Firefighters battled a blaze Monday afternoon that badly damaged the former New Orleans Free School, a historic structure in the Touro neighborhood.

Authorities did not rule out lightning as a cause but said the fire was still under investigation. No one was injured.

The structure at 3601 Camp St. was built in 1903 as the Frank T. Howard Elementary School No. 2 and later housed the Free School. It was sold at auction by the Orleans Parish School Board more than three years ago.

It is being renovated into an upscale apartment complex with some two dozen units — a project that could be delayed by the damage from the fire.

Fire Department Superintendent Tim McConnell said crews arrived just after 4 p.m. to find the attic engulfed in flames. Second and third alarms were quickly struck.

The fire was not declared under control until 6:41 p.m.

Nineteen Fire Department units and 66 personnel were dispatched to the scene as firefighters struggled to reach the heart of the fire, which was at the peak of the roof in the attic.

“There had been lighting strikes all day,” McConnell said. “It was pretty lit up, and the attic did not look good (when he arrived). I’d hate to think what we’d be looking at” had firefighters not responded quickly.

Although the building is being renovated, no work was being done on Memorial Day.

“It will certainly delay the project, but given what you could have here, they’re really fortunate,” McConnell said. “This could have been a catastrophe.”

Follow Jim Mustian on Twitter, @JimMustian.