Mining Contract: Leaky Feeder Mine Communications System
The objective of this contract is to investigate techniques to increase the survivability of leaky feeder communication systems. Leaky feeders are two-way radio systems that feature a base station on the surface that communicates with underground radio units, such as walkie-talkie radios. To allow radio frequencies to function underground, a special cable network is installed underground that is designed to "leak" signal. This allows two-way radio transmissions from underground to the surface.
Contract Status & Impact
Research and in-mine tests were conducted to investigate techniques for hardening and redundancy to make a leaky feeder mine communications system survivable.
- Hardening - Hardening involved improving the ability of the system cable and components to survive and to continue to perform after mine incidents. Some investigated techniques included: cable installation methods, cable stress relief, burying or covering leaky feeder cable, component fire protection, and putting leaky feeder cable in conduit or integrating a messenger.
- Redundancy - For redundancy, after a mine incident occurs and communications are lost in the area, a miner can walk a short distance from the affected area and still communicate with the surface. Techniques investigated included: a loop-around scheme with multiple base stations located at different surface locations, running independent leaky feeder cables in multiple entries, and using antennas and low-cost cables for coverage extension.
The resulting system design uses a Becker Mining Systems ultra high frequency (UHF) leaky-feeder communications system enhanced dramatically to improve its post-accident survivability. The system was installed on a mine-wide basis at the Consol Energy Loveridge Mine for long-term evaluation. It spans an underground distance of 8 miles from the belt slope to the mining sections. Enhancement techniques include:
- Redundant loops to the surface - With a redundant loop, primary and secondary base stations are connected by overland, fiber-optic links, providing alternate communications paths to achieve redundancy. Two redundant loops, which utilize the belt slope and two airshafts, are used in the Loveridge installation.
- Redundant UHF trunks in parallel entries - Since access to the surface is not available beyond the most inby airshaft, redundancy is achieved by installing completely independent UHF leaky-feeder cables in parallel entries, one in the track and another in the belt.
- Coverage extension using low-cost cabling and antennas - With the redundant loops, communication coverage is extended to the belt entry by using low-cost, VHF leaky feeder cable coupled to the main UHF leaky-feeder cable in the track entry. In addition,with redundant UHF trunks in parallel entries, communication coverage is provided in the parallel escapeway by placing antennas in that entry, alternately connecting the antennas to the track and belt leaky-feeder cables. This provides communication in the escapeway if either the track or belt entry leaky-feeder cable becomes non-functional.
Successful demonstrations were conducted for industry, labor, and government partners. Various failure modes were injected in the system to simulate mine emergency events. The system performed as designed, providing communication on either side of the simulated fault to the mine surface and between the two underground locations. The successful, full-scale demonstration of this technology represents a major milestone in NIOSH’s efforts to improve mine emergency communication
This contract is completed. NIOSH will continue to monitor the operation and performance of this installation as the Loveridge Mine uses it as its primary mine communication system.