A fire erupted at historic firehouse in downtown Philadelphia Friday causing extensive damage. The fire started at about 11:30 a.m. at the firehouse located at Fourth and Arch streets in downtown Philadelphia. In an odd twist of irony, firefighters had to turn their water hoses on their own building and attempt to contain the fire. It appears preliminary that the fire may have started in a medical unit ambulance that was parked inside the firehouse. There were no immediate reports of any injuries.