Current trends in reducing
 

ground fall accidents in US coal mines
 

by C. Mark, D.M. Pappas and T.M. Barczak 

C. Mark and T.M. Barczak, members 

SME, and D.M. Pappas are mining 

engineers and civil engineer, 

respectively, at the National Institute 

for Occupational Safety and Health, 

Pittsburgh, PA. 

Abstract Ground falls (roof and rib) have historically been responsible for nearly 50% of

all fatalities in bituminous underground coal mines. In recent years, the number of some

annual ground fall fatalities has approached zero, indicating that significant progress has been

made. On the other hand, the twin disasters at Crandall Canyon in 2007, in which nine miners

perished in violent coal bumps, provided a stark reminder that complacency is premature. One

important success has been a great reduction in the number of miners killed inby roof supports.

Throughout the 1990s, these accounted for nearly half of all roof fall fatalities, but there have

just been two inby incidents since 2005. Progress has also been made in pillar recovery, where

there has been just one fatal incident since 2005. On the other hand, more than 300 miners

continue to be injured each year by rock falling from between supports and 100 more are injured

by rib falls. Together, these two categories also account for a large percentage of recent ground

fall fatalities. Available technologies such as roof screen, rib bolting and inside control roof

bolters could reduce injury and fatality rates if they were used more widely. Further advances in

these areas will likely be the next big advance in ground control safety.

Introduction 

On Aug. 6, 2007, a violent coal bump 

occurred at the Crandall Canyon Mine 

near Price, UT. Six miners working at 

the time of the incident were presumed 

trapped. Once again, the nation was 

transfixed by the drama of a mine rescue. Ten days later, hope turned to horror when three rescuers were killed in 

a second bump. Rescue efforts were 

suspended, and the original six miners 

were entombed in the mine. 

The Crandall Canyon disaster was 

the greatest loss of life caused by a 

ground fall incident in a generation. 

Unfortunately, however, in other ways 

the Crandall Canyon miners were by 

no means unique. Ground falls have 

always been the single biggest killer of 

coal miners, accounting for approximately 50% of all underground fatalities in each decade of the last century. 

Nearly 45,000 coal miners have perished in ground falls in the U.S., mostly 

in small accidents claiming just one or 

two lives at a time. 

Recent decades have seen a substantial reduction in the number of 

ground fall fatalities and, in some years, 

the toll has been measured in the low 

single digits. The improvement can be 

attributed to three factors. The first is 

a reduction in the number of miners. 

For every miner working underground 

today, there were approximately 15 at 

the industry’s peak in 1920. 

The second factor is the development of new technology. For ground 

control, the greatest single technological innovation was roof bolting. Other 

advances have included canopies on 

mobile equipment and automated temporary roof supports (ATRS). 

The third factor is change in the 

“safety culture,” which determines the 

level of risk that miners take (or are 

exposed to) while underground. The 

safety culture includes both regulatory 

mandates and company-specific safety 

policies. Obviously, the safety culture 

has changed dramatically since the 

early 1900s, when, as the old saying has 

it, “it was cheaper to lose a man than a 

mule, because the company could always hire a new man, but had to buy a 

new mule.” 

A close look at the ground fall fatal incident rate during the last century 

underlines the importance of the safety 

culture.1 

 1 Note that by analyzing incident rates, the effect of the number of miners is

eliminated.

Between 1900 and 1968, the 

incident rate was relatively constant, 

fluctuating between about 0.6 and 1.0 

fatalities per million employee hours 

(Fig. 1). Over the next eight years, following the passage of the 1969 Coal 

Mine Health and Safety Act, the rate 

fell to about 0.15, an unprecedented 

75% reduction. Careful analysis indicated that this reduction was not due 

primarily to new technology, but rather 

to widespread application of technolo­
 

gies that were already available. In particular, 

much of the improvement can be attributed to 

the requirement that essentially all roofs be supported according to a mandated roof control plan 

(Mark, 2002). 

