MAPLE CREEK MINE

The Maple Creek Mine, located near Ginger Hill, PA,
uses an MSA DAN 6000 atmospheric monitoring system.
The CO system has replaced point-type heat sensors. The
system has detected CO from a hot gearbox at the face.

The detector was installed February 21, 1990, on a
main-line belt outby two continuous mining sections and
a longwall section. The air velocity at this location was
209 fpm. Mine power was required to operate a de power
supply for the detector, along with the use of a standard
input board supplied by MSA for interfacing to the system.

The detector alarmed at or about 15:25 on April 18, 19,
and 20. Initially the reason was not known. On April 20,
miners were in the vicinity of the detector when it
alarmed. They discovered that the belt was producing
smoke while rubbing the framework when empty and out
of alignment. Intermittent alarming attributed to rock
dusting occurred during week 18 of operation. The in-
spector cleaned the detector on-site. The detector con-
tinued to operate normally until December 25, 1990, when
it again alarmed intermittently. These alarms again were
due to a buildup of rock dust, primarily in the sampling
line.

MARTINKA MINE

The Martinka Mine, located in Fairmont, WV, uses an
MSA DAN atmospheric monitoring system that includes
approximately 100 CO sensors along belt entries. The CO
sensors have replaced point-type heat sensors. The system
has detected three small fires, but failed to detect two
other fires.

The smoke detector was installed March 9, 1990, outby
No. 18 left belt drive. Mine power was required to oper-
ate a de power supply, and the detector interfaced with the
system via a voltage-to-frequency board supplied by the
Bureau. Air velocity at this location was 64 fpm.

During the 44 weeks the detector was in operation,
several alarms occurred because of belts rubbing or over-
heated rollers. On June 12, 1990, the detector alarmed,
causing the mine to place all section crews in intake air,
initiating evacuation procedures. A hot roller was dis-
covered to be smoking. A CO sensor adjacent to the
smoke detector showed no response. The mine based its
decision to treat the smoke alarm as real, even though no
CO was detected, on the fact that previous smoke alarms
had occurred on June 9, 1990, due to cutting and welding,
again without detection by CO sensors. On June 13 and
14, 1990, the detector alarmed because of a rubbing belt,
with no CO indications. The mine found four rollers

frozen on the take-up. On June 15, 1990, evacuation of
five crews was initiated because of smoke detection of a
hot roller, again with no CO readings on the adjacent CO
sensor. In all, there were 25 smoke alarms recorded on
printouts: 17 were due to belts or rollers, 6 were attrib-
uted to cutting and welding, and 2 were intermittent (dust
accumulation).

McCLURE MINE

The McClure Mine, located in McClure, VA, uses an
American Mine Research atmospheric monitoring system.
The monitoring system has replaced point-type heat sen-
sors, and the mine uses belt air to ventilate active sections.
The mine uses diesel equipment for haulage and transpor-
tation in the same entry as the belt. As a consequence,
diesel emissions cause some CO alarms. The system has
not detected CO in the presence of smoke in the belt
entry.

Two detectors were installed on February 13, 1990,
along a main-line belt. Air velocity at this location was
690 fpm at the time of installation, and increased to
1,000 fpm during the test period. Both detectors inter-
faced directly to the monitoring system, although the
VESDA detector required mine power to operate a de
power supply.

During 47 weeks of operation the HRD-2A detector
alarmed 488 times and the VESDA detector alarmed
4 times. Diesel contaminants accounted for 486 alarms on
the HRD-2A detector and 2 on the VESDA detector,
Rock dusting caused two concurrent alarms on both smoke
detectors.

On average, the nuisance alarm frequency due to diesel
exhausts was about three alarms every 2 days. This fre-
quency is about 25% lower than the frequency observed at
the Shoshone Mine, where diesel equipment is also used.

SCOTIA MINE

The Scotia Mine, located near Ovenfork, KY, uses a
Pyott-Boone atmospheric monitoring system. The CO sys-
tem has replaced point-type heat sensors, and the mine
uses belt air to ventilate active sections. Diesels are used
at the mine, but track and belt are located in different,
separated entries. The mine has had a fire that went
undetected by the CO system. .

