IC 9503

INFORMATION CIRCULAR/2008 

Explosion Hazards 

From Methane Emissions 

Related to Geologic Features 

in Coal Mines 

Department of Health and Human Services

Centers for Disease Control and Prevention

National Institute for Occupational Safety and Health
Information Circular 9503 

Explosion Hazards From Methane Emissions 

Related to Geologic Features in Coal Mines 

By James P. Ulery 

DEPARTMENT OF HEALTH AND HUMAN SERVICES 

Centers for Disease Control and Prevention 

National Institute for Occupational Safety and Health
 

Pittsburgh Research Laboratory 

Pittsburgh, PA 

April 2008 
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DHHS (NIOSH) Publication No. 2008–123 

April 2008 

SAFER • HEALTHIER • PEOPLETM 
CONTENTS
 

Page

Abstract............................................................................................................................................

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1 

Introduction 2 

Gas emissions associated with outbursts, blowers, and feeders 3 

Effects of outbursts 3 

Effects of blowers and feeders 4 

Gas emissions associated with geologic features 5 

Effects of adjacent source beds 6 

Effects of roof falls and floor heave ........................................................................................

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6 

Effects of clay veins and other intrusions 7 

Effects of sandstone deposits 10 

 Effects of large- and small-scale faulting 11 

Effects of joints, cleats, and fractures 14 

General remediation considerations 15 

Summary 16 

References 16 

ILLUSTRATIONS 

1. Typical clay vein barrier to methane migration..........................................................................

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8 

2. Methane drainage of a clay vein flow barrier 9 

3. Potential high methane cell bounded by clay veins 9 

4. Methane drainage scenarios for paleochannels 11 

5. Methane drainage of a normal fault from the footwall side 13 

6. Methane drainage of a normal fault from the hanging wall side 13 

7. Methane drainage of a reverse fault from the hanging wall side 14 

8. Methane drainage of a reverse fault from the footwall side 14 
 

 

 

UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT 

cfd cubic feet per day 

 ft foot

 ft3 cubic foot 

m meter 
 

 

 

EXPLOSION HAZARDS FROM METHANE EMISSIONS 

RELATED TO GEOLOGIC FEATURES IN COAL MINES 

By James P. Ulery1 

ABSTRACT 

Explosions in U.S. coal mines have caused death and injury to miners and destruction of 

workings since the first reported explosion in 1810. These explosions are caused when buildups 

of explosive gas and/or dust in the mine are ignited by the presence of a flame or spark. Methane 

gas is inherently generated and held by adsorption in coal and is normally liberated during 

mining. Because this gas is explosive in the range of 5%–15% by volume, fresh air is constantly 

supplied to the working face to prevent the methane/air mixture from reaching this explosive 

range. The required amount of ventilation air is based on estimates of gas release under normal 

conditions. Occasionally, unanticipated and unusually high emissions are encountered, which, 

despite normal ventilation controls, result in an explosive mixture that a spark from a cutting bit 

or electrical equipment can easily ignite. Investigations have shown that such emissions are often 

associated with anomalous geologic features or conditions. Although most operators are aware 

that certain geologic features may adversely affect productivity, few are aware of their potential 

as a gas emission hazard. This report presents a historical framework detailing the impact of 

geologic features on excess gas emissions and resultant mine explosions. It also provides 

operators with specific information on recognizing and alleviating potential hazards from 

methane emissions related to these geologic features.2 

1

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

Pittsburgh, PA. 2

Some material in this report was previously published by Ulery [2006]. However, the report contains additional 

material not reported elsewhere. 
INTRODUCTION 

The first recorded occurrence of a methane explosion and resultant deaths in a U.S. coal 

mine was in 1818 at an operation near Richmond, VA, known as Heath’s pits. Humphrey [1960] 

quotes an 1841 article, noting that in the area “large quantities of [flammable] gas are thrown out 

from the coal in the mines constantly.” 

The first documented mine disaster occurred near Richmond at the Black Heath Mine 

where, on March 18, 1839, an explosion of methane gas killed 53 miners. The explosion was 

described as follows: “Nearly all the internal works of the mine were blown to atoms. Such was 

the force of the explosion, that a basket then descending, containing three men was blown nearly 

one hundred feet in the air” [Humphrey 1960]. 

The Richmond mines were undoubtedly located in the coal-bearing Triassic sedimentary 

basins, which are highly faulted and intruded by igneous sills and dikes. Limited information on 

the gas content of these coalbeds indicates very high methane contents [Diamond et al. 1986], 

and these early explosions were most likely caused by excess gas emissions related to the faulting and igneous activity. The impacts of faulting and igneous activity on methane emissions will 

be discussed more thoroughly later in this report. 

By 1900, fatal explosions had occurred in nearly every state with significant underground 

coal mining activity, and many of these explosions were attributable to methane gas. During 

1870–1890, state mine inspectors detailed 200 gas ignitions that resulted in 368 fatalities in 

Pennsylvania anthracite mines alone [Humphrey 1960]. 

Abnormal, unanticipated mine gas emissions in quantities sufficient to create hazardous 

conditions have often been attributed to various geologic features since the first documented 

methane explosions in mines. For example, geologic features such as faults have long been 

recognized as conduits for gas flow from strata adjacent to mined coalbeds. Other features such 

as sandstone paleochannels, clay veins, and localized folding have also been widely recognized 

for their impacts on gas emissions into mine workings. 

It is not surprising that strata adjacent to mined coalbeds can emit great quantities of 

methane gas into active mine workings. Many researchers have recognized that during the burial 

and diagenesis of the organic matter that ultimately forms minable coalbeds, similar dispersed 

organic matter in adjacent strata can produce methane in quantities far exceeding the storage 

capacity of the coal and surrounding rock [Jüntgen and Klein 1975]. As a result, large quantities 

of methane can remain trapped in these strata. A potential hazard occurs when mining of a 

nearby coal seam creates a pressure regime allowing gas to flow from these strata into the mine 

workings. This flow may be either facilitated or temporarily impeded by the presence of intervening geologic structures or anomalies. 

