thibault said a phone line has been set up so people may call if they have any questions. People can call 486-6500 between 8 a.m. and 4 p.m. After hours, people can call the command center in Illiopolis at 486-7691.

The employees of the plant will continue to be paid and receive benefits while the plant is idle, Thibault said.

The U.S. Chemical Safety and Hazard Investigation Board is investigating the cause of the explosion. Officials from the agency said the investigation could take up to a year and will continue until they understand what happened and how to prevent it from happening again.

Carolyn Merritt, chairman of the chemical safety board, said investigators initially may be at the site for a week or more, interviewing workers, eyewitnesses and emergency responders. They will also collect forensic evidence and review the company's records, procedures and safety history.

"As we develop preliminary findings in the case, we will provide that information to the affected community. At the end of our investigation, the full board will come to the area to present its final report."

Merritt said the Illiopolis event is "among the most serious that the board has investigated in more than six years."

John Reynolds can be reached at 788-1524 or john.reynolds@sj-r.com.