Wireless communication systems give mining rescuers eyes and ears below the earth
As communication is paramount for a speedy and safe underground mine rescue operation, the industry is abandoning easily severable wire-linked underground communication technology in favour of wireless options. But which are the best technologies currently available?
The Turkish disaster that tragically claimed the lives of more than 300 miners working in Soma Holdings's coal mine in May 2014 emphasised the importance of communication technology in the event of an emergency underground.
Not only can sufficient communication tools raise the alarm about potential or current danger, they can also aid recovery by showing the location of individuals and equipment to rescuers on the surface.
Traditionally, communication systems underground relied on some kind of wire-line communication principle, known as a leaky feeder. Due to these systems' need for physical connectivity, they can be easily destroyed in the event of an explosion. Therefore wireless systems using radio-frequency identification (RFID) and through-the-earth-technologies are now more common place in underground mines.
BT - streamlining connectivity underground
British Telecoms (BT) Industrial Wireless provides wireless communications for use in industrial settings, including tools for underground mines. Currently in use in a number of platinum mines, BT Industrial Wireless uses mobile mesh technology which connects communication access points wirelessly via radio frequency (RF) instead of physical cabling. The information is then fed up to a central network and then connects with the central mine system or a data room at the mine.
An upgraded version of the technology, which has more access points, is capable of self healing, meaning that if one or several access points break down the network will still work. The technology also reaches what is known as layer 2 - a layer below the IP layer - and therefore intelligence is done locally rather than at the central controller on the surface.
The self-healing capability of Industrial Wireless is important in an emergency situation because if several of the access points are destroyed in an explosion, communication will still be possible and those above the surface will be able to identify which points are down.
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Meanwhile, BT's Trace technology is useful for collision avoidance and knowing where miners are in the event of an accident. It's a non-traditional RFID technology that uses real-time location services via a number of wireless sensors that can be embedded in a jacket, cap lamp or machine. It tags the sensor to the wireless network to identify where that particular asset is and then sends the data back to the central control room, which has a single glass view of all the operations happening down in the mine.
Gilat Satcom - outdoor satellite quality underground
In June, Gilat Satcom, a leading provider of fibre-based connectivity services, announced the launch of a new system that promises high-quality connectivity to underground miners.
The SuricatePRO system provides coverage extension for standard satellite phones extending telephony underground without loss of signal quality.
According to the company, the technology is easy to implement as customers only need to install outdoor and indoor units connected via fibre cable (up to 6km long). Users will then be able to access the Iridium constellation, a large group of satellites providing voice and data coverage to satellite phones, "as if they had clear sky view".
The technology, which takes advantage of Foxcom's RF-over-fibre technology, whereby light is modulated by a radio signal and transmitted over an optical fibre link to facilitate wireless access from the same antenna, was originally used in underground bunkers operated by military forces for a number of years. Gilat has now adapted the technology for the harsh conditions of an underground mine.
At the time of its launch, Gilat Satcom CEO Dan Zajicek said: "Communicating with workers in underground mines has always been problematical. Our system is extremely reliable, cost-effective and market-proven. We are actively reaching out to mining companies in Africa where we know our system will be of great benefit."
Rescue Dog - new emergency response technology
Rescue Dog has developed a 'highly survivable' post-accident through-the-earth communication system for mine disaster communication.
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The technology, which is pending US Mine Safety and Health Administration (MSHA) approval, consists of a surface unit combined with one or more subsurface units. The surface unit directly communicates with individual activated subsurface units, which means it can communicate with trapped miners, while continually listening for emergency beacons from all additional subsurface units.
The subsurface unit is battery-powered, with enough power to lay dormant for several months. It is housed in an explosion-proof enclosure and is best located in rescue chambers, along mine escape ways, near emergency equipment storage areas or at any point which may be critical during an emergency mine evacuation.
Once the subsurface unit is activated, an emergency beacon is automatically sent to the surface. This beacon continues to periodically transmit until it is acknowledged from an operator at the surface.
Once acknowledged, the subsurface unit is automatically commanded to change to its unique frequency for direct communication with the surface team. If the surface unit is powered up after the emergency beacons are initiated, time tag information is transmitted to the surface to show how long each subsurface unit has been sending emergency beacons.
The Rescue Dog system is omnidirectional and doesn't use conventional loop antennas like other through-the-earth communication equipment, so it is easy to install and there is no need to wrap wires around coal pillars or install large surface loops; however it must be well grounded.
Lockheed Martin - first MSHA-approved through-the-earth-system
Developed in response to 2006 MSHA requirements for better post-accident emergency communication technology, Lockheed Martin's MagneLink technology allows rescuers to communicate directly with trapped miners.
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MagneLink is an MSHA-approved system that provides two-way through-the-earth communication independent of surface or in-mine infrastructure. It uses voice, data and beacon signals to enable communication between rescuers and trapped miners when no other communication system will work.
The layers of rock above a coal mine reduce the strength of any signal that is sent through it, so special signal processing is required to pick up the weak signal and decode the original information.
When a message is sent the system's transport antenna is energised and creates a bubble. The message then bubbles up to the surface and creates a dome of magnetic energy there. If another MagneLink system is nearby it will pick up the message and relay it. The system works at distances ranges up to 1,500ft from subsurface to surface, and 2,500ft horizontally within the mine.
The technology was made in partnership with CONSOL Energy in 2012, and is distributed by Delta Electric.
"The MagneLink MCS is a significant step forward in mining safety technology," said Todd Moore, CONSOL energy's safety director, at the time of its launch.