Roof and rib fall incident trends: 

a 10-year profile

D.M. Pappas and C. Mark

Civil engineer and mining engineer, respectively, 

National Institute for Occupational Safety and Health, Pittsburgh, PA

Abstract

From 1999 through 2008, groundfall events resulted in 75 fatalities, 5,941 injuries and 13,774 noninjury 

roof falls in U.S. underground coal mines, according to the U.S. Mine Safety and Health Administration 

(MSHA). A comprehensive analysis of these events was conducted to better understand where and why 

these incidents occurred. The first segment of the study used the MSHA database to evaluate groundfall injury rate trends related to mining method, year, locality, seam thickness, mine size, coalbeds and 

seasonal effects. In the past decade, roof fall injury rates have dropped 50%, but rib fall injury rates 

have remained constant. Room-and-pillar mines had a roof fall injury rate that was nearly 2.5 times the 

longwall rate. High groundfall rates occurred in the Illinois Basin, a finding that correlates with other 

studies that have shown that roof rock in the Illinois Basin is weaker than that in the central Appalachian 

coalfields. Finally, noninjury roof fall rates in the eastern and central United States were found to be 50% 

higher from July through September, possibly because of the changes in humidity levels that may cause 

shale mine roofs to deteriorate. The second segment of the study evaluated the root causes of failure by 

reviewing all MSHA groundfall fatality reports for 1999-2008. Pillar recovery was the leading cause of 

groundfall fatalities (19%), followed by rib falls, roof skin falls and traveling under unsupported roof 

(16% each). Defining prominent ground control incident trends and hazards will identify areas where 

additional study is needed and where innovative solutions need to be developed to reduce these severe 

occupational hazards.

Introduction

Mining has always been recognized as one of the most 

hazardous occupations in the United States. According to the 

U.S. Bureau of Labor Statistics (2007) and the U.S. Mine 

Safety and Health Administration (MSHA) (2009), a ranking 

of the most hazardous occupations shows that the underground 

bituminous coal mining industry’s fatality rate ranks seventh 

among all U.S. occupations (Fig. 1). Since 1906, nearly 86,000 

underground miners have lost their lives while mining coal. 

Groundfalls were responsible for 45,000 of these fatalities, more 

than all other causes combined. Groundfalls include falls of 

the mine roof and walls, typically referred to in underground 

coal mines as roof and rib falls.

A historical overview of fatality rates for roof and rib falls, 

along with landmark mining events, are shown in Fig. 2. 

Groundfall fatalities averaged around 1,000 deaths every year 

until the early 1930s. Despite the increased mechanization of 

coal mines in the 1930s and the introduction of roof bolts in the 

1950s, prior to the Federal Coal Mine Health and Safety Act 

of 1969, roof fall fatality rates remained essentially constant. 

Implementation of the 1969 act required roof control plans and 

consistent roof support in every mine, which resulted in a 75% 

drop in groundfall fatality rates by the late 1970s (Mark, 2002).

During the past 25 years, the reduction of the groundfall 

fatality rate appears to have slowed or plateaued, even with 

nearly 50% of production in underground coal mines coming 

from the safer longwall mining method. The worst groundfall 

disaster since 1930 occurred in 2007 at the Crandall Canyon 

Mine in Utah, resulting in the death of six workers on August 

6 and three rescuers on August 16.

Nonfatal injuries are another facet of the ground control 

problems in mining. In 2008, for example, 495 workers were 

injured in roof and rib falls, resulting in 18,160 days of work 

lost. Typically, a lost-time ground control injury costs in excess 

of $100,000 (Moore et al., 2010). Groundfall injuries also 

exact a human toll on the injured workers and their families. 

In addition to the injuries, nearly 1,400 noninjury roof falls 

occurred in 2008. These noninjury roof falls were mainly massive falls that were reported to MSHA because they extended 

beyond the height of the bolts, damaged equipment, stopped 

production or disrupted ventilation.

The U.S. National Institute of Occupational Safety and 

Health (NIOSH)’s previous reviews of groundfall injuries 

(Pappas and Mark, 2000; Pappas and Mark, 2003) for 1995-

2001, found several key trends. The mechanized longwall 

process of mining coal with a long continuous slice using self-
advancing roof supports has revolutionized and streamlined 

the system of mining underground coal in the United States. 

This method vastly improves mine productivity and reduces 

exposure to unsafe roof conditions. A comparison of mining 

methods found that the traditional process of room-and-pillar 

mining has at least twice the groundfall injury rate than the 

longwall mining method. Another significant conclusion was 

that high groundfall rates occurred in regions characterized by 

weak roof. For instance, the Illinois Basin’s high groundfall 

Figure 1 — Fatality rate by industry compared to underground mining, based on USBLS (2007) and MSHA (2009) data. 

Figure 2 — Historical groundfall fatality rates, based on MSHA (2009) data for 1906-2008.

rates are associated with several key coalbeds: (1) western 

Kentucky No. 13, (2) Herrin/No. 6/Kentucky No. 11 and (3) 

Springfield/No. 5/Kentucky No. 9. This appears to correlate to 

other studies that have shown that the compressive strengths 

of typical roof rocks in the Illinois Basin are much lower than 

those of their counterparts in the central Appalachian coalfields. 

Finally, roof fall rates were found to be 40-50% higher from 

July through September, possibly due to high humidity, which 

may cause the shale mine roof to deteriorate.
In the past 10 years, the coal industry has seen many dramatic changes. Underground coal production has decreased 

9%, yet underground hours worked increased nearly 20% 

(MSHA, 2009). Because the economic cycles in coal mining 

may affect the dynamics of groundfall injury trends, this study 

was undertaken to update groundfall injury rates and, most 

importantly, to reveal critical, possibly new, ground control 

areas that require additional research attention. 

Table 1 — Attributes of roof and rib fall injuries at room-and-pillar mines, based on MSHA (2009) data for 1999-2008.

Room-and-pillar mine trait Region Hours 

worked

Mines Rib fall 

injuries2

Roof fall injuries2 Noninjury 

roof falls

N % N1 % N % N % N %

Locality Western PA 23,784,492 5 369 6 19 3 163 616 5

Northern WV/ 

OH/MD

28,128,587 6 343 6 22 4 231 6 1,622 14

Southern WV 112,379,537 24 1,567 26 178 32 983 25 2,249 19

VA 45,884,502 10 907 15 64 12 369 9 1,049 9

Eastern KY 80,159,705 17 1,400 23 69 13 659 16 918 8

Southeastern KY 71,508,424 15 996 16 117 21 609 15 1,294 11

Indiana/Illinois 56,944,111 12 191 3 39 7 592 15 2,475 21

Western U.S. 9,614,188 2 136 2 28 5 46 1 190 2

Western KY 39,057,025 8 137 2 13 2 344 9 1,220 10

Alabama 1,249,328 0 32 1 0 0 7 0 16 0

Total 468,709,899 100 6,078 100 549 100 4,003 100 11,649 100

Mine size <50 workers 180,300,649 38 4,898 81 203 37 1,481 37 3,779 32

50–149 workers 178,901,327 38 961 16 248 45 1,520 38 4,224 36

>149 workers 109,507,923 23 219 4 98 18 1,002 25 3,646 31

Total 468,709,899 100 6,078 100 549 100 4,003 100 11,649 100

Seam height3 missing 13,319,671 3 212 3 3 1 111 3 307 3

<=108.9 cm 86,840,764 19 2,233 37 67 12 646 16 1,234 11

109-152.1 cm 154,502,304 33 1,728 28 151 28 1233 31 3,670 32

152.2-182.8 cm 93,219,277 20 849 14 122 22 876 22 2,275 20

>=182.9 cm 120,827,883 26 1,056 17 206 38 1137 28 4,163 36

Total 468,709,899 100 6,078 100 549 100 4,003 100 11,649 100

All room-&-pillar mines 468,709,899 6,078 549 4,003 11,649

1 The total number of mines for 1999–2008 is not mutually exclusive (e.g., if a mine operated all 10 years, it is counted 10 times).

2 All falls resulting in degree of injury 1–6.

3 Approximately 2.8% of the hours worked were at mines that did not report or misreported the seam height and are excluded.