Figure 1 

Historical overview of roof fall fatality rates for underground bituminous 

coal mines, contractors included after 1983 (BOM, MSHA 1900-2009). 

Overview of ground fall fatalities since 1995 

In 1995, the Mine Safety and Health Administration (MSHA) started creating electronic versions of its fatality reports. These are available 

at www.msha.gov/fatals/fabc.htm. A total of 120 

bituminous underground coal miners have been 

killed in ground falls during the period 1995-2009. 

Figure 2 shows that if Crandall Canyon is excluded, there has been a slight downward trend in the 

ground fall incident rate during this period. 

Figure 2
	

Recent ground fall (roof and rib) fatality rates for underground 

bituminous coal mines. The trendline was determined for the data set 

excluding the Crandall incident (MSHA, NIOSH, 1995-2009). 

The 

r-squared for the trend is only 0.33, however, indicating that it has low statistical significance. 

For this paper, each of the fatality reports was 

analyzed in detail. In Fig. 3, the fatalities are categorized by the type of the ground fall hazard. 

Figure 3
	

Classification of ground fall fatalities, proportioned for 1995-2009. 

Includes bituminous operators and contractors. The total number of 

fatalities for the period is 120 (MSHA, NIOSH, 1995-2009). 

The remainder of this paper will be devoted to 

evaluating five of these categories, which together 

accounted for 96 fatalities, representing 80% of all 

the fatalities during the period: 

•	 Fatalities occurring inby support (20%). 

•	 Fatalities during retreat mining (21%). 

•	 Rib falls (17%). 

•	 Rock falls from between or around 

supports (12%). 

•	 Major roof falls not associated with 

retreat mining (10%). 

For each category, this paper will discuss 

trends over time in fatalities (and injuries where 

appropriate). The state-of-the-art in ground control safety technology for each category will also 

be described. 

The remaining 20% of fatalities, or 24 total 

fatalities, involved: 

•	 Coal bursts during retreat mining (11, 

discussed under “retreat mining”). 

•	 Longwall recovery (3). 

•	 Underground construction or roof fall 

rehabilitation (3). 

•	 Longwall face bursts (2). 

•	 Red zone violations (5, discussed under 

“inby roof support”). 

Fatalities occurring inby roof support 

One clear success story told by the ground fall 

statistics is the reduction in the number of fatalities occurring inby support. Although traveling 

inby for any reason has been illegal since the 1969 

Act, throughout the 1970s and 1980s approximately half of all ground fall fatalities were attributed 

to this cause (Peters, 1992). Figure 4 shows that as 

late as 2002, there were still two or three fatalities 

occurring inby each year. Since 2002, however, 
 

there have been just three incidents in bituminous coal mines. 

Figure 4 

Number of bituminous roof fall fatalities inby roof support 

during entry development, including operators and 

contractors (NIOSH, 1995-2009). 

The progress is associated with the industry-wide educational campaign under the slogan “Inby is Out!” Success 

has come none to soon, because it is essential that the new 

generation now entering the mining industry not pick up the 

bad habits of its predecessor. 

Another factor contributing to the reduction in inby fatalities is the development of the concept of the “red zone.”2 

2 Note that the “red zone” concept employed in roof control plans is distinct from the “red zone” that is associated in some

circles with miner positioning relative to moving equipment.

In many roof control plans, miners must now stay outby the 

second row of bolts, particularly when making extended cuts 

or turning a crosscut. There have been three fatalities since 

2002 (one each in 2004, 2005 and 2009) that occurred when 

miners were within the red zones defined for their mine. 

Fatalities occurring during pillar recovery 

Pillar recovery accounts for no more than 10% of the coal 

mined underground, yet it has historically been associated 

with more than 25% of all ground fall fatalities (Mark et al., 

2003). However, recent statistics indicate that progress is 

being made. Prior to 2006, an average of two fatal incidents 

occurred each year during pillar recovery operations. Since 

then there has been just one incident, though unfortunately 

it resulted in a double fatality (Fig. 5). 

