A truck carrying barrels of a chemical crashed and burst into flames, killing the driver and sickening nearly 50 emergency workers who were exposed to the fumes.

The tractor-trailer crashed at about 11:50 p.m. Thursday on a four-lane highway. The highway remained closed in both directions Friday morning.

"It appears the truck's brakes caught on fire and caused the trucker to lose his brakes as the truck was coming off the grade," Deputy K.E. Ball (search) of the Mingo County (search) Sheriff's Department said Friday.

The truck was carrying barrels of a polyurethane-based liquid called RePneu II, which is used to fill the tires of off-road coal mining and construction equipment to prevent flats, Mingo County Emergency Services said.

Firefighters responding to the accident initially thought the leaking liquid was oil, but they began complaining of breathing problems and other ailments. They were taken to Williamson Memorial Hospital for decontamination and treatment for eye and skin irritation.

"It was hard to breathe," said Ball, who was among those seeking treatment. "When I first arrived on scene it was just a fireball, pretty much, a smoky big mess."

One resident near the crash site, which is in a rural area, also sought treatment. John Barrett, emergency department manager at Williamson Memorial (search), said the people brought there were treated and released.

The driver's identity and employer were not immediately known Friday.