Arson investigators as of Monday had not determined the cause of a fire over the weekend at the Toyota Center. The Houston Fire Department was alerted to a fire around 8:30 a.m. Sunday in the lower level of the building under the concourse level. When units arrived, the fire was out due to the sprinkler system. The fire was contained to a small area of the facility. The sprinkler system was put back in service and the building is safe to use, according to officials. Officials said there is no structural damage.