1 INTRODUCTION 

The coal industry trend of mining wider longwall 

panels is continuing throughout the world as 

gateroad development mining struggles to keep 

ahead of production on the longwall face. The mining of longer longwall faces has the advantage of 

less development mining per ton of coal mined on 

the longwall, but can result in increased methane 

emissions. The question asked by ventilation engineers is how much of an increase in methane emissions can be expected with the longer longwall face, 

and how can this be mitigated to maintain a safe underground workplace? An increase in the ventilation 

airflow to dilute the expected increase in methane 

emissions might not be possible because many modern longwalls are at, or near, the reasonably practical 

airflow limits. Therefore, the extra methane emissions will generally have to be handled by a combination of increased ventilation airflow, methane 

drainage and/or production management. 

As part of its mining health and safety research 

program, NIOSH conducted a detailed longwall 

methane emission and mining time study at a mine 

operating in the Pittsburgh Coalbed in southwestern 

Pennsylvania. The initial goal of the experiment was 

to determine the methane emissions from individual 

sections of the longwall face and to extrapolate that 

data to estimate emissions from a longer longwall 

face. Using this approach, the face is divided into 

segments to characterize how methane emission 

rates vary across the face (Diamond & Garcia 1999, 

Schatzel et al. 2006). A graphical solution is then 

used to predict face emissions at longer face lengths 

based on emissions data from shorter faces. One 

shortcoming of this approach is that it assumes that 

the defined segments of the longwall face will continue to emit methane at the same rate with increasing face length. The assumption that a 244 m (800 

ft) long longwall face will have the same methane 

emissions as encountered at the 244 m (800 ft) ft 

point on a 305 m (1000 ft) long face is incorrect because of the variations in coal production, methane 

emission drainage characteristics and coal transport 

factors. 

A detailed and more meaningful analysis of the 

methane sources and their individual contributions to 

the total longwall methane emissions can be obtained from methane concentration data collected at 

the beginning and end of the longwall face, along 

with the shearer location and other relevant ventilation and mining data. The methane emission contributors from the mining of a longwall face that 

were evaluated for this study are: 1) gas released 

from the coal broken by the shearer, 2) gas emitted 

from the broken coal on the face conveyor, 3) gas 

emitted from the coal transported on the belt, and 4) 

background gas emitted from the coal face and from 

the adjoining ribs in the intake airway gateroad entries. Once the methane contributions from the various sources have been defined for an actual longwall 

cutting sequence, the methane emissions from an 

ideal (i.e. delay-free) cut sequence can be predicted. 

The calculated methane emission contributions can 

Predicting methane emissions from longer longwall faces by analysis of 

emission contributors 

R.B. Krog, S.J. Schatzel, 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, Pennsylvania, 

USA 

ABSTRACT: As part of its mining health and safety research program, the National Institute for Occupational Safety and Health (NIOSH) conducted a longwall methane emission and mining time study at a mine 

operating in the Pittsburgh Coalbed to access the methane emission consequences of mining a longer face. 

The methane emission contributors from the mining of a longwall face are: 1) gas released from the coal broken by the shearer, 2) gas emitted from the coal on the face conveyor, 3) gas emitted from the coal transported 

on the belt, and 4) background gas emitted from the coal face and from the adjoining ribs. Based on the results of the study, a set of site-specific mathematical formulas and constants were developed to characterize 

each of the four longwall emission contributors. The mathematical formulas were then applied to longer 

longwall face mining scenarios to predict the methane emissions from these faces. 
then be extrapolated to longer longwall faces, taking 

into account the variations in coal production and 

transport factors, to more accurately predict future 

methane emission rates from longer longwall faces. 

2 METHODOLOGY 

2.1 Underground field study 

Methane concentrations were continuously monitored and recorded on the longwall face for one production shift per day (of the 2 production shifts per 

day) for three consecutive days. There were a total 

of 157 shields on the 315 m (1032 ft) longwall face. 

The methane monitors were located at the 20th, 80th,

and 145th shield locations. Multiple methane sampling concentration values were measured and recorded as an averaged value for each minute. Periodic ventilation airflow measurements were made 

along the longwall face at the location of the methane monitors and at other key locations in the study 

area. The location of the shearer was recorded as 

part of the time study, which also included the time, 

duration, and reason for any mining delays due to 

the following factors: gas, belt problems, face conveyor problems (rock jam), calibration of methane 

sensors, and miscellaneous other problems. 

