Deficiencies in Williams’ safety management led to the explosion at its Geismar, Louisiana, olefins plant on Jun. 13, 2013, which killed two employees and injured 167 others, the US Chemical Safety Board (CSB) has concluded in its final report on the incident. The report comes a month after Williams Partners announced it was seeking to sell its majority 88.5% stake in the plant as it focuses instead on expanding its natural gas business.

The CSB said its investigation revealed a poor process safety culture at the plant, which resulted in a number of process safety management program weaknesses. The company failed to manage or review significant changes, including two that introduced new hazards to the reboiler. These involved the installation of block valves that in this case isolated the reboiler from its protective pressure relief device and the administrative controls that control the position of the valves.

According to the board, Williams also failed to effectively complete a key hazard analysis and develop operational procedures that could have addressed the overpressure in the reboiler, which caused it to rupture and touch off the explosion.

Vanessa Allen Sutherland, CSB’s chairperson, said the accident was preventable and unacceptable, and the report provided important safety lessons that other companies should review and incorporate within their own facilities. She commented: “Most of the accidents the CSB investigates could have been prevented, had process safety culture been a top priority at the facility where the incident occurred. These changes must be encouraged from the top with managers implementing effective process safety management programs.”

Since the incident, Williams has made efforts to improve its process safety management at Geismar, including redesigning the reboilers to prevent isolation from their pressure relief valves, as well as becoming more collaborative in its management of change process and updating its process hazard analysis procedure. However, investigator Lauren Grim said the company should do more to improve and strengthen process safety and culture at the Louisiana facility.

The CSB has recommended that Williams strengthen its existing safety management systems and adopt additional safety programs, to include conducting safety culture assessments, developing a robust safety indicators tracking program and performing detailed process safety program assessments. The board also issued recommendations to the American Petroleum Institute (API), saying it had had identified gaps in API’s industry standard and has advised the institute to strengthen its requirements on “Pressure-relieving and Depressuring Systems” to prevent future similar incidents.

Williams finally restarted its expanded olefins plant in February 2015.