The accident happened near the Hillandale Road exit just before 9 p.m. Wednesday.
One of the barrels of benzyl chloride leaked inside the overturned trailer, slowing plans to right and remove the rig.
City police said that what they called a "freak accident" began when a set of tires came off one axle of a northbound roll-off tow truck owned by Lethal Wrecker Service of Charlottesville, Va. The tires went across the median and hit the side of the southbound tractor-trailer, and it crashed onto its right side on the shoulder of the road.
Police said the driver, Brian Thomas, was listed in critical condition at Duke University Hospital.
Benzyl chloride is a colorless liquid with a pungent odor and is an irritant if the vapor is inhaled, according to the U.S. Environmental Protection Agency and chemical-industry data sheets. It also reacts if it is exposed to water, they said.
The chemical is used in making dyes and pharmaceutical products and as a photographic developer, the EPA said.
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