Mine Rescue and Survival Interim Report (1969) / Chapter Skim
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Appendix B: Communications Subsystem
Appendix B: Communications Subsystem
Pages 22-49
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From page 22... ...
The signals from these transceivers would be relayed by telephone wire to the surface after being converted from the transmitted frequency to a phone line frequency by one or several relay stations underground. To be practical, the relay stations would have to have a range of 1, 000 to 2, 000 ft over which they could receive the transmissions from the portable transceivers.
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From page 23... ...
At frequencies around 1 MHz, where it may be possible to use standard portable transceivers, a skin depth will be of the order of 300 ft in coal and 50 ft in the overburden. In a distance of seven skin depths, a radiated signal is reduced by a factor of 1, 000 by attenuation, and this constitutes a practical limitation for detection with a sensitive receiver.
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From page 24... ...
However, antennas such as might be used on a portable transceiver in a mine opening are very inefficient at these lower frequencies. There is probably an optimum frequency not too far from 1 MHz where the increasing inefficiency of antennas at lower frequencies offsets the increasing penetration obtained.
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From page 25... ...
Power would be applied to either a grounded wire or to a coil of wire. Surface searchers would spot the source of the field and then communicate with the trapped individuals by laying out a large coil on the surface and transmitting downward with high power.
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From page 26... ...
The individual would have to choose a spot with good contact properties, and it may be necessary to provide some sort of meter on the equipment to assure that sufficient current is being driven into the ground to be seen by surface searchers. Surface search equipment would consist of a search coil, if the source is a coil, connected to a sensitive turned voltmeter.
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From page 27... ...
- 27 After this evaluation, parametric trade-off studies, development of prototype beacon and surface equipment, and tests of the prototype should be conducted. Tests of the prototype system should be conducted in all major coal producing areas of the United States to assure penetration of the different overlying formations with sufficient strength that the signal can be detected from a point over the beacon.
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From page 28... ...
Accuracy of only a few hundred feet will be required if each section of the mine is equipped with refuge chambers. The mine map can be used for exact location of the chambers and seismic signals will be used only to determine which of the chambers are occupied.
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From page 29... ...
Location is accomplished by an analysis of the relative arrival times of seismic signals at various elements of a large seismometer array. Two-way communication is achieved through a simple code based on sequences of hammer blows.
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From page 30... ...
This single channel output is transmitted by 1, 320 ft of 2-conductor shielded cable back to the recording equipment at the center of the large square array. Cables are laid out and picked up using portable breast-reels commonly used for seismic exploration work in areas not accessible by trucks.
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From page 31... ...
Tests could then be quickly performed to determine the proper subarray size and configuration for maximum noise rejection. Subarray velocities could also be accurately measured at that time by hammering at selected points in the mine.
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From page 32... ...
will permit rapid array deployment with enough configuration control to permit signal detection and a preliminary rough estimate of the miners' location. It is expected that after signal detection and rough location, the array would be moved so as to be centered over the estimated location and substantially reduce in size.
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From page 33... ...
If not, the four subarrays may be moved to a point above the best location estimate and combined to give a single output with an improved SNR. When ready to communicate, a series of hammer blows on the ground surface will tell the miners that they have been located, that they should stop sending their location code and start sending the prearranged coded message regarding their condition, etc.
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From page 34... ...
Seismic signals have been recorded by down-hole seismometers with a very high SNR at depths of 5, 000 ft. An experiment in shallow refraction seismology has shown good signal amplitudes from hammer blows obtainable with single seismometers at ranges of Z50 meters.
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From page 35... ...
Measurements of seismic velocities and characterization of the ambient noise field in the 25- to 50-Hz band at each mining region prior to emergency use of the system is recommended. Optimum subarray size could be determined, signal velocity more accurately measured, and detection range determined.
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From page 36... ...
Subsurface System The number of subsurface devices required for adequate protection will depend on the size of the mine, the number and distribution of underground crews, and the number and distribution of shafts and refuge chambers. The Bureau of Mines should set the requirements for the number, distribution, and type of subsurface devices.
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From page 37... ...
I , "A New Instrument for Seismic Exploration at Very Short Ranges, " Geophysics, Vol.
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From page 38... ...
In the past six years, men have been trapped in salt mines, potash mines, and tunnels. Although coal mines probably have the highest safety standards of all underground workings, the hazards are greater because most coal seams produce explosive methane gas; coal dust suspended in air is explosive; the coal will burn; coal naturally occurs in fairly weak sedimentary formations in which roof falls are common; and more tons of coal are produced than any other mineral.
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From page 39... ...
3. Employ miners that are trained, if escape seems impossible, to enter refuge chambers if provided or to seek refuge in a deadend entry, barricade themselves, and wait for rescue.
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From page 40... ...
2. Provide a rescue drill capable of: a.
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From page 41... ...
Since the drilling rigs described here are available and can be in use prior to the rest of the proposed system, the following discussion applies to mines without refuge chambers or location beacons. The simplification or elimination of the steps below if the other subsystems are in use is obvious.
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From page 42... ...
The heavier rescue rig would have been dispatched to the drilling site. It may start drilling even before the exploratory hole has found men on the chance that a hundred feet or so of hole may be drilled in a location to which the men may be able to travel.
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From page 43... ...
The hole wall condition could be examined by a down-hole still camera taking pictures every 5 ft or by continuous inspection with a remotely controlled television camera. The large hole would be drilled in one pass.
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From page 44... ...
It should have four forward rotary speeds of about 25, 50, 75, and 150 rpm and one reverse speed of about 30 rpm. There are approximately ten manufacturers of truck-mounted rotary drill rigs and many of them make rigs that would require very little modification to do the exploratory work.
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From page 45... ...
Most coal mines are laid out on a room and a pillar or a panel mining plan. The exploratory hole will be aimed at a mine entry about 20 ft wide between two coal pillars that may be 30 to 80 ft wide.
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From page 46... ...
Reverse air circulation would be used. A 10- to 15-ft-deep cellar would be dug by hand.
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From page 47... ...
- 47 Baskets with a 16-in. outside diameter to surround the lower section of the drillstring should be provided as drill collars.
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From page 49... ...
4 1 TN23 .M56 1969 c.l Mine rescue and survival interim report /
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