Dynamic Failure in Deep Coal: Recent Trends and a Path Forward 

Jeffrey Whyatt, Mining Engineer 

NIOSH - Spokane Research Laboratory
 

Spokane, WA
 

ABSTRACT 

Mining coal in deep, gassy strata is difficult, particularly in 

deep mines of the west. Dynamic failure (bumps, bounces, etc.) is 

commonplace, particularly where strong sandstone strata are 

encountered in the overburden. The disaster potential posed by 

dynamic failure in these mines is examined and found to be 

significant. Recent trends in MSHA reportable bumping of deep 

western coal mines have been increasing. Recent clusters of 

bumps are explored, a number of which have ended badly. The 

mechanisms of these bumps and their interactions with geologic 

structures are explored. Significant progress in controlling these 

hazards depends on a full understanding of their interaction with 

geologic conditions. It is apparent that not all MSHA reportable 

bumps have the same mechanism. These reports describe 

bumping of pillars, rolling of ribs, outbursts of coal, heaving of 

floor, shaking-induced roof falls, etc. Progress depends on 

understanding the underlying mechanisms of these events, and 

then determining which are potentially active at a particular 

location. Designs and other protective measures can then be 

adapted and deployed appropriately. Explicit consideration of 

mechanisms also supports extrapolation beyond experience as 

design extends into new mine geometries, geologies, mining 

methods and increasing depth. Finally, the goal should not be 

only to design hazard out of mines, but also to provide assurance 

that this, in fact, has occurred. Pursuit of this goal has been taken 

up by a major NIOSH research project. The centerpiece of this 

project is development of a Dynamic Failure Control Program to 

monitor evolution of dynamic failure hazards with changing 

geologic conditions to assure that control and protective measures 

are appropriately deployed. 

INTRODUCTION 

The potential for fatal injury and disaster posed by dynamic 

failure in deep coal mines has concerned researchers at the 

National Institute for Occupational Safety and Health (NIOSH). 

This concern led to a research proposal entitled “Dynamic Failure 

Control Program for Deep Coal” that was completed on August 

1st of 2007. Of course, this concern was all too quickly realized in 

the tragedy of Crandall Canyon. This paper presents an overview 

of the trends and dynamic failure mechanisms that focused this 

concern, and the path forward. NIOSH has since initiated a major 

research project based on this proposal. 

Dynamic failure 

Mining at depth necessarily includes yielding of the host 

geology. Yield often occurs in a controlled manner, but can also 

occur dynamically, releasing seismic energy. As a matter of 

custom, dynamic failures are called bumps or bounces, depending 

on local usage. Sudden failures that expel large quantities of rock, 

coal or gas are called rock bursts, coal outbursts and gas 

outbursts, respectively. In addition, seismic energy released by a 

dynamic failure may cause additional damage in insufficiently 

reinforced areas, sometimes called “shakedown damage.” 

Terminology varies widely with locale and may include the terms 

shock bump, district bump, mountain bump, pillar bump, face 

bump, etc. These terms have a variable and at times, tenuous, link 

to a specific failure mechanism that varies with locale. MSHA 

reporting requirements are based on the impact of events, 

uniformly called bumps, with no reference to mechanism. This 

paper follows terminology used by the original source in 

reviewing past events, but the more general term “dynamic 

failure” is used for discussion. 

Experience gained through many sectors of the mining 

industry has shown that dynamic failures can be classified into 

three broad classes based on mechanics. These are: (1) brittle 

failure of the immediate margin of an opening that expels material 

into the opening (outbursts); (2) brittle failure of an entire pillar; 

and (3) failure of strata in the roof or floor, including rock remote 

from the opening. Damage can be direct and/or through seismic 

shaking. The importance of this classification is that each of these 

mechanisms interacts differently with mine geology, ground 

support systems, mine design and active hazard reduction 

measures. In fact, it is possible that measures taken to control 

hazards from one mechanism will be ineffectual, or even 

counterproductive, in controlling hazards from another. 

