Errors in process management and equipment led to a 2013 fatal explosion at the Williams Olefins plant in Geismar, La., an investigation by the U.S. Chemical Safety &Hazards Investigation Board (CSB) recently concluded.
Two workers died and 167 other workers reported injuries after hydrocarbons leaked from a plant operation, formed a vapor cloud, and ignited.
The facility produces ethylene and propylene that are used by the petrochemical industry, said CSB Chair Vanessa Allen Sutherland, who unveiled the board’s conclusions earlier this month in Louisiana.
A “reboiler”—a heat exchanger that supplies heat to a distillation column—catastrophically ruptured and caused the accident, CSB said in its report on the incident. The reboiler that failed was one of two in the system that provided heat to the propylene fractionator—a distillation column that separates propylene and propane.
The second reboiler was a backup and had been off-line for 16 months. Plant officials assumed the backup reboiler was clean and available for use. When the operating reboiler appeared to have fouled, plant operators began to shift operations to the idle reboiler.
The plant operators did not know that the standby reboiler contained hydrocarbons and its pressure relief system was not in proper order, CSB found.
As the reboiler’s heat increased, the confined liquid hydrocarbons expanded, resulting in a quick and dramatic pressure rise within the vessel. The shell ruptured, causing a release, an expanding vapor explosion, and a fire.
A series of process safety management program deficiencies over the 12 years before the accident allowed the reboiler to be unprotected from overpressure problems, according to CSB.
After the incident, Williams Olefins redesigned the reboilers, improved its management-of-change process to be more collaborative, and updated its process hazard analysis procedures, CSB said. Further improvements are needed, the agency added.