Bureau of Mines Information Circular/l977 

Underground Mine Communications 

(In Four Parts) 

4. Section-to-Place Communications 

UNITED STATES DEPARTMENT OF THE INTERIOR 
lJNl'l'EI> STATES DEPARTMENT OF THE INTERIOR 

Cecil D. Andrus, Secretary 

HlJKEAU OF MINES 
This publication has been cataloged as follows: 

Pittsburgh Mining and Safctj Resclarcli Center 

Underground mine communications (in four parts) : 4. 

Section-to-place communications / compiled by staff-Mining 

Research, Pittsburgh Mining and Safety Research Center. 

[Washington] : United States Department of the Interior, 

Bureau of Mines, 1977. 

80 p, . ill, . 28 crn, (!nforrnation circular - k3ureau of Mines , 

87/r5) 

13ibliographie\- p, 29-30, 43, 02, 72, 70. 

1. hlinc cornmunit at ion sy stcms, I. United States, 13ureau of 

Xlines, 11- Title, 111.. Series. United State\, Hureau of \lines, 

lnformat ion c ~rc ular - 13ureau of Minc s : 8745. 

TN23.U71 no. 8745 622.06173 

U,S, l>ept, of the Int, Library 
CONTENTS 

Page 

Abstract ..........o..................................................... 1 

Introduction. ........................................................... 1 

UHF section-to-place radio, by Robert A. Bradburn and Robert L. Lagace.. 3 

Trapped miner location and communication sys tems , by H- Kenneth Sacks. . . 3 1 

Longwall mining communications , by Robert A. Bradburn and 

John D. Foulkes ....................................................... 44 

Medium-frequency mine wire less radio, by Robert L. Chufo , Robert L. Lagace, and Lawrence R. Wilson....... ....................... 63 

Refuge shelter communication system, by H. Kenneth Sacks. ............... 73 

Appendix.--Communication reports....... ................................. 77 
UNDERGROUND MINE COMMUNICATIONS 

(In Four Parts) 

4. Sect ion-to-P lace Commun icat ions 

Cornpi led by Staff-Mining Research 

ABSTRACT 

This Bureau of Mines report on underground mine communications addresses 

methods and equipment to meet the communication requirements of working 

sections and places of coal and metal-nonmetal mines. A review of the status 

of trapped miner detection is also presented. 

INTRODUCTI 

This report focuses on equipment and methods to meet the special communications needs of key individuals in the working sections and places of 

coal and metal-nonmetal mines. Attention is also directed toward recent 

developments in and future plans for locating and communicating with trapped 

miners. 

A wide assortment of techniques and ultrahigh-frequency (UHF) radio hardware by which mine operators can increase the safety and productivity of 

section-place mining operations is now available. Theref ore, a comprehensive 

treatment is given to mine applications and experiences with commercially 

available, MESA-approved , UHF portable radios , repeaters , and accessory hardware. Applications include two-way radio communications between supervisory, 

maintenance, and ventilation personnel working in basic room-and-pillar 

sections; between miners working in sections with special needs, such as 

longwalls and shortwalls, and in sections with full-dimension continuous 

haulage ; between isolated workers (for example, fan-hole drillers) and supervisory personnel; and between section and off-section personnel communicating 

via radio interconnects with mine phone systems. 

To meet miner-on-the-move communication needs, which are difficult for 

UHF radio to satisfy, the Bureau of Mines is developing a medium-frequency 

wireless communication system. The status of the hardware development to date 

and the associated in-mine medium-frequency radio signal measurement program 

are described. 

Longwall mining is a major component of the Bureau's program for 

increasing U.S. coal production, and the number of longwall mining sections in 

the United States continues to increase each year. Therefore, a paper is 
devoted to the special communication and control needs of section foremen, 

roof-support advance personnel, machine operators , and workers at the head 

and tail gates of longwall sections. It covers both U.S. and European 

practices and equipment experiences , and commercially available , MESA-approved 

radio and wired equipment for voice communication, signaling, and control. 

Developing effective and practical means of locating and communicating 

with trapped miners continues to be an issue of priority to the Bureau of 

Mines. A paper on trapped miner location and communication describes the 

present preproduction ultralow-frequency (ULF) e lectromagnetic (EM) 

hardware for use by underground miners and surface rescue teams. Also 

discussed are test results for a simulated mine disaster, the present measurement program to verify performance of the ULF transmitters through a variety 

of overburdens , and planned reliability testing of the transmitters in several 

mines. Lastly, the approach and status of a program to develop a reliable 

mine refuge shelter communication system based on through-the-earth signaling 

techniques are described. 

Throughout the proceedings, mention of trade names is made to facilitate 

understanding and does not imply endorsement by the Bureau of Mines unless 

otherwise stated. 
UHF SECTION-TO- PLACE RADIO 

by 

Robert A. Bradburn' and Robert L. ~a~ace" 

ABSTRACT 

Permissible ultrahigh-frequency (UHF) section radio equipment is available and being successfully used underground in a variety of mine section 

applications, such as on a longwall face, along a full-dimension haulage unit, 

and in a magnetite mine. Moreover, recent experiences with UHF radio in 

several room-and-pillar mine sections have been encouraging. 

With a wide assortment of hardware from which the mine operator can 

choose, section radio systems ranging in complexity from basic portable-toportable communications to systems interconnected with mine-wide phone 

networks can be configured to meet varying requirements. 

INTRODUCTION 

A variety of opportunities for improved safety and management are made 

possible by the use of portable UHF radios in mine working sections. This can 

be appreciated by considering the following instances. 

Better coordination of section activities can be achieved with portable 

UHF radios, resulting in a safer operation; for example, during the movement 

of several mobile machines that must work in concert with each other. In 

many cases the operators cannot see one another, but with a system of 

communications they can effectively work together. Another example in which 

safety is improved by better comunication is the contact that can be established with isolated workers to check their status; for example, fan-hole 

drill operators in iron ore mines. 

Improved management can be realized by means of effective section 

comunication. The foreman can exercise better supervisory control, resulting 

in more efficient utilization of available personnel. Another benefit is the 

reduction of unnecessary travel, an extreme burden when mining low coal, 

particularly on longwalls , Additionally, such workers as repairmen, mechanics, and utilitymen can be quickly reached and dispatched to their place 

of need at the time of need. 

Figure 1 shows a machine operator with a UHF walkie-talkie and a 

special radio headset assembly while at the controls of a continuous miner. 

--- IE lectrical engineer, Industrial Hazards and Communications , Pittsburgh Mining 

and Safety Research Center, Bureau of Mines, Pittsburgh, Pa. 

"~lectrical engineer, Electronic Systems Section, Arthur D. Little, Inc. , Cambridge, Mass. 
FIGURE 1. - Machine operator equipped with radio and headset. 

Although relatively new to the working crews in underground mine sections, it 

is reasonable to expect that UHF radio communication will find increasing 

applications of this type as the quest for expanded productivity intensifies. 

UHF RADIO SYSTEMS IN MINES 

Basic Building Blocks 

The development of a UHF radio system for a mine working section can 

be approached from the standpoint of a basic "building block" philosophy. 

In figure 2, the fundamental building block is the UHF walkie-talkie radio. 

Several of these are sometimes all that is required for an effective section 

wide communication system. Usually, however, certain portable accessories are 

helpful to some miners; namely, speaker-microphone headsets, carrying vests, 

and remote handheld microphones . 

In some situations, it is necessary to extend the range of communications beyond that achievable when transmitting directly between portable 
To mine 

phone system 

units. This can be accomplished by adding a radio 

I repeater to the system. 

A repeater, which can effecInterconnect tively double the area of 

coverage, is essentially a 

Antennas signal booster that transforms weak signals received 

Radiating cable from distant radios into 

signals retransmitted at 

full power. Further enhanceRadio repeater ment is possible by connecting the repeater to its 

antenna by means of a long 

length of special "radiating" 

Portable accessories cable extended into areas 

of poor coverage, such as 

the area along a longwall 

chockway. Radiating cable , Portable radios also known as leaky coax 

or leaky feeder, has the 

characteris tic of allowing 

FIGURE 2. - Building blocks for UHF section radio. radio signals to leak out 

of or into itself at a 

controlled rate. It effectively behaves as a long antenna with the attendent 

capability of following corners and bends. 

For a comprehensive sys tern, some mines may include an interconnect to 

allow communication between a section radio system and the surface or other 

off-section areas by interfacing the radio system with a minewide network, 

such as a page-phone or trolley-phone system. This would be useful, for 

example, for paging key personnel in the section who are out of audible range 

of the section pager phone. However, the interconnect should operate only on 

a selective basis to avoid interference to, or by, the section radios. Hardware for implementing this idea is commercially available, and additional 

equipment will be so in the near future. 

These are the basic constituents of a section radio communication 

system; that is, portable radios and accessories, radio repeaters, radiating 

cable , antennas , and interconnecting hardware. A simple sys tern may cons is t 

of only a few walkie-talkies carried by several selected individuals. A 

more elaborate system might have, additionally, a repeater feeding an 

antenna-terminated radiating cable, and a selective interconnection between 

section communication and minewide communication. Figure 3 shows some of 

the radio hardware that are presently available in MESA-approved versions. 

Tv~ical Communication Ranges 

Almost anyone who has ridden in an automobile is familiar with the radio 

fade that occurs when a car enters a tunnel. A mine can be looked upon as a 

vast network of tunnels going off in various directions. One might expect, 
erally true, and it is not feasible to design practical "wireless" portable 

radios capable of full mine coverage, except possibly for the smallest mines. 

I-Iowever , a 11 is not so pessimistic as the foregoing may suggest. Both theory 

and experience teaches that the propagation characteristics of radio waves in 

mine tunnels improve as the frequency increases into the UHF band. This is 

attributable to a waveguide effect that is prominent when the wavelength of 

the radio wave becomes small compared with the cross-sectional dimensions of 

the tunnel. In the UHF band from 400 to 1,500 megahertz, tunnel propagation 

is suitable enough to provide sectionwide radio coverage. 

Probably the most important factor that determines the ability of UHF 

radio waves to propagate in underground mine tunnels is the cross-sectional 

dimension of the tunnels. In general, a high, wide opening favors good 

propagation, whereas a low, narrow opening presents a less favorable medium 

for radio-wave propagation. Figure 4 shows a comparison in the ability of 

450-megahertz UHF radio waves to propagate in high coal (7 feet) as opposed 

to low coal (3.5 feet), assuming an unobstructed 16-foot-wide entry. The 

comparison also assumes that 2-watt UHF walkie-talkies are the source of 

signal. As indicated in figure 4, communication is possible for ranges up to 

1,500 feet, along a straight entry in high coal, but the range drops to 400 

feet in low coal. Of course the same principles apply to tunnels in 

nonc oa 1 mines . 
!I Portable radio 

Radio path High coal Low coal 

-- Straight line 1500 ft 400 ft 

Around but near 900 ft 300 ft 

-- one corner 

More than 20 ft around 400 ft 200 ft 

one corner 

Second corner Poor 

penetration 4 

FIGURE 4. - Typical ranges in unobstructed mine tunnels. 