Figure 5 

Number of bituminous roof fall fatalities occuring during 

pillar recovery operations, including operators and 

contractors (NIOSH, 1995-2009). 

A key cause of the change has been the widespread adoption of safer retreat mining techniques and technology. Most 

incidents prior to 2002 occurred during the mining of final 

stump, while posts were being set, or because of insufficient 

roof bolt support. In many of these cases, the miners were 

following their roof control plan, but the plan itself proved 

to be inadequate (Mark et al., 2003). A concerted effort by 

MSHA and the National Institute for Occupational Safety 

and Health (NIOSH) (Mark and Zelanko, 2005; Mark et 

al., 2003) promoted the following three steps to safer pillar 

recovery: 

•	 global stability through proper pillar design; 

•	 local stability with proper roof support and 

•	 worker safety through proper section management. 

The Crandall Canyon incident, like the double bump 

fatality at the C-2 Mine in Kentucky 11 years earlier, was a 

clear example of global instability caused by improper pillar 

design. The MSHA Fatality Investigation Report concluded 

that the design at Crandall Canyon was “destined to fail” because the remaining production and barrier pillars were too 

small to carry the overburden load (Gates et al., 2008). The 

report documented how the two pillar design software packages used to develop the design, Analysis of Retreat Mining 

Pillar Stability (ARMPS) and LaModel, were both employed 

improperly, resulting in the flawed design. In the wake of 

Crandall Canyon, MSHA published a Program Information 

Bulletin (MSHA, 2008a) and a Procedure Instruction Letter 

(MSHA, 2008b) on ARMPS to help ensure that pillars are 

designed properly. 

ARMPS was developed by NIOSH in the mid 1990s 

(Mark and Chase, 1997.) Its main strength is that it uses 

a large database of actual mining case histories to suggest 

the proper stability factors (SF) to employ under different 

circumstances. The original database was later updated with 

several hundred retreat mining case histories from mines 

operating at depths in excess of 229 m (750 ft). A key finding 

of the deep cover research was that substantial barrier pillars 

were essential to maintain stability when the mining depth 

exceeds 198 m (650 ft) (Chase et al., 2002; Mark, 2010). 

ARMPS has been used extensively to design pillars and 

evaluate roof control plans in the central Appalachian coalfields for nearly a decade. Since ARMPS came into widespread use, the number of pillar squeezes has been greatly 

reduced and massive pillar collapses have been largely eliminated (Mark et al., 2003). NIOSH has also developed the 

Analysis of Multiple Seam Stability (AMSS) program, which 

extends ARMPS to multiple seam situations (Mark et al., 

2007). 

Global stability is necessary, but not sufficient, for creating a safe working area. Proper roof support is required to 

maintain local stability. The final pillar stump (sometimes 

called the “pushout”) provides critical roof support during 

pillar recovery. Traditionally, miners tried to extract all of the 

coal during pillar recovery and many fatalities occurred during the mining of the final stump. Research has now shown 
 

that the optimum pillar extraction plan leaves a final stump 

that is engineered to provide roof support without inhibiting 

caving (Mark and Zelanko, 2001). Most roof control plans 

that are now in use do not allow the mining of the pushout 

and specify a cut-to-corner distance, ensuring that the stump 

is properly sized. 

One striking feature of the pillar recovery fatalities is that 

in nearly every case, the victim was beneath bolted roof. In 

many cases, bolt failure was itself implicated in the fatality. 

Increasingly, mines are using longer and/or stronger bolts to 

support areas that will be retreat mined. In addition, cable 

bolts or other special bolts are employed in intersections, 

which are the most hazardous locations for miners during 

pillar recovery. 

Traditionally, timber posts provided supplemental support for pillar recovery, but they have many disadvantages. 

Mobile roof supports (MRS) provide better ground control, 

and they can be set remotely, away from the dangers of the 

pillar line. Today, perhaps 50% of all retreat coal is mined 

with MRS, primarily in the thicker seams. Unfortunately, 

several of the victims in pillar recovery fatalities have been 

MRS operators who were standing unnecessarily in unsafe 

locations. These incidents have underlined the third factor, 

effective section management. 

