1 INTRODUCTION 

Continuous enhancements in longwall mining 

equipment have significantly improved face advance 

rates. This increasing longwall advance rate has 

generally outpaced the continuous miner development section advance rate. One potential solution is 

to decrease the relative amount of development mining required by increasing the size of longwall panels, in particular face lengths. However, increases in 

longwall face length can create problems such as increased cumulative face methane emissions and increased potential for methane-related production delays (Krog et al. 2006). This may be further 

exacerbated by the complex airflow movements 

along the face itself. Although airflow movement 

along the longwall face is generally assumed to be 

linear, evidence of exchanges between face and gob 

atmospheres have been noted (Balusu et al. 2001, 

Wendt and Balusu 2001). Other researchers have 

suggested an increased level of opportunity for air 

exchanges between face and gob regions result from 

resistant roof units and associated void spaces behind the longwall face (Noack 1998, Balusu et al. 

2001, Wendt & Balusu 2001). This hypothesis suggests that under certain roof conditions, increased 

longwall face lengths could also increase the void 

space behind the face. This increase in void space in 

the face and gob areas represents an increase in permeability. Most prior research regarding gob permeability addresses airflows in the bleeder entries between mined-out panels (Mucho et al. 2000) or 

characterizations within the longwall gob (Sing & 

Kendorski 1981; Brunner 1985; Karacan et al. 2005) 

and not the near face locations. 

This research effort was designed to address issues in predicting and configuring adequate longwall 

face ventilation when face lengths are increased. 

One goal of this study was to predict the magnitude 

of the increase in the face methane emission rates 

due to an increase in face length. A second goal was 

to characterize air and methane movements along 

the face, as well as the influence of the mining direction of the shearer and production delays, including 

methane delays, on face emission rates. With respect 

to the methane delays, an effort was made to identify 

any potential patterns or causes relative to how, 

when, and where they occur. A final goal was to 

learn how significant changes in the geology, mining 

practices (e.g. methane drainage) and mining conditions might affect methane emission rates. Achieving the goals of the study would increase the industry’s understanding of longwall face emissions and 

associated ventilation issues. Ultimately, the most 

important outcome sought in this research project 

was to enhance miner safety in the underground 

mining environment by reducing the frequency of 

hazardous accumulations of methane on longwall 

faces. 

Prediction of longwall methane emissions and the associated 

consequences of increasing longwall face lengths: a case study in the 

Pittsburgh Coalbed 

S.J. Schatzel, R.B. Krog, F. Garcia, & J.K. Marshall 

U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, National 

Institute for Occupational Safety and Health, Pittsburgh Research Laboratory, Pittsburgh, PA, USA 

J. Trackemas 

Pennsylvania Services Corporation, Foundation Coal Company, Waynesburg, PA, USA 

ABSTRACT: In an effort to increase productivity, many longwall mining operations in the U.S. have continually increased face lengths. Unfortunately, the mining of larger panels may increase methane emissions. 

The National Institute for Occupational Safety and Health (NIOSH) conducted a mine safety research study to 

characterize and quantify the methane emissions resulting from increasing face lengths in the Pittsburgh Coalbed. The goal of this research effort was to provide the mine operator with a method to predict the increase in 

methane emissions from the longer faces for incorporation of additional methane control capacity into the 

mine planning process, if necessary. Based on measured methane emission rates of 0.066 m3

/s (140 cfm) for a 

315 m (1032 ft) face, projected longwall face methane emission rates were 0.090 m3

/s (191 cfm) for a 366 m 

(1200 ft) face, 0.106 m3

/s (225 cfm) for a 426 m (1400 ft) face, and 0.124 m3/s (263 cfm) 488 m (1600 ft) 

face. 
2 METHODOLOGY 

2.1 Study site 

The field site for this study was a longwall coal mine 

operating in the Pittsburgh Coalbed in southwestern 

Pennsylvania. The mine operated three continuous 

miner development units and one longwall system. 