Dynamic failure of deep mines is a longstanding hazard that 

figures prominently in historical disasters. In additional to 

physical trauma, dynamic failure in underground coal mines can 

release large quantities of gas, destroy ventilation controls, and 

provide an ignition source – both directly and through damage to 

equipment. Asphyxiation and gas poisoning are also a threat. 

While disasters are relatively rare, incidents involving damage to 

ventilation controls, disruption of mining, injuries and fatalities in 

coal mines are not. 
 

 

Thus, maintaining control of the yield process and its 

consequences is essential for mining safely, especially as yielding 

increases with depth. The maximum depth of mining for modern 

shield-based longwall systems was reported as 900 m (3000 ft) 

over 25 years ago (1). This limit is rarely breached to this day, in 

part because of dynamic failure hazards. 

0 

2 

4 

6 

8 

10 

12 

14 

16 

Fatal 

Lost Time 

No Days Lost 

Non Injury 

2000 2001 2002 2003 2004 2005 2006 07/07 

ytd 

Reportable Coal Bumps CO & UT 

Figure 1. Recent reportable dynamic failure accidents and 

incidents for 14 deep longwall coal mines in Utah and 

Colorado. 

Dynamic failure and deep coal mining 

Recently, an increasing number of dynamic failures in deep 

mines of Colorado and Utah have caused injuries or disrupted the 

mine sufficiently to be defined as MSHA-reportable coal bumps 

(figure 1). This increase occurred despite a relatively flat level of 

production. Still, these bumps represent only a very small portion 

of the dynamic ground failure events detected by seismic 

monitoring systems. Dynamic ground failure is a common feature 

of underground coal mining, especially for longwall mining in the 

west (2; 3). Many of these have released sufficient seismic energy 

to appear on earthquake monitoring networks, some with 

magnitudes in excess of 4.0 (figure 2). 

Figure 2. Concentrations of mining-related seismic events with magnitude 1.8 and greater 

in the Wasatch Plateau and Book 

The potential for disaster associated with dynamic ground 

failure is difficult to ascertain, and most of the dynamic failures 

captured in figure 2 posed little threat to miners, and had virtually 

no disaster potential. In fact, many of these occur as caving of 

strata shifts stress from panels to gob, a shift that works to reduce 

bump hazard. Some others, however, do represent a potential 

hazard but that potential does not correlate with the amount of 

seismic energy released. Historical cases show that the disaster 

potential can be significant and can take a variety of forms. These 

include both direct impact and creation of an explosive 

atmosphere through gas release and damage to the ventilation 

system. Damage to ventilation disrupts removal of methane, 

potentially creating an explosive atmosphere regardless of 

whether the event releases additional methane. 
 

 

Figure 3. Reportable bumps grouped into clusters by mine and 12-month period through
 

July of 2007.
 

These bumps have tended to occur in clusters as particular 

mines encounter challenging mining conditions (figure 3). 

Clusters are identified as 2 or more reportable bumps occurring 

within a 12-month period. Of these clusters, the largest recently 

ended with closure of the Aberdeen mine. Among the remaining 6 

clusters of three or more events since 1999, 2 ended without 

apparent incident, 2 ended with a design change or move to a new 

area, 1 ended with a fatal accident, and 1 with a fire and 

explosion. Clusters also preceded two earlier instances, the 1998 

Willow Creek fire and the 1996 fatal bump accident at Aberdeen. 

Bumps continue to occur, as do their impacts on industry. 

Figure 4 contains updated versions of Figure 1 that show the 

continuing escalation of bumping, including, in figure 4B, the 

Crandall Canyon tragedy. 

w/o Crandall Canyon 

25 

Fatal 

Lost Time 

20 No Days Lost 

Non Injury 

15 

10 

5 

0 

Reportable Coal Bump Incidents CO & UT 

2000 2001 2002 2003 2004 2005 2006 2007 

A 

Reportable Coal Bump Incidents CO & UT 

45 

40 

35 

30 

25 

20 

15 

10 

5 

0 

Fatal 

Lost Time 

No Days Lost 

Non Injury 

2000 2001 2002 2003 2004 2005 2006 2007 

B

Figure 4. An update to figure 2 to the end of 2007 (A) without and (B) with the Crandall Canyon disaster. 

