California Code, Health and Safety Code - HSC § 14833

Fire company vehicles granted exempt California vehicle registration or displaying exempt California license plates shall be properly insured, marked, and identified as a fire company vehicle. The fire company shall not allow those vehicles to be loaned, rented, or used for personal pleasure or by for-profit businesses for private economic gain of a business or contractor. This limitation is not intended to prohibit or hinder the fire company's legitimate use of fire company vehicles for emergency services, including contract arrangements or agreements to provide temporary emergency services or standby services to organizations or governmental agencies requesting those services.