The methane monitors for this study were located 

at shields number 20, 80 and 145. These positions 

were chosen based on previous studies that indicated 

possible air interactions at the corners of the head 

and tailgate (Diamond & Garcia 1999). Some of the 

headgate air for the first few shields on the longwall 

face can flow behind the shields before reaching the 

longwall face. Airflow from behind the tailgate 

shields can be pulled into the main exhaust system at 

various locations along the face, or face ventilation 

air can travel behind the shields into a bleeder system. This complex interaction of longwall face ventilation airflow and airflow behind the shields was to 

be reduced by the placement of methane sensors approximately 37 m (121 ft, shield 20) from the 

headgate corner and 21 m (69 ft, shield 145) away 

from the tailgate corner of the panel. The methane 

contribution interpretation does not take into account 

the possible effect of ventilation airflow interactions 

with the gob, which is consistent with the initial goal 

of the study. 

2.2 Site specific information 

The physical aspects, equipment, operational, and 

ventilation scenarios of the longwall panel (Fig. 1) 

are very important to the evaluation of methane 

sources because they determine the mathematical 

formulas used in the methane contribution model. 

The site-specific variables for this study are as follows: 

− Three entry gateroad development [#1 belt (intake), #2 track (intake), #3 (return)] on the 

headgate 

− Previous longwall panel mined on the tailgate 

side 

− Exhaust ventilation via bleeder fan 

− Bi-directional cut sequence 

− Shearer depth of cut (web), 1.07 m (42 in) 

− Some intake air brought to face via belt airway , 

therefore, belt coal methane component to account for 

− Panel width (edge-to-edge), 315 m (1032 ft) 

− Original panel length, approximately 3048 m 

(10,000 ft) 

− Remaining panel length at the time of the study, 

1195 m (3920 ft) 

− Longwall face height, 2 m (6.5 ft) 

− Shield width, 2 m (6.5 ft) 

− Total number of shields, 157 (#1 is at the 

headgate and #157 is at the tailgate) 

− Shearer average cut speed, 14 m/min (46 ft/min) 

− Face conveyor length, 315 m (1032 ft) 

− Face conveyor speed, 1.78 m/s (353 ft/min) 

− Longwall face average airflow velocity, 2.54 m/s 

(500 ft/min) 

− Belt speed, 4.06 m/s (800 ft/min) 

− Belt airflow average velocity (intake), 1.93 m/s 

(380 ft/min) 

− The shearer’s location recorded at the location of 

the headgate drum 

Intake Air Shaft

Intake/Return 

Shaft Fan

Bleeder 

Shaft Fan

Figure 1. Study area for longwall face emission investigation. 

2.3 Assumptions 

Methane content of the coal is assumed to be consistent across the longwall face and consistent along the 

# 1 belt rib. No decay function for the components 

sources was modeled because the accuracy of the 

methane readings did not support such detail. Thus, 

the following assumptions have been applied to this 

study: 

− Background methane emissions from the longwall face (active, not idle) are linearly dependent 

on longwall face length. 
− Background rib methane emission from the #1 

belt entry are linearly dependent on the remaining 

length of the longwall panel, but are independent 

of longwall face width or activity. 

− There is no significant interaction between the 

face air and the air in the gob. 

− Stage loader located at the headgate was not incorporated in the simulation. 

− Methane liberation rate at the shearer is proportional to the cut coal volume. 

− Methane liberation rate on the face conveyor is 

proportional to the coal tonnage × elapse time on 

the conveyor. 

2.4 Construction of formulas 

The calculations for the methane contribution model 

are empirical, and site-specific for the longwall 

panel, but the concept can be generally applied to 

other longwall panels. Since the location of the 

longwall shearer is known from the time studies, the 

change in shearer location and the depth of cut can 

be used to determine the volume of coal mined during each minute. The face conveyor and belt speeds 

are known, so the transportation times of the coal after cutting can be determined. The ventilation airflow rates along with the width and remaining length 

of the longwall panel determine the transit time of 

the airflow across the longwall face and for the belt 

entry. 