The smoke detector was installed February 12, 1990, on
a main-line belt. Air velocity at the location was 295 fpm.
Mine power was required to operate a de power supply for
the detector. At the time of installation the Pyott-Boone
system could not accept the 4- to 20-mA signal from the


UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT
fpm foot per minute min minute
m meter ppm part per million

mA __miilliampere v volt



APPENDIX.—LIST OF PARTICIPATING MSHA COAL

Inspector

Joseph R. Karpinsky
Clarence D. Moats
Barry L. Mylan

Bill Wilson

Tom Woods

Walter S. Daniel
Ronald E. Hixson
Eugene A. Kelly
Joseph R. Koscho

William R. Brown
Stephen M. Dubovich
John H. Mull

Alvin Shade

Francis Wehr

Virgil F. Brown,
Paul M. Hall

James F. Bowman
Larry E. Cook
Michael T. Dickerson
Kenny Southern

Mattie R. Beaty
Roy Davidson
Vearl Hileman
Michael L. Jackson
John Wampler

James A. Baker
Roy Davidson
Michael L. Jackson
Charles F. Reece

Tom Engle
Norman G. Page
Diamond R, Waddles

Bill Matekovic
John Thompson

MINE INSPECTORS

MSHA District

2

Mine

Cumberland

Dilworth

Maple Creek

Martinka

Kopperston

McClure

Splashdam

Scotia

Shoshone


PROCEDURES FOR INSPECTION AND TESTING OF INSTALLED SMOKE DETECTOR

Mine n

INSPECTION

VISUAL

NOTE: Inform the CO monitoring system operator of your intentions to

test the smoke detector.

Damage
Sampling port.........e cee ce eee c cece cece ee ee eee eneeees YES NO
Sampling tube.......... cece eee e eee eee e cece e ene eeee YES NO
Detector housing........... cece cece eee ec ee eee eeeeeee YES ~ NO
Detector-Interface board (if installed)............... YES NO
Comments on damage if so indicated:
Dust at sampling port............c cece cece eee HEAVY MODERATE LIGHT
(Lightly tap to remove dust)
Operation
Electrical power 0n?...........c eee e cece cence teen eeee YES *NO
*If no, restore power.
Green light on only?......... cece eee cece eee e ene eeee YES *NO
*If no, what combination of lights are on?
RED RED/GREEN YELLOW YELLOW/GREEN

Reset sensitivity by adjusting Pl: CCW to eliminate Red,
CW to eliminate Yellow.

If it is not possible to restore power and/or reset sensitivity,

terminate test and contact Jerry Morrow at (412) 892-4272 or

Dave Litton at (412) 892-6752.

Figure 4.—Standard inspection form.


INTRODUCTION

SELECTION OF DETECTORS

During 1988 and 1989, the U.S. Bureau of Mines con-
ducted an in-depth survey of commercially available smoke
detectors to determine which detectors had potential for
use in underground coal mines. A major consideration in
this analysis was that the detectors either be impervious to
dust or have the capability to eliminate dust. Based upon
this survey, four candidate smoke detectors were identi-
fied. Three use internal pumps to convey a sample of gas
to the detecting clement for subsequent detection. Such
detectors offer the potential for selective aerodynamic
filtering of the larger dust particles from the flow. One
detector uses a cloud condensation nuclei monitor to
measure the number of smoke particles.

The first detector identified was the latter type. The
Bureau, in previous research studies with a detector of this
type, found that complex valving within the detector was
sensitive to even minute dust levels, rendering the detector
inoperative. Because of this feature, this particular de-
tector was excluded from further study.

The second detector identified was the VESDA smoke
detector, marketed in the United States by Fenwal, Inc.,
and manufactured in Australia. This type of detector uses
a pulsed xenon lamp to measure the light scattered by
smoke particles. In general, this type of detector is classi-
fied as a photoelectric-type smoke detector.

The third detector identified was the Westinghouse
HRD-2A smoke detector, manufactured and sold by the
Fire Safety Systems Division of Westinghouse in the
Netherlands. This detector measures the current reduction
due to smoke particles present in a small ionization cham-
ber and is known generically as an ionization-type smoke
detector.

