(A) Underground use of inby and outby diesel-powered equipment, including mobile equipment, stationary equipment and equipment of all horsepower ratings, shall be approved, operated and maintained only as provided in this chapter, except for emergency fire-fighting equipment to be used specifically for that purpose.
(B) All diesel-powered equipment shall be attended in underground mines while in operation or when the engine is running.
(C) Inby and outby diesel-powered equipment may be used in underground mines if the inby or outby diesel-powered equipment uses an engine approved or certified by MSHA, as applicable, for inby or outby use, that when tested at the maximum fuel-to-air ratio, does not require an MSHA 30 C.F.R. Part 7 approval plate ventilation rate exceeding seventy-five cubic feet per minute (cfm) per rated horsepower. Should MSHA promulgate new regulations that change the 30 C.F.R. Part 7 approval plate ventilation rate, the cfm requirement per rated horsepower will be either increased or decreased on a direct ratio basis as approved by the chief.