In the interests of mine safety and productivity, it is vital that operators are continuously aware of underground conditions and risk profiles, particularly in light of the recent mine collapse at Crandall Canyon Mine in August 2007. The mine made headline news when six miners were trapped by a collapse in August 2007. Ten days later, three rescue workers were killed by a subsequent collapse. Although this disaster was believed to be primarily due to a lack of escape routes, it gets everyone’s attention focused on all coal mine safety issues including communications.
Coal mine operators must be able to locate and communicate with mine workers at all times - particularly in the event of fires, roof falls or other life-threatening situations. It is equally critical that these communication systems stay active during power outages, fan stoppages or gas accumulations.
CSIRO, the Commonwealth Scientific and Industrial Research Organisation, Australia's national science agency, recently visited more than eight underground coal mines to discuss the types of issues confronting surface Control Room operators. A number of common issues were identified including:
- The large variety of diverse and proprietary communication systems that were in use at each site
- Large numbers of system-generated false and misleading alarms
- Time delays in locating and contacting individuals
- A cumbersome manual statutory reporting system
- Extreme workloads in emergency situations
This article provides a brief review of mine communications manufacturers, and the concepts and technologies.
Today's communication systems used in underground coal mines generally employ a hard-wired system or a special cable called a "Leaky Feeder". Fiber optic cables are also used in some applications. Through-the-earth (TTE) and wireless radio systems are less common.
The following will discuss the advantages and disadvantages of various mine communications systems.
Presently Available Through-The-Earth (TTE) Communication Systems
A TTE system likely will have the best chance of providing contact with miners since it offers the best resistance to damage from roof falls, fires and explosions. There are several companies who offer TTE systems. Most are limited to communication from surface-to-underground. Only one system provides communications both surface-to-underground and underground-to-surface, but it is not a portable system. A brief description of each product is provided below.
Flexalert – Mine Radio Systems - Canada
Safety is very serious business, and FLEXALERT offers the fail-safe solution. FLEXALERT replaces the need for stench gas, by facilitating rapid and reliable emergency evacuation, paging and restricted area warnings: employing the latest low frequency telemagnetic technology, the signal can penetrate miles of soil and rock, without any cable. It's easy to install, and generates a single alarm throughout your operation. Click here for more technical information.
PED – Mine Site Technologies - Australia
PED is a through-the-earth communication system installed in over 120 mines. PED's unique ability to transmit directly through hundreds of meters of rock strata enables it to provide true mine wide signal coverage. As such PED is used in many mines as the primary emergency warning system, as well as a general day-to-day communication system.
PED's emergency warning capability is well documented by MSHA, having been credited by MSHA and mine officials as being instrumental in saving five lives at Willow Creek Coal Mine in 1998.
A range of receiver types increases the application of PED to more than just personal paging, as it is also extensively used for remote equipment control and remote blast initiation (see BlastPED below). More information can be found here.
TeleMag - Transtek – United States
TeleMag is a wireless through-the-earth two-way voice and data communication system. It operates at 4 kHz. It is a station-to-station system with limited portability. The underground and surface antennae consist of 60-ft diameter loops. It has been tested to depths of 300 feet. The first demonstration of a prototype system was in August of 2000 (Conti, 2000) at the NIOSH Lake Lynn Laboratory mine. The manufacturer claims installations in several non-coal underground locations.
Other Coal Mine Communication Systems
If you’re interested in learning about underground safety InfoMine’s EduMine offers the following course: