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UNITED STATES DEPARTMENT OF THE INTERIOR 
Information Circular 91 55 

A Review of the Mechanisms 

of Gas Outbursts in Coal 

By David M. Hyman 

UNITED STATES DEPARTMENT OF THE INTERIOR 

Donald Paul Hodel, Secretary 

BUREAU OF MINES 

David S. Brown, Acting Director 
Library of Congress Cataloging in Publication Data : 

, 

* 

Hyman, D. M. (David M.) 

A review of the mechanisms of gas outbursts in coal. 

(Information circular; 9155) 

Bibliography: p. 10 -11. 

Supt. of Docs. no.: 128.27: 9155. 

1. Coal mines and mining. 2. Gas bursts. I. Title. 11. Series: Information circular (United 

States. Bureau of Mines); 9155. 

TN295.U4 [TN313] 622 s [62Z1.81 87-600180 
CONTENTS 

Page 

Abstract ....................................................................... 1 

Introduction ................................................................... 2 

Coal-gas sorption-desorption methods ........................................... 3 

Borehole prediction method ..................................................... 6 

Mitigation of outburst events.* ................................................ 7 

Summary and conclusions ........................................................ 9 

References ..................................................................... 10 

ILLUSTRATIONS 

1 . Methane emissions from mining events ....................................... 3 

2 . Comparison of theoretical coal chip desorption ............................. 4 

3 . Volumes of gas released by outburst events ................................. 6 
UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT 

cm centimeter m meter 

cm3/g cubic centimeter per m 

3 cubic meter 

gram 

mi n minute 

crn3/ (kg 'min2) cubic centimeter per 

kilogram square mm millimeter 

minute 

m3/mt cubic meter per 

g gram metric ton 

h hour MPa megapascal 

kPa kilopascal Pet percent 

L liter s second 

L/min liter per minute 
A REVIEW OF THE MECHANISMS 

OF GAS OUTBURSTS IN COAL 

By David M. Hymanl 

Outbursts are sudden and violent releases of gas and coal that result 

from a complex function of geology, stress regime, and gas pressure and 

content. The Bureau of Mines has reviewed methods for prediction and 

mitigation of such outbursts in use worldwide, as an aid in selecting 

the proper techniques for use in specific mine environments. Outburstprone coal may be distinguished from normal coal by its sorptiondesorption velocity. Three types of methods used to characterize the 

kinetics of sorption-desorption are described; all are based on the 

ability of outburst-prone coal to release, through desorption, methane 

or carbon dioxide much more rapidly than normal coals. Other prediction 

methods, based on borehole samples, are also described. 

Various mitigation methods described and evaluated include (1) working 

the least stressed, less disturbed, lowest gas content seam in multipleseam areas; (2) mine opening geometry; (3) inducer shot firing; (4) 

water infusion; (5) localized stress relief, using boreholes or by cutting a reliever slot in the longwall face; and (6) other gas drainage 

methods. 

- 

~eolo~ist, Pittsburgh Research Center, Bureau of Mines, Pittsburgh, PA. 
INTRODUCTION 

An outburst is defined as a violent, 

simultaneous release of gas(es) and comminuted rock material into a working face 

or the interior of a borehole. In general, an outburst event has the following 

phases (1): 2 

1. A stressed volume of rock containing gas(es) is exposed to a rapid change 

of confining stress. This rock volume 

has been highly fractured as a result 

either of some preexisting geologic disturbance (such as a fault) or of mininginduced stress concent ration. 

2. Gas(es) adsorbed in or contained in 

sandstone or evaporite rocks are rapidly 

released into the fractures , which already contain free gas. When more gas 

enters the fracture space than can be 

transported away through the less permeable rock body, a state of stress due 

to gas pressure may be reached where the 

rock body cannot contain the increasingly 

stressed fractured rock volume. 

3. When the rock body can no longer 

contain the stressed and fractured rock 

volume, containment ceases and the fractured rock mass and gas(es) undergo movement as they are driven by the gas into a 

pressure sink, e.g. , a mine opening or 

borehole. 

4. After the movement of the fractured 

rock and gas(es), there may be continued 

gas flow from the fractured but in-place 

rock that forms the outburst cavity. 

This gas flow generally decreases over 

time. 

Two major theories--the "pocket" and 

the "dynamic" theories--can describe the 

basis of the coal outburst mechanism. The 

pocket theory holds that there exist certain volumes of "soft" or crushed coal 

enclosed by "harder" or less fractured 

coal that form reservoirs of gas contained in the fracture void space. These 

crushed coal volumes are associated with 

faulted or sheared zones and with intensely folded strata. This comminuted 

- 

2~nderlined numbers in parentheses refer to items in the list of references at 

the end of this report. 

coal has little unconfined compressive 

strength and is separated from the mine 

opening by an intact zone of coal under 

sufficient stress to become a "permeability dam." When mine development approaches a "soft coal" region, an outburst can result if the region is not 

sufficiently drained of free gas and/or 

the stresses in the region are not 

dissipated (2). 

The dynamic theory holds that a volume 

of relatively gassy coal, which is highly 

stressed and penetrated by mining-induced 

fractures, is outburst prone. When a 

mine opening and induced stresses approach such a coal volume, the coal fractures, releasing high-pressure desorbed 

gas, and the coal face fails, resulting 

in an outburst (2). 

Common to both theories is high-gascontent fractured coal that is able to 

desorb gas rapidly upon release of confining pressure. This rapid desorpt ion 

feature of outburst-prone coal is the basis for a rather extensive set of predictive methods, which are detailed later in 

this report. 

Other aspects of outburst-prone coal 

include low in situ strength due to fissuring, high free-gas pressure, and association with geologic structures such as 

fracture zones and igneous dikes. These 

aspects are also the basis of a variety 

of predictive methods (2). 

Outbursts in coal mines represent considerable hazards. The most immediate 

hazard is the unexpected inundation of 

the ventilation systems with asphyxiating 

volumes of gas. When methane is the released gas, an explosive hazard can be 

created, possibly exacerbated by ejected 

coal dust. The force of the released gas 

and displaced material can be sufficient 

not only to disrupt mine ventilation but 

to debilitate stoppings and ground control structures such as arches and posts, 

and to injure or kill mine personnel. 

Additionally, an outburst zone presents a 

ground control problem due to the fissile 

nature of the rock that forms the remaining outburst cavity. Furthermore, gas 

may continue to be emitted, and without 
 

where 

V(t) = volume of methane desorbed after 

time t, min, 

A = equilibrium sorption capacity of 

coal at gas pressure, P, kPa, 

to = time constant min related to coal 

chip size, min, 

n = constant related to coal type or 

rank, 

VL = maximum Langmuir sorptive capacity 

of coal sample, cm3Ig, 

ROCK MINED OR OUTBURSTED, rnt 

k L = Langmir strength of attraction 

FIGURE 1.-Methane emissions trom mining events. for gas to sorb, kPa' '. 
The value of to is defined as the time 

required for the subject coal sample of a 

given effective chip size to desorb 63 

pct of its gas content. A calculated to 

range of about 5 to 15 rnin (11) is consistent with microfissure densities with 

corresponding to values for outburstprone coals (&, 12). The coal constant, 

n, had been found empirically to be about 

0.5 for anthracite, 0.33 for bituminous 

coals, and 0.25 or less for outburstprone coal. As studies have indicated 

that some outburst-prone coals do not 

have a markedly different gas content 

than that of normal coal in the same 

coalbed, the same in situ equilibrium gas 

content, A, will be used in the analysis. 

Assuming chat coal chips have been obtained from both a normal coal volume and 

an outburst-prone zone, the relative 

(with respect to a constant) desorption 

curves for normal bituminous (n = 0.33, 

to = 60 rnin), anthracite (n = 0.5, to 

= 60 rnin), and outburst-prone (n = 0.25, 

to = 15 min) coal chip samples are calculated and presented as figure 2. As 

shown in figure 2, the outburst-prone 

coals initially desorb at a faster rate 

than normal coals. The highest contrast 

in desorption rates occurs within approximately the first 10 rnin of desorption time. It is apparent from this 

KEY -- - Outburst-prone coal 

Bituminous coal 

+----- Anthracite 

t 

I 

I 

0 5 0 100 150 200 

TIME, mln 

FIGURE 2.-Comparison of theoretical coal chip desorption. 

simplistic illustration that in order for 

desorption indices to differentiate between normal and outburst-prone coals, 

they must be determined within this short 

span of time. It also follows thai extraordinary care must be exercisec. in 

quickly obtaining and preserving (if 

necessary) coal chip samples for these 

predictive index determinations. One 

should also recognize that preserving 

coal chip samples in a pressurized chamber does not prevent the chips from 

undergoing structural degradation over 

time (5). 

~hree basic classes of tests characterize sorption-desorption kinetics (?). 

The first class comprises volume-desorbed 

methods, or so-called AV methods. One 

such method practiced on a workingmine-section scale is the V3o index (1, 

- 13). The volume of methane emitted 

within the first 30 rnin after shot firing 

is measured and normalized to the mass of 

coal broken by the shot. This value is 

divided by the desorbable gas content 

(qd), which is determined by a coal chip 

desorption test described later in this 

section. Normal coals have a V3o value 

ranging between 0.10 and 0.17, compared 

with about 0.40 for outburst-prone coals 

and '0.60 for outburst coals. This index 

is used in the Federal Republic of Germany as part of a hierarchy of tests to 

assess the risk of encountering an 

outburst. 

Another volume-type index is used primarily in Australia to predict the risk 

of outbursts in advance of mining. This 

test is mainly used for carbon dioxidecoal outbursts (4). The Hargraves AV 

index uses a 4-g sample of drill cuttings 

sized from0.6 to 1.2mm. Thecuttings 

are obtained from a drill hole and sealed 

in a desorption meter within 1 rnin of being cut by the drill bit. The desorbed 

gas volume is measured from 1 to 6 rnin 

after drilling. When this value exceeds 

1.2 cm31g, the subject coal is considered 

outburst prone. This threshold value is 

gas specific and colliery specific. The 

use of a slightly modified AV index with 

a shorter observation period was attempted in Belgium with some success. If 

the volume of gas (V1) desorbed between 

35 and 70 s after drilling is greater 
p, 

y 

the coal. The sample chamber is then 

evacuated before being pressurized with 

methane at about 100 kPa for 90 rnin so as 

to saturate the coal sample. After 

saturation, the sample chamber is connected to an evacuated chamber to reduce 

the pressure in the sample chamber to a 

negative 100-kPa pressure very rapidly. 

The pressure rise is then measured 10 to 

60 s after this chamber pressure reduction. The APo-60 index is equal to the 

pressure rise at 60 s minus the baseline 

pressure rise for the assumed inert (with 

respect to sorption by coal) helium. The 

AP10-60 index is the difference between 

pressure rises measured at the 10- and 

60-s time periods and indicates outburstprone conditions when it is greater than 

about 1.3 kPa. When APo-60 is greater 

than 2 kPa, the sample is considered to 

represent outburst-prone conditions. The 

primary disadvantages of the APo-60 test 

are that it is a laboratory-based determination and requires 6 to 8 h to perform 

(1) 

p

change of desorption rates or desorption 

deceleration. In the Federal Republic of 

Germany a series of calculations is used 

that is based upon the desorption deceleration of borehole cuttings collected 

and sealed in a desorption meter within 

1 rnin of cutting (1, 14). About 10 g of 

coal cuttings in the 0.4- to 0.63-mm size 

range are collected, and the desorption 

rates are measured over a 5- to lO-min 

period. For this time period, a power 

law relationship for desorption rate over 

time is assumed: 

where time (t) is in minutes. 

If this power law relationship is 

obeyed, a plot of logarithmic desorption 

rate versus logarithmic time will yield a 

straight line of slope k. The intercept 

at time = 1 rnin is the desorption rate at 

1 min. When this intercept value is 
the British desorption ratio, where a 

sample's desorbable gas content for a 

certain time period is divided into a 

mine-specific representative desorption 

volume. When this ratio exceeds 4, then 

the sample in question is considered to 

represent an outburst-prone zone (1). 

This property of very rapid desorption 

is a fundamental precondition to the 

would help explain their faster desorption kinetics. One might also expect 

this smaller effective size to contribute 

to increased friability and lower 

strength in comparison to normal coal in 

the same coalbed (10-11). -- Other types of 

outburst-prediction methods also take 

advantage of these aspects. 