The annual production from the mine is approximately 5.9 million t (6.5 million short tons) per year, 

of which 5.0 million t (5.5 million short tons) are 

produced from the longwall mining system. Coal 

thickness at the mine ranged from 2.0 m (6.5 ft) to 

2.4 m (8.0 ft). The depth of cover in the study area 

ranged from 183 m (600 ft) in the headgate area to 

244 m (800 ft) in the tailgate area. The dimensions 

of the study panel were 3250 m (10,650 ft) long by 

315 m (1032 ft) wide (Fig. 1) (dimensions of the 

outlined coal block). The study began with 1250 m 

(4100 ft) of panel length remaining. This panel was 

the third panel mined in a longwall district containing five longwall panels. The longwall bleeder system was ventilated by the use of a centrifugal 

bleeder fan, and four vertical gob ventilation boreholes per panel placed at regularly spaced intervals 

of approximately 610 m (2000 ft) to provide additional methane control capacity. Four horizontal inseam methane drainage boreholes were also present 

adjacent to the gateroads of the study panel. 

Intake Air Shaft

Intake/Return 

Shaft Fan

Bleeder 

Shaft Fan

Figure 1. Longwall face emission study area. 

2.2 Experimental procedure 

The basic methodology for this study was first developed by Diamond and Garcia (1999) for a longwall face emissions investigation at two mines operating in the Pocahontas No. 3 Coalbed, VA. The 

goal of the Diamond and Garcia (1999) study was to 

predict methane emissions rates for 305 m (1000 ft) 

faces based on face emissions monitoring on a 229 

m (750 ft) wide face at the VP-1 and VP-3 mines 

(Fig. 2). In that study, continuous methane emissions 

monitoring was conducted near the headgate and 

tailgate corners. The face was divided into three 

equal segments of about 76 m (250 ft). Average cumulative methane emissions data for each of the 

three segments were plotted as a function of face 

length. Curves were fit to the actual emission data 

and were then extrapolated to the 305 m (1000 ft) 

face widths to predict methane emission rates on the 

longer faces. The data showed that the two mines 

would likely experience significantly different emission rate consequences in response to increasing the 

face lengths by about 76 m (250 ft). This was due to 

variations in mine design and methane control practices between the two mine sites. 

Figure 2. Prediction of methane emissions at greater longwall 

face lengths (Diamond & Garcia 1999). 

For this study in the Pittsburgh Coalbed, continuously recording methane monitors were installed 

along the 157 shields of the longwall face. The 

monitors were sampled at 5 sec. intervals, and 1-

minute average methane concentrations were recorded by data loggers. Airflow measurements were 

made at various locations on the face multiple times 

per shift to provide ventilation airflow measurements for the calculation of emission rates based on 

the methane concentration data. A production time 

study consisting of shearer location on the face (recorded as shield numbers) and shearer mining direction (head-to-tail or tail-to-head) was also conducted 

throughout the three days of the face emissions 

monitoring. One shift was monitored on each of the 

three days of the study. The duration and cause of all 

production delays, the face position at the start and 

end of each shift, the presence of any discernable 

geologic discontinuities or conditions encountered 

along the face, and any other pertinent data or observations were also noted as part of the time study 

record. 

To analyze the movement of methane emissions 

in the longwall ventilation airflow, the face was divided into four segments of equal length. Thus each 

face segment measured approximately 79 m (258 ft) 

(Fig. 3). Methane emission rates were determined 

for each face segment of each pass of the shearer using the associated methane concentration, ventilation 
airflow, and time study data. For this study, three 

continuously recording methane sensors were used 

for face methane monitoring. Since the principal focus of this study was longwall face ventilation and 

methane emissions, the decision was made to position the monitors away from the headgate and tailgate corners to avoid the inclusion of ventilation air 

in these areas which did not traverse the face. The 

methane sensors were installed at shields 20, 80, and 

145 (Fig. 3). The distances from the headgate corner 

to each monitoring location were 35, 158, and 290 m 

(114, 517, and 953 ft) for the 315 m (1032 ft) face 

(Fig. 3). 

TailgateHeadgate

Gob

S

Instrument

locations

290

(953)

157

(516)

35

(114)

315

(1032)

236

(774)

157

(516)

79

(258)

0

Face segment endpoints, distances from headgate

corner, m (ft)

4 3 2 1 (H-T)

(T-H)1a 2a 3a 4a

Face segment identities

Figure 3. Pittsburgh Coalbed longwall face emission study site 

with instrument locations and face segment identities. 

