California Code, Labor Code - LAB § 6313

(a) The division shall investigate the causes of any employment accident that is fatal to one or more employees or that results in a serious injury or illness, or a serious exposure, unless it determines that an investigation is unnecessary. If the division determines that an investigation of an accident is unnecessary, it shall summarize the facts indicating that the accident need not be investigated and the means by which the facts were determined. The division shall establish guidelines for determining the circumstances under which an investigation of these accidents and exposures is unnecessary.

(b) The division may investigate the causes of any other industrial accident or occupational illness which occurs within the state in any employment or place of employment, or which directly or indirectly arises from or is connected with the maintenance or operation of the employment or place of employment, and shall issue any orders necessary to eliminate the causes and to prevent reoccurrence. The orders may not be admitted as evidence in any action for damages, or any proceeding to recover compensation, based on or arising out of injury or death caused by the accident or illness.