UNITED STATES BUREAU OF MINES

UNITED STATES DEPARTMENT OF THE INTERIOR

RI 9572 REPORT OF INVESTIGATIONS/1995

 

A Comparison of Mine Fire Sensors
U.S. Department of the Interior

Mission Statement

As the Nation’s principal conservation agency, the Department of the

Interior has responsibility for most of our nationally-owned public lands

and natural resources. This includes fostering sound use of our land and

water resources; protecting our fish, wildlife, and biological diversity;

preserving the environmental and cultural values of our national parks and

historical places; and providing for the enjoyment of life through outdoor

recreation. The Department assesses our energy and mineral resources and

works to ensure that their development is in the best interests of all our

people by encouraging stewardship and citizen participation in their care.

The Department also has a major responsibility for American Indian

reservation communities and for people who live in island territories under

U.S. administration.
Report of Investigations 9572

A Comparison of Mine Fire Sensors

By R. S. Conti and C. D. Litton 

UNITED STATES DEPARTMENT OF THE INTERIOR

Bruce Babbitt, Secretary

BUREAU OF MINES

Rhea Lydia Graham, Director
International Standard Serial Number

ISSN 1066-5552
CONTENTS

Page

Abstract ........................................................................................... 1

Introduction ........................................................................................ 2

Experimental procedure .............................................................................. 3

Results ........................................................................................... 5

Analysis ........................................................................................... 6

Conclusions ........................................................................................ 8

Acknowledgments ................................................................................... 9

References ......................................................................................... 9

Appendix.—Impact of air velocity on fire events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

ILLUSTRATIONS

1. Plan view of Lake Lynn underground mine, showing configuration for fire detection tests ................. 3

2. Perspective view of underground fire tests, depicting fire sensor location in A-drift, ...................... 4

3. Comparison of CO and PTHS alarm times at an airflow of 0.44 and 0.97 m/s ........................... 5

4. Part per millon of CO during smoldering stage at an airflow of 0.44 m/s ............................... 8

5. Parts per millon of CO during smoldering and flaming stages at an airflow of 0.97 m/s ................... 8

A-1. Sequence of events at fire and observed at 274 m downstream from fire for test fires at two air velocities . . . . 11

TABLES

1. Alarm times for various sensors for tests conducted at an air velocity of 0.44 m/s ........................ 5

2. Alarm times for various sensors for tests conducted at an air velocity of 0.97 m/s ........................ 6

3. Average values of ratio of temperature rise to CO increase ........................................... 7
UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT

cm centimeter kW kilowatt

g/m gram per cubic meter ppm part per million 3

m meter s second

m square meter V volt 2

m/s meter per second EC degree Celsius

min minute EF degree Fahrenheit

kg kilogram g/EC gram per degree Celsius

kJ kilojoule
Fire prevention engineer. 1

Physical scientist. 2

Pittsburgh Research Center, U.S. Bureau of Mines, Pittsburgh, PA.

A COMPARISON OF MINE FIRE SENSORS

By R. S. Conti and C. D. Litton 1 2

ABSTRACT

This U.S. Bureau of Mines (USBM) report discusses the results of research conducted in the USBM

experimental mine at its Lake Lynn Laboratory to determine the alarm times of smoke and carbon monoxide

(CO) sensors, and a point type heat sensor (PTHS) to slowly developing coal-conveyor belt fires. The tests were

conducted at air velocities of 0.44 and 0.97 m/s. The data clearly indicate that smoke sensors provide earlier

warning of fire than 10 ppm CO sensors, and that 10 ppm CO sensors provide earlier warning than PTHS. A

success rate of 1.0 (indicating detection of every test fire) was obtained for both smoke and CO sensors. For the

PTHS, the success rate was 0.57 at the lower air velocity, decreasing to 0 at the higher air velocity. Data are also

presented showing the sequence of fire events and detection events at the two air velocities as a function of time.

Results show that early detection and warning of underground mine fires will improve the probability of miners'

escape.
2

INTRODUCTION

In a recent study in which 214 miners from eight mines both audible and visual signals that permit rapid location of the 3

were asked about mine fire related experiences, 65% of these

miners reported that they see or smell smoke (from any source)

in the mines where they work at least once a month. Twenty

percent of these miners reported being surprised or caught off

guard by the sight or smell of smoke within the because of

either a potentially serious situation or planned maintenance

activities such as cutting and welding. The results of this study

serve to reinforce the importance of early-warning fire detection

systems in underground mines. Personnel may not always be

available to sense the smoke or odor from a developing fire;

whereas, an early-warning fire detection system can

continuously monitor the environment and signal the presence

of a developing fire, as long as the unit is operating properly. 

