MINE COMMUNICATIONS 

An Overview of the Bureau of Mi.nes Communications Research 

Howard E. Parkinson 

Supervisory Electrical Research Engineer 

Industrial Hazards and Communications 

Pittsburgh Mining and Safety Research Center 

Bureau of Mines 

U.S. Department of the Interior 

Pittsburgh, Pennsylvania 15213 

ABSTRACT 

Since 1969, the Department of Interior, Bureau of Mines, has 

carried out communications research. Research has been directed 

toward developing emergency and nonemergency mine comrunications. 

This paper gives an overview of the progress made in the last two 

years. Particular emphasis is given to the overall program, noise 

and signal measurements, systems studies, guidelines, products, and 

demonstrations now being carried on in operating mines. 

INTRODUCTION 

Presently mine communications consists of loudspeaking- or 

paging-type telephones or alternatively, magneto ringing telephones; 

in either case all phones are on a common party line with one telephone for each working section and additional phones at other key 

locations, such as maintenance shops, both underground and on the 

surface. While a few mines have begun to use dial-type telephones 

underground, their use to date has been very limited. Additionally, 

rail transportation systems are typically equipped with carrier 

current phones to provide communications between vehicles and between 

vehicles and a central dispatcher. 

While there have been qualitative indications that mine communication systems need improvement, the exact nature and the extent of 

the modifications required have not been precisely defined. The 

Bureau of Mines has undertaken a program to specifically define the 

areas where improved technology and techniques can be of benefit to 

the mining industry, and through a ~ureau/contractor team, various 

mine communications systems are being developed and, with the cooperation of the mining industry, are being evaluated in underground 

coal mines. 
THE RESEARCH PROGRAM 

The Bureau has developed an approved mine operating/emergency 

communications system complete with simple monitoring and a means 

of communicating with trapped miners. The system is installed in the 

Bureau's Safety Research Mine at Bruceton, Pennsylvania. Simultaneous 

with this inhouse program, the Bureau developed a contractor program. 

The contractor program includes other government agencies, universities, private companies, and mine operators. The contractor program 

has resulted in reports covering (1) electromagnetic noise and propagation measurements within operating mines; (2) survey of existing 

mine communications systems; (3) theoretical and analytical studies 

of particular problems in mine communications; (4) a program for the 

preparation of guidelines for mine communications; and (5) new 

products for underground communications. At this seminar we will 

be reporting on a new mine carrier phone using frequency diversity 

and a new mine communications system using coaxial cable. 

MEASUREMENTS 

The experimental in-mine measurements cover the spectrum of 

interest for electromagnetic communications. As would be expected, 

the electromagnetic noise follows ~urphy 's Law: At very low frequencies, where propagation is independent of the mine openings, noise 

is greatest; and at higher frequencies, where propagation is forced 

to follow the mine openings, the noise is minimal. It is of interest 

to note that about 30 years ago when the Bureau of Mines determined 

the frequency of the trolley wire communications, they selected the 

area of 100 KHz This frequency is a tradeoff between the electromagnetic noise and the electromagnetic propagation efficiency. 

Mine wireless communications are highly desirable. Measurements 

at the ultra high frequencies indicate the following significant 

propagation characteris tics : (1) Attenuation in db increases linearly 

with increasing distance ; (2) horizontal polarization produces significantly lower transmission loss at a given distance than does vertical 

polarization; (3) transmission losses decrease significantly at a 

given distance as the frequency is increased from 200 to 1,000 MHz. 

As an example, with both transmit and receive antennas vertically 

polarized, attenuation in db per 100 feet is 25, 6, and 4 for 200, 415, 

and 1,000 IMz, respectively; (4) signal attenuation immediately around 

a corner is considerable at all frequencies and is about 25, 17, and 

14 db for 200, 415, and 1,000 MHz, respectively; and (5) complete signal 

depolarization is observed around the corner. 
SYSTEM STUDIES 

To more specifically define the problems within mine communications 

systems, surveys have been taken in u~nderground mines to determine the 

key operational parameters, namely (1) the time to reach key personnel 

underground; (2) the traffic density or availability of phone lines as 

a function of time during the working shift ; and (3) reliability and/or 

maintainability of the existing communications equipment. Surveys have 

consisted of full-shif t monitoring of mine telephone lines and carrier 

current rail haulage communication circuits, followed by detailed analysis 

of these recordings to ascertain if there are particular problem areas. 

As an example, the results from a survey of a 4500-ton-per-day mine indicate that the maximum use of the mine telephone was 49 percent of the 

time during the second hour of the shift. During quarter-hour periods 

there were times when the system was used 71 percent of the time. With 

this kind of a system there is a 30 percent chance of finding a busy 

signal on a given call. This is considerably worse than the one chance 

in a thousand which is the standard for commercial telephone circuits. 