A fourth smoke detector, the Becon Mark IV detector,
is also known to be impervious to dust and has been
evaluated by the Bureau in previous research? This de-
tector was excluded because it utilizes a nonexempt source
of radioactivity.

Nine HRD-2A smoke detectors and one VESDA
smoke detector were subsequently purchased by MSHA
and the Bureau. The choice of detectors was made pri-
marily on the basis of cost (five HRD-2A detectors cost
the same amount as two VESDA detectors).

3Pomroy, W. H. Fire Detection Systems for Noncoal Underground
Mines. Paper in Recent Developments in Metal and Nonmetal Mine
Fire Protection. BuMines IC 9206, 1988, pp. 21-27.

Apart from the method of detection, i.e., photoelec-
tric technique for the VESDA detector versus ionization
technique for the HRD-2A detector, the two are similar in
appearance and operation. Figures 1, 2, and 3 are photo-
graphs of the HRD-2A detector, VESDA detector, and
the sampling port used for all detectors, respectively. Both
detectors utilize a small de axial-vane fan to draw air
samples from the desired monitoring location to the
detector. Both detectors operate on 24 V dc and both
have 4- to 20-mA outputs.

From the outset a point should be made that the selec-
tion of these smoke detectors was not intended to exclude

mere

oe
ace ae
fe

Figure 1.-HRD-2A smoke detector installed at Dilworth Mine.


IN-MINE EVALUATION OF SMOKE DETECTORS

By G. S. Morrow! and C. D. Litton®

ABSTRACT

This report presents the results of a U.S. Bureau of Mines evaluation of smoke detectors placed in
conveyor belt entries of underground coal mines. The selected mines are located in six different Mine
Safety and Health Administration (MSHA) districts, are operated by seven different companies, and use
atmospheric monitoring systems from seven different manufacturers. Principal concerns are early
detection and warning of fires, reliability of operation, frequency of maintenance, and adaptability of
detectors to monitoring systems and the mining environment. The data contained in this report provide
for some comparisons between smoke detectors and CO sensors, specifically in the areas of early
detection of fires and susceptibility to nuisance alarms due to diesel exhaust contaminants. Finally,
recommendations for performance standards, sensitivity tests, detector classification, and maintenance
are presented.

‘Electronics technician.
2Supervisory physical scientist.
Pittsburgh Research Center, U.S. Bureau of Mines, Pittsburgh, PA.


A list of the mine sites chosen and other information
for each installation are found in table 1. The dates of
installation and removal of the detectors are found in
table 2.

Subsequent to the selection of the test sites, MSHA
inspectors involved in the test program met for a short

training course on the operation of the smoke detectors
and the procedures to be followed during each weekly
inspection. A standard form was developed for each
inspector to complete after each inspection (fig. 4). When
the form was completed, it was returned to Bureau
personnel and copies were sent to MSHA, Arlington, VA.

Table 1.—Summary of mine test sites and related information

System MSHA Bolt airto Diesel
Mine Owner type district ventilate equipment
face used
Cumberland... 2 Y N
Dilworth .. 2 N N
Kopperston 4 Y N
Maple Creek . . 2 N N
Martinka: 3 N N
McClure . : 5 Y Y
Scotia Pyott-Boone 6 Y Y
‘Shoshone Transmitton 9 Y Y
Splashdam ... Line Power .. 5 Y N
N No.
Y Yes.

Table 2.—Summary of evaluation periods for detectors at each mine test site

Mine Weeks in Date Date Reason for
service installed removed removal

Cumberland ........ 4 2/ 9/90 3/9/90 System power caused fuses to blow in
detector and subsequently damaged
it,

Dilworth! . 18 2/7/90 6/11/90 Dust buildup. Detector used at Bureau
for research

Kopperston:

Original detector... . 1 2/15/90 2/22/90 Original failed,

Replacement detector. 13 2/26/90 5/29/90 Replacement removed because of dust
buildup. Mine operator ended partic-
ipation.

ry 2/21/90 12/26/90 End of evaluation.
44 3/9/90 1/11/91 Do.
a7 2/13/90 1/8/91,
47 2/12/90 1/7/91 Do.
16 4/ 5/90 7/27/90 Removed by company and replaced
with CO sensors.
Splashdam ......... a7 2/14/90 _1/ 8/91 __End of evaluation.

