ELECTROMAGNETIC 

LOCATION SYSTEMS FOR 

METAL/NON METAL MINES 

PREPARED FOR 

UNITED STATES DEPARTMENT OF THE INTERIOR 

BUREAU OF MINES 

Westinghouse Electric Corporation 

GEOPHY SlCAL INSTRUMENTATION SYSTEMS 

3655 FRONTIER AVENUE 

BOULDER, COLORADO 80301 

FINAL REPORT 

CONTRACT NO. J0166100 

MODFY AND TEST ELECTROMAGNETIC: LOCATION SYSTEM 

fN METALINON METAL MINES 

JANUARY 15, 1979 
DIS CLAIMER NOT1 CE 

The views and conclusions contained in this docurtent are those of the 

authors and should not be interpreted as necessarily representing the 

of fi cia1 policies or recomnendations of the Interior Department's Bureau, 

of Mines or of the U.S. Government. 
I i 4. Title aod Subtitle 1 5. Report Date 

REPORT DOCUMENTATION PAGE 

January 15, 1979 

ELECTROMAGNETIC LOCATION SYSTEMS FOR METAL/NON METAL - 

MINES 6. 

7. Author(s) 

A. J. Farstad, R. F. Kehrman 

1. Report No. 3. Recipient's Acceaeton No. 

I 8. Performing Organization Report No. 

1 

2. 

9. Performing Organization Name and Address 10. project/~ask/uork Unf t No. 

I Westinghouse Electric Corporation 

3655 Frontier Avenue 11. Contract or Grant No. 

Boulder, Colorado JQI661QQ 80301 

13. Type of Report I 

12, Sponsoring Organization Name and Address 

Office of the Assistant Director - Mining FINAL 

1 Bureau of Nines I 

Department of Interior 

14. Washington, D. C. 20241 

15. Supplementary Notes 

16. Abstract 

Characteristics of metallnon metal qines were evaluated to determine the 

suitability of applying the U.S. Bureau of Wnes electromagnetic locatgon system 

to the problem of locating trapped driers in metal/non metal mines. Statistical 

distributions of mine depths and overburden conductivities show that the existing 

USBM EM system is inadequate for most metal/non metal mines. 

Alternate approaches to trapped miner location in deep mines were identif ie 

and subsequent field tests were conducted at six (6) mines to evaluate their 

feasibility. The approach considered to be the most promising is one which 

utilizes the existing manpack transmitting system, modified slightly for a dual 

frequency output, in conjunction with a sophisticated signal processing receiver 

on the surface. The main advantage of staying with a "through the earth" approach 

is that the underground equipment can be kept simple, easily maintained, lightweight and inexpensive. 

Trapped miner location, through the earth 

communications, metal/non metal mines, 

e le ct romagne t i c communications 

I 

17. Originator's Key Words 

b 

18. Availability Statement 

L I 

19. U. S. Security Classif. of the Report 

UNCLASSIFIED 

1 

20. U. S. Security Classif. of This Page 21. NO. of Pages 

UNCLASSIFIED 

22. Price 
FOREWORD 

This report was prepared by Wes tinghouse Electric Corporation, Geophysical 

Instrumentation Systems, 3655 Frontier Avenue, Boulder, Colorado 80301 

under USEM Contract Number 50166100. The contract was initiated under 

The Metal and Nonznetal Health and Safety Research Program. It was administered under the technical direction of PM&SRC with Mr. Robert Chufo acting 

as Technical Project Officer. Mr. Robert Carpenter was the contract 

administrator for the Bureau of Mines. 

This report is a summary of the work recently completed as part of this 

contract during the period July 1, 1976 to December 31, 1977. This report 

was submitted by the authors on December 15, 1977. 
TABLE OF CONTENTS 

Section 

1.0 INTRODUCTION AND SUMMARY 

Page 

9 

2.0 METAL/NON METAL MINE CHARACTERISTICS 11 

2.1 Statistical Characteristics of Disaster Case 11 

Histories 

2.2 Statistical Characteristics of Metal/~on Metal 22 

Mine Parameters 

2.3 Mine Construction Techniques 29 

3.0 THEORETICAL CHARACTERISTI CS OF UNDERGROUND ELECTRO- 30 

MAGNE TI C PROPAGATION 

3.1 Effects of Earth Conductivity on Propagation 30 

3-2 Penetration Depth of EM Waves 31 

3.3 Effects of Parasitic Coupling 34 

4.0 SYSTEM REQUIREMENTS FOR LOCATION AND COMMUNICATIONS 38 

WITH TRAPPED MINERS IN METAL/NON METAL MINES 

4.1 Requirements for Through the Earth Uplink 38 

4.2 Requirements for Through the Earth Sidelink 41 

4.3 Portability Requirements 42 

4.4 Permissibility Requiremnts 42 

4.5 Blasting Cap Susceptibility to ULF Transmissions 42 

4.6 Location Accuracy Requirements 45 

5.0 CANDIDATE EM LOCATION TECHNIQUES 4 7 

5.1 Trapped Miner Location Using Repeaters 47 

5.2 Downlink Communications 6 1 

5.3 Trapped Miner Location by Direct Through the 6 1 

Earth Transmission 
Sect ion 

6.0 

TABLE OF CONTENTS 

FIELD TEST PROGRAM 

6.1 Mine Characterization Summary 

6.2 EM Propagation Tests 

CONCLUSIONS 

RECOMMENDATIONS 

REFERENCES 

Page 

65 

65 

76 

110 

114 

115 
LIST OF FIGURES 

Figure Page 

1 Chronological Distribution of Mine Accidents in Metal/ 16 

Non Metal Mines 

2 Chronological Distribution of Mine Fires in Metal/Non 17 

Metal Mines 

3 Chronological Distribution of Mine Explosions in ~etal/ 18 

Non Metal Mines 

4 Chronological Distribution of Roof Falls in Metal/~on Metal 19 

Mines 

5 Chronological Distribution of Flooding Accidents in Metal/ 20 

Non Metal Mines 

6 ~istribution of Deaths in Metal/Non Metal Mine Disasters 2 3 

by State 

7 Distribution of Maximum Working Depths of Metal/Non Metal 24 

Mines in U. S. (Representative Sample - 45 Mines) 

8 Cumulative Distribution of Existing Metal/~on Metal Mines 25 

in the U.S. (Representative Sample of 45 Mines) 

9 Cumulative Distribution of New Mine Shaft Construction in 26 

U.S. (Metal/Non Metal Mines Producing More than 1200 

Tons per Day) 

10 Conductivity Distribution of 17 Selected Metal/Non Metal 28 

Mines 

11 Skin Depth vs . Frequency for Various Conductivities 32 

12 Loop Antenna and Horizontal Coupling Relationships 33 

13 Magnetic Fields vs. Distance from Electric and Magnetic 37 

Source Coupling to a Long Conductor 

14 Atmospheric No-l-se 40 

15 Location of Manpack Transmitter Received by Two Repeaters 48 

16 A, B, C, and D Wireless Digital Repeaters 50 

16 E and F Wireless Digital Repeaters 5 1 
LIST OF FIGURES 

(Cont' d.) 

Figure 

17 

18 

19 

20 

2 1 

22 

23 

Univers a1 Wireless Digital Repeater 

Digital Wireline Repeater Sys tern 

Univers a1 Wireline Digital Repeater 

Analog FM Repeater System 

Universal Analog F'M Repeater 

Top View-Mine with Repeater System 

Relative Induced Voltage in Long Horizontal Dipole from 

Vertical Magnetic Dipole Transmitter 

Block Diagram of Conductivity Measurement System 

Block Diagram of EM Noise Measurement Sys tern 

Conductivity Measurements - Oz ark Mahoning Mne , Rosi clare , I llinois 

Underground Noise Measurements Set-up , Henderson Mine 

Underground Conductivity Measurements , Henderson Mine 

Photograph of WDI 1221 System 

Sample of EM Noise Measured During Task I1 

Generalized Conductivity Ranges for Rocks and Various 

Mineral Host Materials 

fine Rescue Transmitter (attached to Cap Lamp Battery) 

EM Field Measuremnt Equipment 

Multichannel FM Telemetry Filter and Discriminator 

Westinghouse Narrowband FM Transmitter 

Wes tingjhouse Narrowband FM Receiver 

Henderson Mine - Uplink H Measurements 

z 

Mine Map of International Salt Mine 

Big Island Mine 

Page 

52 

55 

56 

57 

58 

60 

64 
LIST OF FIGURES 

(~ont'd.) 

Fi gure 

39 

40 

41 

Page 

Homestake Mine - Lead, South Dakota 87 

Ozark Mahoning Co. - Rosiclare, Illinois 88 

Mine Map of St. Joseph Lead Co. - Fletcher Mine 

Viburnum, Missouri 

Henderson Mine 90 

Sidelink Propagation of ULF Horizont a1 Magnetic Fields 93 

Stauffer Chemical Co. Big Island Mine - Green River, Wyo. 

Sidelink Propagation of ULF Horizontal Magnetic Fields 94 

Stauffer Chemical Co. Big Island Mine - Green River, Wyo. 

Sidelink Propagation of ULF Signals - Fletcher Mine 95 

St. Joe Lead Co. , Viburnum, Missouri 

Signal Propagation of ULF Signals - Fletcher Mine 

St. Joe Lead Co. , Viburnum, Mssouri 

FM Telemetry Configuration 98 

Wes tinghouse Detect or/VCO Network 99 

Wes tinghouse Filter-Dis criminator Sys tern 100 

Reconstructed Manpack Signals 102 

Inductive Repeater Network 103 
LIST OF TABLES 

Table 

1 List of Accidents at Metaland~on/MetalMines and Quarries 

in the U. S. in Which Five or More Lives were Lost 

2 Breakdown of Mining Disasters by Type and Product 

3 Mine - Conductivity Distribution 

4 Summary of Mine Tests 

5 ULF Uplink Propagation Summary 

6 ULF Sidelink Propagation Summary 

7 VLF Voice Communications 

8 Magnetic Field Strength Distribution 

9 Qualitative Assessment of Trapped Miner Locat ion Techniques 

10 Sunnnary of Through the Earth ULF Propagation Results in 

Mines with Overburdens Greater than 300 Meters Deep 

Page 

12 
INTRODUCTION AND S URY 

The U.S. Bureau of Mines has developed an electromagnetic system for 

detecting, locating and communicating with miners trapped in underground coal 

mines. The miners communication unit is a small belt-carried transmitter and 

voice receiver (attached to the miner's cap lamp battery). The transmitter 

is used in concert with a loop of wire deployed on the mine floor to transHlit electromagnetic signals to the surface. These signals are detected by 

the rescue party and used to locate the miners' position. Furthermore, a 

surface transmitter is used by the rescue party to convey voice instructions 

to the miner via baseband audio currents injected into the earth through a 

long horizontal wire antenna. 

The trapped miner communications and location system has been f abricated in a ruggedized package and is presently undergoing extensive testing 

in numerous coal mines in the eastern coal fields of United States. Results 

that have been obtained thus far indicate that the system's performance is 

more than adequate for the vast majority of U.S. coal mines (1,2,3,4, & 5). 

However, this is not expected to be the case for metal/non metal mines, which, 

as a rule, are significantly deeper than the average coal mine. 

The objective of the present research program (Contract No. 50166 100) 

was to determine whether the existing coal Hline trapped miner detection, 

location and communication system could be effectively used in deep metal/ 

nonmetal mines and to identify suitable modifications that could be applied 

to the system to adapt its performance to the deeper mines. Initially, six 

mines were selected for further study on this program; ones at which the 

geophysical characteristics (earth conductivity and background noise) would 

be measured on the surface and in the mine and the communication and propagat ion characteristics would be evaluated and measured on subsequent visits 

to the mines. 

The trapped miner location problem is more severe in metal/non metal 

mines when compared with that of coal mines because of their significantly 

greater depths. Before any modifications could be recommended for the trapped 

miner location system, a statistical study of mine depths was undertaken for 

the metal/non metal mines in the United States. Also the statistical characteristics of mine disaster case histories were developed for metal/non metal 

mines dating back to 1869. 

Candidate approaches to solving the trapped miner locat ion problem 

were identified on this program and can be subdivided as follows: 

( 1) Utilize electromagnetic repeaters distributed along a 

main drift to receive transmissions from manpack transmitters 

and relay the signals to a shaft station repeater for inductive 

propagation up the shaft. 
(2) Utilize a twisted pair cable along the main drift to multiplex 

repeater output signals and deliver the composite multiplexed 

signal to a shaft station repeater at the shaft. 

(3) Utilize a significantly lower frequency manpack transmitter 

and an array of horizontal wire receiving antennas on the 

surface to permit a through the earth uplink even in the deepest 

mines. 

Measurement results obtained on this program have demonstrated the feasibility 

of each of these basic approaches; however, from a practical standpoint, the 

purely "through the earth" mode of operation offers the most promise when one 

carefully considers the harsh mine environment and the attitudes of mine 

company personnel in conjunction with the measurements obtained on this program. Briefly, the main advantage of the "through the earth" approach is 

that the underground equipment can be kept simple, easily maintained, lightweight, inexpensive, etc. Furthermore any increase in system compledty can 

be restricted to the surface signal detection and processing equipment, the 

cost and maintenance of which, need not be the responsibility of the individual 

mine companies. The details behind implementing a "through the earth" system 

are described more fully in the text of this report. 
2.1 Statistical Characteristics of Disaster Case Histories 

Mine Disaster Statistics 

The statistics cited in this report are for underground mining activities and -they exclude accidents that occurred in coal mines (6). Only 

accidents in which five or more fatalities are involved are used in this 

tabulation. Description of each accident arranged chronologically is given 

by Table 1. 

Figure 1 shows that the largest number of mine disasters and deaths 

occurred in the interval from 1890 to 1930, with the period from 1910 to 1920 

showing the greatest concentration of mine disasters of all types. 

Distribution of Disasters by Time 

The period from 1869 until 1890 yielded 7 mine disasters and 86 

fatalities. 

