UNDERSTANDING MINE FIRES BY DETERMINING THE 

CHARACTERISTICS OF DEEP-SEATED FIRES 

 

 

 

 

Michael A. Trevits, NIOSH, Pittsburgh, PA, 

Liming Yuan, NIOSH, Pittsburgh, PA, 

Kara Teacoach, NIOSH, Pittsburgh, PA, 

Michael P. Valoski, MSHA, Pittsburgh, PA and 

John E. Urosek, MSHA, Pittsburgh, PA 

Disclaimer: The findings and conclusions in this report 

are those of the authors and do not necessarily represent 

the views of NIOSH or MSHA. 

Abstract 

A mine fire represents one of the most dangerous and 

challenging safety issues facing underground mine 

operators. Given the right circumstances, a mine fire can 

occur at any location in the active or abandoned mine 

workings, can quickly grow beyond control, and threaten 

the welfare and livelihood of the entire underground 

workforce. The National Institute for Occupational 

Safety and Health (NIOSH), in partnership with the Mine 

Safety and Health Administration (MSHA), has been 

conducting an in-depth program of research addressing 

mine fire prevention, early and reliable fire detection, and 

mine fire suppression technologies. One portion of this 

program is focused on understanding the characteristics of 

mine fire combustion products and flame spread through 

large scale deep-seated (firmly established) fire tests and 

use of computational fluid dynamics (CFD) modeling. In 

this study, two deep-seated fire tests were conducted; one 

fire consisted of coal material and the other utilized the 

two most abundant fuel sources found in a coal mine: coal 

and wooden cribbing blocks. The fires were burned to 

completion while the combustion products were collected 

and analyzed. In addition, an array of thermocouples was 

placed within the body of the material to measure flame 

spread rate. The coal fire test information was then used 

to develop a CFD model of the fire. This paper describes 

the fire tests, provides insight into characteristics of flame 

spread, and presents the CFD modeling work results. 

Introduction 

Fire spread in a coal mine will depend upon the 

thermal and physical properties of the most abundant fuel 

sources (including coal, wooden mine roof supports, and 

conveyor belts), the mine’s ventilation system, and the 

size of the mine opening [1]. Because fuel sources are 

typically distributed throughout a mine, a fire can spread 

quickly over large lateral distances. Moreover, mine fires 

can be especially perilous because the toxic fire products 

can quickly spread far beyond the fire zone and thereby 

expose all underground miners to dangerous and deadly 

conditions. 

The leading causes of U.S. mine fires include flame 

cutting and welding operations, frictional heating and 

ignitions, electrical shorts, mobile equipment 

malfunctions, and spontaneous combustion [2]. The fact 

that mine fires continue to occur emphasizes the 

importance of recognizing and eliminating potential fire 

hazards and the overall need for improved fire control and 

suppression technology. The NIOSH mine fire research 

program is addressing a broad spectrum of problem areas 

facing the U.S. mining industry. The intent of the work is 

to provide the mining industry with an understanding of 

the conditions that could lead to a fire, the capability to 

detect unusual heating or fire conditions, and the 

technology to suppress and extinguish a fire. Work under 

this research program includes testing, evaluating, 

improving and modifying coal mine fire-fighting 

strategies and methodologies through large-scale tests. 

One portion of this work is focused on understanding the 

characteristics of mine fire combustion products and 
 

 

 

 

 

 

 

 

 

 

 

 

flame spread through deep-seated fire experiments and 

use of CFD modeling. 

In 2001, NIOSH and MSHA agreed to partner in 

research studies to develop new understandings of the 

characteristics of mine fires and the capabilities and 

limitations of mine fire suppression technologies. Since 

that time, NIOSH researchers and MSHA technical 

specialists have worked together in the field at actual 

mine fire sites and in the laboratory and each have gained 

new insights into the science of mine fires and fire control 

and suppression technology. This study represents the 

second stage of a series of deep-seated fire tests. The first 

study examined the combustion characteristics of wood 

crib blocks and direct application of fire suppression 

agents [3]. Future work will concentrate on large-scale 

deep-seated coal fires in an underground setting followed 

by remote application of fire suppression agents. It is 

anticipated that these experiments combined with followup CFD modeling work will provide significant 

information about combustion products and flame spread 

rates and will assist in furthering our understanding of the 

evolution and growth of a mine fire. 

