The U.S. Chemical Safety Board (CSB) and Hazard Investigation Board has issued its final report on the explosion and fire that destroyed the Formosa Plastics plant in Illiopolis, IL, April 23, 2004, concluding
that the accident occurred when an operator overrode a critical valve safety interlock on a pressurized vessel making polyvinyl chloride.

Vinyl chloride liquid and vapor discharged into the plant, was ignited, and resulted in a massive explosion.
The CSB found that both Formosa and Borden Chemical, the company from which Formosa purchased the plant in 2002, were aware of the possibility of serious consequences of an inadvertent release
of chemicals from an operating PVC reactor. But the investigation determined

that the measures both companies took were insufficient to prevent human error or minimize its consequences.

The accident resulted in the deaths of five workers and serious injuries to three others. About 150 persons in the small community of Illiopolis were evacuated to avoid contact with toxic fumes and smoke. The facility was heavily damaged and has been permanently closed.

In addition to the final report, the CSB released a safety video that detailed key findings and recommendations and con­tained a computerized animation of the likely scenario of events leading to the explosion.

“People do make mistakes,” said CSB Chairman Carolyn W. Merritt. “And that is why it is all the more important for chemical plants to design systems that take into account the possibility of such errors. This accident occurred be­cause the companies involved did not look closely enough at the potential for catastrophic consequences resulting from human error.”

on the upper level of the reactor building was washing out a reactor with a water blaster. He then should have gone to the lower level to open two valves on the re­actor he was cleaning — a reactor bottom valve and the lower drain valve. From survivors’ testimony and physical evi­dence, the CSB concluded that under the most likely scenario, the worker made an error after descending the stairwell to the lower level. He turned to a different clus­ter of reactors and went to a vessel he ev­idently thought was the one he had started cleaning. It was the wrong reactor.

He opened the drain valve. But the re­actor bottom valve would not open. To prevent an accidental release, that valve was fitted with a safety interlock, which prevented it from opening when the reac­tor was pressurized. However, instead of seeking further information on why the bottom valve wouldn’t open, he attached an air hose that provided the pressure needed for the override — a procedure intended for use only in an emergency.

When the valve opened, the highly sprayed onto the floor and vapor filled the area. Vinyl chloride detection alarms sounded in the area. The supervisor and operators attempted to slow the release by relieving the reactor pressure. Just as the supervisor made an attempt to get to the bottom level via an external stairwell, the vinyl chloride vapor exploded.

The CSB concluded that two of the workers who were killed had been work­ing near the top of the reactor, and two others who were killed had been at the bottom level. A fifth operator died two weeks later. The supervisor and two other workers were seriously injured.

The investigation found that operators had time to evacuate the production build­ing after the release began and alarms had sounded. However, operators remained in the area in a vain attempt to mitigate the release.

CSB Lead Investigator Lisa Long said, “The CSB investigation found that systems and procedures put in place by both Borden Chemical and Formosa were insufficient to minimize

human error. In addition, Formosa did not adequately train and drill its employees to immediately evacuate in case of a major release of hazardous chemicals. Such an evacuation would have saved lives.”

The CSB report said additional safe­guards — such as locks or other devices to secure the interlock system — could have prevented critical valves from be­ing opened when the reactor was pres­surized. Investigators also noted the reactors were grouped into similar sets of four, increasing the possibility of hu­man error. Yet there were no gauges, in­dicators or warning lights to inform operators on the lower level of a reac-tor’s operating status. Operators on the lower level, where the valves were, did not carry radios or have intercoms to communicate with the upper level panel operators.

The CSB found that both Borden Chem­ical and Formosa were aware of the poten­tial for the severe consequences of opening the bottom valve on a reactor under pres­sure. A 1992 Borden hazard analysis rec­ommended safeguards that were never adopted. Later, in 1999, another Borden analysis again identified the same potential consequences — a massive release of vinyl chloride — but determined that the existing safety interlock was sufficient to prevent a serious accident.

In 2003, an operator at the Formosa plant in Baton Rouge, Louisiana, opened the bottom valve on the wrong reactor, releasing 8,000 pounds of vinyl chloride into the atmosphere. Some safety im­provements were made in Baton Rouge but the company determined changes were not needed in Illiopolis because the valve controls were different.

In February 2004, an operator at the Illiopolis plant bypassed a bottom valve safety interlock, releasing a significant amount of vinyl chloride.

After that incident, the company de­termined that additional controls were needed on the interlock. However, the company did not act quickly enough. The fatal explosion occurred just two months later.

The Board issued recommendations to Formosa Plastics Corporation USA, the Vinyl Institute, the National Fire Protection Association, the Environ­mental Protection Agency, and the Center for Chemical Process Safety, an organization of the American Institute of Chemical Engineers.

The Board recommended that For­mosa review the design and operation of all their U.S. PVC facilities. The CSB urged Formosa to ensure chemical processes are designed to minimize the consequences of human error, improve control of safety interlocks, more thor­oughly investigate high-risk hazards, and consider all consequences in near-miss investigations. Formosa was also urged to improve emergency planning and con­duct periodic drills, emphasizing prompt evacuations. FSM

The CSB safety video may be viewed at www.CSB.gov.

The Board does not issue citations or fines but does make safety recommenda­tions to plants, industry organizations, la­bor groups, and regulatory agencies such as OSHA and EPA. For more information, go to www.csb.gov.