From 1890 until 1930, there was a total of 43 mine disasters, resulting in 736 deaths. The years 1930 through 1972 show 15 disasters with 223 

deaths. 22 of the events were caused by fire which resulted in the deaths 

of 531 .miners as shown in Figure 2. Of the remaining disasters, 15 were 

caused by explosions that killed 154 men (Figure 3), 13 were by roof falls which 

killed 90 miners (Figure 4) , 7 were by flooding which caused 168 deaths 

(Figure 5), and 2 disasters brought about 82 deaths by asphyxiation. 

Distribution of Disasters by Type of Event 

Fire is the main hazard in mine disasters and it occurs mre frequently and causes more deaths than all other disasters combined. From 1869 

until 1972, 585 deaths were incurred by fire. The ratio of fire fatalities 

to disaster is higher than any other type of mine disaster, being 24.1 to 1. 

Explosion accounts for the second largest number of deaths in metal/ 

non metal mines in the 1869-1972 interval, showing a deathldisaster ratio 

of 10.3 to 1. 

Flooding, with 168 deaths in 7 disasters, places third in cause of 

death, with a 24 to 1 ratio. 

Roof falls have led to 90 fatalities in 13 events for a ratio of 

6.9, and asphyxiation accounted for 82 deaths for a ratio of 10.2. 

Distribution of Disasters by Mine Type 

Table 2 indicates that copper and gold mines have been involved in a 

major portion of metal/non metal mine disasters, followed by iron and lead/ 

zinc mines. Fire or explosion predominate as the major cause of death, 

regardless of the type of mine involved. 
TABLE 1 Liat of accidents at aretal and nonmetal mines and quarries (except coal mines) in the Lhited States 

in which five or wre lives vere lost 

Date 

1869 - Apr. 7 

Product 

Gold 

Cold 

Copper 

Copper 

Gold 

Copper 

Marb le 

Copper 

Iron 

Cold 

Copper 

Gold 

Gold ' 

Gold 

Copper 

Iron 

Silver-Gold 

Gould 6 Curry 

eversveat-St. 

Lawrence S heldon quarry 

ilver Bow No. 2 

Name of nine 

Kentucky-Yellow 

Jacket-Crown Point 

Yelluu Jacket 

Phoenix 

Belmt 

afield 

Bull Domingo 

P leepy Ho 1 low 

sceola 

Location 

Gold Hill. Nevada 

Gold Hill, Nevada ' 

Phoenix, Nchigan 

Belmont . Mmtana 

Silver Cliff, Colo. 

I.. na Lee 

F 

t. Laurence 

I Virginia City, Nev. 

Butte, Montana 

Butte. Mont. 

Crystal Falls, Mich. 

White Oaks, N. Mex. 

Sleepy Hollow, Colo. 

Calumet, Mich. 

I Leadville . Colo. 

Cripple Creek Dist. 

El Paso Co. , Colo. 

Basin, Mont. 

Butte, Mont. 

Iron Mountain, Mich. 

Killed I Nature of accident References 

Fire in timber. probably from 

candle 

ire from blacksmith forge on 

,300-f oot level. 

xplosion of dynamite caused by 

candle held by miner 

I Fire from blacksmith shop 

spread to magazine of powder and 

then to shaft 

i:xplosives; box of dynamite exploded in boiler room; headfrar~e burned; nren in mine 

suffocated. 

:?ire in shaft station 1,500 level 

cause unknm. 

.Une fire; candle in chute on 400 

level. 

pof f a l l i n underground quarry 

9 ne fire; probably from candle 

t pump station. 

12 

30 ne fire on 27th level; cause 

6 amite explosion from unknown 

ne fire. 20.24 

y funes; cause unknown. 
TABLE 1 List of accidents at metal and nonmetal mines and quarries (except coal mines) in the lbited States 

in which five or mre lives were lost 

References 

20.24 

20 

Date Location Killed Nature of accident 

ire in bunk house at mine 

nt rance . ight shift powder man ate lunch 

.n stub drift powder magazine 

1.200 level near Daly-West ehaft. 

Zandle or cigarette, air was downVirginia City, Mont. 

Butte, Mont. 

Drytom. Calif 

Joplin. Mo. 

Treadvell, Alaska 

Durant, Okla. 

Radereburg, Mont. 

Tonopah . Nev. 

Virginia, Minn. 

Negaunee, Mich. 

Ely, Nev. 

Dome Creek, Alaska 

Hibernia, N. J. 

Ironwood, Mich. 

Ely, Nev. 

Miami, Ariz. 

1903-Nov. 6 

1905-May 12 

1907-Nov. 30 

1909-Feb. 26 

1910-Xar. 2 

1910-Nov. 28 

1911-Jan. 18 

1911-Feb. 23 

1911-Mar. 11 

191 1-May 5 

19 11-Aug. 23 

1911-Sept. 28 

19114ct. 19 

1912-May 13 

1912-July 7 

1913-Apr. 17 

zast. Povder smoke circulated in 

nine but did not get much above 

1,000 at any time. Fumes killed 

a mule in stable off snovsheds at 

Pandora, Colo. 

Park City. Utah 

1901-Nov. 20 

1902-July 15 

Product 

tle 

Nane of Mine 

Cold 

Copper 

Cold 

Lead 

Gold 

Asphalt 

Gold 

Gold 

Silver 

Iron 

Iron 

Copper 

Gold' 

Iron 

Iron 

20.24 

20,24 

22 

ne fire; men overcome by gas 20.22 

2 1 

21.22 

22 

10 amite explosion 21.22 

5 r blast; resulting from 20.22 

cave-in ; threw men against 

walls and timbers. 

Kearsarge 

Cora 

Freemont Consolidated 

Keystone 

Alaeka-Mexican 

Jumbo 

Keating 

Belmont 

Norman mine (open 

pit) 

Hartford-Cambria 

No. 2 

Ziroux 

Shakespeare Placer 

Gold 

Silver 

Lead 

Zinc 

Copper 

Silver 

Smuggler-Union 

Park-Utah 

Copper 

Copper ,Hi ami 
TABLE 1 Liet of accidents at metal and nonmetal minee and quarries (except coal ndnee) in the Lhited States 

in which five or more lives were lost 

Date Product Nam of nine Locat ion Killed Nature of accident References 

1914-Jan. 21 

1914-July 14 

1914-Aug. 4 

1914-Sept. 17 

1914-Nov. 9 

1915-Oct. 19 

19 16-Feb. 14 

1917-Apr. 28 

1917-June 8 

1918-Feb. 21 

1920-Apr. 15 

1922-Aug. 27 

1924-Feb. 5 

1926-Nov. 3 

19274ct. 29 

1927-Nov. 24 

1929-Sept. 4 

1930-June 7 

1930-July 14 

1936-Aug. 13 

1939-Jan. 31 

Boston 

Balkan 

Copper Flat (Steamehovel pit) 

Centennial-Eureka 

Sibley No. 9 shaft 

Granite Mountain 

shaft 

Pennsylvania 

Mountain King 

Granite Mountain 

Amasa-Porter 

Jefferson Island 

Argonaut 

Milford 

Barnes Hecker 

Quincy mine No. 2 

Shaft 

Magma 

Calaveras 

Climax mine 

Glenn 

Mountain City 

Copper Company 

Southern 

Copper 

Iron 

Copper 

Gold 

Iron 

Copper 

Copper 

Gold 

Copper 

Iron 

Salt 

Gold 

Nanganiferous iron 

ore 

Iron 

Copper 

Copper 

Copper 

Molybdenum 

Gold 

Copper 

Zinc 

24 

2 7 

2 7 

2 7 

2 7 

24 

2 7 

2 5 

33 

2 7 

2 6 

2 7 

2 8 

28 

2 8 

2 8 

2 8 

28 

2 9 

30 

Bingham. Utah ine fire; cause unknovn. 

Palatka, Hich. 

HcGi11, Nev. 

Eureka. Utah 

Ely, Minn. 

Butte, Mont. 

Butte, Mont. 

Mariposa County, 

Calif. 

Butte, Mont. 

Crystal Falls, Mich. 

Delcambre, La. 

Jackson, Calif. 

Crosby, Minn. 

Ishpeming, Mich . Hancock, Mich. 

Superior, Arizona 

Copperopolis, Calif. 

Fremont Pass, Lake 

County, Colo. 

Lost Chance, Placer 

County, Calif. 

Mountain City, Elko 

County, Nev. 

T reece , Kansas 

7 

5 

?.fen drovned by rush of sand 

and water into raise. 

Premature blast. 

16 

21 

7 

163 

17 

6 

mamite explosion at shaft collar.27 

l4inefire;asphyxiation. 

Asphyxiation by powder fumes. 

finefire. 

Zave-in caused by inrush of water 

:as explosion 

47 Wne fire; cause unknown. 

41 Inrush of water. 

ck in shaft following 

7 

5 

5 

5 

air blast. 

Shaft fire. 

Zive in stope 

hve-in 

:fine fire in surface building. 

6 

5 'bof fall 
TABLE 1 List of accidents at metal and ncmmetal mines and quarries (except coal mines) in the United States 

in which five or more lives were lost 

References 

30 

32 

31 

31 

3 1 

31 

3 1 

3 1 

3 1 

3 1 

Locat ion 

Silverton, Colo. 

Ducktm, Tenn. 

Shullsburg, Wisc. 

Lark, Utah 

Herron. Hich. 

Bonanza. Utah 

Iron River, 

Hich. 

Moab, Utah 

Belle Isle, La. 

Rosiclare, Ill. 

Kellogg. Idaho 

Killed Nature of accident 

umes from surface fire at 

unnel portal suffocated men in 

Name of Mine 

Pride 

Boyd mine 

C.F. 6 H. 

Lark, U.S. Smelting 

Ref. 6 ring. Co. 

Herron , Alpena 

Enterprises 

No. 1 Incline, 

Am. Gilsonite Co. 

Sherwood Mine, 

Inland Steel Co. 

Texas Gulf Sulfur 

Co. (Harrison 

Internat. . Inc. 

Contractors) 

Cargill Salt Mine 

Barnett Complex 

Mine-Ozark-Mahoning 

Co. 

Sunshine Mining Co. 

Date 

1942-Jan. 9 

1943-Jan. 5 

1943-Feb. 10 

1950-July 16 

19524ct. 30 

1953-Nov. 5 

1959-June 1 

1963-Aug. 28 

1968-Mar. 6 

1971-Apr. 12 

1972-May 2-11 

9 

Product 

Copper, 

zinc, lead, 

gold, 

silver. 

Copper 

Lead, 

zinc 

Lead, zinc 

Gold 

prospect 

Gilsonite 

Iron 

Potash 

Salt 

Fluorspar 

Silver 

mine. 

Asphyxiation by fumes from exlosion of sulphide dust in 

8 

5 

5 

8 

6 

18 

21 

tope. 

.?a ~n buried by cave-in. Six 

others buried by second cave-in 

during recovery work. 

Fire in battery-charging station 

:as explosion in shaft 

Dust explosion. 

:nrush of hot gases and steam. 

:as explosion. 

Yinefire. 

7 

91 

Pphxiation (H2S) 

;tinefire. 

I 



No. of Deaths 

Mine Roof Fall Statis 

13 Accidents 

90 Deaths 

6.9 Deaths /Accid

1.6 ~eaths /Year 

(1890 - 1950) 

.23 Accidentslye

1860 1870 1880 1890 1900 1910 1920 1930 1940 1950 196

Figure 4 Chronological Distribution of Roof Falls in Metal/No
Mine Flooding S

7 Acciden

168 Deaths 

24 ~eath/

1860 1870 1880 i890 1900 1910 1920 1930 1940 1950 

Figure 5 Chronological Distribution of Flooding Accidents in 
Product 

TABLE 2 

BREAKDOWN OF MINING DISASTERS BY TYPE AND PRODUCT 

Go1 d-S i lve r 

Copper 

Iron 

Fatalities . # of Disasters 

365 3 1 

Miscellaneous 83 

(Marb ley Molybdenum, 

Potash, Salt, Gilsonite, 

Fluorspar, Asphalt) 

Type 

11 Fire 

4 Explosion 

1 Flood 

3 Cave-in 

2 Asphyxiation 

9 Fire 

7 Explosion 

2 Roof-fall 

3 Asphyxiation 

1 Fire 

1 Explosion 

2 Cave-in 

6 Flood 

1 Asphyxiation 

2 Fire 

3 Rock-Falls 

4 Explosion 

2 Cave-in 

1 Asphyxiation 
Distribution of ,Disasters by State 

Montana and Michigan, with eleven (11) mine disasters each, have the 

dubious distinction of being involved in 433 of the 585 fatalities recorded 

between 1869 and 1972. 

Idaho, Mbntana, and Minnesota have the highest death/disaster ratios 

as indicated in Figure 6. 

2.2 Statistical Characteristics of Metal/~on Metal fine Parameters 

Mine De~th 

The most critical mine parameter affecting the performance of a manpack trapped miner location system is overburden depth. Information on the 

distribution of maximum working mine depths in 45 of the lnajor metal/non metal 

mines of the U.S. was obtained from the mine operators and is shown in the 

histogram of Figure 7, A cumulative distribution is shown in Figure 8 showing 

the percentage of mines exceeding a given depth for the same 45 mine sample. 

Figure 9 is a cumulative distribution showing new shaft construction at mines 

producing more than 1200 tons per day. The 10% exceedance level (i.e., the 

depth exceeded by only 10% of all mines) for the 45 working mines is 3000 

feet and for the 152 new mine shafts is 2400 feet. If we use 3000 feet as a 

design goal, such that a manpack trapped miner location system must perform 

in a11 mines having depths up to 3000 feet, it will be operational in 

approximately 90% of mtallnon metal mines in the U.S., assuming the sample 

to be truly representative of metal/non-mtal mines in general. 