Objective and Approach 

The objective of this study was to conduct two deepseated fire experiments, including a coal fire and a mixed 

fuel fire (coal and wood cribbing blocks combined), to 

collect combustion product information, measure flame 

spread rates and to study the mechanics of the fire through 

computer modeling. 

NIOSH Fire Suppression Facility 

The fire tests were conducted at the NIOSH Fire 

Suppression Facility (FSF) and MSHA provided 

supplemental gas monitoring equipment for the tests 

along with technical experts to operate the equipment. 

The FSF is part of the NIOSH Lake Lynn Laboratory 

(LLL) which is located approximately 60 miles southeast 

of Pittsburgh, Pennsylvania. The LLL is a world-class, 

highly sophisticated surface and underground facility 

where large-scale explosion trials and mine fire research 

work is conducted [4]. 

The FSF was configured to simulate a 150-ft long 

mine entry. The interior height of the simulated entry is 

7.2 ft and the width is 18 ft. The roof of the simulated 

entry is made of corrugated steel bridge planks, the ribs 

are made of 8-in thick mortared solid concrete blocks and 

the floor is made of reinforced concrete. The interior roof 

is covered with a 2-in thick layer of Fendolite M-II ® (a 

specialized fire resistant mixture of vermiculite and 

Portland cement) and a 1-in thick layer of Fendolite MII® has been placed on the ribs.1

 

1 Reference to product or trade names does not imply 

endorsement by NIOSH or MSHA. 

For ventilation, a 6-ft 

diameter variable speed axivane fan (equipped with a 

pneumatic controller to adjust fan blade pitch) was 

installed at one end of the simulated entry. The fan can 

provide blowing sustained airflow up to about 1150 fpm 

over the cross-section of the entry. Two doors, which 

permit access to the inside of the FSF, are located about 

47 ft from the fan. Figure 1 shows the exterior of the 

FSF. 

Figure 1. Fire Suppression Facility. 

The FSF is equipped with an array of chromel-alumel 

thermocouples (type-K) projecting 1.2-in down from the 

mine roof. The thermocouples are spaced at 10-ft 

intervals starting about 10 ft from the fan leading along 

the centerline to the end of the simulated entry. The 

thermocouples are connected via a wire network to a 

computer-based data acquisition system. During the fire 

tests, temperature data was collected at 10-second 

intervals. Radiation corrections were not made in the 

temperature data. 

The components of the fire gases were measured 

using a 9-point gas sampling array located 20 ft from the 

trailing edge of the burn box used to contain the fires. 

The array consisted of an interconnected network of 1⁄2-in 

diameter black iron pipe set across the width of the mine 

entry. A total of nine, 1/8-in diameter holes were drilled 

into vertical sections of the pipe to sample the fire gases. 

The holes in the pipe were spaced equally apart from the 

roof-to-floor and across the width of the entry. A 

thermocouple was also positioned at each gas sampling 

point to measure the temperature of the fire gases. The 

gases collected at each sample point were mixed together 

in a manifold that penetrated the FSF roof. The manifold 
 

 

 

 

 

 

 

 

was connected to a tubing line that led to the NIOSH and 

MSHA gas analysis equipment. 

The NIOSH infrared gas analyzers measured oxygen 

(O2), carbon monoxide (CO) and carbon dioxide (CO2) 

gas concentrations and the resultant data were collected at 

10-second intervals and recorded by a computer-based 

data acquisition system. In addition, gas samples were 

collected periodically over 3- to 4-minute intervals from 

the gas sampling array and were analyzed using gas 

chromatography. Chromatography analysis of each of the 

gas samples took about ten minutes to complete, therefore 

during each test a sample was collected and analyzed 

approximately every 13-15 minutes. The gases analyzed 

included hydrogen (H2), O2, CO, CO2, methane (CH4), 

acetylene (C2H2), ethylene (C2H4), and ethane (C2H6). 

The NIOSH and MSHA gas analyzers and the MSHA gas 

chromatograph were calibrated before each test. After 

each test, the MSHA gas analyzers were checked with 

fresh air to determine instrument drift. 

