DuPont engineers fatally misjudged the level of flammable vapor inside a 10,800-gallon tank that then exploded during welding at a New York polymer plant in 2010, the U.S. Chemical Safety Board has concluded.
Welder Richard Folaron, 57, was killed instantly and co-worker William Freeburg was injured at DuPont’s Yerkes Plant in Tonawanda, NY, when the tank exploded in a blast that was felt a mile away.
|Firefighters work the scene of a fatal tank explosion at DuPont’s Yerkes Plant in Tonawanda, NY, in November 2010.|
Authorities were baffled by the explosion. DuPont said the tank had been properly emptied and cleaned and hot work permits secured before a subcontractor was brought in to make repairs.
That sub, Mollenberg-Betz Mechanical Contractors, is a century-old family company with a spotless safety record. Both Folaron and Freeburg, who worked for the company, had many years of experience. The contractor and plant had a longstanding relationship.
Lack of Monitoring Cited
The Safety Board, however, traced the disaster to lapses by DuPont.
The board found that DuPont had monitored the atmosphere above the tank, where Folaron was working, but had not monitored the tank interior.
It was the interior where the flammable vapors accumulated and were eventually ignited by Folaron’s welding, CSB said in a final report and investigation video unanimously approved and released Thursday night (April 19).
The Safety Board is an independent federal agency charged with investigating chemical accidents. It does not issue fines or citations, but it does make safety recommendations.
‘Lives Lost from Hot Work’
CSB noted that the DuPont explosion came just a few months after CSB issued a safety bulletin on the dangers of hot work. The bulletin summarized 11 similar fatal incidents.
“Like the incidents described in the bulletin, this was another example of improperly monitored hot work activities involving flammable conditions inside a container,” the report said.
|The U.S. Chemical Safety Board traces the DuPont accident in a video called “Hot Work: Hidden Hazards.”|
CSB chairperson Rafael Moure-Eraso said, “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.”
Anatomy of an Explosion
The Yerkes chemical plant produces polymers and surface materials. The tank that exploded was one of three used to make a polymer called Tedlar. The three tanks were interconnected by an overflow line, CSB said.
The Tedlar process involves making vinyl fluoride into polyvinyl fluoride (PVF), then transferring that slurry from a reactor through a flash tank and then into storage tanks.
Days before the incident, the process had been shut down for tank maintenance due to corrosion on tank agitator supports, CSB reported. 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.
Later, the contractor was brought in to repair the agitator support atop Tank 1. Although the tank remained locked out from the main process, the overflow line connecting the tanks remained open. Folaron was welding atop the 19-foot-tall tank when it exploded; Freeburg was on the ground.
The Safety Board determined that flammable vinyl fluoride had flowed through the overflow line into Tank 1 and accumulated to explosive concentrations.
Although a facility hot work permit had been issued for the task, “the DuPont personnel who signed it were not sufficiently knowledgeable about the Tedlar chemical process,” the Safety Board said.
DuPont’s process hazard analysis “incorrectly assumed that vinyl fluoride in the Tedlar process could not reach flammable levels in the slurry tanks,” said CSB Team Lead Johnnie Banks.
“And, critically, DuPont personnel did not properly isolate and lock out Tank 1 from Tanks 2 and 3 prior to authorizing the hot work. The flammable vapor was able to pass through the overflow line into the tank the welder was working on, unknown to him or to the operators who signed off the hot work permit.”
The CSB also said DuPont should have included the three tanks as part of the Tedlar process covered by OSHA Process Safety Management rules. Yet, on the day of the accident, a compressor failure led to higher concentrations of vinyl fluoride vapor in the polyvinyl fluoride slurry.
|DuPont engineers decided that the tanks could be safely operated with a split pipe, but the Safety Board said the break “provided a potential pathway for flammable VF gas to enter the tanks.”|
Furthermore, the Safety Board found, a U-shaped seal loop on the flash tank overflow line had a “fishmouth” split in the pipe that could emit vinyl fluoride vapor. Engineers decided that operating with the broken seal loop presented no hazards, but the CSB found that the split “provided a potential pathway for flammable VF gas to enter the tanks.”
The report found no wrongdoing on the part of Mollenberg-Betz, but it had several recommendations for DuPont. The board urged the company to:
• Require that all DuPont facilities regularly audit their plant hot work permitting processes. The audit should include identification and mitigation of explosion hazards from hot work.
• Require that all process or vent piping, or similar connections, be positively isolated before beginning hot work.
• Require that tank interiors be monitored for flammable vapor before and during hot work.
Finally, the board noted that the Occupational Safety and Health Administration’s hot work standard does not require gas monitoring inside containers intended for hot work “even though it is recommended by industry safe practice guidelines.”
In a statement issued Friday (April 20), DuPont Yerkes Plant Manager Ronald A. Lee called safety “a core value at DuPont” and said, “[I]t’s our objective to ensure that an incident like the one that took the life of Richard Folaron never happens again.”
Lee said the company had “conducted an exhaustive investigation” into the incident and had “cooperated fully” with the CSB inquiry.
“Many of the agency’s recommendations are closely aligned with the results of our own investigation and have been implemented,” Lee said. “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.”
In May 2011, OSHA cited both DuPont and Mollenberg-Betz in the blast.
DuPont was issued nine violations and fined $61,500. As of Friday, that had been reduced to six violations and a $49,000 fine, but the case remains open.
In March 2011, the plant was cited for one serious violation related to methylene chloride and one other-than-serious violation and fined $5,000. The current fine is $3,750, but the case remains open.
In June 2011, the plant was cited for one serious violation and fined $4,000, but the case was settled for $3,300, OSHA records show.
In addition, OSHA cited Mollenberg-Betz for eight violations and proposed $55,440 in fines. The company is contesting the case.