In this report, gas emissions associated with geologic features will be divided into two 

categories. The first category includes large-scale, immediately recognizable emission events 

such as blowers and outbursts that have a geologic component and often result in catastrophic 

explosions. The historical, documented disasters in U.S. coal mines from these features will be 

summarized. The second category includes emission events that are often distinctly associated 

with geologic features of a more varying scale, such as clay veins, faults, and paleochannel 

deposits. Although occasionally resulting in immediate and catastrophic explosions, more often 

these emissions are subtler and not easily detected without field reconnaissance and instrumentation. However, over time these emissions may also lead to hazardous accumulations of methane 

if not recognized and remedied. Catastrophic explosions associated with the second category are 

also documented in this report. In summarizing all of the explosion disasters, bear in mind that 

2
 
no distinction is made between the casualties resulting from the heat and force of the explosion 

and those attributable to the poisonous afterdamp gases generated by the combustion. Finally, 

established methods to recognize and remedy potential emission hazards related to geologic 

features are summarized. 

GAS EMISSIONS ASSOCIATED WITH OUTBURSTS, BLOWERS, AND FEEDERS 

Outbursts and blowers are distinguished mainly by their duration of occurrence. Outbursts are sudden, often violent expulsions involving large quantities of gas, usually methane. 

Often associated with outbursts are large-scale ejections of coal or rock material. Blowers, on the 

other hand, have historically been viewed as events expending large quantities of gas over an 

extended time period of months, or perhaps years. Blowers are not associated with expulsions of 

coal or rock material. Methane feeders, a subset of blowers, continually expend gas over a long 

period, but at a lower rate. 

Effects of Outbursts 

Although not presently regarded as widespread in U.S. coal mines, outbursts have a 

historical record of occurrence and fatalities in certain mining districts and occur with regularity 

in certain mining districts worldwide. Typically, mines in these districts operate in steeply 

dipping, gassy coal seams that can lie at great depths. The potential for gas outbursts will likely 

increase in the United States as shallower and more easily extracted reserves are depleted, 

forcing mining into deeper, gassier, and more structurally complex seams. In fact, gas outbursts 

have been documented throughout history in U.S. coal mines with similar conditions. 

Large quantities of pressurized gas may also cause “heavy roof falls” or “the bottom 

[floor] to heave” [Beard 1920]. Often these events cause high volumes of gas to be released 

rapidly in outburst-like fashion and may result in hazardous methane accumulations. Humphrey 

[1960] cites the October 28, 1958, explosion at the Burton Mine, near Craigsville, WV, as being 

“caused when a large quantity of methane, released from formations in the roof by large falls 

or emitted from heaving bottom...accumulated in the active working areas and was ignited.” 

It could be argued that such a release is not a true outburst because large quantities of rock 

material were not ejected under pressure. On the other hand, there have been instances where 

roof falls are thought to be driven by gas pressure, so perhaps these instances may indeed be 

regarded as at least “outburst-like.” Other instances where gas outbursts are related to roof falls 

or floor heave are documented in the section below on adjacent source beds. 

In similar fashion, pillar robbing and weighting during retreat mining have also been 

associated with sudden, large, outburst-like releases of gas. These occurrences have resulted in 

ignitions with injuries and fatalities. Humphrey notes that on December 11, 1947, eight miners 

were killed by a methane explosion at the Franklin Colliery in Wilkes-Barre, PA, when “a rush 

of coal occurred...Methane was liberated [and]...an arc ignited the gas.” 

As for actual outbursts, Humphrey also cites a November 25, 1922, explosion at the 

No. 4 Mine in Madrid, NM, that killed 12 miners. The subsequent disaster report noted: “The 

mine is gassy, and outbursts of gas had been occurring.” 

Darton [1915] discusses three gas outbursts in Pennsylvania, two of which occurred in 

eastern anthracite mines in steeply pitching seams. The third took place in western Pennsylvania 

near Connellsville, where Darton notes that 100,000 ft3

 of fresh air per minute for 3 days was 

required to reduce the methane in mine air to safe limits. Darton also summarized extensive 

3
 
European documentation of gas outbursts and concluded that these phenomena were usually 

related to crushed coal zones associated with folds, buckles, and faults. 

Lama and Bodziony [1998] compiled a comprehensive overview of outbursts worldwide, 

including their causative factors and prevention. They concluded that the following factors contribute to outbursts: (1) gas content, (2) gas pressure, (3) permeability, (4) sorption/desorption 

characteristics, (5) stress conditions, (6) coal strength, and (7) geologic factors (often related to 

tectonic activity). Other modern research on these phenomena has demonstrated two major 

indicators of outburst potential in coal mines. The first indicator is the coal lithotype. Beamish 

and Crosdale [1998] demonstrated that coals with high vitrain and/or inertodetrinite lithotypes 

were more likely to retain the large quantities of gas needed to produce outbursts. A second 

indicator, documented by Cao et al. [2001], is the association of outbursts with tectonically 

altered and faulted coals. Cao et al. noted that outbursts in China seemed to be associated with 

tectonic activity that has produced regional thrust and reverse faulting. Such faulting often 

manifests itself in coalbeds because of their brittle nature compared to the surrounding strata. 

The coal adjacent to such faults is often severely crushed and pulverized, resulting in significant 

local changes in the gas storage and migration characteristics of the coal. 

Effects of Blowers and Feeders 

Gas blowers and feeders are not normally associated with modern coal mining in the 

United States, although they have been noted in other mining districts worldwide. Beard [1920] 

defined blowers and feeders as follows: “any continuous flow of gas from a crack or crevice in 

the strata is called a ‘gas feeder’ or simply a ‘feeder.’ The gas flowing from the crevice is known 

as ‘feeder gas.’ When a gas feeder is under high pressure so the gas issues with considerable 

velocity, the feeder is called a ‘blower’ and the gas ‘blower gas.’” 

Darton [1915] summarized blower occurrences worldwide and noted the occurrence of 

“blower-like” features in the Pennsylvania anthracite district. Beard [1920] included the composition of blower gas from Wilkes-Barre, PA. The gas composition was methane 94.2%, ethane 

0.4%, nitrogen 3.3%, carbon dioxide 1.1%, oxygen 0.9%, and carbon monoxide 0.4%. Chance 

[1883], in a report on Pennsylvania anthracite mining, noted that blowers were “very common in 

the mines of the Wyoming district and some of the deeper mines of the Schuylkill region... 

sometimes they are so powerful, and the amount of gas given off so great, that working must be 

suspended for a time.” 