Composition of the Coal and Wood 

The coal used in each test was mined from the 

Pittsburgh Coalbed. The coal was cleaned and sorted 

(mostly 2-in sized pieces) and was stored outside for 

about 6 months. Two coal samples were collected for 

laboratory analyses, including ultimate, proximate and 

heating value determination. The wooden cribbing blocks 

were comprised of a variety of mixed hardwood species 

including ash, cherry, maple, white and red oak, and 

poplar. The blocks were 14 to 20 months old and had 

been stored underground at the LLL for about a year prior 

to the tests. Ten crib blocks (each block measured 6 in 

high, by 8 in wide by 16 in long) were randomly collected 

and 3-in cube-shaped samples were cut from each of the 

selected crib blocks and were sent to an independent 

testing laboratory for moisture, ultimate analysis, and 

heating value determinations. The averaged laboratory 

data for the coal and wood crib samples are shown in 

Table 1. 

Deep Seated Fire Tests 

A 3-ft-long by 2-ft-wide by 1-ft-deep box was 

constructed to hold the coal and wood during the fire 

tests. Legs (6 in) were attached to elevate the box and 

prevent heat damage to the FSF floor. The sides, back, 

and bottom of the box were constructed of expanded 

metal and 1 in angle iron was used as the frame (the front 

and top of the box was left open). The box was equipped 

with 16 chromel-alumel thermocouples (type-K) 

projecting 8 in inward from the sides. The thermocouples 

were spaced at 4-in and then 8-in intervals starting from 

the front of the box and leading towards the back of the 

box. The alignment of the thermocouples formed two 

layers of 8 units and simultaneously formed four rows of 

4 units. This arrangement permitted researchers to 

construct 3-dimensional views of the fires. The 

thermocouples were connected via a wire network to the 

computer-based data acquisition system mentioned 

previously. 

Table 1. Averaged laboratory data from coal and crib 

block samples. 

Parameter Coal Wood 

Sample 

Condition AR1 Dry DAF2 AR Dry DAF 

Moisture, - -

pct 8.90 14.95 - -

Proximate 

Analysis 

Ash 7.23 7.94 - 0.68 0.79 -

Volatile 

Matter 33.73 37.02 40.21 72.54 85.27 85.95 

Fixed 

Carbon 50.15 55.05 59.80 11.85 13.94 14.05

Ultimate 

Analysis 

Hydrogen 5.67 5.14 5.58 6.39 5.54 5.59 

Carbon 68.63 75.34 81.83 42.21 49.63 50.03

Nitrogen 1.26 1.38 1.50 0.16 0.19 0.19

Sulfur 0.66 0.72 0.79 0.12 0.14 0.14

Oxygen 16.56 9.50 10.32 50.44 43.71 44.06 

Ash 7.23 7.94 - 0.68 0.79 -

Heating 

Value, 

Btu/lb 12,202 13,394 14,549 7,184 8,446 8,513 

1 As Received. 

2 Dry Ash-Free. 

The fires were initiated using a natural gas burner 

that was equipped with 60 stainless steel jets (with a rated 

heat output of 44 to 114 kW). The burner was tilted on an 

angle upward toward the box to evenly spread flame 

across the opened front of the box. Natural gas was used 

instead of an accelerant (e.g., diesel fuel) to assist in 

starting the fires because it was more readily consumed 

by the fire and left no residue that could have altered the 

combustion products. It was arbitrarily decided to operate 

the burners for 45 to 60 minutes to ensure that the fires 

would burn without the need to re-light the burners. A 

steel plate was placed over the burners on an angle away 

from the fan across the front of the box creating an air 

deflector. This deflector was necessary to keep the fires 

burning. Figure 2 shows the position of the box in the 

FSF. 

Prior to igniting the fires, the ventilation flow rate 

was measured in front of the burn box and at the gas 

sampling array. At each location, the ventilation air flow 
 

 

 

 

 

 

rate was measured at nine points in the cross-sectional 

area of the mine entry and an average flow rate was 

determined. Table 2 shows the averaged ventilation air 

flow rate data for the tests. It should be noted that the 

ventilation flow rate for Test 2 was more than double that 

of Test 1 because fan problems precluded a sustainable 

lower flow rate. 

Figure 2. Layout sketch of the FSF for the deep seated 

fire tests. 

 

 

 

Table 2 – Average ventilation flow rate information 

for the fire tests. 

Test No. 1 2 

Ventilation flow rate in front of 

burn box, ft/min. 160 350 

Ventilation flow rate at the gas 

sampling array, ft/min. 150 300 

Deep Seated Fire Test 1 

As mentioned previously, two deep-seated fire tests 

were conducted in this study. The first involved 202.5 lbs 

of coal. The coal was placed into the burn box so that the 

leading edge of the pile facing the fan measured 4 in deep. 

