NIOSH Research for Monitoring and Controlling Methane 

at U.S. Underground Coal Mining Operations 

G.V.R. Goodman, C.Ö. Karacan, S.J. Schatzel, R.B. Krog, C.D. Taylor, E.D. Thimons 

National Institute for Occupational Safety and Health, Pittsburgh Research Laboratory, 

Pittsburgh, PA, USA 

ABSTRACT: NIOSH research has focused on the monitoring and the control of methane levels in 

active mine workings. Response times for instrumentation using catalytic heat-of-combustion sensor technology were evaluated. NIOSH research has modelled the flow of methane gas onto longwall faces and gobs, developed engineering controls to limit methane levels during mining, and designed coalbed and gob degasification systems. Available methane control systems have been challenged by recent developments in longwall and room-and-pillar mining systems. This includes increased face advance rates leading to increased productivities, increased longwall panel sizes, and 

the generally deeper workings of U.S. coal mines. The potentially violent nature of any underground 

explosion or ignition requires the measurement, control, and reduction of methane emissions into the 

mine environment for continued worker safety. 

1. INTRODUCTION 

The liberation of methane into underground workings occurs continuously in all coal mining operations. Early attempts to prevent explosions resulting from the ignition of methane gas resulted in 

safer explosives, closed lights for illumination, and the development of permissible electrical equipment. Since the middle of the last century, research to prevent explosions and ignitions has focused 

on controlling the concentrations of methane in active mine workings. Figure 1 shows the injuries 

and fatalities caused by explosions that have occurred in U.S. coal mines since 1990. 

Recent large scale methane explosions in the United States include the July 2000 event at the 

Willow Creek Mine in Utah (2 fatalities and 8 injuries), the September 2001 event at Jim Walter 

Resources No. 5 Mine in Alabama (13 fatalities and 3 injuries), and the January 2003 occurrence at 

the McElroy Mine in West Virginia (3 fatalities and 3 injuries). A frictional ignition in the gob of 

the Willow Creek Mine in Utah in November, 1998 is considered the most likely source of a widespread mine fire that required the sealing of the mine. Other recent underground explosions have 

occurred at the Pinnacle Mine in West Virginia in the fall of 2003 and the frictional ignition and 

subsequent fire at the Buchanan No. 1 Mine in Virginia in February 2005. In January 2006, a methane explosion at the Sago Mine in West Virginia resulted in 12 fatalities and 1 injury. The Darby 

No. 1 Mine explosion in Kentucky in May 2006 led to 5 miners losing their lives. 

Available methane control systems have been challenged by recent developments in longwall 

and room-and-pillar mining systems. This includes increased face advance rates leading to increased productivities, increased longwall panel dimensions, and the generally deeper workings of U.S. 

coal mines. The increasing coal productivities from longwall and room-and-pillar operations can 

lead to greater volumes of coalbed methane gas entering the underground mine environments from 
 

 

 

exposed coal surfaces and from cut coal on the conveyor belting. Production advances in underground coal mining can sometimes outpace existing systems for methane control. Due to the potentially violent nature of any underground explosion or ignition, control and reduction of methane 

emissions into the mine environment in necessary for continued worker safety. This paper provides 

a review of recent NIOSH research for monitoring and controlling face gas levels in longwall and 

room and pillar extraction systems. 

35 

40 

 Fatalities

20 

25 

30 

Number

 Injuries 

15 

5 

10 

0 

1990 1992 1994 1996 1998 

Year

2000 2002 2004 2006 

Figure 1. Number of injuries and fatalities caused by explosions in underground coal mines 

2. NIOSH RESEARCH IN METHANE MONITORING 

To ensure the safety of underground coal mine workers, methanometers are mounted on continuous 

or longwall mining equipment to monitor methane levels. Machine-mounted methanometers are tested and approved by the Mine Safety and Health Administration (MSHA), the regulatory agency 

for the US mining industry. These monitors alert face workers when methane levels reach 1 pct and 

remove power to the mining equipment when levels reach 2 pct. 

The ability of a monitor to provide protection depends upon the accuracy of the reading and the 

response time of the device to changes in methane levels. Calibration procedures are specified by 

the equipment manufacturers and US mining law requires that mine operators check the calibration 

at least once every 31 days. Response times determine how quickly methanometer readings change 

to reflect current concentrations. When a mining machine begins to cut coal, the methane concentrations at the face can rise and fall rapidly. If the methanometer response time is slow, the actual 

concentrations may be higher than the indicated readings. A monitor must not only measure the 

methane concentration accurately but must also respond quickly to changes in concentration in order to indicate a potentially hazardous condition. However, there are no criteria for measuring instrument response times. 

