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nat'i tnst of .stand & tech

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AiiiDt. esT^Dfi 81-2292

Review of Fire Test Methods and

Incident Data for Portable

Electric Cables in Underground

Coal Mines

Emil Braun

Center for Fire Research

National Engineering Laboratory

U.S. Department of Commerce

National Bureau of Standards

Washington, DC 20234

June 1981

Final Report

Sponsored by

U.S. Bureau of Mines

Pittsburgh, Pennsylvania 15213

-QC

100

.U56

31-2292

1931

ie Safety and Health Administration

ildelphia. West Virginia 26059

NATIONAL BUBKAU

OB OTANDARDS

LIBBART NBSIR 81-2292

REVIEW OF FIRE TEST METHODS AND

INCIDENT DATA FOR PORTABLE

ELECTRIC CABLES IN UNDERGROUND

COAL MINES

JUL 2 0 1981 DCrt dec. - Qcroo

• (XSb

JU/

Emil Braun

Center for Fire Research

National Engineering Laboratory

U.S. Department of Commerce

National Bureau of Standards

Washington, DC 20234

June 1981

Final Report

Sponsored by

U.S. Bureau of Mines

Pittsburgh, Pennsylvania 15213

and

Mine Safety and Health Administration

Trialdelphia, West Virginia 26059

U.S. DEPARTMENT OF COMMERCE, Malcolm Baldrige, Secretary

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director
•'** •‘a?- ,X : r: it >.

• -

• ims.t
TABLE OF CONTENTS

Page

LIST OF FIGURES iv

LIST OF TABLES iv

Abstract 1

1 . INTRODUCTION 1

2. TEST METHODS 2 2.1 MSHA Test Method 3

2.1.1 Specimen Preparation .... 3 2.1.2 Preheating 3 2.1.3 Flame Exposure 4 2.2 British Test Method 4 2.2.1 Specimen Preparation 4 2.2.2 Flame Exposure 4

3. INCIDENT DATA 5 3.1 U.S. Coal Mines 5

3.2 British Coal Mines 12

4. DISCUSSION 12

5. CONCLUSIONS 15

6. RECOMMENDATIONS 16

7. REFERENCES 16

iii
LIST OF FIGURES

Page

Figure 1. Comparison of trends for trailing cable fires, electrical

fires, and all fires occurring in U.S. underground coal

mines 10

Figure 2. British coal mine fire experience, comparison of trends

for all fires and electrically caused fires — 1968 to

1975 14

LIST OF TABLES

Table 1. Ignition sources of underground coal mine fires in the

U.S. -- 1950 to 1977 6 Table 2. Number of electrically caused fires in U.S. coal mines — 1950 to 1977 7

Table 3. Causes of trailing cable fires in U.S. coal mines —

1950 to 1977 9 Table 4. Length of trailing cable damaged by fire in U.S. coal

mines -- 1950 to 1977 11

Table 5. Ignition sources of underground coal mine fires in

England — 1968 to 1975 13

iv
REVIEW OF FIRE TEST METHODS AND INCIDENT DATA

FOR PORTABLE ELECTRIC CABLES IN UNDERGROUND COAL MINES

Emil Braun

Abstract

Electrically powered underground coal mining

machinery is connected to a load center or

distribution box by electric cables. The connecting

cables used on mobile machines are required to meet

fire performance requirements defined in the Code of

Federal Regulations. This report reviews Mine

Safety and Health Administration's (MSHA) current

test method and compares it to British practices.

Incident data for fires caused by trailing cable

failures and splice failures were also reviewed.

It was found that the MSHA test method is more severe

than the British but that neither evaluated grouped

cable fire performance. The incident data indicated

that the grouped configuration of cables on a reel

accounted for a majority of the fires since 1970.

Key words: Coal mines; electrical cables; fire

incidents; fire tests; test methods; trailing cables.

1. INTRODUCTION

At the request of the Mine Safety and Health Administration (MSHA) and

the Bureau of Mines (BOM) , the Center for Fire Research at the National Bureau

of Standards initiated a review of current practices for the certification and

approval of portable electric (trailing) cables for use in underground coal

mines.

Underground coal mining machinery is generally electrically driven.