Dynamic failures pose a variety of hazards. Direct impact is, of 

course, a primary threat. For instance, two fatal accidents at the 

Aberdeen mine (1996 and 2006) occurred as outbursts of coal 

from the longwall face (figure 5). Such outbursts are not isolated 

instance – accounting for many of the MSHA-reportable bumps 

reviewed. Many outbursts are not included as their impact did not 

rise to reportable thresholds. In some cases, this may have been a 

matter of luck. 

Direct impact injuries from massive strata failures, as opposed 

to local outbursts, have been comparably rare but can have more 

widespread impact. The Springhill Mine, Nova Scotia Disaster of 

1958 is a well documented example (4; 5). That disaster involved 

sudden failure of massive strata around three adjacent longwall 

panels (450 m [1500 ft] total width) retreating under 1325 m 

(4350 ft) of overburden. Bumping at the mine had been common, 

beginning at an overburden depth of about 610 m (2000 ft), but 

had increased exponentially prior to the disaster (figure 6). 

Injuries rose dramatically as well; 26 injuries from 12 bumps over 

26 years (1932 through March, 1958) to 49 injuries from 16 

bumps in the 6 months prior to the disaster. The panels had been 

carefully aligned in June and July, in an attempt to reduce 
 

 

 

 

 

 

 

bumping. Notley (4) conducted an energy release rate analysis, 

showing that alignment of the panels actually increased bump 

potential, accounting for the sudden increase in damage severity 

that killed 75 miners. Ignition of the explosive atmosphere created 

by this failure could have killed many of the rescuers and 100 

miners who escaped. 

Reported cases show that dynamic failure can initiate a 

disastrous chain of events in a variety of ways. These include 

release and/or ignition of methane (or other volatiles), destruction 

of ventilation controls necessary to remove methane, release of 

asphyxiating or poisonous gas, air blast and/or inundation. 

Li et al. (6) described a major disaster that killed 214 miners at 

Sunjiawan coalmine in Fuxin city, China on February 14, 2005. 

The disaster was initiated by a dynamic failure, detected as a 2.7 

magnitude seismic event that released methane into an already 

gassy mine. Li et al. attribute ignition, some 14 minutes later, to 

sparks induced by “rock movement” (presumably, by continued 

collapse of weakened roof and/or gob). The gas explosion was 

detected as a 0.6 local magnitude seismic event. 

The Dutch Creek No.1 disaster of 1981 was initiated by a 

sudden outburst of methane and coal dust (7), whose subsequent 

ignition by flawed machinery caused 15 fatalities. Bump initiation 

of a fire was reported by Jackson and Merritts (8) at the 

Kenilworth Mine. The role of dynamic failure in the Willow 

Creek fire and explosion is possible but less certain. McKinnery 

et al. (9) report “a sudden release of methane into the face area 

caused the shearer to de-energize” about 90 minutes prior to the 

first explosion and that “interruptions in production caused by 

methane were common.” They attribute ignition to “a roof fall in 

the headgate fringe of the gob” without further elaboration. 

Bumps and outbursts were described as common occurrences. 

In other cases, dynamic failure initiates release of other gases 

and/or water, resulting in poisoning, asphyxiation and/or 

drowning. The Solvay mine collapse of 1995 was the most 

notable of these events. Fortunately, the 5.2 magnitude, 2 square 

km collapse did not cause fatal injury directly or through ignition 

of the substantial release of methane. It did, however, result in 

one fatality from ammonia poisoning. 