A review of Humphrey [1960] indicates that many major and minor explosions of mine 

gas resulted from the ignition of gas from audible feeders, the earliest of which occurred on 

October 27, 1881, when a miner was killed because his open light ignited a gas feeder in the 

Pittsburgh Coalbed in Washington County, PA. 

In terms of fatalities, there were several significant explosions and numerous minor ones 

cited by Humphrey [1960] resulting from the ignition of gas feeders. At the Cumnock Mine in 

Cumnock, NC, an explosion occurred on December 19, 1895, killing 39 miners. In a report of 

the disaster it was noted that “[at the] face...little jets of gas exuded from the seam.” On 

August 1, 1911, an explosion at the Standard Pocahontas Shaft near Welch, WV, occurred due to 

ignition of gas “from audible feeders.” On December 10, 1925, 53 miners were killed at Overton 

No. 2 Mine in Irondale, AL, from a gas explosion. The disaster report noted: “Gas was issuing 

from a feeder in the face.” Other major fatal disasters attributed to gas feeders include: 

4
 
• 13 fatalities at the Irvona No. 3 Mine, Coalport, PA (August 15, 1928); 

• 10 fatalities at the Bates No. 2 Mine, Bates, AR (August 27, 1940); 

• 12 fatalities at the Praco No. 10 Mine, Praco, AL (May 11, 1943); 

• 25 fatalities at the Belva No. 1 Mine, Belva, KY (December 26, 1945); and 

• 5 fatalities at the Buttonwood Colliery in Wilkes-Barre, PA (March 29, 1951). 

Numerous minor disasters related to methane feeders are also listed by Humphrey [1960]. 

In a more recent report, Richmond et al. [1983] noted that methane feeders contributed to 

an explosion at the Dutch Creek Mine near Redstone, CO, killing nine miners on December 28, 

1965. Gas feeders also contributed to an explosion at the Siltex Mine, Mount Hope, WV, on 

July 23, 1966, killing seven miners, and may have played a role in the two Scotia Mine explosions near Whitesburg, KY, that killed a total of 26 men on March 9 and 11, 1976. On June 30, 

2000, the first of three explosions that resulted in the deaths of two miners at Willow Creek 

Mine, Helper, UT, was believed to be propagated in part by gas feeders at the face area. The 

source of the ignition was believed to be a roof fall initially igniting low flash point, higher 

hydrocarbon homologues of methane given off by liquid hydrocarbons found in roof strata at 

the mine [McKinney et al. 2001]. 

Based on past observations, outbursts and blowers are often associated with tectonically 

disturbed strata where gassy coals are mined at considerable depth. Thus, mine planners who are 

aware of such conditions should give some thought to the possibility that they will be extracting 

coal under conditions that have produced these phenomena in other mining districts. 

If large-scale faulting is known and adequately mapped in future development areas, 

a detailed core-drilling program, coupled with gas content testing of core samples and in situ 

pressure measurements, can detect potential outburst-prone areas. Beamish and Crosdale [1998] 

recommend, as do Lama and Bodziony [1998], the use of any one of several published gas 

emission indices as an indicator of proneness to outbursts. 

Since outbursts often occur in “nests” or clusters of several events, often within a 

distance of a few hundred feet laterally, gas drainage programs such as vertical surface 

degasification boreholes, degasification holes drilled horizontally ahead of the face, or (if 

outburst-prone strata are in the roof rock) cross-measure boreholes [Diamond 1994] may reduce 

the severity of these anomalies. Often, such boreholes will penetrate a fault system that has 

altered the coal structure and allowed large quantities of gas to accumulate at great pressure 

behind it. The boreholes are used to degas the outburst-prone area and relieve the gas overpressure that causes outbursts. Beamish and Crosdale [1998] also note that water infusion has 

been used successfully in some countries to reduce outburst hazards. 

Blowers most often emanate from underlying strata. Remediation is recommended by 

using cross-measure holes angled downward from the mine heading to intercept the fissure or 

fault, which acts as a gas conduit. The borehole(s) may then be used to drain gas away from the 

blower outlet in the mine workings. 

 GAS EMISSIONS ASSOCIATED WITH GEOLOGIC FEATURES 

In the United States, gas emission events associated with geologic features constitute a 

fairly common hazard in coal mining. These events are neither as obvious nor as immediate as 

outbursts or blowers; however, they do have the potential to pose significant risk. These events 

are often difficult to detect without the aid of instrumentation and underground surveys. Additionally, detailed mapping of geologic features can assist in predicting potential emission hazards 

5
 
and designing degasification strategies to alleviate these hazards. This section will consider 

techniques to detect and remediate abnormal gas emissions associated with geologic features 

such as adjacent source beds, roof falls, floor heave, clay veins and igneous intrusions, sandstone 

channels or lenses, joints, fractures, and faulting. 

Effects of Adjacent Source Beds 

Coalbeds adjacent to a mined seam can contribute significant quantities of methane gas to 

active workings [Finfinger and Cervik 1979; Ayruni 1984]. Although degasification of these 

seams may be accomplished through vertical or directional surface boreholes, more often, 

in-mine cross-measure, vertical, or directional boreholes are used to prevent explosive accumulations of gas [Finfinger and Cervik 1979; Ayruni 1984; Diamond 1994]. 

Shales and siltstones rich in organic matter often contain significant quantities of methane 

gas [Darton 1915; Johnson and Flores 1998] and may contribute unexpected emissions into 

active mine workings. As their permeabilities are typically low, the large amounts of gas stored 

in these strata may not be released until mining-induced fractures increase their permeability. 

In studying the gas content of U.K. coalbeds, Creedy [1988] concluded that the porosity and gas 

content of coal measure rocks were small. Nevertheless, he did allow that well-developed joint or 

fracture systems play a role in gas release from adjacent strata. It may be assumed that under 

some conditions certain organic-rich rocks adjacent to mined coalbeds have the potential to 

release methane gas at or near the working face in quantities sufficient to create explosive 

conditions. 

