Simulation of spontaneous heating in
 

longwall gob area with a bleederless 


ventilation system


Introduction research is needed to understand the A.C. SMITH AND L. YUAN Spontaneous combustion continues control mechanism and to optimize 

to pose a hazard for U.S. underground A.C. Smith and L. Yuan, member SME, are senior research bleederless ventilation systems. 

coal mines, particularly in western chemist and lead research engineer, respectively, with the Much research has been done 

mines where the coal is generally of Pittsburgh Research Laboratory, National Institute for Occupa- in experimental studies and mathlower rank. Fifteen reported fi res for tional Safety and Health (NIOSH), Pittsburgh, PA. Paper number ematical modeling of spontaneous 

underground coal mines for the period TP-07-048. Original manuscript submitted December 2007. Revised combustion of coals in outside coal 

1990-1999 were caused by spontane- manuscript accepted for publication March 2008. Discussion of stockpiles, as reviewed by Carras and 

ous combustion (DeRosa, 2004), and this peer-reviewed and approved paper is invited and must be Young (1994), but little research is 

10 underground spontaneous combus- submitted to SME Publications Department prior to Nov. 30, 2008. available for spontaneous combustion fires were reported for the period 

2000-2006 (DeRosa, 2007). Spontaneous heating occurs when the heat produced by the lowtemperature 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 conditions and a fire ensues. In spontaneous heating 

events in underground coal mines, large coal masses may be 

involved. The spontaneous heating of coal in mines often 

occurs in a gob area and may not be 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. In the United States, bleederless ventilation systems may be approved by the U.S. Mine 

Safety and Health Administration (MSHA) to serve as a 

spontaneous combustion control method in mines with a 

demonstrated history of spontaneous combustion. Currently, two U.S. coal mines are using bleederless ventilation 

systems.Although these bleederless ventilation systems are 

successful in controlling spontaneous combustion, more 

Abstract 

Although only used in a few U.S. longwall mines, bleederless ventilation systems can be an effective spontaneous 

combustion control method in mines having a demonstrated history of spontaneous combustion. To provide 

insights for the optimization of bleederless ventilation 

systems for U.S. underground coal mines, a computational 

fluid dynamics (CFD) study was conducted to model the 

spontaneous heating in longwall gob areas using a bleederless ventilation system. A single longwall panel with a 

bleederless ventilation system was simulated, and typical 

longwall mine ventilation data were used in the simulations. 

The permeability and porosity profiles for the longwall 

gob were estimated using a geotechnical model and were 

used as inputs for the CFD modeling. The effects of gob 

permeability and resistance of the collapsed entries on the 

spontaneous heating were studied. The effectiveness of 

using nitrogen injection to prevent spontaneous heating in 

the gob was also examined.1 

tion in underground coal mines. Because of the difficulty in conducting 

full-scale spontaneous combustion tests in underground 

coal mines, computational fluid dynamics (CFD) modeling has become an important method to study the spontaneous combustion in underground coal mines. Saghafi 

and coworkers did numerical modeling of spontaneous 

combustion in underground coal mines with a back return 

U-ventilation system (Saghafi et al., 1995; Saghafi and Carras, 1997), 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. Rosema et 

al. (2001) also simulated spontaneous combustion using a 

two-dimensional model. 

To understand the fire hazard caused by spontaneous 

combustion in a gob area, a computational fl uid dynamics 

(CFD) study was carried out by the National Institute for 

Occupational Safety and Health (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 study the spontaneous heating of coals in a longwall gob area utilizing a bleederless ventilation system. 

Gob layout and ventilation system 

In a bleederless ventilation system, the previously 

mined-out panels are usually isolated from the active gob 

and the remainder of the mine. In this study, only the active panel was simulated. The layout of the panel and the 

ventilation system is shown in Fig. 1. The simulated gob 

area is 2,000 m (6,562 ft) long, 300 m (984 ft) wide and 10 

m (33 ft) high starting from the bottom of the coal seam. 