Corners present obstacles to the propagation of UHF radio waves down 

cross tunnels , thereby reducing the communication range as shown. For a 

path that includes one corner, ranges are reduced but improve if one of the 

radios can be moved closer to the corner. However, penetration around a 

second corner is usually poor. To help offset this corner effect, it is good 

practice to transmit from intersections when possible, thus reducing the number of corners that have to be negotiated. Some other cbstacles to radio-wave 

propagation at ultrahigh frequencies are equipment such as shuttle cars and 

machines that reduce the channel cross-sectional area of the tunnels or 

entries, and permanent stoppings . Table 1 shows that when shuttle cars are 

present, for instance, the range is typically reduced by 200 feet in high 

coal and by 50 feet in low coal. On the other hand, some types of permanent 

stoppings can present an almost impenetrable barrier to UHF radio waves. The 

amount of range reduction due to undulations, curves, and other bends in the 

tunnel ranges from moderate to severe, depending on the degree of bend. 

TABLE 1. - Typical range reduction1 due to tunnel obstructions at 450 kilohertz 

Bends.. .................... I Moderate to severe I Moderate to severe 

Low coal (3-1/2 by 16 ft) 

Shuttle car.... ...... feet.. 50 

High coal (7 by 16 ft) 

200 

Permanent s toppings ........ Longwalls ........... .feet.. 

l~or range improvement, use radiating cable and/or repeater. 

Moderate to severe 

1,200 

Moderate to severe 

250 
- Auxiliary radiating cable 

(if required) 

FIGURE 5, - Extending ranges with repeater and radiating cable, 
they are received by radio B. The reverse occurs for transmissions from B 

to A. 

UHF RADIO FOR BASIC ROOM-AND- PILLAR SECTIONS 

Several individuals working in room-and-pillar sections can be equipped 

with walkie-talkie radios. Thus equipped, the section foreman can practice 

better supervision by maintaining instant contact with the various workers. 

Machine operators can coordinate their activities more efficiently, resulting 

in a smoother and safer operation. The shot firer can warn other personnel, 

by radio, when he is about to fire. Unnecessary travel by individuals can 

be eliminated or, at least, reduced. 

The minimum acceptable coverage for a radio system in a room-and-pillar 

section should be at least one-half the area inby the power center. Under 

many circumstances this will provide adequate coverage since most workers are 

usually located in one part of the working section at any one time. However, 

in some circumstances, some workers are likely to be out of range. To 

rectify this, a centrally located radio repeater can be employed to extend 

communication coverage to nearly 100 percent of the section. In some cases, 

it may be necessary to use radiating cable to extend coverage into weak areas. 

In other situations, it may be desirable to locate the repeater at a location 

remote from its antenna; for example, at the section power center. Suitable 

coaxial cable, such as RG-8, which also has radiating properties can be used 

for this purpose. 

UHF section radio has recently been used successfully on room-and-pillar 

working sections at several mines. The Bureau of Mines closely monitored the 

experience gained at two such mines--Jenny mine near Inez , Ky . , and Peabody 

No. 10 mine near Shawnee, 111. In each mine, one working section was operated 

as part of the Bureau-sponsored Inherently Safe Mining System (ISMS) project 

and was provided with UHF radio communication. 

Jennv Mine Ins tallation 

The Jenny mine had a single conventional room-and-pillar section and was 

in production 18 months, the duration of the ISMS project. A layout diagram 

of the working section at that mine is shown in figure 6. The seam height was 

medium low (42 to 48 inches). The section radio system consisted of walkietalkie radios carried by various miners and a radio repeater located at a 

communications center (known as the communication sled), which was placed near 

the power sled. The foreman, mechanic, shot firer, and a utility cleanup man 

were equipped with 2-watt walkie-talkies operating on two channels, 454 and 

457 megahertz. One transmit channel was used for direct portable-to-portable 

communications , and the other channel was used for portable-to-portable 

communications via the repeater. The channel is selected by means of a 

multiposition switch on the HT 220 walkie-talkies. 

The purpose of the repeater at the Jenny mine was twofold: (1) To 

extend coverage beyond the direct portable-to-portable range, and (2) to 

provide an interconnect between the radio system and a system of carrier 
Face 1 20. I- 60' k- phones, which were mounted 

on mobile machines and 

interconnected by means of 

the trailing cable conductors to the machines. It 

was thus possible to 

communicate between roving 

miners equipped with walkietalkies and machine operators equipped with powerline 

carrier phones. Paging into 

the section radio system 

from a surface point was 

also possible via a surfaceto-section carrier-phone 

link and a special interface 

in the communication sled. 

A low-frequency through-theearth radio link between the 

surface and comrnunica tion 

sled was also provided. A 

block diagram of the system 

is shown in figure 7. FIGURE 6, - Section layout of Jenny mine, 

At the Jenny mine, the 

Surface station 

 age) 

1-1 Carrier signal 

F Thru- the- earth signal 

I I 

DC line 

"party line." 

Driller Cutter Bolt 

Utility cleanup 

shot firer Shuttle Shuttle 

Carrier phones Car car 

on machines 

portable radios were used 

extensively by the miners on 

the one daily production 

shift. The most often used 

mode of operation was direct 

portable- to-portable without 

the repeater. However, this 

was largely because the 

repeater and interconnect 

to the machine-mounted 

carrier phones were made 

operational only late in the 

program. The walkie-talkie 

portables by themselves were 

usable over an area 

encompassing more than half 

of the working section. 

Wired links ----- Radio links With the repeater, sectionwide radio coverage was 

FIGURE 7, - Diagram of section communications at possible. The carrier 

Jenny mine, phones were installed mainly 

to demonstrate an alternative communication method for the machine operators. At the termination of 

the project, the portable units showed much evidence of in-mine use, but they 

were all in good working order, except for one defective battery. 
Face area 

Seam 

72 - 

height: I 1 

-80 inches 

Camrnunication sled with / 

Power center 

UHF / \ Beltway repeater and interfaces conveyor 

Peabody No. 10 Mine 

Installation 

At the Peabody No. 10 

mine, one continuous roomand-pillar section was 

devoted to the ISMS demonstration program. This 

section remained in operation for about 1 year. The 

section radio communication 

system was very similar to 

that at the Jenny mine, 

including the machine 

carrier phones and a surfaceto-section interface at a 

communication sled. A 

layout diagram of the 

working section is shown in 

figure 8, and a block 

diagram of the communication 

FIGURE 8, - Section layout of Peabody NO, 10 mine, system is shown in figure 9. 

Trolley wire 

r- 1 Surface phone 

Section radios 

I COmrnunications sled 

Foreman 

Mechanic 

Ventilation 

worker 

Machine 

operator 

Carrier phones 

on 

face machines 

T 

I 

I 

I 

I----- 

Peabody No. 10 mine, 

FIGURE 9. - Diagram of section communications at 

Conditions at Peabody 

No. 10 were much more favorable for radio communication 

than at the Jenny mine, 

mainly because the seam 

height was 6 to 7 feet. 

Direct portab le-to-portable 

communication was generally 

good over an area encompassing up to three-quarters 

of the working section, 

although some dead zones 

were encountered where several corners had to be traversed. When the face was 

at maximum advance from the 

power center, the repeater 

located in the communication 

sled near the power center 

was out of reach of some 

portable radios. This 

could have been rectified by 

extending the repeater 

antenna in toward the face 

area by means of a coaxial 

cable. 
qp

is operated at a location several feet from the machine by means of a wired 

remote control box. A layout diagram of the working section is shown in 

figure 10 which also shows the radio system. The seam height ranges from 

about 30 to 48 inches. 

System Objectives and Equipment for Splashdam Mine 

Early in the program, Bureau personnel and officials of both the 

Splashdam mine and Clinchfield Coal Co. established the following objectives 

for the system: 

1. Primary need.--The operators of three machines (the continuous miner 

and two mobile bridge carriers) should be able to communicate with each other. 

2. Secondary need.--Two roving miners (the foreman and repairman) should 

be able to communicate with the three machine operators and with each other. 

These objectives, together with the results of range tests using UHF portable 

radios on the working section, led to a radio system configuration that has a 

3~lso known as continuous conveyor systems. - 

4~rade name of West Virginia Armature Co. 
FIGURE 10.  Section layout of Splashdam mine showing UHF radio system. 

radio repeater mounted on the No. 1 bridge carrier as depicted in figure 10. 

Although not crucial, it was also decided to include a length of cable 

terminated at each end by an antenna, and extending from the power center 

inby toward the face area paralleling the Long John belt, to improve coverage 

along the center heading of the section. A picture of the cable with the 

antenna connected at each end is shown in figure 11. 

The decision to mount the radio repeater on the No. 1 bridge carrier 

presented a problem, since permissibility is required of any electrical 

equipment installed there, and no approved repeater hardware was available 

at that time. To overcome this problem, the Bureau of Mines repackaged an 

existing portable radio repeater into a certified explosion-proof enclosure 

and obtained a permit from MESA to install it on the machine. Figure 12 

shows an in-mine picture of the repeater main enclosure installed on the No. 1 

bridge carrier. The repeater obtains 120-vac operating power from the 

machine, but also has a standby nickel-cadmium storage battery located inside 

the main enclosure. 

Several control adjustments are accessible on a separate repeater control 

box located on the operator's side of the machine. This control box also has 
operator to use the repeater as a fixed radio for communicating with other 

crew members. This precludes his need to carry a separate portable radio. 

Figure 13 shows a miner at the controls of the No. 1 bridge carrier, and 

speaking into the repeater microphone. 

The portable radios used on this system are 2-watt Motorola HT 220 

units with two transmit frequencies (464.7 and 469.7 megahertz) manually 

selectable by the user. One frequency is used for direct communication 

between portable units, and the other is used for communicating via the 

repeater. A MESA-approved, battery-operated radio repeater not requiring an 

explosion-proof enclosure is now commercially available from Motorola for 

section radio applications. 
FIGURE 12. - Repeater and antenna installation on No. 1 bridge carrier. 

Methods for "Hands-Free" Opera tion 

To facilitate use of the portable radios by machine operators who 

require both hands to operate their machines, three special interfaces were 

developed using commercially available components: 

1. Headset with earmuff-speaker and head-contact microphone: 

Arm-actuated control 

Used at continuous miner 

2. Hardhat-mounted speaker and boom microphone: 

Arm-actuated contr 01 

Used at dust-free location 
FIGURE 13. - Miner speokirig into repeater microplione on No. 1 bridge carrier. 