The following describes the mathematical process 

used in the evaluation. The longwall face was broken down into 61 meter sections (200 ft) to correspond with the width of 30 shields. Since the face 

conveyor speed was 1.78 m/s (350 ft/min), the transport time for coal over 61 m (200 ft) of the face conveyor was (61 m / 1.78 m/s) = 34 seconds, and the 

transport time for the counter flowing ventilation airflow was (61 m / 2.54 m/s) = 24 seconds. Therefore, 

the time for the coal to be transported by the face 

conveyor and the time required for the counter flowing air to transit the same distance adds up to 58 

seconds, which was rounded to 1 minute to match 

the methane concentration readings recorded every 

minute. The emission times for methane from the 

sources of interest as well as transit times for the associated ventilation airflows can be summarized as 

follows: 

− Coal cut by Shearer, 0-2 minutes 

− Coal on face conveyor, 1-3 minutes 

− Airflow along longwall face, 2 minutes 

− Coal on belt, 5 minutes 

− Airflow along belt, 10 minutes 

Therefore, when the shearer is cutting coal, the 

liberation of methane from the coal face will be recorded by the methane monitor located near the tailgate at shield 145, either instantly or up to 2 minutes 

later, depending on the shearer’s location. If the 

shearer is located on the tailgate side of shield 145, 

no extra methane liberated by the shearer will be recorded by the methane monitor. If the shearer is located within 61 m (200 ft) on the headgate side of 

shield 145, then methane liberation due to the cutting of the coal will be recorded for that minute. If 

the coal was cut nearer the headgate, it would take 

up to 2 minutes for the face air to travel to the methane sensor located at shield 145. 

The contribution of methane emissions from the 

coal on the face conveyor is more complicated because coal cut by the shearer can be transported on 

the face conveyor for 1 to 3 minutes. To determine 

the transport time for methane emissions from the 

coal on the face conveyor, the counter flowing 

longwall ventilation airflow and the shearer location/direction-of-travel must be taken into account. 

As an example, coal cut at shield 145 will release 

methane that will be recorded at shield 145 instantly 

(0 minutes). Coal transported on the face conveyor 

will release gas into the face ventilation airflow for a 

total of 3 minutes (0-2 minutes), during which time 

the counter flowing face ventilation will take up to 2 

minutes to reach shield 145, so methane emitted 

from the coal on the face conveyor will be recorded 

at shield 145 for 0-4 minutes in this example. 

Continuing this example, methane emissions 

from the coal on the belt will be recorded at shield 

145 for 5-19 minutes after coal was initial cut at 

shield 145 (2 minutes for the face conveyor, 2 minutes for the face airflow transit time, 1-5 minutes for 

the belt transport time, and 0-10 minutes for the belt 

airflow transit time). Therefore, coal mechanically 

cut by the shearer will affect methane emission levels near the tailgate instantly, and for as long as 19 

minutes after being cut. 

The contributions of methane from individual 

sources over time lead to a simple set of five linear 

equations for shearer, face conveyor, belt, background emissions from the coal face and background 

emissions from the adjoining ribs in the intake 

gateroads, which were solved for each minute of the 

three shifts monitored. Constants in each equation 

were calculated by least-squares, linear regression 

such that the calculated results best matched the actual readings at shields 20 and 145. 

The shield 20 data led directly to calculations of 

the background emission for the #1 belt entry intake 

rib. The total background emission at shield 145 minus the contribution from the belt yields the estimated background component from the longwall 

face alone. Longwall production delays in the cutting sequence are used to define the methane emissions associated with individual component sources. 
3 RESULTS 

The calculated emission constants for each of the 

methane contributor components for each day of the 

study are shown in Table 1 including a three-day average value for these constants. Note that when both 

shield 20 and 145 are used to calculate the constants, 

the background methane emissions can be separated 

into the longwall face and intake rib components by 

the difference between the shield 145 and shield 20 

values. During the evaluation it was determined that 

the readings from the methane sensor at the shield 

80 location were erratic and gave conflicting results 

indicating incorrect data received from this sensor. 

Therefore, constants have only been calculated for 

the shield 20 and 145 locations. 

Table 1. Calculated constants for the emission component 

Conveyor Belt Shearer Background Background

Location used Shield 145 Shield 20

Day 1 Shield 145 only 6.16 1.85 9.03 119

Shield 20 & 145 6.51 1.63 7.95 129 -6

Shield 20 only 8.82 1.42 2.95 1

Day 2 Shield 145 only 4.20 1.99 5.10 123

Shield 20 & 145 4.07 1.55 3.48 149 5

Shield 20 only 4.69 1.12 4.26 24

Day 3 Shield 145 only 4.97 2.40 7.15 194

Shield 20 & 145 6.64 0.72 7.34 246 86

Shield 20 only 6.20 0.51 7.23 94

3-Day Average

Shield 145 only 5.11 2.08 7.09 146

Shield 20 & 145 5.74 1.30 6.26 175 28

Shield 20 only 6.6 1.0 4.8 40

The calculated emission constants are consistent 

for the three days of the study, except for the background methane levels at shield 20. The background 

