Authorities searched Wednesday for a man believed to be missing after a barge carrying thousands of gallons of a gooey petroleum byproduct exploded, caught fire and then sank in a ship canal.

The man was believed to have been working on the vessel when it burst into flames in the Chicago Sanitary and Ship Canal (search) on the city's southwest side, said Mac Meade, a spokesman for the Coast Guard in Chicago. The search was suspended late Wednesday night and was scheduled to resume Thursday morning.

A boiler on the barge apparently exploded, igniting the clarified slurry oil, which is a byproduct created when refining petroleum, said Illinois Environmental Protection Agency (search) spokeswoman Maggie Carson. She said initial estimates indicate the barge was carrying about 13,000 barrels, or more than 500,000 gallons, of it.

"This is a huge volume of petroleum byproduct," she said.

IEPA investigators went to the site of the explosion and crews tried Wednesday night to determine how much of the substance might have spilled into the 105-year-old canal, which serves as a link between the Great Lakes and the Mississippi River (search).

Clarified slurry oil normally has the consistency of honey and becomes thicker in cold water, which could lessen any potential environmental damage, Carson said.

"When a substance is more liquid it spreads farther," she said. "When it congeals or hardens it's easier to gather and remove. It doesn't mean there won't be any problems, but this lends itself to ease in removal."

She said Egan Marine Corp., operated the barge and the company would be responsible for cleaning up any environmental damage.

A woman who answered the phone at the company located in the Chicago suburb of Lemont said they would have no comment.