-- Federal investigators found dozens of safety violations, from defective equipment to poor worker training, at a plastics factory where an explosion killed five people in April.

The Occupational Safety and Health Administration on Friday imposed $361,500 in fines against Formosa Plastics Corp. The investigation did not reach any conclusions about the cause of the explosion.

Formosa spokesman Rob Thibault said the New Jersey-based company plans to challenge OSHA's findings.

"We believe that we operated the plant safely and in accordance with the industry's best practices," Thibault said, noting it had qualified for certification by the highly regarded International Organization for Standardization.

OSHA said it found three "willful" violations at the plant: failing to maintain fire protection equipment, inadequate inspections of equipment used to process dangerous chemicals, and failure to repair equipment involved with dangerous chemicals.

The agency said it found 45 other serious violations. They include hazards related to flammable liquids and ignition sources, insufficient worker training, and a poorly trained and equipped fire brigade.

The plant, about 25 miles east of Springfield, manufactures polyvinyl chloride used in PVC pipe and other materials for construction, medical supplies and automotive parts. It employed 136 people at the time of the explosion, but the factory has shut down, and more than 40 percent of the employees have been laid off.