BOREHOLE PREDICTION METHOD 

During the drilling of boreholes into 

outburst-prone zones, drillers often note 

gas "kicks," increased gas flows, and 

disproportionately large volumes of drill 

cuttings (10). - In the Federal Republic 

of Germany, a drill-cuttings-to-hole 

volume ratio greater than about 3:l to 

7:l is indicative of outburst conditions 

in the coal penetrated by the drill hole. 

The borehole diameters ranged from 50 to 

140 mm in the work reported . A 

French study did not establish an outburst risk threshold for drill cutting 

volumes from 43-mm-diameter drill holes 

even though 2 to about 130 times more 

cuttings were encountered than could be 

accounted for by hole volume (1). Since 

volume measurements of drill cuttings are 

not accurately reproducible owing to differences in bulking between samples, a 

gravimetric method would be more useful. 

A more direct and hopefully more useful 

prediction method based on the sheared 

and/or low-strength qualities of 

outburst-prone coal is presented by 

Kidybinski (15-16), -- whose two papers describe the use of a borehole penetrometer 

with a conical tip to determine faulted 
areas and adjacent zones of relatively 

soft coal, as an outburst prediction 

tool. This use of this tool yields a 

coal and/or rock strength index, Z, that 

is equal to the applied thrust on the 

cone divided by the penetration distance. 

MITIGATION OF 

The ultimate method for preventing an 

outburst event during mining is to predict potential zones of outbursts and 

avoid them or at least reduce their outburst potential. As the outburst mechanism is a complex relationship between 

geologic structure, mining-induced stresses, and gas content and pressure, the 

removal or mitigation of one or more of 

these elements can possibly reduce outburst potential. Geologic structures 

such as faults or sheared zones can be 

avoided to a certain extent. Stresses 

can be reduced by changes in mining 

rates, methods, and geometry. Gas contents and pressures can be reduced by 

drainage. Most of the methods practiced 

throughout the world involve relieving 

stress concentrations and/or in situ gas 

pressure. 

A whole-seam stress reduction method 

applicable in areas where several minable 

coal seams occur in close proximity is 

known as "working the protective seam" 

(I). The idea behind this method is to 

mine the least stressed, and/or lowest 

gas content, and/or least disturbed coalbed of those in a multiple-seam configuration. It is preferred to mine as a protective seam an overlying one, instead of 

an underlying one, unless the outburst 

problems are more severe than the ground 

control problems due to subsidence from 

undermining. If conditions permit, the 

pillars could be superimposed for the 

protective and outburst-prone seams so as 

not to defeat the stress-relief aspect of 

this protective method. Mining the protective seam can also induce some fissuring and thus potentially drain some portion of the gas in the outburst-prone 

seam. Not only does the gas drainage effect tend to help lower the overall gas 

content of the outburst-prone seam, it 

also can help lessen the magnitude of 

the desorption rate by allowing the 

In tests at three mines, the coal 

strength was found to be related to in 

situ gas pressures. Some preliminary 

empirical relationships were developed, 

but more research is required to develop 

a more definitive relationship. 

OUTBURST EVENTS 

desorption process to begin prior to mining. The overall effect of mining a protective seam is to reduce the stress and 

gas dynamic potential fields of the 

outburst-prone seam (17). Thus, it is no 

surprise that this method is one of the 

most effective methods of reducing outbursting probability. Unfortunately, 

this method is applicable only in multiseam configurations. In single-seam configurations, other methods must be 

employed to reach the same end of reducing the stress and gas dynamic potential 

fields of an outburst-prone coalbed. 

Given an outburst-prone coalbed, a 

variety of methods have been practiced to 

relieve stress concentrations. Mine 

opening geometry control is a relatively 

effective method. Stress concentrations 

are greater at the face of a single 

heading or roadway than along a longwall 

face. Retreat longwalls are less prone 

to outbursts than advancing longwalls. 

Pillar extraction is less prone to outbursting than retreating longwalls, but 

this may be due to degassing more than to 

stress relief. The most outburst-prone 

mining operation is when a heading or 

tunnel moves from one coal seam through a 

rock interburden to an adjacent coal seam 

(4). In general, longwall mining methods 

with gate roads not developed more than 2 

m ahead of an advancing longwall face are 

less liable to trigger outbursts than are 

room-and-pillar mining methods (1). 

