The fire that damaged the former Consumers Energy headquarters in downtown Jackson on May 31 was caused by sparks, according to the city Fire Department.
The building was being demolished, and the sparks happened while a worker was cutting metal with a torch.
The sparks caused a fire when they landed in a debris pile.
Six workers were briefly trapped by the fire, but all got out safely.
The company responsible for the salvage operation, Dore and Associates, has been told to have a standby hose line in the building to prevent future fires.