The pile was tapered upward towards the back of the box 

and reached its maximum depth of 8 in at the midpoint of 

the box. Two layers of 8 thermocouples were placed in 

the pile. The top layer was positioned below the surface 

of the coal and the bottom layer was positioned above the 

expanded metal surface. Figure 3 shows two views of the 

box and location of the thermocouples. Figure 4 shows a 

picture of the box just prior to igniting the burner. 

After the burner was turned off (after 45 minutes of 

elapsed time), it was observed that the leading edge of the 

fire was burning intensely. This burning condition was 

needed to ensure that the fire would burn to completion. 

During the test, the collected gas samples showed only 

CO and CO2 were detected in the air stream and the 

concentration of these gases was below the lower reliable 

limit of detection. This was most likely due to the fact 

that the fire was small relative to the size of the FSF and 

the ventilation flow rate. Therefore, this data could not be 

used to calculate the heat release rate of the fire. The fire 

burned slowly from the front to back in 70.5 hrs and 

reached a maximum temperature of 788°C. Figure 5 

shows the time-temperature traces from the 

thermocouples for the test. The figure presents four 

vertical slices through the coal pile at 4-, 12-, 20-, and 28­

in (measured from the leading edge of the box) and shows 

the progression of the fire at these positions over time. 

Figure 3. Airflow, layout of the coal and thermocouple 

array for Test 1. 

Figure 4. Side view of box just prior to Test 1. 

The varied shape of the temperature plots from Test 1 

are believed to be caused, in some cases, by burning coal 

falling away from a thermocouple resulting in a 

temperature decline and in other cases from burning coal 
 

 

 

 

 

falling onto a thermocouple causing the temperature to 

increase or be sustained for a longer period of time. 

A pyrolysis temperature of 525°C was used in this 

study and when the temperature at a thermocouple 

reached this value, the flame front was considered to have 

reached that location [5]. The average flame spread rate 

of this fire was calculated to be 1.1 in/hr. This is a slower 

rate than those measured by Smith (1.9 and 2.1 in/hr) for 

a set of similarly sized coal fires [6]. Also in the previous 

work conducted by Smith, the ventilation flow rate was 

380 + 20 ft/min as compared to 160 ft/min used in this 

test which could account for some portion of the 

difference in the flame spread rates [6]. 

As mentioned earlier, 202.5 lb of coal was consumed 

in 70.5 hrs yielding a mass-loss rate of 2.9 lb/hr. Using 

the heating value of 13,394 Btu/lb from Table 1, the 

mass-loss rate converts to a heat release rate of 

650 Btu/min (11.4 kW). The amount ash remaining after 

Test 1 was 8.8% which was only slightly higher than the 

7.2% average value shown in Table 1, indicating that 

most if not all of the coal was consumed in the fire. 

Deep Seated Fire Test 2 

As described previously, the material used for this 

fire was a blend of the two most common fuel sources 

found in a coal mine, namely coal and wooden cribbing 

blocks. The wood crib blocks were cut into two sizes to 

fit the scale of the box. The larger cut size blocks 

measured 2.8 in by 2.5 in by 22 in and the smaller cut 

blocks measured 2.8 in by 2.5 in by 7.9 in. A total of 

7 large and 9 small blocks were used in this test and the 

blocks consisted of a mix of the various hardwoods 

described previously. A row of blocks (3 large and 

3 small) was placed into the burn box with the long axis 

of the blocks parallel to the long axis of the box. Coal 

was placed into the box to fill the spaces between the 

blocks. A second row of 4 large blocks was placed 

perpendicular to the first row. Again, coal was used to fill 

in the open space between the blocks. The top row of 

blocks was formed by placing 6 small blocks 

perpendicular to the previous row and coal was used to 

fill in the open spaces. A total of 170 lbs of coal and 

42.8 lbs of wood were used in this test. 

The wood and coal mixture was placed in the burn 

box so that the leading edge facing the fan measured 6 in 

deep. The mixture was tapered upward towards the back 

of the box and at the midpoint reached a maximum depth 

of 8 in. As in Test 1, two layers of 8 thermocouples were 

used. The top layer of thermocouples was positioned 

above the second row of wood and the bottom layer was 

positioned above the lowest level of wood. Figure 6 

shows two views of the box and location of the 

thermocouples for the test. Figure 7 shows a picture of 

the box just prior to igniting the burner. 

