Collisions between pieces of equipment as well as between equipment and workers frequently occur inside underground tunnels, owing to limited visibility coupled with a confined work environment. To address this problem, a Bluetooth-beacon-based proximity warning system (PWS) capable of preventing collisions inside underground tunnels has been proposed. The proposed PWS receives signals from Bluetooth beacons attached to bodies of mine workers and/or their equipment via smartphones installed in vehicles, thereby providing drivers with primary (caution) and secondary (warning) alerts in stages, based on the intensity of received signals. After identifying suitable received signal strength indicator (RSSI) threshold values corresponding to the caution and warning zones, a field test was performed inside an underground tunnel based on results obtained from a preliminary experiment. Using collective results obtained during 50 experimental repetitions, the accuracies of the first and second alert occurrences in the caution and warning zones were determined to be 93% and 95%, respectively. The proposed Bluetooth-beacon-based PWS was demonstrated to be effective for preventing collisions inside underground tunnels. In addition, the proposed system is relatively inexpensive, and its functions can easily be extended via the use of smartphone applications.
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