Besides mine opening several 

stress-relief measures are practiced at 

the mine face level. Inducer shot firing 

is employed in several countries to 

relieve stress accumulations and to trigger outbursts in a relatively controlled 

fashion. One form that inducer shot firing takes is destressing at the ends or 

gate road faces of a longwall panel. 

This precautionary shot firing involves 

drilling holes outby the gate road faces, 
usually to a depth of about 3.7 to 4.6 m, 

although in Turkey holes up to 8.3 m deep 

are used (8). These holes are charged 

with explosives. When an outburst-prone 

zone is predicted within the longwall 

face area, shot firing is performed by 

detonating explosives in boreholes across 

the longwall face on both sides of the 

suspected zone (1). The explosive 

charges can be detonated either simultaneously (camouf let) for maximum shock 

loading, or with short delays to facilitate mucking operations. A variation on 

this shot-firing theme is termed pulsed 

infusion shot firing. For this method 

boreholes 4 to 9 m deep are drilled, 

charged with submarine explosives, filled 

and pressurized with water, and detonated. Although shot firing has been 

used with some success in controlling the 

occurrence of outbursts and in mitigating 

to some extent the severity of further 

outbursts in the treated area, it is an 

inherently hazardous practice; also the 

deleterious effects of expelled coal and 

gas due to outbursting still occur and 

must be considered when using these 

techniques. To a limited extent, the 

erection of a barricade 8 to 15 m from 

the face can mitigate these deleterious 

effects. Unfortunately, such barricades 

introduce problems for postshot face 

ventilation gas checks (4). 

A less energetic method of destressing 

and fracturing an outburst-prone zone in 

a coalbed is through water infusion. 

Water infusion for destressing is a modified form of water infusion for dust and 

gas emission control. It is performed 

where prediction methods such as proximity to a fault, high PO-60 values, or 

discharge of a large relative volume of 

drill cuttings indicate an outburst-prone 

z one. The infusion method has been 

implemented in the Federal Republic of 

Germany (19) by drilling 50-mm-diameter 

boreholesat a spacing of three to four 

gate road widths in the suspect zone. 

The boreholes are drilled into the suspect zone and generally are less than 10 

m from the face; depending on the nature 

and extent of the suspected outburstprone zone, they can be up to 60 m from 

the face. Water is pumped into the holes 

at about 70 to 100 L/min, at pressures up 

to 40 MPa but averaging 11 to 23 MPa. 

Each hole pattern is infused sequentially 

until either cracking or separation of 

the coalbed occurs. The infused water 

both redistributes stress and forces free 

gas in the fractures away from the face. 

Water infusion becomes hydraulic f racturing when a series of pressure pulses are 

applied to the water in the hole. A 

major drawback to water infusion is that 

its degassing or gas-displacing effects 

are relatively short-lived; consequently, 

it must be performed frequently, potentially interfering with production. 

Localized stress relief can be accomplished through the use of boreholes in 

terms of relieving both local stress and 

gas pressure. These st ress-relief boreholes have diameters of about 82 to 300 

mm. An effective borehole diameter is 

found by drilling holes of progressively 

larger diameters until an excessive volume of cuttings is discharged, indicating a miniature outburst event in the 

hole. The relief hole spacing is found 

by reducing borehole spacing until no 

audible stress readjustments are heard 

(4) as the holes are bored. The length 

of these boreholes is 10 to 25 m in advance of the face. Additionally, cavities can be excavated at some depth in 

the borehole to trigger an outburst in 

the borehole to further relieve stress 

and gas pressure. This practice is known 

as "perforation" in Hungary and has also 

been used in the U.S.S.R. and Australia. 

A considerable drawback to perforation is 

controlling the coal dust and gas ejected 

from the hole. 