Figure 5. Time-temperature traces from thermocouples 

for Test 1. The terms RB, LB, RT and LT refers to the 

right bottom, left bottom, right top and left top 

respectively. Note data from RT4, RT20 and RT28 was 

omitted due because of instrument failure. 
 

 

 

Figure 6. Airflow, layout of the coal and thermocouple 

array for Test 2. 

Figure 7. Side view of box as configured for Test 2. 

The ventilation air was increased by almost 100% for 

this test because there were problems maintaining a 

sustained airflow at lower flow rates. The burner was 

turned off after 60 minutes and the fire was observed to 

be burning intensely. As in the previous test, the 

collected gas samples showed that the concentration of 

the combustion products in the air stream were below the 

lower reliable limit of detection. This was again most 

likely due to the fact that the fire was small relative to the 

size of the FSF and the ventilation flow rate. Therefore, 

this data could not be used to calculate the heat release 

rate of the fire. Figure 8 shows (as in the previous test) 

time-temperature traces from the thermocouples and 

presents four vertical slices through the coal and wood 

mixture at 4-, 12-, 20-, and 28-in from the leading edge of 

the box. The figure illustrates the progression of the fire 

at these positions over time. 

Figure 8. Time-temperature traces from the 

thermocouples for Test 2. 
 

 

 

 

 

 

 

 

 

 

 

 

As in Test 1, the varied shape of the temperature 

plots from Test 2 are believed to be caused, in some 

cases, by burning material falling away from a 

thermocouple resulting in a temperature decline and in 

other cases from burning material falling onto a 

thermocouple causing the temperature to increase or be 

sustained for a longer period of time. 

The mixed fuel fire burned faster than the coal fire 

and was completed in about 36 hrs. The maximum 

observed temperature of this fire was 1163°C. As in Test 

1, the flame spread rate of the fire was measured when the 

temperature of the fire was reached 525°C at a 

thermocouple location. The average flame spread rate 

was calculated to be 2.0 in/hr (about 82% faster than the 

coal fire in Test 1). Again, this faster rate can be 

attributed to the increased ventilation flow rate and the 

fact that the wood most likely burned at a faster rate than 

the coal. 

As mentioned previously, 170 lb of coal was 

consumed in 36 hrs yielding a mass-loss rate of 4.7 lb/hr. 

Using the heating value of 13,394 Btu/lb from Table 1, 

the mass-loss converts to a heat release rate of 

1050 Btu/min (18.4 kW). This fire also consumed 

42.8 lbs of wood yielding a mass-loss rate of 1.2 lb/hr. 

Using the heating value of 8,446 Btu/lb from Table 1, the 

mass-loss converts to a heat release rate of 170 Btu/min 

(3.0 kW) producing a combined heat release rate for the 

fire of 1220 Btu/min (21.4 kW). The amount ash 

remaining after Test 2 was 7.2% which was only slightly 

higher than the 5.9% value calculated from the coal and 

wood ash data shown in Table 1, indicating that most if 

not all of the coal and wood was consumed in the fire. 

CFD Modeling of Flame Spread 

for the Coal Fire 

Flame spread in the coal fire was simulated using 

Fire Dynamics Simulator (FDS), a computational fluid 

dynamics (CFD) program developed by National Institute 

of Standards and Technology. Because of its very 

complicated geometry, no attempt was made to simulate 

the mixed fuel fire. FDS is a three-dimensional, large 

eddy simulation model developed to study the transport of 

smoke and hot gases during a fire in an enclosed space. 

FDS is the most widely used large eddy simulation model 

in the fire science field and has demonstrated good 

agreement with experimental data in numerous validation 

studies. The model uses finite difference techniques to 

solve the Navier-Stokes equations numerically for fluid 

flow with a mixture fraction combustion model. Most 

mine combustibles undergo combustion by a gas phase 

reaction of the volatiles generated by the pyrolysis of the 

material. The pyrolysis front advances as a reaction front 

into the solid fuel leaving behind a char layer [1]. The 

FDS includes a pyrolysis model. 

