Federal investigators: Forgotten work lights and failed inerting led to Dow Plaquemine blasts

PLAQUEMINE, La. — The first sign that something was wrong, Toni Smith recalled, was not the roar of an explosion but the way her mobile home suddenly jolted.

“I was sitting in the house watching TV, and the next thing I know, my whole trailer shakes,” she said. “First thing I said was, ‘Something happened at Dow.’”

When she stepped outside her trailer park a block from the Dow Louisiana Operations complex on the night of July 14, 2023, she saw a towering fireball and a cloud of flame rising over the plant in Plaquemine, just south of Baton Rouge. Parish officials ordered residents within a half-mile to shelter indoors, turn off their air conditioning and wait.

Nearly three years later, a federal investigation has concluded that the explosions that lit up the Mississippi River petrochemical corridor — and unleashed more than 31,000 pounds of a cancer-causing gas — began with something nobody outside the plant could see: work lights left inside a steel vessel and nitrogen that quietly leaked away over years.

In a final report released Feb. 26, the U.S. Chemical Safety and Hazard Investigation Board said the disaster at Dow’s ethylene oxide unit “should never have happened,” finding that a string of preventable failures in maintenance, monitoring and equipment design allowed a routine restart to escalate into a series of explosions.

The board’s 87-page report describes how metal debris from the forgotten lights punctured a rupture disc, how a supposedly inert line had slowly filled with air, and how a relief system routed burning gas straight into a vessel filled with ethylene oxide, known as EtO — a highly flammable, reactive chemical that federal regulators classify as a human carcinogen.

No deaths or injuries were reported among workers or nearby residents. But the Chemical Safety Board, or CSB, estimated $43 million in property damage and said Dow’s complex released a total of 31,525 pounds of EtO during the incident and subsequent cleanup and de-inventory.

“It is fortunate that no one was killed or seriously injured,” CSB Chair Steve Owens said in a statement. “But this catastrophic incident should never have happened.”

A chain of failures

The explosions began in the Glycol II ethylene oxide finishing unit, one of 23 production units at Dow’s sprawling Louisiana Operations facility, which employs more than 1,200 Dow workers and about 1,400 contractors.

During a planned turnaround in May and June 2023, workers entered a large reflux drum in that unit as a confined space to perform inspection and maintenance. They brought in portable explosion-proof work lights to illuminate the dark interior. When the job was done and the vessel was closed for startup, some of those lights remained inside.

The board found Dow relied on a “vessel closure” form for the reflux drum, but concluded the procedure did not clearly require a count of tools and equipment entering and leaving the vessel or a final verification that it was clean and empty.

Once the unit resumed operation, the lights left inside degraded and broke apart in the flowing ethylene oxide. Pieces of metal migrated downstream to a product cooler, where they punctured a rupture disc that was part of the cooler’s emergency pressure-relief system. The damage allowed ethylene oxide to flow into connected relief piping.

That piping segment, located between the rupture disc and a pressure-relief valve, was supposed to be filled with nitrogen to prevent any flammable mixture from forming. Dow had pressurized it with nitrogen during maintenance in 2020.

But the CSB said there was no continuous monitoring or regular check to make sure the nitrogen stayed in place. Over roughly two years, slow leaks bled the nitrogen out. Air seeped in. By July 2023, the line contained air, not an inert gas.

The board said that when ethylene oxide entered that air-filled piping after the rupture disc was punctured, it formed a flammable mixture that ignited. Investigators could not identify a specific ignition source. The flame front traveled through about 50 feet of piping, increasing the pressure enough to lift the nearby relief valve.

That valve opened into the vapor space of the same reflux drum where the work lights had originally been left behind. Inside, the burning gas heated the ethylene oxide vapors, triggering a rapid decomposition reaction that caused pressure to spike and the vessel to fail catastrophically.

The resulting explosion produced the large fireball captured on surveillance cameras and cellphones and sent more flames and pressure waves through adjacent equipment in the unit.

“The cause of the incident was the puncture of a rupture disc by metal debris that allowed the introduction of ethylene oxide into piping that contained air,” the CSB wrote. “The ethylene oxide ignited, and the ethylene oxide and combustion products propagated through pressure-relief piping to a reflux drum that was filled with ethylene oxide.”

Safety issues beyond one plant

The board pinpointed three broad contributing factors: weak vessel-closure and foreign-material controls, failure to maintain an inert atmosphere in critical piping and a pressure-relief design that discharged back into a large ethylene oxide vessel.

In the report, supervisory investigator Mark Wingard said the case underscored how seemingly small oversights in maintenance can have outsize consequences.

“Companies must ensure that equipment is clean and verified before startup, that inerting systems are actively monitored, and that pressure-relief systems are designed to prevent flame propagation,” Wingard said.

The board noted that after the explosions Dow implemented a new global vessel-closure process and a “Global Foreign Materials Exclusion Standard” for large-diameter vessels, and did not issue a specific recommendation to the company on that point. It did, however, call on Dow to identify all ethylene oxide lines at its facilities that are or should be inerted but are not continuously monitored — and either eliminate them or install proper inerting and monitoring systems.