Examples of disasters related to adjacent source beds include the disaster at the Blue 

Canyon Mine, Lake Whatcom, WA, on April 18, 1895. During drilling and blasting of bottom 

rock, an explosion occurred from “[g]as [that] was evident in quantity and under pressure in the 

strata” [Humphrey 1960]. A deadly explosion at the Stag Canon No. 2 Mine, Dawson, NM, on 

October 22, 1913, killed 263 men. The mine was not considered gassy and “was usually free of 

firedamp except for occasional pockets, coming from the roof” [Humphrey 1960]. It is, however, 

not entirely clear from the description if the gas was involved in the disaster. On January 13, 

1926, an explosion at the No. 21 Mine, Wilburton, OK, killed 91 miners. The gas that was 

ignited here “had been coming in large quantities from roof cracks” [Humphrey 1960]. 

Remediations of gas emission hazards associated with adjacent source rocks may be 

accomplished through surface degas holes [Diamond 1994]. In deeper coalbeds, cross-measure 

degasification holes have been used to degas overlying strata in Europe and the United States 

with good success [Campoli et al. 1983; Venter and Stassen 1953]. Also, degasification by either 

in-mine boreholes (vertical or cross-measure) or directional boreholes from the surface may also 

be used for degasification of adjacent strata above or below the coalbed. 

Effects of Roof Falls and Floor Heave 

Humphrey [1960] documents numerous mine disasters related to the ignition of large 

quantities of gas released from roof falls or floor heave. One example is the January 27, 1891, 

explosion at the Mammouth No. 1 Mine, Mount Pleasant, PA. The explosion killed 109 miners 

and was caused by “fire-damp...mostly if not all generated by the [roof] fall” [Humphrey 1960]. 

Another example is the May 19, 1902, disaster at the Fraterville Mine, Coal Creek, TN, which 

killed 184 miners. The gas that exploded “was liberated from overhanging strata by the ‘creep’ 

that had begun with unusual violence shortly before the explosion.” On February 8, 1906, at the 

6
 
Parral Mine, Parral, WV, 23 miners were killed when a “heavy fall of roof in an intake aircourse 

liberated gas which...was ignited by [an] open light...Gas was liberated for several days after the 

explosion.” At the McClintock Mine, Johnston City, IL, 33 miners were killed on January 25, 

1924, when “gas from the broken roof...came in contact with...open lights.” On January 28, 

1931, 28 miners were killed at the Little Betty Mine, Dugger, IN, when “roof falls released gas 

and pushed it...over...open lights of loaders” [Humphrey 1960]. Another serious disaster cited 

by Humphrey is the July 15, 1940, methane explosion at the Sonman East Mine, Portage, PA, 

in which 63 men were killed. In this event, a “body of methane was released from overlying rock 

strata by a fall in a room.” 

Excess, unanticipated methane emissions from floor strata have also been associated with 

fatal mine explosions. Humphrey [1960] cites an explosion at the Starr No. 3 Mine, Henryetta, 

OK, on April 8, 1943, that killed four miners and resulted from an “open light; gas from floor.” 

He also cites a May 9, 1943, explosion that killed three men at the Superfuel Mine, Paris, AR, 

that was caused by an “open light; methane released by heaving bottom.” The Sun Excelsior 

Mine, near Excelsior, AR, suffered a catastrophic explosion on February 8, 1948. Eight men 

were killed when “[h]eaving action of the floor...released methane,” which was subsequently 

ignited [Humphrey 1960]. 

In the Pennsylvania anthracite region, Humphrey [1960] cites an explosion that killed 

10 miners at the Schooley Shaft, Exeter, PA, on April 10, 1947. “[M]ethane issued from crevices 

in the floor in finished workings” and was ignited. He also cites an explosion on September 11, 

1933, at the Oakmont Mine, Barking, PA. Seven miners were killed when “gas...was 

ignited...from cracks in the bottom.” 

More recently, the first of two explosions that ultimately killed 13 miners on September 

23, 2001, at Jim Walter Resources, Inc.’s No. 5 Mine, Tuscaloosa, AL, was attributed to release 

of gas from a roof fall [McKinney et al. 2002]. As mines continue to extract deeper seams, the 

potential for significant emissions from roof and floor strata must be considered in planning. 

Due to the extremely unpredictable nature of phenomena such as floor heave and roof 

falls, remediation techniques beyond increased ventilation air quantities are not practical. 

However, if emissions from one of these events continue over an extended period, then some 

type of gas feeder is present. The source of the feeder should be determined and possible 

degasification strategies considered. 

Effects of Clay Veins and Other Intrusions 

Clay veins or clastic dikes are sedimentary intrusions, usually from overlying strata, that 

intercept the coal in a vertical or near-vertical orientation. Their appearance in cross-section is 

not unlike an igneous dike, hence their name. Clay veins, which are generally composed of very 

fine-grain sediment or clay, are virtually impermeable barriers to gas migration in coalbeds 

(Figure 1). Therefore, they tend to have a “damming” effect on gas flow when approached 

during mining. When a mining machine penetrates a clay vein in a gassy seam, high methane 

emissions may occur at the face. Clay veins tend to be systematic in occurrence and are often 

related to differential compaction/diagenetic processes, but can also be influenced by tectonic 

processes [Chase and Ulery 1987]. Historically, these features have also been referred to as slack 

veins, horsebacks, rolls, and clay slips. 

7
 
Figure 1.—Typical clay vein barrier to methane migration. 

Clay veins have a well-documented history of causing unexpected high gas emissions in 

the Pittsburgh Coalbed during mining [McCulloch et al. 1975]. Studies in northern West Virginia 

have documented high gas flow rates (>80,000 cfd) from low-angle cross-measure holes penetrating clay veins near a gas-bearing sandstone above the Pittsburgh Coalbed [Ulery and Molinda 

1984]. Gas flow increased from 47,000 to 80,000 cfd when a horizontal in-mine degasification 

borehole penetrated a clay vein approximately 800 ft from the face [Prosser et al. 1981]. In a 

different horizontal gas drainage borehole, the gas flow increased from 144,000 to 214,000 cfd 

after intercepting a clay vein approximately 2,200 ft from the face. 

