California Code, Labor Code - LAB § 7959

Rescue crews shall be familiar with all emergency equipment necessary to effect a rescue or search for missing employees in case of an accident or explosion.  Such rescue crews shall hold practices with equipment and using emergency rescue plan procedures at least once monthly during construction or operation of the tunnel or underground mines.  At least one rescue crew shall be maintained above ground at all times and within 30 minutes travel of the tunnel or underground mine site classified as gassy or extrahazardous.