115 

BEST PRACTICES TO MITIGATE INJURIES AND FATALITIES FROM ROCK FALLS 

Christopher Mark, Ph.D., Section Chief 

Anthony T. Iannacchione, Ph.D., Deputy Director 

National Institute for Occupational Safety and Health 

Pittsburgh, PA 

INTRODUCTION 

 Falls of ground continue to be one of the most 

serious causes of injury to U.S. miners. Of the 256 

fatal injuries that occurred in mining between 1996 

and 1998, 52 (20%) were caused by falls of ground 

(Table I). Falls of ground affect some sectors of 

the mining industry more severely than others. For 

instance, nearly 40% of the 98 coal mine fatalities 

between 1996 and 1998 were caused by falls of 

ground. Underground miners are at much greater 

risk than surface miners. Nearly half (45 out of 

101) of underground mine fatalities were attributed 

to roof, rib and face falls, while less than 5% of the 

155 surface fatalities were caused by falls of 

highwalls or slopes. 

Sources of Data

 All of the injury data examined in this study 

were derived from MSHA’s Fatal Investigation 

Reports (www.msha.gov)and the MSHA accident 

database. Because falls of ground often result in 

serious injury, MSHA Fatal Alert Bulletins and 

Fatal Investigation Reports provide a useful 

snapshot of ground control issues in the mining 

industry. MSHA requires that mines file a report 

on every reportable accident that occurs, 

containing information on the accident’s location, 

severity, classification, activity, and nature of 

injury, etc. A short narrative is generally included 

as well. Accident reports can be searched by many 

of the above fields. 

 From 1996 to 1998, miners suffered a total of 

55,096 injuries, which ranged in severity from 

death (degree 1) to injuries with no days away 

from work nor restricted duty (degree 6). Six 

percent of the total injuries were from falls of 

ground, including machine accidents where caving 

rock was coded as the source. As the data in Table 

II indicate, 98% of all non-fatal fall of ground 

injuries occurred in underground mines, with 

underground coal mines accounting for 83% of the 

total. 

 Table II also shows the distribution non-fatal 

fall of ground injuries by severity and commodity. 

The injuries are classified into Lost Time Injuries 

that resulted in permanent disability (degree 2) or 

days off work (degrees 3-4), and Injuries Without 

Lost Time that resulted in no more than restricted 

duty (degree 5-6). Overall, groundfall injuries 

appear to be more serious than other types of 

mining injuries. 65% of all ground fall injuries 

resulted in lost time compared to 54% of all types 

of mining injuries. 
116 

Table I - Fatalities from 1996 to 1998 by commodity for both falls of 

ground and other mining classifications

1996 1997 1998 Total 

Underground 

Surface 

& Prep. 

Plants 

Underground

Surface 

& Prep. 

Plants 

Underground

Surface & 

Prep. 

Plants 

Underground

Surface 

& Prep. 

Plant 

Coal falls of ground 13 1 9 0 14 1 36 2 

Coal total 33 6 22 8 22 7 77 21 

Metal falls of ground 1 0 2 1 3 0 6 8 

Metal total 5 3 7 5 5 5 17 13 

Nonmetal falls of ground 0 0 0 0 0 0 0 0 

Nonmetal total 0 1 1 2 2 4 3 7 

Stone falls of ground 2 2 1 1 0 1 3 4 

Stone total 2 25 2 26 0 23 4 74 

Sand/Gravel falls of ground 0 0 0 0 0 0 0 0 

Sand/Gravel total 0 11 0 17 0 12 0 40 

Total falls of ground 16 3 12 2 17 2 45 7 

Total Mining 40 46 32 58 29 51 101 155 

Legal Framework 

 Laws governing mining in the U.S. are listed 

in the Code of Federal Regulations under Title 30 - 

Mineral Resources. 

 Underground coal mining roof control is 

covered in 18 subsections within Part 75. While 

each of these sections outlines an important step in 

controlling falls of ground, some sections are cited 

more frequently in Fatal Investigation Reports. 