A stress-relief technique practiced in 

the U.S.S.R. is the cutting of a reliever 

slot in the longwall face. A cutting 

cable saw is used to cut an 80mm slot 

about 3 to 5 m deep, effectively undercutting the face. Different slot orientations and cutting depths are used, 

depending on local conditions (17). - Relief of excess stress removes, 

through redistribution, a portion of the 

triggering energy for an outburst. The 

reduction of gas pressure as well as gas 

content also removes potential energy 

from an outburst-prone zone. An 

outburst-mitigation method therefore reduces gas pressure in a gas drainage 
borehole, as well as reducing stress con- A gas drainage experiment was conducted 

centrations to a limited extent. in an Australian coalbed containing shear 

In general, gas drainage boreholes have zones that were outburst prone (21). The 

smaller diameters (40 to 100 mm) than experiment consisted of drillis three 

stress-relief boreholes. The strategy in 100-mm-diameter holes parallel to each 

gas drainage is to degas volumes of rock other and separated by about 10 m. The 

in advance of mining with lateral and holes were drilled to 23-, 45-, and about 

vertical holes in gate roads and faces 601x1 depths. The longest hole penetrated 

(6). It has been found that open hole or a shear zone. Gas pressure and flows 

free-flow drainage is not as effective or were monitored for about 140 days. The 

efficient as applying a negative pressure shortest hole produced 0.35 L/min per 

of 7 to 40 kPa. Studies (1, 17, 3) have meter of length, the 45-m hole produced 

shown that application of a slight nega- about 2 L/min per meter, and the hole 

tive pressure to increase the borehole that penetrated the shear zone produced 

pressure sink increased gas output from 63 L/min per meter. The gas pressure in 

the drainage holes by factors of 2 to 4 the shear zone dropped from an initial 

times compared with free-flow drainage. 410 kPa to about 200 kPa after 30 days 

What determines the spacing of boreholes and to about 100 kPa after 80 days. The 

in a gas drainage plan is a complex func- depth of the coalbed was about 500 m, and 

tion of coalbed permeability, gas pres- the holes were drained without the apsure, pressure gradient, degree of water plication of suction. When mining intersaturation, gas dynamics of the coal, and cepted this drained shear zone, no outduration of drainage. A Chinese experi- bursts occurred. In another experiment 

ment (1) involved the drilling of 22 gas in the same mine, 40-kPa suction was apdrainage holes of 75-mm diam into an plied to boreholes, yielding 200- to 400- 

outburst-prone coalbed. These holes were pct increases in flow rates. The range 

monitored for 19 months. When mining of influence for drainage holes in this 

operations penetrated the drained zone, mine was estimated to be about 30 m. 

no outburst events occurred. A 6- to 7-m While not all gas drainage exercises 

radius of influence was calculated, reported in the literature have prevented 

indicating that a 10- to 15-m gas drain- outbursts, they have been somewhat efage hole spacing would be effective for fective in draining gas and reducing 

this mine. The Japanese (20) performed a gas pressure in advance of mining. 

gas drainage study in which 65- to 90-mm Gas drainage works best in outburst 

boreholes were drilled at 10- to 20- zones where the coal is crushed or 

spacings. The gas drainage was aided by comminuted, as in a fault or shear 

suction. During drainage, test holes zone. Outburst-prone zones where the 

were bored and gas pressure and flow mea- coal is relatively intact are not very 

surements were made. Mining was started amenable to gas drainage without the 

when the test boreholes showed that gas application of borehole stimulation 

pressures and flows had been lowered. techniques. 

This gas reduction occurred after 1 to 2 

months. 

SUMMARY AND CONCLUSIONS 

The body of scientific literature that 

describes outburst mechanics, preconditions, prediction techniques, and prevention or defensive measures is extens ive. Effective management of outburst 

zones requires that they be predicted in 

advances of mining by geological investigations to delineate fault or shear 

zones and igneous intrusions. A variety 

of physical testing methods is available 

to predict outbursts, centering on relatively rapid (on the order of minutes) 

desorption tests. Borehole prediction 

methods rely on the instability and fissile nature of outburst-prone coal or gas 

and comminuted coal expulsions from boreholes. As outbursts are a complex function of geology, stress regimes, and 
gas contents, available defenses attempt an outburst-prone zone has been defined 

to relieve stress and gas pressures once and geologically mapped. 

REFERENCES 

1. Baker, A. Outbursts in Coal 

Mines. IEA Coal Res., 1984, 55 pp. 

