About 2,500 people were evacuated from four communities in northeast Butler County tonight after fuming sulphuric acid leaked from the Indspec Chemical Corp. plant.

Three people were transported to the hospital with respiratory problems, but it was unclear whether they were related to the acid leak.

Officials with the Butler County Emergency Management Agency said the leak occurred just after 5 p.m. when a tank containing the acid overflowed. Thirty employees who were inside the plant at the time were immediately evacuated.

Agency officials said the leak was contained by 9:30 and that the acid cloud that hovered over the valley was dissipating.

They hope to get residents back into their homes later tonight.

Firefighters and other emergency responders knocked door-to-door on homes located within a 2-mile radius of the Indspec plant in Petrolia to tell residents to evacuate. The affected areas were Parker, Fairview, Washington and Concord townships.

Shelters were set up at Karns City High School and the Bruin Fire Department.

Fuming sulfuric acid is dangerous in high concentrations, according to officials.

"Of course, the concern here is ... the potential for respiratory damage and skin burns, things like that," said Freda Tarbell, spokeswoman for the state Department of Environmental Protection.