Clay veins and related features have also been responsible for documented mine 

disasters. On November 9, 1888, 40 miners were killed by a gas explosion at Shaft No. 2, 

Frontenac, KS. It was noted in the investigation that the operation had “never seen gas in the 

mine except when cutting horsebacks or slips” [Humphrey 1960]. At the Hillside No. 1 Mine in 

Johnstown, PA, five miners were killed by a gas explosion on August 9, 1928. The explosion 

was caused when “a nonpermissible mining machine cut through a clay slip in a room face, 

releasing gas, which was ignited by an arc from the machine” [Humphrey 1960]. 

Only in-mine experience can alert the operator to potential gas emission problems due to 

the presence of clay veins. If excessive gas emissions are encountered when mining through 

these features, then underground mapping of clay veins is needed to predict their locations in 

future developments. Since clay veins frequently can extend hundreds of feet along a given trend 

[Chase and Ulery 1987], predicting a vein’s occurrence in a developing section will allow the 

operator to anticipate and/or alleviate the potential problem. 

8
 
Figure 2.—Methane drainage of a clay vein flow barrier. 

Figure 3.—Potential high methane cell bounded by clay veins. 

Horizontal degasification boreholes drilled ahead of the face and penetrating the clay vein 

are the most economical means of controlling high emissions from a clay vein network (Figure 2, 

borehole A). Although mapping a clay vein network to delineate an isolated cell (Figure 3) 

allows it to be degassed through a surface borehole (Figure 2, borehole B), this is a costprohibitive method, necessitated only in extreme cases. 

9
 
In addition to clay veins, other intrusions can be igneous in nature. Igneous intrusions 

into coal seams and coal measure rocks generally will be either discordant features such as dikes, 

which cut across bedding planes, or concordant features such as sills, which are injected parallel 

to bedding. Such features are not found frequently in underground coal mines, but they are not 

uncommon either. However, massive discordant features such as plutons are rare in coal measure 

strata. Igneous intrusions typically inject magmatic rock at elevated temperatures, and their 

presence alters and increases the thermal maturity (rank) of nearby coal seams and organic 

matter in rocks [Dutcher et al. 1966]. The degree of coal alteration caused by an igneous 

intrusion depends on many factors, including the intrusion’s temperature, thickness, distance 

from the coal seam, and cooling rate. Such thermal alteration of organic matter is accompanied 

by methane gas generation. For a given coalbed, areas affected by igneous intrusions can be 

expected to have higher gas contents than normal [Gurba and Weber 2001]. Larger igneous 

intrusions such as sills may also be responsible for potentially high carbon dioxide concentrations in some coal basins [Clayton 1998]. 

Discordant igneous dikes, like clastic dikes, can act as a barrier to gas migration and can 

present similar hazards when mined through. Predicting igneous dikes in developing sections is 

best accomplished by detailed underground mapping in adjacent developed sections. Controlling 

potential gas emission hazards associated with igneous dikes, as with clastic dikes, is best 

accomplished by horizontal boreholes drilled from the face and penetrating the dike. 

Concordant igneous features such as sills usually cover a far greater lateral extent than 

dikes and can elevate the thermal maturity and gas content of a coalbed over a similarly large 

area [Gurba and Weber 2001]. The greater lateral extent of these features, however, is more 

conducive to prediction and mapping through conventional exploratory core drilling programs. 

If associated gas contents and emissions present a potential hazard, premining degasification 

through conventional surface degasification boreholes is the optimal method to alleviate this 

hazard. 

Effects of Sandstone Deposits 

Previous work by Darton [1915] and Price and Headlee [1943] documented the presence 

of sandstone paleochannel and other lenticular sandstone deposits adjacent to mined coalbeds as 

potential gas reservoirs. The gas in these deposits either migrated from subjacent coalbeds or 

organic-rich rock strata, or arose from organic matter deposited with the sand. These gas-bearing 

sandstones generally have a greater permeability than the surrounding rock strata, and once a 

pathway is established to mine workings via relaxation of natural joint patterns or other fissure 

systems, emissions from these sandstones may be quite pronounced. 

Excess gas emissions from a sandstone paleochannel migrating through clay vein-related 

fractures have been documented at a mine in the Pittsburgh Coalbed in northern West Virginia. 

A sandstone paleochannel deposit above the Pittsburgh Coalbed acted as a significant gas 

reservoir, exhausting nearly 400,000 cfd of methane into a methane drainage system for 2 years 

[Ulery and Molinda 1984]. Humphrey [1960] cited an example of a disaster related to gas 

emissions from sandstone roof strata when “gas...released by breaking of the sandstone roof” 

was ignited at the Shannon Branch No. 3 Mine, Capels, WV. The explosion on May 13, 1927, 

killed eight miners. 

Evaluation of the gas content of the sandstone using direct testing of cores, well testing, 

or direct gas measurements is necessary to determine if these emissions are sufficient to pose a 

potential hazard. The lateral extents and trends of the problematic sandstone deposits should be 

10
 
Figure 4.—Methane drainage scenarios for paleochannels. 

delineated using an exploratory core drilling program with appropriate hole spacings 

[Houseknecht 1982]. 

Remediation of these methane sources is best accomplished using vertical surface 

degasification boreholes (Figure 4, borehole A). If the sandstone body is in the roof or floor 

strata, in-mine degasification boreholes may be the most economically viable solution. Vertical, 

in-mine cross-measure, and horizontal degasification boreholes are shown in Figure 4 as boreholes B, C, and D, respectively. The same configurations of surface or in-mine boreholes would 

also be applicable to gassy sandstone deposits in floor strata. 

Surface degasification wells usually require both dewatering and hydraulic fracturing to 

be most effective. Water must also be removed from horizontal, cross-measure, or vertical underground degasification boreholes to effectively produce gas [Diamond 1994]. 

Effects of Large- and Small-Scale Faulting 

Large-scale faults are loosely designated as being tectonically activated, structurally 

mappable features, with areal extents greater than 500 m (1,640 ft) and vertical movement of 

at least 10–20 m (33–66 ft). Usually, the presence of large-scale faulting is known from regional 

geologic mapping and/or exploration coreholes. If the mined coalbed contains such faults and is 

of a gassy nature, the operator should be aware of the potential effects of these faults on 

premining gas drainage schemes and/or gas flow into mine workings [Diamond 1982]. 