Between 1996 and 1998, a total of 30 citations 

were given to mines following fatal accidents, 

citing 6 of the 18 sections (Table III). The most 

frequently cited subsection was 75.202 - Protection 

from falls of roof, face, and rib. Section 75.202 

requires that ground support must protect persons 

from hazards related to falls of the roof, face or 

ribs and coal or rock bursts in areas where they 

work or travel. It also states that no person may 

work or travel under unsupported roof unless in 

accordance with special procedures. Another 

common citation listed was violation of the Roof 

Control Plan. The language also states that 

additional measures shall be taken to protect 

persons if unusual hazards are encountered. 

 Underground metal/nonmetal mining roof 

control is covered in 9 subsections within Part 57. 

Between 1996 and 1998, the most frequently cited 

subsection following fatalities was 57.3200, which 

requires that hazardous ground conditions be taken 

down or supported before other work or travel is 

permitted (Table IV). The law also requires that 

the affected area be posted with a warning against 

entry and, when left unattended, that a barrier be 

installed to impede unauthorized entry. Many of 

the Fatal Investigation Reports reveal that geologic 

structures contributed to the conditions referred to 

in subsection language. In four of the reports, 

inadequate examination of ground conditions was 

cited. 
117 

Surface mining ground control is covered in nine 

subsections within Part 56 for metal/ nonmetal 

mines and 15 subsections with Part 77 for coal 

mines. Several violations cited subsection 56.3200, 

which requires hazardous ground conditions to be 

taken down or supported before work or travel is 

permitted. The directive states that until corrective 

work is completed, the area shall be posted with a 

warning against entry and, when left unattended, a 

barrier shall be installed to impede unauthorized 

entry. 

GROUNDFALL HAZARDS AND BEST 

PRACTICES TO CONTROL THEM

 The 51 Fatal Investigation Reports from 1996 

to 1998 provide a window on the most significant 

groundfall hazards facing today’s miners. Some of 

these hazards, such as geologic features, affect all 

miners to one degree or another. Others are 

specific to the commodity or mining method. 

Table II- Non-fatal fall of ground 

injuries from 1996 to 1998.

Severity Commodity UndergroundAll 

other 

Total 

Lost time 

injuries 

(Degree 

2 to 4) 

Coal 1807 23 1830 

Metal 140 5 145 

Nonmetal 15 0 15 

Stone 14 9 23 

Subtotal 1976 37 2013 

Injuries 

without 

lost time 

(Degree 

5 and 6)

Coal 777 9 786 

Metal 269 3 272 

Nonmetal 23 1 24 

Stone 16 7 23 

Subtotal 1085 20 1105 

All nonfatal 

injuries 

Coal 2584 32 2616 

Metal 409 8 417 

Nonmetal 38 1 39 

Stone 30 16 46 

Total 3061 57 3118 
118 

Geologic Discontinuities

 Mines are unique structures because they are 

not constructed of man-made materials, such as 

steel or concrete, but are rather built of rock, just 

as nature made them. Thus, integrity of a mine 

structure is greatly affected by the natural 

weaknesses or discontinuities that disrupt the 

continuity of the roof and rib. Geologic 

discontinuities can originate while the material is 

being deposited by sedimentary or intrusive 

processes, or later when it is being subjected to 

tectonic forces. Depositional discontinuities 

include slips, clastic dikes, fossil remains, bedding 

planes, and transition zones. Structural 

discontinuities include faults, joints, and igneous 

dikes. 

Table III - Violations of Part 75 from fall of 

ground Fatal Investigation Reports, 1996-1998.