These events are consistent with the overall history of bumping 

in coal mines. Iannacchione and Zelanko (10) constructed a 

database from MSHA (and earlier, USBM) reportable accidents 

and incidents between October 12, 1936 and January 21, 1993. 

The database contained 172 specific bump events that caused 87 

fatalities and 163 injuries. These events are a small minority of 

coal bumps, but are the most severe, causing injury and/or a 

significant disruption of mining activity. 

The database includes 36 bump events associated with 

longwall mining, the first in 1970. Of these, 12 occurred along the 

longwall face, 7 within the tailgate, 2 within the headgate, 13 

along the face and tailgate (combined), and 2 in longwall setup or 

bleeder entries. The most significant hazard was found to be 

ignition (by the bump and/or of gas released by the bump). Four 

such events were found, all in western longwall mines. Coal beds 

were included in each entry, allowing identification of bumpprone seams, nearly half of which were located in Colorado and 

Utah. Thus, there is good reason to believe that dynamic failures 

of ground have the potential to cause disastrous events in deep 

western coal mines. 

Figure 5. Fatal injury from coal outburst at the Aberdeen 

mine (MSHA fatalgram, 1996). 

Figure 6. Histogram showing quasi-seismic events 

per month during mining of the last three longwalls 

at Springhill Mine (3). 

Geologic features and dynamic failure 

Dynamic failures are often associated with particular geologic 

features, including discontinuities, sand channels, brittle 

intrusions, etc., although these relationships are often mine 

specific. Such features may concentrate stress, increase 

brittleness, reduce mine stiffness and/or locally weaken the rock 

mass, thereby nucleating a dynamic failure. Recognition of 

geologic features that have this potential, and knowledge of their 

location, is central to any control effort. 

Considerable efforts have been made to identify geologic 

features associated with ground hazards in deep western coal 

mines, many of which are regional in scale. Phillipson (11) 

reviewed ground conditions and associated geology in nine 
 

 

 

 

western coal mines (Colorado, New Mexico and Utah). All but 

one of these mines used a longwall method, and all were located 

in or near the Piceance, Uinta and San Juan basins. Roof and 

pillar failures were found to be associated with “subtle joint 

zones, and subtle low-angle fault zones that are suggestive of 

bedding plane faults.” Phillipson found that these controls to be 

independent of more well known sedimentary controls on ground 

instability (compaction, slickensides, weak lithology) and to be 

“relatively continuous along strike at the mine scale.” Thus, these 

features can be projected from single encounters within gateroads. 

Relevant sedimentary features include sand channels and 

facies changes in surrounding strata create a locally strong roof 

(or floor). Cantilevers of strong strata over the gob and/or 

bridging of the gob concentrate stress on nearby pillars and 

abutments. Dynamic failure can occur in the highly stressed 

abutments or as cantilevers and bridges fail (which can cause an 

air blast as well). Such failures are a characteristic of western coal 

mines. Koehler (12) documents this relationship through the long 

history of Utah’s Sunnyside mine. Osterwald (13) and Osterwald 

et al. (14) provide comprehensive reviews of geologic features 

related to bumps in the Sunnyside District (Carbon County, 

Utah). 

Discontinuities within strong strata are often important, 

particularly where clamping stresses are weak, allowing caving 

and subsidence of even massive strata. For example Osterwald et 

al. (14, p. 43) found subsidence propagating through massive 

sandstone strata above the Sunnyside coal bed, including the 

Castlegate Sandstone, from mining 2400 ft below surface. Most 

subsidence was found to follow joints and faults, particularly 

where lateral constraining pressure is low. In addition, Osterwald 

et al. describe subsidence cracks developing in massive strata 

daylighting in cliffs, sometimes decades after completion of 

mining. 

Maleki (15) describes north-south and east-west trending joint 

sets that persist throughout the geologic column. The east-west 

orientation is dominant in the Book Cliffs region (rotating locally 

to the northwest at Dugout Canyon and Soldier Creek). Generally, 

Books Cliffs joints are poorly developed with rough, undulating 

surfaces, low-to-medium persistence along both strike and dip, 

and filled with calcite at depth (16). 

