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What was the threat from gas leak that jammed traffic over the Delaware River?

There have been "numerous explosions" of ethylene oxide in industrial situations; the bridge was shut as a precaution

Damage from a 2004 ethylene oxide explosion that wrecked a California sterilization facility
Damage from a 2004 ethylene oxide explosion that wrecked a California sterilization facilityRead moreU.S. Chemical Safety and Hazard Investigation Board

In the wake of Sunday's precautionary seven-hour closing of the Delaware Memorial Bridge and resulting traffic jams due to an ethylene oxide leak at Croda's neighboring chemical plant — which Croda in a preliminary investigation blamed on a bad pipe gasket —  James Markos, a risk and reliability engineer and former chemical-plant power supervisor, sends this link to a U.S. Chemical Safety and Hazardous Investigation Board (CSB) video.

It shows how ethylene oxide can endanger lives and property when it catches fire.

The video and text explain an ethylene oxide explosion at a Sterigenics medical equipment sterilization plant in Ontario, Calif., back in 2004.  A two-ton door was blown 75 feet, the lab was wrecked (its steel walls badly bent), and the nearby control room cut apart by blown-out windows and falling computers. Four workers were injured.

There have been "numerous explosions" of ethylene oxide in industrial situations, due to incomplete monitoring and lack of training, sometimes magnified by lack of proper equipment, CSB says.

In the California plant, technicians and their supervisor, while testing the unit after a successful sterilization, bypassed procedures for repeatedly flushing the gas out of the unit before opening it, because they thought the lengthy process was unnecessary with sterilization materials removed. Lacking monitoring sensors, they didn't realize the gas remained in explosive concentrations, the board found. So when the gas reached a burner flame, it ignited, with "catastrophic results."

Fourteen years later, at Atlas Point, Croda installed monitors and sensors earlier this year when it finished the new ethanol-to-ethylene oxide unit where a pipe leaked Sunday. The unit remained closed after the bridge and the other operations at the 140-acre plant complex reopened late Sunday.

Besides Croda's on-site monitors, state officials set up field monitors by the bridge and on other properties bordering the site soon after the leak was reported Sunday at 4:15 p.m. Fire company and Croda officials say monitors showed ethylene oxide concentrations outside the plant property did not reach dangerous levels. But the bridge was still closed as a precaution until after 11 p.m.

Ethylene oxide is also toxic, and a carcinogen for people who are regularly exposed to it. But the escaped gas dissipates harmlessly, if it can be diluted before it reaches a flame or spark, company and state officials said. Firefighters poured water to spread the gas and ensure it wouldn't blow up. Delaware state environmental officials are continuing their investigation.

A check of state records shows a handful of environmental violations at the site since Croda took over in 2007, and none in nearly four years:

In January 2015, Croda told the state Department of Natural Resources and Environmental Control that emissions from a new electric generator, which burns gas from Wilmington's Cherry Island landfill, "far exceeded" its permitted discharge of nonmethane organic compounds. Three days later, the company said it had fixed the problem. The state had the company detail what went wrong and how it was fixed, and give "reasonable assurance" it wouldn't happen again.

In 2014, Croda missed a state deadline for its operating permit renewal, which was later granted on schedule.

In May 2008, less than a year after taking over the plant from another British company, Uniqema, Croda told state environmental officials it had released 96 pounds of ethylene oxide into the atmosphere from an uncontrolled machine.

"Croda did not understand which chemicals it was processing at the time of the incident, nor did it recognize the presence of ethylene oxide" in the tank that leaked, and it took too long to report the leak, according to the violation notice. The state also told Croda to document what happened, as the law requires.

Earlier in 2008, an annual compliance review (partly covering the period Uniqema ran the plant) found "several instances where required monitoring (of boiler emissions) was either not conducted or not reported as required."  The department threatened to pull Croda's operating permits unless it explained what happened and why it wouldn't likely happen again.