The ventilation airways are 2 m (6.6 ft) high and 5 m (16.4 

ft) wide. The ventilation scheme is a simple “U” bleederless ventilation system. In the model, all entries inby the 

longwall face were treated as though they were collapsed. 
 

 

 

 

 

FIGURE 1 Typical ventilation pressures for 

the bleederless ventilation system Layout of longwall panel and ventilation system. were used in the simulation. The pressure was -76.2 mm (-3 in.) water gauge 

at the intake inlet and -88.9 mm (-3.5 

in.) water gauge at the return outlet. 

To control the airflow quantity to the 

longwall face, the wall roughness was 

adjusted to have a realistic intake airNumerical modeling 

A commercial CFD program, FLUENT2, from Fluent 

Inc., was used in this study to simulate the gas fl ow and 

spontaneous heating in the longwall gob areas. The gas 

flow in the longwall gob area was treated as laminar fl ow 

in a porous media using Darcy’s law, while the gas fl ow in 

the ventilation airways was simulated as fully developed 

turbulent fl ow. 

The permeability and porosity distributions of the gob 

area were based on geotechnical modeling of longwall mining in the Pittsburgh coal seam and the associated stressstrain changes using Fast Lagrangian Analysis of Continua 

(FLAC)) code (Esterhuizen and Karacan, 2005). For a 

Pittsburgh coal seam longwall panel, the permeability values in the gob area were estimated to vary from 3.0 x 104

 to 

8.5 x 105 millidarcies (md), while the porosity value varies 

from 0.17 to 0.41 based on the modeling result from FLAC. 

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 the permeability calculation is given in Esterhuizen 

and Karacan (2007). The porosity profile in the gob was 

similar to the permeability profile except the maximum 

and minimum values are 0.41 and 0.17, respectively. It is 

assumed that these permeability and porosity fi les do not 

change with the gob height.The detailed permeability profiles are presented in Yuan and Smith (2007). 

FIGURE 2 

Flow path lines colored by velocity magnitude (m/s) in gob area: (a) in the 

whole gob and (b) near the face. 

flow rate of 30 m3

/sec (64,000 cu ft/ 

min). A simulation was conducted fi rst 

without coal oxidation and without methane emissions 

to obtain a steady-state fl ow field. Then, simulations with 

coal oxidation were conducted using the steady-state solution as the initial conditions. The face was assumed stationary during the simulations. 

Flow patterns inside the gob 

The flow patterns of air inside a gob will have a signifi ­

cant effect on the spontaneous heating of coals, because 

the oxygen needed for the oxidation is provided by the 

airflow and the heat generated from the oxidation may 

be carried away by this airflow. Fresh air flowing into a 

mine is usually contaminated by strata gas, dust and diesel exhaust, when it moves through the longwall face and 

into the return or cross the gob. The airfl ow inside a gob 

is expected to be three dimensional, with the fl ow in the 

vertical direction weaker than in the other two directions 

due to reduced permeability and pressure gradients. To 

visualize the flow patterns inside the gob, a virtual horizontal reference surface was created 1 m (3.3 ft) from 

the bottom of the mined coal seam floor. This was done 

to compare the results with respect to this horizontal 

reference surface. Figure 2, (a) and (b), show the flow 

path lines colored by velocity magnitude in the gob area. 

The path lines show that flow through the gob itself was 

mainly concentrated behind the shields. At the headgate 

side, air leaked through the shields but some fl owed back 

into the face again through the shields 

near the tailgate side. These fl ow path 

lines were generated by releasing 30 

massless particles that were evenly distributed along a line that is 1 m (3.3 ft) 

away and parallel the face shields. The 

color of the fl ow path lines represents 

the velocity magnitude, while the numbers of flow path lines in a certain area 

represents the amount of the airfl ow in 

that area.The single flow line some distance into the panel indicates that the 

quantity of airflow there is very low. 