The north-south joint set, non-parallel with major grabens 

formed in tension, is dominant in the Wasatch Plateau. Jointing is 

better developed, surfaces are smoother and persistence is 

medium to high, particularly for the north-south set. Underground 

measurements show the north-south set is the only wellpronounced set in the Blackhawk formation that overlies a 

number of coal seams, and underlies the Castlegate sandstone. 

Strike-slip faults are oriented NE/SW and NW/SE. Horizontal 

stress measurements show a continued relaxation of east-west 

stress. 

Defects in hard sandstone strata have also been suggested by 

seismic analysis. Boler et al. (17) analyzed a 3.6 magnitude 

seismic event that occurred at the Soldier Creek Mine, adjacent to 

the Dugout Mine, in the Book Cliffs District of Utah. The event 

completely destroyed twenty-four 18 by 18 m (60 by 60 ft) 

pillars, turning them into “piles of broken coal.” The pillars were 

being mined in retreat in a 480 ft wide panel isolated from a 

neighboring panel by a 18 m (60 ft) barrier. In addition, a row of 

pillars was left on either side of the barrier. The failed pillars were 

beneath 380 m (1250 ft) of cover, but overburden varied widely, 

ranging from 300 to over 450 m within this 425 m long panel. 

The event buried a worker up to his chest in fine coal and 

initiated an air blast. Floor heave of up to 1.2 m (4 ft) occurred in 

several places, primarily involving 0.5 m (1.5 ft) of bottom coal. 

Seismic first motions from regional nets were uniformly 

implosional. Boler et al. placed the event origin in strong 

sandstone well above the mining horizon, and argue that failure 

likely occurred on a pre-existing normal fault (although any plane 

of weakness would likely have sufficed). 

Agapito and Goodrich (18) characterize geology of the region 

relevant to dynamic failure as follows (quoting): 

1) Thick, competent overburden strata that tend to bridge 

and interlock, creating high abutment stresses. 

2) Numerous channels that cause high stress concentrations. 

3) Very competent and strong immediate roof and floor 

sandstone/siltstone strata that confine/load the coal and 

resist breakage. 

4) Uncleated or poorly cleated, strong coal that sustains high 

stress and tends to fail suddenly. 

They also note the occurrence, in places, “of very soft shales 

and mudstones in the immediate roof” that are prone to bumptriggered falls. 

In situ stress characteristics can also be important. Agapito et 

al. (19) report on a 3.4 Magnitude floor bump at the West Elk 

Mine in Colorado that caused floor heave of as much as 2.5 m. 

The heave was located in a 3 entry tailgate between mined panel 

and a barrier abutment, under 640 m of overburden. A nearby 

stress measurement found horizontal principal stresses of 5.5 and 

24.2 MPa. The maximum horizontal stress at this site is 

significantly higher than the trend established by six other stress 

measurements at the mine, suggested existence of a local stress 

concentration. A survey of stress measurements at North Fork 

Valley mines shows a consistently strongly biaxial stress field, 

with the maximum horizontal stress trending parallel to the valley 

(roughly ENE). 

Elevated horizontal stresses also figure in a dynamic failure 

within the Lorraine coal field (France). Driad-Lebeau et al. (20) 

reported that a fatal accident resulted from a 3.6 magnitude 

dynamic failure that occurred 1250 m below surface, damaging 

the main gate 200 m in front of a 250 m wide longwall panel. 

Multiple panels, separated by barriers, had largely shielded the 

panel from vertical stress, which was measured to be only 20% of 

overburden. However, a strong sandstone underlying mining, 

combined with a high horizontal stress field, was not destressed. 

Previous significant seismic events (to 2.5 magnitude) did not 

suggest the hazard. They had been concentrated in barrier pillars 

between panels that were carrying largely vertical stress. 

