A seemingly simple maintenance error resulted in the deaths of two workers, injuries to 30 others, and $40 million in property damage at a Texas chemical manufacturer, according to an investigation and report by the US Chemical Safety and Hazard Investigation Board (CSB).
The accident took place in July 2021 at the LyondellBasell Industries complex in La Porte, near Houston, in the acetic acid production unit. The facility is the third-largest acetic acid producer in the US. The CSB’s report found that the inadvertent removal of pressure-retaining components of a valve caused the release of nearly 75,000 kg of an acetic acid mixture. The incident killed two contract workers, severely injured a third, and sent some 29 others to hospital.
“Even a simple task can turn deadly if it is not performed properly,” CSB Chairperson Steve Owens says in a press release. The incident involved a common plug-valve system, and CSB found similar serious incidents in which these valves were taken apart when removing connected equipment.
The CSB report urged improvements in signage and worker training and even a manufacturer design change to avoid such accidents in the future. The CSB is an independent federal body that investigates the cause of chemically related accidents; its final report for LyondellBasell was released May 25.
The incident began when a small leak was found upstream from the acetic acid reactor. The company shut down the reactor to fix the leak and perform other maintenance. During the maintenance process, contract workers attempted to disassemble the plug valve, and they partially removed pressure-retaining bolt nuts and a valve cover.
They then pried a stuck coupler from the plug valve, which inadvertently removed the valve cover and plug, releasing a pressurized mixture of acetic acid and other chemicals at a temperature of 115 °C. Three workers were badly burned and inhaled the chemical mixture; two died.
CSB found four other serious accidents in North America since the 1970s involving plug valves and pressure-retaining systems. The incidents, which led to seven deaths, were caused by a combination of human error and insufficient training. The board recommended approaches such as coloring pressure-retaining bolts in red or adding written instructions to the physical system. A more thorough approach would involve redesigning the pressure-retaining and plug-valve system to make disassembly safer.
The CSB notes that, after the incident, LyondellBasell installed tamper-resistant mechanisms and tags on the valve cover fasteners of plug valves to help prevent the inadvertent removal of pressure-retaining components while the valves are in service. LyondellBasell officials did not respond to requests for comment.