Methods

The primary raw data for this first segment of the study 

was obtained from MSHA’s accident/injury and employment 

databases (MSHA, 2009). The study examined the closeout 

data for 1999-2008 for underground bituminous coal mines, 

excluding contractors. The portion of this study that evaluated 

groundfall injuries by coalbed type used the years 1999-2007 

because the coalbed updates for 2008 were not available. 

Groundfall injuries include all roof and rib falls listed in the 

database, as well as injuries classified as “machinery,” where 

the source of injury was caving rock. Analysis of the incident 

narratives revealed that the vast majority of these “machinery” 

groundfalls involved the roof rather than the rib, and so all 

were categorized as roof falls.

Groundfall incidents were categorized by the following 

four types:

• Fatal roof or rib fall incidents (degree of injury: 1).

• Roof fall injury incidents resulting in death, permanent 

disability, days away from work only, days away from 

work with restricted activity, days of restricted activity 

only, or no lost workdays or restricted activity (degree 

of injury: 1–6).

• Rib fall injury incidents resulting in the same types of 

injuries as listed for roof fall injury incidents (degree 

of injury: 1–6).

• Noninjury reportable roof fall incidents (degree of injury: 

0). The federal 30 CFR 50.20-5 (CFR) requires that 

any active working section with a roof fall that occurs 

above the roof bolt anchorage, impairs ventilation or 

impedes passage be reported.

Injury rates were computed by calculating the number 

of roof or rib fall incidents for every 200,000 hours worked 

underground. The number of hours worked by 100 full-time 

miners per year is approximately 200,000. Noninjury rates 

were computed by calculating the number of noninjury roof 

falls (i.e., reportable roof falls) divided by the underground 

production (in million metric tons, Mt). This rate was normalized based on production, rather than hours worked, because 

production generally relates to the amount of roof exposed 

during the mining process. 

The two methods of mining (room-and-pillar and longwall) 

were separated for most of the analyses. The longwall mines 

were identified for each year by review of the annual longwall census and knowledgeable mining personnel. Typically, 

80%–90% of the production from longwall mines comes from 

the longwall face and the remainder from gate road development. No attempt was made to apportion production between 

gate road development and longwall face. Therefore, all production originating from these longwall mines was assumed 

to be longwall production. In mines that were not identified 

as longwall, their production was considered to be room-andpillar mine production.

Major coal-producing locations in the United States were 

examined to identify trends. The eastern and southeastern 

Kentucky localities have minimal longwall production, and 

the Alabama location has minimal room-and-pillar production. 

Because of low production, groundfall rates from these areas 

are not included in this analysis.

The MSHA database reports a seam height for each mine, 
defined as the average height of the coal seam currently being mined. Seam height is not necessarily the mining height, 

which sometimes includes roof and floor rock that is often 

removed due to equipment size. There may be some variation 

in the actual seam height at the site of the incident; but to be 

consistent, this study used the MSHA-reported value. Four 

categories of seam heights were selected based on distribution 

of employee hours and other constraints: a thin seam height 

is less than or equal to 108.96 cm (42.9 in.); medium seam 

height is 109.22-152.14 cm (43-59.9 in.); thick seam height 

is 152.40-182.62 cm (60-71.9 in.) and ultrathick seam height 

is greater than or equal to 182.88 cm (72 in.). 

Approximately 3% of the total room-and-pillar underground 

production and 1% of the total longwall production were from 

mines where no seam heights were recorded or where the seam 

heights were misreported. These mines were excluded from 

this segment of the study.

Mine size is based on the average annual number of employees working in the underground mine. The following three 

categories of mine size were selected for this study and are 

based on distribution of employee hours: small-sized mines 

(fewer than 50 workers), medium-sized mines (50-149 workers) 

and large-sized mines (more than 149 workers).

The second segment of this study is a review of the actual 

MSHA (2008) fatality reports. To obtain a greater understanding 

of the specific hazards associated with roof or rib fall fatalities, 

all groundfall fatality reports for 1999–2008 for underground 

mining were examined. This second segment includes bituminous operator and contractor fatality reports, whereas the 

first segment did not include contractor incidents. The fatality 

reports provide much more information than can be obtained 

from the MSHA injury narratives, which are brief and do not 

include detail. The cause of failure for each groundfall fatality 

was reviewed by several individuals to minimize subjectivity; 

the various causes of failure were then categorized into eight 

groundfall groups. To establish long-term frequency trends, 

some of these categorized groundfall groups were reviewed 

back to 1995. 

Results and discussion

This study is broken into two segments associated with 

an in-depth assessment of the MSHA injury database and a 

detailed review of the actual MSHA fatality reports.

Analysis of MSHA injury database. Table 1 breaks 

out several characteristics with room-and-pillar coal mines, 

including locality, mine size and seam height. Table 2 lists 

these same characteristics for longwall mines. 

Table 2 — Attributes of roof and rib fall injuries at longwall mines, based on MSHA (2009) data for 1999-2008.

Longwall mine 

characteristic Region Hours worked Mines Rib fall injuries2 Roof fall injuries2 Noninjury roof falls

N % N1 % N % N % N %

Locality Western PA 61,017,685 20 61 13 44 16 240 22 278 13

Northern WV/

OH/MD 73,252,320 24 96 20 41 15 155 14 337 16

Southern WV 34,187,120 11 67 14 31 11 184 17 385 18

Virginia 10,579,732 3 18 4 5 2 25 2 86 4

Eastern KY 1,900,600 1 5 1 2 1 11 1 37 2

Southeastern 

KY 1,234,825 0 5 1 1 0 8 1 8 0

Indiana/Illinois 21,007,442 7 25 5 21 7 219 20 443 21

Western U.S. 51,138,410 17 133 28 91 32 72 6 313 15

Western KY 5,641,605 2 10 2 7 2 69 6 106 5

Alabama 46,840,227 15 59 12 38 14 125 11 132 6

Total 306,799,966 100 479 100 281 100 1,108 100 2,125 100

Mine size <50 workers 530,144 0 9 2 1 0 2 0 11 1

50–149 workers 20,178,166 7 84 18 31 11 94 8 203 10

>149 workers 286,091,656 93 386 81 249 89 1,012 91 1,911 90

Total 306,799,966 100 479 100 281 100 1,108 100 2,125 100

Seam height3 missing 4,228,928 1 11 2 5 2 22 2 1,554 73

<=108.9 cm 0 0 0 0 0 0 0 5,804 273

109-152.1 cm 25,388,890 8 47 10 20 7 86 8 11 1

152.2-182.8 cm 44,860,454 15 61 13 26 9 159 14 203 10

>=182.9 cm 232,321,694 76 360 75 230 82 841 76 1,911 90

Total 306,799,966 100 479 100 281 100 1,108 100 2,125 100

All longwall mines 306,799,966 479 281 1,108 2,125

1 The total number of mines for 1999–2008 is not mutually exclusive (e.g., if a mine operated all 10 years, it is counted 10 times). 2 All falls resulting in degree of injury 1–6.

3 Approximately 1.4% of the hours worked were at mines that did not report or misreported the seam height and are excluded.

Specific factors 

that quantify these mine attributes for the 1999-2008 analysis 

include the number of hours worked underground, number of 

mines and the number and percentage of rib fall injuries, roof 

fall injuries and noninjury roof falls.

Mining method. One of the most definitive factors affecting 

roof fall incident rates is the mining method. Table 3 compares 

the attributes of the two mining methods, including numbers 

and percentages for production, groundfall incident frequency 

and groundfall incident rates. Remarkably, the 48 longwall 

mines produced as much coal tonnage as the 608 room-andpillar mines, but accounted for only 22% of the total roof fall 

injuries for both mining methods; in comparison, the remaining 

78% of the total roof fall injuries occurred in room-and-pillar 

mines. According to Fig. 3, the roof fall injury rate for roomand-pillar mines is more than double the roof fall injury rate 

for longwall mines. The lower rate of roof fall incidents for 

longwall mines may be related to the continuous protection 

provided by the longwall face supports at the active mining 

face and the greater number of support workers located away 

from the mining face. 

A similar ratio of incidents for the two mining methods was 

identified for noninjury roof falls—15% from longwall mines 
and 85% from room-and-pillar 

mines (Table 3).

Table 3 — Comparison of mining methods, based on MSHA (2009) data for 1999-2008.