Overburden Conductivity 

Overburden conductivity measurements were made at 7 mines on this 

contract. The results of these conductivity measurements were combined with 

measuremnts made by Westinghouse personnel on previous mine visits to arrive 

at the conductivity distribution curve for the 17 mines shown in Table 3 and 

in Figure 10. Based on this particular representative 17 mine sample, the 

10% exceedance level (i.e. the level of conductivity exceeded by only 10% of 

the mines) is about 1.15 X 10-I nhos/m. It is important to note however that 

this unusually high value of conductivity for the 10% level was influenced 

greatly by two mines in particular; Berkely Pit Copper Mine in Butte, Montana 

and the International Salt Mine in Avery Island, Louisiana. Both of these 

mines had relatively shallow maximum overburden depths, 700 and 880 feet 

respectively. Thus it may be sonewhat pessimistic to relate this particular 

10% level to all metallnon metal mines since the deepest mines such as those 

found in the Coeur d'Alene district of Idaho and the Homestake gold nine in 

Lead, South Dakota have measured conductivities subst ant ially lower than 10-I 

mhos/m. 
Montana Michigan Colorado California Nevada Ut ah Minne

Ave. Deathsl~is- 23.6 15.8 8.2 18.5 13.6 15.2 23

aster Figure 6 Distribution of Deaths in MetalINon Metal Mine Disasters by 
U 

a b 

a 

w 

0 

0 

0 

Cr, - 

li 

5 

2-I 

; 

- 

0 

l-l 

l-l t 

(d i 

x 

0 

m 

-- - -7 1 

- 

r d - 

C_--j___ - - 

-.I 

1 I 1 I 
WWIMGHOUSE ELECTRIC CORPORATION 

Depth, Feet 
WESTINGHOUSE ELECTRIC CORPORATION 
TABLE 3 

Mine -Conductivity Distribution 

Mine 

1. Berkely Pit 

2. International Salt 

3. Knob Hill 

4. Big Island 

5. Fletcher 

6. Inexco 

7. Latrobe 

6. Copper Queen 

9. Ozark Mahoning 

10. Galena 

11. Caladay 

12. Idarado 

13. U.S. Tunnel 

14. Henderson 

15. Sunshine 

16. Homestake 

17. TOSCO 

Locat ion 

Apparent 

Conductivity 

Butte, Montana 1.95 X lo-' 

Avery Island, La. 9.3 X lo-2 

Republic, Wash. 6 X 

Green River, Wyo. 2 X lo-Z 

Viburnum, Mo. 1 X lo-2 

James town, Colo. 

Latrobe , Pa. 

Bisbee, Arizona 

Rosi clare , Ill. 

Wallace, Idaho 

Wallace, Idaho 

Telluride , Colo. 

Idaho Springs, Colo. 

Empire, Colo. 

Kellogg, Idaho 

Lead, South Dakota 

Rifle, Colo. 

Percent of 

Exceedance 

5.9 
APPARENT CONDUCTIVITY (mhosh) 

Figure 10 Conductivity Distribution of 17 Selected Metall~on Metal Min
2.3 Mine Construct ion Techniques 

Room & Pillar 

The mst common underground mining method used in large scale metal/ 

non metal mines in the U.S. is room and pillar which accounts for over 75% 

of all mines (7). Room and pillar mines offer a wide flexibility for antenna 

deployment and allow the trapped miner to achieve the maximum transmitting 

monent for a given length of antenna wire. The maximum practical depth for 

room and pillar workings depends on the strength of the pillars. The deepest 

room and pillar mines in North America are about 3200 feet below the surface. 

Extraction efficiency in room and pillar mining decreases as mine depth increases; thus the practical limit of slightly over 3,000 feet. 

Vein Mining: 

Vein deposits are often found in metal mines such as silver, zinc, 

lead and gold. Such deposits are usually mined by a variation of three basic 

methods : (1) Shrinkage stoping, (2) Square-set stoping, and (3) Cut and fill 

stoping. In some of the wider and stronger veins, with more competent walls, 

open stoping ~thods are used. 

Vein deposits present unique mining problems because the deposits tend 

to be irregular, often steeply inclined and sinuous along strike and dip. The 

width of mineralization can vary from a few inches to hundreds of feet. However, average mining entry widths vary from 5 to 30 feet. Vein structures have 

been traced for miles along a strike and for thousands of feet down dip. 

As far as communications and location equipment deployment is concerned, 

vein mines offer the greatest challenge. Because of the narrow entry widths 

and lack of adjacent return entries, it is difficult to find a suitable location 

for deployment of large area loop antennas. Antenna deployment in vein mines 

will probably be restricted to long horizontal wire antennas or small area 

loops with modular stacking. In some cases it is possible to deploy a large 

area vertical loop by utilizing two adjacent levels connected by stopes. 
3.0 THEORETICAL CHARACTERISTICS OF UNDERGROUND ELECTROMAGNETIC PROPAGATION 

3.1 Effects of Earth Conductivity on Propagation 

Earth conductivity plays an important role in determining the propagation characteristics of electromagnetic energy in the earth. The importance 

of measuring earth conductivity at mines stems from the fact that more and 

more low frequency electromagnetic communications and telemetry systems are 

coming into use for underground wireless links used in comunicatfons and 

mnitoring as well as trapped miner location. By characterizing the geophysical 

properties of the mine overburdens prior to testing the electromagnetic 

penetration capability, a more complete understanding of the propagation 

phenomena is gained. This understanding improves as more mines are visited 

and a more comprehensive data base is accumulated relating conductivity to EM 

propagation characteristics. As our understanding improves for a small group 

of test mines, the results can be characterized, given the conductivity and 

depth, and extrapolated to a much larger group of mines to determine the following: 

(1) Whether a through the earth system is even feasible at a 

particular mine. 

(2) If feasible, what would be the required transmitter power 

and receiver sensitivity needed to insure a reliable EM wireless 

link? 

(3) What is the maximum bandwidth and/or data rate that can be 

utilized at the particular mine? 

The basic objective of Contract 50166100 was to determine what mdifications were needed to make the existing through-the-earth ULF trapped miner 

location system usable in metal/non metal mines. The field program was set up 

in two phases: 

Phase I: To obtain a geophysical characterization of six (6) test mines 

for advanced prediction of electromagnetic propagation capability. 

Phase 11 : To measure electromagnetic propagation in the same mines and 

to demonstrate ways to achieve trapped miner location with modified 

system concepts. 

By correlating observed electromagnetic propagation phenomena in these mines 

with calculations and predictions based on geophysical measurements, e.g., 

conductivity, one can then apply the results to a much larger class of mines, 

and thus determine their equipment requirements prior to a mine visit. 
3.2 Penetration Depth of EM Waves 

The solution to the wave equation for a sinusoidally varying plane 

wave propagating through a finitely conducting medium is 

whe re 

a is the attenuation constant in nepers/meter 

is the phase constant in radianslmeter 

an d z represents the propagation distance in meters. 

For any conducting medium, and in particular for a homogeneous semiinfinite earth, the EM wave penetration depth or "skin depth" is defined as 

the distance in which the wave is attenuated to l/e (36.8%) of its initial 

value at the surface. Referring to expressions (1) and (2), it is seen that 

this distance is reached when z = l/a. This quantity is usually denoted 

by the symbol 6. 

1 7 

meters. 

C1 = - =d+ 

The penetration depth expression can be simplified, assuming a nonmagnetic 

material, as follows: i.e. p = po = 4n X henrieslm. 

503 meters. 6=JGF 

Figure 11 shows the variation of 6 with frequency for various conductivities. 

The foregoing analysis has been applied to a homogeneous medium. 

When horizontal stratification and inhomogeneities are present, the expression 

for penetration depth (3) is no longer valid. For such cases, each problem 

must be treated individually, taking into account all of the wave reflection 

at the boundaries and the complex field combinations that result in each of the 

layers. 

In analysing low frequency electromagnetic propagat ion in mines, the 

term "skin depth" is used mrely as a parameter to characterize penetration 

distance in the medium and not to imply that plane wave propagation exists for 

localized ULF transmitting sources. For localized ULF transmitting sources, 

such as those used for mine rescue purposes, the pertinent fields produced are 

the induction fields, modified by losses in the earth. The magnetic field 

strengths, as a function of distance from the transmitting source, can be 

calculated for a particular mine situation, given the conductivity , the frequency 

and the penetration distance through the conducting medium. Figure 12 shows 
1 o6 

lo5 

, lo4 

lo3 

1 02 

1 o1 

1 10 1 o2 lo3 1 o4 

FREQUENCY, IN Hz 

gure 11 Skin Depth vs. Frequency for Various Conductivities (k = E/~ 

32 
Penetration into medium 2 in skin depths 6 

Figure 12 Electromagnetic Attenuation in Conducting 

Media 
the attenuation constants IG~, IDI and IA~ as a function of penetration 

distance into the condufkftng mdium which are used to modify the basic induction 

field equation, H = ( -3 ) to determine the magnetic field strength for the 

2 7r z 

different types of antenna coupling shown. 

The feasibility of a through the earth ULF uplink can be determined 

for any mine if one knows the mine overburden thickness and conductivity and 

the expected electromagnetic noise background as a function of frequency. 

Suppose, for example, that we have a mine with the following parameters: 

Overburden thickness, (z) = 500 meters 

Conductivity , (a) = 0.1 mhos/m 

Surface EM noise, (Hn) = 1.0 yA/m in a 1 Hz BW 

2 and assume an in-mine transmitting moment of INA = 1000 amp turns m . 

The vertical magnetic field calculated for the above parameters is as 

f 0 llows : 

HZ (vA/m) Signal to Noise (dB) 

The above illustrates that the uplink signal could just barely be detected in a 

1 Hz bandwidth at 10 Hz but could not be detected at the higher frequencies 

under the stated conditions. If information on background noise vs frequency 

is known about a particular mine site, it can be used, along with the other calculations, to determine the optimum frequency for an uplink system, assuming that 

feasibility exists. 

3.3 Effects of Parasitic Coupling 

It is well known that electromagnetic wave behavior is influenced by the 

presence of metallic conductors. The foregoing discussion (Sections 3.1 - 3.2) 

is restricted to the special case of a homogeneous conductive medium. In practice 

this condition is never really encountered, although an analysis based on the 

assumption of homogeneity is often helpful in estimating field strengths produced 

by a given transmitter operating in an environment characterized by its equivalent 

"effective" conductivity . (The effective conductivity would be defined, in this 

case, as that conductivity which would produce the measured field strength for a 

homogeneous conducting medium, given the actual transmitting moment and propagat ion 

distance , ) 
The assumption of homogeneity is even more unrealistic when considering 

ULF and VLF propagat ion characteristics in underground mines particularly those 

with a comprehensive network of underground pipes and rails. However, from a 

communications standpoint, this anomalous condition can be utilized to enhance 

the range of underground comunications equipment far beyond that which could 

be expected for homogeneous mdia or, for that matter, even free space. 

Tests performed above ground by Westinghouse personnel in 1973 near 

suburban and rural powerlines and pipelines have shorn that low frequency signals 

can be carried with low attenuation over considerable distances (up to 14 miles 

on less than 20 watts of transmitter power) in spite of periodic pipeline 

insulation joints and powerline grounds (8). 

The theory for computing the electromagnetic fields as a function of 

distance and frequency from horizontal line sources located at the earth's 

surface is well established (9) and will not be covered in detail in this report. 

A special case of the above problem is one in which the line source can be 

considered short with respect to the propagation distances involved and hence 

be treated as a dipole antenna. The expression for computing the fields of 

a dipole antenna is given as follows : 

H = INA IDL 

3 ampslm 

2 ITd 

where : 

2 INA = the current moment of the antenna in amp turns m . I DI = an attenuation factor based on the electrical conductivity 

of the propagation medium. 

d = the propagation distance in meters. 

In free space, ID/ = and the magnetic field is simplified to 

INA H=- ampslm. 

 IT d3 

For a line source, the current moment is computed on the basis of a return 

current path in the earth at a depth of &% where 6 specified the skin depth 

of the wave in the conducting medium. The skin depth (6) is given by 

=$$ meters. 

Consequently, for a single line source of length (R) meters and a ground return 

current path, the moment is (10). 

2 INA = I& 65 amp m . 
For a horizontal loop source lying on the ground, the expression for 

calculating the magnetic field as a function of distance from the loop in 

free space is also 

Here the computation of INA is more straight-forward and involves the product 

of the current, the number of turns of wire, and the physical area of the loop 

in square meters. 

The presence of a long conductor in the vicinity of the dipole transmitter alters the electromagnetic field pattern by effectively concentrating 

the energy along the conducting pipe or wire. The electric or magnetic 

transmitting source induces longitudinal currents into the conductor which 

travel down the conduct or with low attenuation and generate secondary elect romagnetic fields in the vicinity of the conductor. As distance increases along 

the conductor, the received field strength would be expected to fall off initially 

as inverse distance cubed, consistent with the dipole coupling from the primary 

source moment. At greater distances, a much lower attenuation with distance 

is seen as the secondary fields from the currents induced in the conductor 

beco~ the dominant contributing factor in the total field strength measured 

at that point. 

If the conducting pipeline or powerline network branches off in a 

variety of directions from the main path, the energy carried thereon will 

divide and follow the branch lines as well as the main line. This will effectively 

reduce the energy carried on any one line and thus reduce the total range of 

coupling obtainable. 

Figure 13 shows the magnetic field vs. distance from both a magnetic 

and electric dipole coupled to a long powerline and pipeline. This data was 

obtained in 1974 along 95th St. 10 miles east of Boulder, Colorado. It bears 

striking resemblance to the sidelink propagation data obtained underground at 

the various mines visited on the subject program for the U.S. Bureau of Mines 

(see Section 6.0). Signal enhancements due to coupling, as high as 60 dB, 

are not uncommon, either above ground or underground. This phenomenon can be 

effectively utilized underground to provide sidelink propagation from trapped 

miner transmitters to a shaft area to aid in identifying vertical level of 

entrapment . 
Figure 13 Magnetic 121elds ve. Mstance from Electric and FIil&?netic 

Source Coupling to a Long Conductor. 