at shield 20 represents the methane load from the intake ribs, which should be fairly consistent. However, this value varied considerably over the three 

days of the study, starting out as a minor negative 

value in day one, to a high positive value in day 

three. The reason for this dramatic increase is most 

likely caused by the intersection of a horizontal degas hole located outby and up wind of the shield 20 

methane sensor. The background rib value at shield 

20 for day one, calculated using data from both sensors, results in a small negative value, which translates to only 0.0014 m3

/s (3 cfm). After considering 

the consistency of the emission constants for the 

other three components (face conveyor, belt, and 

shearer) from shields 20 and 145 individually and 

combined, it was decided to use the three-day average for shields 20 and 145 for further evaluation of 

the background emission component. Using the average for shield 20 and 145 will also separate the 

background emission component into its two parts 

(i.e. methane emissions from the face and from the 

intake ribs), thereby giving a more accurate prediction for longer face lengths. 

The calculated average methane emission rates 

for each contributor are shown in Tables 2 and 3. 

Table 2 shows the methane contributors solved using 

the daily constants for shields 20 and 145. Table 3 

shows the methane contributors solved using the 

three-day average constants for shields 20 and 145. 

The ‘total’ values in Table 2-3 are the calculated average methane for the individual days. The ‘actual’ 

values are the recorded methane for the individual 

days, and in Table 3, they do not exactly match the 

calculated ‘total’ values. 

Table 2. Daily methane emission contributor averages and percentages using daily shield 20 & 145 constants (top of table 1). 

Shield 20 & 145 Conveyor Belt Shearer Face Rib Total Actual

Daily results (m3

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

Day 1 0.012 0.015 0.005 0.027 -0.001 0.057 0.057

Day 2 0.005 0.014 0.004 0.028 0.002 0.052 0.052

Day 3 0.007 0.006 0.005 0.030 0.019 0.068 0.068

Average 0.008 0.012 0.005 0.029 0.006 0.059 0.059

Shield 20 & 145 Conveyor Belt Shearer Face Rib Total Actual

Daily results (cfm) (cfm) (cfm) (cfm) (cfm) (cfm) (cfm)

Day 1 26 31 10 57 -3 121 121

Day 2 11 29 8 60 3 111 111

Day 3 15 14 11 64 40 143 143

Shield 20 & 145 Conveyor Belt Shearer Face Rib Total Actual

Daily results (%) (%) (%) (%) (%) (%) (%)

Day 1 22% 26% 8% 47% -3% 100% 100%

Day 2 10% 26% 7% 54% 3% 100% 100%

Day 3 10% 9% 8% 45% 28% 100% 100%

Average 14% 20% 8% 49% 9% 100% 100%

Table 3. Daily methane emission contributor averages and percentages using average three-day shield 20 & 145 constants 

(bottom of table 1). 

Shield 20 & 145 Conveyor Belt Shearer Face Rib Total Actual

3-Day average (m3

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

Day 1 0.011 0.012 0.004 0.028 0.006 0.061 0.057

Day 2 0.010 0.012 0.004 0.028 0.006 0.060 0.052

Day 3 0.008 0.010 0.003 0.028 0.006 0.056 0.068

Average 0.010 0.011 0.003 0.028 0.006 0.059 0.059

Shield 20 & 145 Conveyor Belt Shearer Face Rib Total Actual

Average results (cfm) (cfm) (cfm) (cfm) (cfm) (cfm) (cfm)

Day 1 23 25 8 60 13 129 121

Day 2 21 25 8 60 13 127 111

Day 3 18 21 6 60 13 119 143

Shield 20 & 145 Conveyor Belt Shearer Face Rib Total Actual

3-Day average (%) (%) (%) (%) (%) (%) (%)

Day 1 19% 20% 7% 49% 11% 106% 100%

Day 2 19% 22% 7% 54% 12% 114% 100%

Day 3 13% 15% 4% 42% 9% 83% 100%

Average 17% 19% 6% 48% 11% 101% 100%

3.1 Gas delays 

The background face and rib emissions represent 

about 59% of the total daily emissions; however, this 

is somewhat misleading because these emissions 

continue throughout the entire shift, including during 

mining delays. In contrast, the shearer, face conveyor, and belt emissions are intermittent sources 

(i.e. they are only a factor during active mining on 

the face and during coal transport), but they are the 

primary contributor to longwall face gas delays, as 

shown in Table 4. 