Attribute Mining Method

Room and pillar Longwall1

Number % Number %

Production

Metric tons produced (millions) 1,637 49 1,679 51

Underground hours (millions) 469 60 307 40

Average number of underground workers/year 22,251 62 13,681 38

Average number of mines/year 608 93 48 7

Groundfall frequency

Roof/rib fall fatalities 59 83 12 17

Roof fall injuries2 4,003 78 1,108 22

Rib fall injuries2 549 66 281 34

Noninjury roof falls 11,649 85 2,125 15

Groundfall incident rates3

Roof/rib fatalities/200,000 hours 0.025 0.015

Roof fall injuries/200,000 hours 1.71 0.72

Rib fall injuries/200,000 hours 0.234 0.183

Noninjury roof falls/million metric tons 7.12 1.27

1 Longwall data includes gateroad development.

2 All falls resulting in degree of injury of 1 to 6 between 1999-2008.

3 The combined rates are the total number of incidents divided byte total number of hours worked or 

total tonnage mined.

 One reason longwall mines have lower noninjury 

roof fall rates is that fewer entries 

are mined, resulting in less exposed 

roof and most of the production 

comes from the longwall face, 

which is continuously supported 

and has minimal roof exposure. 

Conversely, the rib fall injury rate 

for both room-and-pillar mines and 

longwall mines are nearly identical. This may be because many 

room-and-pillar mines work thinseams, where the rib fall hazard is 

minimal, while nearly all longwalls 

are mining thicker seams.

Because there is such a large 

and distinct difference between 

the groundfall safety records of 

the two mining methods, they 

will be evaluated separately in the 

remainder of this report.

Trends over time. In the past 

10 years, productivity (metric 

tons/worker) in underground 

coal mines has dropped 9% for longwall mines and 20% for 

room-and-pillar mines (Fig. 4). For the room-and-pillar sector, 

during this period the number of workers increased by 12%, 

production decreased by 10% and there were 126 fewer mines. 

The number of longwall mines dropped by 10 over the same 

10-year period, while the number of workers remained steady 

and production dropped by 7%. A previous study found that 

periods of increasing productivity are often associated with 

decreasing incident rates (Spokes, 1986). However, during this 

recent period of decreasing productivity, the converse has not 

been the case. The roof fall injury rates decreased by more than 

50% in the 10-year period (Figs. 3 and 5) for both methods. 

Figure 3 — Groundfall injury rates by mining method, based 

on MSHA (2009) data for 1999-2008.

Figure 4 — Productivity by mining method, based on MSHA 

(2009) data for 1999-2008.

Figure 5 — Comparison of roof fall injury rate and productivity, based on MSHA (2009) data for 1999-2008.

These decreases in both roof fall injury rates and productivity may, perhaps, be attributed to the recent coal boom. After 

years of struggling financially, many coal mines were able to 

finally invest in updated equipment, better technology and more 

workers; these factors may have led to lower productivity and 

decreased roof fall injury rates. 
For both mining methods during the 10-year period, rib fall 

injury rates have shown a slight increase, while reportable noninjury roof fall rates were essentially constant (Figs. 6 and 7).

Figure 6 — Rib fall injury rates, based on MSHA (2009) 

data for 1999-2008.

Figure 7 — Noninjury roof fall rates, based on MSHA (2009) 

data for 1999-2008.

Fatal roof and rib falls were examined and grouped together, 

because these incidents occur infrequently and sporadically. 

Fatal groundfall rate trends were plotted for 10 years, with the 

data indicating no definitive trends in the fatality rate (Fig. 8). 

Figure 8 — Groundfall fatality rates, based on MSHA (2009) 

data for 1999-2008.

However, grouping the groundfall fatalities by decade (Fig. 9) 

shows that in the 1980s, an average of 27.3 groundfall deaths 

occurred each year. 

Figure 9 — Groundfall operator fatality rates and averages 

by decade, based on MSHA (2009) data for 1999-2008.

By the 1990s, the average dropped in half 

to 12.7 annual deaths and, by the first decade of the 21st century, it dropped in half once again to an average of 6.8 deaths 

per year. A review of the detailed MSHA groundfall fatality 

reports and classification of these incidents are presented in a 

later portion of this paper.

Locality. A review of roof fall injury rates at longwall 

operations (Fig. 10) in all coal mining locations in the United 

States found that western Kentucky and Illinois/Indiana had 

roof fall injury rates that were nearly three times the national 

longwall average. Conversely, the western United States and 

northern West Virginia/Ohio/Maryland had roof fall injury 

rates that were at least 40% lower than the national average. 

Figure 11 shows similar trends for reportable noninjury roof 

falls in longwall mines. Western Kentucky and Illinois/Indiana 

again had noninjury roof fall rates that were about three times 

the national rate, while western United States and northern 

West Virginia/Ohio/Maryland together with Pennsylvania 

again had the lowest rates.

Roof fall injury rates for room-and-pillar mines (Fig. 10) 

did not vary dramatically among localities. However, the rate 

of noninjury reportable roof falls for room-and-pillar mines 

(Fig. 11) exceeded the national room-and-pillar mine average 

by nearly 50% in northern West Virginia/Ohio/Maryland and 

Illinois/Indiana. 

Overall, it appears that Illinois/Indiana and western Kentucky 

tend to have higher roof fall incident rates than other areas. 

Geologic conditions seem to be the most likely explanation 

(Molinda et al., 2008). One recent study compared the measured uniaxial compressive strength of roof rocks in the Illinois 

Basin with that of roof rocks from southern West Virginia. The 

study involved more than 800 rock units and 10,000 laboratory 

strength tests. It concluded that for each of the three major 

rock types (shale, siltstone and sandstone), the strength of the 

Illinois Basin variety was less than 50% of the strength of the 

same rock type in West Virginia (Rusnak and Mark, 2000).

It is intriguing that longwall mines in the northern Appalachian region had lower-than-average noninjury roof fall 

rates, while the rates for the region’s room-and-pillar mines 
were average or higher than average. Most of the 

longwalls in northern Appalachia are extracting 

the Pittsburgh seam, where the typical roof is 

also quite weak. However, most of these longwall mines drive their development entries with 

single-pass continuous miners with integral roof 

bolters. This mining method results in narrower 

gateroad entries (typically less than 5 m wide) 

which, combined with the near-immediate installation of roof support, greatly improves overall 

roof stability. Nearly every other U.S. longwall 

mine employs the “place changing” mining 

method, with separate mining and roof bolting 

machines, and entries that are 5.5-6.2 m wide.

Figure 10 — Roof fall injury rates by region, based on MSHA (2009) data 

for 1999-2008.

Figure 11 — Noninjury roof fall rates by region, based on MSHA (2009) 

data for 1999-2008.

The rib fall injury rates for both mining methods (Fig. 12) show that the western United States 

had rates that were double the national rate. 

Figure 12 — Rib fall injury rates by region, based on MSHA (2009) data 

for 1999-2008.

High 

rates for room-and-pillar mines are also found in 

three of the four central Appalachian regions. This 

trend may be related to a recent study that found 

just 40 deep cover (depth greater than 1,000 ft) 

mines in this area, but these mines accounted for 

about one quarter of all rib fall injuries in roomand-pillar mines nationwide (NIOSH, 2010). In 

addition, during this period, few of these operations employed any rib support.

Seam height. Mines operating in thin seams 

<108.96 cm (43.9 in.) tend to be smaller mines that 

exclusively use the room-and-pillar extraction 

methods, whereas longwall mines operate only in 

a few medium seams 109.22-152.14 cm (43-59.9 

in.), with the majority of longwall mines operating in thick seams >152.4 cm (60 in.). Because 

there is not a wide distribution of seam heights 

for longwall mines, data from room-and-pillar 

mines will only be used in this analysis. Figure 

13 shows the results of reportable noninjury roof 

fall rates, based on seam height, and indicates that 

thin-seam mines had a 30% lower noninjury roof 

fall rate than the national average. Conversely, 

the ultrathick seams had a 20% higher (Fig. 13) 

noninjury roof fall rate than the national average. 

However, a further inspection of these noninjury 

falls reveals that they occur predominantly in 

the Illinois Basin area (Fig. 14). The weak roof 

rock typically encountered in the Illinois Basin 

is the most likely explanation for the higher roof 

fall rate in those mines. Once the Illinois Basin 

mines are removed, the noninjury roof fall rate 

for the remaining ultrathick-seam mines is not 

significantly above the overall average.