‘Detector was reinstalled on 10/1/90 and remains functional underground at Dilworth for evaluating

methods of reducing false alarms due to rock dust.

?Data pertain to both VESDA detector and HRD-2A detector used at this mine.


IC} 9311

| | lisa

BUREAU OF MINES
INFORMATION CIRCULAR/1992

In-Mine Evaluation of Smoke Detectors

By G. S. Morrow and C. D. Litton

UNITED STATES DEPARTMENT OF THE INTERIOR


ACKNOWLEDGMENTS

The authors wish to thank Jack Tisdale, chief, Division
of Safety, and Larry Brown, safety and health specialist,
MSHA, Arlington, VA, for their assistance in selecting
mine sites; Ed Miller, chief, Ventilation Division, Bill
Francart, supervisory mining engincer, Gary Wirth, min-
ing engineer, John Baron, electronics technician, and

Ed Chuhta, mining engineering technician, MSHA (Tech-
nical Support), Pittsburgh, PA, for technical assistance at
the selected mine sites; and the coal mine inspectors listed
in the appendix, who performed the testing of the detec-
tors at each site.

TEST RESULTS

Through January 11, 1991, when all detectors except for
the one at Dilworth Mine had been removed, a total of
340 weeks of continuous service had been logged. The
total summary of alarms is shown in table 3. If the nui-
sance alarms due to diesel contaminants are subtracted
from the total, then 54 alarms occurred during this study.
Of these 54, 20 were found to be real alarms, the result of
frictional heatings or frozen idlers that could have develop-
ed into a fire. Of the remaining 34 alarms, 11 were the
result of rock dusting, 6 were the result of dust accumu-
lation, and 17 were the result of welding and cutting.

These 34 nuisance alarms represent a total average fre-
quency of 0.1 alarms per week (1 alarm every 10 weeks).
None of the alarms due to dust accumulation occurred
earlier than week 13. It is also worth noting that the air
velocities in the mines where dust accumulation alarms
occurred were relatively low (50 to 209 fpm).

For the mines using diesel-powered equipment, only the
installation at Shoshone Mine allowed a true comparison

of the CO levels at the time of smoke alarm. As indicated
in the following summary, the number of CO readings may
be categorized in terms of exceeding some level of CO.
Figure 5 shows the actual CO levels at the time of smoke
alarm as discussed above.

The following is a detailed summary of the results of
the evaluation at each mine site.

CUMBERLAND MINE

Located near Waynesburg, PA, this mine uses a Con-
spec atmospheric monitoring system. The point-type heat
sensors have been replaced by the monitoring system, and
active sections are ventilated with belt air. The CO system
has detected several heatings due to faulty belt rollers.
The system has not detected a few occurrences of belts
rubbing the framework, producing smoke, but little CO.

Table 3.—Summary of smoke detector alarms for each mine test site

Air Dust Welding Fires,
Mine velocity, Rock accumu- and Diese! friction, — ‘Total

fpm dusting lation cutting heatings,

etc.
Cumberland . 170 o- 0 0 NAP 0) 0
148 2 1 Ct) NAp ° 3
50 2 1 ° NAp ° 3
209 C) 2 C) NAp 3 5
64 ° 2 6 NAp 7 25
HRD-2A detector... 1,000 2 ° ° 486 ° 488
\VESDA detector 1,000 2 0 0 2 ° 4
Scotia 295 3 ° " 1 ° 15
Shoshone 180 C) 0 ° 83 C) 83
Splashdam 282 ) 0 C) NAp C) °
Total . 1 6 17 872 20 626

NAp Not applicable.


FUNCTION TEST

With housing open and green light visible, introduce smoke to the
sampling port. Observe the following:

Green light turns off as red turns on?........... oe VES NO
When smoke clears, observe the following:
Red light turns off as green turns on?....... eee eee VES NO

If the detector does not respond to the test smoke, yet appears to
remain operational, the sampling tube may be blocked. Disconnect
the tube at the detector housing and introduce smoke there. If
detector responds properly, check sampling tube for blockage.
Repeat test to verify proper operation. Terminate test.