The calculated methane contributions (Table 4) 

clearly show that the head-to-tail passes experience 

higher methane concentrations than the tail-to-head 
passes. The time study data for the three days of the 

study showed 19 gas delays (shutdowns of mining 

equipment due to excessive methane concentrations) 

on 10 of the 11 head-to-tail passes. The average location for the gas delays on the head-to-tail passes 

was at about shield 119, 245 m (804 ft), or 78% of 

the distance down the longwall face from the 

headgate corner. 

Table 4. Methane contribution percentages from longwall 

emission contributors during gas delays compared to daily averages for a 315 m (1032 ft) longwall face. 

Methane contributions Conveyor Belt Shearer Background

Three day averages 17% 19% 6% 59%

Gas delays No.

Cutting gas delays 23 32% 18% 9% 42%

Head-to-Tail gas delays 19 33% 18% 9% 41%

Tail-to-Head gas delays 4 26% 18% 8% 48%

There were four gas delays recorded on three of 

the nine tail-to-head passes. The average location for 

the gas delays on the tail-to-head passes was at about 

shield 71, 146 m (480 ft), or 46% of the distance 

down the longwall face from the headgate corner. 

The average duration for all 23 gas delays was seven 

minutes irrespective of cutting direction. 

The relative contribution of the components of 

the average daily methane emissions is not as significant as it is the relative contribution of the components in the peak levels that causes gas delays. 

Table 4 shows that during the periods of gas delays, 

the methane contributions from the face conveyor 

and shearer dramatically increase in total percentage. 

3.2 Cutting direction and delays 

The direction of cutting is very important to methane 

emissions on the longwall face because at the end of 

a head-to-tail pass, the face conveyor, shearer, and 

belt are all contributing gas at or near their maximum rate. The tail-to-head passes do not have coincidental maximums for face conveyor, shearer, and 

belt emissions, so a more consistent emission rate 

occurs over the entire cut sequence, which explains 

the less frequent gas delays on tail-to-head passes. 

Of the 11 head-to-tail passes over the three shifts 

that were monitored for this study, not one full speed 

cut was made without a gas delay. The first head-totail pass on day one had two belt delays. The remaining 10 cuts all had gas delays. Of the nine tailto-head passes, three had gas delays, three were cut 

at a slower speed for unknown reasons, and three 

were cut full speed without any delays. 

Figures 2-6 show the calculated methane contributor components for day one using the three-day 

average constants of shield 20 and 145 from Table 1. 

The calculated methane contribution is a multiplication of the three-day average constant of shield 20 

and 145, and the formula results for each minute for 

day one. Figure 2 shows the actual methane emissions measured at shield 20 and 145, and the 

shearer’s location for day one. Figure 3 shows the 

calculated shearer and conveyor emissions for day 

one along with the shearer’s location. Figure 4 

shows the belt and background emissions along with 

the shearer’s location. 

0.00

0.02

0.04

0.06

0.08

0.10

17:00 18:00 19:00 20:00 21:00 22:00 23:00 0:00

Time

Methane Emissions m3/s

0

50

100

150

200

250

Methane Emisions cfm

Shearers' Shield Location

Shearer Location

Measured Methane Shield 145

Measured Methane Shield 20

Figure 2. Recorded methane emission data at shield 20 and 145 

and shearer’s location, study day one. 

0.00

0.02

0.04

0.06

0.08

0.10

17:00 18:00 19:00 20:00 21:00 22:00 23:00 0:00

Time

Methane Emissions m3/s

0

50

100

150

200

250

Methane Emissions cfm

Shearers' Shield Location

Shearer

Shearer Location

Face Conveyor

Figure 3. Calculated shearer and face conveyor coal transport 

methane contribution based on the shearer’s location, study day 

one, 315 m (1032 ft) face. 

0.00

0.02

0.04

0.06

0.08

0.10

17:00 18:00 19:00 20:00 21:00 22:00 23:00 0:00

Time

Methane Emissions m3/s

0

50

100

150

200

250

Methane Emissions cfm

Shearers' Shield Location

Shearer Location

Background

Belt

Figure 4. Calculated belt coal transport and background methane contributions based on the shearer’s location, study day 

one. 

