Bringing safety to underground mines

Traditionally, the basic mobile communication requirements of underground mines have been analog two-way voice radios and low-speed data links. With the tremendous development of open standard data communication products, safety and monitoring systems and protocols for wired and wireless applications, TCP/IP and 802.11 are now the de facto standards. These standards have paved the road for the realisation of the mines’ high-speed communications systems.

Historically, the mining industry has been very slow at adopting new technologies such as monitoring and trapped-miner search systems. Early mine technologies were focused on monitoring equipment, atmosphere, fire and conveyors.

Over the last 30 years this approach has drastically changed. Mining injuries and fatalities have decreased dramatically, due, in part, to tighter government regulations and standards combined with the increase in communications, safety and monitoring.

Mining operators are now regulated more strictly and work actively to improve communications, working conditions and increase safety for their employees.

The Mine Improvement and New Emergency Response Act 2006 (MINER) sets the regulatory limits for communications, tracking and search systems for mine operators. The result of these advancements can be seen in a steady decrease in fatalities, injuries and illnesses within the industry.

The increased demands for reliable communications, safety and monitoring systems in underground mines and tunnels have stimulated the need for capable infrastructure and communication protocols.

To design communications and safety solutions for coal mining, it takes more than just technology - it takes underground intelligence and expertise in communications, safety and asset monitoring.

Mine Radio Systems (MRS) is a major supplier of what it claims are the world’s most advanced, performance-driven, scalable and reliable communications technologies. Over the last 25 years it has been geared to improve efficiency, underground to surface communications, safety, monitoring and productivity in the mining and tunnelling industries.

An example of the company’s expertise has been the installation of equipment for a large mine operator in Central America.

With the construction of two portals about 4270 and 2400 m, the need for an effective, reliable, rugged communications, safety and monitoring system was established.

The requirements included two-way voice communications, portable and mobile radio capabilities, video and UHF surface links. The solution, which needed to be implemented, had to be capable of future mine expansion and future safety regulatory expansion, without the cost and production loss of a new system. The company installed FLEXCOM which allowed for future expansion of the mine and future, stricter regulations. The new system supported all voice, video and data operations simultaneously, giving the mine operator confidence to move forward with expansion.

As the mine expanded, a new borehole was begun that added another 4300 m portal, leading to the need to increase the communications system. Additional voice, video and data systems were installed and integrated into the initial system, which was then operating four individual voice channels and four analog video channels.

Due to the distance between the mine portal and the control room, UHF links were included to allow communications to the underground working areas from the control room. The video channels were used to visually monitor the conveyor belts leaving the mine.

As construction continued, both working areas were reached underground and head ends were moved to the upper main areas on the surface and combined together. A borehole was used to connect the leaky feeder cables underground. Four independent cables were fed through the bore hole, two of which feed the mains towards the portal and the other two which feed the mains towards the long wall to provide redundancy should one line fail.

This allows for straightforward troubleshooting from the surface and simple repairs if necessary.

The overall scale of the mine posed a lot of challenges for the company. The size and distance between portals and surface areas caused a loss of communications as these locations were outside the surface coverage area of the new installation.

The solution was to install a repeater at the entry point at the north portal. This is a bidirectional device that communicates with the leaky feeder system underground as a portable radio would on channel 1 and then rebroadcasts it to the surface using a simplex frequency.

The surface simplex links for channel 6 and 7 were disabled to allow these frequencies to be used to create full-duplex surface repeaters for underground channels 1 and 3. This increased the range of radio-to-radio communication on the surface as well as maintaining the links to the control room.

A problem encountered was crosstalk from one channel to the others. This was caused by intermodulation problems between channels. The company conducted an intermodulation study to minimise the crosstalk and to eliminate the problem in the future. A new mine channel allocation table was created and all portable radios were reprogrammed to accommodate the new plan.

Unknown activity by personnel using PTT on portable radios is a very serious and potentially dangerous situation. This can occur in any mine at any time, causing a severe safety and communications issue. If a channel is locked up unknowingly by mine personnel and a situation occurs, all communications and safety alerts can’t be sent to miners underground.

The company needed to implement a solution to avoid this, so it introduced a push-to-talk ID system that allows management to determine who is locking out the channel and to pinpoint their location. Mine personnel could then be deployed to locate the individual to de-key the radio and free up the channel.

Over the last four years the Central American mine operator has been implementing solutions and upgrading its components to meet the requirements of the MINER Act. The FLEXCOM system will be replaced with MultiCOM that allows advanced diagnostics.

Since the opening of the Central American mine in 2000, it has grown to become one of the largest coal mines in the region, with a distance that covers 22 km needing to be supported by a communications solution.

With the new expansion, surface coverage is essential. MultiCOM allows all video, voice and data channels to be interconnected and broadcast above ground on simplex VHF links. The two main channels can broadcast on the surface over simplex UHF links which allows the surface workforce to communicate to mine personnel underground. This will allow the mine operators to monitor the health of the system from the control room promoting proactive maintenance and monitoring as against a reactive response.

The MINER Act now requires all new and current mining operation to comply with a set of regulations governing the required use of (a) two-way, radios, post-accident communications between underground and surface personnel, and (b) electronic tracking of underground workers.

As a result, a new upgraded solution was required immediately and the company is currently working with the mine to implement its Helian underground safety solution, where tracking beacons will be installed at all refuge stations and every 600 m feet along the mains, head gates and tail gate. On the working face, including the long wall, tracking beacons will be installed every 60 m. This allows the mine operators to know, at any given time, the last known location of all personnel in the mine.

As future expansion in the mine continues, the company is working closely with the mine operators to develop new and sophisticated solutions to increase the communications and safety for mine personnel.

The Helian safety and asset monitoring solution works seamlessly with MultiCOM and offers extra layers of safety. The monitoring includes a personal transponder and search unit that provide a means of locating trapped miners.

Mine Radio Systems

www.mineradio.com