The importance of geologic work in support of coal mine 

design, and the costs of inadequate geologic support, is widely 

recognized. For instance, Kelly (21) found that that “many coal 

mining projects in Australia have suffered as a result of 

inadequate or incorrect geologic assessment.” Moreover, 

problems have often occurred despite good geologic work 

because of “poor communication through project phases as well 

as an insufficient understanding of consequence” related to a 

particular structure. 

In a telling example, Ghose (22) attributed the Kottadih panel 

collapse in India to “inadequate support capacity where the 

support design had been based on data from a single borehole 
 

 

 

 

 

 

 

which failed to detect the massiveness of overlying strata.” The 

collapse destroyed 55 of 83 shields and initiated a spontaneous 

combustion event (23). The oversight was not isolated. Singh (24) 

attributed failure of a number of high-profile longwall projects in 

India to “a single technical reason – the presence of massive overlying roof strata.” In some cases, the oversight was likely in 

anticipating the consequences, rather than the physical presence, 

of massive strata. 

Rixon (25) discussed mine mapping in the context of longwall 

mining in Australia. Mapping is defined as “systematic recording 

of mine geology, mine roadway stability and geotechnical 

conditions,” placing a firm emphasis on ground behavior. Simple 

observations that can be made and mapped include estimates of 

roadway closure, support deformation, deformational features 

(fault slip, etc.). These observations should address four questions 

as follows: 

1) Is any deformation related to minor geological structures, 

or is it of a more pervasive nature? 

2) Do systematic differences exist in the locus of failure in 

weaker areas? 

3) What inferences can be made about the stress field? 

4) Has the initial design been validated? 

Such observations augment records from instrumentation, 

especially of the longwall (shield leg pressures, closure, etc.). 

Rixon argues that “current good practice is to continuously close 

design loops by observation and measurement of mine geology 

and geotechnical performance, which can then be compared with 

the initial information and design assumptions.” 

Iannacchione et al. (26) review use of hazard maps, rock mass 

classification systems and monitoring data for assessing roof fall 

risk. Maps show where deterioration is expected, providing an 

opportunity for reinforcing support prior to development of a 

significant hazard. However, an inspect and correct loop does not 

work well for anticipation of dynamic failure hazards for a 

number of reasons. These include: 

3⁄4 Dynamic failure may nucleate remote from accessible mine 

openings. 

3⁄4 Structure loading and local stiffness matter, but are difficult 

to observe. 

3⁄4 Dynamic failure occurs suddenly, there is no weakening 

process in time. 

3⁄4 Gas pressures and content are not directly observable. 

However, comparing maps of actual roof fall hazards, as noted 

during pre-shift and other inspections with hazard maps reveals 

where ground conditions are deviating markedly from 

expectations. Deviations caused, perhaps, by undiscovered or 

unappreciated geologic conditions, some of which might increase 

the potential for dynamic failure. Significant deviations from 

expected conditions should be taken as a clear warning that the 

chance of a surprise, perhaps even a disaster, are increased. Such 

a deviation also calls into question the reliability of design 

decisions made to maintain safety and preclude disaster. 

Stewart et al. (27, 28) describe a systematic effort to use 

stability mapping software (30) to anticipate difficult mining 

conditions. The software was used to create a hazard map of 

expected conditions (figure 7) that was used to plan local 

variations in roof support. One interesting feature is inclusion of a 

simple elastic model. Geology and yielding are ignored in 

calculating stresses, but are then added empirically as another 

hazard “factor.” The actual hazard level plotted is the weighted 

sum of a variety of factors, typically adjusted to reflect local 

experience. This approach is a good starting point for developing 

hazard maps specific to dynamic failure. The chief requirements 

for such an extension would be improved insight into key 

geologic conditions, specific consideration of different modes of 

dynamic failure and identification of observations and 

measurements that are sensitive to failure potential. 

Figure 7. Longwall panel hazard map (27). 

