Effects of ventilation and gob characteristics on spontaneous 

heating in longwall gob areas 

L. Yuan 

NIOSH Pittsburgh Research Laboratory, Pittsburgh, Pennsylvania, USA 

A.C. Smith 

NIOSH Pittsburgh Research Laboratory, Pittsburgh, Pennsylvania, USA 

ABSTRACT: In the U.S. coal mining industry, most spontaneous combustion fires occur in longwall or workedout gob areas. In order to reduce the fire hazard caused by spontaneous combustion, it is important to understand 

how ventilation and gob characteristics affect the spontaneous heating process. Given the difficulty to conduct 

field tests in such an environment, a computational fluid dynamics (CFD) study was conducted to investigate the 

effects of ventilation and gob characteristics on the spontaneous heating process in longwall gob areas. Two 

longwall panels with a bleeder ventilation system were simulated. The spontaneous heating is modeled as the lowtemperature oxidation of coal in the gob using the Arrhenius rate law and kinetic data obtained from previous 

laboratory-scale studies. The heat generated from the spontaneous heating is transported by convection and 

conduction, and oxygen and the oxidation products are transported by convection and diffusion. Unsteady state 

simulations were conducted with different ventilation conditions and gob permeability distributions. The 

ventilation parameters varied in the simulations are the pressure at the bottom of the bleeder shaft and regulator 

resistance in the second entry inby the longwall face. 

1 Introduction 

Spontaneous combustion continues to pose a hazard for the 

U.S. underground coal mines. Approximately 17% of the 

87 total reported fires for underground coal mines for the 

period 1990–1999 were caused by spontaneous combustion 

(DeRosa, 2004). The risk of an explosion ignited by a 

spontaneous combustion fire is also present in those mines 

with appreciable levels of methane emissions. In fact, three 

of the mine fires from the reported period resulted in 

subsequent methane explosions. Spontaneous combustion 

occurs when the heat that is produced by the low

temperature reaction of coal with oxygen is not adequately 

dissipated by conduction or convection, resulting in a net 

temperature increase in the coal mass. Under conditions 

that favor a high heating rate, the coal attains thermal 

runaway and a fire ensues. The spontaneous combustion 

potential of coals can be evaluated qualitatively in a

laboratory using one of four commonly used methods: 

adiabatic calorimetry, isothermal calorimetry, oxygen

sorption, and temperature differential methods. Although 

laboratory results are valuable, their extrapolation to the 

mining environment has not been completely successful 

because of complicated scaling effects that cannot be

reproduced in small-scale experiments. In actual

spontaneous heating events in coal mines, much larger coal 

masses may be involved. The spontaneous heating of coal 

in mines often occurs in a gob area and is not easily 

detected. The amount of coal that accumulates in these 

areas and the degree of ventilation can combine to give 

optimum conditions for spontaneous combustion.

Although much research has been done in experimental 

studies and mathematical modeling of spontaneous 

combustion of coals (Carras and Young, 1994), most of the 

research was focused on small coal stockpiles. Saghafi et 

al. (1995, 1997) did numerical modeling of spontaneous 

combustion in underground coal mines with a back return 

U-ventilation system, but their work was limited to two 

dimensions. Balusu et al. (2002) conducted a CFD study of 

gob gas flow mechanics to develop gas and spontaneous 

combustion control strategies for a highly gassy mine. 

Singh et al. (2002) developed a risk management plan for 

Australian mining operations in seams prone to 

spontaneous combustion. 

In order to reduce the fire hazard caused by

spontaneous combustion in a gob area, a computational 

fluid dynamics (CFD) study was carried out by NIOSH to 

model the spontaneous heating in longwall gob areas under 

realistic mine ventilation conditions and methane 

generation rates. In previous NIOSH research, a CFD 

model was developed to describe the ventilation pathways 

through the immediate gob under different ventilation 

schemes (Yuan et al., 2006), and to simulate the 

spontaneous heating of coals in a two-panel gob area using 

a bleeder ventilation system (Yuan and Smith, 2007). In 

this paper, the CFD model was used to examine the effects 

of changing ventilation parameters and gob characteristics, 

such as its permeability distribution, on spontaneous 

heating in longwall gob areas. 
 