To analyze the acquired methane emissions data, 

the longwall face segments were designated as 1, 2, 

3, and 4, as numbered from the headgate for head-totail (H-T) passes, and were designated as 1a, 2a, 3a, 

and 4a, for tail-to-head (T-H) passes as numbered 

from the tailgate as shown in Figure 3. Average 

methane emission rates were computed for each of 

the face segments using simple algebraic formulas to 

determine the methane volume emitted, which was 

then divided by the time required to mine each face 

segment. Consequently, a total of four methane 

emission rates were computed for each pass of the 

longwall shearer in each direction. A sample face 

segment methane emission rate calculation is shown 

in Table 1. This sample shows methane emissions 

data from a shearer pass through face segment 3 

with no delays. Methane emissions measured during 

the mining of this segment are determined as the difference in emission rates at two continuously recording methane sensors, while the shearer position 

for each minute of mining is shown relative to the 

longwall shields. From this data, average methane 

emission rates can be determined for each segment. 

 All three methane sensors were used in this 

analysis, with the nearest downstream methane sensor used to compute the methane emission quantities. The transit time for ventilation air to flow along 

the longwall face was determined, and the duration 

of airflow from the end of a face segment to the sensors ranged from 0 seconds to about 1 minute in 

computing methane emission quantities. This airflow transit time along the face was ignored in the 

computations for the following reasons: 1) even the 

longest transport time (one-minute) to a methane 

sensor is small compared to the time required for the 

shearer to mine the segment, 2) according to the protocol, the methane produced in the mining of the 

face segment was measured after the shearer actually 

passed the methane sensor to allow time for the instrument to respond to methane in the airstream, and 

3) the recorded methanometer data were averaged 

over each minute of monitoring. 

Table 1. Sample calculation of emissions data for face segment 

3 acquired during day 1 of the face emissions study 

Time 

cutting 

face 

segment, 

h:min

Recorded 

shearer 

position, 

sheild 

number

CH4 

emission 

rate at start 

(sheild 80), 

m3

/s 

CH4 emission 

rate at end 

(sheild 145), 

m3

/s 

CH4 

emission 

during pass 

in face 

segment 3, 

m3

/s 

20:39 88 0.021 0.079 0.059

20:40 0.021 0.099 0.078

20:41 0.021 0.099 0.078

20:42 0.021 0.099 0.078

20:43 116 0.021 0.099 0.078

20:44 120 0.041 0.099 0.058

Due to the location of the recording methanometers (Fig. 3), face segments 1, 4, 1a, and 4a are actually shorter than the specified 79 m (258 ft) length. 

In segments 1 and 4a, all ventilation airflow passing 

across the segment reaches one or more of the methane sensors. For face segments 1a and 4, all of the 

ventilation airflow does not reach the sensors (Fig. 

3). Consequently, for face segments 4 and 1a, some 

assumptions were made based on general trends in 

the methane emissions data to determine methane 

emission quantities when the shearer was on the 

tailgate side of the methane sensor located on shield 

145 (Fig. 3). In applying this methodology, the following assumptions have been made to project 

methane emissions to longer faces: 1) the mine advance rate and the frequency of mining delays will 

occur at about the same rate; 2) face methane emissions are assumed to be constant within each segment; 3) all sources of methane emissions change at 

a constant rate with increased face length; and 4) the 

solutions are site specific for the Pittsburgh Coalbed, 

the ventilation configuration, and the methane drainage systems applied at the study mine site. 
3 RESULTS AND DISCUSSION 

3.1 Analysis of the methane emission data from the 

315 m (1032 ft) longwall face 

On the study panel, belt air was used on the longwall 

face (Fig. 4). After the shearer completed a T-H 

pass, sumped in, and began an H-T pass, methane 

carried to the face from the belt line made up the 

great majority of the methane measured at the shield 

20 methanometer. Under these circumstances, the 

data showed that methane emissions at the shield 20 

location frequently exceeded those at the shield 80 

location (i.e. non-linear airflow along the longwall 

face. Consequently, for analytical purposes, face 

emissions were assumed to be zero for the first 20 

shields of an H-T pass (up to 35 m, 114 ft from the 

headgate corner). Although this may not be a totally 

accurate assumption, data analysis indicated that the 

level of methane emissions in this portion of the face 

was quite low, usually measured as between 0.0 and 

0.021 m3

/s (0 to 44 cfm). This portion of the longwall panel is near the previously developed headgate 

entry, so there is a significant opportunity for the 

migration of methane out of this portion of the unmined solid coal block prior to mining. 