Mobile machines, not battery powered, are connected to a load center or distribution box by portable electric (trailing) cables. These cables are stored

on cable reels mounted on the mobile machinery. The cable reels are designed

to maintain positive tension on the trailing cable during reeling and unreeling

1
operations as well as to form an interface between the cable and the machine.

According to the Code of Federal Regulations [1] , trailing cables must (1)

have current carrying capacities consistent with the Insulated Power Cable

Engineers Association standards and (2) exhibit flame-resistant properties.

Cable lengths are limited to a maximum of 500 feet. Longer cable lengths are

permitted, but under reduced maximum current loads.

MSHA permits the use of temporary splices in trailing cables provided

that they are made in a "workmanlike manner" and are mechanically strong and

electrically insulated. Splice kits are provided by manufacturers for this

purpose. The materials used in these kits must also meet the same fire test

requirements imposed on trailing cables. The maximum number of temporary

splices permitted in a single length of trailing cable is not made clear by

the regulation. There are two references in Title 30 of the Code of Federal

Regulations regarding the number of permitted splices in a portable (trailing)

cable. The Code of Federal Regulations state in section 18.35 paragraph 8

that a single length of portable cable may not have "more than five well made

splices." Section 75.603, however, states that any trailing cable may not

have more than one temporary splice.

This report reviews MSHA’s current test method and compares it to

British practices. Incident data for fires caused by trailing cable and splice

failures are also reviewed.

2 . TEST METHODS

Many countries require fire testing of electrical cables as part of

their qualification for use in underground mining. However, since some incident data are readily available for British underground coal mining operations,

their test method was selected for comparison to MSHA test procedures. Both

the United States and the United Kingdom perform fire tests on the original

cable, but, because MSHA allows a trailing cable to have not more than five

temporary splices, splicing materials are also tested for fire resistance.

The British do not permit mine operators to use temporary splices in trailing

cables

Numbers in brackets refer to the references at the end of this report.

2
2.1

MSHA Test Method

The test for the flame resistance of cables is described in section

18.64 of the Code of Federal Regulations, Title 30. In performing the test,

a 914 mm (3 ft) length of cable is horizontally mounted in a rectangular

enclosure 432 x 368 x 991 mm (17 x 14-1/2 x 39 in) and, after preheating the

conductors to 204 °C (400 °F) with an electric current, the cable is exposed to

a premixed methane flame from a Tirrell burner for 1 minute.

The test requires that two out of three specimens either self-extinguish

within 4 minutes or that the burn length be less than 6 inches.

The test procedure is divided into three parts: (1) Test specimen

preparation and mounting; (2) Preheating of the specimen; and (3) Flame

exposure.

2.1.1

Specimen Preparation

A single cable specimen 914 mm (3 ft) long is placed on a supporting

rack composed of three asbestos-covered metal rods. The rods are spaced

such that 406 mm (16 in) are between the left and center rods and 203 mm

(8 in) are between the right and center rods. For a single conductor cable,

the free conductor ends are connected to a source of electric current.

Multiconductor cables are wired so that all conductors are in series. The

free ends are then connected to a low voltage, high current power supply.

Conductor temperature is monitored by placing a thermocouple in contact

with one of the conductors in a cable. The thermocouple is located 660 mm

(26 in) from the left end of the specimen. This is accomplished by slitting

the insulation down to a conductor and forcing the thermocouple into it. The

insulation is then replaced and bound over the thermocouple.

Splice kits are tested by assembling a suitable approved cable with the

splice kit and testing the assembly according to the flame-resistance test for

cables

2.1.2

Preheating

This test method uses an electric current five times the conductor

rating to preheat the test specimen. The current is applied to the cable

specimen until the instrumentated conductor has reached 204 °C (400°F) at

which time the external flame source is applied. Since the applied voltage

3
is not defined, low voltage high current sources have been employed.

Initially, MSHA used an autotransformer to apply A.C. current to the cable

specimen. Currently, MSHA uses a constant current low voltage D.C. source.

Full power is applied to the cable specimen at the start of the test. The

rate of heating is controlled, primarily, by the cable's thermal inertia.

2.1.3 Flame Exposure

The test method employs a Tirrell gas burner as an external ignition

source. The burner is adjusted to produce an overall flame height of 127 mm

(5 in) with an inner cone height of 76 mm (3 in) . The distance between the

top of the burner and the bottom of the cable specimen is 76 mm (3 in) . The

type of gas is not defined, but MSHA currently uses a fuel source that contains

93 percent methane.