Subsection 

Violated Title Number 

75.202 Protection from falls of 

roof, face, and ribs 

18 

75.203 Mining method 1 

75.204 Roof bolting 0 

75.205 Installation of roof support 

using mining machine with 

integral bolter 

0 

75.206 Conventional roof support 0 

75.207 Pillar recovery 0 

75.208 Warning devices 0 

75.209 Automated temporary roof 

support systems 

1 

75.210 Manual installation of 

temporary support 

0 

75.211 Roof testing and scaling 0 

75.212 Rehabilitation of areas 

with unsupported roof 

1 

75.213 Roof support removal 3 

75.214 Supplemental support 

materials, equipment, and 

tools 

0 

75.215 Longwall mining systems 0 

75.220 Roof control plan 6 

75.221 Roof control plan 

information 

0 

75.222 Roof control plan--

approval criteria 

0 

75.223 Evaluation and revision of 

roof control plan 

0 
119 

 Discontinuities occur in many shapes and 

sizes and are generally difficult to recognize in 

advance of mining. They often contribute to fatal 

accidents, frequently in combination with other 

factors. Miners, and particularly roof bolt 

operators and face drillers, need to be trained to 

recognize geologic discontinuities as soon as they 

are exposed by mining. They must also be aware 

of the proper support techniques and have the 

necessary support materials available. 

Underground Coal Mine Hazards

Between 1996 and 1998, 36 underground coal 

miners were killed in 33 separate incidents. Table 

V lists the hazards that contributed to these 

incidents and their frequency. In some cases, more 

than one hazard was involved. For example, 13 

fatalities occurred during pillar extraction, with 3 

of the accidents resulting from premature 

intersection collapses. 

Unsupported roof. Roof bolts and the Automated 

Temporary Roof Support (ATRS) are the first lines 

of defense against roof falls in underground coal 

mines. When miners go under unsupported roof, 

they are completely unprotected. Between 1996 

and 1998, approximately 25% of coal mine roof 

and rib fatalities occurred when miners were 

beyond roof supports. While there are no grounds 

for complacency, the recent record does represent 

an improvement from a decade ago, when nearly 

50% of ground fall fatalities occurred beneath 

unsupported roof (Peters, 1992). The improvement 

was achieved through new equipment, 

enforcement and a persistent educational 

campaign. 

 During the early 1990's, the U.S. Bureau of 

Mines conducted an extensive series of interviews 

with miners to determine why they might go out 

under unsupported roof (Peters, 1992). The most 

common response was that they had 

unintentionally walked out beyond the supports. 

The most effective countermeasure, then, is to 

ensure that all areas of unsupported roof are 

clearly posted with highly visible warning devices. 

 Training is also essential. Mallett et al. (1992) 

argue that verbal admonitions and threats of 

discipline are less effective than training that 

graphically imparts the severe consequences of 

roof falls. 

Table IV - Violations to Part 57 from fall of ground

Fatal Investigation Reports, 1996-1998.

Subsection 

Violated 

Title Number 

57.3200 Correction of 

hazardous conditions

6 

57.3201 Location for 

performing scaling 

1 

57.3202 Scaling tools 1 

57.3203 Rock fixtures 0 

57.3360 Ground support use 0 

57.3400 Secondary breakage 0 

57.3401 Examination of 

ground conditions 

4 

57.3460 Maintenance between 

machinery or 

equipment and ribs 

0 

57.3461 Rock bursts 0 
120 

 Finally, the prevalence of dangerous behavior 

depends greatly on the miner’s perception of the 

company’s policy concerning going under 

unsupported roof, on how that policy is enforced, 

and on the attitude and behavior of his supervisor 

and coworkers. The best prevention programs 

involve high-level managers who directly 

communicate their commitment to the goal of 

keeping people away from unsupported roof. 

Roof bolter safety. Roof bolt operators are on the 

front line in the fight against ground falls. They are 

continually exposed to roof and rib hazards, and 

historically they have experienced more 

groundfall-related injuries than any other 

occupation in mining. While large roof and rib 

falls have been responsible for several fatalities, 

most injuries are caused by relatively small pieces 

of rock. 

 The roof bolt machine, with its ATRS and 

canopy, is the critical piece of safety equipment. It 

should always be in proper operating condition 

before use. The proper bolting sequence, as 

defined in the Roof Control Plan, must always be 

followed. Several fatalities have resulted when 

operators of single-boom machines installed bolts 

out of sequence and placed themselves under 

unsupported roof. 

 Rehabilitation of roof falls and construction of 

overcasts and boom holes present special hazards. 

In many such areas the roof is unusually high, and 

often the ATRS cannot effectively contact it. If 

the ATRS cannot be set against the top, it is 

necessary to set jacks for temporary support or use 

a manufacturer’s approved ATRS extension. Two 

roof bolt operators have been killed in recent years 

while bolting high top during mine construction 

activities. 