Figure 5 shows all components and the calculated 

total methane emissions for day one. Figure 6 shows 

the calculated vs. measured methane for shield 145 
during day one, along with the four gas delays that 

correspond to the to the high methane emissions. 

0.00

0.02

0.04

0.06

0.08

0.10

17:00 18:00 19:00 20:00 21:00 22:00 23:00 0:00

Time

Methane Emissions m3/s

0

50

100

150

200

250

Methane Emissions cfm

Shearer Calculated Background

Belt Face Conveyor

Figure 5. Calculated individual methane contributors and total 

calculated methane emissions for study day one. 

0.00

0.02

0.04

0.06

0.08

0.10

17:00 18:00 19:00 20:00 21:00 22:00 23:00 0:00

Time

Methane Emissions m3/s

0

50

100

150

200

250

Methane Emissions cfm

Measured

Calculated Belt Delays

Gas Delays

Figure 6. Calculated vs. actual measured methane emissions, 

315 m (1032 ft) longwall face, study day one, using the threeday average, including four gas delays. 

3.3 Predicting methane emissions on longer 

longwall faces 

Simply determining the methane emissions at the 

corner of the tailgate and then linearly extrapolating 

the results to longer faces does not take into account 

the effect of coal production and transport factors. 

The simple assumption that a longer face will only 

have increased background face emissions and no 

contribution from the other components (shearer, 

face conveyor, belt) is incorrect, because productivity (coal volume mined/hour) will be increased for a 

longer face since the cut cycles are face length dependent. The mine used a bi-directional cut sequence. At longer face lengths, the wedge/sumping 

times are assumed to be the same as for the base 

case, but the cutting times will increase proportionally to the face length, minus the sumping distance. 

Assuming that the longwall face conveyor can 

keep up with the shearer and the shearer cuts at the 

same speed over the greater face length, it then follows that the productivity of the shearer will increase 

because a greater percentage of time will be allotted 

to cutting, than sumping. Therefore, the total methane liberation from the mined coal during a shift 

would increase, but the shearer’s emission rate during cutting will remain the same for a longer longwall face, if the cutting speed remains constant. The 

rib emission will be linearly dependent on the remaining length of the panel. The background emissions for the longwall face will increase linearly with 

face length, however where the belt line in used as a 

source of face air the background emission from the 

intake rib will remain constant. 

The face conveyor, if operating at the same 

speed, will transport a greater volume of coal per 

hour for a longer longwall face because of the higher 

shearer utilization time for coal cutting versus sumping. In addition, the face conveyor will also transport 

the coal over a greater distance and for a longer 

time, thereby increasing the methane emissions from 

this component on a longer longwall face. The belt 

emissions are a function of the amount of coal on the 

belt and the transport time. The belt transport time 

(dependent on remaining panel length and belt 

speed), will be the same for different longwall 

widths, and only the increased amount of coal produced by the shearer working on a longer longwall 

face will effect the belt emissions. The belt emissions can also reach a steady-state maximum when 

the entire belt is full with coal, thereby limiting the 

upper limit of belt emissions regardless of panel 

width. 

The calculated results for methane emissions on 

longer longwall faces are predicted for a location 

approximately 15 m (50 ft) outby the tailgate corner, 

before any possible interaction with the gob gas near 

the tailgate. Figure 7 shows two full cuts without delays for a 305 m (1000 ft) wide longwall panel. The 

predicted peak methane emission of 0.110 m3

/s (234 

cfm) closely matches the maximum values recorded 

during the study, 0.099 m3

/s (210 cfm) (Fig. 2). Figure 8 shows the predicted methane emissions for two 

full cuts without any delays for a 488 m (1600 ft) 

wide longwall panel. The calculated peak methane 

emissions for the 488 m (1600 ft) wide longwall 

panel [0.152 m3/s (322 cfm)] are 37% higher than 

for a 305 m (1000 ft) wide longwall panel [0.110 

m3

/s (234 cfm)] (Table 5). 

Coal on the face conveyor had the largest calculated increase in methane emission rates on the 

longer longwall faces, while coal cut by the shearer 

and on the belt had no increase (Table 5). The face 

conveyor’s methane emission increase is due to the 

increased length and time that the coal will be carried by the conveyor. Keeping the length of the remaining panel (and hence, the length of the belt) 

constant at 1195 m (3920 ft) for each of the increased face length emission calculations precludes 

any extra peak methane load being emitted by coal 

on the belt. 
0.0897

0.0638

0.1104

0.0593

0.000

0.020

0.040

0.060

0.080

0.100

0.120

0.140

0.160

0 10 20 30 40 50 60 70 80 90

Time (minute)

Methane Emissions m3/s

0

50

100

150

200

250

300

350

Methane Emissions cfm

Shearer location

Calculated Shearers Location

Conveyor Belt

Shearers Background

H-T, 20 Min T-H, 20 Min

Sump, 8 Min Sump, 8 Min

Figure 7. Two full-cut passes without delays for 305 m (1000 

ft) longwall face length. 