If the detector does not respond to smoke at housing inlet,
terminate test and contact Jerry Morrow or Dave Litton.

ABOVE GROUND

Return to monitoring station and verify alarm response on computer.
Clear alarm.

If alarm was not activated, have system operator check communication to
detector and/or alarm threshold levels.

If problem is identified and the system restored to normal operation,
describe what was found and what was done.

Obtain from the operator a copy of the past week’s alarm printout.

Sign and date this form below and return to Jerry Morrow, U.S. Bureau of
Mines, P.O. Box 18070, Pittsburgh, PA 15236, along with the alarm
printout. Retain a copy for your records and sénd an additional copy to
Larry Brown, 4015 Wilson Blvd., Arlington, VA 22203.

Signature Date

Figure 4.—Standard inspection form—Continued.


Figure 2.-VESDA smoke detector installed at McClure Mine.

other smoke detectors. The selection of detectors was
made on the basis of potential to function reliably in an
underground environment. This work was done as part of
the Bureau’s program to enhance mine safety.

SELECTION OF MINE SITES

Subsequent to the selection of detectors, MSHA and
Bureau personnel met to select mines to serve as test sites
for evaluation of the detectors. In selecting test sites,
three factors were considered. The first factor was ac-
cessibility of the mine site to Bureau and MSHA person-
nel, Although one site in the Western United States was
chosen, the remaining sites were in the Eastern United

Figure 3.—End-of-line sampling port used at all test sites.

States, in close proximity to the Bureau’s Pittsburgh Re-
search Center (PRC). A second factor was the constraint
that each mine have in place a CO monitoring system.
Additionally, a concentrated effort was made to select
mines that used different atmospheric monitoring systems.
The rationale for this constraint was that smoke detectors
must interface with existing systems and some concern was
expressed as to the potential difficulty of providing the
appropriate electrical interface from one system to the
next. A third factor was to determine whether the detec-
tors were susceptible to false (nuisance) alarms caused by
diesel exhaust contaminants, so some mines using diesel-
powered equipment were chosen.

Nine mines were identified as test sites. In eight of
these mines, a Westinghouse HRD-2A smoke detector was
interfaced with the atmospheric monitoring system and
installed along the belt entry. In the ninth mine (McClure
Mine) both the HRD-2A and the VESDA smoke detec-
tors were installed within the belt entry. This mine was
chosen for evaluation of both detectors because it uses
dicsel-powered equipment, and it was of interest to deter-
minc the relative alarm frequency of both detectors to
diesel-produced contaminants to see if one detector was
less prone to nuisance alarms than the other.


CONTENTS

Selection of detectors .........
Selection of mine sites ...........0.
Acknowledgments
Test results ...... .
Cumberland Mine ..
Dilworth Mine . .
Kopperston Mine . . .
Maple Creek Mine . .
Martinka Mine . .
McClure Mine ..
Scotia Mine .
Shoshone Mine
Splashdam Mine .
Conclusions ......
Recommendations . seme renee ence reccccceces . eee eccerccece sees
Appendix—List of participating MSHA coal mine inspectors... +. . 0s. sss sss . . . 2B

ILLUSTRATIONS

HRD-2A smoke detector installed at Dilworth Mine
VESDA smoke detector installed at McClure Mine

End-of-line sampling port used at all test sites ....
Standard inspection form ... 2... .00eeeeeeeees bebeeenees
Smoke detector nuisance alarms versus CO levels for 42-day period at Shoshone Mine ....... +...

VSenp
muUwwn

TABLES

r

Summary of mine test sites and related information .
2. Summary of evaluation periods for detectors at each mine test site .
3, Summary of smoke detector alarms for each mine test site .......



detector. On April 2, 1990, Pyott-Boone developed and
installed interface circuitry and modified its software to
allow for aboveground monitoring of the detector.
During the 47 weeks of operation, the detector alarmed
15 times, Cutting and welding caused 11 alarms, with con-
current CO readings of 10 ppm 3 of the 11 times. One
alarm occurred because of diesel emissions, and three
brief alarms occurred as the entry was being rock dusted.

SHOSHONE MINE

The Shoshone Mine, located near Hanna, WY, uses a
Transmitton atmospheric monitoring system. The CO sys-
tem supplements point-type heat detectors. The mine uses
diesel equipment, and employs a two-entry longwall de-
velopment system for some of its sections.

