Ariz. Rev. Stat. § 27-365
The underground use of any internal combustion engine is declared unlawful, unless after application filed with the inspector he approves the equipment for safe use in the type of underground work for which the application is filed and finds that the atmospheric conditions in the underground workings where the equipment is to be used are such that the operation of such equipment will not endanger the health or safety of any employee. If the application is approved by the inspector, the operation of the designated equipment shall be lawful only if and so long as it is operated and maintained in accordance with recommendations made public from time to time by the inspector, and only upon the condition that when air quality becomes unsafe operation of the equipment shall be stopped by the operator until air quality again becomes safe either by increasing ventilation or by correcting mechanical imperfections in the equipment, whichever is found to be the cause of the unsafe quality of the air.
A.R.S. § 27-365