These large faults may act as barriers to gas flow, especially if they contain impermeable 

fault gouge or if the displacement locates impermeable rock above or below the mined coal seam 

that abuts against it. If mine development proceeds through the fault by sloping the heading 

upward or downward into the displaced seam, the potential exists for excess methane emissions. 

Large-scale faults may also act as conduits for potentially high emissions, or even 

blowers, from gas-enriched strata above or below the mined coal seam. Therefore, it would seem 

likely that such faults could easily become pathways for gas emissions into mine workings from 

adjacent source beds. In the United States, Clayton et al. [1993] noted similar findings in the 

Black Warrior Basin. Emissions may increase when there is stress redistribution as mining 

approaches a large-scale fault. In Germany, Thielemann et al. [2001] showed that in unmined 

regions, normal faults regularly act as gas conduits for surface emissions into the atmosphere 

from deep formations such as coalbeds. They further demonstrated that distinctly higher rates of 

11
 
surface gas emission occurred from normal faults in mined areas. This was presumably caused 

by the increased permeability of the fault and associated strata in response to mining. 

Degasification of potential problem areas associated with large-scale faulting may best be 

accomplished through surface boreholes if the faulted areas in question are well mapped. Otherwise, unexpected problems associated with large-scale faulting may be alleviated through crossmeasure boreholes designed to penetrate the fault zone and/or the source bed. 

Humphrey [1960] cites three examples of mine disasters related to methane emissions 

and faults. On December 11, 1947, eight men were killed at the Franklin Colliery, Wilkes-Barre, 

PA, when gas associated where “the coal had pinched out at a fault” was ignited. On January 18, 

1957, five miners were killed by a gas explosion at the Evan Jones Slope, Jonesville, AK, where 

“ventilation was inadequate to prevent accumulations of methane...along the fault line.” Twelve 

men were killed on April 18, 1946, at the Great Valley Mine, McCoy, VA, when “[g]as released 

from a fault in the face...was ignited.” 

Small-scale faults are distinguished from large-scale faults by their limited mappable 

extent both laterally and vertically. Small-scale faults have limited extent and are often vertically 

confined to one or two strata. They may also be related to differential sediment compaction 

phenomena. Examples of small-scale faults are illustrated by Iannacchione et al. [1981]. 

Little documentation is available on the effects of such features on gas emissions. These 

types of faults, should they impact methane emissions, could possibly act as barriers to gas 

migration, forming “dams” of potentially dangerous gas buildups behind them [Iannacchione 

et al. 1981]. When these features are mined through, the “dammed” gas may release suddenly, 

possibly creating explosive conditions. Although prediction of these small-scale features can be 

difficult even with detailed underground mapping, degasification through short horizontal or 

cross-measure boreholes ahead of the working face is feasible if the faults can be anticipated and 

mapped. The coalbed near these features often displays abnormal thickening, undulations, or 

pulverizations, possibly indicating that faults are being approached. 

Whether large- or small-scale, faults are generally classified as either normal or reverse. 

Normal faults are usually associated with tensile forces and are likely to act as conduits for gas 

flow. Reverse faults are often associated with mountain building tectonics and regional compression forces. Low-angle reverse faults are termed “thrust faults” and are often very large-scale 

regional features. Since these faults are associated with compression forces, they are likely to be 

barriers to gas flow. 

When a mine entry approaches a normal fault on the footwall side, the remaining coal 

reserve ahead of (and below due to the fault) the approaching entry often poses an emissions 

hazard (Figure 5). Although the normal fault may potentially be an effective gas conduit, it is not 

as open to flow as the normal coal cleat system until mining redistributes the stresses. Therefore, 

potentially hazardous gas buildups may occur at the coal/fault interface. When ramping downward to extract the remaining reserves, hazardous conditions may arise when the built-up gas is 

released into the mine entry. Optimum degasification of such potential hazards is best accomplished using surface degasification wells (Figure 5, borehole B) or directional drilling from the 

mine entry (Figure 5, borehole A). A normal fault encountered from the lower “hanging” wall 

side (Figure 6) can best be degassed using vertical surface degasification wells (Figure 6, 

borehole A). 

12
 
Figure 5.—Methane drainage of a normal fault from the footwall side. 

Figure 6.—Methane drainage of a normal fault from the hanging wall side. 

Degasification of a reverse fault, approached on the hanging wall side (Figure 7), is best 

accomplished using surface degasification wells (Figure 7, borehole C). Other options include 

vertical in-mine boreholes (Figure 7, borehole A) or directional in-mine boreholes (Figure 7, 

borehole B). A reverse fault approached on the footwall side can be degassed with cross-measure 

holes (Figure 8, borehole A) or surface degasification holes (Figure 8, borehole B). 

13
 
Figure 7.—Methane drainage of a reverse fault from the hanging wall side. 

Figure 8.—Methane drainage of a reverse fault from the footwall side. 

Effects of Joints, Cleats, and Fractures 

Joints, cleats, and fractures are related to the confining stress fields during burial, diagenesis, and uplift. Joints are closely spaced with even walls, while fractures are more widely 

spaced with irregular walls. Joints usually occur in pairs at an approximately 90° orientation, and 

in coal seams these joint sets are called cleats. The main joints and cleats, termed “systematic 

joints” and “face cleats,” of any given set are generally more continuous and offer major migration pathways for gas. Nonsystematic joints and butt cleats are turned 90° to the main features 

and generally abut against the systematic joints and face cleats, making them notably less 

continuous. Coal seam extraction allows the cleats to expand through a redistribution of the 

14
 
stresses, which in turn encourages gas migration through the coal. Stress redistribution also 

opens joints and fractures in roof and floor strata, allowing gas migration from adjacent strata. 

Prediction and remediation of abnormal gas emissions are difficult given the unpredictable spacing of fractures. Joints and fractures act as conduits for gas to reach the mine workings 

from great distances within the seam and/or other source beds adjacent to the worked seam. It is 

probably safe to assume that many gas blowers and feeders are associated with jointing and/or 

fracturing of the coal and adjacent strata. These types of hazards are most often recognized when 

mining equipment is deenergized due to excess face emissions. 