The detector was installed April 5, 1990, in a two-
entry section in the belt entry return air. Eighty-three
alarms occurred during the period of April 28, 1990,
through June 9, 1990 (42 days); all were attributed to
diesel emissions. During the same period, a companion
CO sensor had 516 readings of 0 to 4 ppm, 985 readings
of 5 to 9 ppm, 533 readings of 10 to 14 ppm, 146 readings
of 15 to 19 ppm, and 253 readings in excess of 20 ppm.

These smoke detector alarms and CO levels due to
diesel exhaust allow for a direct comparison of the nui-
sance alarm frequency for the two types of detectors. For
the smoke detector, this alarm frequency is about two per
day. For CO at the 10-ppm level, the alarm frequency is
22 per day. For CO at the 15-ppm level, the alarm fre-
quency is 10 per day. At the 20-ppm CO level, the alarm
frequency is still six per day, or three times greater than
the alarm frequency for the smoke detector:

While the absolute number of nuisance alarms due to
diesel emissions appears high, as it was for the smoke
detector at McClure Mine, the actual alarm frequency is
significantly lower than that of CO sensors. It should also
be noted that the smoke detector continuously operated at
its maximum level of sensitivity, thus increasing its poten-
tial to respond to diesel contaminants. At this level of
sensitivity, the equivalent CO detection level from a small
coal fire is typically in the range of 3 to 5 ppm. As a re-
sult, the smoke alarm frequency should be compared with
the CO alarm frequency at the CO level of 5 ppm. If this
comparison is made, then the 5-ppm CO alarm frequency
was 46 per day, or 23 times greater than the smoke alarm
frequency.

Even though the nuisance alarms are not eliminated,
their frequency is reduced significantly. It is possible that
by decreasing the smoke detector sensitivity by a small
amount, these alarms could be reduced even further.

In general, the smoke alarms correlated with significant
increases in the CO levels. With the exception of two
alarms on May 2, 1990, and May 4, 1990, the average CO
reading at the time of the smoke alarm ranged from a low
of 3 ppm to a high of 34 ppm, with the average level being
17 ppm. On June 9, 1990, the sampling tube was moved
into intake air and the alarms ceased. On July 27, 1990,
the operator decided to remove the detector from the
mine, could not be convinced to relocate it in the mine,
and returned it to the Bureau.

SPLASHDAM MINE

‘The Splashdam Mine, located near Haysi, VA, uses a
Line Power Manufacturing atmospheric monitoring system.
The system has replaced point-type heat sensors, and the
mine ventilates active sections with belt air. The system
has detected some small fires and heatings in the past.

The detector was installed February 14, 1990, on a
main-line belt that shares the entry with the track (electric
trolley). Air velocity at the location was 282 fpm. No
alarms occurred during 47 weeks of operation. The sam-
pling line had to be cleaned once because of buildup of
rock dust.

The principal concerns mentioned in the abstract—early
detection and warning of fire, reliability of operation,
frequency of maintenance, and adaptability to monitoring
systems and the mining environment—were successfully
evaluated. All detectors easily interfaced with existing
monitoring systems. Adherence to a maintenance schedule
suggested in the Conclusions and Recommendations sec-
tions of this report will ensure successful operation of
detectors in the mining environment. The ability of the
detectors to provide early detection and warning of fire
was proven at the Martinka and Maple Creek Mines,
where friction-induced smoke from belts and rollers was
detected without the presence of CO. Finally, considering
that these particular detectors were not designed for the
harsh environment of a coal mine, the overall reliability of
operation was excellent.


(0.044) and one-tenth (0.022) of the critical level
for visibility (0.22 m*) discussed by Jin.” Alarm levels at
greater optical densities could degrade the potential for
escape.

3. Some method should be developed to ascertain
whether or not the detector is sensitive to dust. This could
take the form of a standard test, or it could be a technical

74in, J. Studies of Emotional Instability in Smoke From Fires. J.
Fire and Flammability, v. 12, April 1981, pp. 130-142.

decision based upon the operational characteristics of the
detector.