Fresh Air

Return/Bleeder Air

Face Air

Mining Direction

Mining Direction

Tailgate

Headgate

Gob

S

Belt entry

Figure 4. Ventilation configuration at study site. 

The sums of gas emissions from the eight face 

segments for the H-T and T-H passes were normalized to match actual gas emission totals measured at 

the shield 145 methane emissions monitor. A total of 

24 passes were analyzed and three of those passes 

were not complete data sets. No passes were eliminated from the data set due to production delays. A 

total of 27 methane-related delays were noted during 

the study: 4 on the first day, 11 on the second day, 

and 12 on the third day. Methane delays were typically of short duration, averaging about 7 minutes. 

Consequently, separation of data with methane delays to view only data showing uninterrupted passes 

was not possible because of the high percentage of 

passes affected by short duration methane delays. 

The cumulative methane emission rates for the 

face segments for each of the three days of the study 

are shown in Figure 5 and Table 2. Face methane 

emission rates were consistently higher by about 

41% in the H-T passes than in the T-H passes, in 

part because of the longwall face mining sequence 

which produced a much longer “wedge” cut towards 

the tailgate than towards the headgate entry and the 

slower shearer cutting rate in the T-H passes due to 

panline loading. Methane emissions were lowest on 

day 2, [0.042 m3

/s (88 cfm)] of the methane emission monitoring study and highest [0.061 m3

/s (129 

cfm)] on day 3 at shield 145. One contributing factor 

to the changes in methane emission rates over the 

course of the study is thought to be the proximity of 

gob vent boreholes (GVB’s) located near the tailgate 

side of the panel. The study area was approaching 

the maximum distance between gob vent boreholes 

(GVB’s), where the next borehole would be intercepted two days after the study was completed. This 

may account for a general increase in methane concentrations prior to the next GVB coming on line, 

GVB 46-4 (Fig. 6). 

0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

0 50 100 150 200 250 300 350

Distance From Headgate Corner, m

 Determined Cumulative Methane (CH4)

 Emissions, m3/s

0

20

40

60

80

100

120

140

160

180

0 200 400 600 800 1000

Ft

Cfm (CH4)

Day 1 H-T

Day 1 T-H

Day 2 H-T

Day 2 T-H

Day 3 H-T

Day 3 T-H

Figure 5. Cumulative longwall face methane emissions for the 

three days of monitoring. showing the face segments endpoints. 

Table 2. Cumulative face segment emission rates determined 

for each day of study. 

Face 

segments, H-T m3

/s (cfm) m3/s (cfm) m3/s (cfm)

1 0.007 (14) 0.010 (22) 0.020 (42)

2 0.016 (34) 0.016 (34) 0.053 (112)

3 0.050 (106) 0.035 (74) 0.067 (143)

4 0.081 (171) 0.046 (98) 0.088 (187)

Face 

segments, T-H 

1a 0.045 (96) 0.037 (78) 0.069 (147)

2a 0.036 (77) 0.032 (67) 0.059 (125)

3a 0.008 (17) 0.015 (32) 0.051 (109)

4a 0.000 (0) 0.009 (19) 0.027 (57)

Day 1 values Day 2 values Day 3 values 

The measured average daily methane emission 

rates varied from about 0.046 m3/s (98 cfm) to about 

0.088 m3/s (187 cfm) on head-to-tail passes over the 

three days of the study (Fig. 5) (Table 2). Production 

delays due to increasing methane concentration were 

most common when the shearer was near the tailgate 
side of the longwall face of the H-T pass, but began 

occurring with increasing frequency at locations 

nearer the headgate side of the face as the study progressed over the three days. An analysis of methane 

emissions from individual face segments (Table 3) 

suggests potential causes of this behavior. 