After the cable has been preheated to 204°C (40Q°F) , the flame is

applied to the lower surface of the cable 356 mm (14 in) from the left end

for 1 minute. At the end of this exposure period, the burner is withdrawn

and the current is disconnected.

2.2 British Test Method

The British test for resistance to flame of trailing cables for mining

purposes is described in BS 708 [2]

,

with reference to BS 738 [3]

As in the

MSHA test, BS 708 tests a horizontally-mounted cable specimen exposed to a laboratory burner. The exposure time is 5 minutes. A sample is considered

self-extinguishing if flaming ceases within 30 seconds of removal of the

exposure source and the total length of damaged cable does not exceed 152 mm

(6 in)

2.2.1 Specimen Preparation

A 305 mm (12 in) long specimen of finished cable is held horizontally

(the method of mounting is not described) in a metal enclosure —914 mm (36 in)

high, 457 mm (18 in) wide, and 305 mm (12 in) deep. No additional preconditioning or preheating of the cable specimen is required.

2.2.2 Flame Exposure

The Barthel burner described in BS 738 is used as the ignition source in

this test method. This is a spirit burner using industrial methylated spirit

(alcohol) as the fuel. The flame height is correctly set when a bare copper

4
wire 0.71 mm (0.028 in) in diameter inserted into the flame 51 mm (2 in) above

the top of the burner melts within 6 seconds.

For the actual test, the burner is positioned at an angle of 45° to the

horizontal with the top of the burner 51 mm (2 in) from the bottom of the

specimen. The flame is applied normal to the longitudinal axis of the specimen

for 5 minutes.

3 . INCIDENT DATA

A comprehensive collection of fire incident data for underground coal

mines was obtained from the Allen Corporation [4]This report contained an

annotated bibliography of U.S. coal mine fire reports from 1950 to 1977,

including MSHA incident reports. This study did not include explosions or

fires that resulted from explosions. However, it did include fires that later

caused an explosion. Since 1967, MSHA has defined a reportable fire incident

as one in which (1) an individual is injured or killed or (2) the fire persists

for at least 30 minutes from the time of discovery.

Several summary reports received from England were reviewed [5,6]. While

not providing specific information on trailing cable incidents, gross comparisons were made between British experience and United States experience with

electrical fires.

3.1 U.S. Coal Mines

Allen Corporation compiled records of a total of 1,019 underground coal

mine fires that occurred between 1950 and 1977. Table 1 lists the sources of

ignition of these fires and the frequency of occurrence. Electrical failures

caused the largest number of fires, 63.3 percent, followed by frictional heating, 9.8 percent, and spontaneous combustion, 7.3 percent. On an annual basis

electrical failures have accounted for a large fraction of the total number

of underground coal mine fires. Table 2 shows that from 1950 to 1977 the fraction of electrical failures compared to all fires ranged between 43 and 73

percent. After 1970 improvements in fire safety performance have appeared

across all aspects of mining, but the significance is unclear due to changes

in the reporting requirements. These requirements were defined in the Federal

Coal Mine Health and Safety Act of 1969. After 1969, reportable fire incidents

were limited to those that either persisted for more than 30 minutes after

discovery or an injury occurred. The total number of fire incidents caused by

5
Table 1 Ignition sources of underground coal mine fires

in the U.S. — 1950 to 1977

Ignition Source Number of Incidents Percentage

Electrical 645 63.3

Friction 100 9.8

Spontaneous 74 7.3

Welding/cutting 34 3.3

Explosives 17 1.7

Vandalism 12 1.2

Engine or 12 1.2

clutch overheat

Open flame 10 1.0

Adjacent or 9 0.9

surface fire

Other 6 0.6

Unknown 100 9.8

Total 1,019 100

6
Table 2. Number of electrically caused fires in U.S.

coal mines — 1950 to 1977

Electrical

Time Period Failures

’50-' 52 12

1 53- ' 55 62

’56-' 58 111

' 59- '61 114

' 62- ' 64 101

' 65- ' 67 105

* 68- ' 69 74

' 70- ' 71 23

' 72- ' 73 21

' 74- ' 75 10

' 76- ' 77 12

Percentage for

All Fires Electrical Failures

28 43

110 56

168 66

184 62

150 67

149 70

101 73

46 50

38 55

20 50

25 48

7
electrical failures has been consistently decreasing since 1967, along with

the total number of all fire occurrences.