The CSB also directed recommendations to the National Fire Protection Association and the American Society of Safety Professionals, urging them to revise three widely used standards — NFPA 350 and 326, and ANSI/ASSP Z117.1 — to spell out requirements for ensuring vessels are clean, free of tools and equipment, and “ready for startup” after confined-space work.

As of the report’s release, those recommendations remained open, pending responses from the standards bodies.

Community under a cloud

For people living within sight of the plant’s flare stacks, the technical details arrived long after the fear.

Iberville Parish officials issued a shelter-in-place order late on July 14 for residents within a half-mile of Dow’s complex, affecting hundreds of households. Authorities urged people to stay inside, shut windows and doors and turn off air conditioning until the order was lifted around 3:40 a.m. the next morning.

Dow and the Louisiana Department of Environmental Quality deployed air monitors around the site. The company said data from its monitors, state regulators and a third-party contractor showed no hazardous levels of ethylene oxide outside the plant’s fence line.

“Air monitoring is ongoing by Dow, the Louisiana Department of Environmental Quality and a third-party monitoring service, and there has been no indication of community impact,” the company said in a social media update at the time.

Some residents and advocates were unconvinced. The region, often called “Cancer Alley,” is an 85-mile corridor between Baton Rouge and New Orleans lined with more than 200 refineries and chemical plants. It is home to largely Black and working-class communities and has long been the focus of environmental justice campaigns and lawsuits over pollution and land-use decisions.

“There was a mushroom cloud over Baton Rouge, or near Baton Rouge,” said Anne Rolfes, director of the Louisiana Bucket Brigade, an environmental advocacy group. She called the company’s messaging “absurd” and said it reflected “the cloak of secrecy and the lack of transparency that big corporations like Dow benefit from.”

State inspection records show that water used to fight the fire and cool equipment drained into plant containment areas and then into a canal that leads toward Dow’s outfall on the Mississippi River. A Louisiana Department of Environmental Quality inspector reported that one water sample taken July 15 contained 39 parts per million of ethylene oxide, while a separate lab analysis found much lower levels.

Industry guidance cited in that report lists 41 parts per million as a maximum safe concentration for ethylene oxide in water. The variation in readings, and the lack of public clarity about where samples were taken, fueled frustration in nearby neighborhoods.

The explosions were not the first serious incident associated with Dow’s Glycol II unit. A 2019 tank rupture at the same part of the complex sent a shock wave that residents said rattled homes miles away. In late 2022, a large release from the unit involved thousands of pounds of ethylene, methane and ethylene oxide, according to state records. A chlorine leak at a tenant facility on the site, Blue Cube, also prompted shelter-in-place orders in 2022.

Enforcement and investor scrutiny

The 2023 ethylene oxide release also drew the attention of federal regulators beyond the CSB.

In October 2023, the U.S. Environmental Protection Agency’s Region 6 office conducted a Risk Management Program inspection at Dow’s Louisiana Operations, citing the Glycol II incident as the trigger. The Risk Management Program, established under the Clean Air Act, governs how facilities that handle large quantities of hazardous chemicals assess and control the risk of catastrophic releases.

EPA issued an inspection report in January 2024. On Jan. 3, 2025, the agency’s enforcement division sent Dow a notice letter alleging 21 violations of Risk Management Program and Clean Air Act requirements at the Plaquemine site and inviting the company to confer. Dow disclosed the notice in a quarterly filing and said it was cooperating with EPA and discussing potential civil penalties and corrective actions.

The same filing noted that on Aug. 29, 2025, a securities class action was filed in federal court in Michigan, claiming Dow’s stock had traded at artificially inflated prices in part because the company allegedly understated environmental and safety risks, including those arising from the Plaquemine incident and the EPA enforcement case. Three shareholder derivative suits followed, accusing some officers and directors of breaching their fiduciary duties.

Dow has said it is defending against the litigation and that, as of late 2025, it did not expect the environmental proceedings to have a material effect on its overall financial condition.

The company shut down ethylene oxide production at the Glycol II unit after the explosion and declared force majeure on certain ethylene oxide and derivative products, affecting chemical supply chains across the region. Industry analysts reported tighter availability and higher prices for ethylene oxide-based products in the months that followed.

Lessons in the last few minutes before startup

For the CSB, the Plaquemine disaster is the latest in a series of investigations that point to similar vulnerabilities: the final steps of maintenance and startup, where a missed bolt, a misaligned valve or a forgotten tool can undermine multiple engineered safeguards.

In its report, the board urged chemical manufacturers to treat foreign-material control in vessels as a formal, auditable process, to monitor inerting systems continuously rather than as one-time steps, and to scrutinize relief-system designs for how flames and pressure can propagate, not just where they discharge.

Those recommendations now sit with Dow and with standards organizations whose guidance shapes practices across the industry.

In Plaquemine, residents remain within sight of the towers and tanks along the river. Many stayed through the 2019 tank rupture, the 2022 leaks and the 2023 fireball; many say they expect more flaring and more late-night alerts.

The July 2023 explosions ended without fatalities, and the company and regulators say they found no dangerous levels of ethylene oxide outside the plant fence during the crisis. But for people who watched a mushroom cloud rise over their homes and waited hours under shelter-in-place orders, the latest report offers a different conclusion: what happened nearby was not a freak accident, but the result of systems that failed to catch errors in time.