Mining Telephones and Signaling Devices for Mining Operations
Posted on 05/03/08 @ 9:23pm by
Max Griffin
Working in the mines is tough, hard work. It has many hazards and dangers that come with working underground. Gas and dust, low oxygen, equipment failures, Power outages, cave-ins. just to name a few. One of the most important safety features in the mines is the telephone and or signaling devices, They are something you depend on, you expect them to work at all times. You need to know they are in perfect working order, and made for the situation at hand. I want to go over the things you need to look for when installing and operating telephones and signaling devices in the mines. These are often lifelines from trapped miners to the safety crews above. So it is of the utmost importance to check and inspect these devices before each shift enters the mine. You can't be too cautious when it comes to the lives of your miners.
Telephones and signaling devices must be made durable in their construction, easy to operate, and suitable for the rugged conditions of underground work. They will not have an explosion hazard under normal conditions if used in gassy or dusty mine atmospheres.
Specific Requirements for Approval of Telephone and Signaling Devices.
The circuits external to telephones and signal devices shall be intrinsically safe; Which means, the electrical design and construction of the telephones and signal devices shall be such that neither contact between wires of the external circuits or contact with tools or other metal objects with external terminals and circuits will result in electrical sparks capable of igniting an explosive methane-air mixture (or such mixtures of coal dust in suspension) during normal operation of the telephones or signal devices.
All parts used during normal operation which are capable of producing sparks that might ignite explosive methane-air mixtures must be enclosed in explosion-proof compartments. All openings in the casings of such compartments shall be adequately protected. It is recommended that openings be as few as possible. All joints in the casings of an explosion-proof compartment shall be metal-to-metal, and designed to have a width of contact, measured along the shortest path from the inside to the outside of the compartment, of not less than 1 inch if the unoccupied volume (air space) in the compartment is more than 60 cubic inches. For unoccupied volume of 60 cubic inches or less, a 3/8-inch width of contact will be acceptable.
All bolts and screw holes shall be "blind" or bottomed if the omission of a bolt or screw would otherwise leave an opening into the compartment. An adequate lock or seal shall be provided to prevent tampering and possible exposure of spark-producing parts by unauthorized persons.
Battery cells must be placed in an explosion-proof compartment or in one that is locked or sealed, and the terminals and the connections shall be arranged and protected so that no meddling, tampering, or other electrical connections can be made with them.
Manufacturers must furnish adequate instructions for the installation and connection of telephones and signal devices so that the safety of these devices and other circuits will not be diminished by improper installation. MSHA reserves the right to require the attachment of wiring diagrams to the cases of telephones and signal devices.
If electric light bulbs are used in signaling devices, they will either be equipped with effective safety devices, such as are required for permissible electric mine lamps, or enclosed in explosion-proof compartments. (In this case, the requirements of the current schedule for mine lamps will apply.)
Line powered telephones and signaling devices or systems will be equipped with standby power sources that have the capacity to enable the devices or systems to continue functioning in the event of power failures, or emergency cut offs. Manufacturers must furnish instructions for the proper maintenance of standby power sources.
Isolation or insulation of communication conductors
Telephone and low-potential signal wire shall be protected, by isolation or suitable insulation, or both, from contacting energized power conductors or any Mineother power source.
Communication conductors on power pole
Telegraph, telephone or signal wires shall not be installed on the same crossarm with power conductors. When carried on poles supporting powerlines, they shall be installed as specified by the National Electrical Code.
Lightning protection for telephone wires and ungrounded conductors.
Ungrounded power conductor or telephone wire that leads underground and is directly exposed to lightning shall be equipped with suitable lightning arrestors of approved type within 100 feet of the point where the circuit enters the mine. Lightning arrestors shall be connected to a low resistance grounding medium on the surface and shall be separated from neutral grounds by a distance of not less than 25 feet.
Hoisting procedures
When a manually operated hoist is used, a qualified hoistman shall remain within hearing of the telephone or signal device at all times while any person is underground.
Signaling
There shall be at least two effective approved methods of signaling between each of the shaft stations and the hoist room, one of which shall be a telephone or speaking tube.
Communication with refuge chambers.
Telephone or other voice communication shall be provided between the surface and refuge chambers and such systems shall be independent of the mine power supply.
Each automatic elevator should be provided with a telephone or other effective communication system by which aid or assistance can be obtained promptly.
Telephone or other suitable communications should be provided at points where men or supplies are regularly loaded on or unloaded from the belt conveyors.
Communication facilities; main portals; installation requirements.
Telephone or equivalent two-way communication facility shall be located on the surface within 500 feet of all main portals, and shall be installed either in a building or in a box-like structure designed to protect the facilities from damage by inclement weather. At least one of these communication facilities shall be at a location where a responsible person who is always on duty when men are underground can hear the facility and respond immediately in the event of an emergency.
Telephone service or equivalent two-way communication facilities, shall be provided between the surface and each landing of main shafts and slopes and between the surface and each working section of any coal mine that is more than 100 feet from a portal.
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