Figure 6. Actual portions of the study panel monitored for face 

methane emissions and associated methane drainage borehole 

locations. 

Table 3. Face segment emission rate data shown for combined 

averaged H-T, T-H passes. 

Face

 segments m3

/s (cfm) m3/s (cfm) m3/s (cfm)

1, 4a 0.003 (7) 0.010 (20) 0.023 (49)

2, 3a 0.009 (18) 0.006 (13) 0.029 (61)

3, 2a 0.031 (66) 0.018 (37) 0.011 (24)

4, 1a 0.020 (42) 0.008 (18) 0.016 (33)

Day 1 Day 2 Day 3

Average face methane emissions rates were calculated for each of the four face segments and each 

pass direction. These values varied during each pass 

and varied over successive days of the study. This 

variation in behavior can be viewed more clearly in 

Figure 7, which shows the average methane emissions from each segment alone (H-T and T-H combined data) during the three days of monitoring (Table 3). Figure 7 shows that the methane emissions 

produced during passes on day 1 were relatively low 

[from 0.003 to 0.009 m3

/s (7 to 18 cfm)] in the segments nearest to the headgate (1, 2, 3a, 4a). Emissions increased significantly in segments 3 and 2a

[0.031 m3

/s (66 cfm)], and diminished somewhat 

from that level toward the tailgate in segments 4 and 

1a. On day 2, methane emission rates in the near 

headgate segments 1 and 4a were higher than on day 

1 [0.010 m3

/s (20 cfm)], and then decreased in the 

next segments, 2 and 3a [0.006 m3

/s (13 cfm)]. Similar to day 1, methane emissions increased in face 

segments 3 and 2a [0.018 m3

/s (37 cfm)] and then 

decreased slightly in the face segments towards the 

tailgate, i.e. face segments 4 and 1a [0.008 m3

/s (18 

cfm)]. On day 3, methane emissions were much 

higher [0.023 m3

/s (49 cfm)] near the headgate face 

segments 1 and 4a than during the prior two days of 

the study (Table 3). The methane emissions rate increased in the next face segments [0.029 m3

/s (61 

cfm)] 2 and 3a, but then decreased significantly in 

face segments 3 and 2a [0.011 m3

/s (24 cfm)], with a 

slight increase [0.023 m3

/s (49 cfm)] in the tailgate 

segment face segments 4 and 1a (Fig.7). 

0.00

0.01

0.02

0.03

0.04

0 50 100 150 200 250 300 350

Distance from headgate corner, m

Methane emissions, m3/s

0

20

40

60

80

0 200 400 600 800 1000

Distance, ft

Methane, cfm

Day 1 Avg

Day 2 Avg

Day 3 Avg

3 Day Avg H-T pass

3 Day Avg T-H pass

Figure 7. Average methane emission rates for each day of 

study determined for each face segment (the zero emission 

value assumed for the start of segment 1 and the end of segment 4a have been omitted). 

Methane drainage via horizontal boreholes near 

the face emission study area may have contributed to 

the variable methane emissions characteristics observed on the face. Two horizontal boreholes produced gas from the Pittsburgh Coalbed on the longwall panel near the study area. One hole was drilled 

on each side of the panel, and the holes were oriented parallel to the gateroad entries, about 30 m (98 

ft) from the respective gateroads (Fig. 6). The holes 

were drilled towards the advancing face, and terminated in the study area. Prior to interception by mining, the holes were filled with water. 

On day 2 of the study, the presence of a horizontal borehole on the face was noted near the tailgate 

side of the panel at shield 140. On day 3 of the 

study, the interception of the horizontal borehole 

near the headgate at shield 23 was observed. It is 

likely that coalbed methane production from the first 

borehole encountered near shield 140 on the tailgate 

side of the face had decreased the methane content 

of the Pittsburgh Coalbed in the vicinity of the borehole. Consequently, after the borehole was intercepted on day 2 of the study, methane emissions 

dropped towards the tailgate side, as shown by the 

comparison of face segments 4 and 1a on day 1 

[0.020 m3

/s (42 cfm)] versus those on day 2 [0.008 

m3

/s (18 cfm)] (Fig. 7). A similar drop in methane 

emission rates was not observed in face segments 

near the head gate from day 2 and day 3 when the 

borehole hole was intercepted near shield 23 (Table 

3). It is not known if methane emissions would have 

diminished in the region of face segments 1 and 4a if 

the study had been continued for another day. Not 
all of the horizontal boreholes have the same time to 

produce gas prior to interception by longwall mining. 