Procedures for measuring such times were developed for use underground and in the laboratory. Work by Taylor et al. (2002) measured response times of three different catalytic heat of com­
 

 

 

 

 

 

bustion type methanometers currently approved for underground use in the US. Using 2.5% calibration gas, they measured times ranging from 29 to 40 sec for a 90% response. The difference in 

response times between these instruments was attributed primarily to differences in the designs of 

the sensor heads. In these tests, gas was applied to the sensor head via a calibration cup which is typically used underground to calibrate the sensors. However, this arrangement altered the normal 

flow of gas around and through the sensor head. Subsequent analyses by Taylor et al. (2004) used 

a test box to more accurately measure response times without the use of the calibration cup (Fig. 2). 

The test box provided a way to expose the sensor heads to gas in a way that more closely simulated 

underground flow conditions on a mining machine. Response times for the three monitors mentioned in the earlier study varied from 23 to 29 sec for a 90% response to a 2.5% methane mixture. Although the researchers found that dust cap and flame arrester design did impact response 

time, no attempts were made to optimize their designs. 

Figure 2. Test box for determining response times (Taylor et al. 2004) 

3. NIOSH RESEARCH IN FACE EMISSIONS MODELING 

Variability in emissions on longwall faces can arise from changes in geologic conditions, changes 

in surface relief which can affect reservoir conditions, and changes in the mechanical behaviour of 

the overburden which can affect abutment pressures, fracture formations and permeabilities. Elevated methane levels can slow the cutting rate of the shearer or continuous miner to allow bleed-off 

of excess gas. One study noted more frequent methane-related delays when mining near the tailgate 

(Schatzel et al. 2006). 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

These delays increased in number as the face moved to a maximum distance away from a borehole exhausting in the gob. Other studies showed more delays due to elevated gas levels when mining from the headgate to the tailgate (Krog et al. 2006). Despite the apparent abundance of data 

concerning methane levels on longwall faces, little published data exists on their effects on continuous mining operations. 

Prior monitoring studies directed at longwall face emissions have indicated that only a small 

portion of the overall methane emission and gas production is emitted at the mine face (Diamond 

& Garcia 1999). However, these emissions can be critical in terms of underground safety. High productivities can elevate methane emissions along the longwall face making it difficult to meet statutory limits on methane concentrations. The current industry trend towards larger panels, particularly towards increasing face lengths, can present additional challenges for longwall face ventilation 

(Balusu et al. 2006, Schatzel et al. 2006). These include increased resistance to airflow and decreased velocities at the tailgate leading to potential methane layering. Also, wider panels can lead 

to increased methane emissions from the exposed face and from the cut coal lying on the face conveyor (Krog et al. 2006). 

A methodology developed by Diamond & Garcia (1999) predicted future methane emissions 

for two future 300 m faces based on emissions measured on current 230 m wide faces. Curves were 

fit to the actual emission data and then extrapolated to the 300 m face widths to predict methane 

emission rates on these longer faces. The data showed that the two faces would likely experience 

significantly different emission rate consequences in response to increasing their panel widths. Variabilities in mine design and methane control practices between the two sites were the primary causes of the different predicted methane emissions rates. 

Other researchers produced similar empirical models of methane emissions, although some caution was necessary in extrapolating these results to other sites. A data set was analyzed using two 

independent methods and many of the findings were consistent (Krog et al. 2006, Schatzel et al. 2006). 

Krog calculated methane emissions for a 480 m longwall face. These emissions were based on computed constants associated with specific methane sources (shearer, face conveyor, belt, background 

emissions from the coal face and background emissions from the adjoining ribs in the intake gateroads) and a zero time delay “idealized” longwall face pass of the shearer. Schatzel predicted lower 

face emission rates for a face length of 490 m by incorporating production delays and average 

emission rates in his calculations. 

4. NIOSH RESEARCH ON ENGINEERING CONTROLS 

Much of the work of the US Bureau of Mines and the National Institute for Occupational Safety 

and Health dealt with improving the flow of fresh air to the cutting faces on longwall and roomand-pillar mining systems. Historical overviews of ventilation designs for underground coal mining 

are given in Reed & Taylor (2007) and Kissell (2006). 

