Cleanup efforts are underway at Legislative Mall less than 24 hours after the blaze which did extensive damage to the north wing. (Delaware State News/Dave Chambers)

DOVER — A Wednesday fire in Legislative Hall started due to an exhaust pipe igniting flammable material in the attic, the city of Dover announced Thursday. The total damage has not been determined, but Dover Fire Chief Mark Hall said Wednesday it was “extensive.” Officials said Thursday most of it was water damage.

Dover Fire Marshal Timothy Mullaney concluded the fire had started accidentally from an exhaust pipe stretching from a backup generator in the basement. Contrary to some earlier speculation, the flames did not begin with the generator but started in the attic when combustibles caught fire during a full load test of the generator.

The fire occurred in the north wing, which contains offices for some state representatives and aides. It was put out within two hours.

The majority of the damage came from water sprayed by firefighters to douse the flames. Some small pieces of the ceiling fell in the stairwell leading to the second floor, and several offices, especially those on the second floor, will need remodeling. The smell of smoke hung heavy in the air inside the capitol Wednesday evening.

The building contains a number of historic paintings of past governors. The damage to those is not yet known.

The Dover Fire Department was notified Wednesday at approximately 2:17 p.m., Dover Public Affairs and Emergency Management Coordinator Kay Sass said in a Thursday release.

While the General Assembly is not in session, a handful of legislative aides and others were in the building when the flames broke out. They were evacuated by Capitol Police as smoke spread.

About a dozen fire trucks from Camden, Magnolia, Little Creek and Dover fire departments responded within the next two hours, while surrounding roads were blocked off.

A Little Creek firefighter was treated at the scene and released, and a member of Capitol Police was taken to Kent General Hospital for smoke inhalation as a precautionary measure. He has since been released, Ms. Sass said.

The building was closed Thursday and will be shut down Friday as well, as crews from the state, the city and the cleanup company Servpro work to estimate the damage and repair what they can.

Office of Management and Budget spokeswoman Jessica Eisenbrey said officials hope to reopen the capitol Tuesday. She did not know when the extent of the damage would be determined. Whether cleanup and repair costs are paid for by the state has not been released, although Ms. Eisenbrey said she believes insurance would likely cover it.

Several meetings scheduled for Thursday were moved across the street to the Tatnall Building.