DOVER, Delaware (AP) -- A chemical released into the air from an industrial plant Friday sent 23 people to the hospital and closed some roads, officials said.

The release of the chemical at Dow Reichhold Specialty Latex was visible around a railroad tanker car parked on the plant site, state police spokesman Cpl. Jeffrey Whitmarsh said.

The rail car contained styrene, which is potentially flammable and can cause irritation if inhaled, Whitmarsh said.

Pam Chase told The (Wilmington) News Journal that she could see a "mist across the ground" and a "steam or fog along the tracks."

"It was a real strong smell of burning plastic," she said.

John Hughes, secretary of the Delaware Department of Natural Resources and Environmental Control, said first responders reported that the leak was a result of a defective valve on a railroad tanker car carrying 20,000 pounds of styrene. Officials believed the cause was a buildup of pressure in the tanker, he said.

"I've been told it's stopped leaking, but it's not capped," Hughes said late Friday. "It's not safe at this point."

Darrel Cole, spokesman for the Delaware Department of Transportation, said much of Route 13 was closed and traffic was being diverted to Route 1, where tolls were being waived.

Although residents were not ordered to evacuate, those who wished to leave were directed to Dover High School. No one was at the school late Friday.

Twenty-three people went to Kent General Hospital for treatment of nausea and headaches, said Pamela Marechi, a hospital spokeswoman. Twenty-one were released.

Residents within five miles of the plant were urged to stay indoors, turn off air conditioning and close vents into their houses, Whitmarsh said.

Reichhold site manager Michael Galbus said the company would not make a statement until Saturday.

Styrene is used by chemical companies that make plastics, synthetic rubber, resins and insulators, according to the Environmental Protection Agency's Web site. Styrene vapor irritates the eyes, the nose, and the throat and can adversely affect the human nervous system.

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