425 Meter llorizontal Electric Dipole (4) 

I - 1.5 aqeres 

f - 10.5 kllz 

100 Hrter Square Ilorlzontal Loop 

I - 3 amperes 

f - 10.5 kliz 

P = 10 Watte 

slde of the road 

under the powerline 

Theoretical 

magnetic field 

i n free apace 

Poverliru, cut-off 

Dlrtmce from Source (d) , lea 
SYSTEM REQUIREMENTS FOR LOCATION AND COMMUNICATIONS WITH TRAPPED 

MINERS IN METALINON METAL MINES 

Based on the statistical study of mine parameters discussed in Section 

2.2 for &tal/~on Metal Mines in the United States, we can define a worst case 

mine as one having both a 10% exceedance depth and a 10% exceedance conductivity. 

* 

Assumptions 10% Exceedance Depth = 3000 ft. (915 m) 

10% Exceedance Conductivity = 1.15 x 10-1 &os/m. 

Requirements for Through the Earth Uplink 

Assume f = 1000 Hz 

Skin depth (6) is computed as follows: 

= 47 meters at f = 1000 Hz. 

Thus 915 meters of overburden represents 19.5 skin depths of attenuation. 

This is consistent with an attenuation IGI of 4.54 X 

The surface magnetic field strength (H ) obtained in this case is 

z computed as follows : 

H = z 

INA' GI 9.43 X X INA 

2 Trz 3 

where IG I is the attenuation factor obtained from an extrapolation 

of the curve in Figure 12. 

Assuming that a surface field strength of . 1 pA/m is required fo fo detection and location of a trapped miner, a magnetic moment of 1.06 X 10 amp 2 turns m would be required for the 10% exceedance mine as described above. This 

value of transmitting moment is not practicable when one considers the portability 

and power restriction of the transmitter. 

However, if we reduce the frequency to 10 Hz, the skin depth becomes 

1484 6=m 503*3 = - = 470 meters at f = 10 Hz. dF 

* This figure is based on the 10% exceedance level for a representative sample 

of 45 rnetal/non metal mines in the United States. 
Thus the 915 meter overburden depth is reduced to only 1.95 skin 

depths and the attenuation I GI becomes .58. The transmitting moment required 

to penetrate this overburden is now computed as follows: 

H = z 

INA -1 @Im 

27T z 

3 

INA = 10~',(2rz3) = 830 amp turns m 2 

G 

which is a practical value for a trapped miner to achieve in an underground 

met a1 /non met a1 mine. 

Another important factor which must be considered in going from 1000 Hz 

to 10 Hz is the increase in background noise experienced at 10 Hz. This is 

generally on the order of about 30 dB as shown in Figure 14. This partially 

nullifies the enhancement in signal to noise ratio gained by going to 10 Hz; 

however, the increase in signal strength far outweighs the increase in noise 

so the net result is a significant Improvement in expected system performance. 

Further enhancement of the detection capability on the surface can be 

achieved by using a long wire receiving antenna in place of a magnetic dipole 

(loop). By using a grounded wire electric field antenna that is long with 

respect to the mine depth, the mutual coupling between it and an underground 

dipole antenna can )e made to vary as inverse distance (112) rather than inverse 

distance cubed (l/z ) as in the dipole-dipole case (11). 

Calculations show that for a grounded wire length roughly twice the 

observer depth, the fields below the wire are essentially those of an infinite 

line source (12). The conventional use of the long horizontal wire antenna 

on the surface has been as a transmitting antenna to communicate a voice downlink 

signal to the trapped miners. However, the mutual impedance and the coupling 

relationship between the surface and underground antenna is the same regardless 

of which one is used as transmitter and which one is used as receiver. Thus 

the (l/z) coupling relationship is retained and signal detection capability is 

enhanced. 

This concept has been proven out in practice on at least two occasions 

(13) 

a At the Sunshine Mine in Kellogg, Idaho, a 1900 Hz uplink 

signal was received on a 4000 ft horizontal wire in a 50 Hz 

receiver bandwidth whereas the same signal could not be detected 

using a 500 turn 15" diameter receiving loop and the same 

receiver. (Overburden depth was 4800 ft.) 
10 100 1000 

Frequency (Hertz) 

Figure 14 Atmospheric Noise 
e At the Pocahontas Mine No. 1, Grundy, Virginia, a 1900 Hz 

uplink signal was received on a 2000 ft horizontal antenna in 

a 3 Hz receiver bandwidth whereas the same signal could not be 

detected using a 500-turn 15" diameter receiving loop and the 

saE receiver. (Overburden depth was 2300 ft .) 

Hence, in the light of the above discussion, it can be concluded that 

detection of through the earth uplink signals can be accomplished in a socalled " 10% exceedance" metallnon-metal mine using practical low power t rapped 

miner transmitters provided that frequency is reduced low enough to make 

through the earth attenuation relatively insignificant. For the 10% exceedance 

mine, frequency must be kept in the vicinity of 10 Hz for detection with magnetic 

dipole receive antennas but could go higher when using long horizontal wire 

receiving antennas. 

There are logistic problems associated with using frequencies as low 

as 10 Hz when attempting to conduct hand-held direction finding operations. 

The earth's magnetic field induces high levels of noise in the loop for even 

the slightest movement of the loop. Consequently, when using a loop for direction 

finding of trapped miners at f = 10 Hz, the loop must be firmly planted in 

position using a tripod or equivalent, before readings can be taken at each 

individual posit ion. 

When using a horizontal wire antenna for direction finding, it is somewhat impractical to successively move the antenna around to locate the miners 

position as can be done with a loop. In the case of using a horizontal wire 

antenna for determining the trapped miners position, it would be more feasible 

to deploy an array of such antennas in the form of a grid network. Then, by 

analyzing the receiving pattern created by the signals received on all of the 

antenna elements, a judicial extrapolation of the trapped miners position can 

be made. However, this scheme is not recommended unless it is first determined 

that the signals are not detectable using the loop receiving antenna. 

4.2 Requirements for Through the Earth Sidelink 

In metal/non metal mines, unlike coal mines, there usually exists more 

than one level of mining activity going on simultaneously. Consequently, there 

is a requirement for knowing not only the miners horizontal coordinates but also 

on what mining level he is trapped. This introduces a requirement for horizontal 

propagation from the trapped miners transmitter to a section of the mine where 

the signal could be relayed up to the surface by some other means or the signal 

could be received by lowering a wideband receiver and loop. This would normally 

be done either at the shaft or a borehole, so the problem is one requiring a 

maximum sidelink propagation range from the miners area of entrapment to insure 

adequate signal detection at the vertical probe location. 
Fortunately, sidelink propagation is enhanced considerably by the 

network of pipes and other conductors that are present to varying degrees 

in virtually all metallnon metal mines. Tests performed at the metal/non 

metal mines on this project verify coupling enhancements of up to 55 and 60 dB 

over signals expected in free space for those particular distances. Coupling 

to underground conductors improves with increasing frequency; consequently 

some type of dual frequency transmitting system is needed to satisfy the 

requirements for both uplink and sidelink transmission simultaneously. A 

system to accomplish this is described in Sections 5.0 and 8.0 of this report. 

4.3 Portability Requirements 

For a trapped miner transmitter to be effective, it should be small 

enough to be carried on the miner at all times. In view of what the miner 

must already carry (i.e. cap lamp battery, self rescuer, etc.) it would not 

be practical to burden him with any significant additional bulk or weight 

that might impede his efficiency or productivity. A practical limit for a 

trapped miner transmitter would be about lb. , which is about the weight of 

the present USBM Coal Mine Trapped Miner Transmitting unit. A significant 

weight advantage is gained by using the miners cap lamp battery as a dc power 

source. Based on results obtained on this program and others (1-6) , the cap 

lamp battery provides sufficient voltage and power for the transmitting 

unit. 

4.4 Permissibility Requirements 

There are no permissibility restrictions for the vast majority of 

metal/non metal mines in the United States since most of the mines are non-gassy. 

Exceptions to the rule are the Trona Mines in the Green River formation which 

do emit an extremely small amount of methane (less than .I%). The mdification 

philosophy developed on this contract to adapt the USBM Coal Mine Trapped 

Miner Location System to use in metallnon metal mines does not entail any 

increase in power or voltage on the part of the underground transmitter. Consequently, the modified transmitting unit will retain its existing intrinsic 

safety rating, as presently certified. 

4.5 BlastingCap Susceptibility toULFTransmissions 

Of much mre concern to the Metal Non Metal Mining Industry is the potential 

effect of the ULF transmitter on electrical blasting caps. Basic information 

on the mechanism of RF initiation, tables of safe distances, and data on 

commn RF sources are given by the IME (14). Tables of safe distances were 

derived from analytical worst case calculations based upon an assumed 40 M, 

no-fire level of commercial blasting caps. 

The theory of wave antennas was employed by the IME for electric blasting 

caps deployed within the fields emanating from various transmitting 

sources. It was assumed that the field structure from the broadcast band 
antennas was in the Fresnel (near) zone and that for higher frequencies, the 

caps were located in the Fraunhofer (far) zone. At the low operating frequencies under consideration, the IFE correctly noted that the primary mechanism for induced currents would be simple magnetic induction since the magnetic 

flux would be the predominant factor. 

Regarding the 40 mW, it was noted that members of the IME do not design 

commercial blasting caps with firing levels below 0.2 amperes, and with a 

conservative resistance of 1 ohm, the resulting power dissipation is 40 milliwatts. Stray currents caused by dc or 60 Hz ac power sources can deliver 

power to electric blasting caps very efficiently. For this reason, a safety 

factor of 5 was imposed by the IME to define the "potential hazard level" 

for stray sources of current which might come in direct contact with caps. 

The lowest firing level (0.25 amperes) was reduced to 0.05 amperes for a 1-ohm 

bridge wire to arrive at the following definition: "a stray voltage source 

capable of developing 50 mV or more across a 1 ohm resistance constitutes a 

potential hazard to commercial e.b. caps manufactured in the U.S.A. Note that 

50 mV across 1 ohm represents 2.5 M. " The IME goes on to note that at 

frequencies above 28 MHz, the tables of safe distances are very conservative. 

The hazards in the broadcast band are less conservative in that "there is one 

chance in a thousand for premature initiation caused by induced RF in the 

broadcast band provided ( 1) the e.b. cap is perfectly matched to the pickup 

antenna, (2) the pickup antenna is ideal in configuration (tuning) and 

orientation, and (3) the pickup loop is located at a peak of a fringe in the 

Fresnel zone. The IME then concluded that "the possibility of simulating such 

circumstances in the 300-3000 Hz band are even more remote since such long 

blasting circuits are impractical, e.g., such long leading lines cannot be 

used to successfully initiate e. g. cap rounds. " They recommended, nevertheless, 

that tests shoulc be conducted to properly assess the hazard. These are 

described in the following paragraph. 

Electric Blasting: C~D Tests 

On a previous Bureau of Mines project, a test program was conducted to 

determine the likelihood of blasting caps being set off by ULF electromagnetic 

transmissions (15). DuPont No. 6 electric blasting caps with 10-foot leg 

wires were tested under safe conditions in a field near Boulder, Colorado. 

The caps were inserted into the soil a few inches to permit safe firing, and 

the lead wires were kept shunted until the test was ready to begin. The 

instrument at ion included a Wavetek signal generator, an amplifier, matching 

transformer, a sensitive voltmeter, and a 1-ohm resistor with a voltmeter to 

indicate current level. Tests were run at frequencies of 60, 120, 200, 275, 

500, 700, 1000, 2000, 2750, and 5000 Hz. At each frequency, the terminal 

voltage and line current were recorded at several steps as the voltage was 

increased to the firing point. From this data, magnitude of impedance and 

power dissipation in the cap were calculated. Since only 10 caps were used to 

complete these tests, there is an insufficient amount of data for statistical 

inference; however, the data for resistances falls within published figures 

and hence it is felt that these tests will be useful for estirrrating the potential 

hazards at ULF (300-3000 Hz). 
The IME definition that if 2.5 mW is dissipated in the caps, a potential 

hazard exists, is extremely conservative in the opinion of Westinghouse. It 

was found, in the Westinghouse tests, that with voltages in the range of 

50 mV to 100 mV across the caps, gives a resistance of 1.5 ohms (+0.15 - 0.07) 

for ULF. From this, it was found that 2.5 n%d will be dissipated when the 

current is about 48 milliamps. The Westinghouse tests showed that 100 to 

500 mW was required to fire caps with currents in the range 250 to 550 milliamps. The firing voltage was in the range 450 to 900 mV and the resistance 

at the firing point was about 0.1 ohm higher owing to heating. Thus, even 

the 40 n5d no-fire level is a conservative figure. 

Susceptibility of Caps 

How close can the electromagnetic communication antennas be to blasting 

caps? The IME suggests that there dows not appear to be an RF initiation 

hazard in the normal storage and transportation of electric blasting caps, 

as long as they are in their original carton. The calculations discussed below 

show further that there is only a remote chance for initiating e.b. caps 

when they are deployed for maximum coupling to either the underground manpack 

loop antenna or a horizontal wire antenna on the surface. Therefore, caps 

which are in the original packaged condition should never be initiated by 

electromagnetic radiation from the manpack loop or horizont a1 wire transmitting 

antennas. The calculations are based on the characteristics of No. 6 instant aneous electric blasting caps. 

As suggested by the IME, magnetic induction was considered to be the 

most hazardous mechanism. Considering an electric cap with the lead wires 

shunted, the maximum ULF induction will occur when the lead wires are arranged 

in a circular shape so as to enclose a maximum area. The equivalent circuit 

for each cap is simply the resistance of the wire in series with the resistance 

of the cap, and if several caps are connected in series and arranged in a 

circle which is immersed in a uniform magnetic field with flux normal to the 

loop, the current that is induced into the sh0rte.d circuit is given by: 

where : 

f = frequency, Hz 

A = area of loop, M 2 

H = magnetic field intensity, amps/meter 

R = total series circuit resistance in ohms. 