 Roof bolt operators are also responsible for 

protecting the entire crew with high-quality bolt 

installations. Poorly installed roof bolts can be 

worse than none at all, because they provide a 

false sense of security. Manufacturers’ 

recommendations regarding resin spin and hold 

times must always be followed. Holes must be 

drilled to the proper length (not more than oneinch deeper than the bolt’s length). The torque on 

tensioned roof bolts must be checked as required 

by CFR 75.204(f). 

Skin failures of roof and rib. Skin failures are 

those that do not involve failure of the roof support 

elements, but result from rock spalling from 

Table V - Factors in underground coal mine fall 

of ground fatalities.

Factor 1996 1997 1998 Total 

Pillar extraction 4 4 5 13 

Inby roof support 4 0 5 9 

Intersections 1 3 2 6 

Geology 1 4 1 6 

Rib 2 3 0 5 

Construction 1 0 3 4 

Skin Control 1 0 2 3 

Longwall face 1 1 0 2 
121 

between roof bolts, around ATRS systems, or from 

ribs. They are of particular concern because they 

cause injuries and fatalities to workers who should 

have been protected by supports. In 1997, 98% of 

the 810 roof and rib injuries suffered by mine 

workers were attributed to skin failures (Bauer et 

al., 1999). 

 Roof skin failures almost always involve 

pieces of rock that are less than 0.6 m (2 ft) thick. 

About 40% of the 669 roof skin injuries in 1997 

involved roof bolt operators, and occurred beneath 

the ATRS. The other roof skin injuries occurred 

beneath permanent support and involved workers 

in a wide variety of activities. Common roof skin 

control techniques include oversized plates, header 

boards, wood planks, steel straps, meshing, and (in 

rare instances) spray coatings (sealants). 

 Between 1996 and 1998, rib failures resulted 

in 6 fatalities in underground coal mines. Only one 

of these fatal injuries was to a face worker, the 

other five were all mechanics and electricians 

performing their duties well outby the face. Nearly 

80% of the 128 rib injuries that occurred in 1997 

took place beneath permanently supported roof. 

Non-fatal rib injuries resulted in an average of 43 

lost workdays each, versus 25 days for the average 

roof skin injury. 

 The seam height is the single greatest factor 

contributing to rib failures. The seam height was 

greater than 2.5 m (8 ft) in all six of the fatalities, 

and was greater than 3 m (10 ft) in three of them. 

The incidence of rib injuries increases dramatically 

once the seam height reaches 2.2 m (7 ft). 

Interestingly, mines with the very thickest seams 

see lower rib injury rates, probably because most 

of them routinely use rib support. No rib support 

was used in any of the six fatal accidents, however. 

 Rib failure is often associated with rock partings 

and/or discontinuities within the pillar, or with 

overhanging brows created by roof drawrock. The 

most effective rib supports employ full planks or 

mesh held in place by roof bolts. 

Pillar recovery. Pillar recovery has always been 

an integral part of U.S. underground coal mining. 

It can be a less capital-intensive, more flexible 

alternative to longwall mining for small, irregular 

reserves. A recent study estimated that pillar 

recovery accounts for about 10% of the coal mined 

underground (Mark et al., 1997). 

 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. Historically, retreat mining has 

accounted for a disproportionate number of roof 

fall fatalities, including 13 between 1996 and 

1998. Three of the accidents during this period 

resulted in double fatalities. 

 Traditional roof control plans require that 

numerous timber posts be set during each stage of 

pillar recovery. Recently, Mobile Roof Supports 

(MRS) have become available that replace many 

of the timbers (Figure 1). MRS resemble longwall 

shields mounted on bulldozer tracks. They can 

have many safety advantages over timbers. In 

particular, they are more effective as roof supports, 

they do not require workers to approach the 

mined-out gob area to set them, and they reduce 

the potential for materials handling injuries (Chase 

et al., 1997). 