The ultra-thick seams had a 50% higher 

groundfall fatality rate than the national average 

(Fig. 15), which is in contrast to the thin and 

medium seams that had fatality rates 30% lower 

than the national rate. This significantly higher 

fatality rate can be attributed to the Crandall 

Canyon disaster, which occurred in an ultrathick 

seam and represented 30% of the ultrathick seam, 

room-and-pillar mine fatalities.

Figure 16 shows that, nationwide, rib fall 

injury rates increase approximately in proportion to the seam height. A deeper look at the 

locations of these rib fall rates (Fig. 17) shows 

that the ultrathick seam mines in the western 
United States and in southern 

West Virginia had rib fall 

rates that were significantly 

above the industry average. 

Figure 13 — Noninjury roof fall rates by seam height for 

room-and-pillar mines, based on MSHA (2009) data for 

1999-2008.

Figure 14 — Comparison of noninjury roof fall rates for 

Illinois Basin and the remaining United States, based on 

MSHA (2009) data for 1999-2008.

Figure 15 — Groundfall fatality rates by seam height for 

room-and-pillar mines, based on MSHA (2009) data for 

1999-2008.

Figure 16 — Rib fall injury rates by seam height for roomand-pillar mines, based on MSHA (2009) data for 1999-2008.

Figure 17 — Rib fall injury rates for ultra-thick seams by region, based on MSHA (2009) 

data for 1999-2008.

The ultrathick coal seams in 

the western United States are 

much thicker than elsewhere, 

averaging 263 cm (104 in.) 

compared to the rest of the 

country at 223-230 cm (88-

90 in.) (Fig. 18). Perhaps as 

the mining height increases, 

a great surface area of the rib 

is exposed and is at risk of 

becoming unstable or prone 

to collapse. The western U.S. 

coal mines are also associated 

with deeper coalbeds (Mark 

et al., 2009). Another contributing factor related to the 

higher rib fall injury rates in 

the ultrathick seams is the 
bump/burst events that routinely occur in the western United 

States and are categorized in the MSHA database as rib fall 

incidents. Analysis of the rib fall incident narratives indicates 

that one-third of the rib fall injuries in the western United 

States are associated with bump/burst events.

The reasons for the high rib fall injury rate in southern West 

Virginia’s ultrathick seam mines are less clear. Unlike the 

western United States, the ultrathick seam mines in southern 

West Virginia have average seam heights that are similar to 

or less than the national ultrathick seam heights (Fig. 18). 

Figure 18 - Average seam thickness for ultra-thick seams by region, based on 

MSHA (2009) data for 1999-2008. 

Western Pennsylvania also has a severe rib fall injury rate for 

room-and-pillar mines, but this may be a statistical anomaly 

because of the small number of mines in this category.

Mine size. The proportion of room-and-pillar mine sizes are 

fairly evenly distributed among the three mine-size categories 

(i.e., small, medium, and large) based on underground hours 

worked (Table 1). However, longwall mines are disproportionately distributed among the three categories, with 93% 

falling into the large-mine category (Table 2). Therefore, the 

mine-size analysis includes only the room-and-pillar mines.

The analysis found that there were 

only minor differences between the 

mine-size groupings for the injury and 

reportable noninjury groundfall incident 

rates. However, the fatality rate for small 

mines (< 50 workers) was about twice 

that for smaller mines (Fig. 19). 

Figure 19 — Groundfall fatality rates by mine size for roomand-pillar mines, based on MSHA (2009) data for 1999-2008.

Approximately 60% of the fatal room-and-pillar 

groundfalls from 1999 through 2008 

occurred in mines with <50 workers. 

The Crandall Canyon disaster again 

explains some of this discrepancy, but 

the small mine fatality rate is still high, 

even with those nine deaths removed. 

An elevated groundfall fatality rate in 

small mines was also identified in two 

studies, one in the early 1980s and one 

in the late 1990s (Pappas, 1987; Pappas 

and Mark, 2000).

Coalbed. A critical analysis was conducted to determine if certain coalbeds 

were more susceptible to groundfall. 

Every coalbed is assigned a three- or 

four-digit identification bed code number by the U.S. Geological Survey. Frequently, several coalbed names are grouped 

together in one code number since they are geologically similar. 

Because the coalbed is not a defined parameter in the MSHA 

database, bed codes from 1999 through 2002 were obtained 

from the U.S. Department of Energy’s Energy Information 

Agency and updated using the various state agency websites 

that compile coalbed classifications for individual mines. This 

data was merged with the MSHA employment and injury data 

associated with every underground coal mine in the study. Bed 

codes were identified for 90% of the room-and-pillar mines, 

accounting for 96% of the hours worked at room-and-pillar 

mines. Bed codes were identified for every longwall mine in 

this study.

To filter out coalbeds with low production and ambiguous 

incident rates, all coalbeds with fewer than nine million tons 

produced (cumulative 1999–2007) were removed from the 

analysis. For comparison purposes, a national roof fall rate was 

determined from the entire dataset, which included incidents 

from all coalbeds. The more significant coalbeds were selected 

by calculating the percentage that the coalbed groundfall rate 

exceeded the national rate. All coalbeds with extreme rates 

(higher or lower than the national rate by at least 25%), are 

listed regionally for room-and-pillar mines (Tables 4a, 5a 

and 6a) and longwall mines (Tables 4b, 5b and 6b). A critical 

factor in evaluating coalbed groundfall rates is the proportion 

of production represented in each region with the extreme 

groundfall rates. The broad regions used in Tables 4-6 are not 

necessarily the same as the more specific regions used in the 

earlier analyses (shown in Figs. 10-12). Many coalbeds in these 

specific regions were found to overlap; broader regions were 

found to be a more accurate method of defining the location 

of coalbeds (e.g., the central Appalachian area is comprised of 

southern West Virginia, Virginia and eastern and southeastern 

Kentucky).

The most notable trends in Tables 4a-4b are the high noninjury roof fall rates in the Illinois Basin coalbeds. For longwall 

mines, coalbeds that account for 100% of the coal production 

in that region (i.e., all longwall mines) have exceptionally high 

noninjury roof fallrates. The same trend is also found for roomand-pillar mines, where coalbeds accounting for 91% of the 
Table 4a — Extreme noninjury roof fall rates by coalbed for room-and-pillar mines, based on MSHA (2009) data for 1999-2007.

Mining 

method Region Coalbed 2 Bed code

No. UG 

workers

Underground 

hours 

worked

Underground 

production 

(metric 

tons)

Representation 

of production 

by region

No. 

Mines1

No. 

Noninjury 

roof 

falls

Noninjury 

roof fall rate 

falls/million 

metric tons

Above/ 

below 

national rate

Room-andPillarNorthern 

Appalachian

Upper 

Kittanning 76 3,841 7,979,284 24,316,755 44% 68 565 23.235 226.4%

High Rates Sewickley 29 1,225 2,392,396 8,814,187 51 144 16.337 129.5%

Upper 

Freeport 71 3,690 7,730,388 28,104,466 111 405 14.411 102.5%

Pittsburgh 36 2,417 4,857,596 15,293,166 69 138 9.024 26.8%

Central 

Appalachian

Jawbone/

Iaeger 266 3,150 5,852,508 15,939,548 4% 125 206 12.924 81.6%

Pocahontas No. 12 311 1,520 3,127,059 8,549,472 64 82 9.591 34.8%

Kellioka 152 2,416 5,446,341 15,815,355 64 140 8.852 24.4%

Illinois Basin Danville/

No. 7 480 2,573 5,993,202 22,249,348 91% 16 273 12.270 72.4%

Springfield/

No. 5/KY 

No. 9

489 20,600 48,260,389 209,520,412 146 1992 9.507 33.6%

Herrin/No. 6/

KY No. 11 484 9,144 20,399,665 91,716,293 75 820 8.941 25.6%

Room-andPillarCentral 

Appalachian Glamorgan 185 1,921 3,416,299 8,380,872 36% 88 23 2.744 -61.4%

StocktonLewiston/

Mercer

Low Rates 103 3,230 6,822,547 33,539,857 57 103 3.071 -56.9%

Lower Cedar 

Grove/Elkhorn No. 2

154 3,291 6,366,000 20,609,795 126 70 3.396 -52.3%

Winifrede/

Hazard No. 5 121 4,359 9,468,744 42,158,759 94 152 3.605 -49.3%

Eagle 176 3,070 6,347,100 21,822,016 64 87 3.987 -44.0%

Alma/Elkhorn No. 1/

Blue Gem

157 6,159 11,659,956 32,327,749 284 141 4.362 -38.7%

Powellton 170 4,077 9,522,024 34,570,247 75 155 4.484 -37.0%

Darby/Owl/ Jellico 151 17,680 37,457,321 120,781,921 544 542 4.487 -37.0%

Splash Dam 210 2,825 5,057,584 12,215,997 125 62 5.075 -28.7%

Illinois Basin W. KY No. 