There were a total of 243 reported fire incidents in coal mines

attributable to trailing cable failures (table 3) in the United States from

1950 to 1977. This represents 24 percent of all fire incidents and 38 percent

of the fire incidents caused by electrical failures. Trailing cable incidents

have been as few as one in the 1950 to 1952 period and as high as 51 during

the 1956 to 1958 period. Since 1972, there has been an average of one trailing cable failure reported per year. Figure 1 compares the number of incidents

of trailing cable fires and electrical fires to the total fire incident data

from 1950 to 1977. While the total coal production in the U.S. during this

period has remained constant, at approximately 300 million short tons per year

[4]

,

the total number of reported fire incidents has been declining since 1961.

Table 3 is a tabulation of the causes of trailing cable fires in U.S.

coal mines from 1950 to 1977. Thirty-three percent of the failures were caused

by defective temporary splices. Between 1970 and 1977, defective temporary

splices accounted for 24 percent of the failures. In 29 incidents the splice

failure occurred with the spliced section of cable wound on the cable reel.

Electrical short circuits accounted for 26 percent of the total number of

trailing cable failures. These were equally divided between the cable failing on the reel and cable failures on extended portions of the cable. Mobile

machinery driving over trailing cables is also a frequent cause of cable

failures—19 percent. However, since 1972, cases of fire resulting from

machinery crushing a cable have not been reported. On the other hand, temporary splice failures resulting in fire have continued to occur.

Table 4 is a description of the amount of cable destroyed per incident.

In 56 percent of the cases this has not been specified. The loss of an entire

cable reel occurred in 15 percent of the cases. Of the remaining 29 percent

of the fire incidents, 63 damaged cable lengths between 0.6 M and 120 M, while

in five cases more than 120 M were lost. In only three cases was there less

than 0.6 M lost. The data were divided into two categories —pre 1967 and post

1967. The data indicate that all fires involving very long cable lengths have

been greatly reduced. From 1968 to 1977, only two cable fires destroyed 30 M

to 120 M of cable and no cable fires have been reported to have destroyed more

than 120 M of cable. A comparable reduction in the number of incidents involving very short lengths of cable was also noted. This reduction, however, may

be due to the previously mentioned changes in reporting requirements.

8
Table 3. Causes of trailing cable fires in U.S.

coal mines — 1950 to 1977

1950-61 1962-69 1970-77 Total

Defective temporary splice — extended 35 16 1 52 — reeled 5 21 3 29

Electrical short on cable — extended 19 11 1 31 -- reeled 11 17 3 31

Machine crushed cable — other 14 13 2 29 — own 8 8 - 16

Overheated cable

-- reeled 7 2 3 12 — extended 5 1 1 7 Junction box short 4 2 1 7 Insulation failure (abrasion) 5 1 - 6

Roof fault 5 1 - 6

Defective permanent splice - 1 1 2 Miscellaneous 2 3 - 5

Unknown 7 2 1 10

Total 127 99 17 243

9
Z 3 e J3 « L 0 ^ HCU-T>(UC-MW

10

Figure

1.

Comparison

of

trends

for

trailing

cable

fires,

electrical

fires

and

all

fires

occurring

in

U.S.

underground

coal

mines
Table 4. Length of trailing

in U.S. coal mines

cable damaged by — 1950 to 1977

fire

Length 1950-67 1968-77 Total

Less than 0.6M 3 - 3

0.6M - <3M 19 1 20

3M - <30M 13 5 18

30M - <120M 23 2 25

Greater than 120M 5 - 5

Cable reel 24 13 37

Not specified 117 18 135

Total 204 39 243

11
3.2 British Coal Mines

Several summary fire incident reports were obtained from Her Majesty's

Chief Inspector of Mines and Quarries, London, England. The British reporting

system appears to be more comprehensive, in that any fire incident is reportable. The summary reports all fire incidents from 1968 to 1975. These data

are summarized in table 5. The number one cause of underground coal mine

fires in England is the conveyor belt system. This is followed by electrical

failures—21 percent. During the same period, the U.S. experience showed that

62 percent of all fires were electrical in origin while only 18 percent could

be attributed to the conveyor system.

