California Code, Public Utilities Code - PUC § 7724.1

(a) If a person reasonably, and in good faith, believes that the directions or orders given by the secretary or the commission would substantially endanger the public safety or the environment, the person may refuse to act in compliance with the orders or directions of the secretary or the commission. The person shall state, at the time of the refusal, the reasons why the person refuses to follow the orders or directions of the secretary or the commission. The person shall give the secretary or the commission written notice of the reasons for the refusal within 48 hours of refusing to follow the orders or directions of the secretary or the commission.

(b) In any civil or criminal proceeding commenced pursuant to Section 7724, the burden of proof shall be on the responsible party or potentially responsible party to demonstrate, by clear and convincing evidence, why the refusal to follow the orders or directions of the secretary or the commission was justified under the circumstances.