Production delays also affected face methane 

emission rates. Production delays, including those 

due to high methane emissions result in lower calculated pass segment methane emission rates because 

the time to complete the pass segment increases 

while the longwall face equipment is idle. Therefore, 

the increased number of methane-related production 

delays on day 3, and to a lesser extent on day 2, resulted in lower average methane emission rates on 

some individual pass segments, particularly on tailgate side face segments 4 and 1a (Fig. 7). Although 

day 3 of the study produced the highest cumulative 

methane emission rates for complete passes, these 

values would have been even higher had the methane-related delays not occurred, which resulted in 

reduced average emission rates on those individual 

pass segments. 

3.2 Predicting methane emission rates for longer 

longwall faces in the Pittsburgh Coalbed 

Graphs of the cumulative measured average methane 

emission rates for the 315 m (1032 ft) panel face 

segments in both the H-T and T-H directions are 

shown in Figure 8. From these data, two leastsquares linear regression curves were calculated to 

predict methane emissions for longer face lengths of 

366 m (1200 ft), 426 m, (1400 ft) and 488 m (1600 

ft) in the Pittsburgh Coalbed. To create trend line A, 

all H-T and T-H passes were averaged and then an 

overall average emission pass plot was created. 

Trend line A was fit to this overall average emission 

pass data (Fig. 8). Trend line A predicts face emission rates of 0.077 m3

/s (163 cfm), 0.091 m3/s (193 

cfm), and 0.106 m3

/s (225 cfm), for face lengths of 

366 m (1200 ft), 426 m, (1400 ft) and 488 m (1600 

ft), respectively (Table 4). The equation for trend 

line A is given (in metric units) and the R2

 value of 

the curve fit to the data is 0.993. It should be noted 

that the emission rate for a 315 m (1032 ft) face is 

based on a projection of the cumulative emissions 

data from the face segments projected from shield 

145 to shield 157 or 290 m (953 ft) from the 

headgate corner using data from all of the longwall 

passes. Trend line B was fit to the H-T passes only 

(Fig. 8). Since most of the delays occurred and 

higher face methane emission rates occurred on the 

H-T passes, this plot may be more representative of 

problematic concentrations of face gas than trend 

line A, which includes the generally lower T-H pass 

face emission rate data (Fig. 8). Using trend line B, 

with an R2

 value of 0.983, to predict methane emissions on longer longwall faces for lengths of 366 m 

(1200 ft), 426 m, (1400 ft), and 488 m (1600 ft) 

yields 0.090 m3

/s (191 cfm), 0.106 m3/s (225 cfm), 

and 0.124 m3

/s (263 cfm), respectively, as compared 

to the 0.066 m3

/s (140 cfm) value for the base 315 m 

(1032 ft) panel (Table 4). 

y = 0.0002329x - 0.00783

R2

 = 0.993

y = 0.0002784x - 0.0123

R2

 = 0.983

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0 100 200 300 400

Distance From Headgate Corner, m

Determined Cumulative Methane (CH4)

 Emissions, m3/s

0

20

40

60

80

100

120

140

160

180

200

220

240

260

280

0 200 400 600 800 1000 1200 1400 1600

Ft

Cfm (CH4)

3 Day Avg all passes

3 Day Avg H-T pass

3 Day Avg T-H pass

Trend line A (3 Day Avg

All passes)

Trend line B (3 Day Avg

H-T pass)

Figure 8. Methane emission prediction curves for the Pittsburgh Coalbed; trend line A based on average emission data; 

trend line B based on H-T pass emission data. 

Table 4. Face methane emission predictions based on projections made from face segment methane emissions determinations. 