This equation was used to calculate the currents induced into various blasting 

cap configurations using large areas, a frequency of 3000 Hz, and the maximum 

transmitting currents which may be realized with the ULF manpack transmitter. 
In the mine it was assumed that the worst condition would be in 

conventional mining where a face has been drilled and loaded with 10 shots 

distributed over the face having an area of 10 feet by 20 feet. Each cap 

is assumd to have a resistance of 1.5 ohms, and for caps used in the mine 

with iron leg wires, the total resistance is 4.5 ohms for each cap and leg 

wire. Conditions were calculated under which a current of 40 milliamps would 

be induced into the cap circuit. It was found that a magnetic field of 

2.25 amperes per meter would induce 48 milliamps into the 10-cap circuit. 

Since the maximum magnetic field generated by the manpack transmitter will be 

less than ? amp per meter in the center of the loop antenna, the chance for 

initiating electric caps would be extremely remote. If a single cap with 

16 foot leg wires was arranged in a loop inside of the manpack antenna loop 

for maximum coupling, it was found that a magnetic field of about 1.5 amps 

per meter would induce only about 40 milliamps into the cap loop. 

4.6 Locat ion Accuracy Requirements 

In addition to the requirements for detecting the trapped miner's signal, 

there are also requirements for the system to effectively locate his position 

in the mine. The previous system developed for coal mine use concent rated 

on determining the x, y coordinates of the miner and assumed that the z 

coordinate (depth) was known. However, met al/non met a1 mines, unlike coal mines , are generally multilevel mines where several levels are being mined simultaneously. Consequently, it is important to be able to locate the trapped 

miner's position in terms of x, y and z coordinates. 

A through-the-earth null detection technique can be used to identify 

the horizontal (x, y) coordinates in the same manner as the present BuMines 

system developed for coal mine use. The accuracy with which the horizontal 

coordinates can be determined is dependent upon the overburden depth, the 

terrain irregularities, and conducting anomalies, (pipes, power cables, etc. ) 

particularly those near the surface receiving site (16, 17). At the extremely 

deep mines such as the Homestake Mine in Lead, South Dakota, the horizontal 

coordinates of a trapped miner can be determined only in a gross sense. 

However such informat ion, coupled with information on the miners vertical 

location and a copy of the mine map, could be used to reduce the area of uncertainty to several hundred feet in deep mines. Information of this type 

would be of great value during a rescue operation at a deep metal/non metal mine. 

Location accuracy would improve for shallower mines where more sharply defined 

field pattern information can be obtained on the surface. 

Vertical location can be determined by recording field strengths on a 

multichannel receiver connected to a broadband loop and preamp lowered down 

a shaft or borehole. Assuming the mine is laid out with a network of water 

pipes and other conductors on each working level, the trapped miner's signals 

can be easily transmitted from his position of entrapment to a shaft location 
by mutual coupling to one of the pipes in the vicinity. Determination of 

vertical level of the miner's position could be made on the basis of field 

strength amplitude vs. depth of the probe. It is assumd that in most cases 

the field strength will peak at the shaft depth containing the trapped miner 

and his transmitter, since the conductors around which the signals couple are 

generally installed horizontally along each level. The requirements for 

vertical location accuracy should be such that the true vertical level determination is unambiguous (i .e. less than 100 ft .) 
CANDIDATE EM LOCATION TECHNIQUES 

There are two basic approaches that can be taken to achieve the 

capability of locating trapped miners in deep metal/non metal mines. 

(1) Use the existing USBM coal mine manpack transmitter as the 

first link of a repeater chain to convey information on the 

miners position to the surface. 

(2) Use a modified version of the USBM coal mine manpack transmitter to convey information on the miner's position to the surface 

via a direct through the earth propagation path. (This has been 

discussed to some extent in Section 4). 

The above approaches are based on communications equipment operating at 

frequencies in the ULF (Ultra Low Frequency) VF (Voice Frequency) and VLF 

(Very Low Frequency) ranges. Approach No. 1 would u.tilize VF (300-3000 Hz) 

and VLF (3-30 kHz) while approach No. 2 would utilize ULF (3-300 Hz) and 

VF (300-3000 HZ) . 

There has also been considerable interest and experimentation by 

other contractors in the use of MF (Medium Frequencies) for mine comunications. MF covers the frequency range from 300 kHz-3 MHz and normally requires 

that an additional coupling agent such as a cable or pipe be present for 

signals to propagate readily in mines, especially those with high ground 

conductivity . Almost all mines contain the necessary coupling agents - 

therefore MF is a viable operating frequency for communicating in most 

mines, and could also be utilized for communicating between repeaters in 

approach No. 1. Each of these approaches warrants careful consideration and 

should be analyzed in light of their respective advantages and disadvantages. 

Before undertaking a comparison of relative advantages and disadvantages, 

each approach will be discussed separately. 

5.1 Trapped Mner Location Using Repeaters 

Repeaters can be used to detect the presence and amplitude of manpack 

signals and to relay this information vertically or horizontally. The repeater 

spacing will be determined by the range of the manpack transmitter, range of the 

repeater, and the number of repeaters which must hear the manpack transmitter. 

If more than one repeater can hear a manpack transmitter, then location can be 

more accurately determined by triangulation. See Figure 15. 

Each repeater relays the received strength of the manpack signal so 

that radial distance from the repeater can be estimated. In Figure 15, with 

two repeaters responding, the manpack transmitter could be at either point A or B. 

If three or more repeaters respond to a single manpack transmitter signal, the 

location of that particular manpack can be determined without ambiguity, 

provided that the repeaters are not colinear. If triangulation is not possible, 

the only location information which can be derived from a single repeater 

response is that the manpack transmitter is somewhere on the circumference 

of a circle which has a radius proportional to the received signal strength. 

However, this simple interpretation is further complicated by the presence 

of conducting objects in the mine so even the circle radius is only approximate 

at best. Some practical schemes for using repeaters are described as 

follows : 

Di~ital Wireless Repeaters 

A string of digital wireless repeaters responds to a common manpack 

transmitter frequency and communicates with itself on a different set of 

repeater frequencies. See Figure 16A. Each repeater tells the next repeater 

down the line of the presence and amplitude of a received manpack signal and 

the output of the last repeater (R4) contains the sum of the information 

acquired by all of the repeaters. The presence and amplitude information is 

formatted in a digital data block as shown in Figure 16B. 

The first repeater in the string (Rl) continuously initiates the transmission of the data block and, as it ripples down the drift, each successive 

repeater updates its own reserved data segment. The presence of information 

in a data segment tells of the presence of a manpack signal and its amplitude. 

For example, suppose repeaters 1 and 2 are receiving a manpack signal from 

a transmitter which is located equidistant between R and R (See Figure 16C). 1 The data block transmitted from R4 will look like Figure 166. 

There is a delay between the tirne R1 begins receiving a manpack transmission and the tim when the formatted data block leaves R4. This delay is 

dependent on the number of repeaters in the string and the length of the data 

block. (See Figure 16~). The delay is estimated in Figure 16F. This delay 

could be reduced using a non return to zero (NRZ) code. However, this 

introduces an additional requirement for an external clock. 

A block diagram of a universal wireless digital repeater is shown in 

Figure 17. Only the local oscillator crystals would change from one repeater 

to the next. Note that each unit has dual frequency reception capability; 

one channel to sense the ULF manpack signals and the other channel to sense 

the digital information being transmitted from the preceding repeater. The 

output of the last repeater in the string (R4) may be transmitted up the 

shaft to the surface on a twisted pair, via more repeaters or on a multiplexed 

data system, such as the Collins Hoist Communications System. 
Shaft 

3 bit Binary number indicates 

Data Block 

tdata sec long 

Time 

B. 

Data Sync. 

Pulse A segment of the Data Block is 

reserved to be formatted by each repeater 

signal strength of received MP 

signal. 

b r J 

b , R2 R1 

Figure 16 .A, B, C, and D. Wireless Digital Repeaters 

Manpack Transmitter 

f 

R3 

b 

R 4 

I 

I 

b 
-1 Receive 

Transmit 

I I 

Receive ~ranx 11 

Receive - I 

Manpack I 

Transmitter 

Free Running 

Data 

Sync. 

Pulse 

14 tdelay - 

.4 sec '-\ 

Estimation 

Data Segment 

t data 

1. Assume repeater receiver bandwidth is 5 Hz 

2. Rise time of repeater receiver is about .25 sec 

3. Assume that .4 sec is needed to detect a pulse 

4. Each data segment contains 3 pulses 

5. Data sync signal is .5 sec. 

6. Then, total t for 4 repeaters is: data 

t = 4(3 X .4 S) + .5 S = 5.3 Sec data 

7. Total ripple delay for 4 repeaters is: 

t = 4(5.3 S) = 21.2 Sec delay 

Figure 16 E and F. Wireless Digital Repeaters 

5 1 
Man Pack Receiver 

Repeater Transmitter 

Figure 17 Universal Wireless Digital Repeater 
Surmnary of System 

Advant ages 

1. Relatively simple repeaters. 

2. Modulation is digital, high signal to noise ratio. 

3. Easily expandable. 

4. No wiring between repeaters, increasing reliability . 5. Entire repeater, battery, and antenna could be buried 

for protection. 

6. Permits location by triangulation if more than one repeater 

can hear the manpack. 

7. If any one repeater in the string stops working, breaking 

the link, it might be possible to hear others from other 

points in the mine. 

Dis advan t ages 

1. Time delay between the manpack signal and the end of the 

st ring. 

2. Location accuracy is so~what limited, particularly if only one 

repeater can hear the manpack. 

3. Location is more complicated if any one repeater is receiving 

more than one manpack signal. 
A string of repeaters, each similar to the digital wireless repeater, 

is connected to a common transmission line as shown in Figure 18A. Each 

repeater transmits on its own frequency and encodes amplitude information 

just as the wireless repeater. See Figures 18B and C. All repeaters are 

operating in parallel, simultaneously, and the data block of each is much 

shorter than the data block of the wireless series string. 

A block diagram of a digital wireline repeater is shown in Figure 19. 

Summary of System 

Advantages (Over the Wireless System) 

1. Time delay is less (divided by number of repeaters). 

2. A repeater receiver is not needed. 

3. The transmitter consurns less power. 

Dis advant aEes 

1. Cabling between repeaters is required making the system less 

reliable. 

2. Installation costs are greater. 

3. Bandwidth requirement of the shaft cable and amplifier system 

is greater. 

An FM repeater system is identical to the wireline system except that 

the repeater transmitter is modulated directly by the received manpack signal. 

The FM carrier demodulated at the surface is a faithful reproduction of the 

timing and amplitude of the manpack signal. A block diagram is shown in 

Figure 20A. The frequency spectrum of the signals on the shaft cable is 

shown in Figure 20B. A block diagram of an FM repeater is given in Figure 2 1. 

Summary of System 

Advan t ages 

1. No time delay. 

2. A repeater receiver is not needed. 

3. The transmitter will consurn less power than the digital wireless 

repeater. 

4. Both amplitude and timing information are recovered in the 

detected audio of the FM receiver at the surface. 
f Shaft 

t data 

B Time 

Data 

Sync. 

\ 

Pulse Data Segment 

Data Block 

tdata 4e-c long 

1 All occur simultaneously 

and asynchronously 

Figure 18. Digital Wireline Repeater Sys tem 
Manpack Receiver 

Transmission Line 

Transmitter 

Transmitter Formatter 

Figure 19 Universal Wireline Digital Repeater 
Shaft 

DC 100 kHz 

Narrow Band FM Repeater Signals 

Figure 20 Analog FM Repeater System 
Manpack Receiver 

Figure 2 1 Universal Analog FM Repeater 

58 
Disadvantages 

1. Cabling between repeaters is required making the system 

less reliable. 

2. The bandwidth of the shaft cable and/or amplifying system 

must be greater. 

Intenration of Several Repeater St rings 

If several repeater strings are in operation, possibly in different drifts 

on different levels, many signals will be received at the surface and must 

be decoded to successfully locate a trapped miner. 

Figure 22 is a conceptual top view of a mine with several drifts each 

containing a string of repeaters. A cable for each drift comes to the surface, 

or a multiplex system combines the signals from several strings for transmission upward. 

If cable is used for uplink transmission, and the repeaters are wireless 

digital types, one narrow band signal for each drift comes to the surface. 

(For Figure 22, 4 total). If the repeaters are wireline digital types, a 

narrow band signal for each repeater comes to the surface (13 total). If 

the repeaters are analog FM types, a wideband signal for each repeater comes 

to the surface (13 total). 

Data Readout 

Regardless of which type of repeater scheme is used, the data received 

by the repeaters will have to be combined or multiplexed in some manner, transmitted up the shaft (cable or hoist communication system) and demultiplexed, 

sorted out and displayed. A convenient visual means of displaying the incoming 

data in real time would be to use an illuminated scale model consisting of an 

array of lights, each representing a different repeater in the mine. These 

lights would be fastened securely along scaled down models of the actual mine 

drifts and would be wired in such a way that they would light in accordance 

with the repeater response in the mine. The number and concentration of 

repeater lights illuminated along with their relative brightness would serve 

to indicate the general location of the source transmitter. 

In parallel with the illuminated scale model of the mine, a digital 

printer could be used to record the number of repeaters responding, the 

relative amplitudes, the time of day and date. This, of course, would require 

the appropriate logic interface circuitry between the multiplexed data received 

at the hoist house and the digital printer input. 

Expected Location Resolution 

Locating trapped miners in deep mtal/non metal mines is an extremely 

difficult and complex problem, and with the location schems described, a 

precise location would be virtually impossible. However, these schemes do 

offer promise in (1) detecting the presence of a trapped miner or miners on 

a particular level of the mine, and (2) providing a general location as to 

his whereabouts based on the number and location of repeaters that respond 

to the manpack transmission arnd the relative strengths of their received 

signals. In those mines whose conductivity depth products are such that 

wireless uplink transmission is possible directly, the location can be 

determined in the conventional manner by searching for an omnidirectional null 

in the horizontal magnetic field at the surface. Generally it is possible to 

determine location to better than 10% of the overburden depth using this 

technique. 