0.084

0.152

0.124

0.000

0.020

0.040

0.060

0.080

0.100

0.120

0.140

0.160

0 10 20 30 40 50 60 70 80 90

Time (minute)

Methane Emissions m3/s

0

50

100

150

200

250

300

350

Methane Emissions cfm

Shearer Location

Calculated Shearer Location

Conveyor Belt

Shearer Background

H-T, 33 Min T-H, 33 Min

Sump, 8 Min Sump, 8 Min

Figure 8. Calculated methane emissions for two full cuts without delays for a 488 m (1600 ft) longwall face. 

Table 5. Calculated rates for methane emission contributors on 

idealized passes on longer longwall faces. 

Face Width Conveyor Belt Shearer Background Peak

(m) (m3

s) (m3s) (m3s) (m3s) (m3s)

305 0.040 0.027 0.009 0.035 0.110

366 0.048 0.027 0.009 0.040 0.124

427 0.056 0.027 0.009 0.046 0.138

488 0.064 0.027 0.009 0.052 0.152

Face Width Conveyor Belt Shearer Background Peak

(ft) (cfm) (cfm) (cfm) (cfm) (cfm)

1000 85 58 18 73 234

1200 101 58 18 86 263

1400 118 58 18 98 292

1600 135 58 18 110 322

Percent relative to 305 m (1000 ft) longwall face

Face Width Conveyor Belt Shearer Background Peak

305 m (1000 ft) 100% 100% 100% 100% 100%

366 m (1200 ft) 120% 100% 100% 117% 112%

427 m (1400 ft) 140% 100% 100% 134% 125%

488 m (1600 ft) 160% 100% 100% 150% 137%

The background emissions increase with increases in the face length due to the increase in exposed longwall face area. The methane contribution 

from the ribs in the gateroads does not increase because the length of the gateroads remains constant in 

these calculations. 

One other consideration that should be noted in 

the evaluation of the influence of increased face 

length on longwall methane emissions is that the 

longer longwall faces will theoretically have higher 

coal productivity because a greater percentage of 

time will be spent cutting coal and not sumping. As 

an example, the 488 m (1600 ft) wide longwall panel 

will emit 37% more methane at its peak (Table 5, 

Fig. 8), but will also increase coal productivity by 

11% (Table 6). 

Table 6. Percent in total methane emissions and coal production for longer longwall faces. 

Face Width Peak Average Productivity

Methane Methane Tonnage

305 m (1000 ft) 100% 100% 100%

366 m (1200 ft) 112% 113% 104%

427 m (1400 ft) 125% 128% 108%

488 m (1600 ft) 137% 141% 111%

3.4 Reducing shearer speed to reduce peak methane 

emissions on head-to-tail passes 

As mentioned previously, the highest predicted 

methane emissions for longer longwall faces are 

near the end of the head-to-tail cuts when the emissions from the coal on the face conveyor and belt are 

at their highest (Table 4). During the three shifts 

monitored for this study, not one of the 11 head-totail passes was completed at full speed without a gas 

delay. The average gas delay occurred around shield 

119, 245 m (804 ft) from the headgate and averaged 

seven minutes. Slowing down the shearer for the 

second half of the face traverse will reduce the peak 

methane emissions and give a more consistent emission level, as demonstrated by decreasing the shearer 

speed factor in the emission equations generated for 

this study. The results of the influence of shearer 

traverse speed on emissions for the 485 m (1600 ft) 

panel are shown graphically in Figure 9. 

