Unattended : Any machine or device that is not regularly operated by a miner or not in direct line of sight of a miner that is assigned within 500 ft of the equipment during each production shift
NFPA 120 Standard for Fire Prevention and Control in Coal Mines, 2004 ed. http://catalog.nfpa.org/NFPA-120-Standard-for-Fire -Prevention-and-Control-in-Coal-Mines-Prior-Years- P4167.aspx, (Std: FrPrev and Control in Coal Mines - Amer) {252 NFC}