Personnel must also be trained in the proper response to an

early-warning signal from a fire detection system. When miners

are not properly trained, the potential for disaster is imminent.

As an example, a fire at the Bullitt Mine, Appalachia, VA,

March 9, 1994 (1), destroyed over 55 m of conveyor belt after 4

the belting came in contact with an energized trolley wire.

During the event, the carbon monoxide (CO) monitoring system

responded at 9 ppm, however, the alarm warning was dismissed

as "probably welding smoke." A short time later, the miner who

was welding inadvertently discovered the fire while answering

the mine phone, and initiated fire-fighting activities. In many

cases, fire-warning systems respond to an incipient fire, but

these responses are dispensed as glitches in a sensor or planned

maintenance activities in the area. It is important that any

significant response from an underground fire sensor be immediately investigated, and that a standard procedure be

developed for response to sensor alerts and alarms. 

During the period of 1983 through 1993, the Mine Safety compare their response time to that of typical PTHS, a series

and Health Administration (MSHA) investigated 118 5

reportable underground mine fire incidents, or an average of 11

fires per year. Forty of these underground mine fires involved

conveyor belts. Federal regulations, as spelled out in 30 CFR

Part 75 Subpart L-Fire Protection (2), require that automatic

fire-warning devices be installed on each underground belt

conveyor. Sensors so installed shall give a warning

automatically when a fire occurs on or near a belt and provide

fire.

In a mine fire, early detection maximizes the potential for

escape from, and control of, the fire because more time is

available to execute successfully these procedures. Generally,

miners responding during the incipient stage of a fire (a fire

too small to present a significant safety threat), increase their

chance of extinguishment, provided they have adequate firefighting equipment and skills. To optimize the detection

process, the choice of fire parameter to detect plays a major

role. However, this choice is also tempered by the availability

and sensitivity of the detectors used. A related factor is the

number of sensors required, because cost, both in capital

expenditures and in labor needed to maintain a system, tend to

increase as the number of sensors increases. 

Optical sensors and PTHS must be spaced closely in a mine

entry. This is because optical sensors require a line of sight to

the fire. For PTHS, close spacing is necessary because the hot

gases from a fire cool rapidly once expelled into the mine's

ventilation airflow. Smoke and carbon monoxide sensors may

be placed at fairly large intervals because the ventilation

airflow carries the CO and smoke to the sensors and because

the CO and smoke are not dissipated once they are produced.

However, these spacings cannot be too distant, or the earlywarning capability CO and smoke sensors provide will be lost

due to long transit times between sensors.

Previous studies (3-4) examined the effects of buoyancy on

the alarm times of fire sensors. The results of these investigations indicated that maximum spacings for CO and

smoke sensors may be in the range of 300 to 600 m without

serious degradation of early-warning capability. To evaluate

CO and smoke sensor responses at these distances, and to

of tests using small coal-conveyor belt fires was conducted in

the Lake Lynn Experimental Mine (LLEM). Seven tests were

conducted at an average air velocity of 0.44 m/s and seven

tests at an average air velocity of 0.97 m/s. During these tests,

the relative alarm times for three types of sensors (CO, PTHS,

and smoke) were measured and compared. Such information

is vital to assess the relative level of fire protection that can be

provided for underground mines.

EXPERIMENTAL PROCEDURE

The USBM Lake Lynn Laboratory, formerly a limestone underground research mine (new workings) are 2.16 m high

mine (5), is now a multipurpose mining research facility. and 5.97 m wide, for an average cross-sectional area of

Figure 1 shows the laboratory's underground layout and

aboveground quarry area. The average entry dimensions in the

Based on a recent research study conducted by Conti and ohters, USBM, 1994. 3

Italic numbers in parentheses refer to items in the list of references at teh end 4

of this report.

The mine fire statistics were obtained from the file of Federal Mine Safety and 5

Health Administration (MSHA) mine fire investifation reports maintained at MSHA's

Pittsburgh Safety and Health Technology Center.

