CSB determined the explosion was caused by the ignition of flammable vinyl fluoride inside a large process tank, a hazard that was overlooked by DuPont engineers. The CSB found that that sparks or heat from the welding, which took place on top of the tank, most likely ignited the vapor. A proposed recommendation urges DuPont to require monitoring the inside of storage tanks before performing any hot work, which is defined as welding, cutting, grinding or other spark-producing activities.
“Safety is a core value at DuPont. It is based on our commitment to the idea that all accidents are preventable,” said Ronald A. Lee, plant manager at DuPont Yerkes. “So, it's our objective to ensure that an incident like the one that took the life of Richard Folaron never happens again.”
He said DuPont conducted an exhaustive investigation of the Nov. 9, 2010 incident and cooperated fully with the Chemical Safety Board throughout its investigation. “Many of the agency's recommendations are closely aligned with the results of our own investigation and have been implemented. Overall, the Yerkes site has made numerous improvements in the past 18 months and has – to date – worked almost 500 consecutive days without an event-related injury,” Lee added.
A CSB 11-minute safety video titled, "Hot Work: Hidden Hazards," utilizing computer animation to depict the sequence of events leading to the tragedy, is available on CSB’s Web site.
“I find it tragic that we continue to see lives lost from hot work accidents, which occur all too frequently despite long-known procedures that can prevent them,” said CSB Chairperson Rafael Moure-Eraso, noting CSB issued a safety bulletin on the dangers of hot work in March 2010. “Facility managers have an obligation to assure the absence of a flammable atmosphere in areas where hot work is to take place. Explosion hazards can be eliminated by testing inside tanks as well as in the areas around them.”
The Explosion
The accident occurred at the DuPont chemical plant in Tonawanda, a suburb of Buffalo, which employs approximately 600 workers. The facility produces polymers and surface materials for countertops, sold under the trade names Tedlar and Corian. The process for making Tedlar involves transferring polyvinyl fluoride (PVF) slurry from a reactor through a flash tank and then into storage tanks. The tanks were also inter-connected by an overflow line. The CSB found the company erroneously had determined that any vinyl fluoride vapor that might enter the tanks would remain below flammable limits.
Days before the incident, the process had been shut down for tank maintenance due to corrosion on tank agitator supports. The fill lines were locked out for safety. Tanks 2 and 3 were repaired and the process restarted, but work on tank 1 was delayed because the necessary parts were not available. Finally, a contract welder and foreman were engaged to repair the agitator support on top of tank 1. Although tank 1 remained locked out from the main process, the overflow line that connected tank 1 to tanks 2 and 3 remained open.
CSB determined that flammable vinyl fluoride flowed through the overflow line into tank 1 and accumulated to explosive concentrations. Investigators found that while a facility hot work permit was issued for the task, the DuPont personnel who signed it were not sufficiently knowledgeable about the Tedlar chemical process.
Although DuPont personnel monitored the atmosphere above the tank prior to authorizing hot work, no monitoring was done inside the tank to see if any flammable vapor existed there. The CSB investigation found the hot work ignited the vapor as a result of the increased temperature of the metal tank, sparks falling into the tank or vapor wafting from the tank into the hot work area.
The explosion blew most of the top off the tank, leaving it and the agitator assembly hanging over the edge. The welder died instantly from blunt force trauma, and the foreman received first-degree burns and minor injuries.
CSB voted on several proposed recommendationsto DuPont. These include enforcing safety procedures for hot work permits and ensuring explosion hazards associated with hot work activity are recognized and mitigated; revising corporate procedures to require all process piping and vent piping be positively isolated before authorizing any hot work, and to require air monitoring for flammable vapor inside tanks and other containers where hot work is to be performed.