3. Machine-mounted loudspc~~~ker andextended microphone: 

Lever-actuated control 

Equipment off operator 

Used at outby bridge carrier 

The method for hands-Lree contro 1 dc?velopecl for the continuous-miner 

operator employs an earmuff-spertkc K .i-.;c.mbly with a head-contact boneconductance microphone. Figurc 1; sllo~ss a man wearing the assembly. The 

microphone, rather than protruding in front of the miner's face, makes contact 

with the top of the head. The rniner 5s , therefore, able to wear a dust 

respirator over his mouth. Thc stand 11-d press-to-talk control supplied with 

the equipment utilizes a pushh~~~to~l :situated at the end of a small 

extension cord. For hands-free control, tlle 1311rc,1u has incorporated certain 

modifications and substitutcri <I ~!~ini,~ti~rc~ leather-encased switch situated so 

that the transmitter can be kc.vc.tl 1)v .i;nvenlcnt. of the user's upper arm. This 
The third method for 

hands-free operation of a 

portable radio (fig. 16) 

was developed for use at 

No. 2 bridge carrier to free 

the operator of the burden 

of carrying a radio on his 

person. An interface box, 

into which a portable radio 

FIGURE 14. - Miner wearing accessory headset with ear- can be plugged, has promuff speaker and head-contact microphone, visions for attaching a 

trolley-phone loudspeaker, 

a microphone, and an 

external press-to-talk switch. The press-to-talk switch has a sensitive 

6-inch-long lever-actuator that can be operated by a bump of the knee or other 

body part. A strong permanent magnet is attached to the base of the switch 

housing and allows positioning in a location convenient to the operator. A 

section of flexible "gooseneck" tubing, with a hook on one end for hanging the 

microphone, extends from the speaker housing. By this arrangement, the microphone position can be adjusted for convenience. 
FIGURE 15. - Miner wearing hands-free hardhat accessory for dust-free location. 

Another feat.ure of the foregoing interface was incorporated to compensate 

Tor the wide changes in ambient noise level. By means of a two-position 

toggle switch on the speaker housing, either the full volume output of the 

speaker or a reduced and adjustable volume can be selected by the operator. 
p

on the miner's belt in a leather holster, which is a standard accessory. An 

extension speaker-microphone with a flexible cord that plugs into the radio 

can be used for initiating or receiving a communication. A miner using a 

radio in this fashion is shown in figure 17. 

The Splashdam mine experience thus far has yielded some valuable information regarding the use of portable radio equipment on a low-coal mine section. 

The Bureau plans to continue to monitor this program closely, to participate 

actively in it, and make necessary or desirable system improvements as well. 
FIGURE 17. - Miner using portable radio with speaker-to-microphone extension accessory. 

UHF RADIO FOR LONGWALLS AND SHOR'IWALLS 

Longwalls 

On longwall sections, a communication requirement not generally being met 

is personal communication for miners on the face; that is, portable walkietalkie-type communication. With some exceptions, truly wireless radio for 

longwalls is not feasible at ultrahigh frequencies. However, cable-aided 

UHF radio is feasible, and is presently the best choice for obtaining the 

linear tunnel coverage required on a longwall section. 

The environment on a longwall is usually harsh. Figure 18, which shows 

a shearer machine and operator under the protective canopy of roof-support 

chocks, illustrate this clearly. Certain individuals should be able to communicate from any location along the chockway without the fatiguing ordeal of 

crawling a distance to a page phone. A cable-aided UHF radio system provides 

that capability. Table 2 summarizes the important points regarding the design 

and implementation of a longwall UHF radio system. 
FIGURE 18. - ll lustration of longwal 1 working environment. 

TABLE 2. - Ranges of completely wireless communication system 

for lonrwalls at 450 mepahertz 

Truly wireless communications is not feasible except under some special 

and favorable conditions such as a shield-type roof support system in high 

coal or on the shorter faced high-coal longwalls. This is due to the substantial range reduction that results from the presence of both the chock 

roof-support and conveyor systems and the cutting machine. Therefore, the 

best choice usually is to employ a radiating leaky feeder cable extending 

Type of roof 

support 

Chocks ........... Shield..... ...... 

Range with no machine, 

feet 

High coal 

300 

1,000 

Range reduction caused by 

shearer machine, feet 

Low coal 

150 

15 0 

High coal 

100 

3 00 

Low coal 

50 

5 0 
along the chockway area. On shorter faces, a radiating cable extending along 

the length of the longwall and passively terminated at each end with a suitable antenna can provide face coverage without a repeater. A radio repeater, 

connected to the cable at one end, is needed on longer faces, or when coverage 

to the head entry outby the headgate is required. Presently, a passive system 

using Andrews Corp. Radiax slotted-type radiating cable is in operation on 

a short-face longwall section at Clinchfield Coal Co. 's Moss No. 2 mine near 

Dante , Va. 

A repeater-based configuration for a longwall UHF radio system is shown 

in figure 19. In this system, good radio coverage can be expected along the 

face area and into the head entry for several hundred feet. If the repeater 

should fail, direct communication between portable radios i s s t i l l possible 

at reduced range. This system can be implemented using commercially available 

battery-operated hardware that is also MESA-approved (fig. 20). The tone 

remote adapter (fig. 19) provides a surface-to-section link, and will be 

available in the near future. The Bureau of Mines has performed a number of 

experiments with radiating cable on a number of longwall sections, and has 

also established that inexpensive RG-8 flexible coaxial cable can be used in 

place of the more expensive, rigid Radiax radiating cable for repeater-based, 

cable-aided UHF radio ins tallations on longwalls . Howeber , there has not yet 

been enough in-mine experience to determine whether the RG-8 cable is 

sufficiently rugged for this kind of application. 

Shortwalls 

A shortwall section has characteristics of both a longwall and a fulldimension section. Roof-support equipment, for example, is similar to that 

used on longwalls. On the other hand, the coal is mined by a continuous miner 

which, in some cases , feeds onto an articulated mobile conveyor system similar 

to the equipment used on full-dimension sections. The congested situation 

in the areas between the chocks and coal face presents an unfavorable condition for radio-wave propagation, but the distance along the face is typically 

only about 150 feet. 

For a radio system to be effective on a shortwall, comunication should 

be possible in the face area, along the chockway, and for several hundred 

feet into the head entry. Many radio system configurations are possible, but 

a logical choice would be to place a repeater at the end of the chockway by 

the head entry. The repeater should operate into two remotely located 

antennas, one for coverage in the face and chockway areas, and the other for 

coverage in the head entry area. 

A more detailed coverage of longwall mining communications is presented 

in the paper on Longwall Mining Communications. 
FIGURE 20. - A MESA-approved UHF Motorola repeater and battery unit, with "hardhat" 

antenna and HT 220 walkie-talkies. 
FIGURE 21. - Fan-hole drill operator wearing portable radio and special accessories in 

metal mine. 
INTERCONNECTS TO MINE PHONE SYSTEMS 

An interconnect between a section radio system and a minewide phone 

system is an extremely useful concept. For example, the ability to reach key 

section personnel from the surface is facilitated if the individual can be 

paged by radio. Because section page phones are often inaudible due to high 

ambient noise, it can take up to a half hour, or more, to contact a paged 

individual from the surface. Conversely, the ability to initiate a call to 

the surface or at least, answer a page with one's radio, would eliminate the 

distractive necessity of walking (or crawling) to the section phone. 

An interconnected comunication system can also introduce a factor of 

safety. In time of emergency, for example, quick communication means faster 

evacuation or first aid. Another example is the ability to maintain contact 

with certain isolated workers who, for practical reasons, cannot have a 

phone near them. 

An important consideration when planning to interconnect section radio 

systems and minewide comunication is that the interconnection should be made 

to function on a selective basis. The two systems should be isolated, except 

when actual communication to or from the section is desired. Otherwise, 

intolerable interference may result. 

Some interconnecting hardware that incorporates the desirable features 

mentioned has been developed (table 3). Some of this equipment was built for 

experimental use and is not sold commercially. Other equipment, being of 

recent development, has not yet been released for commercial sale, but will 

be available in the near future. 

TABLE 3. - Interconnecting hardware 

For mines that have a Collins MCM telephone system, an interconnect will 

soon be available, allowing selective interfacing between section radios and 

the wired phone system. Figure 22 shows a diagram of a section radio system 

interconnected with a minewide MCM communication system by means of a Collins 

interconnect. Calling the section radios from an off-section phone is 

accomplished by dialing an assigned number. Initiating calls from a section 

portable radio can be accomplished in either of two ways: by transmitting 

carrier bursts from a radio three times in quick succession, or by transmitting a switched-on tone from a radio having that capability. 

Type 

MCM (telephone to 

radio). 

Tone remote-control 

adapter. 

Trolley phonelradio 

coupler. 

Carrier phone/~HF 

repeater interface 

Interconnects from section 

radio system to-- 

MCM telephone system.. .... 

Dedicated phone line.. .... 

Trolley-phone system ...... 

Face machine carrier 

phones. 

Manufacturer 

Collins Radio... 

Motorola.... .... 

Collins Radio... 

FMC/~aitronics/ 

Motorola. 

Availability 

Soon. 

Do . 

Prototype. 

Special 

, design. 
,Sect ion Interface radio 

I Incoming call 1 section I Dial special extension numbers 

phone to be connected to section rad ios 

L Three brief bursts of carrier 

or 

A switched-on tone allows 

connection to dispatcher 

Dispatcher can transfer call 

to any other mine telephone 

FIGURE 22. - lnterconnect between section radio and MCM telephone system. 

FIGURE 23. - lnterconnect between surface station and 

section radio. 

M IC MESA approval is 

pending on a tone remoteremote 'peeker control interface made by 

Motorola that allows operaIn this system, which 

requires a dedicated (singlepurpose) phone line, section 

radio communication can be 

tion of a section radio 

Monitors communications repeater from a remote locaTransmits remotely tion such as a mine office. 

Walkie-talkie 

continuously monitored over the remote speaker. If someone wants to call into 

Sect ion , 

the section from the surface, the repeater transmitter can be keyed remotely 

radio 

from the surface station, and messages spoken into the remote microphone will 

J Interface1 

be heard on the section radios. The system is expandable using the single 

dedicated phone line. 

Figure 23 is a block diagram , 

LICENSE S AND APPROVALS 

Federal law requires a license to operate radio equipment of the type 

reported herein. It is issued for a periodof5 yearsbythe Federal Comrnunications Cormnission (FCC). The ultrahigh-frequency spectrumis relatively uncrowded, 

and frequency allocation is no problem, except possibly in heavily populated 

repeater 

section radio interconnect. 

isolator Dedicated phone line showing a surface station-to- 
urban areas. Nevertheless, one can expect that it may take up to 9 months 

to obtain a license from FCC. Radio equipment suppliers assist their 

customers in filing the necessary forms, and they can also furnish important 

information regarding this matter. 

Portable two-way radio equipment, bearing MESA approval for use in mines , is available from several manufacturers as listed in table 4. Competent 

repair facilities, both factory authorized and independent, are located in 

larger towns. Most mines in the United States are located within at least 

50 miles of such facilities. 

TABLE 4. - Manufacturers of MESA-approved portable two-way radios 

Manufacturer I Frequency I Type of I Portable repeater 

Motorola Communications and 

Electronics 

Ft. Lauderdale, Fla. 

Harris RF Communications 

Rochester, N .Yo 

RCA Corp. (Communication Systems) 

Meadowlands, Pa. 

range 

VHF, UHF 

The State of Pennsylvania, Department of Environmental Resources, Office 

of Deep Mine Safety, requires special approval on electrical equipment used 

in Pennsylvania mines. For this reason, mine operators in Pennsylvania should 

determine, before purchasing, that any radio equipment destined for use 

underground is approved both by MESA and the State. 

