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CSB Announces Findings into DuPont Fatal Accident

Graham Marshall - Monday, May 07, 2012

The U.S. Chemical Safety Board (CSB) has determined that an explosion at a DuPont facility in the USA that killed one contract welder and injured his Foreman in 2010, was caused by the ignition of flammable vinyl fluoride inside a large process tank, a hazard which had been overlooked.

The accident occurred at the DuPont chemical plant in Tonawanda. 

The facility produces polymers and surface materials for countertops.

The process for making the polymers involves transferring polyvinyl fluoride (PVF) slurry from a reactor through a flash tank and then into three storage tanks.  The tanks were also inter-connected by an overflow line. 

Days before the incident the process had been shut down for tank maintenance.
 
The tank fill lines were correctly locked out for safety.

Tanks 2 and 3 were repaired and the process restarted, but work on tank 1 was delayed due to a lack of parts.

Although tank 1 remained locked out from the main process, the overflow line remained open which connected tank 1 to tanks 2 and 3.

The CSB found DuPont erroneously had determined that any vinyl fluoride vapor that might enter the tanks would remain below flammable limits.

The CSB determined that flammable vinyl fluoride flowed through the overflow line into tank 1 and accumulated to explosive concentrations.

Although DuPont personnel monitored the atmosphere above the tank prior to authorizing hot work to restart once parts became available, 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.

The welder died instantly from blunt force trauma, and the foreman received first-degree burns and minor injuries.

CSB Team Lead Johnnie Banks said, “Our investigation found that DuPont’s process hazard analysis incorrectly assumed that vinyl fluoride in the process could not reach flammable levels in the slurry tanks.  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.”

Noting the CSB issued a safety bulletin on the dangers of hot work in March 2010, 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.  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.”

This is the 2nd fatal accident involving DuPont locations in the USA recorded in 2010.

 

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