5.2 Downlink Communications 

It is assumed that wireless downlink communications will be achievable 

at any mine in the United States by virtue of the fact that a high power 

source could be made available to drive high levels of audio current into 

long grounded antennas on the surface or into large area loops. This assumption 

is supported by field results obtained by Westinghouse personnel at more than 

25 mines where downlink voice communications could always be achieved with 

power levels on the order of 100 watts, even to depths as great as 5000 feet. 

With the miners some day being equipped with combination ULF transmitter/ 

voice receivers, the downlink communications will offer a new dimension to 

the location process. That is if the miner can intelligently key his transmitter 

in response to questions by the surface rescue crew, he could provide the 

surface with whatever knowledge he may have about his location of entrapment. 

5.3 Trapped Miner Location by Direct Through the Earth Transmission 

Up to now, we have considered, for extremely deep mines, systems which 

utilize the existing USBM coal mine trapped miner transmitter operating 

at frequencies 1000 Hz - 3000 Hz as a first link of a repeater chain. The 

trapped miner signals would be relayed from the region of entrapment to the 

surface via a horizontal path to the shaft and from the shaft to the surface 

by a hoist communications system. From field data obtained on this program 

to date, this approach will work. However, there is some question as to the 

cost effectiveness and optimization of this approach. 

The following discussion describes a new concept for a system which 

is designed to perform effectively in locating trapped miners in the deepest 

mines of the United States and requires only a slight modification of the 

existing manpack transmitter system with no additional underground equipment. 

In the proposed system, most of the added sophistication in the total system is 

concentrated in the surface receiving equipment and therefore has little impact 

on system cost or mine acceptance, since few, if any, mines would be required to 

have this equip~nt. 
System Concepts 

a Utilize a wire grid network of receiving antennas on the surface 

to completely encompass the area of possible entrapment. Use 

wire lengths approximately equal to the depth of the mine. (If 

this is not practical, use wire lengths at least one half of the 

mine depth.) Connect the terminals of each antenna to a different 

channel of a multichannel discretely tunable synchronous detection 

receiver. (Deployment of the wire grid receiving network would take 

place as soon as the mine emergency is identified.) 

8 The underground manpack transmitters will be designed to transmit 

signals on a 50% duty cycle with the following waveform configuration: 

The above waveform will contain energy primarily at two fundamental 

frequencies 1/T and 1/T2. (e. g. T2 = 100 T1 and thus f = 100 f2) . 1 

The low frequency fundamntal frequency will be used for synchronous 

detection of through-the-earth uplink signals while the high frequency tones 

superimposed thereon will be used for horizontal transmission of signals to 

a multichannel receiver with a broadband loop and preamp lowered down the 

shaft. 
This type of transmitting configuration for trapped miner detection, 

identification and location has the following advantages. 

a Utilizes simple low cost equipmnt underground carried by 

the individual miner. 

a Obviates the need for expensive cabling, telemetry , repeaters 

and receivers. 

a Greatly minimizes or eliminates the maintenance requirement 

for underground systems. 

a Simultaneously provides a low frequency signal for through 

the earth uplink (i*e. 10 Hz-30 Hz) and an intermediate frequency 

(1000 Hz - 3000 Hz) signal for sidelink level identification. 

a Sidelink detection and level identification is accomplished by 

lowering broadband antennalpreamp down the shaft. 

Location determination is accomplished by synchronously detecting and 

comparing low frequency signals ( 10-30 Hz) received on each element of the 

orthogonal network of horizontal wire antennas. By using long wire receiving 

antennas, on the surface and loop antennas underground, we can effectively 

approach electromagnetic coupling characteristics which vary as inverse distance 

(l/z) rather than ( 1/z3) as is the case with dipole transmitting and receiving 

antennas. Also, by using synchronous detection, with an integration period of 

10 seconds, we effectively obtain a signal to noise improvement of 

10 log (251.1) = 24 dB over that of the existing location receiver, which 

has a 25 Hz effective bandwidth. 

The identification of the trapped miners ' horizontal location is 

determined roughly by comparing the signal amplitudes of each element of the 

receiving array. For a vertical magnetic transmitting dipole (horizontal loop 

deployed by a trapped miner) the relative electric field pattern will look 

approximately as shown in Figure 23 for the different mine depths represented. 

This figure is based on a free space assumption, which is only an approximation 

at frequencies in the 10 Hz - 30 Hz range at conductivities of o = mhos/m. 

The X,Y coordinates of the trapped miners location is determined by the projected 

null locations as observed by plotting the amplitudes of received signals from 

each of the receiving antennas. 

Likewise the miners ' vertical location can be identified by lowering 

the intermediate frequency receiver down the shaft, and looking for the level 

which produces the greatest signal amplitude at a frequency exactly equal to 

100 times that of the low frequency detected on the surface. 

* The intermdiate frequency ( 1000 Hz - 3000 Hz) could possibly be much 

greater. Recent studies by another contractor, as yet unpublished, have 

shown that MF communications (300-3000 kHz) offers a viable alternative 

to in-mine comunicat ions. 
Figure 23 Relative Induced Volt age in Long Horizontal Wire Antenna from 

Dipole Transmitter 
6.0 FIELD TEST PROGRAM 

Two series of field tests were conducted on this program: (1) Mine 

Characterization Tests, and (2) Communications and Propagation Tests. A total 

of seven mines were visited in all, six of which were visited for both sets 

of field tests. 

6.1 Mine Characterization Summary 

The objective of Task I1 was to visit six (6) mines considered to be 

representative of various mtal/non met a1 environments. The purpose of the 

visit was to measure the paramters relevant to electromagnetic detection and 

location of, and communication with trapped miners. Testing was performed 

during these visits to determine the degree of applicability which coal mine 

trapped miner technology has to metal/non metal mines. The parameters and 

observations gathered at the six mines were used to formulate the design 

specifications for specific items of location-communication hardware. 

The parameters measured at each mine site included the following: 

Overburden 

Conductivity (surf ace and subsurface) 

Surface EM noise 

Subsurface EM noise. 

Observations of the following parameters were also made : 

Mining characteristics (entry type, ore type, et c.) 

General geological relationships 

Distribution of metallic conductors (rails, pipes, cables, etc.) 

Nine depth and lateral extent 

Environment a1 factors (humidity, temperature, gasses, and 

corrosives, dust, et c. ) 

Topography and ground cover. 

Conductivity and noise measurements were made using existing equipment 

configured as described in Figures 24 and 25 and pictorially in Figures 26 

and 27. Other information was obtained during the on-site visits, from appropriate mine personnel or from existing data bases (such as USGS and USBM 

libraries, previous USBM contract results, local geological societies and others) . 
GENERATOR CONSTANT CURRENT 

Figure 24 Block Diagram of Conductivity Pkasurement System 


Ffgure 2 7B ' Undergrounti Conductivity Measurements , Henderson Mne 

6 9 
Conductivity Measurements 

In order to fully evaluate the effects of the conducting mine overburden on uplink and downlink electromagnetic propagation, it is necessary 

to know somthing about the layering structure and/or any anomalous structures 

such as faults, dikes, or mineral veins in the mine overburden. A good method 

to examine overburden electrical characteristics is to make surface conductivity 

soundings. Surface conductivity soundings of the overburden are obtained by 

transmitting a known current (I) (either dc or commutated low frequency ac) 

into the ground through a pair of ground electrodes and measuring the induced 

volt age (V) response between another pair of ground electrodes located some 

distance away. This is shown in Figure 24. The mutual impedance (Z) between 

the two pairs of electrodes is given by Z = - ohms. The measured mutual I impedance, in conjunction with a known electrode geometry, yields a value for 

apparent conductivity (a). Expressions for determining apparent conductivity 

from mutual impedance measurements can be found in any good geophysics text 

such as Keller and Frischknecht, (18). 

By successively expanding the spacing between the current electrode 

pair and the voltage electrode pair, the resulting measurements yield 

information from increasing depths in the earth. Measurements of this sort 

will yield the sequence of high and low conductivity layers in the subsurface 

section. For example, a soil layer overlaying gravel or bedrock gives a 

distinctive sequence of conductivity readings and can be used to estimate the 

depth to the various layer interfaces as well as the individual electrical 

characteristics of each layer. A systematic method for interpreting conductivity 

soundings in terms of equivalent earth layers has been developed. In many 

cases a knowledge of the conductivity or resistivity layering structure is 

sufficient to produce accurate predictions of propagation characteristics 

through the overburden. 

In order to evaluate the possible effects of the mineralized zone 

within a mine on the elect romagnetic propagation characteristics, it was deemed 

necessary to make conductivity measurements within the mine. In order to do 

this, a battery operated conductivity unit was borrowed from Melvin Lepper of 

the USBM-DMRC. This unit proved very effective for rapid underground measurements 

in areas where 110 V power was not available. 

Noise 

Electromagnetic noise waves vary significantly depending on a number 

of factors including mine power type and distribution, proximity to power 

sources, season, time of day, and others. 

On the surface, the background noise and interference in the frequency range 

of interest is made up largely of atmospheric noise from world wide thunderstorms 

and man-made interference from power lines. Man-made interference occurs at known 
discrete frequencies (60 Hz and its harmonics) and can usually be avoided in 

narrowband receiving systems by j udicious choice of operating frequency, 

highly selective bandpass filters and deep notch filters tuned to the interfering frequencies . However, atmospheric noise is distributed across the 

entire frequency band and cannot be eliminated in this manner. Consequently, 

it very often constitutes the absolute limitation in the signal to noise 

performance of low frequency receiving systems such as the ones used by the 

Bureau of Mines for uplink communications, 

Noise measuremnts were made both on the surface and underground using 

the configuration in Figure 25. The ferrite loop antenna was usually oriented 

in two mutually perpendicular horizontal positions and vertically at each 

measurement site so that a relatively complete picture of noise distribution 

could be made. At each mine, measurements were made at suspected noisy and 

quiet locations above and below ground. 

Noise data were recorded through the preamplifier and onto magnetic tape 

cassettes. Playback was into a Tektronix WDI 1221 signal processor (see Figure 

28) . Processing included removal of the effects of the recording response 

function, performing a Fast Fourier Transform and plotting the spectrum in a 

log frequency format. Some typical noise data are shown in Figure 29. The 

upper portion is the time domain signal, the bottom, the frequency domain 

amplitude spectrum. It is interesting to note that in this particular 

example, which was the worst case of electromagnetic noise measured during 

Task 11, the dominant frequency is on the order of 3 kHz. This could represent 

a harmonic coupling resonance for the particular conductors, transformers and 

other hardware near the measurement site, or it could have been produced by 

ac machinery operating nearby. Other noise plots are contained in the 

individual site reports submitted previously on this contract . 

Field Test Results 

Field tests were conducted at six mines. These are shown in Table 4 

along with some key information. Complete site reports were prepared and 

submitted earlier on this contract. Conductivity results are shown in 

Figure 30. Conductivity measuremnts are very important for system design 

in several cases. At the Henderson Mine, the effects of the sulfide halo, 

detected by the conductivity survey, indicates a possible high attenuation zone 

between the mine and surface. Likewise, at the Big Island Mine, a high conductivity member of the overlying Green River or Uintah Formations could 

present a problem for through the earth communications with the existing coal 

mine system. 

The noise data are in good agreement with measurements made during 

other mine characterization programs. One obvious difference is the seemingly larger variety of uses of electrical power at n-etallnon metal mines, 

and also the lack of large scale distribution systems as found in coal mines. 

Generally speaking, metal/non metal mines are noisier on the surface and 

quieter underground than coal mines. 

1000 FIz 

Figure 29 Sample of EM Noise Measured During Task I1 
TABLE 4 

SUMMARY OF MINE TESTS 

MINE LOCATION DEPTH OF TESTS CONDUCTIVITY N

Feet mho/m 

Surface S ubs ur face --?

1. Henderson Empire, Colo. 2 300 7 x 3 x 

Molybdenum 

2. Homestake Lead, South Dakota 2300, 4100 

Gold 

3. Fletcher Bunker, Missouri 1000 

Galena 

C 4. Ozark Mahoning Cave-in-Rock, 111. 550 

Fluorspar 

5. Big Island Green River, Wyo. 850 

Trona 

6. Idarado Ouray, Colo. 2900 

Sulfides 

7. International Avery Island, La. 500, 770, 880 

Salt 

Footnotes 

la. In /I2 shaft house lb. At end of Urad tunnel 

2a. Near powerline on surface 2b. 2300 foot level 

3a. Underground near /I31 shaft 3b. Underground near transformer 

4a. Near powerline on surface 4b. Near /I7 shaft underground 

5a. Base of service shaft, above 5b. Underground north end of mine 

ground 

1 x 5 x 

9.3 X - 

6a. Manhois t replacement orebody 6b. Manhoist replacement orebody 

(NW-SE orientation) (NE-SW orientation) 
Ozark Mahonine 

7 x 10-4 

Fletcher 

1.5 X 10- 

Figure 30 GENERALIZED CONDU(;TIV

HOST MATERIALS. (SWA
6.2 EM Propagation Tests 

The same mines that were visited for purposes of mine characterization 

measurements were revisited at a later date to conduct EM propagation measurements. The equipment used for the ULF uplink and sidelink propagation measurements was as follows : 

ULF Transmitter, Collins Model PN622-2 375 (See Figure 31) . ULF Receiver, Collins Model PN622-26 32 (See Figure 32). Associated Substitution Calibration Equipment 

For the twisted pair multichannel telemetry test performed in the 

International Salt $line, a filter-discriminator as shown in Figure 33 was used. 

Narrowband FM voice tests were performed using a Westinghouse 23-channel 

developmental system with carrier frequencies ranging from 5 kHz to 115 kHz. 

This system is shown in Figures 34 and 35. 