Standard Communications 

Wilmington, Calif. 

DISCUSSION AND RECOMMENDATIONS 

bat teryl 

RJ N 

Initial resistance to the use of radios by section workers can be 

expected. A gradual phasing-in period is suggested. When full implementation 

is in effect, using the radios will be second nature to them. 

hardware available 

Yes 

lR--Rechargeable ; N-~Nonrechargeab le . 2MESA-approved version. 

VHF, UHF 

When communicating with a machine operator, it is usually preferable 

to keep the radio gear off the man when possible. This constraint spurred 

the development of the special interface and the repeater control box for the 

bridge carriers at Splashdam mine. 

It is difficult to equip a continuous-miner operator. He not only works 

in a dusty environment and has to wear a respirator, but he also requires both 

hands to operate his machine. The special accessory developed for the 

continuous-miner operator at Splashdam mine is satisfactory for this 

R, N Yes 
application, but other avenues are being explored with the expectation that 

an improved accessory will soon be developed. 

Hardhat and headset accessories are generally not comfortable for a 

miner to wear. However, when a miner is required to communicate in a noisy 

environment, these accessories are the only choice, unless a machine-mounted 

loud speaker interface can be provided. 

Although the HT 220-type radios used at some of the reported installations are fairly rugged and appear to require minimal maintenance, newer, 

MESA-approved portable radios (the MX 300 type), which are smaller and lighter, 

are now available and recommended over the HT type. 

If a radio system is installed at a mine, it is imperative that a 

responsible individual be designated to take care of the radios. His 

responsibilities should include simple maintenance chores such as cleaning 

and basic testing to determine operational status of individual units. He 

would issue the radios on a checkout basis and see that they are returned. 

He would also send radios to authorized shops when necessary for repair or 

periodic performance tests. 
BIBLIOGRAPHY 

Bradburn, R. A. Instruction Book--Section Radio System for Splashdam 

Mine. Bureau of Mines unpublished report, 1976, 12 pp. ; available for 

consultation at Bureau of Mines Pittsburgh Mining and Safety Research 

Center, Pittsburgh, Pa. 

Bradburn, R. A. , and H. E . Parkinson. Two-Way Communications With Face 

Machine Operators. Mine Communications, Proceedings: Bureau of Mines 

Technology Transfer Seminar on Mine Communications, Bruceton, Pa., 

March 21-22, 1973. BuMines IC 8635, 1974, 87 pp. 

Chironis , N. P. The Jenny Mine. . . . .New Proving Ground for BureauSponsored Advanced Mining Machines and Equipment. Coal Age, v. 79, 

NO. 9, 1974, pp. 78-82. 

Emslie, A. G. , R. L. Lagace, and P. F. Strong. Theory of the Propagation 

of UHF Radio Waves in Coal Mine Tunne 1s. IEEE Trans. on Antennas and 

Propagation, v. AP-23, No. 2, 1975, pp. 192-205. 

Ginty, J. J., R. L. Lagace, and P. G. Martin. Applicability of State-ofthe-Art Repeaters for Wireless Mine Communications, Final Report. 

Task B, Task Order No. 1, 1975, 38 pp. (Bureau of Mines 

Contract H0346045) ; available from National Technical Information 

Service , Springfield , Va . , PB 249 830/A~. 

Lagace, R. L. , M. L. Cohen, A. G. Emslie, and R. H. Spencer. Propagation 

of Radio Waves in Coal Mines, Final Report. Task F, Task Order No. 1, 

1975 (Bureau of Mines Contract H0346045); available for consultation 

at Bureau of Mines Mining and Safety Research Center, Pittsburgh, Pa. 

Lagace, R. L., and H. E. Parkinson. Two-Way Communications With Roving 

Miners. Mine Communications, Proceedings : Bureau of Mines Technology 

Transfer Seminar on Mine Communications , Bruceton , Pa. , Mar. 21 -23, 

1973. BuMines IC 8635, 1974, 86 pp. 

Lagace, R. L. Emergency and Operational Mine Communications. Part IV. 

Theory of Wireless Propagation of UHF Radio Waves in Coal Mine Tunnels, 

Final Report, 1974, 44 pp. (Bureau of Mines Contract H0122026); 

available from National Technical Information Service, Springfield, Va., 

PB 235 069/A~. 

Mountain, N. L. , and J. V. Nickel. Recent Developments in Communications 

and Fan Monitoring for Underground Mines. Proc. 3d W. Va. Univ. Conf. 

on Coal Mine Electrotechnol. , Morgantown, W. Va. , August 1976; available for consultation at Bureau of Mines Mining and Safety Research 

Center, Pittsburgh, Pa. 
10. Roetter, M. F. , A. G. Emslie , R. L. Lagace, and P. F. ~'~rien. Longwall 

Mining Communications, Final Report. Task 11, Task Order No. 2, 

1976, 56 pp. (Bureau of Mines Contract H0346045); available for 

consultation at Bureau of Mines Pittsburgh Mining and Safety Research 

Center, Pittsburgh, Pa. 
TRAPPED-MINER LOCATION AND COMMUNICATION SYSTEMS 

by 

H. Kenneth sacks1 

ABSTRACT 

The history of coal mine disasters has established a need for a simple, 

reliable system for locating and communicating with miners trapped underground. 

Such a system will not only increase the chances of success rescue, but will 

also reduce the risks to the rescue team. The Bureau has developed such a 

system by using several principles of electromagnetic theory The Bureau is 

presently testing the system for performance (transmission capability through 

a variety of overburdens) and reliability (ruggedness of use in mine 

environments). 

INTRODUCTION 

The most feared occurrence in underground coal mining is an explosion 

of gas or coal dust. In the period 1911-69, about 6,000 miners have been 

killed in 290 major disasters involving explosions. The immediate concern 

after each such incident is whether there are survivors and, if so, how they 

can be rescued. To this end, both mining companies and Government agencies 

have encouraged and financed the development of rescue teams and equipment. 

Specifically, as a result of a study performed by the National Academy of 

Engineers, the Bureau of Mines has been developing systems for locating and 

communicating with workers trapped underground. Such systems will contribute 

to the overall safety of the underground coal miner. 

The Need To Locate 

The problems facing rescue teams have been well documented in a number 

of historical surveys of mine disasters. Searching a mine after a fire or 

explosion is a slow and often dangerous job. The 13-man rescue party killed 

following the Scotia mine disaster is an example. Besides the inherent 

dangers involved, the rescue team must first decide where to begin its search. 

The area to be searched may be large. After an explosion, miners who manage 

to escape can direct rescue teams to those parts of the mine where others may 

remain trapped. The nature of the mine workings and the circumstances of the 

explosion can also be used in locating survivors, but all of these techniques 

are based on guess work. Accurate knowledge of the location of trapped men 

cannot only increase their chances for survival, but can reduce the hazards 

to the rescue team that might conduct an unnecessary, futile search in 

dangerous areas. 

lsupervisory electrical engineer, Industrial Hazards and Communications, 

Pittsburgh Mining and Safety Research Center, Bureau of Mines, Pittsburgh, 

Pa. 
FIGURE 1, - Part of Belva mine showing area to which miners retreated and erected 

imperfect barricade, 

hand, is complex and stationary. Its deployment 

site must be carefully 

selected. If it is not 

within 2,000 feet of the 

signal source, it probably 

will not work. In a large 

mine, this limitation is 

a serious handicap. In 

mountainous terrain, setting 

up the seismic geophones can 

present difficult problems 

as well. 

3. A prototype model 

of the original underground 

miner-carried transmitter 

has been converted to 

receive voice messages from 

the surface (fig. 6). This 

FIGURE 4. - Portable ULF EM receiver and loop antenna capabilitv is not available 

in use at a simulated mine disaster. with the seismic system. 
The trapped-miner transmitter (fig. 2) weighs one-half pound and can 

be worn by a miner; a second version has been built (fig. 7) that is encased 

with a caplamp battery. In an emergency, and when it is decided that all 

routes of escape are closed, the transmitter unit is opened up. It contains 

90 feet of 16-gage wire. This is uncoiled, laid out in as large a loop as 

possible, and connected to the transmitter. The transmitter is then attached 

to the battery (fig. 8). The transmitter and loop antenna produce a magnetic 

field (fig. 9) much like a bar magnet. The direction of these signal-field 

lines can be used to pinpoint the location of the underground loop antenna. 

By measurements taken on the surface, the surface location above the antenna 

can be determined within 50 feet. The signal is a short 1,000-hertz tone 

transmitted once a second to make it readily distinguishable from the background electrical noise. The unit will continue to transmit for at least 

24 hours. When operating, the signal can penetrate as much as 1,000 feet of 

overburden and be detected on the surface. 

Several prototype transmitter units being tested also contain a voice 

receiver, which allows rescue crew voice transmissions to be heard, and a 

special button for sending a continuous tone rather than an intermittent beep. 

In this manner, once contact with the surface is made, the miner can relay 

information to the surface using a simple code, like one long for NO, and two 

longs for YES. However, even if this feature is not used, the transmitted 
O C> 

. - IS, 

E .f Q) > n .- 2: 

2 2 

2 

LLY 
FIGURE 8. - ULF EM transmitter connected to cap-lamp battery and loop antenna. 

signal will allow the surface crew to fix the transmitter location as 

previously discussed. 

Operation of Surface EM Equipment 

The surface equipment consists of 

1. A helicopter receiver(figs. 3, 10) for surveying a large area 

rapidly. 

2. Miner-carried receivers (fig. 4) for accurately locating the underground transmitter unit. 

3. Voice transmission equipment (fig. 11) for establishing two-way 

communications with the trapped miners. 

For a large minc,ahelicopter wouldbeusedtoscanthe large surface search 

area above the mine workings. The helicopter-based equipment is not designed 

to pinpoint the exact location of an underground transmitter, but rather to 
detect whether any trapped 1 

/ / miner EM signal is present. 1 

Each underground transmitter 

is designed to operate on 

one of several fixedfrequency channels to prevent nearby transmitters 

Surface from interfering with one 

another. Therefore, the 

helicopter receiver has been 

designed to listen simul- 

- taneously to six different 

Mine "channe 1 s . I' Once a s igna 1 

is detected, the pilot can 

radio his approximate 

position and indicate the 

channel detected to the 

surface rescue crew. 

The surface crew minercarried receiver uses a 

simple loop antenna 

(fig . 4). Pinpointing the 

location of the trapped 

miner EM signal is similar 

FIGURE 9. - Magnetic field produced by the ULF EM to radio direction finding. 

transmitter. As shown, the field lines The received signal is 

resemble those of a simple bar magnet heard as a chirp every 

so that directly over the antenna, the second, and is also shown as 

a meter reading. If the field is vertical. loop is turned to give the 

lowest signal, the plane of the loop will point in the direction of the signal 

source. By repeating this procedure at several positions around the approximate transmitter location, the true location of the underground transmitter 

can be found. Using this information in conjunction with a mine map, the 

rescue team can then determine the best approach. 