12.9 m .2

The fire detection studies reported here were conducted in

A-drift. A detailed layout of a typical underground fire and

detection scenario is shown in the perspective view in figure 2.

During the experiments the normal airflow in the mine was

reversed, so that the combustion products were exhausted

through the main fan. The airflows can be adjusted by
3

Figure 1

Plan view of Lake Lynn underground mine, showing configuration for fire detection tests.

selecting one of the four speeds of the main fan, positioning the intake sampling port of the smoke sensor. The CO sensor was

moveable bulkhead door in D-drift and E-drift, and erecting calibrated and smoke detectors functionally tested before each

temporary stoppings at the last crosscuts of B- and C-drifts. experiment. The outputs of the fire sensors were connected to

The air velocity was measured with a handheld vane- a 24-channel analog to digital (A/D) converter that transmitted

anemometer 15.2 m downstream of the fire zone prior to the data to a computer for storage. The data were logged at 1 s

starting the test. The crosssection of the entry was divided into intervals.

12 quadrants; the measured values from each quadrant were The CO alarm level was set at 10 ppm. The smoke sensor

averaged. A PTHS (a K-type thermocouple, detail 1 of and DDD were arbitrarily set to alarm when the threshold

figure 2) was placed near the roof 3.65 m downstream from the voltages reached 0.5 and 0.02 V, respectively. A detailed

center of the test fire and was considered to be in alarm when description of typical output traces and response times of the

the measured air temperature exceeded 57.2 EC (135 EF), the various fire sensors used in similar experiments can be found

lowest alarm temperature for point-type heat sensors (6). in reference 7. 

Three other sensors were located, as shown in detail 2 of The DDD (8) is a novel device that can be used to disfigure 2, in the entry cross section at a point 274 m downstream

of the fire zone. A diffusion-type electrochemical CO sensor

was mounted at the roof and denoted as CO roof. An

ionization-type smoke sensor with internal sampling pump was

mounted on the rib, with the intake sampling port

located beside the CO-roof sensor. A prototype dieseldiscriminating smoke detector (DDD) was mounted beside the

criminate between smoke produced by a fire and smoke

produced by a diesel engine. The detector uses a pyrolysis

technique whereby a sample of smoke-laden gas passes

through a short, heated tube. Within this tube, fire smoke

particles pyrolyze (or re-burn), increase in number

concentration, and decrease in average size; diesel smoke

particles are unaffected. The DDD was developed by the
4

Figure 2

Perspective view of underground mine, showing configuration for fire detection tests.

USBM to reduce the numerous false alarms in mines that utilize 10.2- by 22.8- strips of rubber conveyor belting, 1.1-cm thick,

diesel equipment, which makes detection of fires complicated were evenly distributed throughout the coal pile. Additionally,

because of the background levels of diesel emissions. This two 22.8-cm by 61-cm strips of the same belt were placed on

detector was incorporated in99999to the current tests to top of the coal pile and the pile was seeded with approximately

compare its response time to a more conventional smoke 0.75 kg of pulverized Pittsburgh coal dust. Full electrical

detector and to CO sensors. power was applied to the heating elements at the start of each

The scenario studied was a slowly developing coal- test. Visible smoke from the coal pile was usually observed in

conveyor belt fire. Seven 220-V electric strip heaters, with a 3 to 4 min, with flames emanating from the coal about 9 min

combined power rating of 9.5 kW, were embedded into a 1.2- later. The strips of conveyor belting on top of the coal pile

by 1.2-m coal pile containing 75 kg of Pittsburgh coal. Six ignited at some later time during the tests.

RESULTS

Figure 3 shows typical traces of the air temperature near the of the thermocouple, T , is 57.2 EC; the alarm level of the CO

roof at a distance of 3.65 m downstream from the center of the sensor, CO , is 10 ppm. The levels of CO measured are the

fire and the bulk average CO levels at a distance of 274 m actual levels produced at the fire at some earlier time because

downstream of the fire as a function of time. The alarm level the airflow must transport the CO from the fire to the sensor. 

A

A
5

Figure 3

 Comparison of CO and PTHS alarm times of 0.44 m/s (top)

and 0.97 m/s (bottom).