The British data indicate that they have large fluctuations in the number

of fire incidents per year. Figure 2 compares these annual variations in the

number of all fire incidents to the number of fire incidents per year caused

by electrical sources. While electrically caused fires have varied from year

to year, the variations have not been as great as seen in the total fire incident count. The British, unfortunately, do not classify trailing cable fires

separately from other electrical fires. However, their description of several

electrically caused fires do not appear to contain any involving trailing

cables. Qualitatively, many of the British incidents appear to be due to

arcing or overheating of the cable following the breakdown of insulation on

electrical equipment.

4. DISCUSSION

The United States and British fire test methods for the evaluation and

qualification of trailing cables expose a single length of cable to a small

ignition source. The cable, held in a horizontal position, is exposed to an

external open flame source. The U.S. test method appears to have a more

severe exposure, even though the flame exposure in the British test method is

five times longer. This is true because the U.S. test method has a preheating procedure that elevates the cable core to a steady-state temperature of

204°C (400°F). Heat losses from the cable's insulating jacket to its core

are minimized. However, in the British test, the flame exposure begins with

the cable at ambient conditions. This maximizes the heat losses to the cable

core, increasing the time to bring the insulation to its combustion temperature. Because of this energy imbalance between the two test methods, it is

difficult to assess the importance of the differences between their acceptance

criteria. The United States permits after-flame times of up to 4 minutes,

while the British limit after-flame times to less than 30 seconds.

12
Table 5. Ignition

fires in

sources

England

of underground

-- 1968 to 1975

coal mine

Number of Incidents Percentage

Conveyor belts 181 45.3

Electricity 84 21.0

Mechanical friction 38 9.5

Locomotives 33 8.3

Spontaneous 31 7.8

Explosives 7 1.8

Cutting/welding 6 1.5

Miscellaneous 6 1.5

Unknown 14 3.5

Total 400 100

13
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14

and

electrically

caused

fires

—

1968

to

1975
Since the British do not allow cables to be temporarily spliced, they

have experienced no fires caused by splice failures. In the United States,

temporary splices are permitted and account for 34 percent of all the trailing

cable failures prior to 1967 and 24 percent since that time. In a survey

conducted in 1962, Williams and Devett [7] found that of 232 splices studied

in the field only 3 percent had all the characteristics desirable in splicing

techniques (i.e., mechanically strong, electrically insulated, flexible, and

sealed against moisture) . King, et al. [8]

,

found that flexure testing of

unspliced and spliced cables yielded a significantly lower life cycle to

failure for spliced cables. For one cable type and splicing technique, their

data also appear to indicate approximately a 50 percent reduction in life

cycle to failure for field spliced cables as compared to laboratory spliced

cables.

Early work by Ilsley and Hooker [9] involved the study of the heating of

trailing cables. They recommended the derating of cable current-carrying

capacity. In part, current MSHA ampacity tables are based on the work of

Ilsley and Hooker. Hanslovan [10] recently investigated the causes of damage

to trailing cables. He studied seven stresses that are placed on a trailing

cable under field conditions. Among these stresses was temperature fluctuations. Hanslovan measured cable temperatures on reeled cables. He found

that maximum reeled cable jacket temperatures measured underground could be

in excess of 120°C (250°F) . He did not measure the jacket temperatures in

the vicinity of a cable splice. With the increased potential for high resistance shorts, larger temperature extremes should be expected. Lupton, et al.

[11] , demonstrated that flame propagation and char zone as well as after-flame

time increase with increasing cable temperatures. Yuwata and Nakada [12]

showed that grouped cables produced higher temperatures than single cables

and ignited more readily. Cables on a cable reel should perform in a similar

manner.

5. CONCLUSIONS

(1) In a comparison of United States and British test methods, the U.S.

test procedure appears to be more sensitive because of preheating requirements.

(2) The incident data indicates that:

• The number of electrical fire incidents involving portable cables

as well as all fires in U.S. coal mines have been declining since 1967, and

15
• Since 1970, the majority of trailing cable fires have been caused

by cable failures with the cable wound on a reel.

• The existing U.S. test is reducing the fire problem.

(3) The current test procedure does not appear to be able to predict

grouped cable performance as found with a reeled cable. The presently utilized

ampacity tables are based on individual cable performance in air. Conductor

temperatures will exceed the rated value in a reeled configuration and insulation temperatures will be higher.

