CSB Issues New Incident Reports, Final Findings on PEMEX, Dow Chemical Releases

The U.S. Chemical Safety and Hazard Investigation Board released a new volume of incident reports and two final investigation findings covering fatal and high-consequence chemical releases in Texas and Louisiana.

The agency, based in Washington, D.C., said Volume 4 of its Incident Reports summarizes 13 serious chemical incidents in California, Indiana, Louisiana, Tennessee, Texas, Utah and Virginia. According to the CSB, the events resulted in two fatalities, 10 serious injuries and more than $1 billion in property damage. The reports are based on information submitted under the agency’s Accidental Release Reporting Rule.

Among the incidents highlighted are two 2025 events involving workers opening the wrong equipment during maintenance. At a refinery in Martinez, California, contract workers inadvertently opened a pipe flange on an active system during turnaround preparations, releasing and igniting flammable hydrocarbons and causing an estimated $924 million in damage, according to the CSB. In Freeport, Texas, a maintenance worker disassembled a rupture disc holder in an active chlorine system, releasing about 8,000 pounds of chlorine, causing one serious injury and triggering a shelter-in-place order. The CSB said the piping had been incorrectly isolated and tagged.

According to the CSB, the four volumes of Incident Reports issued to date cover 81 serious incidents in 31 states involving 16 fatalities, 75 serious injuries and more than $4.5 billion in property damage.

Last month, the agency also released its final report on the Oct. 10, 2024, hydrogen sulfide release at the PEMEX Deer Park Refinery in Deer Park, Texas. Two contract workers died and 13 others were transported to medical facilities after more than 27,000 pounds of hydrogen sulfide were released during maintenance in the refinery’s amine unit, said the CSB.

According to the report, workers from Repcon Inc. mistakenly opened a flange on piping containing pressurized hydrogen sulfide, rather than a nearby section that had been cleared. The release continued for nearly an hour before emergency responders stopped it. 

The CSB concluded the incident resulted from a failure to positively identify the correct equipment before opening the piping. Contributing factors included gaps in work permitting, hazard assessments in an active unit and deviations from established procedures. The agency issued recommendations to the refinery and to the American Society of Mechanical Engineers to develop guidance for marking equipment prior to opening.

In a separate final report, the CSB detailed the July 14, 2023, explosions and ethylene oxide release at Dow Chemical Company’s Louisiana Operations Glycol II plant in Plaquemine. According to the agency, more than 31,000 pounds of ethylene oxide were released after a reflux drum catastrophically failed, prompting a shelter-in-place order affecting hundreds of residents.

The CSB determined the incident began when ethylene oxide entered pressure relief piping that contained air and ignited. Metal debris from portable work lights left inside a reflux drum during prior maintenance punctured a rupture disc, allowing the material to enter the piping. The agency also cited inadequate vessel closure practices, failure to maintain an inert atmosphere in pressure relief piping and pressure relief system design that allowed flame propagation into the drum.

As a result, the CSB issued recommendations to Dow and to standards organizations, including the National Fire Protection Association and the American Society of Safety Professionals, aimed at improving vessel closure verification, inerting controls and confined space guidance.