The Croda chemical plant at Atlas Point on the Delaware River, which was recently expanded by its British owners to produce two tons of hazardous ethylene oxide per hour so the material didn't have to be shipped from Texas by rail, was shut down due to a leak on Sunday afternoon, stopping holiday traffic on I-295 over the Delaware Memorial Bridge and jamming drivers on the direct routes between New York and Washington, D.C.

Hazardous materials crews converged on the plant as traffic was diverted off both spans of the bridge just north of the 140-acre complex, causing extensive traffic jams along I-95, I-495, the New Jersey Turnpike, and feeder routes in Delaware, New Jersey, and Delaware County, Pa. The Delaware River and Bay Authority, which maintains the bridge, and New Castle County police, who cover the area including the plant, had no immediate reports of injuries. The bridge reopened to motorists around 11:30 p.m.

In a statement after the bridge reopened, Croda marketing officer Cara Eaton said the gas was contained, added that local emergency responders had left the site, acknowledged the "significant inconvenience," and promised an investigation in hopes of not doing it again.

The plant, which employs 250 after its recent expansion to make surfactants for a long list of industrial customers, had been faced with a possible shutdown after Sunoco's ethylene plant, 12 miles north on the Pennsylvania-Delaware state line, caught fire and burned in 2009. Sunoco decided that plant wasn't worth fixing. Its successors converted the adjacent oil refinery into a gasworks, though they continued to use the ethylene site to burn waste fuels, for which they were fined $750,000 by Delaware last year.

Sunoco's shutdown cut off the key raw material Croda used to help Atlas Point's clients make antifreeze, DuPont crop-seed coatings, and the mixing and separating agents used in processed foods, natural-gas fracking, and other industries, among other ethylene-derived materials.

Instead of closing, the company invested $170 million — with $2.5 million from Delaware taxpayers, plus tax abatements — to make ethylene from ethanol, the same simple alcohol that makes you drunk. The job employed 250 temporary contractor workers during its two-year construction, and added 35 permanent workers represented by the United Steelworkers to the 215 working there before the expansion.

Useful as it is, ethylene is explosive, a carcinogen, and poisonous — a base for pesticides and the lethal mustard gas outlawed after World War I. DuPont made ethylene at its sprawling Chambers Works across the river from Atlas Point, but that plant (now operated mostly by spin-off Chemours) has reduced operations. After Sunoco shut its ethylene works, the closest U.S. suppliers were in the Houston-area petrochemical complex.

When Sunoco put Croda on notice, "the ethylene world was in flux," Bob Stewart, who managed Atlas Point at that time, said in an interview before Sunday's leak. Stewart  is now Croda's managing director of operations, overseeing Atlas Point and other works in places including Mill Hall, Pa., near Lock Haven, and the research lab in Edison, N.J.

"Suppliers didn't want the risk of sending railcars north" with the danger of leaks, he told me. They urged Croda to shut the Delaware River plant and build a new facility near the Gulf Coast.

"We looked at relocation," Stewart said. But Croda had already invested $100 million in Atlas Point since taking over the site in 2006. Among other "sustainable" processes meeting a company mandate to reduce its carbon footprint, Croda updated a pipeline to burn waste gas from Wilmington's nearby Cherry Island landfill, installed LED lighting, and added a solar panel electric field (which it's now expanding).

Most important, Stewart said, his specialized, reliable workforce — the plant claimed over a million work-hours since its last time-lost injury — was unwilling to move all the way to the Gulf Coast: "That wasn't the life they were used to."

So, instead of writing it down as a loss, Croda bought an ethylene production process using silver as a catalyst to make the chemical from common ethanol. Refined from grain or farm waste, ethanol is flammable — usually added to U.S. automotive fuel — but much safer than ethylene to ship by rail. The process was already in use at plants in China and India, but Atlas Point was its first U.S. installation, Stewart said. Croda hired Rockwell Automation to build a digital-process control and monitoring system for the 120,000-square-foot plant expansion.

The plant turns a ton and a half of ethanol and a ton of oxygen into two tons of ethylene oxide and a half-ton of carbon dioxide every hour it's running. A lab staff headed by Amanda Marchese monitors processes and samples purity through a wall-sized electronic board linking to sensors across the works.

For all the investment, Croda's veteran workforce was the plant's key asset, said Tessa Myers, vice president of sales for Rockwell Automation, who visited Atlas Point on her way to a Rockwell conference at the Convention Center this month. "There's been a significant demographic shift in manufacturing," with relatively few young workers entering the field, but knowledgeable veterans retiring. (Stewart says he's recruited ex-DuPonters, among others.)

Myers said skilled staff are needed to run and monitor automated systems. That includes specialized contractors, like Applied Control Engineering of Newark, Del., which has been installing automation projects at Atlas Point under a series of owners since 1994, said manager Chris Hudson.

State grants from the Delaware Strategic Fund, approved in 2015, included $300,000 for retaining and retraining workers already on the site, $700,000 for creating new jobs (Croda has exceeded the promised combined job total), and $1.5 million as the maximum-allowed state contribution to the construction project, according to state spokesperson Michael Chesney.

The state figures it will make the money back in the form of increased income taxes, part of a strategy of redeveloping the state's Delaware River industrial corridor and preventing active sites like Croda from reverting to industrial ruins like the steelworks in nearby Claymont and New Castle or the former DuPont plant at Repaupo, across the river in New Jersey.