4. A reasonable testing and maintenance schedule
should be designed for smoke detectors. Based upon‘the
data acquired in this study, an inspection and function-
al test of the detectors should occur at intervals of 2 to
4 weeks. Periodic maintenance, which would include
cleaning the detector head, should occur at intervals of
8 to 10 weeks. A log of inspections and maintenance
should be kept and documented.


Library of Congress Cataloging in Publication Data:

Morrow, G. S. (Gerald S.)
In-mine evaluation of smoke detectors / by G.S. Morrow and C.D. Litton.

Pp. cm. — (Information circular; 9311)
Includes bibliographical references.
1. Coal mines and mining—Fires and fire prevention. 2. Fire detectors—Testing.

3. Mine haulage—Safety appliances. I. Litton, C. D. (Charles D.) II. Title. III.
Series: Information circular (United States. Bureau of Mines); 9311.

TN295.U4 [TN315] 91-44309 CIP



Information Circular 9311

In-Mine Evaluation of Smoke Detectors

By G. S. Morrow and C. D. Litton

UNITED STATES DEPARTMENT OF THE INTERIOR
Manuel Lujan, Jr., Secretary

BUREAU OF MINES
T S Ary, Director


30

ad KEY
26 * Number of CO _|
i: readings with-
in indicated
24P ranges during ~]
the same
wo 27 time period
=
a 20- 4
—¢
a
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16} 4
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516A ¥985 ) | 5334] 11464 (253,
0-4 5-9 10-14 15-19 >20

RANGE OF CO LEVELS, ppm

Figure 5.—Smoke detector nuisance
for 42-day period at Shoshone Mine.

arms versus CO levels

The smoke detector was installed February 9, 1990, on
a main-line belt with three active sections inby the detector
location. The air velocity at this location was 170 fpm.
Power was obtained from a nearby CO sensor. The detec-
tor interfaced with the system via a 4- to 20-mA accessor
provided by Conspec. After 2 weeks of operation the de-
tector intermittently alarmed and then failed the following
day. Upon inspection, the internal fuse of the detector
was found to be blown. The fuse was replaced and the de-
tector was brought back on line. Two weeks later similar
indications prior to the fuse being blown resurfaced. The
mine was directed to disconnect power to the detector.
Attempts were made to schedule troubleshooting to deter-
mine the cause of the failures, and later to remove the
detector from service. After several attempts to visit the
mine, the detector was finally recovered in July 1990.

After testing in the laboratory the detector was found to
be damaged, possibly by the monitoring system power, to
the extent that manufacturer repairs were warranted.

DILWORTH MINE

The Dilworth Mine, located in Rices Landing, PA, uses
a Conspec atmospheric monitoring system to monitor CO,
belt operations, silo storage, and river levels. The Con-
spec system supplements a Femco point-type heat sensor
system.

The detector was installed February 7, 1990, on a main-
line belt entry with an air velocity of 146 fpm. Power was
obtained from a nearby CO sensor. The detector inter-
faced with the system via a 4- to 20-mA accessor provided
by Conspec. The detector functioned properly until week
18, when the mine reported intermittent alarms lasting 10
to 20 min, but with no recurring pattern. The detector
was removed, cleaned, and monitored continuously on a
Conspec system at the Bureau with no alarms recorded.
The mine had reported brief alarms from the detector
while rock dusting. From July 30, 1990, to reinstallation in
the mine on October 1, 1990, the detector was used for
research purposes at the Bureau and functioned properly.
The addition of a settling chamber on the sampling line,
along with the insertion of honeycomb mesh at the end of
the sampling tube, reduced but did not eliminate false
alarms due to rock dusting. The detector remains in place
to further research methods to reduce rock dust alarms.

KOPPERSTON MINE

The Kopperston Mine, located near Kopperston, WV,
uses a Femco atmospheric monitoring system. Active sec-
tions are ventilated with belt air, and the point-type heat
sensors have been replaced with CO sensors. The CO sys-
tem has detected several instances of hot belt rollers, along
with nuisance alarms due to cutting and welding.

