Recent tragedies at the Sago Mine, the Aracoma Alma Mine, and the Darby Mine have brought renewed attention to an old problem: situational awareness in mine emergencies. Improved communication is a partial, but not a complete, solution to the problem. Mine emergencies often involve dense smoke and dust that impair visibility and disorient even those familiar with the mine layout. Additionally, miners overcome by carbon monoxide cannot communicate useful information to potential rescuers. Location awareness is an important aspect of the overall problem of situational awareness.
In too many cases, mine fatalities might have been avoided if rescuers knew the location of trapped or disabled miners.In the event of trouble, knowing the precise location of the miners at risk can greatly assist rescuers. The more quickly the rescue team can reach miners at risk, the more likely the rescue operation will be successful.
Currently, there is no technology capable of determining the precise location of underground miners. Interim location solutions being rushed into mines in the wake of recent tragedies are unlikely to provide the necessary precision and performance. The results of the present effort indicate that Near-Field Electromagnetic Ranging has great promise for providing accurate real-time location information of miners.
Near-Field Electromagnetic Ranging
Since 2002, the Q-Track Corporation has been pioneering a novel approach to real-time location systems (RTLS) called Near-Field Electromagnetic Ranging (NFER®) technology. Operating in the AM broadcast band (530-1710kHz) under Part 15 power levels, NFER® systems achieve tracking accuracies on the order of 1-3ft (30cm-1m) or better at ranges of 100-200ft (30-60m) in complicated indoor environments. NFER® systems take advantage of the far greater complexity of near-field signals to track on multiple signal characteristics such as the phase difference between electric and magnetic signal components. By transmitting at the higher power levels allowed in coal mines and operating at lower frequencies, range can be extended substantially relative to what Q-Track has achieved in above-ground tracking. We chose 575kHz as a good starting point for initial prototypes and testing.
Current NFER prototypes could be the basis of a tracking system with a range of about 150-200m (450-600ft). Reasonably foreseeable improvements could substantially extend the range to about 600-800m or 1800-2400 feet. With this kind of range, we can envision deploying a relatively limited number of receivers and obtaining accurate location information throughout mines of substantial size.