 

 

 

 

 

 

 

2 Gob Layout and Ventilation System 

A typical longwall district in an underground coal mine 

may consist of multiple panels. These panels are typically 

ventilated using bleeder fans to ventilate the mined out 

panels and the gob area of the active panel. In this study, 

this situation is simulated with two panels, one as a minedout panel and the other one as an active panel, utilizing a 

bleeder system ventilated by a bleeder fan. The layout of 

the two panels and the ventilation system is shown in 

Figure 1. Each simulated gob area is 2,000 m long, 300 m 

wide, and 10 m high starting from the bottom of the coal 

seam. The ventilation airways are 2 m high and 5 m wide. 

Panel A represents the completed panel, while panel B 

represents the active one. The ventilation scheme uses a 

three-entry gateroad system. This scheme and the panel 

dimensions are typical of longwall mines operating in the 

Pittsburgh coal bed of the Northern Appalachian Coal 

Basin. In the model, it is assumed that the middle entry 

between panel A and B and an entry on panel A’s tailgate 

side are partially open. All crosscuts between the first and 

second entries inby the longwall face on the headgate side 

of panel B are open. For modeling purposes the bleeder 

entries at the back end of the gob are represented as one 

entry connecting to the bleeder fan. Four regulators are 

located at the end of the second and third entries inby the 

longwall face and the two tailgate entries, respectively, for 

controlling the bleeder ventilation. 

bleeder fan regulator 4 

return 

Panel A (mined out) regulator 3 

Panel B (active) 

regulator 2 

face 

B Tailgate 

intake 

A Tailgate 

A Headgate 

B Headgate regulator 1 

Figure 1. Layout of longwall panels and ventilation system. 

3 Low Temperature Coal Oxidation 

The chemical reaction between coal and oxygen at low 

temperatures is complex. Generally, three types of 

processes are believed to occur (Carras and Young, 1994). 

These are: (i) physical adsorption; (ii) chemical adsorption 

which leads to the formation of coal-oxygen complexes 

and oxygenated carbon-species; and (iii) oxidation in 

which the coal and oxygen react with the release of 

gaseous products, typically carbon monoxide (CO), carbon 

dioxide (CO2), and water vapor (H2O). 

The moisture content of coal can play an important role 

in the low temperature coal oxidation. The interaction 

between water vapor and coal can be exothermic or 

endothermic depending on whether the water condenses or 

evaporates. Smith and Lazzara (1987) found that, initially, 

the rate of temperature rise depends on the heat-of-wetting. 

Later the heating curves pass through an inflection point, in 

which neither the heat-of-wetting mechanism nor the 

oxidation mechanism dominates. In the final phase, the 

oxidation mechanism dominates. Smith and Glasser (Smith 

and Glasser, 2005) concluded that adsorption of water 

vapor does not in itself compete with the low-temperature 

oxidation in terms of ‘heat generation’, but appears to 

speed up the oxidation rate, and possibly plays a catalytic 

role. 

In this study, the effect of water vapor is not 

considered, and only the coal oxidation is simulated. The 

chemical reaction between coal and oxygen is simplified 

as: 

Coal + O2 → CO2 + 0.1CO + heat 

The detailed chemical structure of coal is not clear and 

varies with the rank and origin of coal. According to 

experimental data (Smith et al., 1987), one mole of coal 

reacting with one mole of oxygen generates one mole 

carbon dioxide and roughly 0.1 mole carbon monoxide 

plus heat at the early stage of coal oxidation. The 

dependence of the rate of oxidation on temperature and 

oxygen concentration can be expressed in the form: 

n Rate = A[O ] exp(−E / RT) (1) 2 

Where: 

A = preexponential factor (/s) 

E = apparent activation energy (kJ/mol) 

R = gas constant (kJ/mol-K) 

n = apparent order of reaction 

T = absolute temperature (K) 

[O2] = oxygen concentration (kmol/m3

) 

The value of apparent activation energy, E, of different 

coals can very between 12 and 95 kJ/mol. The preexponential factor, A, depends more on coal rank and 

measurement method, and has a typical value between 1 

and 7×105

 /s. In this study, the activation energy and preexponential factor data for the most reactive coal of the 24 

U.S. coals tested by Smith and Lazzara (1987), designated 

as No. 80-1, was used to represent the worst-case 

spontaneous combustion scenario. The value of the 

apparent order of the reaction, n, in low-temperature 

oxidation studies of coal and other carbonaceous materials 

has been shown to vary from ~0.5 to 1.0 (Carras and 

Young, 1994), and is about 0.61 for some U.S. coals 

(Schmidt and Elder, 1940). The physical and kinetic 

properties of the coal layer are listed in Table 1. 