The detector was installed February 15, 1990, along a
main-line belt outby a longwall section. Air velocity at this
point was 50 fpm. The detector did not require any inter-
face to the system. The first inspection revealed a cold
solder joint that caused intermittent alarms. The original
detector was replaced with a spare in week 2. Intermittent
alarming occurred after week 13 of operation. Mine per-
sonnel said that often the entry is heavily rock dusted.
These alarms were of the same pattern observed at Dil-
worth Mine. The detector was removed, cleaned, and
monitored, The detector was returned to the inspector
for reinstallation. The mine requested that it not be
reinstalled,


CONCLUSIONS

The final results are presented in terms of the type of
problem encountered.

Electrical and Electronic. Aside from some initial
problems in trying to interface the detectors with the ex-
isting atmospheric monitoring systems, no major electrical
or electronic problems were encountered that were at-
tributed to the detectors. The detector installed at Cum-
berland Mine was thought to be damaged by the monitor-
ing system power.

Alarms. Several instances were noted where the de-
tectors discovered heatings along the belt in some form or
other. Aside from the diesel alarms, the primary sources
of false alarms were rock dusting (11 total), dust ac-
cumulation (6 total), and cutting and welding (17 total).
The fact that alarms occurred during rock dusting implies
that some method should be found to eliminate or reduce
the dust transported to the detector. This would eliminate
such alarms and tend to reduce subsequent alarms that

occur because of buildup of dust. Further, routine main-
tenance and cleaning of the detector head at intervals of
about 8 to 10 weeks should eliminate alarms due to dust
accumulations, and are recommended for future smoke de-
tector installations,

The HRD-2A smoke detector experienced several
alarms due to diesel-powered equipment emissions. Al-
though alarms did occur, the frequency of alarms was less
than that of CO sensors (see figure 5 and Shoshone Mine
summary). The alarm rate of the VESDA detector to die-
sel exhaust contaminants was much lower, which is most
likely due to the principle of operation of this device. Die-
sel particles have small diameters and their scattering effi-
ciency is significantly less than that of fire smoke particles.
Photoelectric-type smoke detectors may have significant
potential for use in mines with diesel-powered equipment,
because these detectors are less sensitive to diesel par-
ticulate matter, but this aspect of fire detection needs to
be further validated.

RECOMMENDATIONS

Based upon the results of these studies, the following
recommendations are made regarding performance stand-
ards for use of smoke detectors in underground coal
mines.

1. No smoke detector should be used unless it has
been approved by MSHA according to performance stand-
ards. In the United States, both Underwriters Labora-
tories, Inc and Factory Mutual Research Corp$ have
standard approval tests for smoke detectors. In addition
to sensitivity testing, smoke detectors that have been ap-
proved have also undergone rigorous testing for reliability
and should perform well in most applications. The results
of this evaluation support that conclusion.

2. A performance test should be designed to determine
the detector’s sensitivity to both smoldering coal and small,
flaming coal fires. This test should be added since no

‘Underwriters Laboratories, Inc. Smoke Detectors for Fire Pro-
tective Signalling Systems. Standard for Safety, UL268, February 1986,
pp. 23-32.

‘Factory Mutual Research, Smoke Activated Detectors for Auto-
matic Fire Alarm Signalling, Approval Standard 3230-3250, February
1976, 5 pp.

other laboratory performs this testing, yet most under-
ground mine fires typically involve coal at some stage
in their development. The test should follow a standard
sensitivity test in a well-defined smoke box, such as the
one described by Underwriters Laboratories.

Further, it is recommended that the results of these
additional tests be used to place smoke detectors in a two-
tier classification. The first tier, class 1, would represent
smoke detectors that always respond at smoke optical den-
sities of less than 0.022 m‘. The second tier, class 2,
would represent smoke detectors that always respond at
smoke optical densities of less than 0.044 m’. If a smoke
detector responds at optical densities of less than 0.022 m*
in 100% of the tests it becomes a class 1 detector. If a
smoke detector responds at optical densities of less than
0.044 m* in 100% of the tests, independent of the number
of times it responds at 0.022 m* or less, it becomes a
class 2 detector. Any smoke detector that does not re-
spond at an optical density of less than 0.044 m* in 100%
of the tests fails and cannot be approved for use in under-
ground coal mines. The values chosen represent one-fifth

‘Work cited in footnote 4.