A Way Forward 

Dynamic failure is often unpredictable in both space and time 

because of our limited geologic insight, and the highly nonlinear 

nature of event initiation. However, it is equally clear that these 

events should not be ignored, but actively managed. In each of the 

clusters with an adverse outcome, initial events rising to the level 

requiring reports to MSHA occurred before later events with 

more severe consequences. It is also probable that other events 

and conditions arose that indicated heightened risk. 

Detection of events and conditions indicative of heightened 

hazard requires an ongoing, organized program that does not now 

exist in deep coal mines in the western U.S. This lack is both 

operational and regulatory. NIOSH proposes to address this gap 

by developing a Dynamic Failure Control Program with 

specific measures for implementation in deep western coal mines 

(figure 8). 

The Dynamic Failure Control Program is a framework for 

actively managing dynamic ground failure hazards that includes 

site assessment, design, monitoring, active hazard reduction and 

miner protection elements. These elements function within an 

ongoing feedback loop (figure 8) that detects and responds to 

variations in site conditions, ensuring operation within bounds of 

a safe design throughout the life of a mine in spite of unexpected 

and varying geologic conditions. The loop can function within a 

variety of management structures – the key is continuous 

attention to hazard changes. Over the long term, the feedback 

loop should improve as well as maintain the inherent safety of 

both mining operations and emergency response plans. 

Implementation of the program in deep western coal mines 

requires specific developments throughout the framework 
 

 

 

 

 

elements for each of three dynamic failure mechanisms. These 

mechanisms are sudden failure of pillars, outbursts of coal and 

gas from highly stressed ribs, and the breakage (caving and 

heaving) of strata. The aims are to [1] develop a method for 

identifying observations and accessible measurements that reflect 

the level of dynamic failure hazard and threshold values at which 

these hazards become significant, [2] identify and/or develop 

practical means for making such observations and measurements 

in a fast-moving longwall panel, [3] establish a safe, effective 

means for reducing dynamic failure hazard, and [4] evaluate and 

adapt measures to protect miners from dynamic failure. 

Implementation of the framework is based on an existing site 

model and associated mine design. The geomechanical model 

underlying the design is necessarily built upon incomplete and 

imperfect information. Ideally, the design will explicitly state 

important assumptions and expected behaviors that can be 

checked and monitored during mining. A program of observation 

and monitoring should also be implemented to detect local 

occurrences of hazardous geologic and stress conditions. This 

program will determine where active measures should be 

employed to mitigate hazards and the degree to which hazards are 

actually removed. Protective measures should be employed where 

significant hazards remain. Experience gained in monitoring 

conditions and hazards are used to identify further exploration 

needs and hence, to refine the geomechanical model and design. 

In developing this framework and associated measures, priority is 

given to: first designing hazard out of the mine; then to actively 

reducing remaining hazards wherever possible; and finally to 

applying protective ground support measures. This sequence 

could also be described as a best-practices decision tree. 

Continuous application of the framework should improve inherent 

design safety while facilitating adaptation to changes in geology 

and ground conditions. 

Active management of dynamic failure has been accomplished 

for mining of other commodities (gold, etc.) and elsewhere in coal 

(30) but site-specific elements of these programs have yet to be 

successfully adapted to contemporary deep western coal mine 

conditions. As noted in the review, some previous attempts were 

blamed for hazardous bumps. As a result, the prevailing industry 

view appears to be that control methods have “not yet 

demonstrated satisfactory results under continuous operating 

conditions” and “can be hazardous if not properly 

implemented” (18). 

This project is designed to overcome these objections by 

developing and, with the assistance of collaborating mines, 

implementing and optimizing a program tuned for deep western 

coal conditions. This goal requires development of supporting 

technical means in a number of areas. These have been organized 

into 7 technical products. These products are: 

1) Guidelines for assessing the robustness of designs for 

dynamic failure control. That is, for assessing the 

sensitivity of designs to departures from key assumptions 

and errors in key inputs. 