13 482 653 1,545,287 9,057,404 3% 12 19 2.098 -70.5%

1 The total number of mines for 1999-2007 is not mutually exclusive (if a mine worked all nine years, it is counted nine times).

2 Excludes coalbeds with less than 9 million tons for 1999-2007.

Table 4b — Extreme noninjury roof fall rates by coalbed for longwall mines, based on MSHA (2009) data for 1999-2007.

Mining 

method Region Coalbed 2 Bed code

No.UG 

workers

Underground 

hours 

worked

Underground 

production 

(metric 

tons)

Representation of 

production by 

region

No. 

Mines1

No. Noninjury roof 

falls

Noninjury 

roof fall 

rate falls/

million 

metric 

tons

Above/ 

below 

national 

rate

Longwall Northern 

Appalachian Upper Freeport 71 1,496 3,288,242 23,014,517 3% 9 47 2.042 61.4%

High Rates Central 

Appalachian

Alma/Elkhorn 

No. 1/Blue Gem 157 1,114 2,805,529 8,936,880 90% 7 39 4.364 244.8%

Darby/Owl/

Jellico 151 741 1,900,600 8,511,052 5 37 4.347 243.5%

Upper Alma/

Alma A 156 1,457 3,261,595 13,828,333 6 47 3.399 168.6%

Powellton 170 1,099 2,784,709 12,653,594 8 33 2.608 106.1%

Eagle 176 5,383 12,862,791 65,661,292 28 152 2.315 82.9%

Pocahontas 

No. 3 344 7,982 17,261,528 66,998,359 26 140 2.090 65.1%

Southern 

Appalachian Pratt/Corona 227 2,526 5,553,543 25,536,993 22% 9 64 2.506 98.0%

Illinois Basin Springfield/No. 

5/KY No. 9 489 6,221 14,601,051 66,508,393 100% 14 313 4.706 271.9%

W. KY No. 13 482 1,454 3,311,715 14,157,666 5 63 4.450 251.6%

Herrin/No. 6/KY 

No. 11 484 3,291 6,920,811 32,930,280 14 135 4.100 223.9%

Longwall Northern 

Appalachian Pittsburgh 36 49,635 112,698,999 638,752,782 95% 128 503 0.787 -37.8%

Low Rates Central 

Appalachian

Lower Cedar 

Grove/Elkhorn 

No. 2

154 493 1,075,294 12,618,884 6% 3 6 0.475 -62.4%

Southern 

Appalachian

Blue Creek/Mary 

Lee 280 15,273 33,876,693 83,940,082 73% 43 54 0.643 -49.2%

Western USA Upper Hiawatha 1,847 1,647 3,326,723 57,287,896 67% 9 2 0.035 -97.2%

Hanna No. 5 1,820 1,141 2,424,633 21,877,364 8 1 0.046 -96.4%

Lower Sunnyside 1,802 878 1,999,146 18,382,537 7 1 0.054 -95.7%

Wadge/Roland 

of Tuff 1,750 2,844 6,208,771 67,025,030 9 20 0.298 -76.4%

Hiawatha 1,846 2,344 4,718,039 39,319,055 15 15 0.381 -69.9%

Blind Canyon 1,855 1,292 2,551,196 18,016,004 5 9 0.500 -60.5%

D Seam 1755 2,648 5,289,815 59,850,807 14 38 0.635 -49.8%

1 The total number of mines for 1999-2007 is not mutually exclusive (if a mine worked all nine years, it is counted nine times).

2 Excludes coalbeds with less than 9 million tons for 1999-2007.
room-and-pillar production in the region have high noninjury 

roof fall rates. The four coalbeds with the highest noninjury 

roof fall rates in the Illinois Basin include the (1) Springfield/

No. 5/Kentucky No. 9, (2) Herrin/No. 6/Kentucky No. 11 , (3) 

Danville/No. 7 (room-and-pillar only) and (4)Western Kentucky No. 13 (longwall only). Several of these same coalbeds 

also had high roof fall injury rates (Tables 5a-5b). However, 

fewer Illinois Basin coalbeds had high roof fall injury rates 

(compared to noninjury roof fall rates), and they accounted 

for only 26% of the room-and-pillar production and 71% of 

the longwall production. Certainly, a unique set of geological 

circumstances are responsible for this regional concentration 

of roof falls, as mentioned previously.

Table 5a — Extreme roof fall injury rates by coalbed for room-and-pillar mines, based on MSHA (2009) data for 1999-2007.

Mining 

method Region Coalbed 2 Bed code

No. 

Workers

Underground 

hours

Underground 

production 

(metric 

tons)

Representation 

of production by 

region

No. 

Mines1

No. 

Roof fall 

injuries

Roof 

injury rate 

(falls/200khrs)

Above/ 

below 

national 

rate

Room-andpillar high 

rates

Central 

Appalachian Eagle 176 3,070 6,347,100 21,822,016 27% 64 93 2.930 63.1%

Jawbone/

Iaeger 266 3,150 5,852,508 15,939,548 125 79 2.700 50.2%

Powellton 170 4,077 9,522,024 34,570,247 75 118 2.478 37.9%

Coalburg/

Hazard 

No. 7

111 8,063 16,584,352 74,604,733 221 202 2.436 35.6%

Imboden/

No. 6/KY 

No. 11

168 12,536 28,513,845 96,858,114 245 325 2.280 26.9%

Illinois Basin Herrin/No. 

6/KY No. 11 484 9,144 20,399,665 91,716,293 26% 75 252 2.471 37.5%

Room-andpillar low 

rates

Northern 

Appalachian

Lower 

Freeport 74 1,822 4,180,325 16,503,700 9% 37 19 0.909 -49.4%

Central 

Appalachian Splash Dam 210 2,825 5,057,584 16,503,700 8% 125 24 0.949 -47.2%

Glamorgan 185 1,921 3,416,299 12,215,997 88 17 0.995 -44.6%

Lower 

Winifrede 122 1,013 2,360,274 8,380,872 19 12 1.017 -43.4%

Pocahontas 

No. 12 311 1,520 3,127,059 9,942,945 64 18 1.151 -35.9%

Illinois Basin W. KY No. 

13 482 653 1,545,287 9,057,404 3% 12 2 0.259 -85.6%

1 The total number of mines for 1999-2007 is not mutually exclusive (if a mine worked all nine years, it is counted nine times).

2 Excludes coalbeds with less than 9 million tons for 1999-2007.

Table 5b — Extreme roof fall injury rates by coalbed for longwall mines, based on MSHA (2009) data for 1999-2007.

Mining 

method Region Coalbed 2 Bed code

No. Workers

Underground 

hours

Underground 

production 

(metric 

tons)

Representation 

of production 

by region

No. 

