Cal. Penal Code § 451.1

(a) Notwithstanding any other law, any person who is convicted of a felony violation of Section 451 shall be punished by a three-, four-, or five-year enhancement if one or more of the following circumstances is found to be true: (1) The defendant has been previously convicted of a felony violation of Section 451 or 452. (2) A firefighter, peace officer, or other emergency personnel suffered great bodily injury as a result of the offense. The additional term provided by this subdivision shall be imposed whenever applicable, including any instance in which there is a violation of subdivision (a) of Section 451. (3) The defendant proximately caused great bodily injury to more than one victim in any single violation of Section 451. The additional term provided by this subdivision shall be imposed whenever applicable, including any instance in which there is a violation of subdivision (a) of Section 451. (4) The defendant proximately caused multiple structures to burn in any single violation of Section 451. (5) The defendant committed arson as described in subdivision (a), (b), or (c) of Section 451 and the arson was caused by use of a device designed to accelerate the fire or delay ignition. (b) The additional term specified in subdivision (a) shall not be imposed unless the existence of any fact required under this section shall be alleged in the accusatory pleading and either admitted by the defendant in open court or found to be true by the trier of fact.