2) Method for estimating potential methane release from 

dynamic failure. 

3) Guidelines for monitoring design performance in 

controlling dynamic failure hazard and disaster potential. 

4) Recommendations for longwall panel hazard assessment 

and monitoring. 

5) Characteristic site models for assessing dynamic failure 

mechanisms in deep western coal mines. 

6) Recommended methods for active management of 

dynamic ground failure hazard. 

7) Recommended ground support measures for containing 

dynamic failure hazard. 

Figure 8. Elements of the Dynamic Failure Control Program. 

SUMMARY 

Mining under threat of dynamic failure is a challenge to many 

sectors of the mining industry, many of whom have made 

remarkable progress in control. Dynamic failure hazards are a fact 

of life in deep western coal mines in the U.S. While a variety of 

methods and tools have been developed for addressing these 

hazards in various districts worldwide, none have been 

successfully adapted to deep U.S. coal conditions, particularly 

those of deep western coal. Moreover, there is a conspicuous lack 

of a program for dynamic failure control, as has been developed 

elsewhere (e.g. Germany – see Brauner (30)). 

Nonetheless, a number of promising elements and trends are in 

place that could be brought together to form such a program. A 

first element (and essential foundation) is a fundamental 

understanding of dynamic failure mechanisms and methods for 

modeling their occurrence. These are sudden failure of pillars, 

outbursts of coal and gas from highly stressed ribs, and the 

breakage (caving and heaving) of strata. Some methods exist for 

assessing the potential for the occurrence, but these have not been 

extended to monitoring points or “sentinel measurements” that 

indicate the level of hazard – or even whether fundamental mine 

design assumptions have been violated. Some progress has been 

made in considering the influence of geology but these have been 

aimed primarily at roof falls. Generally, then, there is a lack of 

insight into the level of dynamic failure hazard. 

A variety of tools for removing and/or controlling hazards 

have been developed, but none have been successfully adapted to 

routine use in deep U.S. conditions – and some have a reputation 

as being hazardous in these conditions. Development and 

adaptation of such tools is discussed in a companion paper at this 

conference. Overall, selection and adaptation of appropriate tools 

is needed, but little progress is evident. One exception may be 

recent attempts to limit miner exposure through automation of 

longwall faces. 
A good foundation is required for reducing this hazard – a 

foundation that includes good fundamental understanding, 

advancing technical tools, and good examples of hazard control 

programs operating in reasonably similar geologic settings. 

Moreover, favorable trends in coal bed methane recovery and 

longwall automation promise to increase the range and feasibility 

of both hazard assessment and control within an integrated 

Dynamic Failure Control Program. However, successful 

development will require active collaboration between 

government, industry and academia; a collaboration that NIOSH 

is actively pursuing. 

Our conclusions echo those of many others with interests in 

deep coal mining. For instance, Agapito and Goodrich (18) 

concluded that “safety problems caused by bumps in the Wasatch 

-Book Cliffs region of Utah highlight the need for improvement 

in avoiding, predicting and mitigating these events. This is critical 

as mines become deeper.” They made five more specific 

recommendations for minimizing and mitigating bump hazards 

more generally (i.e. not limited to potentially disastrous bumps. 

These were, paraphrasing [1] detection of geologic structures that 

exacerbate bumping, [2] mine design that minimize high stresses, 

[3] longwall equipment that protects miners, [4] operational 

practices that limit miner exposure to high stress areas, and [5] 

develop and demonstrate safe destressing methods. 

Finally, Agapito and Goodrich called for seeking improvement 

“in a cooperative manner between the mining industry, equipment 

manufacturers, and research and regulatory agencies.” We concur, 

and hope to build cooperative relationships between NIOSH and 

other interested parties to achieve our common goals. Hopefully, 

this paper marks NIOSH’s entry into the discussion – and efforts 

to reduce the disaster potential of dynamic failure in deep western 

coal mines. 

 

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