The most obvious solution to this problem would be to increase ventilation to the face. 

If past experience indicates that excess emissions may be encountered in a developing section, 

the mine operator should consider a horizontal borehole drainage system or surface methane 

drainage holes to degas the section prior to mining. Mine operators should always be aware of 

regional joint and fracture trends to facilitate prediction and remediation of abnormal emissions 

associated with these geologic features. 

GENERAL REMEDIATION CONSIDERATIONS 

When abnormal methane emissions occur in quantities sufficient to cause repeated 

production interruptions, operators must consider the possibility that they have a gas problem. 

To determine the most appropriate course of remediation, the operator must make thorough 

evaluation of the cause, extent, and severity of the problem. For many smaller mine operators, 

little in-house expertise is available to make such evaluations. These operators must rely on 

outside or contracted assistance. 

The cause of the gas emission problem can range from underestimating the original gas 

content of the seam to dealing with gas sources outside the mined seam. Determining the extent 

of the problem may involve additional gas content testing [Diamond and Schatzel 1998] of the 

mined coalbed through exploratory boreholes or may involve extensive underground surveys, 

mapping, and instrumentation. Remediation may involve increasing face airflow or may entail 

labor-intensive drilling of surface or in-mine degasification boreholes. Surface degasification 

programs generally require fewer boreholes, but need good geologic control to effectively target 

and hit the gas-bearing zone. Both dewatering and hydraulic fracturing are required for surface 

degasification to be optimally effective. In-mine programs generally require more boreholes and 

dewatering, but less hydraulic fracturing. In-mine degasification programs require a piping 

network to transmit gas from the boreholes to the surface. If either the surface or in-mine 

degasification program affects the mine ventilation system, an alternate ventilation plan must be 

submitted and approved by the Mine Safety and Health Administration. Using the gas for 

cogeneration applications may reduce energy costs to the mine operator and help offset the costs 

of the degasification program. 

Additional considerations for implementing any degasification system are equipment 

mobilization costs and accessibility to borehole drilling sites. Surface degasification sites may be 

inaccessible due to topography, landowner issues, or environmental constraints. In-mine programs may also have accessibility constraints due to poor roof or floor conditions or other 

mining-related issues. 

Finally, operators must consider who will operate and maintain the system once installed. 

If installed in-house, personnel may need to be permanently assigned to the project. If outside 

contractors are used for installation, they may need to be retained for long-term operation, and 

15
 
maintenance or mine personnel may need training to operate and maintain the system once the 

contractor departs. 

The economics of any degasification system under consideration involves weighing the 

pros and cons of all of these factors. A flowchart and excellent overview of this decision-making 

process are presented by Wang and Mutmansky [1998]. 

SUMMARY 

Geologic features have a long historical association with excess gas emissions in coal 

mines and fatal disasters. Occasionally, these emissions are of such volume that the normal mine 

ventilation practices are inadequate to maintain a safe environment. In such cases, explosive 

mixtures of gas and air can occur and, if ignited, can lead to catastrophic results. Mine operators 

need to be cognizant of how such features may lead to hazardous explosive conditions and vigilant for signs of any unusual gas emissions. Operators of deeper, gassier mines in structurally 

complex areas must be aware that although outburst and blowers are not common, the potential 

and precedent for their occurrence exists. Finally, operators should be prepared to evaluate 

potential problems and implement remedial measures best suited to the specific geologic 

anomaly present. 

Large sandstone units above or below the mined seam are a common cause of excess 

emissions. These features are mappable and readily degassed through surface or cross-measure 

borehole drainage configurations. Large- and small-scale faults can also impact emissions by 

either damming gas flow behind them or acting as a conduit to allow gas migration from adjacent 

units. Depending on the fault configuration and source of excess emissions (the seam itself or the 

adjacent strata), degasification is accomplished via in-seam, cross-measure, or surface boreholes. 

Jointing and fractures may act as pathways for feeders or blowers. Increasing frequency 

of these features in gassy mines often necessitates increased ventilation. Clay veins and igneous 

dikes can also influence emissions, but are much more difficult to map and predict. Usually these 

features act as dams to gas flow and are best relieved through in-seam horizontal or crossmeasure boreholes. 

REFERENCES 

Ayruni AT [1984]. Theory and practice of mine gas control at deep levels. Rockville, 

MD: Terraspace, Inc. 

Beamish BB, Crosdale PJ [1998]. Instantaneous outbursts in underground coal mines: 

an overview and association with coal type. Int J Coal Geol 35(1–4):27–55. 

Beard JT [1920]. Mine gases and ventilation. 2nd ed. McGraw-Hill Book Co., Inc. 

Campoli AA, Cervik J, Schatzel SJ [1983]. Control of longwall gob gas with crossmeasure boreholes (upper Kittanning coalbed). Pittsburgh, PA: U.S. Department of Interior, 

Bureau of Mines, RI 8841. NTIS No. PB 84–159540. 

Cao Y, He D, Glick DC [2001]. Coal and gas outbursts in footwalls of reverse faults. 

Int J Coal Geol 48(1–2):47–63. 

Chance HM [1883]. Report on the mining methods and appliances used in the anthracite 

coalfields. Harrisburg, PA: Second Geological Survey of Pennsylvania. 

Chase FE, Ulery JP [1987]. Clay veins: their occurrence, characteristics, and support. 

Pittsburgh, PA: U.S. Department of Interior, Bureau of Mines, RI 9060. NTIS No. PB 87– 

204517. 

16
 
Clayton JL [1998]. Geochemistry of coalbed gas: a review. Int J Coal Geol 35(1–4): 

159–173. 

Clayton JL, Leventhal JS, Rice DD, Pashin JC, Mosher B, Czepiel P [1993]. Atmospheric methane flux from coals: a preliminary investigation of coal mines and geologic structures 

in the Black Warrior basin, Alabama. In: Howell DG, ed. The future of energy gases. Reston, 

VA: U.S. Department of Interior, U.S. Geological Survey, USGS Professional Paper 1570, 

pp. 471–492. 

Creedy DP [1988]. Geological controls on the formation and distribution of gas in British 

coal measure strata. Int J Coal Geol 10(1):1–31. 

Darton NH [1915]. Occurrence of explosive gases in coal mines. Washington DC: U.S. 