ULF UD link Measurements 

Table 5 summarizes the wireless ULF uplink propagation data obtained at 

the six metal non-metal mines indicated in the table. Overburden depths range 

from a low of 135 meters at the Ozark Mahoning Fluorspar Mine to a high of 

792 Eters at the Henderson Molybdenum Mine. The Honestake Gold Mine had an 

overburden depth of 2073 meters; however, signals were not detected on the 

surface at this mine, although they were detected at an intermediate level. 

The calculated field strengths based on conductivity measurements 

obtained earlier were in reasonably good agreement with the measured magnetic 

field strengths in all cases except at the Homestake Mine. Here the measured 

field strength for an in-mine uplink path was about 42 dB lower than the 

expected value based on the conductivity of that particular mine. Barring 

equipment malfunction as a possible cause for this discrepancy, the only other 

possible explanation would be that the intervening workings with all their 

rnetal rails etc. could have acted as a shield in preventing the propagation 

of signals through to the upper levels. 

In all of the other tests, the received signals were suitable for 

trapped miner location, even those measured at the Henderson Mine through a 

792 meter (2600 ft) overburden. The frequency variation of uplink field strengths 

measured at the Henderson Mine is shown in Figure 36. The negative transmission loss characteristics observed at the Henderson Mine are undoubtedly 

caused by the fact that the uplink transmitter was located within 1000 feet 

horizontal distance from the shaft on the 8100 ft level. This was the furthest 

possible distance available for equipment deployment. For the Henderson Mine 

tests , a special West inghouse developed mult ifrequency transmitter was used. 

This transmitter is equipped with a 13 frequency pushbutton controlled 

synthesizer and a switching amplifier coupled to a 20 turn loop antenna. It 
Figure 31 Mine Rescue Transmitter (attached to Cap Lamp Battery) 
Figure 32 EM Neld Measurement Equipment 

7 8 
Hgure 33 Multichannel FM Telemetry Filter and Discriminator 

7 9 
Yim 34 Westinj$ouse Narrowband FM Transdtter 

80 
Figure 35 Wes tinghouse Narrowband FM Receiver 
TABLE 5 

ULF UPLINK PROPAGATION S-Y 

Mine Overburden Frequency Moment Measured Calculated Mea

Depth (2) f INA Conductivity Field Strength Fie

(Meters) (Hz) (amp-tam ) (*os /m) ~@/m I-I 

(Subsurface) 

International Salt 152 10 50 19 88 9.3 X lo-2 27.4 35.

Stauf fer 1050 36 5 3 X 1.12 1.

Homes take 

Ozark Mahoning 

E t 1 

St. Joe (Fletcher) 29 8 10 50 20 46 1 X 7.07 3,

I I 

30 30 2046 1 X 3.10 2.

Henderson 79 2 630 1798 3 x 280 2.

I1 750 16 79 242 2 I I 

11 

9 30 1739 213 2 

I I 

11 1050 16 79 184 1I I 

11 

1350 16 79 144 

I I 

I I 

1650 1655 113 

I I 

I I 2250 1319 058 

I I 

11 2430 1439 056 

I I 

I I 2730 1319 043 

I I 

I1 30 30 10 79 029 I I 

I I 3330 959 .022 

I I 

* Negative transmission losses should be treated as transmission gains. 

is designed primarily to establish a high current moment in a relatively 

small area. However, even though it is entirely battery operated, it is 

not portable to the extent that a miner could routinely carry it on his belt 

while conducting his other tasks. 

Figures 37 through 42 show the underground workings at each of the 

mines visited during the EM propagation test phase of this contract. It is 

immediately apparent in glancing at these figures how the metal/non metal mine 

layouts differ from one mine to the next and how they differ from typical coal 

mines. 

Based on the results obtained in these field exercises, the existing 

USBM trapped miner EM Location System is not adequate, as it now stands, to 

be effectively used in locating trapped miners in the deeper metal/non metal 

mines such as Homestake and possibly some of the deep mines in the Coeur dlAlene 

district of Idaho. However, with relatively minor modifications to the trapped 

miner manpack transmitter and by replacing the simple analog narrow band 

receiver with a more powerful signal processing receiver, even the deepest mines 

can be effectively penetrated with trapped miner location information. A more 

detailed discussion of this approach is given in the recommendations in Section 8. 

ULF Sidelink Measurements 

Measurements of ULF sidelink propagation were conducted at 5 of the 

6 mines visited during the propagation test phase of this program. The main 

things to be learned from these tests were: (1) How well and over what 

distances do ULF and VLF signals propagate horizontally in typical metal/non 

met a1 mines. (2) What effect does in-mine conductors, such as pipes, rails, 

cables, etc. , have on ULF and VLF sidelink propagation characteristics. 

In a trapped miner location system utilizing the concept of horizontal 

signal telemetry from the point of entrapment to a shaft location on the same 

level as discussed in Section 5.1, the importance of studying sidelink 

propagation characteristics cannot be underestimated. Table 6 summarizes the 

results obtained at the five (5) mines. Of the 5 mines, three of them 

(Stauffer, Homestake and Ozark Mahoning) offered the opportunity to deploy the 

transmitting loop antenna with one side directly beneath an underground water 

line. At these three mines, the resulting field strengths measured in the drift 

containing the pipe exhibited EM coupling enhancements on the order of 40-50 dB 

relative to the calculated free space field strength for that antenna moment. 

At the two remaining mines, International Salt and St. Joe Minerals, 

there was evidence of a much lower level of coupling enhancement , probably 

due to unavoidable coupling to the pipe network at greater distances from the 

transmitter. In all cases, the measured fields were rarely less than the free 

space equivalent value, indicating that the presence of the mine conductors 

can be effectively utilized to enhance underground ULF propagation, and, when 

ignored, will in no way be detrimental to the propagation characteristics. 


WESTING HOUSE ELECTRIC CORPORATION 

Scale: 1" = 200' 

Deployed in 

this Stope 

Homes take Mine 

Lead, South Dakota 

6800' Level 

Track 

A 3 .I 'A 
Antenna 

Figure 40 

Mine Map of 

Ozark Mahoning Co. 

Rosiclare , Ill. 

Scale : 1" = 50' 
ment Location 

Voice Trans- 

Mine 

TABLE 6 

L?F S IDEL INK PROPAGAT ION SUMMARY 

Overburden Frequency Moment Maximum Max

Depth (2) f INA Detection Enh

(.meters) (Hz) (hos /m) Dist. (dB 

(meters) 

International Salt 

Stauf fer 

Hollhes take 

Ozark Mahoning 

St. Joe 

(Fletcher) 
Figures 4 3 and 44 show the sidelink propagation characteristics 

measured at the Stauffer Big Island Mine where tight coupling to the water 

pipe was in effect. Note the large positive deviation of the measured field 

strength above the free space coupling line. On the other hand, Figures 45 

and 46 show the sidelink propagation characteristics obtained at the 

St. Joe Minerals (Fletcher Shaft) where little or no apparent coupling was 

present. Here, the fields fell off according to the inverse distance cubed 

relationship as expected for free space conditions. 

VLF Voice Measuremnts 

Narrowband FM voice tests were conducted in five of the six mines 

using prototype VLF equipment developed by Westinghouse in 1974. The main 

purpose of these tests was to determine the feasibility of using VLF FM for 

sidelink telemetry of trapped miner signals. These measurements were only of 

a qualitative value since the FM communications transmitter and receiver were 

uncalibrated. However comparison could be made of the range of voice communications coverage achieved in the different mines as a function of transmitting 

moment, frequency and proximity to conducting objects (see Table 7. ) 

The longest range of intelligible comunications (2160 meters) was 

achieved in the Stauf fer Mine at Green River, Wyoming where the 30 kHz 

t ansmission was fed into a tuned loop antenna with a moment of 112 1 amps turns f 

m and coupled to a conducting water pipe about 5 meters away. Continuous 

mnitoring of voice reception as a function of distance from the transmitter 

was achieved using an electric "golf cart" vehicle for mobility underground. 

At the other mines where FM voice measurements were made, significantly 

lower transmitting moments were used, resulting in shorter ranges of communications coverage. However, the measurements did show that VLF FM does offer 

a mans of telemtering trapped miner location data to a shaft location. In 

so= cases such as at the Stauffer Mine, the range of VLF voice transmission 

actually exceeded the narrowband ULF code range primarily because of the 

lower background noise experienced in the VLF bands. 

Analog Telemtrv of ULF Sienals 

Tests were conducted at the International Salt Mine to evaluate the 

feasibility of telemtering manpack location signals from the output of several 

Collins Model PN622 2632-001 receivers to a central location in the mine for 

composite uplink transmission. The basic configuration used in this particular 

mine test is shown in the block diagram of Figure 47 and schematics of Figures 

48 and 49. Here the receivers were deployed about 1000 feet apart in the 

mine and were all tuned to the sam channel (Ch. 51) to receive the same 

frequency. The results of this test are purely qualitative since the receivers 

were not calibrated for this exercise. Nevertheless they do demonstrate the 

feasibility of combining the outputs of several location receivers via FM 

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100 1000 

DISTANCE FROM CENTER OF TRANSMITTING LOOP WETERS) 

Figure 46 Signal Propagation of ULF Signals - Fletcher Mine, St. Joe 

Viburnum, Missouri 
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telemetry into a twisted pair cable deployed along a main drift. Figure 50 

shows the discriminated output of the signals after they were separated by 

filtering in the filter discriminator circuit. It is apparent from these 

recordings that the repetitive location signal at the three receiving locations 

is recognizable. The lowest trace was obtained at a receiving location 

within 50 feet of a conveyor belt and it shows the highest background noise 

level. Even so, the presence of the signal is unmistakable in the high noise 

environ~nt of this location. The equiprent used to telemeter the location 

signals from their respective receiving locations is somewhat crude, but not 

so crude that it cannot demonstrate the feasibility of this technique. The 

telemetry equipmnt was fabricated by Westinghouse several years ago for use 

on a seismic telemetry program. It was modified for use on the present program. 

One feature that was clearly demonstrated by this test was the ability to mix 

a number of VCO output signals together merely by connecting their output 

terminals directly across a twisted pair cable at their respective receiving 

locat ions. Twisted pair cable is relatively inexpensive and could effectively 

serve as a suitable tele~try link in a mine location network for deep mines 

where it may be impossible to transmit directly to the surface with portable 

equipment. 

F'M telemetry equipment is readily available off the shelf from companies 

such as Tri-Corn, Develco and others. With commercially available telemetry 

subsystems, it would be possible to configure a mine location network which 

could give calibrated information on field strength for each of the receiving 

locations being telemtered to a receiving location. This could be accomplished 

using an automatic gain circuit in the receiver with a readout of both 

gain and amplitude. Digital techniques would be preferred in transmitting both 

gain and amplitude information. The analog FM circuitry described here could 

also be used for transmitting digital information - the only modification 

required would be in the receiver. logic. 

Inductive Re~eater Conce~ts 

The International Salt Mine in Avery Island, Louisiana has a mined out 

level at 500 feet which could be utilized for deploying a large inductive 

repeater network to facilitate uplink, downlink and sidelink communications 

at frequencies from d. c. to 100 kHz. The repeater network could take the 

form of a network of loops or horizontal wire antennas to act as passive 

repeaters to spread the electromagnetic energy throughout the mine. One 

advantage of using horizontal wire antennas instead of loops is the broad 

frequency band that can be accommodated without the need for tuning the 

antennas. Figure 5 1 shows a sample deployment of horizontal wire antennas 

deployed in the form of a grid network in a hypothetical mined-out area of a 

mine. In this example there are eight long horizontal wire antennas, each 

energized to carry a current of 1 ampere. 

WESTINGHOUSE ELECTRIC CORPORATION 

Figure 5 1 Inductive Repeater Network 
The vertical magnetic fields are computed as a function of x, y 

coordinates in the antenna field itself as follows: The vertical magnetic 

field produced by A, A', B and B' vary with distance in the y dimension as 

- If we assume that I = IA, = IB - IB, = I A 

In a similar manner, we can compute the magnetic field contribution 

from C, C' , D and D' which vary with distance in the x direction 

Surmning the contributions from all current lines and evaluating 

H as a function of x and y, we get z 

If we allow the current I to equal 1 ampere, we obtain the following field 

strength distribution shown in Table 8. 
Table 8 

Magnetic Field Strength Dist ributisn 
Table 8 

- X 

m 

90 

90 

90 

90 

90 

90 

90 

90 

90 

110 

110 

110 

110 

110 

110 

110 

110 

110 

150 

150 

150 

15 0 

15 0 

15 0 

150 

150 

150 

( continued) 
Table 8 

- X 

m 

190 

190 

190 

19 0 

190 

190 

190 

190 

190 

2 10 

210 

2 10 

210 

2 10 

2 10 

2 10 

210 

210 

250 

250 

250 

250 

250 

250 

250 

250 

250 

( continued) 
Table 8 (continued) 

The foregoing computations in Table 8 show that detectable sipal 

strengths are produced anywhere inside the illustrated grid network for 

antenna currents of 1 ampere, and for that matter, even as low as 10's of 

milliamperes. Note that in Table 8 the field strength distributions exhibit 

a certain amount of symmetry. Also, it is observed that in every other square 

in the antenna grid pattern, the current flowing in the line segments 

enclosing that square are in opposition and the resulting field strengths are 

down by at least 20 dB from the squares where loop current is in the same 

direction. However, the fields produced in these opposing loop squares are 

still well above the level of detectability which is about 1 pA/m. 

