PORT ALLEN — A mixture of heated asphalt and a water-based additive being pumped ashore from a barge Monday night produced a foul-smelling steam that drew complaints from residents and prompted emergency responders into action, Fire Chief Rick Boudreaux said.

The incident occurred while the barge, carrying the type of asphalt used to construct roads, was offloading its cargo into a bulk storage tank at the Center Point Terminal tank farm in Port Allen, Boudreaux said Tuesday.

The asphalt has to be liquefied — heated to about 260 degrees Fahrenheit — before it can be pumped into a tank, Boudreaux said.

Companies generally mix an oil-based additive with the asphalt before pumping it into tanks, he said.

On Monday, however, the asphalt was mixed with ammonia and the water-based additive, the chief said.

As the mixture rose in temperature it produced a thick, pungent steam that wafted throughout the city around 6:30 p.m., Boudreaux said.

Emergency personnel responding to the scene determined the steam was non-hazardous, Boudreaux said.

Mayor R.J. Loupe said, however, the steam was strong enough to burn his eyes and throat.

“They’re saying it’s non-hazardous.” Loupe said. “That’s the part I’m trying to understand.”

Center Point Terminal currently has 11 tanks on property within 1,000 feet of Rivault Park and the Oaks subdivision in Port Allen.

Several residents living in the vicinity have complained that the tanks — full of bunker fuel and asphalt — emit strong odors that have caused residents to suffer from sore throats, migraines and nausea.

In March 2007, the company petitioned the Louisiana Department of Environmental Quality to build three additional 200,000-gallon tanks at the tank farm, said Chris Piehler, administrator of inspection for DEQ.

The state approved those permits in February 2010, Piehler has said.

Center Point also has outlined preliminary plans to build seven more tanks at some future time, records show.

In response, the city hired the McGlinchey Stafford law firm to attempt to prevent any new tanks from being built. But Kai Midboe, an attorney with the firm, has said the city has little legal recourse because the tanks are located on property owned by the Port of Greater Baton Rouge.

Instead, Midboe suggested the best course of action for the city would be to ask DEQ to study the land for contaminants and to request that Center Point install air scrubbers to limit the effects of any noxious odors the tanks may emit.

Center Point representatives were not available for comment Tuesday.