The June 13 fire at ThorSport Racing was accidental, starting in mulch underneath stairs of a patio and causing an estimated $10 million in damages, according to a report released Wednesday by the Ohio State Fire Marshal.

ThorSport fields four entries in the Camping World Truck Series and, thanks to the help of firemen, was able to salvage 15 of 18 trucks from the early-morning fire. However, the team will be forced to rebuild approximately 40 percent of its 100,000-square-foot shop in Sandusky, Ohio.

The report, by assistant state fire marshal Jeff Koehn, stated that investigators could not rule out smoking materials as the heat source for the fire, but the interviews investigators conducted offered no proof that anyone was smoking in that area that day, and the water used to fight the fire washed away a large portion of the mulch from the building.

The automatic sprinkler system and fire alarms did not activate because the fire spread from the exterior into the roofline and the walls -- above and beyond the reach of the sensors and sprinkler heads, according to the report. The fire, reported at 12:51 a.m., was discovered by the lone shop employee working in the building, who had gone to the suspension room to get a phone charger and could see and smell the smoke coming from the basement. He went to the basement, where he could see the fire through holes in the block basement wall, and then he traveled approximately 500 yards to find a security guard to report the fire.

The team has relocated to various buildings in the Sandusky area as the current shop is being rebuilt. The suspension and fabrication shops were destroyed in the fire.