Mines1

No. Roof fall 

injuries

Roof 

injury rate 

(falls/200khrs)

Above/ 

below 

national rate

Longwall 

high rates

Central 

Appalachian Powellton 170 1,099 2,784,709 12,653,594 44% 8 24 1.724 127.4%

Darby/Owl/

Jellico 151 741 1,900,600 8,511,052 5 11 1.158 52.7%

Eagle 176 5,383 12,862,791 65,661,292 28 72 1.120 47.7%

Illinois Basin W. KY No. 13 482 1,454 3,311,715 14,157,666 71% 5 60 3.624 378.0%

No. 5/

Springfield/

KY No. 9

489 6,221 14,601,051 66,508,393 14 186 2.548 236.1%

Longwall 

low rates

Northern 

Appalachian Clarion 87 1,442 3,344,288 11,877,851 2% 6 3 0.179 -76.3%

Southern 

Appalachian Pratt/Corona 227 2,526 5,553,543 25,536,993 22% 9 12 0.432 -43.0%

Illinois Basin Herrin/No. 6/

KY No. 11 484 3,291 6,920,811 32,930,280 29% 14 18 0.520 -31.4%

Western USA Wadge/Roland of Tuff 1,750 2,844 6,208,771 67,025,030 96% 9 3 0.097 -87.3%

Castle Gate A 1,830 1,583 3,487,030 21,145,399 10 2 0.115 -84.9%

Blind Canyon 1,855 1,292 2,551,196 18,016,004 5 2 0.157 -79.3%

Fruitland 

No. 8 1,488 1,302 2,936,028 28,336,005 5 3 0.204 -73.0%

Hiawatha 1,846 2,344 4,718,039 39,319,055 15 7 0.297 -60.9%

Lower Sunnyside 1,802 878 1,999,146 18,382,537 7 3 0.300 -60.4%

Hanna No. 5 1,820 1,141 2,424,633 21,877,364 8 4 0.330 -56.5%

Upper 

Hiawatha 1,847 1,647 3,326,723 57,287,896 9 6 0.361 -52.4%

D Seam 1,755 2,648 5,289,815 59,850,807 14 11 0.416 -45.1%

B Seam 1,753 4,395 8,792,193 74,436,886 25 23 0.523 -31.0%

1 The total number of mines for 1999-2007 is not mutually exclusive (if a mine worked all nine years, it is counted nine times). 2 Excludes coalbeds with less than 9 million tons for 1999-2007.

Other troubling trends from this analysis were the exceptionally high (greater than 100% higher than the national 

rate) noninjury roof fall rates associated with 44% of the 

room-and-pillar production in the northern Appalachian region, specifically the Upper Kittanning, Sewickley and Upper 

Freeport coalbeds (Table 4a). Weaker geology is the most likely 

explanation (Mark et al., 2004). The data also confirms that, 

despite the weak roof, longwall mines in the northern Appalachian region (Pittsburgh coalbed) maintained an admirable 

record, with noninjury roof fall rates significantly lower than 

the rest of the country for 95% of the longwall production in 
Table 6a – Extreme rib fall injury rates by coalbed for room-and-pillar mines, based on MSHA (2009) data for 1999-2007.

Mining 

method Region Coalbed 2 Bed code

No. UG 

Workers

Underground 

hours

Underground 

production 

(metric 

tons)

Representation 

of production 

by region

No. 

Mines1

No. 

Rib fall 

injuries

Rib fall 

injury rate 

(falls/200khrs)

Above/ 

below 

national 

rate

Roomand- pillar 

- high rates

Northern 

Appalachian

Upper Kittanning 76 3,841 7,979,284 24,316,755 23% 68 16 0.401 72.9%

Pittsburgh 36 2,417 4,857,596 15,293,166 69 8 0.329 42.0%

Central 

Appalachian

Eagle 176 3,070 6,347,100 21,822,016 46% 64 24 0.756 226.0%

Pocahontas 

No. 12

311 1,520 3,127,059 8,549,472 64 11 0.704 203.2%

Powellton 170 4,077 9,522,024 34,570,247 75 21 0.441 90.1%

Alma/Elkhorn No. 

1/Blue Gem

157 6,159 11,659,956 32,327,749 284 25 0.429 84.8%

Lower Winifrede 122 1,013 2,360,274 9,942,945 19 5 0.424 82.6%

Winifrede/Hazard No. 5121 4,359 9,468,744 42,158,759 94 18 0.380 63.9%

Pocahontas 

No. 11

318 2,157 3,686,514 10,257,263 113 7 0.380 63.7%

Imboden/Warfield 168 12,536 28,513,845 96,858,114 245 45 0.316 36.1%

Jawbone/Iaeger 266 3,150 5,852,508 15,939,548 125 9 0.308 32.6%

Pardee/Parsones/

Limestone

126 1,474 2,620,248 9,170,018 68 4 0.305 31.6%

Kellioka 152 2,416 5,446,341 15,815,355 64 8 0.294 26.6%

Darby/Owl/Jellico 151 17,680 37,457,321 120,781,921 544 55 0.294 26.6%

Room-andpillar - low ratesNorthern 

Appalachian

Middle Kittanning 80 1,764 3,368,944 15,784,209 73% 45 0 0.000 -100.0%

Lower Freeport 74 1,822 4,180,325 16,503,700 37 0 0.000 -100.0%

Upper Freeport 71 3,690 7,730,388 28,104,466 111 4 0.103 -55.4%

Lower Kittanning 84 6,295 12,961,566 59,074,308 195 10 0.154 -33.5%

Sewickley 29 1,225 2,392,396 8,814,187 51 2 0.167 -27.9%

Central 

Appalachian

Splash Dam 210 2,825 5,057,584 12,215,997 17% 125 1 0.040 -83.0%

Sewell 285 1,898 3,926,347 11,985,683 76 1 0.051 -78.0%

Stockton-Lewiston/Mercer103 3,230 6,822,547 33,539,857 57 3 0.088 -62.1%

Glamorgan 185 1,921 3,416,299 8,380,872 88 2 0.117 -49.5%

Pocahontas No. 3 344 2,443 4,696,647 11,293,561 90 3 0.128 -44.9%

Hazard No. 4 135 11,320 24,161,669 79,800,733 294 18 0.149 -35.8%

Illinois Basin W. KY No. 13 482 653 1,545,287 9,057,404 68% 12 0 0.000 -100.0%

No. 5/Springfield/

KY No. 9

489 20,600 48,260,389 209,520,412 146 14 0.058 -75.0%

Danville/No. 7 480 2,573 5,993,202 22,249,348 16 2 0.067 -71.2%

1 The total number of mines for 1999-2007 is not mutually exclusive (if a mine worked all nine years, it is counted nine times). 2 Excludes coalbeds with less than 9 million tons for 1999-2007.

Table 6b – Extreme rib fall injury rates by coalbed for longwall mines, based on MSHA (2009) data for 1999-2007.

Mining 

method Region Coalbed 2 Bed code

No. UG 

workers

Underground 

hours

Underground 

production 

(metric 

tons)

Representation 

of production 

by region

No. 

Mines1

No. 

Rib fall 

injuries

Rib fall 

injury rate 

(falls/200khrs)

Above/ below national 

rate

Longwall 

High Rates

Central 

Appalachian

Upper Alma/

Alma A

156 1,457 3,261,595 13,828,333 41% 6 5 0.307 69.4%

Eagle 176 5,383 12,862,791 65,661,292 28 17 0.264 46.0%

Illinois 

Basin

W. KY No. 13 482 1,454 3,311,715 14,157,666 12% 5 5 0.302 66.8%

Western 

U.S.

Lower 

Sunnyside

1,802 878 1,999,146 18,382,537 48% 7 9 0.900 397.4%

D Seam 1,755 2,648 5,289,815 59,850,807 14 16 0.605 234.2%

Blind Canyon 1,855 1,292 2,551,196 18,016,004 5 5 0.392 116.6%

Hiawatha 1,846 2,344 4,718,039 39,319,055 15 8 0.339 87.4%

Wadge/Roland of Tuff1,750 2,844 6,208,771 67,025,030 9 8 0.258 42.4%

Longwall 

Low Rates

Northern 

Appalachian

Upper 

Freeport

71 1,496 3,288,242 23,014,517 5% 9 0 0.000 -100.0%

Clarion 87 1,442 3,344,288 11,877,851 6 0 0.000 -100.0%

Central 

Appalachian

Lower Cedar 

Grove/ Elkhorn No. 2

154 493 1,075,294 12,618,884 45% 3 0 0.000 -100.0%

Pocahontas No. 3344 7,982 17,261,528 66,998,359 26 6 0.070 -61.6%

Alma/Elkhorn 

No. 1/Blue 

Gem

157 1,114 2,805,529 8,936,880 7 1 0.071 -60.6%

Southern 

Appalachian

Pratt/Corona 227 2,526 5,553,543 25,536,993 22% 9 3 0.108 -40.3%

Illinois 

Basin

Herrin/No. 6/

KY No. 11

484 3,291 6,920,811 32,930,280 29% 14 2 0.058 -68.1%

Western 

U.S.