In order to simulate the spontaneous heating of coal in 

longwall gob areas, the source of coal needs to be defined. 

The coal source can be coal left from the mined coal seam 

or other overlying or underlying coal seams. In this study, 

the Pittsburgh coal seam was considered, with a 1-m-thick 

Pittsburgh rider coal sequence less than 1 m above the 

main coal seam. The rider coal sequence was modeled as 

caving into the gob after the main coal seam was 

completely mined out. Figure 2 shows the cross section of 

two longwall panels with the caving coal layer at the 

bottom of the gobs. The coal pillars remaining along the 

perimeter of the gob were also considered as a coal source. 
 

 

 

 

 

 

 

 

 

 

 

 

 

The oxidation of coal will occur on any available coal 

surface including both external and internal pore surfaces. 

The reaction rate of spontaneous heating of coal in coal 

Table 1. The physical and kinetic properties of the coal 

layer. 

Coal density 1300 kg/m3 

Coal specific heat 1003.2 J/kg-K 

Coal conductivity 0.1998 W/m-K 

Heat of reaction 300 kJ/mol-O2 

Activation energy 66.5 kJ/mol 

Pre-exponential factor 6×104

 /s 

Coal particle diameter 10 cm 

Initial coal temperature 300 K 

stockpiles was found to be related to the external surface 

area for nonporous coal particles with small pore 

diameters, and weakly related or not related to particle size 

for small porous coal particles with larger pore diameters. 

It is difficult to define a coal particle size distribution in the 

coal layer in the gob area because of the large gob size. 

The parameter that affects the heat generation and 

dissipation during the spontaneous heating process is the 

coal surface area available in a unit volume, or surface-tovolume ratio. The surface-to-volume ratio used in the 

simulations is 36/m, which is equivalent to an average coal 

particle diameter of 10 cm. The heat generated from 

oxidation will be dissipated by conduction and convection 

while the oxygen and oxidation products are transported by 

convection and diffusion. 

gob: mined-out gob: ac ive panel B 5m

2m 

panel A 

10m

1m

caved rider coal middle undisturbed caved 

coal sequence entry rock coal
 

Figure 2. Cross section of two longwall panels with caving 

coal layer. 

4 Estimation of Gob Permeability 

The permeability and porosity distributions of the gob 

areas were based on geotechnical modeling of longwall 

mining in the Pittsburgh coal seam and the associated 

stress-strain changes using FLAC1

 (Fast Lagrangian 

Analysis of Continua) code (Esterhuizen and Karacan, 

2005). In FLAC modeling, mining was simulated in 

1

 Reference to a specific product is for informational 

purposes and does not imply endorsement by NIOSH. 

increments, starting from one side of the grid and 

advancing to the other side. Extraction of the coalbed was 

modeled by removing elements over the height of the 

coalbed. The process of gob formation was modeled by 

first deleting rock elements in the roof of the coalbed, so 

that they are stress relieved, followed by inserting gob 

properties in these elements. Gob properties were also 

inserted in previously mined coalbed elements, so that the 

gob filled the mined void. In the gob caved area, the recompaction of the caved rock has a significant effect on its 

permeability. Stress changes in the rock in the gob cause 

changes in the fracture apertures which then impact the 

permeability. Immediately behind the advancing face, the 

caved rock is loosely stacked and has an estimated porosity 

of approximately 0.4. As the mining face advances away 

from this caved rock, the weight of the overburden 

gradually increases and re-compacts the caved rock. This 

loading or stress in the caved material increases 

exponentially, until the full overburden load is supported 

by the caved material. The re-compaction, estimated with 

the FLAC model’s assigned strength and mechanical 

properties of the gob material, results in a reduction in the 

void space within the broken rock rubble and, therefore, 

significant changes in permeability. A simple relationship 

was used to estimate the changes in permeability in the 

caved rock based on the Kozeny-Carman equation: 

3 n k = f ( 2 ) (2) 

(1− n) 

Where: 

 n = porosity 

k =permeability (m2

) 

For a Pittsburgh coal seam longwall panel, the 

permeability values in the gob area were estimated to vary 

from 3.0x10-11 to 8.5x10-10 m2

, while the porosity value 

varies from 0.17 to 0.41. Around the perimeter of the gob 

and immediately behind the face shields, the permeability 

and porosity values were the largest, while near the center 

of the gob, these values were the smallest due to 

compaction. A detailed description of permeability 

calculation is given in Esterhuizen and Karacan (2007). 

