Mines generally use reliable and effective communications systems for routine operations, but these systems require hard-wired networks, power supplies, and other infrastructure that are likely to be damaged by a catastrophic event, such as a fire, explosion, roof fall, or water inundation. Technologies are needed that will enable communications systems to function in post-disaster environments. Additionally, prior to the MINER Act, communications were only required at select locations in the mine leaving a large percentage of the mine area where communications was not required and generally not available. Systems are also needed to track the locations of mine workers during rescue operations. However, an electronic tracking system requires a reliable communications signal to relay location information to the surface. Technical barriers to in-mine or through-the-earth signal propagation must be overcome before reliable emergency communications and miner tracking will reach acceptable functionality. The post-disaster coal mine environment creates unique safety and survivability considerations for emergency mine communications and tracking systems. This page summarizes those issues and presents an overview of mine communications and tracking technologies. More detailed information is available from communications and tracking research papers listed on the Emergency Response and Rescue Downloadable Mining Publications page. Mine CommunicationsPresent communications systems for underground mines can be hard-wired or wireless. Each approach has certain strengths and weaknesses. Post-disaster procedures create unique challenges in a coal mine environment for either type of system. Underground coal mines are subject to the build-up of methane gas unless there is continual ventilation of the mine. When a disaster occurs, power to the mine is often cut and ventilation controls are sometimes compromised. This safety issue must be addressed when designing wireless communications for underground coal mines (i.e., the systems must not create sparks that could ignite a gassy atmosphere). Such permissible designs usually limit the output power of devices, making transmission from the mine to surface more challenging. The common practice of cutting power introduces another concern; providing power to electronics during a disaster will require backup power supplies. NIOSH is focusing on low-voltage power supply technologies and related issues through a multi-discipline Working Group. Communications systems must also be able to survive a disaster. Mine disasters such as explosions and roof collapses release destructive forces that are hard to imagine. In some cases, the forces have been so strong that it is unlikely that any exposed components would have survived over thousands of linear feet of mine entries. As other communications systems have done for years, mine communications systems will need to achieve survivability and reliability through hardening and system redundancy:
Wired CommunicationsWired communications require the miner's device to be tethered to some type of cabling to carry voice and or data. Examples include twisted pair, coaxial cable, CAT5 and fiber optic cables, and trolley wire (normally used to power mine locomotives, but it can also act as conveyor for medium frequency signals). Hardware includes dedicated telephones, walkie-talkies, paging devices, and similar technologies. While sufficient for routine mine communications, cables are very vulnerable as they can be destroyed or rendered inoperable by fires, explosions, roof falls, battery failure, or mine electrical power failure. Additionally, relying on wired communications such as mine phones leaves vast areas of the mine where a miner that is injured or trapped will have no communications to the surface or rescue personnel. Wireless CommunicationsWireless communications allow communications with a miner without the need for a tethered wire. Wireless communications (walkie talkie and cell phone functionality) are a unique challenge in underground coal mines. Not all radio signals will propagate down a coal mine entry due to the electrical properties of the coal and surrounding strata.
The attributes of the various parts of the radio spectrum are discussed more fully in the various papers in the Emergency Response and Rescue Downloadable Mining Publications page. Combining the attributes of the various wireless frequencies and systems could provide a survivable mine-wide wireless communications systems but would require that the systems are interoperable. The NIOSH Communications Road Map (PDF, 955 KB, 2007) provides an example of how such a system could work. Miner TrackingAnother issue is being able to identify the location of miners in the event of a mine emergency. Miner tracking systems use wireless communications technology and can be integrated with communication networks. There are three types of tracking systems. All rely on a communication link to the surface that may be susceptible to damage from explosions, fires, or roof falls.
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