It is estimated that a six-channel phone system would be required to 

bring the system to commercial standards. 

Further examination of data reveals that the duration of a given 

c a l l o r an attempted call is very short. For many mines of this 

size the survey shows that the average time to reach key personnel 

underground is about 30 minutes. In case of emergency this time may 

be invaluable. In terms of operational efficiency the cost of a highproduction section may be $700 an hour; hence, if a maintenance foreman 

is needed, his value to the total operation can be rather significant 

and the need to reach him promptly cannot be overstated. 

In the same mine the carrier current phones, which are used 

primarily for dispatching of vehicles on the haulageway, were found 

to have a probability of being busy approximately 10 percent of the 

time. However, because these phones serve as a safety control system 

for the traffic on the haulageway, it is not deemed advisable to provide additional channels. 

Existing equipment was found to be operational; however, the quality 

of the audio was often less than desirable for intelligible communications. In one particular system the lack of intelligibility was traced 

to improper alignment of the trolley wire phones. In another case the 

trouble was traced to phone line grounding which was causing extensive 

hum on the mine phone system. 
GUIDELINES 

The Bureau in the past has mostly restricted itself to the approval 

of communications equipment on the basis of permissibility. Other 

industries have developed standards relative to comnications equipment, design, operation, and maintenance. The mining industry needs 

similar cornmupications guidelines, and the Bureau is presently 

developing guidelines for the mine telephone system. Guidelines will 

be established for the installation , maintenance, and tests of wired 

mine communcation systems using the magneto- and pager-type mine telepnone equipment The guidelines will cover such aspects of the system 

as the mounting of phones, the hanging of cable, selecting wire and 

cable, care and service of handsets and hook switches, checking of 

batteries, measuring of signals, and instructions for inspectors to 

be used in the examination of an operating system. 

Consideration will be given to the test equipment required to 

check battery status, phone line impedance characteristic, phone line 

and/or equipment grounding, signaling, message handling capabilities 

and other system and equipment characteristics that need to be 

checked to ascertain that the phone system is operational and can 

be depended upon in the case of an emergency. 

After completing guidelines for the mine telephone system, 

additional guidelines will be prepared for the trolley wire phone 

system. 

NEW PRODUCTS 

During the past two years the Bureau has had developed the 

following new communication products for the mining industry: (1) Trapped 

miner locator transmitter; (2) trapped miner portable receiver; (3) trapped 

miner helicopter-borne receiver; (4) call alert paging transmitter; 

(5) call alert paging receiver; (6) belt box page phone; (7) frequency 

diversity trolley wire and hoist rope phone; (8) mine telephone to 

public phone interconnect; (9) carrier phone to wireless radio interconnect; and (10) mine communications and monitoring phone for coaxial 

cable. A contract is now underway to develop a wireless radio system 

capable of communicating 1350 feet between two roving miners. A 

portable transceiver and a repeater are being developed. 

DEMONSTRATIONS 

New phone systems are being installed, not only by the Bureau 

of Mines but by mine operators. During this seminar, papers will be 

presented on (1) new communications center for Ohio Valley Division, 

by Randy Fizer, Ohio Valley Division, Consolidation Coal Company; 

(2) a permissive diallpage telephone for coal mining communications 

by Ken Betch, Gaitronics Corporation, George Trace, Southern Ohio 

Coal Company, and Paul B. Day, Gaitronics Corporation; and (3) a 
new whole-mine communications system 'by John Combellick, Collins Radio 

Company. As indicated in the Bureau systems study, each of these 

systems has multiple channels. The paper by John Combellick describes 

the system the Bureau of Mines will be demonstrating at U.S. steel's 

Robena complex. This is a whole-mine communications and monitoring 

system. The phone line is a 7/8-inch coaxial cable. The phones are 

novel--there is a pushbutton dial and a private-line capacity for 100 

simultaneous phone conversations. The phones are designed to reach 

individuals. When the phone is rung, an electromagnetic call alert 

signal is transmitted to the individual being called. Each key person 

has his own call alert receiver. Special haulageway phones have 

CO monitoring, and section phones have CO, methane, and air ventilation monitoring. Air split phones have extensive monitoring in the 

fresh air and the return air. You will learn about the system from 

John Combellick. 

The Bureau, in the coming year, will also be demonstrating a mine 

cornmunicati.ons system for mines producing less than 400,000 tons per 

year. 

CONCLUSIONS 

Techniques and technology are available to overcome many of the 

operational problems of underground mine communications. These 

techniques are being reduced to hardware that will be usable for 

the mining industry. The problems of underground mine communications 

can be solved; this paper presents a variety of concepts that have 

been developed and experimentally evaluated in mines. No single 

concept provides a universal solutiom, but hybrid systems which 

address all problems can be and are being implemented. In the course 

of this seminar, this section and the section to follow, you will 

learn more of the details of the advances in mine comunications.