A new chemical reactor at the Croda chemical plant at Atlas Point remained closed Tuesday, while work elsewhere at the 140-acre complex returned to normal, a day and a half after a flammable gas leak shut the twin Delaware Memorial Bridge spans and snarled traffic for more than seven hours. No one at the plant, which employs 250, was injured.

The company said its initial finding was that an "incorrect gasket fitted on one of the pipes during the plant construction" failed Sunday afternoon, causing the leak.

Company and state investigators are continuing to review the accident at Croda's ethanol-to-ethylene oxide unit that the state of Delaware wanted badly for its aging riverside industrial corridor.

The Atlas Point plant — which dates to 1937, 14 years before the first bridge span — has used ethylene oxide for years, but only recently started producing it at a new facility on site.

Sunday marked "the longest closure of both spans during my 27 years" at the Delaware River and Bay Authority, which owns the bridges, "and I couldn't find any such occurrence" in William J. Miller's 1983 history of the bridge, Crossing the Delaware, said authority spokesperson James Salmon.

At least "70 percent" of the volatile organic compound in a storage tank on the site escaped on Sunday afternoon, George Greenley, a spokesperson for the Holloway Terrace Volunteer Fire Company, which was among the first responders, told local media on Sunday. A revised permit that the state granted for the facility on June 7 describes processing tanks of up to 50,000 gallons. Company, state, and fire company officials have declined to estimate how much gas ultimately leaked.

The leak was reported to local fire companies, who initially recorded it as a building fire, at 4:15 p.m. Sunday. The Delaware Department of Natural Resources and Environmental Control rushed hazardous-materials staff to assist Croda staff at the plant, and set up monitors on the bridge, where they soon detected traces of ethylene oxide.

The commission shut the bridge at 4:23 p.m., at the request of Croda and Holloway Terrace, according to spokesperson Salmon. Rob Snyder, deputy chief at the Holloway Terrace company, said they acted in "an excess of caution." Police sent "reverse 911" calls urging residents of the nearby Collins Park development and parts of nearby New Castle to stay indoors.

Monitors showed "there was no point at which there was an unsafe level of ethylene oxide in the air outside the facility perimeter," Croda said in a statement the next day. The bridge commission says DNREC and Croda both told it the ethylene oxide concentrations on the bridge side of the property line did not exceed federal OSHA exposure limits.

Besides its volatility, federal officials say short-term exposure to the gas can cause  lung injury, headache, nausea, vomiting, diarrhea, and shortness of breath. Long-term exposure can cause cancer.

"There was concern that if people were stuck on the highway or the bridge there could be safety issues," Shawn Garvin, the former Environmental Protection Agency official who heads DNREC, told me later. "We did find elevated levels" of ethylene oxide, he added.

Fire crews spent the evening helping Croda staff spray water onto the ethylene oxide facility, pipes, and surroundings to dissipate the leak. The company declared the leak contained, and the commission reopened the bridges at 11:23 p.m.

Croda marketing director Cara Eaton said: "We are now conducting a systematic review of all other equipment on the ethylene oxide plant pipework. Until this work is completed, and we, along with regulatory authorities, are confident that the plant can resume safe operations, we will not manufacture ethylene oxide. This process is anticipated to be completed, carefully and thoroughly, over the next two weeks."

Garvin, the DNREC chief, said he wouldn't predict how long his department's probe will last. The ethylene oxide unit "is still down until we can figure out what happened," he added. He praised local and state first responders and the bridge commission, who all "did this the way it should be done."

Like many chemical makers aware of public sensitivity to pollution, Croda cultivates a reputation as a careful, environmentally conscious operator. "My bet, Croda did everything by the book," said Craig Melville, of Maple Glen, a retired chemical distributor who handled Croda products as well as those made by Dow, DuPont, FMC, and other producers. "They know it's a dangerous chemical," he added. "Things happen like this all the time in Texas, sort of goes with the business."

The Gulf Coast is where most U.S. ethylene oxide is made, and where Croda had considered relocating the Atlas Point works after its previous supplier, Sunoco's chemical unit, stopped ethylene production in Marcus Hook due to a fire. Melville said it's in the chemical industry's interest — and in the Philadelphia area's — to continue producing basic industrial compounds close to customers who rely on their products.