When a signal is detected by the surface crew, the voice transmitter can 

be set up. This is really a large version of the underground transmitter 

consisting of a loop of wire 300 feet in diameter and a powerful audio 

amplifier. This equipment would only be usedifthe miners were known to have 

units containing voice receivers. 

Detailed information on the performance, construction, and theory of 

this equipment can be found in the bibliography. 
FIGURE 11. - Equipment deployed on the surface for transmitting voice through the earth to 

trapped miners, 
FIGURE 12, - Airborne helicopter ULF EM receiver searching area over Robena No. 1 mine 

for trapped-miner EM signals, 
OUTLOOK FOR THE FUTURE 

The success of the EM system depends on a number of factors, including 

the local electrical resistivity of the earth, overburden depth, manmade and 

natural electrical noise at the site, and the presence of metal cables or 

buildings. To better understand how these factors vary for U.S. coal mines, the 

Bureau is presently conducting an EM survey at 100 coal mines. This survey 

will give a good picture of the likely performance of our present system 

for the wide variety of overburdens found in U.S. coalfields. The hardware 

will also be tested in several mines over a long period of time to see if it 

meets the necessary requirements of ruggedness and reliability. The outcome 

of these programs will clearly determine the strengths and weaknesses of the 

present system and indicate the future course of the trapped-miner program. 
Humphrey, He B. Historical Summary of Coal Mine Explosions in the U.S., 

1810-1958. BuMines Bull. 586, 1960, 280 pp. 

National Academy of Engineering. Mine Rescue and Survival, Final Report. 

Open File Rept. 4-70, 1970, 81 pp. (Contract No. SI90606). 

Keenan, C. M. Historical Documentation of Coal-Mine Disasters in the 

U.S. Not Classified as Explosions of Gas or Dust: 1846-1962. BuMines 

Bull. 616, 1963, 90 pp. 

Harrington, D. , and W. J. Fene . Barricading as a Life-Saving Measure 

Following Mine Fires and Explosions. BuMines MC 42, 1946, 80 pp . 

Geyer , R. G. Thru-the-Earth Electromagnetics Workshop. BuMines Open 

File Rept . 16-74, 1973, 217 pp. ; NTIS PB 231 154/~~. 

Farstad, A. J. Electromagnetic Location Experiments in a Deep Hardrock 

Mine. BuMines Open File Rept. 28-72, 1973, 54 pp.; NTIS PB 232 880/~~. 

Farstad, A. J. , C. Fisher, Jr. , R. F. Linfield, and J. W. Allen. EM 

Location System Prototype and Communication Station Modifications. 

BuMines Open File Rept. 68-73, 1973, 107 pp.; NTIS PB 226 600/A~. 

Farstad, A. J., C. Fisher, Jr., R. F. Linfield, R. 0. Maes, and 

B. Lindeman. Trapped Miner Location and Cmunication System Development Program. Volume 1. Development and Testing of an Electromagnetic Location System. BuMines Open File Rept. 41(1)-74, 1973, 

181 pp. ; NTIS PB 235 605/A~. 

Linf ield, R. F. , A. J. Farstad, and C. Fisher, Jr . Trapped Miner 

Location Communication System Development Program. Volume IV-- 

Performance Test and Evaluation of a Full Wave Location Transmitter. 

BuMines Open File Rept. 41(4)-74, 1973, 52 pp; NTIS PB 235 608/A~. 

Powell, J. A. An EM System for Detecting and Locating Trapped Miners. 

BuMines RI 8159, 1-976, 15 pp. 

"open File Reports are available for consultation at the Bureau of Mines 

libraries in Pittsburgh, Pa. , Denver, Colo. , Twin Cities, Minn. , and 

Morgantown, W. Va. , and at the Central Library, U.S. Department of the 

Interior, Washington, D .C. 

Items with NTIS/PB numbers are available from the National Technical Information Service, Springfield, Va. 22161; please mention the PB number when 

ordering. 
LONGWALL MINING COMMUNICATIONS 

Robert A. ~radburn' and John D. Foulkes2 

ABSTRACT 

The Bureau of Mines investigated the communication needs associated with 

longwall mining. The program had the following objectives: 

1. Survey currently available communication equipment. 

2. Review practices in European mines. 

3. Determine problem areas requiring further research. 

4. Develop guide lines . 

5. Make recommendations for improved equipment design. 

Certain problem areas associated with the use of pager phones have been 

isolated,and a set of design requirements for improved longwall pager phones 

has been prepared. Some European equipment that fulfills these requirements 

has also been identified. 

Enhancement of a longwall communication system by the inclusion of UHF 

walkie-talkie radios is outlined, along with special techniques necessary to 

make that type of radio usable on the longwalls. Truly wireless radio for 

the longwall is considered achievable at special lower frequencies, and 

suitable hardware may be forthcoming. 

The study resulted in three crucial recommendations pertaining to longwall communications : 

Improve communication in advance longer term automation. 

2. Pursue a variety of approaches for improved face communication. 

3. Consider using European equipment. 

'~lectrical engineer, Industrial Hazards and Communications , Pittsburgh Mining 

and Safety Research Center, Bureau of Mines, Pittsburgh, Pa. 

2~lectrical engineer, Electronic Systems Section, Arthur D. Little, Inc . , Cambridge, Mass. 
INTRODUCTION 

Robinson Run mine near Shinnston, W. Va., has two longwall sections among 

several room-and-pillar working sections. Late in January 1976, 23 employees 

working on one of the longwall sections produced 12,395 tons of coal over a 

24-hour period, a world record. Although longwall machines are common in 

Europe, there are only about 80 longwall systems in operation in the United 

States, and they mine less than 5 percent of the l at ion's coal production. 

Virtually all of the equipment is imported, and it represents a minimum capital investment of $1 to $2 million per installation. In actuality, longwall 

mining presently plays a small, but specialized, role in the overall picture 

of U.S . underground coal mining. 

In spite of these somewhat unimpressive statistics, the Federal Bureau 

of Mines and the U.S. mining industry are paying close attention to longwall 

mining. The reasons for this are threefold: 

1. There is general agreement that, because of its potential for high 

productivity (cited previously), this mining technique will grow rapidly. 

2. U.S. manufacturers are beginning to produce their own equipment, 

and this should reduce lead times currently needed to acquire longwall 

machinery and spare parts from overseas. 

3. Longwall mining is becoming increasingly automated, and it is a 

technique that lends itself to automation. 

Starting about 2 years ago, the Bureau of Mines began to investigate 

the communication needs and equipment associated with longwall mining* The 

program included a study of voice communication, both intraface and minewide, 

communication for control purposes, and monitoring. The Bureau learned that 

the three types of communication are closely interrelated in longwall mining 

to the extent that most European equipment integrates all of them into a 

single system. For example, if monitoring equipment detects a machine fault, 

the machine stops automatica lly . 

The Bureau program had the following five objectives: 

1. Survey communication needs and the equipment currently available to 

meet them. 

2. Review European practices , experience, and equipment, since longwall 

mining is the dominant form of underground coal mining in Europe. 

3. Determine the problem areas, if any, that would require further 

research and development. 

4. Develop guidelines for design, installation, and maintenance of 

longwall communication s stems. 
5. Make recommendations in regard to new equipment design and advanced 

research and development. 

Communication is a key and integral factor of any mining process. It is 

so vital, in fact, that it is clear that equipment manufacturers should 

include communication as an integral part of the overall longwall system 

design. This paper will concentrate on the voice communication aspects of 

longwall mining. 

1 DESCRIPTION OF LONGWALL MINING TECHNIQUE 

An understanding of the mechanics of longwall mining is essential for 

an appreciation of telecommunication needs. The longwall mining technique 

uses roof supports to enable an entire block of coal (as large as 5,000 by 

600 feet) to be removed. In the United States, head and tail entries are 

first driven to the rear of the panel (fig. I), and then the longwall retreats, 

thereby removing the entire seam between the head and tail entries. 

1 Each longwall system installation must be custom built for the seam it 

is to mine. The upper portion of figure 2 shows one of the basic "building 

blocks" of the system, the so-called roof support, which includes hydraulic 

rams that allow the roof plates to be individually raised and lowered. A 

number of roof supports are placed next to each other (as shown in the lower 

portion of figure 2), to provide cover for the miners operating the mining 

machine. The machinery on the left is placed against the coal face. It consists of a plow or a shearer mining machine used to remove the coal and a 

chain conveyor for haulage. 

The coal is removed from the face by using e 

shearer. The plow is a bidirectional cutting and 

typically moves at speeds of 3 to 4 ft/sec along 

I 

Direction of mining 

I 

FIGURE 1. - Plan of longwall section. 

ither a plow (fig. 3) or a 

loading machine which 

the face; it is pulled or 

driven by a chain, and takes 

shallow cuts a few inches 

deep under the control of 

the headgate operator; that 

is, an operator located on 

the fresh-air side of the 

longwall. The plows are 

usually the preferred longwall machine in very low 

coal. Figure 4 shows a 

Belgian miner remote ly controlling the movement of a 

plow; figure 5 is a plan 

view of plow machine 

installations. 

The shearers are much 

bulkier machines than plows, 

and are impractical for use in 

very low coal because of tight 
The value of voice communication is not readily documented; however, 

any information that could be exchanged between the trapped miners and the 

rescuers during a rescue effort would be advantageous. Such information as 

unusual conditions known to the miners trapped or medical advice for them to 

follow until aid arrived are two examples. In other words, a system that 

would provide the location of trapped miners and permit cmunication with 

them would increase the probability of their rescue and reduce hazards to the 

rescue and recovery team. 

DESCRIPTION OF SYSTEMS 

Electromagnetic and Seismic Systems 

The Bureau has developed two systems for locating and communicating with 

trapped miners: a seismic system and an electromagnetic (EM) system. The 

seismic system relies on detection of minute ground vibrations resulting from 

a miner(s) banging on the roof or ribs with some heavy object found in the 

mine. This system is essentially operational and is being tested at numerous 

mine sites. 
FIGURE 2. - Hydraulic roof-support equipment and chain conveyors for longwall faces. 
FIGURE 3. - Coal being removed from face by plow (top) and shearer (bottom), 

clearances and dust problems. However, shearers may be selected in preference to plows where there are hard inclusions in the coal seam, or when roof 

conditions are difficult. The shearer usually rides on the conveyor and 

requires an effective guidance system to avoid damage to the pan line and to 

prevent derailment. As the shearer moves along the face, cutting typically to 

a depth of 2 feet, it is controlled by traveling operators. In Europe, the 

shearers are radio-remote-controlled to reduce the exposure of operators to 

dust and enable them to work from a more effective vantage point. In the 

United States, the use of radio remote control is still under investigation. 
FIGURE 4. - Belgian miner controlling movement of plow by remote control, 

FIGURE 5. - Plan view of plow-machine installations. 