There was no flow line deeper into the 

gob, indicating the airflow rate is too 

low to be represented by a single fl ow 

line. If more massless particles are released, it will make the fl ow path lines 

too crowded to see near the face area. 

The flow from tailgate to headgate was 

caused by shock losses.The air velocity 

ranged between 1 x 10-5 to 3 x 10-5 m/ 

sec (0.002 to 0.006 ft/min) in the gob 

near the shields, and there was nearly 

no flow farther away from the shields 

into the gob. 
 

 

 

 

 

Low-temperature coal oxidation 

The low-temperature coal oxidation was simulated 

the same way as for the bleeder ventilation system, as 

described in the authors’ previous study (Yuan and Smith, 

2007). Here, only a brief description is provided. 

The chemical reaction between coal and oxygen is 

simplifi ed as: 

Coal + O2

 → CO2 + 0.1CO + heat of reaction 

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 

Rate = A[O2]n exp(-E/RT) 

where 

A is the pre-exponential factor, 

E is the apparent activation energy that is the energy 

needed to initiate a chemical reaction, 

R is gas constant, 

n is the apparent order of reaction, 

T is the absolute temperature and 

[O2

] is the oxygen concentration. 

In this study, the activation energy and pre-exponential 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. Schmidt found the value of the 

apparent order of the reaction (n) 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. 

To simulate the spontaneous heating of coal in longwall gob area, the source of coal needs to be defi ned. The 

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

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

2-m- (6.6-ft-) thick main coal seam was considered with a 

1-m- (3.3-ft-) thick rider sequence 1 m (3.3 ft) above the 

main coal seam. The rider seam was modeled as caving 

into the bottom of the gob after the main coal seam was 

completely mined out. 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 external and internal pore surfaces. 

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 surfaceto-volume ratio.An average coal particle diameter of 100 

mm (4 in.) and a surface-to-volume ratio of 36 m-1 were 

used in the simulations. The heat generated from oxidation will be dissipated by conduction and convection while 

the oxygen and oxidation products are transported by 

convection and diffusion. 

Methane emission 

Methane emission was also considered in the simulation because it affects the oxygen concentration distribuTable 1 

The physical and kinetic properties of the coal layer. 

Property Units Value 

Coal density kg/m3 1,300 

Coal specifi c heat J/kg-K 1,003.2 

Coal conductivity W/m-K 0.1998 

Heat of reaction kJ/mol-O2 300 

Activation energy kJ/mol 66.5 

Pre-exponential factor K/s 1.9×106 

Coal particle diameter mm 100 

Initial coal temperature K 300 

tion in the gob. Generally, the U.S. mines using bleederless 

ventilation systems liberate very little methane. The 

methane emission rate for one of these mines is about 

1,840 m3/d (65,000 cu ft/day) (MSHA, 2002). This value was used for methane emission from the overlying 

rider coal seam that caved into the bottom of the gob 

in this study, and the emission was assumed to reduce 

linearly with the distance away from the face towards 

the back end of the panel. These values were entered 

into FLUENT using C subroutines. If the same methane 

emission rate is maintained, the gob will eventually be 

full of methane. However, the time to reach this steady 

state could be several months long. Additionally, the 

coal oxidation is taking place. In this study, the methane emission and oxidation were assumed to start at 

the same time, which is closer to real situation and also 

represents the worst-case scenario. Figure 3 shows the 

steady-state methane concentration distribution in the 

gob.The methane concentration was 100 percent, except 

for the area close to the face. 

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 a thermal runaway. The time to reach a 

thermal runaway is called the induction time. When the 

coal temperature reaches 500° K (440° F), the spontaneous heating mechanism changes to rapid combustion 

FIGURE 3 

Steady-state methane concentration distribution in the 

gob (1 = 100 percent). 
FIGURE 4 

Temperature distribution (K) in the gob after 20 days: (a) 

in the whole gob and (b) near the face. 

