Police said troopers and the Illinois Department of Transportation were on the scene, about 1/4-mile north of La Grange Road near Hodgkins, starting just after 8 a.m.
I-55 shut down in south suburbs for hazmat situation
The Summit Fire Chief said a car cut off the semi truck carrying hydrogen peroxide.
The chief said the truck driver slammed on his breaks, causing the chemicals to shift and leak in the trailer, causing the spill on I-55 that led to an all-day clean up and traffic nightmare for over nine hours.
A disabled semi on the right shoulder of the outbound lanes was found to be leaking hydrogen peroxide, state police said.
Multiple fire service agencies and a hazmat clean-up crew are on the scene.
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A chemist from the University of Chicago, John Anderson, provided some insight on the potential dangers of large quantities of hydrogen peroxide.
"It also can be explosive too," Anderson said. "So if you have the wrong thing come in contact with it, they can explode. It can also react with other chemical compounds... gasoline or something like that near it."
ISP had asked to choose alternate routes.
ABC7 spoke with a driver getting off the interstate who said traffic was a mess.
"I mean it's a mess," Larry Springer said. "There's cars backed up everywhere. It's a parking lot."