Face 

segments m (ft) m3

/s (cfm) m3/s (cfm) 

1, 4a 79 (258) 0.012 (26) 0.012 (26)

2, 3a 157 (516) 0.026 (56) 0.028 (60)

3, 2a 236 (774) 0.047 (99) 0.051 (107)

4, 1a 290 (952) 0.061 (129) 0.072 (152)

projection 315 (1032) 0.066 (140) 0.075 (159)

projection 366 (1200) 0.077 (163) 0.090 (191)

projection 426 (1400) 0.091 (193) 0.106 (225)

projection 488 (1600) 0.106 (225) 0.124 (263)

Distance from 

headgate corner 

Average 3 day pass 

combined H-T, T-H 

data

Average 3 day 

H-T passes only

4 SUMMARY AND CONCLUSIONS 

It should be noted that the results of this study to 

predict longwall face methane emissions at increasing face lengths is site specific and includes all delays which occurred during the monitoring period. 

Due to the higher rate of face methane emissions 

measured during H-T passes, linear trend line B was 

fit to only the averaged H-T passes, and is considered a better predictor of hazardous methane emission conditions on longer faces at the study site than 

an analysis using all of the data. Using trend line B 

developed from the H-T pass data, longwall face 

lengths of 366 m (1200 ft), 426 m (1400 ft), and 488 

m (1600 ft) were predicted with an R2

 value of 

0.983. Using trend line B, the predicted face methane emissions represent increases of 36%, 61%, and 

88% for 366 m (1200 ft), 426 m (1400 ft), and 488 

m (1600 ft) faces respectively, as compared to the 

base 315 m (1032 ft) face. 

This methodology allowed for the computation of 

a total of eight methane emission rates from head-totail (H-T) and tail to head (T-H) passes. Analysis of 

the monitoring data suggests that horizontal methane 
drainage boreholes appeared to be effective in reducing methane emissions from the face in the vicinity 

of the borehole near the tailgate. A similar borehole 

intercepted near the headgate on day 3 did not appear to reduce emissions, but a subsequent day of 

face emissions monitoring was not conducted that 

could have confirmed that boreholes impact. The 

data also showed evidence of non-linear airflows, 

i.e. interactions of the longwall face air with airflows 

behind the shields. This was evident where belt air, 

carrying methane from the transported cut coal, increased concentrations near the headgate, while 

lower methane concentrations were measured at the 

mid-face location. Methane delays were most frequent when the shearer was mining near the tailgate. 

Methane delays on the longwall face increased in 

number from the first to third day of the study as the 

longwall face reached the approximate maximum 

distance from the nearest operating gob vent borehole (GVB) prior to interception of the next GVB, 

two days after the completion of the study. 

With the determination of multiple emission rates 

over the length of a longwall face, the described 

method provides insight into changing emissions 

rates along the face due to all influential factors. The 

authors suggest that for projected increased methane 

emissions on wider panels, the methodology described by Krog et al. (2006), using this same data 

set in a companion paper, represents a more rigorous 

analysis of the methane source components contributing to the projected increased methane emissions. 

Thus, this companion analysis provides additional 

insights on appropriate control measures to address 

the projected increases in methane emissions, although it should be noted that both are empirical in 

nature and site specific. The longwall face methane 

emission predictions made by Krog et al. (2006) using the same data set are of greater magnitude than 

predictions appearing in this report. The primary 

reasons for differing face emissions predictions are: 

1) the predictions made by Krog et al. were for peak 

load conditions and the predictions appearing here 

are for averaged data, and 2) the predictions made 

by Krog et al. were for an “idealized” cut sequence 

with no delays where the methane predictions in this 

analysis included all production delays occurring in 

the data set. 

Providing scientific predictions of the methane 

emission consequences of implementing mine design changes, such as increasing longwall panel face 

lengths, was the primary goal of this research effort. 

With these methane emission predictions, adequate 

engineering and administrative controls can be implemented in advance to ensure that the underground 

workforce is not exposed to potentially hazardous 

concentrations of methane. Mine designers and ventilation engineers have several options at their disposal to deal with the higher emissions associated 

with increased longwall face length, such as increasing face ventilation airflow, utilizing or increasing 

methane drainage capacity, and ventilation system 

changes, or as a last, reducing the mining rate on the 

longwall. 

5 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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