What to Know The leak of a flammable chemical from a plant next to the Delaware Memorial Bridge forced a sudden closure of the bridge Sunday evening.

Bridge officials said chemical plant staff requested the closure as a precaution. The shut down caused a traffic nightmare.

Ethylene oxide, a flammable and potentially hazardous chemical, was leaking from the plant.

The leak of a highly flammable chemical from a plant next to the Delaware Memorial Bridge forced an emergency shutdown of the dual-span suspension bridge on Sunday, creating a traffic nightmare during the travel rush home from the Thanksgiving holiday.

The closure happened around 5 p.m. Sunday after ethylene oxide began leaking from the Croda Atlas Point chemical plant on the Delaware side of the bridge's span. The plant, located along Cherry Lane in New Castle, Delaware, is closest to the northbound span which carries cars into New Jersey.

The Delaware River and Bay Authority said plant staff requested the bridge closure as a precaution.

Ethylene oxide is a highly flammable and acute exposure can cause lung damage and nausea, according to the Occupational Safety and Health Administration. It is typically used as an ingredient to make other chemicals and can have a sweet smelling odor.

A firefighter at the hazmat scene told NBC10 that measuring equipment showed a high risk of explosion and thus warranted the highway shut down.

George Greenley, spokesman for Holloway Terrace Fire Company, told The Associated Press that if the gas cloud "would have had an ignition source it could have been catastrophic."

Fire officials waited for pressure to dissipate in the pipes at the plant before reopening the bridge around 11:30 p.m. — more than six hours after it was closed.

He says the cloud of chemical gas was "of such magnitude that it easily could have" reached the bridge.

A Croda spokesperson said it's too early to know specifics about what led to the leak, but that the company is working with state environmental control to monitor the impact.

The bridge's sudden closure during the final hours of the Thanksgiving travel rush resulted in a traffic nightmare in Delaware and New Jersey — the two states the bridge connects.

An average of 80,000 vehicles cross the span which feeds the New Jersey Turnpike and I-295 in New Jersey and I-95 in northern Delaware.

Bridge officials described the roads leading to the spans as a "parking lot" at the start of the closure.

The New Jersey Turnpike Authority reported a backup of at least 2.5 miles in the southbound lanes headed for the bridge. Traffic was detoured off the turnpike at Exit 2 and onto U.S. 322.

The Croda spokesperson said the company deeply regrets the leak and that more information about what happened would be released as soon as it became available.