0.131 0.127

0.078

0.123

0.000

0.020

0.040

0.060

0.080

0.100

0.120

0.140

0.160

0 10 20 30 40 50 60 70 80 90

Time (minute)

Methane Emissions m3/s

0

50

100

150

200

250

300

350

Methane emissions cfm

Shearer Location

Calculated Shearer Location

Conveyor Belt

Shearer Background

H-T, 38 Min T-H, 33 Min

Sump, 8 Min Sump, 8 Min

14 m/min

12 m/min

10 m/min

Figure 9. Calculated influence of reduced shearer transit time 

pass for 485 m (1600 ft) longwall face, shearer traveling at 14 

m/min for the first 250 m of the head-to-tail cuts, then at 12 

m/min, and finally at 10 m/min to the tailgate. 
The reduction in methane emission rates resulting 

from slowing down the shearer transit time is dramatic, with only 86% [0.152/0.131 m3

/s (278/322 

cfm)] of the peak methane emissions being encountered. The five extra minutes required to cut the 

head-to-tail pass due to the reduced shearer transit 

time (Fig. 9) is still less than the observed average 

gas delay of seven minutes for head-to-tail passes. 

With the slowing of the shearer transit time on headto-tail passes, the calculated peak methane emission 

values based on the cutting direction are now within 

7% of each other, as compared to the 20% difference 

for the full speed head-to-tail pass (Figure 8). 

3.5 Converting Belt entry to return to eliminate belt 

methane emissions 

The conversion of the #1 belt entry to return airflow, 

and the conversion of the #3 return entry to intake 

could increase total airflow at the longwall face, as 

well as eliminate the belt coal methane emission 

component from the total methane emission load 

reaching the tailgate corner of the face. The primary 

drawback to this arrangement is that the #3 entry 

ribs tend to have a higher background methane emission rate than the #1 entry, due to the virgin coal 

along the #3 entry’s rib. 

4 CONCLUSION 

Coal production and transport factors have a dynamic effect on methane emissions experienced on 

the longwall face. With a detailed mining time study 

and associated methane concentration data across a 

longwall face, the methane emission contributions 

from the major coal production and transport components can be mathematically determined. The site 

specific layout and position of the longwall panel determines the regression constants for the calculations 

since methane emission contributions change 

throughout the mining of the panel. The mathematical concept can be used to estimate the methane 

emissions for wider and longer longwall panels. In 

addition, the concept can be used for evaluating 

mine design, ventilation as well as engineering and 

operating measures to control the expected increases 

in methane emissions. The component source approach can be applied to other coalbeds provided 

that coalbed-specific methane emission characteristics are known or can be measured. 

The expected peak methane emission increases 

for wider longwall panels result primarily from the 

coal transported on the face conveyor and the background emissions from the exposed coal on the face. 

The methane emission increases related to the transport of coal on the face conveyor is unavoidable for 

longer longwall faces, unless the shearer’s transit 

speed is reduced at the end of a head-to-tail pass. 

Methane emissions associated with the cutting of 

coal on the face by the shearer will remain constant 

at longer longwall face lengths, so long as the transit 

speed remains the same. 

Methane emissions from the coal transported on 

the belt is the only component that can be altered by 

engineering and ventilation practices such as coursing the belt air away from the face. The background 

face methane emission contribution can be reduced 

by the use of or more extensive methane drainage 

techniques. Long-term methane drainage will also 

reduce the methane content in the coal and thereby 

reduce the shearer and conveyor methane components. 

In summary, mine designers have several options 

to reduce or dilute methane emissions expected from 

wider longwall panels, such as the following: 

− Increasing ventilation airflow quantities to the 

longwall face 

− Reducing the shearer transit speed, especially on 

head-to-tail passes 

− Utilizing or increasing methane drainage techniques will reduce emissions from all the considered sources by reducing the methane content of 

the coal 

− Implementing ventilation design changes, e.g. not 

coursing the # 1 belt entry’s ventilation airflow to 

the face 

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. 

6 REFERENCES 

Diamond, W.P., Garcia, F. 1999. Analysis and prediction of 

longwall methane emissions: a case study in the Pocahontas 

No. 3 Coalbed, VA. NIOSH Report of Investigations (RI 

9649). 

Gillies, S. 2000. Maximising coal production in the presence of 

H2S seam gas, Final report: The University of Queensland, 

Queensland, Australia: The University of Queensland 

Karacan, C.O., Diamond, W.P., Esterhuizen, E, Schatzel, S.J., 

2005. Numerical analysis of the impact of longwall panel 

width on methane emissions and gob gas ventholes, Alabama Coalbed Methane Symposium, Tuscaloosa. 

Schatzel S.J., Trackemas J., Krog R.B., Garcia F., Marshall 

J.K., 2006. Prediction of the methane emission consequences of increasing longwall faces widths: a case study in 

the Pittsburgh coalbed, 11th U.S./North American Mine 

Ventilation Symposium. Penn State.