FIGURE 7. - A typical longwall operation. 
VOICE COMMUNICATION ON LONGWALLS 

Requirements 

A representative longwall face crew might be comprised of a foreman, two 

shearer operators, three chock advance miners, one or two mechanics, and 

headgate operator, and one miner at the tailgate. Voice communication is 

frequently required between the headgate and tailgate and to the section 

foreman, wherever he is located. 

Figure 8 typifies the conditions encountered in longwall mining. Since 

the miners must work under rather crowded conditions, starting and stopping 

the conveyor and mining machines are particularly crucial operations when it 

is essential that everyone on the face knows what is happening. During 

maintenance operations,frequent interchange of information between miners 

working at various points along the face is typical. With improved comrnunication channels, the capability of describing and locating problems and 

coordinating maintenance efforts reduces downtime--and downtime is critical 

in longwall productivity. 

Figure 9, a longwall ins tallation in low coal, dramatica lly illustrates 

the limited working space in longwall mining. The area consists of a long 

lateral tunnel in which equipment may be easily damaged. Moreover, it is 

fatiguing to travel any appreciable distance to get to pager phones placed 

along the face, and the noise background is high. Therefore, a pager phone 

designed specifically for longwall mining applications should meet the 

following requirements : 

1. Minimum size. 

2. Rugged case. 

3. Direct acoustic energy a long the face. 

4. Rugged cable and connector design to survive in a harsh environment. 

5. Sufficient power to permit operation along the maximum length of the 

longwall. 

6. Certain control and signaling features that can be incorporated into 

the pager phone system. 

7. Speakers protected from blasting damage. 

Pager Phones 

U.S. longwall faces commonly use standard U.S. pager phones as a means 

of intraface communication, but the U.S. pager phones do not provide an 

adequate face communication system. Major problems are as follows : 
FIGURE 9. - Difficult working environment found in longwall mining. 
Amplifier Un~t Type 15840 

FIGURE 10. - British Sivad pager phone, 

 he use of company names is for informational purposes only and does not 

imply endorsement by the Bureau of Mines. 
$7,000, but this is still at least twice as much as a U.S. pager phone system. 

Secondly, there are a limited number of suppliers. Thirdly, a mine may have 

to either carry its own inventory, or expect long lead times in getting spare 

parts. Finally, in-house maintenance skills have to be developed. However, 

given the high cost of a longwall system (on the order of $1 to $2 million), 

a proper understanding of the value of a good pager phone system in reducing 

downtime indicates that solutions tothese problems are worth considering. 
Radio communications for longwall 

(UHF - Unaided) 

UHF Radio Equipment 

Within the scope of the 

~ureau's program, the feasibility 

of using two-way portable radio 

equipment was investigated. 

Ideally, all the miners on the 

Typical Range longwall face would carry small, 

Low coal: 100 - 200 feet 

High coal: 250 - 350 feet 

light, walkie-talkies , making wireless communication possible to any 

part of the face area, and, to a 

Special condition: Shield support, high coal limited extent, down the head 

Up to 1,000 feet entry. The Bureau has conducted 

several experiments using UHF FIGURE 12. - Typical ranges found in longwall radios for this purpose. In these 

UHF rod io commun icat ions. experiments , 2-watt , minepermissible, portable walkieRadio comrnunlcatlons for longwall 

(UHF - Cable aided, pass~vei 

talkies were used. As shown 

in figure 12, when the units 

are used by themselves, 

effective communication is 

limited in low coal to a 

Typ~cal Range 

LOW coal: 250 - 350 feet 

High coal: 400 - 500 feet 

distance ranging from 100 to 

200 feet, and in high coal 

from 250 to 350 feet. 

(Under some special conditions, such as a shield 

support system in very high 

FIGURE 13. - Enhancement of UHF radio communication coal, the range is good for 

range using leaky-feeder coaxial cable. about 1,000 feet .) These 

distances can be increased 

if a leaky feeder coaxial cable is strung along the face and terminated with 

antennas (fig. 13). A passive cable of this type assists transmission and 

increases the communication distance to 250-350 feet in low coal and 400-500 

feet in high coal. 
feeder applications. The 

Bureau of Mines has also 

experienced success in using 

less expensive RG8 /U cable , which has the advantage of 

mechanical flexibility. 

This type cable, however, is 

not recommended for passive 

systems, but only those 

using a repeater. Other 

forms of leaky-feeder cables 

have been developed in 

Europe . 

FIGURE 15. - MESA-approved Motorola UHF repeater 

battery pack with "hardhat" antenna 

HT 220 walkie-talkies. 

and 

and 

One of the disadvantages of the standard walkietalkie is that it requires 

at least one hand to operate 

it, and some longwall miners 

require both hands free to 

operate their equipment. 

Figure 18 shows a 
FIGURE 17. - Three types of UHF antennas used to terminate leaky-feeder cable. 
Japanese low-frequency 

inductive radio that was 

tried, with limited success, 

on a low-coal longwall 

FIGURE 18. - Chest-mounted UHF radio offers "hands- The Lee Engineerfree" operation. ing Division of Consolidation Coal Co. has recently 

developed a medium-frequency radio that may have promise as a useful longwall 

communication aid (fig. 20). 
FIGURE 20. - Medium-frequency radio and antenna developed by Lee Engineering. 
RECOMMENDATIONS 

Effective communication is an integral and vital part of the longwall 

mining process. As a result of this study, it is believed that four important 

recommendations can be made. The first is that equipment manufacturers should 

include communications equipment as an integral part of the design of the 

overall longwall installation. The second is that a variety of alternatives 

to the face communication system can and should be considered for meeting the 

needs of specific longwall installations because no single type of system is 

suited to a11 situations. These alternatives include the following: 

Rugged pager-phone systems designed specifically for the face environment, 

and incorporating signaling and control functions, as well as the loudspeaking telephone. 

UHF portable radio operating either wire less or cable-aided. 

LOW-frequency/medium-frequency portable wireless radio communication when 

it becomes available. 

The third recommendation is that in spite of the potential problems of dealing 

with an overseas manufacturer, present and future owners and operators of 

longwall sys tems should consider using European equipment. The fourth is that 

development of improved communication systems and remote control equipment for 

longwall operations can and should proceed in advance of the longer term 

projects aimed at achieving substantial automation of longwalls. 
BIBLIOGRAPHY 

1. Dushac , H. Longwall Remote Control Systems. Proc . 3d WVU Conf . on Coal 

Mine Electrotechnol., Morgantown, W. Va., August 1976, pp. 24:l-24:6; 

available for consultation at Bureau of Mines Mining and Safety 

Research Center, Pittsburgh, Pa. 

2. Lagace, R. L. , M. L. Cohen, A, G. Emslie, and R. H. Spencer. Propagation of 

Radio Waves in Coal Mines, Final Report. Task F, Task Order No. 1, 1975 

(Contract H0346045); available for consultation at Bureau of Mines Mining and Safety Research Center, Pittsburgh, Pa. 

3. Leish, E . A. Longwall Communications. Pres . at American Mining congress ' 

Coal Convention, Detroit, Mich. , May 10-13, 1976; available as reprint 

from American Mining Congress, Washington, D.C. 

4. Mountain, N. L., and J. V. Nickel. Recent Developments in Communications 

and Fan Monitoring for Underground Mines. Proc. 3d WVU Conf. on Coal 

Mine Electrotechnol. , August 1976, pp. 16: 1-16: 14; available for 

consultation at Bureau of Mines Mining and Safety Research Center, 

Pittsburgh, Pa. 

5. Roetter, M. Re, A. G. Emslie, R. L. Lagace, and P. F. 0'~rien. Longwall 

Mining Communications, Final Report. Task 11, Task Order No. 2, 1976 

(Contract H0346045); available for consultation at Bureau of Mines 

Pittsburgh Mining and Safety Research Center, Pittsburgh, Pa. 

6. Wolfendon, J. , and D. Hartley. Horizon Control System Designs for Longwall Face Machines. Proc. 3d WVU Conf. on Coal Mine Electrotechnol., 

August 1976, pp. 29:l-29:15; available for consultation at Bureau of 

Mines Mining and Safety Research Center, Pittsburgh, Pa. 
MEDIUM-FREQUENCY MINE WIRELESS RADIO 

by 

Robert L. Chufo ,l Robert L. Lagace ,2 and Lawrence R. wilson3 

ABSTRACT 

The Bureau of Mines is developing a medium-frequency , wireless cornrnunications system for use in the working areas and haulageways of U. S. coal 

mines to satisfy needs not met by present radio equipment. Signal strength 

measurements taken at several mines to date have shown that the low frequencymedium frequency wireless range attainable in different coal seams can be 

highly variable, but that the most favorable overall performance occurs in 

the medium-frequency band of approximately 300 to 1,000 kilohertz. 

Two prototype portable medium-frequency radio units and a fixed station 

radio unit have been designed and fabricated to provide two-way voice communications between roving miners. A range of 1,350 feet in conductor-free 

areas is the goal- These prototype units are being tested in several mines 

across the country, in conjunction with a signal-strength measurement program 

to determine the most favorable operating frequencies and methods of improving 

the performance and applications of medium-frequency mine wireless radio. 

INTRODUCTION 

MI? mine wireless radio is intended to meet roving miner communication 

needs similar to those met by UHF section-to-place radio. As descri.bed in the 

paper dealing with UHF section-to-place radio being presented in this seminar 

session, the miners involved are typically section foremen, maintenance 

workers, ventilation crews, and machine operators. An effective mediumfrequency radio system would answer the following communication needs: 

1. Miners working on basic room-and-pillar sections and on sections with 

special needs, such as longwalls, and sections having full-dimension haulage 

sys tems . 

2. Miners operating vehicles in mines with trackless and trolleyless 

haulage (discussed in IC 8744). 

3. Members of rescue teams during mine rescue operations, thereby 

removing the need for inconvenient trailing wires. 

'Electrical engineer, Industrial Hazards and Communications , Pittsburgh Mining 

and Safety Research Center, Bureau of Mines, Pittsburgh, Pa. 

2~lectronic Systems Section, Arthur D. Little, Inc., Cambridge, Mass. 

3~ollins Radio Group, Rockwell International, Cedar Rapids , Iowa. 
Present commercially available UHF portable and mobile radio equipment 

is well suited for satisfying many of these communication needs. However, 

radio signals in the UHF band suffer from one disadvantage that can sometimes 

be serious; for example, in cases where it is essential that two miners 

communicate around more than one corner and through certain kinds of permanent 

ventilation stoppings . The UHF radio communication range can be severely 

reduced in either case. This range reduction occurs because UHF radio waves 

tend to be confined within the boundaries of mine tunnels. Medium-frequency 

waves, on the other hand, propagate or travel through the coal seam as if the 

network of mine tunnels were not there. 

The underground coal mining industry's extensive and long-standing 

experience with trolley-wire carrier-phone systems has shown that a mine's 

electrical wiring, tracks, trolley wires, phone lines, and air lines can be 

used to carry low-frequency radio signals throughout underground coal mines, 

even to locations some distance from the trolley wire-rail haulage system. 

Recently, the Bureau of Mines bought and tested underground some prototype 

335-kilohertz portable radios that are manufactured in South Africa. The 

wireless communication ranges obtained with these units were quite good and, 

in fact, much greater than originally anticipated from theoretical predictions. 