Management begins before mining, with crew training 

that focuses on the roof control plan and hazard identification. A careful geologic survey of the section should be conducted before mining commences and pre-shift evaluations 

and test holes should be used to identify hazards as the section is retreated. Good supervision means ensuring that the 

plan is followed precisely every time, that miners always are 

stationed in safe locations and that safe operating procedures 

are followed for the MRS units and the other equipment on 

the section. 

Rib falls 

Falls of coal and/or rock from the sidewalls of coal mines 

or pillar ribs injure approximately 100 coal miners annually. 

As Fig. 6 indicates, the number of injuries has actually been 

trending upward in recent years. 

Figure 6
	

Number of bituminous rib fall operator injuries, excluding 

bursts (MSHA, NIOSH, 1995-2009). 

In addition, rib falls have 

killed 23 mineworkers since 1994, including three more rib 

fall fatalities during the first seven months of 2010. 

Increased risk of rib falls is associated with thicker coal 

seams and higher stress levels. Analysis of the 23 fatal incidents reveals that all but three occurred at depths exceeding 

183 m (600 ft) and the mining height was at least 2 m (7 ft) in 

every case. On the other hand, more than half of the rib fall 

injuries that occurred in the 2005-2007 period were in mines 

where the reported seam height is less than 2 m (7 ft). 

Technology is available to prevent rib fall injuries. Rib 

bolting can be highly effective and it is routinely employed by 

many U.S. coal mines, particularly in the West, where thicker 

seams are prevalent. A recent Australian research project 

concluded that under more difficult conditions, the rib support system “should incorporate mesh that is firmly secured 

to the ribline with steel bolts and plates” (Colwell and Mark, 

2005). It is significant that apparently only two of the 23 U.S. 

fatality sites were even rib bolted. 

About a quarter of the rib fall fatalities were suffered by 

roof bolter operators. In every case, the machine involved 

was an “outside control” roof bolter, where the operator 

works between the coal rib and the machine. A much safer 

alternative is the “inside control” (or “walk through”) roof 

bolter that removes the operator from direct contact with the 

rib. Such machines are available for mining heights as low 

as 127 cm (50 in.). 

Rock falls from between or around supports 

Since the 1969 act, any roof that coal miners work under 

is required to be supported. Yet, as Fig. 7 shows, more than 

300 coal miners are injured each year by rock falls while they 

are beneath supported roof. 

Figure 7 

Number of bituminous roof fall operator injuries, including 

machinery-related roof falls (MSHA, 1995-2009). 

Another 15 miners were killed 

by these rock falls during the first decade of the 21st century. 

The problem is that roof supports, like bolts or ATRS, are 

designed primarily to prevent large rock falls and major roof 

collapses. They do not protect miners from smaller pieces of 

rock that fall from between or around the supports. Figure 8 

shows the size of a rock that fell between roof bolts and killed 

one miner in 2008. 

Technology is available to prevent the majority of these 

injuries and fatalities. Surface controls like straps, headers 

and large roof bolt plates can help, but by far the most effective prevention technique is roof screen. Screen works 
 

best because it can cover almost the entire roof (Robertson 

et al., 2003). Screen also offers a first line of defense for roof 

bolter operators by confining or deflecting small rocks that 

can come loose during drilling or bolt installation. Numerous studies have now shown that mines that use screen routinely have much lower rates of “struck by” rock fall injuries 

(Molinda and Klemetti, 2008). 

Unfortunately, many mines do not use roof screen because they think installing it would be awkward, time consuming and expensive. However, studies reported by NIOSH 

have shown that simple machine modifications, well-planned 

supply methods and best-practice installation techniques can 

minimize the effects of roof screen installation on a mine’s 

overall mining cycle (Compton et al., 2008). Moreover, at 

many mines, the savings in workers compensation costs alone 

could cover much of the cost of roof screen (Moore et al., 

2010). 

