BARKEYVILLE, Venango County — An industrial explosion that witnesses say sent a ball of flame skyward this morning across from Barkeyville Travel Center closed down nearby roads and sent two men to the hospital with minor burns.

Fire companies from three counties — Venango, Mercer and Butler — spent about three hours at the scene of the explosion and subsequent fire at Health Oil Inc. on Route 8, said Gerry Rea, chief of Clintonville Volunteer Fire Department.

Firefighters arrived at the business at about 8 a.m. today, after a million-gallon storage tank that normally holds gasoline exploded while it was being cleaned by two company employees.

Rea said the two men, who were not immediately identified, were taken by Superior Ambulance to Grove City Medical Center with minor burns.

“They were very lucky,” Rea said.

It was not immediately clear what caused the tank to explode. Andy Restauri, the company’s vice president of operations, said the tank, which sits among other similarly-sized storage tanks in an above-ground storage facility, held less than one inch of a gasoline byproduct.

That liquid is left after the gasoline is drained from the tank.

Witnesses said a ball of flame accompanied the explosion.

Jackie Stewart of Clintonville, who is a cashier at a BP gas station across the road from the storage facility, said she and other employees at the store were watching the tank smoke shortly before 8 a.m. when they heard a “whooshing” sound and then saw “this huge ball of flame (emerge) and the lid come off.”

“It was a huge ball (of flame),” Stewart said. “You could hear it coming.”

The explosion prompted the state Department of Transportation to shut down two access ramps along Interstate 80 while emergency crews worked to contain the blaze.