For the lower air velocity (v = 0.44 m/s, figure 3 top), this o

transport time is 10.4 min; while the transport time at the higher

air velocity (v = 0.97 m/s, figure 3 bottom) is 4.7 min. Once o

the smoke and DDD sensors alarmed (274 m downstream from

the fire) at the lower air velocity (figure 3 top), more than 3 min

elapsed before the average CO level reached a 10-ppm alarm.

At the 10-ppm alarm, the thermocouple 3.65 m downstream

from the center of the fire indicated a 28 EC rise in the ambient

temperature (T = 10 o EC), some 19 EC below the PTHS alarm

level. When the CO alarmed (10 ppm) at the higher air velocity

(figure 3 bottom), the temperature was 8 to 9 EC cooler than

the temperature measured at the lower air velocity. The

average alarm time of both smoke and DDD sensors at the

higher air velocity was 9.8 min, nearly 13 min before the 10

ppm CO alarm measured at the lower air velocity. The average

alarm time of both smoke and DDD sensors at the higher air

velocity was 9.8 min, nearly 13 min before the 10 ppm CO

alarm.

Table 1 shows the alarm times for the four sensors evaluated

at the lower air velocity. The last row of table 1 is the average

alarm time for all the tests for which alarm occurred. For the

smoke, DDD, and CO sensors, alarm occurred for each test

(100% success rate), while for the PTHS, alarm occurred in

only four of the seven experiments (a 57% success rate). Even

though the PTHS was located only 3.65 m downstream, it took

significantly longer for this sensor to alarm than any of the

others tested.

Table 1.—Alarm times, in minutes, for various sensors for tests

conducted at an air velocity of 0.44 m/s

Test Smoke DDD 10-ppm CO 57.2 EC

PTHS 

1 ......... 14.4 17.6 18.9 26.3

2 ......... 17.1 18.0 21.2 26.6

3 ......... 14.7 16.5 20.0 25.0

4 ......... 16.5 15.6 19.2 NA 

5 ......... 12.0 14.2 19.9 NA 

6 ......... 15.9 17.7 22.7 NA 

7 ......... 17.3 18.6 21.4 20.2

 Average . . 15.4 16.9 20.5 24.5

DDD Diesel discriminating detector.

NA No alarm.

PTHS Point type heat sensor.

Observed averaging flaming 12 min.

Table 2 shows the alarm times for all tests conducted at the

higher air velocity. For these tests, the PTHS did not alarm at

all, indicating a 0% success rate for the data obtained. These

data indicate that as the air velocity increases, it becomes much

more difficult for the PTHS to alarm due to more rapid cooling

of the buoyant hot gases. It is also possible that the hot gases

passed underneath the PTHS at the higher air velocity,

eventually contacting the roof at some farther distance

downstream. This latter effect was observed in the

stratification of CO reported previously (4), where, at the

higher air velocity, a greater degree of roof stratification was

detected at a distance of 45.7 m downstream of the fire than at

a distance of 15.2 m downstream.

Table 2.—Alarm times for the various sensors for tests

conducted at an air velocity

Test of 0.97 m/s

Test Smoke DDD 10-ppm CO

1 . . . . . . . . . . . . . . . 8.7 11.7 22.4

2 . . . . . . . . . . . . . . . 8.6 11.0 24.8

3 . . . . . . . . . . . . . . . 9.1 9.9 22.7

4 . . . . . . . . . . . . . . . 7.6 11.2 23.3 

5 . . . . . . . . . . . . . . . 7.4 10.4 22.3

6 . . . . . . . . . . . . . . . 9.6 12.3 21.2

7 . . . . . . . . . . . . . . . 8.5 10.7 22.1

 Average . . . . . . . . 8.5 11.0 22.7

DDD Diesel Discriminating Detector 

Observed average flaming 10.3 min

.

ANALYSIS

These data also allow for the comparisons of previous the roof and the bulk average CO levels that are produced as a

empirical expressions (3) derived for the air temperature near function of air velocity and heat release rate. For air
0 ' D & R

& '

0

D

R

&

' @ 0

' &

0  @ 0

0  @ 0

' @ 0 % & @ 0

' % & @

0

& '

% &

B

6

(1)

(2)

(3)

(4)

(5a)

(5b)

(6)

(7)

(8)

temperature, the heat release rate, Q necessary to produce an The CO that is produced during the flaming stage of the @

f

air temperature near the roof, T , at some distance downstream R

of the fire, R, is given by:

 where, D = density of air = 1.2 x 10 g/m 3 3

C = heat capacity of air = 1.088 x 10 o

-3

A = entry cross section, m , o

2

v = air velocity, m/s, o

T = initial, ambient temperature, EC, o

R = distance downstream from center of the

 fire, m,

H = entry height, m, 

and W = entry width, m.

