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MINE SERVICES |
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Communications |
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Communications
As in the world at large, major changes in communications within coal mines has been seen over recent years, although satellites have naturally had little impact on underground systems. For many years telephones were the only means of verbal communication across mines and from underground to surface, often with several phones on a common line (not a big problem but known to cause embarrassment at times). Other limited signaling systems such as bells or lights in shafts or along haulage systems existed but were limited in extent and in messages able to be sent.
The use of longwalls led to the development of voice communications using speaker sets spaced across the face area (generally known as "DAC" systems). Such systems are now commonly utilised on conveyor belts throughout the mine.
Two way radios for mine wide use have been developed, relying often on aerials run along roadways around the mine and/or on "leaky feeder systems" which enabled power cables installed around the mine to be used as aerials. Reception is usually limited to a fairly short distance from aerials or cables (radios can usually receive messages from a base station for a greater distance than they can transmit, so personnel can be called to an alternative system to communicate fully). The effectiveness of these systems relies on the aerial being well maintained.
Conventional two-way radios, adapted for use in mines, can be used over limited distances (generally line of site or close to it), and are commonly used for communication with drift transports and more frequently now being used by such people as surveyors, personnel installing major items, shaft top to bottom, etc.
Modern telephone systems can be used for calls to multiple locations (e.g. to give an emergency warning to several locations at once) and can often be connected to external phone systems if required. Permanent connection is possible, but control of unauthorized phone calls could be problematic.
A system widely used now, known as a "PED" system allows short word messages to be sent via personal cap lamps. The person's attention is attracted by the cap lamp flashing and the message appears on a LED screen on the cap battery. Messages can be sent to individuals, specified groups or generally. This system also relies on an aerial, though this can be run as a loop on the surface if surface conditions are amenable.
To an increasing extent, individual communication systems are being connected to others by various means to effectively increase their range or use (e.g. DAC systems being connected to control rooms).
Audible and/or visual signaling systems are still widely used to communicate safety messages such as pre-start alarms on conveyors, transport operating in drifts, reversing alarms on vehicles, etc, though many people would not include these in communication systems.