The same profile was also applied to panel B. The porosity 

profiles in the two panels were similar to those 

permeability profiles except the maximum and minimum 

values are 0.41 and 0 17, respectively. It is assumed that 

these permeability and porosity profiles do not change with 

the gob height. The detailed permeability profiles were 

described by Yuan and Smith (2007). 

5 Numerical Modeling 

A commercial CFD program, FLUENT, from Fluent, Inc., 

was used in this study to simulate the air flow and 

spontaneous heating in the longwall gob areas. The air 

flow in the longwall gob area was treated as laminar flow 

in a porous media using Darcy’s law, while the air flow in 

the ventilation airways was simulated as fully developed 

turbulent flow. 
 

 

 

 

 

 

 

Methane emission was also considered in the 

simulation because it affects the oxygen concentration 

distribution in the gob. Methane is continually liberated 

from the face and from the overlying rider coal seam 

reservoir. The methane from the overlying coal seam 

reservoir is assumed to be released uniformly along the 

border between the gob and the reservoir. Using ventilation 

data from a local Pittsburgh coal seam mine, the amount of 

methane released from the reservoir in this simulation is 

0.13 m3

/s for panel B and 0.024 m3/s for panel A. The 

methane emission rate from the face to the panel B is 0.014 

m3

/s. These data were entered into FLUENT using C 

subroutines. 

The boundary conditions for ventilation pressures used 

in the simulation were also obtained from a local 

Pittsburgh coal seam mine’s ventilation data. The pressure 

was -747 Pa (-3.0 in.) at the intake inlet, -872 Pa (-3.5 in.) 

at the return outlet, and -2739 Pa (-11.0 in.) at the bottom 

of the bleeder shaft. The wall roughness of the ventilation 

airways was adjusted to have a total intake airflow rate of 

41 m3

/s in the active longwall panel. The pressure drop 

through the two regulators located at the second and third 

entries inby the longwall face were also adjusted to have an 

airflow rate entering onto the face of 28 m3

/s. The pressure 

drop at regulator 3 was adjusted to have a longwall face 

return airflow rate of 24 m3

/s and 4.7 m3/s airflow 

reporting to the bleeder system for the active panel. The 

flow rate in the entry on panel A’s tailgate side was 3.3 

m3

/s by adjusting the pressure drop at regulator 4. 

A simulation was conducted first without coal 

oxidation to obtain steady state flow field and gas 

distributions. Then, the unsteady simulation with coal 

oxidation was conducted using the steady state solution as 

the initial conditions. The face was assumed stationary 

during the simulation. 

6 Flow Patterns Inside The Gob 

The flow patterns inside a gob will have a significant effect 

on the spontaneous heating of coals because the oxygen 

needed for the oxidation is provided by the air flow, and 

the heat generated from the oxidation may be carried away 

by the air flow. Fresh air flowing into a mine is 

contaminated by strata gas, dust and diesel exhaust etc. 

when it moves through the longwall face and into the 

return or across the gob. The air flow inside a gob is 

expected to be three dimensional with the flow in the 

vertical direction being weaker than in the other two 

directions due to reduced permeability and pressure 

gradients. In order to visualize the flow patterns inside the 

gob, a virtual horizontal reference surface was created 1 m 

from the bottom of the mined seam floor. Comparison of 

model results is with respect to this horizontal reference 

surface. Figure 3 shows the flow path lines colored by 

velocity magnitude in the two gob areas. The path lines 

indicate that the flow was mainly from the headgate side to 

the tailgate side in the two panels. At the face, air entered 

into the gob through the face shields and the tailgate area 

and flowed to the middle entry between the two panels. 

The higher velocities of air traveling through the gob itself 

were between 1.5x10-4 to 2.5x10-4 m/s (0.03 to 0.05 fpm) 

near the back end of panel B. Figure 4 shows the oxygen 

distribution in the two panels for a steady-state case 

considering methane emissions but no coal oxidation. For 

this condition, the oxygen concentration was at 21% in 

most of mined-out panel A. In the active panel, B, the 

oxygen concentration close to the entry inby the longwall 

face was below 21% because of methane emissions from 

the overlying coal seam reservoir. The pressure drops at 

the regulators and air quantities in each entry for the base 

case simulation are listed in Table 2. 

Table 2. Pressure drops at the regulators and air quantities 

in each entry for the base case simulation. 