2. Shepard, Jo, L. KO Rixon, and L. 

Griffiths. Outbursts and Geological 

Structures in Coal Mines: A Review. 

Int. J. Rock Mech., Min. Sci. & Geomech. 

Abstr., v. 18, 1981, pp. 267-283. 

3. Hargraves, A. J. Particular Gas 

Problems of Australian Deep Coal Mining. 

Paper in Third International Mine Ventilation Congress (Harrogate, England, June 

13-19, 1984). Inst. Min. and Metall., 

1984, pp. 127-133. 

4 . -- . Instantaneous Outbursts of 

Coal and Gas - A Review. Proc. Australasian Inst. Min. and Metall., No. 258, 

Mar. 1983, pp. 1-37. 

5. Lama, Ro Do Adsorption and Desorption Techniques in Predicting Outburst of Gas and Coal. Paper in Symposium on the Occurrence, Prediction, and 

Control of Outbursts in Coal Mines. 

Australasian Inst. Min. and Metall. , 1980, pp. 173-191. 

6. Patching, To Ha, and J. C. Boltham. Occurrence, Research, and Control 

of Sudden Outbursts of Coal and Gas in 

Canada. Dep. Energy, Mines and Resources, Mines Branch, Ottawa, Canada, 

Reprint Series RS28, 1967, 29 pp. 

7. Vandeloise, Ro Survey of New 

Methods Used in Belgium. Paper in Symposium of Coal and Gas Outbursts (Nimes, 

France, NOV. 25-27, 1964), United 

Nations, New York, 1967, pp. 46-71. 

8. Saltoglu, S. The Presentation, 

Evaluation, and Fighting Procedures of 

the Sudden Gas and Coal Outbursts in the 

Zonguldok Coal Field of Turkey. Paper in 

Ninth World Mining Congress, Federal Republic of Germany, May 11-21, 1976, pp. 

1-10; available from Do Me Hyman, Bu- 

?lines, Pittsburgh, PA. 

9. Litwiniszyn, Jo A Model for the 

Initiating of Coal-Gas Outbursts. Int. 

3. Rock Mech., Min. Sci. & Geomech. 

Abst. , V. 22, NO. 1, 1985, ppo 39-46. 

10. Paul, K. Forewarning and Prediction of Gas Outbursts in a West German 

Coal Mine. Paper in Symposium on the 

Occurrence, Prediction, and Control of 

Outbursts in Coal Mines (Supplement). 

Australasian Inst. Min. and Metall. 1980, 

pp. 1-21. 

11. Brown, K. Me, N. Rigby, and Go Re 

Barker-Read. Gas Emission and Outburst 

Predictions. Paper in Third International Congress on Mine Ventilation 

(Harrogate, England, June 13-19, 1984). 

Inst. Min. and Metall., 1984, pp. 151- 

155. 

12. Airey, Ee Me Gas Emission From 

Broken Coal, An Experimental and Theoretical Investigation. Int. J. Rock 

Mech., Min. Sci. & Geomech. Abstr., v. 5, 

1986, pp. 475-494. 

13. Noack, K. , KO Paul, and F. Poertge. Present Stage in the Prevention of 

Outbursts of Gas and Coal in the West 

German Bituminous Coal Mines. Paper in 

Proceedings of 20th International Conference of Safety in Mines Research 

Institute, (Sheffield, England, Oct. 3-7, 

1983). pp. B3, 1-20; available upon request from Do Me Hyman, BuMines, 

Pittsburgh, PA. 

14. Janas, He Improved Method for Assessing the Risk of Gas/Coal Outbursts. 

Paper in Second International Mine Ventilation Congress (Reno, NV, Nov. 4-8, 

1979). Soc. Metall. Eng. AIME, 1980, pp. 

372-377. 

15. Kidybinski, A. Experiment With 

Hard Rock Penetrometers Used for Mine 

Rock Stability Predictions. Paper in 

Proceedings of the Fourth Congress of the 

International Society for Rock Mechanics 

(Montreux, Switzerland, Sept. 2, 1979). 

A. A. Balkema, 1979, pp. 293-301. 

16. -- . Significance of In Situ 

Strength Measurements for Prediction of 

Outburst Hazard in Coal Mines of Lower 

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