(Babrauskas, 2003). Therefore, the simulations focused on 

the self-heating mechanism at temperatures below 500° 

K (440° F). 

Figure 4, (a) and (b), show the temperature distribution in the gob after 20 days. The maximum temperature 

at that time was only 302.8° K (85.4° F). The maximum 

temperature rise, 2.8° K (5° F), occurred in the corner of 

the gob between the face and the intake entry. There was 

very little or no temperature rise in the other areas.This is 

because oxygen was nearly all consumed by coal oxidation 

in the gob, as shown in Fig. 5. Only at the intake corner 

was enough oxygen supplied to maintain the spontaneous 

heating. This is much different from the case with a bleeder ventilation system, where temperature rise occurred 

along the face and behind the shields in the gob (Yuan and 

Smith, 2007). At any given time over 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 to as the maximum temperature in 

the gob at a given time. Figure 6 shows the maximum temperature versus time histories from the simulation compared with the case with the bleeder ventilation system. 

With the bleederless system, the maximum temperature 

was 302.8° K (85.4° F) after 20 days, while the maximum 

temperature reached 500° K (440° F) in eight days in the 

bleeder system simulation. The maximum temperature 

occurred at the corner on the headgate side for the bleederless system, while it occurred along the face and behind 

the face shields for the bleeder system. 

Effect of gob permeability. The gob permeability 

has a major effect on the spontaneous heating in the gob 

because it affects the quantity of air flowing into and 

through the gob. To examine the effect of the gob permeability on the spontaneous heating for the bleederless 

system, a simulation was conducted with the permeability 

increased 100 times. Figure 7 shows the maximum temperature versus time histories for the increased permeability 

simulations for the bleederless and bleeder systems. With 

the increased permeability, the maximum temperature 

reached 500° K (440° F) in about 22 days compared to 

only a 2.8° K (5° F) rise in the previous simulation for the 

bleederless system. Additionally, the induction time for 

the bleederless system simulation was reduced by 14 days 

compared with the bleeder system simulation. It should 

be noted that with the permeability increased 100 times, 

the temperature rise only occurred at the corner of the 

intake entry, shown in Fig. 8. 

Effect of resistance at collapsed entries. In this study, 

all entries inby the longwall face were treated as though 

they were collapsed, and the permeability and porosity 

at these areas were calculated using FLAC program. This 

represents a full compaction situation for these areas with 

large resistances. In reality, these entries may remain partially open and have much lower resistance, especially at 

the early stage of the panel life. It is important to simulate 

spontaneous heating with lower resistance value at these 

entries.A simulation was conducted with the permeability 

of the collapsed intake entry, backend entry and return 

entry set at 7 x 109 md, which was the value chosen for the 

middle entry in our previous simulation with the bleeder 

ventilation system (Yuan and Smith, 2007). Figure 9 shows 

the temperature distribution in the gob after 20 days from 

the simulation. The temperature rise still occurred at the 

corner of the intake entry but no longer directly behind 

the shields. The temperature rise, instead, occurred along 

the intake entry, because of lower resistance in the intake 

entry.The maximum temperature was about 315° K (107° 

F) after 20 days, compared to 302.8° K (85.4° F) for the 

case shown in Fig. 4, indicating a slightly higher rate of 

maximum temperature rise. 

Effect of nitrogen injection. Although the bleederless 

ventilation system appears to significantly reduce the rate 

FIGURE 5 

Oxygen concentration distribution in the gob after 20 

days (1 = 100 percent). 
 

of maximum temperature rise in the gob compared to the 

bleeder system, a thermal runaway could still occur under 

favorable gob conditions such as a high permeability and 

a reactive coal, as shown in Fig. 7. Certain types of control 

methods may be needed to reduce the hazard from spontaneous combustion fires. One method is nitrogen inertization 

in which nitrogen is injected into the gob to reduce the oxygen concentration to a value that cannot sustain coal oxidation. This method has been effectively used at the San Juan 

coal mine with a bleederless ventilation system (Bessinger 

et al., 2005). In Australia, CFD modeling and field tests were 

conducted to optimize inertization strategies to prevent 

heatings and fires in longwall gobs (Balusu et al., 2006). 