Pressure drop at regulator 1 1942 Pa 

Pressure drop at regulator 2 1743 Pa 

Pressure drop at regulator 3 448 Pa 

Pressure drop at regulator 4 1594 Pa 

Airflow at longwall face 28 m3

/s 

Airflow at return 24 m3

/s 

Airflow at regulator 1 5.7 m3

/s 

Airflow at regulator 2 3.8 m3

/s 

Airflow at regulator 3 6.6 m3

/s 

Airflow at regulator 4 3.3 m3

/s 

Airflow at bleeder fan 21 m3

/s 

Figure 3. Flow path lines colored by velocity magnitude 

(m/s) in gob areas. 

7 Simulation Results and Discussion 

Spontaneous heating can begin at ambient temperature 

when coal is exposed to oxygen. As the coal oxidizes, the 

coal temperature increases slowly. The temperature rise 

usually consists of two stages. The first stage is a slow 

temperature rise while the second one is a fast temperature 

rise, or thermal runaway. The time to reach a thermal 

runaway is called the induction time. When the coal 

temperature reaches about 500 K (227 C), the spontaneous 

heating mechanism changes to rapid combustion 

(Babrauskas, 2003). So the simulations were focused on 

the self-heating mechanism at temperatures below 500 K. 

Simulation of spontaneous heating of coals was first 

conducted with the boundary conditions described in the 
 

 

 

Numerical Modeling section, and it was used as the base 

case. The simulations were then conducted using different 

ventilation conditions and permeability distributions, and 

the results were compared with those from the base case. 

Figure 5a shows the temperature distribution in the two 

Figure 4. Contours of oxygen concentration (1=100%) in 

gob areas without coal oxidation. 

panels after about 9 days for the base case. It is apparent 

that temperature increases occurred in three areas. These 

areas appeared more apparent in digital figures than in 

printed figures. Area I is the area close to the active tailgate 

and around the return. Area II is the area nearby the 

crosscuts close to the back end of the active panel B, and 

area III is around the middle entry at the back end of the 

mined-out panel A. Figure 5b shows the temperature 

increases in area I. There was very little or no temperature 

rise in areas other than areas I, II and III. This is because 

all oxygen was nearly consumed by coal oxidation at the 

periphery of the gob areas and no oxygen was available 

inside the gobs, as shown by the oxygen concentration in 

Figure 5c. The rate of temperature rise in three areas was 

also different. At any given time during the simulation, 

there existed a maximum temperature somewhere in the 

gob area. From a fire safety point of view, this maximum 

temperature represents the worst-case scenario. Hereafter, 

this temperature is referred as the maximum temperature in 

the gob at a given time. 

7.1 Effect of Pressure at the Bottom of Bleeder Shaft 

Three simulations were conducted with different pressures 

at the bottom of the bleeder shaft: -1743 Pa (-7 in.), -3735 

Pa (-15 in.) and -4980 Pa (-20 in.) to determine the effect 

of gob pressure differential on the spontaneous heating 

process. The pressure used in the base case was -2739 Pa (­

11 in.). Figure 6 shows the maximum temperature obtained 

somewhere in the gob versus time for the three pressures 

compared with the base case. The general trend is that with 

the lower pressure at the bottom of the bleeder shaft, the 

rate of the maximum temperature rise increased. This is 

probably because the lower pressure in the bleeder system 

increases the pressure differential across the gob which 

increases the velocity and therefore quantity through the 

gob. With the pressure increased to -1743 Pa (-7 in.), the 

induction time increased about half a day compared with 

the base case. When the pressure was decreased to -3735 

Pa (-15 in.), the induction time was nearly the same as the 

base case, but the temperature rise rate increased greatly in 

the second stage. With the pressure decreased to -4980 Pa 

(-20 in.), the rate of temperature rise just increased slightly 

compared with -3735 Pa (-15 in.) pressure, indicating 

enough oxygen was supplied by the ventilation to sustain 

the spontaneous heating process with the pressure of -3735 

Pa (-15 in.) under the simulated conditions. 

Area I 

5b 

5c 

Area I 

Area III 

Area II 

5a 

Figure 5. Temperature and oxygen concentration 

distributions for the base case after 9 days. 5a: temperature 

in entire gob (K); 5b: temperature in area I (K); 5c: oxygen 

concentration (1=100%). 
 