Figure 9 shows the physical model of the coal pile, 

the burner, and the FSF. The dimensions for the model 

FSF were 18 ft wide by 7.2 ft high (the same as the actual 

FSF). For the simulation the length of the FSF was 

limited to 19.7 ft. The coal was modeled as a rectangular 

volume with dimensions of 3 ft long by 2 ft wide by 8 in 

high. The burner was modeled using its average heat 

release rate of 81 kW. In the simulation, the burner was 

kept on for 50 minutes. The airflow velocity at the inlet 

of the model FSF was 157 fpm similar to Test 1. Eight 

surface thermocouples were created in the simulation and 

were designated as T1 to T8. The thermocouples were 

located in the top of the pile similar to those in Test 1. 

Thermocouples T1 and T5 were located at the 4 in 

position, T2 and T6 were at 12 in position, T3 and T7 

were at the 20 in position and T4 and T8 were at the 28 

in position (as measured from the leading edge of the 

box). 

Figure 9. The physical model of coal pile, burner 

and the simulated FSF. 

In the simulation, the coal was treated as a 

continuous-medium with constant physical properties. 

The coal density was 1330 kg/m3

; coal specific heat was 

1.05 kJ/kg-K; coal conductivity was 0.24 W/m-K; and the 

heat of combustion for the coal was 13,460 Btu/lb. In the 

simulation, the pyrolysis front advances with an 

endothermic heat of reaction. The heat of pyrolysis was 

209 kJ/kg, and the pyrolysis temperature of the coal was 

525°C [5]. 

Figure 10 shows temperatures at different 

thermocouple locations as calculated in the simulation. 

Only temperatures at thermocouples T1-4 are presented. 

As mentioned previously, the varied shape of the 

temperature plots from Test 1 are believed to be caused, 

in some cases, by burning coal falling away from a 

thermocouple resulting in a temperature decline and in 
 

 

 

 

 

 

other cases from burning coal falling onto a thermocouple 

causing the temperature to increase or be sustained for a 

longer period of time. In the simulation however, this 

could not be duplicated because the coal was treated as a 

continuous medium and as such the temperature plots do 

not fall off quickly as observed in Test 1. It can be seen 

from the figure, the surface temperature increased slowly 

at the beginning except for thermocouple T1 which 

increased quickly because it was close to the ignition 

burner. This stage is a typical pre-heating period. After 

reaching about 450°C, the temperature increased very 

quickly to 700°C, indicating the arrival of the flame. The 

flame spread rate was 2.1 in/hr from T1 to T2, 2.9 in/hr 

from T2 to T3 and 3.1 in/hr from T3 to T4. 

Figure 10. Time-temperature traces from the 

thermocouples for the CFD coal fire simulation. 

Discussion 

Figure 11 shows time-average temperature traces for 

thermocouples at each location for both tests. The plots 

were constructed by determining the average temperature 

for all thermocouples at each position (4-, 12-, 20-, and 

28-in from the leading edge of the box) over the life of the 

test. The plot shows how differently these fires behaved. 

The coal fire burned slower and at a lower average 

temperature while, the mixed fuel fire burned faster and 

was significantly hotter than the coal fire. Part of the 

difference between the two tests can be attributed to the 

fact that the wood components in Test 2 were not evenly 

sized relative to the coal pieces. This difference was 

considered in the design of the experiment and it was 

decided that the larger wood pieces more closely 

approximated that found in a coal mine. Given that the 

wood burned at a faster rate than the coal, the flame front 

would also move faster through the coal and wood 

mixture. Also, some of the difference between the two 

fires can be attributed to the variation in ventilation air 

speed. A CFD analysis by Edwards and Hwang showed 

that the flame spread rate in a simulated coal lined tunnel 

was strongly sensitive to ventilation air speed [1]. Further 

experimentation is warranted to indentify the exact 

relationship between flame spread and ventilation air 

speed. 

Figure 11. Time-average temperature plots at each 

position for Tests 1 and 2. 

Table 3 shows a comparison of the parameters from 

Test 1 with the FDS simulation of the coal fire. 

Compared to Test 1, the maximum surface temperatures 

as estimated in the simulation are very close to those 

measured in the test. However the simulation 

overestimated the flame spread rates. This is probably 

because the coal pile was treated as a continuous medium 

in the simulation, while in Test 1 it consisted of packed 

pieces of coal. With the continuous medium, heat 

conduction is stronger than in packed coal pieces leading 

to higher flame spread rate. 

