30 CFR §75.1908

1. (a)Heavy-duty diesel-powered equipment includes—
   1. (1)Equipment that cuts or moves rock or coal;
   2. (2)Equipment that performs drilling or bolting functions;
   3. (3)Equipment that moves longwall components;
   4. (4)Self-propelled diesel fuel transportation units and self-propelled lube units; or
   5. (5)Machines used to transport portable diesel fuel transportation units or portable lube units.
2. (b)Light-duty diesel-powered equipment is any diesel-powered equipment that does not meet the criteria of paragraph (a).
3. (c)For the purposes of this subpart, the following equipment is considered attended:
   1. (1)Any machine or device operated by a miner; or
   2. (2)Any machine or device that is mounted in the direct line of sight of a job site located within 500 feet of such machine or device, which job site is occupied by a miner.
4. (d)Diesel-powered ambulances and fire fighting equipment are a special category of equipment that may be used underground only in accordance with the mine fire fighting and evacuation plan under § 75.1502.