Using the simulation conditions and a pre-exponential 

factor of 3.8 x 106 K/s, which resulted in the temperature 

distribution shown in Fig. 8, the nitrogen was injected at the 

corner of the intake entry at nitrogen flow rates of 0.236 and 

0.472 m3/s (500 and 1,000 cu ft/min). This served to dilute 

the oxygen concentration of the air flowing into the corner 

of the gob. Figure 10 shows the maximum temperature versus time histories with nitrogen injections compared with 

no nitrogen injection for the case. For the 0.236 m3/s (500 

cuft/min) injection rate, the induction time was increased 

about two days, and the time to reach 500° K (440° F) was 

significantly increased.With the 0.472 m3/s (1,000 cu ft/min) 

injection rate, the induction time was increased about fi ve 

days, and the maximum temperature reached only 472° K 

(390° F) after 30 days. The location of the maximum temperature rise with nitrogen injection remained near the 

corner of the intake entry, the same as without nitrogen 

injection. As shown in Fig. 11, nitrogen was forced to fl ow 

in the direction of ventilation air at the corner of the intake 

entry. More work is needed to study how to effectively prevent spontaneous heating of coal at the corner of the intake 

entry using nitrogen injection. 

It should be pointed out that the ventilation system used 

in this study was an exhaust system. With the exhaust system, the exhaust fan sucks air from the face and the gob. A 

blowing system can also be used with the bleederless ventilation system.With the blowing system, air is blown into the 

face and the gob.This can pressurize the gob to some extent 

and push gases away from the face.The detailed implication 

of the blowing system on coal spontaneous heating process 

in the gob will be investigated in our future study. 

FIGURE 8 

Temperature distribution (K) in the gob with gob permeability increased 100 times. 

FIGURE 6 

Maximum temperature (K) versus time histories. 

FIGURE 7 

Maximum temperature (K) versus time histories with gob 

permeability increased 100 times. 

Conclusions 

CFD simulations were conducted on the spontaneous heating of coal in the gob area of a longwall panel 

with a bleederless ventilation system. In these simulations, the longwall face was stationary.The effects of gob 

permeability and resistance of the collapsed entries on 

the spontaneous heating in the gob were investigated. 

Simulation results demonstrate that under typical ventilation conditions, the bleederless system would greatly 

reduce the rate of temperature rise in the gob compared 

with the bleeder system. With the bleeder system, the 

temperature rise occurred along the face and behind 

the shields in the gob, while with the bleederless system, 

the temperature rise occurred only at the corner of the 

intake entry. 

With the increased permeability, the induction time 

to thermal runaway was reduced by 14 days. When the 

collapsed entries had a lower resistance, the temperature 

rise occurred still at the corner of the intake entry, but 

no longer directly behind the shields, instead along the 

intake entry.The rate of maximum temperature rise was 

also slightly increased. Nitrogen injection at the corner 

of the intake entry appears to increase the induction 

time of the spontaneous combustion, but the optimum 
 

 

 

 

 

 

 

 

 

locations and flow rates of nitrogen injections need to be 

determined in future simulations. 

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 permeability 

and porosity data used in this study with the longwall panel 

setup and ventilation conditions stated in the paper. ■

References 

Babrauskas, V., 2003, Ignition Handbook, Fire Science Publishers, 

Issaquash, WA. 

Balusu, R., Deguchi, G., Holland, R., Moreby, R., Xue, S., Wendt, M., 

and Mallett, C., 2002, “Goaf gas flow mechanics and development of gas 

and Sponcom control strategies at a highly gassy mine,” Coal and Safety, 

No. 20, pp. 35-45. 

