Va. Code § 45.2-824
Diesel-powered equipment may be utilized underground with the written approval of the Chief. The Chief shall adopt regulations necessary to carry out the provisions of this section. Such regulations shall require that the air in each travel way in which diesel equipment is used, and in any active workings connected thereto, be of a quality necessary for a safe, healthful working environment. The minimum quantity of ventilating air that shall be supplied for a permissible diesel machine in a given time shall conform to the quantity shown on the approval plate attached to the machine. Every diesel machine or piece of equipment shall be maintained in such manner that the exhaust emissions meet the standards to which the machine or equipment was manufactured.
Va. Code § 45.2-824