Equation 1 can be rearranged to yield an expression for the

temperature increase near the roof

From reference 3, the bulk average level of CO is given by

where B is the production constant for CO. From reference CO

3, B has a value of 5.68 for styrene butadiene rubber (SBR) CO

conveyor belts and, for coal, is given by the expression

From the experimental section, the surface area of exposed

conveyor belt strips is 0.28 m and the exposed top surfaceof 2

the coal is 1.20 m . The ratio of belt surface to coal surface is 2

0.23. If a reasonable assumption are made that the fraction of

total Q due to conveyor belt sca f les with the fraction of exposed

surface area and the remainder of the total heat Q scales with f

the exposed surface area of the coal, then:

firecan then be expressed as:

Combining equations 5a and 5b yields:

The ratio of temperature rise near the roof, T -T , to the R O

ppm of CO is equation 2 divided by equation 7. For R = 3.65

m, H = 2.16 m, and W = 5.97 m, this ratio is

At v = 0.44 m/s, equation 8 yields a value of 0.64, and at v = o o

0.97 m/s, the value is 0.68. Table 3 shows the average value of

the ratio of temperature rise to CO increase for each of the test.

The average measured values for all the tests during the

flaming stage were 0.62 at v = 0.44 m/s and 0.65 at v = 0.97 o o

m/s, in good agreement with the predicted values.

Table 3.-Average values of the ratio of temperature 

rise (T - T ) to CO increase R o

Test No. V = 0.44 m/s V = 0.97 m/s o o

1 .......................... 0.52 0.80

2 .......................... 0.72 0.54

3 .......................... 0.60 0.62

4 .......................... 0.76 0.55

5 .......................... 0.65 0.67

6 .......................... 0.45 ND 

7 .......................... 0.63 0.73

 Average ................... 0.619 0.652

ND No data.

v Air velocity. o

When only coal is present as the combustible (as is typically

the case during the early stages of fire in conveyor belt entries),

then it becomes possible to estimate the levels of smoke and

CO that are produced at a given temperature rise near the roof

and at a fixed distance from the fire. In particular, it is of

interest to make this determination for point-type heat sensors

with alarm temperatures of 57.2 EC (6) and spaced a maximum

distance of 15.24 m from the fire, the minimum spacing

specified in the regulations (2).

Combining equations 2, 3, and 4, the level of CO can be

expressed as a function of temperature rise near the roof by:
' & @ & @ R

' & @ &

& '

& @ 0

& ' & @ & R

& ' & @ &

7

(9)

(10)

(11)

(12)

(13)

Figure 4 

Part per million during smoldering and flaming stages at

an airflow of 0.97 m/s

Figure 5

Parts per million of CO during smoldering stage at an

airflow of 0.44 m/s

Since the fire can originate at any point within this spacing of

15.24 m, the integral average of equation 9 from R = 0 to R =

15.24 m represents a reasonable estimate of the average level

of CO as a function of temperature rise near the roof.

Assuming H = 1.83 m, and W = 6.10 m, the integral average

value becomes:

For smoke, the level of optical density (D) is given by the

expression (3):

Combining equations 2 and 11 yields:

The integral average of equation 12 over the distance from R =

0 to R = 15.24 m at the assumed values of H and W yields:

Assuming that T = 57.2 R EC and T = 18.3 O EC (a maximum

air temperature underground), then equation 10 indicates that,

for air velocities greater than 2.3 m/s, the estimated CO is less

than 50 ppm. Equation 13 would indicate that for any air

velocity less than 9.7 m/s, the critical level of optical density for

human escape for someone familiar with the escapeway (0.22

m ) (9) is also exceeded. At a typical air velocity of 1.0 m/s, -1

the smoke optical density at PTHS alarm is 0.52, more than

twice the critical level of optical density.