Castle Gate A 1,830 1,583 3,487,030 21,145,399 5% 10 2 0.115 -36.6%

1 The total number of mines for 1999-2007 is not mutually exclusive (if a mine worked all nine years, it is counted nine times). 2 Excludes coalbeds with less than 9 million tons for 1999-2007.
that region. In central Appalachia, 36% of the room-and-pillar 

production was linked to coalbeds with low noninjury roof fall 

rates and 90% of the longwall production linked to coalbeds 

with high noninjury roof fall rates (Tables 4a-4b). The four 

most problematic coalbeds were the (1) Alma/Elkhorn No. 1/

Blue Gem, (2) Darby/Owl/Jellico, (3) Upper Alma/Alma A 

and (4) Powellton coalbeds.

Similar to rib fall injuries is the central Appalachian region, 

where coalbeds representing 46% of the room-and-pillar 

production and 41% of the longwall production have rib fall 

injury rates that exceed the national average (Tables 6a-b).

A severe rib fall injury rate, several magnitudes higher than 

the national rating, is associated with 48% of the longwall 

production in the western United States (Table 6b). The thick 

seams and deep overburdens associated with the western United 

States probably contribute to the rib control 

problems and make the rib face more prone to 

mountain bumps and bursts. Conversely, the 

roof fall injury trends in the western United 

States were significantly lower than the national 

rate and represented 96% of the longwall production in this region (Table 5b). These low 

roof fall injury rates can be attributed to the 

nearly universal use of roof screening in the 

western United States (Compton et al., 2008). 

Seasonal patterns. The chronological quarterly roof fall rates were evaluated to determine 

if seasonal patterns, such as fluctuations in 

temperature, barometric pressure and humidity, affect the number of groundfall injuries. 

Because the mines in the western United 

States are located mostly in arid climates and 

experience minimum fluctuations in humidity, the data from Colorado, New Mexico, 

Montana, Utah and Wyoming were evaluated 

separately. Although monthly production data 

is not compiled, quarterly production data was 

accessed from MSHA’s Standardized Information System (MSHA, 2010), which allowed the 

groundfall incidents to be normalized based on the quarterly 

underground production. Figure 20 shows that the noninjury 

roof fall incident rate was fairly consistent, except for the third 

quarter (July–September), where the roof fall rate was more 

than 50% higher than the overall average for the other three 

quarters. Possibly, this trend indicates that mine air is becoming more humid during the late summer months and that the 

moisture is disintegrating the shale roof, resulting in a greater 

frequency of massive roof falls. Further confirmation of this 

hypothesis is provided by the data from the western mines, 

which have less change in humidity and do not display a 

seasonal trend (Fig. 20). 

Figure 20 — Noninjury roof fall rates by quarter for both mining methods, 

based on MSHA (2009 and 2010) data for 1999-2008.

Other studies have found similar seasonal patterns. The U.S. 

Bureau of Mines (Stateham and Radcliffe, 1978) found in its 

report of investigations that humidity has a strong influence 

on roof fall occurrence rates. Those results indicated that the 

probability of a roof fall is greatest in August and lowest in 

February.

Analysis of MSHA fatality reports. For the second segment 

of the study, the individual MSHA fatality reports (MSHA, 

2008) were reviewed, and critical details related to the cause 

of the incident were compiled for both bituminous operator 

and contractor groundfall incidents. From 1999 through 2008, 

66 of these events resulted in 75 fatalities (71 operator and 

four contractor), which accounted for 38% of all underground 

fatalities (Fig. 21). 

Figure 21 — Proportion of groundfall fatalities compared 

to all fatalities, based on MSHA (2008) data for 1999-2008.

Figure 9 shows groundfall operator fatalities 

by decade for the past 30 years. With each passing decade, the 

number of groundfall fatalities has dropped by half, and the 

fatality rates by about 20%–25%, from the previous decade. 

Because yearly groundfall fatality rates from this past decade 

(1999–2008) are volatile (Fig. 8), these rates were converted 

into three-year, running-average fatality rates in Fig. 22. There 

are slight downward trends in both room-and-pillar and longwall 

groundfall fatality rates, but the R-squared values are very low.

Pillar recovery. The process of pillar recovery removes 

the main support for the overburden and allows the ground to 

cave. As a result, the pillar line is an extremely dynamic and 

highly stressed environment. Safety depends on controlling 

the caving through proper extraction sequencing and roof 

support. As shown in Fig. 23, pillaring fatalities accounted for 
19% of all groundfall fatalities during 1999–2008, including 

two multiple fatality incidents. According to Fig. 24, most 

of these roof fall incidents occurred in the earlier part of this 

period (prior to 2001). Only one incident, a multiple fatality, 

has occurred since the end of 2005. The improvement has been 

attributed to widespread use of safety technologies, including 

mobile roof supports, engineered final stumps and additional 

roof support (Mark et al., 2009).

Figure 22 — Three-year running average of groundfall fatality rates, based on MSHA (2008) 

data for 1999-2008. The fitted curves are logarithmic for the room-and-pillar mines and linear 

for longwall mines.

Rib failures.Rib failure is often associated with rock partings, 

discontinuities within the pillar or overhanging brows created 

by roof drawrock. During the past 10 years, rib failures resulted 

in 12 fatalities, or 16% of all groundfall fatalities, as shown in 

Fig. 23. 

Figure 23 — Causes of groundfall fatalities, based on MSHA 

(2008) data for 1999-2008.

These rib fall fatalities do not include bursts, which were 

included for previously 

reported rib fall injuries; 

burst fatalities will be 

addressed separately 

in this paper. Although 

rib fall fatalities are at 

about the same level 

as they were during the 

previous study (Pappas 

and Mark, 2000), rib fall 

injuries have generally 

increased (Fig. 6). As 

mentioned previously, 

seam height is a significant factor in rib failures. Because the seam 

height defines only the 

average height of the 

seam, mining height is 

a more accurate value 

available only with the 

more detailed fatality 

reports. Mining height 

defines the actual height 

of the mine opening at 

the site of the fatality, which may include roof rock. The average mining height related to all rib fall fatalities was 248.92 

cm (98 in.) compared to 172.72 cm (68 in.) for the average 

roof fall fatality. All rib fall fatalities occurred with mining 

heights greater than 208.28 cm (82 in.). In addition, the incidence of rib fall injuries increases dramatically once the seam 

height reaches above 182.88 cm (6 ft), as shown in Fig. 16. 

For room-and-pillar mines, the rib fall injury rate exceeds the 

national average by 45% for seam heights greater than 182.88 

cm (72 in.) (Fig. 16).

Roof-skin failures. Most roof-skin injuries occur under 

permanently supported roof and involve workers in a wide 

variety of activities. Roof-skin failures are incidents that do 

not involve failure of the roof-support elements, but result 

from rock spalling from between roof bolts or automated 

temporary roof-support systems. Roof-skin failures are of 

particular concern, because they cause injuries and fatalities 

to workers who should have been protected by these support 

systems. A previous study (Pappas and Mark, 2000) found 

roof-skin fatalities to be the fourth-leading cause of groundfall 

(12% of fatalities during 1996-1999) compared to this current 

study, in which roof-skin fatalities are the third-leading cause 

of groundfalls (16% of fatalities 1999-2008). The median size 

of a fatal roof-skin failure in this study is approximately 1.31 

m x 1.28 m x 0.146 m (4.3 ft x 4.2 ft x 0.48 ft) compared 

to 1.34 m x 1 m x 0.125 m (4.4 ft x 3.3 ft x 0.41 ft) in the 

previous study. By far, the most effective roof-skin-control 

method is the use of roof screening (Compton et al., 2008). 

Other common roof-skin-control techniques include oversized 

plates, header boards, wood planks, steel straps and (in rare 

instances) spray-on coatings.

Unsupported roof. Twenty years ago, nearly 50% of all 

groundfall fatalities occurred beneath unsupported roof (Peters, 

1992). Although there are no grounds for complacency, the 

current fatality trend for miners traveling under unsupported 

roof has been significantly reduced to 16% of all groundfall fatalities (Fig. 23). Figure 25 shows that the number of 

unsupported-roof fatalities dropped dramatically during the 

past 14 years, and that only three fatalities have occurred in 

the past six years. The improvement was achieved through new 
equipment, enforcement and a persistent educational campaign 

organized by MSHA.