However, the tests left some doubt as to whether 335 kilohertz was the most 

favorable operating frequency in U.S. coal mines. In addition, these particular units showed some size, weight, and supplier disadvantages. 

In view of these problem areas, the Bureau of Mines initiated a 

measurements and hardware development program to resolve these issues and 

help to develop a medium-frequency unit that would meet the portable wireless 

communication needs that remained unsatisfied by UHF radio. The program 

objectives were to determine which operating frequencies in the low- and 

medium-frequency radio bands are best suited to wireless applications in U.S. 

room-and-pillar coal operations, to design associated small, lightweight 

portable equipment for use by the U.S. mining industry, and to achieve a radio 

range of 1,350 feet without the aid of mine wiring. 

DISCUSSION OF EQUIPMENT AND MEASUREMENTS 

The medium-frequency wireless program is being pursued simultaneously on 

two fronts : 

1. A prototype hardware development effort, based on the favorable 

results of an initial set of radio propagation measurements in the Pittsburgh 

coal seam. 

2. A more extensive set of propagation measurements, covering several 

coal seams, to acquire data on which to base improvements to the prototype 

hardware. 

Medium-Frequency Mine Wireless Radio Hardware 

The present prototype medium-frequency mine wireless radio is a singlefrequency (520-kilohertz) FM system developed by Collins Radio for the Bureau 
in the upper compartment of 

the belt-carried unit. The 

lower, detachable cmpartment houses the rechargeable 

battery and intrinsic safety 

protection circuitry. 

Figure 2 illustrates 

the size and shape of the 

oval-loop antenna and the 

easily accessible controls 

and connectors located on 

the top of the portable unit. 

Included are three 

connectors : one for the 

speaker-microphone , one for 

the antenna, and a third for 

connecting a battery charger. 

Thus, the battery may be 

conveniently charged through 

FIGURE 1. - Miner equipped with portable medium-fre- a connector without removing 

quency mine wireless radio and loop the battery compartment. 

antenna. 
FIGURE 2. - Closeup of portable medium-frequency mine wireless radio and oval-shaped 

bandolier loop antenna. 

The unit has also been designed so that the transmitter-receiver electronics 

in the upper compartment are not exposed when the battery compartment is 

removed. Continuous controls for volume and squelch, and a toggle-switch 

control for push-to-talk (PTT), voice-operated transmission (VOX), and on/off 

functions are included. 

Figure 3 shows a miner using an in-mine fixed-station installation 

consisting of a transmitter-receiver unit and rib-mounted single-turn rectangularly shaped loop antenna (approximately 6 by 24 feet). Figure 4 is a closeup 

view of the fixed-station transmitter-receiver unit. The electronics and 

rechargeable battery are mounted in a heavy-duty, splashproof enclosure that 

is corrosion-resistant to withstand the mine environment. The loudspeaker 

provides paging capability to miners near the fixed station and is 
FIGURE 4. - Closeup of fixed-station medium-frequency mine wireless radio. 
aeto eacote. 

Figure 5 illustrates the preferred antenna orientation in the coal seam 

waveguide within which the radio waves propagate or travel. 

Rock 

h'o Coal seam 

Transmitting loop antenna Receiving 

0 

loop antenna 

Rock 

FIGURE 5. - Coal seam waveguideand preferred antenna orientations for medium-frequency 

mine wireless radio. 
The "trapping" occurs mainly because the electrical conductivity of the 

surrounding rock above and below is much higher than that of the coal. This 

trapping, together with the very low value of coal seam conductivity at the 

Ireland mine, is the primary reason for the better-than-anticipated signal 

propagation results. 

The operating frequency of 520 kilohertz for the prototype mediumfrequency radio equipment was chosen on the basis of these results, and a 

previous finding (from comprehensive in-mine noise measurements by the 

National Bureau of Standards) that mine-generated electrical noise levels 

generally decrease with increasing frequency. A higher frequency was not 

selected to avoid the AM broadcast band which starts at 540 kilohertz. 

To determine whether the favorable Ireland mine propagation conditions 

are typical or exceptional forU.S. coal mines, similar propagation measurements are being performed and analyzed for other mines in the Pittsburgh seam 

and for mines in other major U.S. coal seams. These measurements are expected 

to provide a firmer foundation on which to base the selection of the most 

favorable operating frequencies for the MI? mine wire less radio equipment, and 

on which to predict the expected radio performance in different mines. 

The need to verify the expected propagation conditions in other mines is 

illustrated by table 1, which shows the dranatic differences in attainable 

communication ranges for two widely separated values of coal seam conductivity 

at selected frequencies in the 10- to 1,000-kilohertz band. The range 

estimates for oCoar = 1.4 X log4 mho/m represent the Ireland mine conditions; 

those for 0, = lo-' mho/m represent a mine with coal conductivity near the 

high end of the range of values expected for bituminous coals. It is also 

worth mentioning here that although the quiet-location range estimates are 

readily applicable to conductor-free areas, the noisy-location range estimates 

are probably pessimistic. The noisy locations are likely to occur in the 

vicinity of electrical conductors, which aid signal propagation as well as 

introduce electrical noise. 

TABLE 1. - Range estimates for medium-frequency wireless portable F'M radios1 

high-conduc tivity rock above and be low the c oa 1. 

Coal conductivity , 

.coal (mho/m) 

Frequency, 

kHz 

CASE I 

Communication range, feet 

1 X10°2 

1 x10-2 

1 X10'2 

Quiet locations 

(receiver noise only) 

Noisy locations 

(mine electrical noise 

dominating) 

10 

100 

1,000 

CASE I1 

150 

200 

150 

1.4~10'~ 

1.4~10'~ 

1-4x10'~ 

50- 150 

100- 200 

75- 125 

 or two high-coal seams having different coal conductivities. but the same 

57 -5 

350 

920 

45 0 

950 

1,200 

50- 450 

400- 950 

57591,125 
- 

- 

Pocahontas No. 3 seam 

Pittsburgh seam 

(Ireland, Robinson Run, and Federal No. l mines) 

I 1 I I I IIIII I h 

Results from the inmine propagation measurements program through March 

1977 show that signal attenuation rates can vary widely, 

particularly between mines 

in different coal seams. 

Furthermore , the Pittsburgh 

seam is the most favorable 

of the seams measured to 

date. Figure 6 illustrates 

the radio signal attenuation 

rates obtained in mines in 

three coal seams; namely, 

the Pittsburgh seam in 

northern West Virginia 

(Consolidation coal's Ireland and Robinson Run mines, 

and Eastern Associated 

coal's Federal No. 1 mine), 

the Pocahontas No. 3 seam in 

Virginia (Is land Creek ' s 

VP No. 1 mine), and the 

Herrin No. 6 seam in 

southern Illinois (Inland 

200 500 1000 2000 steel's No. 1 mine and 

FREQUENCY, kilohertz Peabody coal's No. 10 mine). 

The Herrin No. 6 seam FIGURE 6. - Medium-frequency radio signal attenuation exhibits the highest losses 

rates for mines in three coal seams. to date, the Pittsburgh seam 

the lowest. 

Data is expected from an additional five mines, including mines in lowcoal seams. The results of these measurements will not only be used to define 

the most favorable operating frequencies for production versions of the 

medium-frequency mine wireless radio equipment, but also to establish guidelines to assist the coal industry in selecting and installing such equipment 

for use in underground coal mines. 

OUTLOOK 

The prototype medium-frequency wireless radios have been tested in underground mines in two coal seams: Inland steel's No. 1 mine near Sesser, Ill. , 

in the Herrin No. 6 coal seam, and Island Creek coal's VP No. 1 mine, Keen 

Mountain, Va., in the Pocahontas No. 3 seam. These tests were conducted as 

part of the ~ureau's program to investigate the propagation characteristics 

of mines in different coal seams. The test results for these 520-kilohertz 

prototype radios indicate a conductor-free area communication range of about 

500 feet in VP No. 1 and Inland No. 1, the range at a specific frequency 

being largely dependent on the conductive properties of the coal and, to a 

lesser extent, on seam thickness and conductive properties of the surrounding 
rock. Somewhat longer ranges are expected for mines in the Pittsburgh coal 

seam, which appears to have more favorable propagation conditions. The test 

results also showed that ranges well in excess of the 1,350-foot goal are 

possible when the radios are used in the presence of mine conductors along 

haulageways and on working sections. Similar results have been obtained by 

the Lee Engineering Division of Consolidation Coal Co. with a 425-kilohertz 

portable medium-frequency radio recently developed by Lee Engineering for use 

on longwalls and haulage loop-arounds . 

Further underground testing of the prototype MF mine wireless radios will 

be performed in conjunction with the propagation measurements planned for 

several mines in high-production coal seams. The results of these tests and 

the propagation loss measurements will be used to improve the design, performance, and application of future models of the medium-frequency mine 

wireless radio. 
BIBLIOGRAPHY 

Anderson, D. T., and L. R. Wilson. Mine Wireless Communication System 

for Coal Mines. Proc. 3d WVU Conf. on Coal Mine Electrotechnol. , August 1976, pp. 18:l-18:lO; available for consultation at Bureau of 

Mines Mining and Safety Research Center, Pittsburgh, Pa. 

Bensema , W. D. , M. Kanda , and J . W . Adams . Electromagnetic Noise in 

Robena No. 4 Coal Mine. NBS Tech. Note 654, 1974, 44 pp. (Bureau of 

Mines Contract H0133005). 

. Electromagnetic Noise in Itnamm Mine. NBS , NBSIR 74-390, 1974, 

38 pp. (Bureau of Mines Contract H0133005). 

Emslie, A. G., and R. L. Lagace. Propagation of Low and Medium Frequency 

Radio Waves in a Coal Seam. Radio Sci., v. 11, No. 4, 1976, 

pp. 254-261. 

Kanda, M. , J. W. Adams , and W. B. Bensema. Electromagnetic Noise in 

McE lroy Mine. NBS , NBSIR 74-389, 1974, 28 pp. (Bureau of Mines 

Contract H0133005). 

Lagace, R. L., M. L. Cohen, A. G= Emslie, and R. H. Spencer. Propagation 

of Radio Waves in Coal Mines, Final Report. Task F, Task Order No. 1, 

1975, 70 pp. (Bureau of Mines Contract H0346045); available for 

consultation at Bureau of Mines Pittsburgh Mining and Safety Research 

Center, Pittsburgh, Pa. 

Wait, J. R. Note on the Theory of Transmission of Electromagnetic Waves 

in a Coal Seam. Radio Sci. , v. 11, No. 4, 1976, pp. 263-265. 
REFUGE SHELTER COMMUNICATION SYSTEM 

by 

H. Kenneth sacks1 

ABSTRACT 

Communication systems capable of transmitting ultralow-frequency signals 

through the earth have been developed, and a contractual effort is now in 

progress to develop a reliable refuge shelter communication system based on 

through-the-earth signaling concepts. Designs have been completed, and the 

first working model will be finished and ready for testing in mid-1977. 

