The Fairlawn Fire Department has ruled arson as the cause of Saturday’s fire at Cornus Hill Mansion, Chief Russell Hose said Tuesday.

About 9 p.m. Saturday, the Fairlawn Fire Department responded to a fire at the vacant mansion at 2544 Chamberlain Road. By then, it was engulfed in flames.

Responders included seven fire departments, eight fire apparatuses, six utility vehicles and 40 firefighters, Hose said.

After nearly 12 hours of battling the blaze, Hose said a third of the mansion was destroyed and the rest heavily damaged from smoke and heat. No one was injured.

The Code 10 Fire Investigation Team — a group of a dozen independent investigators from different fire departments on the west side of Summit County — and the State Fire Marshal’s Office were requested for a formal investigation less than two hours after the fire started.

They began a preliminary investigation in the late hours of Saturday as firefighters continued battling the blaze. Both agreed with the arson ruling.

Hose said the fire marshal’s office sent an investigator to the scene Tuesday to conduct another investigation.

“The investigators were able to rule out all accidental causes, despite the structural integrity being compromised, prohibiting investigators from digging out and sifting through fire debris safely,” Hose said in a written statement.

Hose said the incident will remain under investigation as police search for a suspect.

The 10,864-square-foot mansion, built in 1935, once belonged to Russell Firestone. He was the second son of Firestone tire company founder Harvey Firestone, and he moved into the home in 1937.

The Ohio Blue Ribbon Arson Committee is offering a reward of up to $5,000 for any information leading to the arrest and conviction of those responsible for the fire.

Contact the Fairlawn Police Department at 330-670-4300 with any information.

Theresa Cottom can be reached at 330-996-3216 or Follow her on Twitter @Theresa_Cottom.