The wire grid antenna field concepts are applicable to detection and 

location of trapped miners for those situations where an uplink assist is 

needed. The terminals of the wire grid adjacent pairs, i.e., A & A', B & B', 

C & C' , etc. can be connected to underground receivers. The identification 

of the trapped miner's location is determined roughly by comparing the 

signal amplitudes of each element of the receiving array, as described in 

Section 5.3. This information can be relayed up to the surface via a hoist 

uplink system which is comzrrercially available, with each output of the antenna 

grid pairs multiplexed together using an array of tone frequencies. The 

composite signal can be demultiplexed at the surface and displayed in a 

visual format for location identification. The miner can use different frequencies on the sarrvs level since the wire grid repeater network is essentially 

broadband and the grid pair receivers can be made to synchronously sequence 

through a list of frequencies used by the tradped miner transmitters. By 

displaying the data on the surface in real time, a synchronization network in 

the subsurface equipmnt can be used to identify the output in terms of trapped 

miner location, frequency and time . 
Most of the extremely deep metal/non metal mines in the United States 

are multilevel mines and could conceivably devote one of their intermediate 

mined out levels for use as an antenna grid repeater network. Experience has 

shown that long horizontal wire antennas function well as receiving antennas 

for low frequency signals. Furthermore, they can accept broadband information 

without the need for sequential antenna tuning. This latter fact makes such 

an antenna system well suited for use as a ULF scanner for trapped miner 

identification and location. The wire grid receiving antenna concepts can 

be carried one step further and deployed on the surface for location of trapped 

miners in mines having no available intermediate levels for antenna deployment. Granted, there are logistic problems associated with deployment of a 

large wire grid on the surface; however, in special cases a wire grid network 

could be simulated by a series of adjacent square loops with each adjacent 

loop representing a different receiving channel. A comparison of field strengths 

received from such a network can form a pattern to guide the rescue party 

to the trapped miner's location. 
7.0 CONCLUSIONS 

0 The results of the field measurements made on this contract show that 

there are several ways in which a trapped miner EM location system can be 

implemented in deep metal/non metal mines. Basically these can be categorized 

under two main subheadings as follows : 

( 1) Underground repeater network with hoist uplink comunications . 

(2) Through the earth uplink location system with surface and 

downshaft receivers . 

The results of the field measurements and supporting studies show that both 

approaches are technically feasible. However, the latter approach (2) is 

probably more cost effective and workable, considering all of the technical 

and political ramifications involved in Government, Industry, and Labor 

Relations in the mining industry. Table 9 qualitatively summarizes the 

technical and practical aspects of each of the above approaches. 

o If a purely "through the earth" approach is adopted for a metal/non 

metal location system, a downlink voice capability could also be implemented 

as part of the system using baseband audio current transmission into the 

wire grid deployed on the surface for receiving trapped miner signals. The 

antenna grid would then be time shared with a push-to-talk switching arrangement on the surface. 

0 Wired systems for telemetry and repeater applications underground are 

not too practical in the light of statistics developed on past mine disaster 

case histories. Wired repeaters are especially vulnerable to mine accidents 

involving fire; statistics show that fire is the.main hazard in metal/non 

mine disasters and it occurs more frequently and causes more deaths than all 

other disasters combined. 

8 Wireless telemetry of ULF trapped miner signals to the shaft area is 

possible by virtue of electromagnetic coupling to the network of pipes and 

cables found in virtually all &tal/non metal mines. This enhancement in 

underground wireless propagation from the individual trapped miner transmitters to the shaft area lends itself to a method of vertical location 

determination utilizing a broadband downshaft receiver. 

a &tal/non metal mines, in general, exhibit overburden conductivities 

which are lower than coal mine overburden conductivities, thus enhancing 

the practicability of implementing a truly "through the earth" location 

system for these mines. 

o Blasting cap susceptibility studies show that the chance of ULP trapped 

miner transmitters setting off blasting caps stored in a box is virtually 

non existent and the chance of them setting off a wired array of caps ts extremely remote. However, the problem does become more critical at higher 
TABLE 9 

Qualitative Assessment of Trapped Miner Location Techniques 

Assessment Criteria Quality (Method 1) 

Overall Location Effectiveness Good 

Horizont a1 Coordinate Determination Good 

Vertical Coordinate Determination Good 

Portability (Underground Equipment) Good 

Portability (Surface Equipment) Fair 

Survivability Fair 

Reliability Fair 

Initial Cost to Mine Co. Poor 

Maintenance Cost Fair 

Surface Deployment Logistics Good 

Method 1 

Method 2 

Quality (Method 2) 

Good 

Fair 

Good 

Excellent 

Fai r 

Excellent 

Excellent 

Excellent 

Excellent 

Fair 

- Underground network of repeaters to receive signals 

from trapped miners and relay signals up the hoist. 

- Modified low frequency (10-30 Hz) through the earth 

uplink location sys tem with surface multichannel signal 

processing capability and downshaft receivers for vertical 

location determination. 
frequencies where free space wavelengths are comparable to blasting cap 

or blasting cap array dimensions. This is one of the primary obstacles 

to the full utilization of VHF and UHF systems in underground mines using 

electric blasting caps. 

Table 10 summarizes the through the earth propagation data obtained by 

Westinghouse personnel on USBM and MESA sponsored field programs since 1973. 

Only those mines with overburdens greater than 300 meters are shown in this 

table. The data from these mines show that trapped miner signals were detected 

over the range from -26 dI3/ A/m to 15 dB/ A/m. In each of these instances 

a simple code communications link could be established with the trapped miner, 

i.e. (voice downlink - code uplink). Furthermore, the uplink signals were 

suitable for reasonably accurate determination of the miners location. A 

rule of thumb established from past experience is that the uncorrected null 

location based on uplink magnetic field strength profiles is accurate to within 

5% of the overburden depth of the mine. Note that in Table 10, there are two 

instances where the uplink signals were not detectable using a 1.5" diameter 

receiving loop but were easily detected using a 2000-4000 ft horizontal wire 

receiving antenna. Results of this type serve to verify the enhancement in 

electromagnetic coupling expected between a dipole transmitter and a non 

dipole receiving antenna (i.e. long horizontal wire) as described in Section 5.3. 
TABLE 10 

Summary of Through the Earth ULF Propagation Results in Mines with Overburdens Greater 

@ Signals not detectable on 15" Loop 

Downlink Data Only 

Mine 

Robena 114 

Geneva 

Galena 

Sunshine 

11 

Pocahontas 81 

Loveridge 

Virginia 

Pocahontas 113 

Highsplint 

Henderson 

Fletcher 

Location 

Fordyce, Pa. 

Price, Utah 

Wallace, 

Idaho 

11 

I I 

Grundy, Va. 

Fai rview , W. Va. 

Keen Mountain 

Va. 

Highsplint, 

Kentucky 

Empire, Co. 

Viburnum, Mo. 

Date 

1973 

1973 

19 73 

19 74 

I1 

19 74 

19 77 

1977 

19 76 

19 77 

1977 

Overburden 

Depth 

Meters 

300 

350-580 

9 15-1310 

82 3- 146 3 

11 

6 70 

409 

36 6 

42 7 

79 3 

30 0 

Overburden 

Conductivity 

mhos/m 

.011 

.017-.021 

.006 

.0013 

1 I 

.0033 

017-,033 

.012-.066 

.0017-,014 

,0003 1-. 00055 

.01 

Frequency 

Hz 

1050- 30 30 

922-2900 

330-10 kHz 

19 00 

11 

1900 

630-3030 

11 

I I 

6 30-3330 

1050- 30 30 

Momnt _ 

amp turns mL 

1366 

1135-2511 

11,700 

3272 

I I 

2 150 

1856-817 

19,5 75 

1278-6 39 

1800-960 

2046 

Receiver 

Bandwidt

Hz 

2 

2 

2 to 6 

2 

50 

2 

25 

25 

25 

25 

2 5 
8.0 RE COMMENDAT IONS 

After careful consideration of the requirements for an EM trapped 

miner location system and in view of the results obtained on this program, 

Westinghouse recommends that a through-the-earth low frequency (10-30 Hz) 

approach be followed in the development of a new system. Since, in the 

event of a mine emergency, voice cornmications will be desired with the 

trapped miners, a long wire surface antenna system will probably be deployed 

for that purpose anyway. This sam antenna or antenna array could be time 

shared with the voice transmitter and used with the surface receiver to 

detect the uplink transmissions from the trapped miner. An array of these 

antennas in the form of a grid can then be used to locate the source of the 

underground transmissions. 

Identification of vertical level of entrapment can be achieved by 

using a trapped miner transmitter capable of dual frequency transmission as 

described in Section 5.3. The higher frequency component of the transmitted 

waveform will be designed to couple into existing mine pipes and cables 

on that level and thus propagate with low attenuation over to the vicinity 

of the shaft. A broadband loop and preamp can be lowered down the shaft 

and used to record amplitudes of different frequen'cy signals as a function 

of depth. 

The advantages of this approach over a multi-element repeater approach 

is mainly in reliability and maintainability since the only underground 

equipment required will be the trapped miner's manpack transmitter. 

Westinghouse recommends as a logical follow-on effort to this program, 

further development and testing of a dual frequency transmitter as described 

in Section 5.3. The field testing on the follow on program should be performed at a mine representative of worst case conditions such as ~omestake's 

gold mine in Lead, South Dakota or equivalent. If such a system could be 

demonstrated successfully at a mine of this type, it would firmly establish 

the feasibility of this approach and insure successful performance at virtually every mine in the United States. 
REFERENCES 

Wes tinghouse Electric Corporation, 1st Preliminary Field Evaluation 

of USBM Coal Mine EM Location System, October, 1976. 

Wes tinghouse Electric Corporation, 2nd Preliminary Field Evaluation 

of USBM Coal Mine EM Location System, Decenber, 1976. 

West inghouse Electric Corporation, 3rd Prelininary Field Evaluation 

of USBM Coal Mine EM Location System, April 1977. 

Wes tinaouse Electric Corporation, 4th Preliminary Field Evaluation 

of USBM Coal Mine EM Location System, May 1977. 

Westinghouse Electric Corporation, 5th Preliminary Field Evaluation 

of USBM Coal Mine EM Location System, August 1977. 

Hyvarinen, J., et al, "Major Disasters at ~etal/~on Metal Mines and 

Quarries in the United States," Bureau of Mines Circular 

No. 7493, April 1949. 

Dravo Corp . , "Analysis of Large Scale Underground Non-Coal Mining 

Methods, I' USBM Contract Report, January 19 74. 

Farstad, A. J. , "Transmission of Signals by Coupling to Overhead 

Conductors and Buried Pipelines, " West inghouse Research 

Report 74-7H2COMSY-MI, February 19 74. 

Large, D. B. and L. Ball, "Magnetic Field Excited by a Long Horizontal 

Wire Antenna near the Earth's Surface," Westinghouse Research 

Report No. 69- 1H2-GEOEX-Rl , May 1969. 

Wait, J. R. , "~ropagation of ELF Electromagnetic Waves and Project 

~anguine/~eafarer, " IEEE Journal of Oceanic Engineering, 

Vol. OEl, No. 2, April 1977. 

Large, D. B. , L. Ball and A. Farstad, "~adio Transmission to and 

from Underground Coal Mines - Theory and Measurement ," IEEE 

Trans. Communications COM-2 1, March 19'73. 

Murphy, J. N. and H. E. Parkinson, "Underground Mine Communications," 

Proc. IEEE, Vol. 66, No. 1, January 1978. 

Cook, William C., et al, "Mine Emergency Operations Group Field Test 

and Operations Program," IESA Final Report, January 1975. 

Radio Frequency Energy - A Potential Ilazard in Use of Electric 

Blasting Caps, Inst. of Makers of Explosives, safety Publicat ion 

No. 20. 
REFERENCES 

(continued) 

Maxwell, E. L., et al, "Coal Mine Rescue & Survival System," Vol. I1 

Communicatio~ls & Locat ion Subsystem Final Report , West inghouse 

Electric Corporation, September 1971. 

Farstad, A. J., et al, "Development and Testing of a CW Electromagnetic Location System," Westinghouse Report on Contract 

H0220073, April 1973. 

Allen, J. W. , et al, "Mine Emergency Operations Program," Final Report 

(EM System Analysis - Appendix) , June 19 72. 

Keller, G. and F. Frischknecht, Electrical Methods in Geophysical 

Prospecting, Pergamon Press, Oxford, England, 1966. 

The Mining and Scientific Press, 1867 to 1922. 

Engineering and Mining Journal, 1874 to 1947. 

Higgins, Edwin, Fires in Lake Superior Iron Mines: Bureau of Mines 

Tech. Paper 59, 1913, p. 9. 

Ingalls, W. R. , Douglas, James, Finlay, J. R. , Channing, J. Parke, 

and Hammond, John Hays, Rules and Regulations for Metal Mines: 

Bureau of Mines Bull. 75, 1915, pp. 254-276. 

Bowles, Oliver, Safety in Stone Quarrying: Bureau of Mines Tech. Paper 

111, 1915, p. 45. 

Fay, Albert H., Metal-Mine Accidents in the United States During the 

Calendar Year 1918: Bureau of Mines Tech. Paper 252, 1920, pp. 72-73. 

Bowles , Oliver, and Crawshaw, J. E. , A Fatal Blasting Accident : Bureau 

of Mines Rept. of Investigations 2126, 1920, 3 pp. 

Pickard, B. 0. Lessons from the Fire in the Argonaut Mine: Bureau of 

Mines Tech. Paper 363, 1926, 39 pp. 

Adams, William W. , Metal-Mine Accidents in the United States During the 

Calendar Year 1925 : Bureau of Mines Bull. 282, 1927, pp. 105-106. 

Adams, William W., Metal-Mine Accidents in the United States During the 

Calendar Year 1930: Bureau of Mines Bull. 362, 1932, p. 92. 

Adams, W. W. , and Kolhos, M. E. , Metal-Mine Accidents in the United 

States During the Calendar Year 1936 : Bureau of Mines Bull. 422, 

1939, p. 1. 
REFERENCES 

(Cont inued) 

30. Adam, W. W. , and Kennedy, F. J. , Metal- and Nonmet al-Mine Accidents in 

the United States During the Calendar Year 1942: Bureau of Mines 

Bull. 461, 1945, p. 21. 

31. Unpublished Reports of the Bureau of Mines. 

32. Bureau of Mines, Fires, Gases, and Ventilation in eta1 Mines: Minersf 

Circ. 55, 1946, p. 90. 

33. Bureau of Mines, Health and Miscellaneous Hazards in Metal Mines: 

Minersf Circ. 57, 1946, pp. 29-30. 

34. Denver Rocky Mountain News, September 27, 1895.