INTRODUCTION 

When it appears to be impossible to escape, or imprudent to attempt 

escape, following a mine fire or explosion, miners are trained to isolate 

themselves from toxic gases and smoke by erecting barricades of brattice 

cloth on a wooden frame. From 1909 to 1961, more than 800 trapped coal 

miners were rescued from behind barricades. In the past two decades, 62 

miners were rescued from behind barricades and 27 died behind inadequately 

constructed barricades. 

The majority of deaths following explosions result from carbon monoxide 

poisoning. Barricading, when possible, can be a life-saving measure. However, 

roof falls and secondary explosions pose further hazards to miners trapped 

underground. In three instances in the last 20 years, multiple explosions 

have occurred. As a solution to this problem, the National Academy of 

Engineering has suggested sectional or central refuge chambers. 

Central refuge chambers have been established by some companies. Small 

chambers (fig. 1) in earlier times were not uncommon for protection during 

shotfiring. The main disadvantage of a central chamber is that it is likely 

to be some distance away when needed. An analysis of mines on an individual 

basis would be needed before selecting this type of protection. However, if 

a chamber were constructed, some form of communication to the surface would 

be necessary to inform rescue crews that the chamber was being used and of the 

condition of its occupants. 

lsupervisory electrical engineer, Industrial Hazards and Communications, 

Pittsburgh Mining and Safety Research Center, Bureau of Mines, Pittsburgh, 

Pa. 
-inch plank 

air l ine 

Cool 

Section A-A 

Scale, feet 

FIGURE 1. - Diagram of refuge chamber. 

DISCUSSION OF PLANNED SYSTEM 

Communication to a refuge shelter could be provided by means of a borehole equipped with a telephone pair connecting to the surface, by existing 

wiring within the mine, or by some form of through-the-earth system. In all 

probability, two systems would be used. The in-mine telephone system would 

be the least reliable after an explosion, unless the cable installation had 

been specifically hardened. Boreholes could prove highly reliable, but a 

problem could assuredly occur if the chamber locations were moved. 

The most re liable alternative would be a through-the-earth communication 

system. As a result of the ~ureau's trapped-miner location and roving miner 

paging programs , s ys tems for transmitting ultra low-frequency signals through 

the earth have been developed. In fact, contractual effort is now in progress 

to develop a reliable refuge shelter communication system based on these 

through-the-earth signaling concepts. 
In case of an emergency, FIGURE 2. - Artist's concept of the refuge shelter the cover of the through-thetransmitter-receiver unit. earth transmitter-receiver 

will be opened. This will 

automatically turn the system on and cause it to begin transmitting a special 

low-power drain signal. Until this uplink signal is answered by associated 

surface-based equipment, no other messages can be transmitted by the underground unit. This mode of operation was chosen to prevent a drain of battery 

power by futile message transmissions before the arrival of people and equipment to receive the transmissions on the surface above the shelter. Once an 

answer has been received from the surface-based unit, the full range of 

allowed two-way communication will be possible. 

PROGRESS TO DATE 

All designs have been completed, and the first working model will be 

finished in the summer of 1977 for subsequent testing underground. 
BIBLIOGRAPHY 

1. National Academy of Engineering. Mine Rescue and Survival. Final Report. 

BuMines Open File Rept. 4-70, 1970, 81 pp. ; available for consultation 

at the Bureau of Mines libraries at Denver, Colo. , Minneapolis, Minn. , and Pittsburgh, Pa.; at Coal Mine Safety District A Office and Subdistrict Offices, Pittsburgh, Wilkes-Barre, and Johnstown, Pa., and 

St. Clairsville, Ohio; at Coal Mine Safety District B Office and 

Subdistrict Off ice , Mount Hope and Morgant own, W . Va . ; at Coal Mine 

Safety District C Office, Norton, Va.; at the Alaska Field Operation 

Center, Juneau, Alaska, the Eastern Field Operation Center, Pittsburgh, 

Pa. , the Intermountain Field Operation Center, Denver, Colo . , and the 

Western Field Operation Center, Spokane, Wash. ; at the Mines Systems 

Engineering Group, Denver, Colo. ; and at the Central Library, U.S . Department of the Interior, Washington, D .C . 
APPENDIX --COMMUNICATION REPORTS 

The following is a list of reports available in the area of communications. These reports may be obtained from the National Technical Information 

Service (NTIS) , U.S . Department of Commerce, Springfield, Va. 22161. 

Microfiche copies are $2.25 each, and paper copies are available at the prices 

indicated. 

Company name NTIS No. NTIS price Title 

West inghouse Coal Mine Rescue and Survival 

PB 208 266 $5.50 V. 1--Survival Subsystem 

PB 208 267 9.00 V. 2--Communications/Location 

Subsys tem 

PB 208 268 9.00 V. 3--Rescue Subsystem 

Ja H. Crary PB 213 204 9.00 Determination of the Electromagnetic Environment 

A.D.Little PB218688 4.00 A Field Program and Instrumentation 

System for EM Noise Measurements 

A.D.Little PB218658 4.50 Assessment of EM Noise Measurements 

Taken by Bureau of Mines 

Contractors 

Westinghouse PB 226 600/A~ 5.50 EM Location System Prototype and 

Georesearch Communication Station Modification 

West Virginia PB 225 862/AS 6.00 Analysis of Communication Sys tems 

University 

National Bureau PB 226 773/A~ 4.00 Survey Report of the USBM EM Noise 

of Standards Measurement Program 

National Bureau PB 226 781/AS 3.50 Applicability of Speech Bandwidth 

of Standards Compression Techniques in Mine EM 

Communications 

Colorado School PB 231 154/A~ 7.75 Thru-the-Earth Electromagnetics 

of Mines Workshop 

Mine Safety 

Appliances 

Develop, Assemble, and Ins tall a 

Permissible Surveillance and Communication System in the Bureau of 

Mines Mining and Safety Research 

Center Coal Mine, at Bruceton, Pa. 

4 .OO V. 1--System Description 

4.50 V. 2--Circuit and Installation 
Company name NTIS No. NTIS price Title 

Westinghouse PB 232 880/AS $4.50 E lectromagnetic Location ExperiGeoresearch ments in a Deep Hardrock Mine 

Continental Oil PB 232 887/A~ 5.50 Seismic Miner Detection and LocaCo tion System; Phase I--Final Report 

A. D. Little 

Westinghouse PB 235 604 

(set) 

PB 235 6051~~ 

Survey of EM and Seismic Noise 

Related to Mine Rescue 

Communicat ions 

6 .OO V. 1--Emergency and Operational 

Mine Communications 

10.50 V. 2--Seismic Detection and Location of Isolated Miners 

21.50 Trapped Miner Location and Communication Sys tem Development Program 

7.50 V. 1--Development and Testing of an 

EM Location System 

4.50 V. 2--DetectLon and Location of 

Entrapped Miners by Seismic 

Means (by Dr. S. J. Duda) 

5 -00 V. 3--Monitoring, Locating, and 

Communication System for 

Normal Mine Operation and 

Post-Disaster Rescue 

Operations 

4.50 V. 4--PerformanceTestandEvaluation of a Full Wave Location 

Transmitter 

Collins Radio PB 237 218/~~ 4.00 System Study of Coal Mine 

Communicat ions 

Colorado School PB 237 852/A~ 5.50 Research on the Transmission of EM 

of Mines Signals Between Mine Workings and 

the Surface 

A. D. Little PB 240 5521~~ 4.50 Investigation of Communication Standards as Related to Coal Mines 

Collins Radio PB 240 481/A~ 3.50 Waveform Generator for EM Location 

of Trapped Miners 

National Bureau COM 741 1688/A~ 4.00 Surface Magnetic Field Noise Meaof Standards surements of Geneva Mine 

National Bureau COM 741 1687/A~ 6 .OO Electromagnetic Noise in Grace Mine 

of Standards 
C ompa ny name- NTIS No. NTIS price Title 

National Bureau COM 741 1717/AS $6.75 Electromagnetic Noise in McE lroy 

of Standards Mine 

National Bureau COM 741 1718/AS 5.50 E lectromagneti-c Noise in Itmann 

of Standards Mine 

National Bureau COM 741 1450/AS 4.50 Time and Amplitude Statistics for 

of Standards E lectromagnetic Noise in Mines 

National Bureau COM 751 0258 6.00 ElectromagneticNoise inLucky 

of Standards Friday Mine 

Continental Oil PB 243 068/As 5.00 SeismicMineMonitorSystem-- 

Co Phase IV report 

Continental Oil PB 241 504/AS 4.00 Seismic Mine Monitor System-- 

Co. Phase I1 report 

A. D. Little Technical Services for Mine Communications Research 

PB 249 829/As 5.00 Task D--Applicability of Available 

Frequency Multiplexed Carrier 

Equipment 

PB 249 830/As 5.00 Task B--Applicability of State-ofthe-Art Repeaters for Wireless 

Mine Communications 

PB 249 831/As 5 -00 Task A--Applicability of State-ofthe-Art Voice Bandwidth Compression Techniques for Wireless Mine 

Communications 

Collins Radio PB 244 896/A~ 20.00 Research and Development Contract 

(set) for Coal Mine Communication 

Sys tems 

PB 244 897/AS 4.50 V. 1--Summary and Results of System 

Study 

PB 244 898/As 5.50 V. 2--Mine Visits 

PB 244 899/AS 7.50 V. 3--TheoreticalDataBase 

PB 244 900/AS 4.50 V. 4--Environmental Measurements 

Continental Oil PB 251 705/AS 4.00 Seismic Mine Monitor System 

Co. 
The following publications are available without charge from the Publications Department, U.S . Bureau of Mines, 4800 Forbes Avenue, Pittsburgh, 

Pa. 15213: 

Lamonica, J. A*, R. L. Mundell, and T. L. Muldoon. Noise in Underground Coal 

Mines. BuMines RI 7550, 1971, 11 pp. 

Lee, F. R. Permissible Mine Equipment Approved by the Bureau of Mines During 

1967-68. A Supplement to Bulletin 543 and Information Circulars 8220, 8299, 

and 8372. BuMines IC 8463, 1970, 25 pp. 

Lepper, C. M., and J. H. Scott. An Improved Electrical Resistivity Field System for Shallow Earth Measurements. BuMines RI 7942, 1974, 20 pp. 

Parkinson, H. E. Mine Pager to Public Telephone Interconnect System. BuMines 

RI 7976, 1974, 14 pp. 

U.S. Bureau of Mines (Staff--Mining Research). Mine Communications. Proceedings : Bureau of Mines Technology Transfer Seminar, Bruceton, Pa. , Mar. 21-22, 1973. BuMines IC 8635, 1974, 86 pp. 

In addition, Preprint No. 76-F-133, entitled "A Review of Research on 

Underground Mining Comrnuni~ations,~' by John N. Murphy and Howard E. Parkinson 

is available from the Society of Mining Engineers of AIME, 540 Arapeen Drive, 

Salt Lake City, Utah 84108. 

U.S. GOVERNMENT PRINTING OFFICE: 1977-703-001 I74