Photo copyright Williams Olefins

Findings from an internal investigation by Louisiana-based Williams Olefins have shown that the fire and explosion that killed two people and injured 77 others on June 13 were caused by a ruptured reboiler and the vapor cloud it released.

The preliminary report concluded that the explosion at the company's Geismar plant in Louisiana occurred after the vapor escaped the reboiler and caught fire seconds later. So far, the investigation has been unable to identify the source of heat or flame that ignited the vapor cloud, Williams Olefins stated.

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The report also found that there was an unidentified amount of hydrocarbon liquid in the reboiler, which should not have been there. The reboiler, a type of heat exchanger, was in standby mode at the time of the explosion but investigators believe that the extra pressure that the liquid created must have caused the rupture and the subsequent fire. The reboiler had a pressure relief system installed but, at the time, this was isolated from the heat exchanger. Williams Olefins pointed out that the conclusions in the report are not final because tests on metals involved in the explosion are still going on.

Meanwhile, the incident is still being investigated separately by the Occupational Safety and Health Administration (OSHA) and the U.S. Chemical Safety Board.