 

Following the Roof Control Plan is absolutely 

critical to safe pillar recovery operations. Fatality 

investigations have frequently found that lifts were 

too wide, too deep, or out of sequence. The Plan 

may also specify the minimum dimensions of the 

remnant coal left in place called stumps and 

fenders. However, the Roof Control Plan is a 

minimum plan, and additional supports should be 

used at any indication of bad roof. 
122 

 The recovery of the final stump, or pushout, is 

the most hazardous aspect of pillar recovery 

operations. During the past 20 years, nearly half of 

all fatalities during retreat mining have occurred 

while the pushout was being mined. The pushout 

should never be mined if conditions do not look 

safe or if adverse conditions arise during mining. 

All unnecessary personnel should remain outby the 

intersection at all times during pillar recovery, but 

especially while the pushout is being mined. 

Extended cuts and remote control mining.

Extended (deep) cut mining is where the 

continuous mining machine advances the face 

more than 6 m (20 ft) beyond the last row of 

permanent supports. The development of remotecontrol for continuous miners (Figure 2), spray fan 

systems, and flooded-bed scrubbers has provided 

the technology to enable deep cuts. By 1997, about 

75% of all underground labor hours were worked 

at mines with extended cut permits. However, 

extended cuts raise a number of ventilation, 

ground control, and human factors issues. Between 

1988 and 1995, extended cuts may have been a 

factor in 26% of all roof fall fatalities in 

underground coal mines (Bauer et al., 1997). 

Figure 1. - Mobile Roof Supports (MRS)for retreat mining 
123 

 In practice, many mines with permits only 

take extended cuts when conditions allow for 

them. Where the roof is competent, extended cuts 

are routine. At the other extreme, when the roof is 

poor, miners may not even be able to complete a 6 

m (20-ft) cut before the roof collapses. A 

premature roof collapse can trap the continuous 

miner or endanger the crew, or it can 

create uneven and hazardous conditions for the 

roof bolters. Where premature collapses are likely, 

additional roof supports (extra bolts, planks, mesh 

or straps) should be used within the last two rows 

of supports to prevent the fall from overriding 

these supports. 

 Remote control mining allows the operator to 

stay further back from the unsupported roof, but it 

also removes him from the protection provided by 

the canopy. The freedom of movement, combined 

with a lack of visibility, can tempt the operator to 

stray into dangerous locations. Several fatalities 

have occurred during the mining of the first cut in 

a 90 degree crosscut to operators who had gone 

inby permanent supports (Figure 3). In response, 

some companies have limited the length of the 

initial cuts in a crosscut to 20 ft, and others have 

angled the crosscuts to provide better visibility. 

Hazards in Underground Metal and Nonmetal 

Mines

 Between 1996 and 1998, nine fatal fall of 

ground injuries from eight different accidents 

occurred in underground metal and nonmetal 

mines (Table VI). Two major contributing factors 

were the failure to conduct proper roof and rib 

examinations and problems with removing loose 

rock. Overall, metal and nonmetal underground 

mines have lower ground fall injury rates than coal 

mines. 

Large openings. Many metal/nonmetal mines 

have large openings, especially nonmetal stone and 

salt mines and metal mines with stopes Large mine 

openings have roof or back greater than 5 m (16 ft) 

high, with spans greater than 10 m (30 ft) wide. 

Figure 2. - Miner operating a continuous mining machine by remote control 
124 

When the back is high, a miner’s ability to observe 

the ground conditions is greatly reduced. 

Additionally, many metal/nonmetal mines use roof 

bolts on an infrequent basis. Ventilation of large 

openings is sometimes poorly controlled, 

promoting dramatic fluctuations in humidity, and 

sometimes fog. High humidity can cause even 

strong rocks to split and crack, creating hazards for 

miners. Because of these factors and others, mines 

with large openings rely on mining both a stable 

roof beam and a stable roof line to reduce ground 

control hazards (Iannacchione et. al, 1998(a)). 

 A stable roof beam is generally massive, 

strong, thick, and persistent. Natural laminations, 

bedding planes, or interfaces between rock layers 

often provide the best roof lines (Figure 4). If a 

natural smooth roof plane does not exist, special 

blasting procedures like pre-splitting or smooth 

blasting can be used to produce an artificial 

smooth roof plane. Conversely, poor blasting 

practices often have a negative influence on roof 

and rib stability. Overbreak can damage the roof 

and rib rock, while bootlegs (poor rock breakage at 

the end of a blasthole due to inadequate explosive 

burn) can leave broken rock along uneven rib and 

face surfaces. 