Department of Interior, Bureau of Mines, Bulletin 72. 

Diamond WP [1982]. Site-specific and regional geologic considerations for coalbed gas 

drainage. Pittsburgh, PA: U.S. Department of Interior, Bureau of Mines, IC 8898. NTIS No. 

PB 83–157685. 

Diamond WP [1994]. Methane control for underground coal mines. Pittsburgh, PA: U.S. 

Department of Interior, Bureau of Mines, IC 9395. 

Diamond WP, Schatzel SJ [1998]. Measuring the gas content of coal: a review. Int J Coal 

Geol 35(1–4):311–331. 

Diamond WP, LaScola JC, Hyman DM [1986]. Results of direct-method determination 

of the gas content of U.S. coalbeds. Pittsburgh, PA: U.S. Department of Interior, Bureau of 

Mines, IC 9067. NTIS No. PB 86–205325. 

Dutcher RR, Campbell DL, Thornton CP [1966]. Coal metamorphism and igneous 

intrusives in Colorado. In: Given PH, ed. Coal Science, American Chemical Society, Advances 

in Chemistry Series, Vol. 55, pp. 708–723. 

Finfinger GL, Cervik J [1979]. Drainage of methane from the overlying Pocahontas No. 4 

coalbed from workings in the Pocahontas No. 3 coalbed. Pittsburgh, PA: U.S. Department of 

Interior, Bureau of Mines, RI 8359. NTIS No. PB 296 882. 

Gurba LW, Weber CR [2001]. Effects of igneous intrusions on coalbed methane 

potential, Gunnedah basin, Australia. Int J Coal Geol 46(2–4):113–131. 

Houseknecht DW [1982]. Probability of encountering coalbed discontinuities during 

vertical and horizontal borehole drilling. Pittsburgh, PA: U.S. Department of Interior, Bureau of 

Mines, RI 8665. NTIS No. PB 82–232091. 

Humphrey HB [1960]. Historical summary of coal-mine explosions in the United States, 

1810–1958. Washington DC: U.S. Department of Interior, Bureau of Mines, Bulletin 586. 

Iannacchione AT, Ulery JP, Hyman DM, Chase FE [1981]. Geologic factors in predicting 

coal mine roof-rock stability in the upper Kittanning coalbed, Somerset County, PA. Pittsburgh, 

PA: U.S. Department of Interior, Bureau of Mines, RI 8575. NTIS No. PB 82–145376. 

Johnson RC, Flores RM [1998]. Developmental geology of coalbed methane from 

shallow to deep in Rocky Mountain basins and in Cook Inlet-Matanuska basin, Alaska, U.S.A. 

and Canada. Int J Coal Geol 35(1–4):241–282. 

Jüntgen H, Klein J [1975]. Formation of natural gas from coaly sediments (in German). 

Erdöl und Kohle Erdgas Petrochemie 28(2):65–73. 

Lama RD, Bodziony J [1998]. Management of outburst in underground coal mines. Int J 

Coal Geol 35(1–4):83–115. 

McCulloch CM, Diamond WP, Bench BM, Deul M [1975]. Selected geologic factors 

affecting mining of the Pittsburgh coalbed. Pittsburgh, PA: U.S. Department of Interior, Bureau 

of Mines, RI 8093. NTIS No. PB 249 851. 

17
 
McKinney R, Crocco W, Tortorea JS, Wirth GJ, Weaver CA, Urosek JE, Beiter DA, 

Stephan CR [2001]. Report of investigation, underground coal mine explosions, July 31­

August 1, 2000. Willow Creek mine, MSHA ID No. 42–02113, Plateau Mining Corporation, 

Helper, Carbon County, Utah. Arlington, VA: U.S. Department of Labor, Mine Safety and 

Health Administration, CAI–2000–18/19. 

McKinney R, Crocco W, Stricklin KG, Murray KA, Blankenship ST, Davidson RD, 

Urosek JE, Stephan CR, Beiter DA [2002]. Report of investigation, fatal underground coal mine 

explosions, September 23, 2001. No. 5 Mine, Jim Walter Resources, Inc., Brookwood, 

Tuscaloosa County, Alabama, ID No. 01–01322. Arlington, VA: U.S. Department of Labor, 

Mine Safety and Health Administration, CAI–2001–20 through 32. 

Price PH, Headlee AJW [1943]. Natural coalbed gas in West Virginia. AAPG Bull 27(4): 

529–537. 

Prosser LJ Jr., Finfinger GL, Cervik J [1981]. Methane drainage study using an underground pipeline, Marianna Mine 58. Pittsburgh, PA: U.S. Department of Interior, Bureau of 

Mines, RI 8577. NTIS No. PB 82–142860. 

Richmond JK, Price GC, Sapko MJ, Kawenski EM [1983]. Historical summary of coal 

mine explosions in the United States, 1959–81. Pittsburgh, PA: U.S. Department of Interior, 

Bureau of Mines, IC 8909. NTIS No. PB 83–184226. 

Thielemann T, Krooss BM, Littke R, Welte DH [2001]. Does coal mining induce 

methane emissions through the lithosphere/atmosphere boundary in the Ruhr basin, Germany? 

J Geochem Exploration 74(1–3):219–231. 

Ulery JP [2006]. Managing excess gas emissions associated with coal mine geologic 

features. In: Kissell FN, ed. Handbook for methane control in mining. Pittsburgh, PA: U.S. 

Department of Health and Human Services, Public Health Service, Centers for Disease Control 

and Prevention, National Institute for Occupational Safety and Health, DHHS (NIOSH) Publication No. 2006–127, IC 9486, pp. 97–112. 

Ulery JP Molinda GM [1984]. Influence of overlying strata on methane emissions in a 

northern West Virginia coal mine. Pittsburgh, PA: U.S. Department of Interior, Bureau of Mines, 

RI 8879. NTIS No. PB 84–235282. 

Venter J, Stassen P [1953]. Drainage and utilization of firedamp. Washington DC: U.S. 

Department of Interior, Bureau of Mines, IC 7670. 

Wang A, Mutmansky JM [1998]. Economic decision making for methane drainage systems for underground coal mines. Min Eng 50(3):69–74. 

18
 
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