MANSFIELD - Fire officials Saturday were still investigating the cause of a fire at a local lumber business Friday night.

The blaze was reported about 9 p.m. at National Lumber at 245 Oakland St., tying up local and area town firefighters for several hours.

“The cause is still under investigation, but we are leaning toward accidental,” Deputy Fire Chief James Puleo said, adding the town’s electrical inspector has ruled out an electrical cause.

The fire was confined to a tool room inside the warehouse, Puleo said.

The deputy fire chief estimated damage at a minimum of $20,000.

“There were a lot of tools damaged plus the structure and water damage,” Puleo said.

There were no problems with nearby fire hydrants as they had been shoveled out.

“The biggest issue we had was locating the fire because there was a lot of smoke, but the guys used a thermal imaging camera,” Puleo said of a camera that shows hot spots. “The sprinkler system held the fire from spreading.”

That sprinkler system had to be shut off and the lumberyard hired a “fire watch” overnight.

Foxboro sent a ladder truck and Norton sent a fire engine to the scene. Plainville covered the fire station.

Firefighters cleared the scene about 1 a.m.