It was about a year ago when on July 14 at 9:15 p.m., an explosion occurred at the Dow Louisiana Operations’ Glycol II plant in Plaquemine, Louisiana. Shortly thereafter, multiple explosions and fires damaged nearby piping and equipment, including a reflux drum.

This incident resulted in substantial property damage at the facility but no injuries. However, over 31,000 pounds of ethylene oxide (EtO), a cancer-causing substance, released during the incident forcing local authorities to issue a shelter-in-place, affecting hundreds of nearby residents, according to a preliminary update report from the Chemical Safety and Hazard Investigation Board (CSB).

The site’s industrial park has 23 production units that manufacture more than 50 different intermediate and specialty chemical products used to produce many other compounds. One chemical manufactured at the Dow LAO facility’s Glycol II plant is EtO. As of June 10, 2024, there were 1,274 Dow employees at this facility.

Reactive Chemical
EtO, a known carcinogen, is a flammable, colorless gas. It is a reactive chemical with a lower flammability limit of 2.6 percent and an upper flammability limit of 100 percent. EtO can ignite without the presence of oxygen, but oxygen makes EtO more reactive and likely to ignite.

The most common way that people end up exposed to EtO is by inhaling air that contains EtO, according to the U.S. Environmental Protection Agency (EPA). Long-term regular exposure to EtO can be harmful, as it is carcinogenic and mutagenic. According to the National Institute for Occupational Safety and Health (NIOSH), an EtO minimum concentration in air of 800 parts per million (ppm) is “immediately dangerous to life or health.”

Schneider Bold

On the night shift of July 14, the Glycol II plant was operating under normal conditions when at 6:52 p.m., high vibrations triggered an automatic shutdown of one of the two reflux pumps operating.

Dow operations employees began troubleshooting the pump.

Dow operations personnel were able to return the pump to operation two minutes later at 6:54 p.m.; however, the reflux pump’s vibrations were still higher than normal but below the high-high vibration interlock alarm setting.

Following the reflux pump shutdown, from 6:52 p.m. to 9:15 p.m., the EtO finishing operations process experienced numerous upsets, which resulted in multiple high-level alarms in the reflux drum. Process operators continuously tried to stabilize the level in the reflux drum until 9:15 p.m.

That is when an explosion occurred in the vicinity of the reflux drum. Two Dow operators were working nearby, observed the explosion, and quickly returned to the control room.

Simplified process flow diagram of the EtO Finishing Process.
Source: CSB

Reflux Drum Fire
Following the initial explosion, a fire developed near the reflux drum. Shortly after the initial explosion, the reflux drum, which was half-full of liquid EtO, exploded. At the time of the incident, the reflux drum had an emergency pressure-relief valve, but the valve was unable to prevent the reflux drum from exploding.

Witnesses reported additional explosions as the fire continued to burn through the night. Dow reported 31,525 pounds of EtO released during the incident, which included the de-inventorying and cleanup following the fire.

After the explosion, the Iberville Parish Council Office of Emergency Preparedness issued a shelter-in-place for residents living within a half-mile of the Dow facility. The shelter-in-place lifted at 3:40 a.m. Saturday, July 15.

The fire from the incident was fully out by 5 a.m. on Sunday, July 16. Dow spent the remainder of the day ensuring all fires associated with this incident had been put out. At 8:19 p.m. that evening, the company reported to the Louisiana Department of Environmental Quality all fires were out at the facility.

There were no injuries reported because of the incident and Dow estimated property damage to be $1.5 million.

The Glycol II plant contains multiple processing areas, including the EtO production unit. To produce EtO, Dow’s EtO production unit reacts ethylene and oxygen. The EtO is then further processed through finishing operations, which purify the EtO. The EtO finishing operations contain distillation columns to remove impurities from the final EtO product.

EtO Flows to Multiple Locations
In the EtO finishing operations section of the Glycol II plant, purified EtO flows from the top of a distillation tower, becomes condensed, and then goes to a reflux drum. The EtO in the reflux drum flows to multiple locations through its reflux pumps. The EtO can pump back to the distillation column to end up used as reflux, recycled back to the reflux drum, or go to storage tanks as a final product. EtO flow to the storage tanks also includes pumping the EtO through a heat exchanger, called the product cooler.

The reflux drum was a horizontal vessel constructed of SA-285-C carbon steel. Its maximum allowable working pressure (MAWP) was 75 pounds per square inch gauge (psig) at a temperature of 450° F. An emergency pressure-relief valve set to relieve at 75 psig protected the reflux drum from overpressure. A turnaround occurred at the Glycol II plant from May to June 2023. As part of the turnaround work, workers internally cleaned and inspected the reflux drum.

The product cooler had an MAWP of 570 psig on its tube side, where EtO was present. Dow equipped the product cooler with a rupture disk and an emergency pressure-relief valve installed in series for overpressure protection. The rupture disk had a rated burst pressure of 248 psig at a temperature of 104° F, and the emergency pressure-relief valve was set to relieve at 265 psig. The piping between the rupture disc and the emergency pressure-relief valve was four-inch diameter pipe 80 feet long. The discharge piping from the emergency pressure-relief valve went back into the vapor space of the reflux drum.

CSB is continuing to gather facts and analyze several key areas involved in this incident, including:

  • Emergency pressure-relief systems scenarios
  • Reactive chemical hazards
  • Reactive material emergency pressure-relief system design
  • Maintenance procedures and practices
  • Relevant facility, corporate, and industry standards

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