If the spacing for PTHS was increased to 38.1 m, then the

estimated levels of CO and smoke at PTHS alarm would

increase by about 60%. If a typical CO alarm level is taken to

be 10 ppm at an air velocity of 1.0 m/s, then for the PTHS

system to be equally sensitive, either the PTHS alarm

temperature or the spacing, or both, should be reduced. For

instance, if the spacing remains the same, then from equation

10, the value of T -T at the level of 10 ppm CO would be 6.2 R O

EC, indicating an alarm temperature of 24.5 EC. If the alarm

temperature were to remain 57.2 EC, then to reach this alarm

temperature at 10 ppm CO, the spacing (from equation 9)

would be reduced to 0.20 m.

These types of estimates clearly indicate the improvement in

early-warning fire detection that can be realized using either

CO or smoke sensors rather than PTHS. The use of CO or

smoke sensors would, in many cases, result in the detection of

smoldering fires, whereas PTHS would not.

While prolonged periods of sustained smoldering

combustion are never guaranteed, it is instructive to assess the

levels of CO produced during this stage of the fire. If the travel

time of the CO from the fire to the sensor is subtracted from the

actual times at which CO levels were measured by the sensor,

then these levels correspond to the bulk average CO levels

produced at the fire location. Figures 4 and 5 depict the bulk

average levels of CO from the fire and the time required to

produce sufficient levels of CO to reach its 10 ppm alarm level

at both airflows, respectively. Time "0" corresponds to the

instant of flaming ignition of the coal pile and not to the time

when power was supplied to the electrical heaters. The

negative time corresponds to the smoldering stage, the positive

time to the flaming stage. At teh higher air velocity of 0.97 m/s

(figure 5), at the time flame erupts, the CO level is 4 ppm and

reaches its level of 10 ppm 9.4 min after flaming. Perhaps of

greater interest is figure 4 for the lower air velocity of 0.44 m/s.

At 0.7 min before flame erupts, the CO level has reached the 10

ppm alarm level. If flaming had never occurred, the heating

would still have been detected by the CO sensor located

downstream.

This is not the case for the PTHS. At the time flame erupts,

there is virtually no increase in the air temperature. It is not

until the flame has reached a significantly greater intensity that

the air temperature near the roof at a distance of 3.65 m
8

 downstream reaches 57.2 EC. The data from USBM RI 9380 sensors alarmed 5 to 6 min before flaming occurred, and at CO

(3) indicate that belt ig-nition (had one been present in a typical levels in the range of 1 to 3 ppm, indicating their earlier

end-use config-uration) could have occurred at a much lower

fire in-tensity (15 kW). At both air ve-locities, the smoke

warning capability.

CONCLUSIONS

The data and analysis clearly show for the experimental of fires in their incipient, smoldering stages is a viable

configuration considered that smoke sensors provide earlier possibility in many instances. The use of smoke sensors

warning of fire than 10 ppm CO sensors, and that 10 ppm CO enhances this possibility. The data also allow for estimates of

sensors provide earlier warning than PTHS. For smoke and CO and smoke optical density levels that would be present if

CO sensors including the DDD, the success rate was 1.0, detection was via PTHS spaced at intervals of 15.2 and 38.1 m.

meaning that every test fire was successfully detected. For the These levels are significantly greater than the recommended

PTHS, at the lower air velocity, the success rate was 0.57; at the alarm thresholds for CO and smoke sensors. The data clearly

higher air velocity, the success rate was 0. Other thermal indicate the effects of air ve-locity on the detection times that

sensors such as a distributed fiber optics system have shown were realized for each type of sensor. Air velocity also impacts

promise for early warning (10). When life and property the relative se-quence of events observed during the stages of

depend upon the sensor's ability to detect a fire, these latter

values for the PTHS are less than encouraging. The data also

indicated that at the lower air velocity, 10 ppm of CO was

produced prior to flaming, demonstrating that the detection

fire development (appendix). These results clearly indicate that

the likelihood of miners' escaping from underground mine fires

will improve with earlier detection. 

ACKNOWLEDGMENTS

The authors wish to thank the following members of the Linda L. Chasko, physical science technicians for their

USBM Pittsburgh Research Center for their important assistance during experimental setup and running of the

contributions: Kenneth W. Jackson and Fred-derick C. experiments.