In addition to ventilation airflow, water sprays control methane levels on continuous and longwall mining operations by increasing the turbulence needed to improve mixing and dilution of the 

gas. Work conducted in a full-scale continuous miner test gallery showed the effects of water sprays 

on methane levels measured at the face (Taylor & Zimmer 2001). Four separate spray systems were tested. This included a top spray manifold above the cutter head with 10 sprays oriented toward 

the face, a similar manifold with 10 sprays oriented 30 degrees to the return side of the machine, 

a side spray manifold consisting of 4 sprays mounted vertically on the upwind side of the cutter head, 

and an underboom spray manifold consisting of 4 sprays mounted beneath the cutter boom. 

The results showed that the underboom spray manifold produced lower methane concentrations 

when used with the top sprays oriented toward the face, as opposed to 30 degrees to the return side. 
 

 

 

When operating the side spray manifold, the 30 degree-oriented sprays produced lower methane levels than the top sprays oriented toward the face. This was attributed to the angled top sprays providing improved removal of the gas from the face area. When used with the underboom and side 

spray manifolds, no differences in average face gas concentrations were apparent with use of either 

top spray manifold. 

A series of laboratory evaluations examined the selection, placement, and operation of water 

sprays to control gas levels around a continuous mining machine (Goodman et al. 2006). This work 

evaluated the impacts of three different water spray configurations. The first was the standard spray 

system consisting of 24 sprays positioned above, below, and along the sides of the cutter head (Fig. 3). 

The second configuration added two external sprays approximately 4 m from the cutter head along 

the body of the continuous miner and on top of the cutting boom, while the third placed six additional sprays under the cutting boom. Using sulfur hexafluoride as a surrogate for methane gas, concentrations were measured on the left and right sides of the cutter head. The sprays design incorporating the standard spray system plus the 4 external sprays provided the best control of face gas levels by increasing air velocity around the cutter head. This study did not recommend use of the underboom sprays because they increased gas concentrations. 

Figure 3. Water spray systems used in testing 

Water sprays on a longwall shearer are typically oriented in a “shearer-clearer” pattern using 

a combination of low pressure (410 kPa) sprays on the cutting drums and higher pressure (1030 kPa) 

sprays on the shearer body. This system, originally designed to control respirable dust, was improved with the addition of two sprays on the headgate splitter arm and three sprays on the tailgate splitter arms. These sprays forced the airflow toward the face side of the shearer body and then toward 

the downwind side of each cutting drum, flushing out methane accumulating in these areas (Kissell 

2006). 

5. NIOSH RESEARCH IN COAL BED AND GOB DEGASIFICATION 
 

 

 

 

 

 

 

 

Should increases in ventilation or changes in operational parameters be unable to control face gas 

levels, methane drainage remains the most viable option for mine operators. Most of the methane 

drainage applications in the United States have involved horizontal in-seam boreholes and vertical 

gob gas ventholes (GGV). Cross-measure boreholes have had limited application in the United States, their use being more widespread in European operations. The history of methane drainage is 

quite extensive and has been well-documented in the literature (Diamond 1994, Thakur 2004). 

In-seam boreholes drilled from underground workings have been used to remove coalbed methane from both longwall faces and gateroad development entries. This technique has been applied 

widely in the US coal mining industry and has the advantage of controlling methane emissions in 

both areas. Successful application of this drainage technology still involves keeping the drilling progress sufficiently ahead of mining activities such that the coal seam has adequate time to degas prior 

to extraction. 

In-seam boreholes can be oriented roughly parallel to the longwall face or can be directionally 

drilled perpendicular to the mine face (Fig. 4B). The impacts of borehole pattern and completion 

parameters were modeled (Karacan et al. 2007). This work showed that the most effective pattern 

for draining methane from a longwall panel was the tri-lateral arrangement that created three branches off of a single borehole. The greatest reductions in methane emissions were achieved by degasifying before and during panel extraction. In-seam holes can also be drilled in the longwall block 

parallel to the developing gateroads to capture gas from the longwall panel that would otherwise 

migrate to gateroads and require dilution by ventilation air (Diamond 1994). These wells act as 

shields preventing the migration of methane from the surrounding roadways into the development 

entries. 