Table 3 Comparison of Test 1 data to FDS simulation. 

FDS 

Parameter Test 1 Simulation 

Ventilation rate, fpm 160 157 

Average flame spread rate, 

in/hr 1.1 2.7

Maximum temperature, °C 788 777 
 

 

 

 

 

Summary 

In this study, two, deep-seated fire tests including a 

coal fire and a mixed fuel fire (coal and wood combined), 

were conducted in partnership with MSHA at the NIOSH 

Fire Suppression Facility to collect combustion product 

information, measure flame spread rates, and to study the 

mechanics of the fire through computer modeling. These 

tests are part of a large-scale fire test program that is 

ongoing at the NIOSH Lake Lynn Laboratory. 

Unfortunately because of the small size of the fire tests, 

relative to the FSF, we were unable to collect meaningful 

fire combustion product information. 

A comparison of the two fire tests showed that the 

fires behaved differently with the coal fire burning more 

slowly and achieved a lower temperature than the mixed 

fuel fire. Part of the difference can be attributed to the 

fact that the wood components in Test 2 were not evenly 

sized relative to the coal pieces. This difference was 

considered in the design of the experiment and it was 

decided that the larger wood pieces more closely 

approximated that found in a coal mine. Given that the 

wood burned at a faster rate than the coal, the flame front 

would also move faster through the coal and wood 

mixture. Additionally, the difference in the ventilation 

flow rates between the two tests undoubtedly contributed 

to the rate of flame spread (1.1 in/hr with a ventilation 

flow rate of 160 ft/min for the coal fire test versus 

2.0 in/hr with a ventilation flow rate of 350 ft/min for the 

mixed fuel fire test). 

CFD modeling of the Test 1 showed the maximum 

surface temperatures in the simulation were very close to 

those measured in the test. But the flame spread rates 

from the simulation are higher than those estimated in the 

test. This is probably because that the coal pile was 

treated as a continuous medium in the simulation, while in 

Test 1 it consisted of packed pieces of coal. The results 

from this modeling exercise will be used in the design of 

the follow-up large-scale underground deep seated coal 

fire experiments with remote fire suppression 

applications. 

Acknowledgments 

The authors would like to recognize 

Melanie D. Calhoun and Edward J. Arnold, MSHA, 

Richard A. Thomas, John Soles, NIOSH and the NIOSH 

staff at the LLL, for their professionalism, dedication, and 

assistance in the conduct of the field work for this study. 

We would also like to recognize Thomas A. Gray, 

Tetra Tech, and Charles R. Wiedrich, MSHA for their 

expertise in providing the technical review of this paper. 

References 

1.	 Edwards, J.C., and C.C. Hwang, 2006. CFD 

Modeling of fire spread along combustibles in a mine 

entry. In: SME Annual Meeting and Exhibit. 

Preprint 06-027. Littleton, CO: Society for Mining, 

Metallurgy, and Exploration, Inc., pp. 1–5. 

2.	 National Institute for Occupational Safety and 

Health, 2008. NIOSH Mining Webpage, 

<http://www.cdc.gov/niosh/mining/topics/topicpage1 

9.htm>, November 26. 

3.	 Trevits M.A., A.C. Smith, J.E. Urosek, M.P. Valoski, 

2007. Evaluation of deep-seated crib block fires and 

direct-application fire suppression agents. In: SME 

Annual Meeting and Exhibit. Preprint 07-130. 

Littleton, CO: Society for Mining, Metallurgy, and 

Exploration, Inc., pp. 1–14. 

4.	 National Institute for Occupational Safety and 

Health, 1999. "Lake Lynn Laboratory (flyer)," 

Pittsburgh, PA: U.S. Department of Health and 

Human Services, Public Health Service, Centers for 

Disease Control and Prevention, National Institute for 

Occupational Safety and Health, Publication No. 99­

149, 1 p. 

5.	 Hertzberg, M., I.A. Zlochower and J.C. Edwards, 

1988. Coal particle pyrolysis mechanisms and 

temperatures, US Bureau of Mines Report of 

Investigation 9169, 39 p. 

6.	 Smith, A.C., D. Ng, W. Ryan, C.P. Lazzara, 1991. A 

method to evaluate the performance of coal fire 

extinguishers, US Bureau of Mines Report of 

Investigations 9392, 11 p.