Balusu, R., Ren, T., Humphries, P., O’Grady, P., and Havery, Y., 2006, 

“Proactive inertization to prevent heatings and fires in longwall goafs,” 

Coal International, Vol. 254, No. 3, pp. 30-37. 

Bessinger, S.L., Abrahamse, J.F., Bahe, K.A., McCluskey, G.E., and 

Palm, T.A., 2005, “Nitrogen Inertization at San Juan Coal Company’s 

Longwall Operation,” paper 05-032, presented at the SME Annual Meeting, Salt Lake City, UT. 

Carras, J.N., and Young, B.C., 1994, “Self-heating of coal and related 

materials: models, application and test methods,” Progress in Energy and 

Combustion Sciences, Vol. 20, pp. 1-15. 

DeRosa, M., 2004,“Analysis of mine fires for all U.S. underground and 

FIGURE 9 

Temperature distribution (K) in the gob with a lower 

resistance in collapsed entries. 

FIGURE 10 

Effect of nitrogen injection on the maximum temperatures in the gob. 

FIGURE 11 

Nitrogen concentration distribution in the gob after 20 

days with nitrogen injection rate of 0.236 m3/s (500 cuft/ 

min) (1 = 100 percent). 

surface coal mining categories, 1990-1999,” NIOSH Information Circular 

9470. 

DeRosa, M., 2007, personal communication. 

Esterhuizen, G.S., and Karacan, C.Ö., 2005,“Development of numerical models to investigate permeability changes and gas emission around 

longwall mining panels,” Process AlaskaRocks 2005, 40th US Symposium 

on Rock Mechanics, Anchorage, AK, June 5-26. 

Esterhuizen, G.S., and Karacan, C.Ö., 2007,“A methodology for determining gob permeability distributions and its application to reservoir modeling of coal mine longwalls,” SME 2007 Annual Meeting, Denver, CO. 

MSHA, 2002, MSHA Ventilation Specialists Training Course,“Bleeder 

and Gob Ventilation Systems,” Course of Instruction Series CI 42a. 

Rosema,A, Guan, H., and Veld, H., 2001,“Simulation of spontaneous 

combustion, to study the causes of coal fi res in the Rujigou Basin,” Fuel, 

Vol. 80, pp. 7-16. 

Saghafi,A., and Carras, J.N., 1997,“Modeling of spontaneous combustion in underground coal mines: application to a gassy longwall panel,” 

Proceedings of the 27th International Conference of Safety in Mines Research Institute, pp. 573-579. 

Saghafi, A., Bainbridge, N.B., and Carras, J.N., 1995, “Modeling of 

spontaneous heating in a longwall goaf,” Proceedings of the 7th US Mine 

Ventilation Symposium, pp. 167-172. 

Schmidt, L.D., and Elder, J.L., 1940, “Atmospheric oxidation of coal 

at moderate temperatures,” Industrial and Engineering Chemistry, Vol. 32, 

pp. 249-256. 

Smith,A.C., and Lazzara, C.P., 1987,“Spontaneous Combustion Studies of U.S. Coals,” Report of Investigations 9079, U.S. Bureau of Mines. 

Smith, A.C., Miron, Y., and Lazzara, C.P., 1987, “Large-scale Studies 

of Spontaneous Combustion of Coal,” Report of Investigations 9346, U.S. 

Bureau of Mines. 

Yuan, L., and Smith, A.C., 2007, “Computational fluid dynamics modeling of spontaneous heating in longwall gob areas,” preprint 07-101, presented at the SME Annual Meeting, Feb. 25-28, 2007, Denver, CO. 

Yuan, L., Smith, A.C., and Brune, J.F., 2006, “Computational fl uid dynamics study on the ventilation flow paths in longwall gobs,” Proceedings 

of the 11th U.S./North American Mine Ventilation Symposium, University 

Park, PA. 

Footnotes 1

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. 2

Reference to a specific product is for informational 

purposes and does not imply endorsement by NIOSH.