 

 

 

 

7.2 Effect of Resistance in the Second Entry inby The 

Longwall Face 

Figure 7 shows the effect of resistance of regulator 2 on the 

spontaneous heating process in the gob. The pressure drop 

at regulator 2 was about 1743 Pa (7 in.) in the base case. It 

was increased to about 3735 Pa (15 in.) in one case by 

increasing the resistance at the regulator, and was 

decreased to about 187 Pa (0.75 in.) in another case by 

decreasing the resistance. Results show that with the 

increase of resistance at regulator 2, more air was pushed 

into the gob, thus the rate of maximum temperature rise 

increased. With the decrease of the resistance at regulator 

2, less air was moving into the gob, leading to longer 

induction time for the spontaneous combustion, about two 

days, compared to the base case. Because of lower total 

levels of oxygen provided to the gob through the second 

entry inby the longwall face, the spontaneous heating in 

area II nearly disappeared, as shown in Figure 8. 

350 

00 

50 

500 

Maximum temperature (K) 

-7 in. 

-11 in. (base case) 

-15 in. 

-20 in. 

0 1 2 3 5 6 7 8 9 

Time (day) 

300 

Figure 6. Simulated maximum temperature-time histories 

in gobs for different pressures at bottom of bleeder shaft. 

300 

350 

00 

50 

500 

Maximum temperature (K) 

7 in. pressure drop at regulator 2 

(base case)

15 in. pressure drop at regulator 2 

0.75 in. pressure drop at regulator 2 

0 1 2 3 5 6 7 8 910 

Time (day) 

Figure 7. Simulated maximum temperature-time histories 

in gobs for different pressure drops at regulator 2. 

7.3 Effect of Gob Permeability 

The gob permeability has a major effect on the 

spontaneous heating in the gob because it affects the 

quantity of oxygenated atmosphere air flowing into the 

gob. In order to examine the effect of gob permeability, the 

permeability distribution for the base case was increased 

10 times, decreased 10 times, decreased 100 times, and 

increased 100 times, respectively, in the simulations. 

Figure 8. Temperature distributions in the gob areas after 

about 9 days (with 0.75 in. pressure drop at regulator 2). 

Figure 9 shows the maximum temperature versus time 

histories in the gobs for the four different permeability 

distributions compared with the base case. With the 

permeability increased 10 times, the induction time was 

reduced about half a day and the rate of temperature rise 

increased at the second stage. When the permeability was 

increased 100 times over the base case, the induction time 

was nearly the same, but a slightly faster rate of 

temperature rise compared with the 10 times increase. 

When the permeability was decreased 10 times and 100 

times, respectively, the two maximum temperature rise 

curves were nearly overlapped, indicating that further 

decrease of permeability had no effect on the rate of 

maximum temperature rise. The induction times for these 

two cases were increased about 2.5 days compared with the 

base case. When the permeability was decreased 10 times 

and 100 times, respectively, there was no temperature rise 

in area II, probably because of insufficient amount of 

oxygenated atmosphere into the gob. This is shown in 

Figure 10 for 10 times decrease. 

8 Conclusions 

CFD simulations were conducted to investigate the effects 

of ventilation parameters and gob permeability on the 

spontaneous heating in longwall gob areas. Simulation 

results demonstrate that under typical three-entry bleeder 

ventilation conditions, increasing the pressure differential 

across the gob area increased the rate of maximum 

temperature rise in the gob. However, the increase had no 

effect on the induction time. Conversely, decreasing the 

pressure differential across the gob increased the induction 

time while the rate of maximum temperature rise did not 

change significantly. With the increase of permeability, the 

induction time was decreased, while decrease of 

permeability increased the induction time. The results 

indicate that spontaneous combustion thermal runaway can 
be delayed through reducing the pressure differential 

across the gob or reducing the resistance at regulator 2 

while still maintaining methane concentrations at different 

check points under allowable concentrations in the bleeder 

system. 

Because of the complexity of the problem and lack of 

field data for gob permeability and porosity distribution, 

the results reported here are valid only for the longwall 

panel setup and the permeability and porosity data used in 

this study, in addition to the ventilation conditions stated in 

the paper. 

500 

base case 

increased 10 times 

increased 100 times 

decreased 10 times 

50 decreased 100 times 

00 

350 

300 

0123 56789

Time (day) 

Maximum temperature (K) 

 

 

 

 

 

 

 

 

 

 

 

10 

Figure 9. Simulated maximum temperature-time histories 

in gobs for different gob permeability distributions. 

Figure 10. Temperature distributions in the gob areas after 

about 9 days (with permeability decreased 10 times). 

9 Disclaimer: 

The findings and conclusions in this report are those of the 

authors and do not necessarily represent the views of the 

National Institute for Occupational Safety and Health. 

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