Bursts. Bursts, also known as mountain bumps, are sudden 

violent ground failures of highly-stressed coal. Typically, bursts 

are not a separate category, but have been included under the 

rib fall category. However, largely due to the recent Crandall 

Canyon disaster, burst incidents accounted for more than 13% 

of all groundfall fatalities during the past 10 years (Fig. 23). 

Bursts generally occur when the coal deposit is sandwiched 

between strong floor and roof strata, where the overburden 

exceeds 305 m (1,000 ft), and where longwall or pillar-retreat 

mining is employed. These types of incidents are usually 

limited to the coalfields of the western United States and the 

central Appalachian region. In fact, all of the recent fatalities 

occurred in the Utah coalfields.

Figure 24 — Fatality trends for pillaring operations, based on MSHA (2008) data for 1995-2008.

Figure 25 — Fatality trends for travelling under unsupported roof, based on MSHA (2009) data for 1995-2008.

Massive falls. Massive roof falls, typically as large as an 

entire coal mine intersection, can usually be attributed to the 

failure of the roof-support system. In 70% of the massive fall 

fatalities, geologic discontinuities, such as transition zones 

with slickensides, horseback and drag folds, were contributing 

factors. These roof defects were either undetected or were not 

recognized as hazardous. Other fatalities occurred when the 

depth of cut or width was not reduced due to adverse conditions, and/or supplemental support was not used. Other failures 
were attributed to weathered rock near the outcrop during the 

development of a mine opening, or to a fall during rehabilitation of a previous fall.

Other roof fall fatalities. Roof falls that do not fit into any 

of the previous categories comprised 11% of all groundfall 

fatalities, or eight fatalities. Four fatalities in this category are 

associated with miners working in “red zone” areas. These red 

zone areas are noted in many recent roof-control plans where 

miners must stay outby the second row of roof bolts, particularly 

when making extended cuts or turning a crosscut. Perhaps the 

recent downward trend in inby fatalities mentioned earlier can 

be partially attributed to this “red zone” concept (Mark, 2009). 

The 5th and 6th fatalities are associated with longwall mining. 

One miner was changing shearer bits over a hanging brow that 

fell, and the other miner was drilling into the roof between the 

longwall shield tips and the face. The 7th fatality is due to a 

rock fall during slope sinking. Finally, the last fatality resulted 

from a complex situation where a boom hole was blasted out, 

and the miner was attempting to install roof bolts without an 

automated temporary roof support system (ATRS) due to the 

extreme height involved.

Research application

Despite the fact that groundfall injuries have decreased 

in the past decade, there is a definite need to identify areas 

where continued or new research is needed to accelerate this 

downward trend. Probably the most noticeable trend within 

this data review was the higher noninjury and injury roof fall 

rates that continue to plague the Illinois Basin. It appears that 

geological conditions of regional coalbeds are the controlling 

factor associated with a weaker roof. Further study of this phenomenon is needed, as well as practical preventative methods 

to mitigate noninjury and injury roof falls. Techniques such 

as reduction of entry widths, cable bolting combinations, roof 

screening and sealants that prevent rock weathering might be 

highly effective. It is speculated that the use of single-pass 

continuous miners used with integral roof bolters is beneficial 

in reducing roof fall injury rates in the northern Appalachian 

coalfields, and perhaps experimentation with this machinery 

in the Illinois Basin might yield valuable results. In addition, 

the weathering issue can be related to the higher trend of roof 

falls during the summer months, possibly due to changes in 

humidity levels that may cause moisture sensitive mine roofs 

to deteriorate. Perhaps the use of mine air conditioning during the summer months or the use of an inexpensive spray-on 

coating could minimize these problems. Another research area 

that needs to be addressed are the high rib fall injury rates in 

central Appalachia and the western United States. Identifying 

the most appropriate rib support for different mining applications might be the most effective role for research in this area.

Conclusions

The consequences of roof fall and rib fall incidents are 

extensive, ranging from the economic loss of equipment and 

production to fatal and nonfatal injuries that result in lasting 

physical and financial impairments suffered by the victims 

and the victims’ families. In addition, the mining industry is 

severely impacted by these injuries, as well as thousands of 

noninjury incidents that damage equipment, stop production 

or disrupt ventilation. This study used a two-pronged approach 

in analyzing the current trends in groundfall injuries. The 

largest portion of the study used the MSHA database, where 

groundfall injury rates could be determined based on mining 

method, yearly trends, locality, seam height, mine size and 

seasonal effects. The second segment of the study reviewed the 

MSHA groundfall fatality reports to break down the specific 

causes of groundfall incidents. Mines using the room-and-pillar 

mining method had a roof fall injury rate that was 2.4 times 

the longwall roof fall injury rate.

The study found that, compared with the previous decade, 

groundfall fatality rates decreased by 25%, and the number of 

fatalities was cut in half. Roof fall injury rates dropped 50% 

for both the longwall and the room and pillar mining methods. 

Overall, however, longwall mines compiled a much better 

groundfall safety record. Longwall mining accounted for 51% 

of the production and 40% of the hours worked, but only 17% 

of groundfall fatalities, 22% of the roof fall injuries and 15% 

of the noninjury roof falls.

The regional analysis showed that mines in the Illinois Basin 

(western Kentucky and Illinois/Indiana) had roof fall injury 

and noninjury rates that exceeded the national rate. Their high 

rates are attributable to the generally weak roof rocks that are 

found in the region. Nearly every coalbed that is mined in the 

region was associated with high roof fall rates.

In contrast, longwall mines in the northern Appalachian area 

(Pennsylvania, Ohio and northern West Virginia) had lower than 

average rates, despite their weak roof. The integral continuous 

miners used in the region, which develop narrow entries that 

are supported immediately, are the likely explanation. However, 

several coalbeds in the region had exceptionally high noninjury 

roof fall rates for the room-and-pillar mining method.

Rib fall injury rates in the western United States were double 

the national rate for both mining methods, due to their thick 

seams and deep cover. However, western U.S. longwalls had 

very low roof fall injury rates, because of the widespread use 

of roof screen.

Nationwide, ultrathick seam room-and-pillar mines (seam 

heights greater than 182.88 cm (72 in.)) had a 45% higher rib 

fall injury rate than the national average. These higher rates 

are concentrated in the western United States and southern 

West Virginia. Ultrathick seam mines also had a 50% higher 

groundfall fatality rate, primarily due to the large number of 

rib fall fatalities in the Crandall Canyon Disaster and the prevalence of retreat mining operations in southern West Virginia. 

A review of seasonal patterns revealed that, for mines located in the eastern U.S., the third quarter (July–September) 

had a 50% increased risk of noninjury roof falls compared to 

the other three quarters. This is likely due to higher humidity 

levels during the summer months, which was further confirmed 

by the observation that there was no seasonal trend in the roof 

fall data from the western mines.

A total of 66 fatal groundfall incidents, resulting in 75 fatalities, occurred from 1999 through 2008. The detailed MSHA 

fatality reports were probed to identify the underlying causes. 

During this period, pillar recovery was still the leading cause 

of groundfall fatalities, responsible for 19% of the total. However, in the latter part of the study period, the pillar recovery 

fatality frequency dropped due to the widespread use of safer 

pillar recovery techniques. The second-leading cause was rib 

falls, resulting in 16% of the fatalities. All the rib fall fatalities 

occurred with seam heights greater than 208.28 cm (82 in.); 

62% of the fatalities occurred with overburden depths greater 

than 213.40 m (700 ft).

Roof-skin fatalities that occurred beneath supported roof, 

accounted for another 16% of the total. Roof-skin incidents are 

of particular concern, because they also were responsible for 
almost all of the more than 400 roof fall injuries that occurred 

each year. Nearly all of these incidents could be prevented by 

better surface controls, such as roof screen. In recent years, the 

number of fatalities caused by miners going under an unsupported roof has dropped significantly; however, these fatalities 

still accounted for 16% of all groundfall fatalities during the 

period. Coal bursts accounted for 13% of all groundfall deaths, 

most of which occurred at the Crandall Canyon mine in 2007. 

Massive roof falls, linked to roof support failures, resulted in 

nearly 9% of groundfall fatalities and more than 1,000 noninjury roof falls that occur each year. They underline the need 

for better design of roof support systems. 

These groundfall statistics and fatality report trends offer the 

most current profile of roof and rib falls in the United States. 

This study identifies areas where additional research is needed 

so that innovative solutions can be developed to reduce these 

severe hazards to underground mine workers.

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