A reservoir model was developed to assess the impact of shielding boreholes on methane emissions rates during development of gateroad entries (Karacan 2007). The model included a three-entry headgate and tailgate layout. A number of operational, geologic, and reservoir factors were included in the model to assess their impacts on emissions and on the ventilation flow required to control those emissions. The results showed that degasification using shielding boreholes decreased 

emissions 25% compared to the unshielded case. Shielding wells located close to the gateroads and 

operated for longer times were more effective in reducing methane inflows. Another study used an 

artificial neural network to design a coal bed degasification system using site- and mine-specific 

parameters (Karacan 2008). 

Vertical gob gas ventholes are drilled over longwall panels to drain gas from the gob as the panel is extracted (Fig. 4A). The use of GGV’s is widespread in the US longwall coal mining industry and NIOSH has conducted considerable research to optimize their performances (Diamond 1994). 

For instance, increasing GGV diameter resulted in more methane production, although gas concentration could be diluted by the inclusion of more mine air. Locating the bottom of the GGV in the 

cave zone of the gob also removed mine ventilation air. Karacan et al. (2005) studied the effects of 

increasing face length on GGV performance. The performance and configuration of GGV’s can vary widely although these methane drainage boreholes generally undergo a peak production period 

shortly after undermining. The methane flow rate then declines and reaches a long production tail 

at a lower rate. The conventional design of GGV’s includes surface exhausters that produce a negative pressure on the boreholes to enhance coalbed gas production. It is a widely-held industry belief 

that these methane drainage boreholes reduce emission rates at longwall faces, although no clear 

cut quantification of this effect has been documented. 

The use of coalbed methane drainage in room-and-pillar operations (mains and sub-mains) is 

less common than in longwall mining operations. Possible benefits of methane drainage include reduced ventilation costs, a modest increase in coal reserves, and reduced cost due to a reduction in 

methane-related downtimes (Wang & Mutmansky 1999). However, methane drainage appears to 

be economic for a room-and-pillar operation only if the methane content of the coal is at least 19 

m3

/tonne. As a comparison, the economic limit for methane drainage on a longwall operation is 12 
 

 

m3

/tonne. Such estimates, however, made no allowances for variations in permeability, porosity, or 

other factors impacting gas production. 

Figure 4. Schematic representation of longwall mining environment 

and commonly used degasification borehole types (Karacan 2008) 

SUMMARY 

Available methane control systems have been challenged by recent developments in longwall and 

room-and-pillar mining systems including increases in panel dimensions, increased advance rates, 

and increased working depths. Due to the potentially violent nature of any underground explosion 

or ignition, control and reduction of methane emissions into the mine environment in necessary for 

continued worker safety. 

To ensure the safety of the nation’s underground mine workers, methanometers are placed on 

mining equipment to monitor gas levels during the shift. The protective capability of a methanometer depends upon the accuracy of that device and the response time as methane levels change during mining. NIOSH examined the response times of three methane monitors approved for underground use. Methane gas was initially introduced to each methanometer via a calibration cup attached to the sensor head, a procedure found to provide an unrealistic assessment of response times. 
 

 

 

 

 

 

 

 

 

 

 

 

Subsequent testing introduced the methane gas into a large test box, a configuration that was determined to more accurately mimic underground conditions. 

Past work showed that only a small percentage of the methane originated at the face area, with 

most of the gas coming from the gob area. NIOSH research identified those areas where methane 

control could be critical for longwall operations, i.e. mining towards the tailgate especially at a maximal distance from a gob gas venthole. Models have been developed to predict both current and future methane emissions on longwalls. Some of the models were used to estimate emissions for wider longwall faces, a path that many coal operators are taking. 

Engineering controls have been extensively researched by NIOSH to control methane accumulations while mining. These have included the improved application of ventilation airflow to dilute 

and remove harmful gas levels and the development of more effective water sprays systems to increase mixing and turbulence. Such spray systems include the shearer clearer for longwall operations and the use of top sprays, external sprays, and underboom sprays on continuous mining equipment. 

NIOSH has a long history of work in methane degasification involving the use of horizontal inseam boreholes and vertical gob gas ventholes. Reservoir models have been used to assess the impacts of shielding boreholes on gateroad developments and to evaluate the effects of reservoir parameters on emissions levels. This work has modelled the impacts of borehole pattern and design 

and the effects of increasing face length on gob gas venthole performance. 

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