Cal. Lab. Code § 7968

In any gassy tunnel or underground mine, the division may order work halted until adequate testing can be completed to determine the level of hazard from gases or vapors. A notice of such shutdown shall be filed by the division inspector with his superiors as soon as practicable. Any overruling of such order must be made by the chief or his designated representative and must be in writing. An onsite inspection must be made by the person overruling an inspector’s order prior to resumption of work.