Roof bolter machine manufacturers also offer a number of products that can directly reduce the risk of rock fall 

injuries. Inside control machines greatly facilitate screen 

handling and installation, particularly when equipped with 

semi-automated material handling systems (Robertson and 

Mark, 2004). Before purchasing a new roof bolting machine, 

or introducing an old machine into a different mine, mine 

operators should carefully evaluate all the potential ground 

fall hazards and ensure that the equipment will address them. 

Existing roof bolters can also be retrofitted with “flipper 

pads” and other safety devices that provide extra protection 

from rocks falling during roof bolting operations. In 2008, 

a 25-year-old roof bolting machine operator was killed in 

Indiana when a piece of rock fell from beyond permanent 

support and cantilevered outby, pinning him against the foot 

cylinder of the pressurized ATRS (MSHA, 2008c). 

Figure 8 

Photograph of rock that fell from between roof bolts and 

fatally injured a mineworker (MSHA, 2008). 

Massive roof falls 

Massive roof falls are those that extend higher into the 

roof than the anchorage horizon of the roof bolts. Such roof 

falls must be reported to MSHA if they occur in actively traveled parts of the mine, even if they do not result in an injury. 

More than 1,000 reportable noninjury roof falls occur each 

year (Fig. 9). 

Figure 9
	

Number of bituminous noninjury roof falls reported to MSHA 

(MSHA, 1995-2009). 

These roof falls can threaten miners, damage 

equipment, disrupt ventilation and block critical emergency 

escape routes. Roof collapses also helped trigger the 2001 

mine disaster in Alabama, which took 13 lives (McKinney 

et al., 2004). 

Massive roof falls usually provide enough warning that 

miners are seldom caught beneath them. However, since 

2004, eight coal miners have been killed by roof falls that 

extended above the bolts. In early 2010, two miners were 

killed when 23 m (75 ft) of roof collapsed on them while 

they were operating a continuous miner (MSHA, 2010). In 

another incident, three miners were traveling into the mine 

on a mantrip, when they realized the intersection they were 

passing through was about to collapse. While two miners 

barely escaped, the third, a 26-year-old mechanic, was buried 

under 1.8 m (6 ft) of rock (MSHA, 2006). 

Every massive roof fall represents a failure of the installed roof support system at that location. Wide mining 

spans can also increase roof fall rates (Mark and Barczak, 

2000). This is why more than two-thirds of all roof falls take 

place in intersections, even though intersections constitute 

much less than one-third of all drivage underground. Focusing additional support on intersections can be an effective 

control strategy. The extra support can consist of longer, 

stronger primary bolts or supplemental supports, such as 

cable bolts. 

After studying roof falls at 40 coal mines, NIOSH developed the Analysis of Roof Bolt Systems (ARBS) software 

package to help mine planners select the most appropriate 

roof bolt system for their conditions (Mark et al., 2001). Unfortunately, even with tools like ARBS, roof support design 

is still more of an art than a science. However, if a mine is 

regularly experiencing roof falls, increased levels of support 

are clearly warranted. 

Conclusions 

Ground falls continue to be a major hazard in underground coal mining. The mining community can be proud of 

the progress that has been made in reducing fatalities occurring inby support and during pillar recovery. Unfortunately, 

the trends in other accident categories are not so encouraging. Hundreds of injuries and several fatalities occur each 

year as a result of rock falling from between supports, rib falls 

and major roof collapses. 

Most ground fall incidents could be prevented by available technologies, such as roof screen or rib support. Today, 
 

the most conscientious mining companies are taking steps to 

change their safety culture, by systematically implementing 

ground fall prevention technologies and lowering the risk 

that their miners face. It is to be hoped that the rest of the 

industry will soon follow. 

Disclosure 

The findings and conclusions in this report have not been 

formally disseminated by the National Institute for Occupational Safety and Health and should not be construed to 

represent any agency determination or policy. 

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Downloadable video available from http://www.cdc.gov/niosh/mining/products/product65.htm.