(4) The U.S. regulations are ambiguous with regard to the number of

permitted splices in a trailing cable.

6 . RECOMMENDATIONS

(1) Clarify current regulations regarding the number of permitted splices

in a trailing cable.

(2) Develop ampacity tables for reeled cables.

(3) Develop a fire test for cable performance that evaluates cable

performance while on the reel.

7 . REFERENCES

[1] Code of Federal Regulations, Title 30, Section 18.64.

[2] British Standard 708, Trailing cables for mining purposes, British

Standard Institution.

[3] British Standard 738, Definitions for the nonignitable and selfextinguishing properties of solid electrical insulating materials

(including classification and methods of test) , British Standard

Institution

[4] McDonald, L. B., An annotated bibliography of coal mine fire reports,

Allen Corporation of America, Final Report, U.S. Bur. Mines Contract

No. J0275008 (February 1979).

16
[ 5 ] Department of Trade and Industries, Report of H. M. Chief Inspector of

Mines and Quarries for 1972, Her Majesty's Stationery Office, London,

England (1973)

[6] Health and Safety Executive, Mines and Quarries, 1975, Her Majesty's

Stationery Office, London, England (1976)

[7] Williams, F. A. and Devett, W. R. , Prevailing practices in splicing

electric trailing cables in coal mines, U.S. Bur. of Mines, IC 8090

(1962)

[8] King, R. H. , Morley, L. A., and Stefanko, R. , Guidelines for improving

trailing cable splice performance. Society of Mining Engineers, AIME

,

Transactions, Vol. 258, No. 3 (September 1975).

[9] Ilsley, L. C. and Hooker, A. B. , The overheating of rubber-sheathed

trailing cables, U.S. Bur. of Mines, RI 3104 (1931).

[10] Hanslovan, J. J. , Trailing cable damage—causes and prevention, mine

power systems research (in four parts) 1. trailing cables, U.S. Bur.

of Mines, IC 8799 (1979)

[11] Lupton, E. C. , Thalmore, C. D. , and Obsasnik, J. , Some differences noted

in the flammability of wire constructions between testing at room

temperature and at elevated conductor temperature. Proceedings of the

24th International Wire and Cable Symposium (AD-A017787) (November 18-20,

1975) .

[12] Yuwata, Z. and Nakada, T., Ignition properties of cables owing to

overload current, Furukawa Denko Jiho, Vol. 62, pp. 79-91 (Japanese,

English summary) (1977) .

17
NBS-114A (rev. 2-80

U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

1. PUBLICATION OR

REPORT NO.

2. Performing Organ. Report No. 3. Publication Date

SHEET (See instructions) NBSIR 81-2292 June 1981

4. TITLE AND SUBTITLE

REVIEW OF FIRE TEST METHODS AND INCIDENT DATA FOR PORTABLE ELECTRIC CABLES IN

UNDERGROUND COAL MINES

5. AUTHOR(S)

Emil Braun

6. PERFORMING ORGANIZATION (If joint or other than NBS. see instructions) 7. Contract/Grant No. national bureau of standards

DEPARTMENT OF COMMERCE 8. Type of Report & Period Covered

WASHINGTON, D.C. 20234

Final Report

9. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street. City. State. ZIP)

U.S. Bureau of Mines Mine Safety and Health Administration

Pittsburgh, Pennsylvania 15213 an Triadelphia, West Virginia 26059

10.

SUPPLEMENTARY NOTES

J Document describes a computer program; SF-185, FIPS Software Summary, is attached.

11.

ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bl bliography or literature survey, mention it here)

Electrically powered underground coal mining machinery is connected to a load

center or distribution box by electric cables. The connecting cables used on mobile machines are required to meet fire performance requirements defined in

the Code of Federal Regulations. This report reviews Mine Safety and Health

Administration’s (MSHA) current test method and compares it to British practices. Incident data for fires caused by trailing cable failures and splice

failures were also reviewed. It was found that the MSHA test method is more

severe than the British but that neither evaluated grouped cable fire performance. The incident data indicated that the grouped configuration of cables

on a reel accounted for a majority of the fires since 1970.

12.

KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate key words by semicolon s)

Coal mines; electrical cables; fire incidents; fire tests; test methods; trailing cables

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