Bernick, electronics technicians, Richard W. Pro and

REFERENCES

1. Roberts, G., D. McGlothlin, and M. Jackson. Bullitt Mine. MSHA 6. Custer, R. L. P., and R. G. Bright. Fire Detection: State-of-the-Art. U.S.

Accid. Invest. Rep., Mar. 9, 1994, 16 pp. Dep. Commerce/NBS, NBS Techn. Note, TN 839, June 1974, 13 pp.

2. .U.S. Code of Federal Regulations. Title 30--Mineral Resources; Chapter 7. Conti, R. S., and C. D. Litton. Response of Underground Fire Sensors:

I--Mine Safety and Health Administration, Department of Labor; Parts 0 to 199, An Evaluation. USBM RI 9412, 1992, 13 pp.

1990, 762 pp. 8. Egan, M. R. Diesel-Discriminating Detector Response to Smoldering

3. Litton, C. D., C. P. Lazzara, and F. J. Perzak. Fire Detection for Fires. USBM IC 9353, 1993, 9 pp.

Conveyor Belt Entries. USBM RI 9380, 1991, 23 pp. 9. Jin, T. Studies of Emotional Instability in Smoke from Fires. Fire and

4. Conti, R. S., and C. D. Litton. Effects of Stratification on Carbon Flammability, V. 12, April 1981, pp. 130-142.

Monoxide Levels From Mine Fires. Paper in Proceedings of Sixth Ventilation 10. Dobroski Jr., H. and R. S. Conti. Distributed Temperature Sensing for

Symposium, Salt Lake City, UT, June 21-24, 1993. Soc. Min. Metall., and Underground Belt Lines. Paper in Proceedings of New Technology in Mine

Explor., Inc. (SME), Littleton, CO., 1993, ch. 73, pp. 489-494. Health and Safety (SME Annu. Meet. and Exhibit, Phoenix, AZ, Feb. 24-27,

5. Mattes, R. H., A. Bacho, and L. V. Wade. Lake Lynn Laboratory: 1992). Soc. Min., Metall., and Explor., Inc. (SME), Littleton, CO, 1992, ch.

Construction, Physical Description, and Capability. USBM IC 8911, 1983, 40 3, pp.21-28

pp. 
9

APPENDIX—IMPACT OF AIR VELOCITY ON FIRE EVENTS

A developing mine fire triggers a sequence of events. The location prior to flaming ignition. It should be realized that the

observation (or detection) of these events is a function not only time noted for the odor event could very well depend on the

of the location of an observer (or detector) relative to the sensitivity of each olfactory sense.

location of the fire, but also of the air velocity. Figure A-1 At the higher air velocity the observed (detected) events are

shows the sequence of events observed (or detected) during the displaced by the travel time of 4.7 min from the events

tests reported in this report. In the upper portion (figure A-1) occurring at the fire location. The events of odor, visible

are the events at v = 0.44 o m/s, while in the lower portion are smoke in entry, smoke alarms, and flaming ignition occurring

the events at v = 0.97 m/s. The open bars represent the events at the fire location are almost identical to the same events at the o

at the fire location; the diagonal-lined bars represent the events lower air velocity. However, the levels of 5, 10, and 15 ppm

observed (or detected) at a distance of 274 m downstream of CO at the fire location are recognized later due to their greater

the fire. dilution at the higher air velocity. The observed (detected)

At the lower air velocity there is a very consistent and the 274 m location actually occur before flaming ignition of the

regular sequence events at the fire and also at the observer coal due to the shorter travel time.

(detector) location. The observed (detected) events are The air velocity impacts these events through both dilution

displaced by the travel time of 10.4 minutes from the events and travel time effects. All the events observed (detected) at

occurring at the fire. However, all the events observed the 274 m location occur prior to alarm of a PTHS located at

(detected) actually transpire subsequent to flaming ignition of the fire source. The data clearly show the advantages of smoke

the coal due to this long travel time, even though odor, visible and CO sensors compared with the PTHS that were evaluated

smoke in the entry, smoke alarms, 5 ppm, and 10 ppm CO during these tests.

actually occur at the fire

events of odor, visible smoke in the entry, and smoke alarms at
10

Figure A-1

Sequence of events at fire and observed (detected ) at 274 m. downstream from

fire for test fires at two air velocities.

INT.BU.OF MINES,PGH.,PA 30158