Figure 3. - Unsafe location for a continuous mining machine operator while mining a crosscut 
125 

Scaling. Scaling is necessary to remove loose 

rock from the sidewalls (rib) and hanging walls 

(roof) of mine openings. It is particularly 

important when the rock and ore are removed by 

blasting, as in most underground metal and 

nonmetal mines. 

 Scaling may be conducted either with a handheld pry bar or with mechanical equipment. 

Mechanical scalers usually remove the greatest 

portion of the loose rock, using an assortment of 

prying, or hammering scraping attachments. Hand 

scaling is often conducted by a worker mounted in 

a lift basket in high openings. 

 A study of accidents in underground stone 

mines between 1985 and 1994 found that nearly 

one-third of the ground control injuries involved 

scaling (Grau and Prosser, 1997). More than 90% 

of these involved hand scaling. Mechanical scaling 

generally affords greater protection, because the 

miner is positioned in a protective cab at a greater 

Figure 4. - Smooth roof line produced by a persistent bedding plane lamination within the roof 

rock beam 

Table 6 - Factors associated with the 9 metal/nonmetal underground fatalities, 1996-1998.

Date Commodity Factor State Type of 

fall Job Mining 

height, m 

11/4/98 Metal 

inadequate 

examination/failure to 

remove loose ground 

CO Rib Driller 3 

3/4/98 Metal failure to remove loose 

ground AZ Roof Installing 

support NA 

1/19/98 Metal failure to support or remove 

loose ground MO Roof Surveying 4.9 

4/1/97 Stone inadequate 

examination/geology TN Rib Driller 7.6 

2/5/97 Metal unsafe location NV Roof Scaling 2.4 

2/3/97 Metal large span/geology TN Roof Driller 5.5 

7/24/97 Metal unsafe practice/loose ground NV Rib Driller 12.2 

5/10/96 

(double 

fatal) 

Stone 

failure to support loose 

ground MO Roof Blasters 7.6 
126 

distance from the loose rock. The data from this 

study also showed that the extremities and limbs 

were the body parts most often injured during 

scaling. Arm and leg padding, such as worn by 

athletes, may be one way to cushion the blow from 

falling rock and may also lessen the severity of an 

accident. 

Global Safety Strategies

 Best practices, as discussed in the previous 

section, generally address ground control safety in 

the immediate vicinity of the miner. Creating a 

stable mine environment begins much earlier, 

however, during the process of mine design. 

Ground monitoring can also be central to the 

creation of a ground control safety culture at a 

mine. 

Safe Mine Design: Mine design includes pillar 

sizing, layout of drifts and entries, dimensions of 

openings, and artificial support. Mine planners 

seek optimum designs that balance the competing 

goals of ground control, ventilation, equipment 

size, production requirements, and costs. In recent 

years, a number of design aids have been made 

available to assist with the ground control aspects 

of design. 

 The role of pillars is to support the great 

weight of the overburden above the mine. No manmade supports (except filled stopes in metal 

mines) have anything near the tremendous loadcarrying capability of mine pillars. Longwall panel 

extraction, pillar recovery, and multiple seam 

operations can all increase pillar loads, and 

benching can reduce pillar strength. 

 Mining layout can often be used to minimize 

the effects of geologic hazards. Traditionally, 

features such as joints, cleats, and faults have been 

considered in design. More recently, horizontal 

stress has become an important concern. Global 

plate tectonics are the primary source of horizontal 

stress in mines, and measurements have shown that 

horizontal stresses are often three times as great as 

vertical overburden stresses. Horizontal stresses 

have caused roof potting, cutter roof, and roof falls 

in coal and limestone mines (Mark and Mucho, 

1994; Iannacchione, 1998b). Their destructive 

effects can be reduced by orienting the mine so 

that most of the drivage parallels the direction of 

the maximum horizontal stress. 

 The maximum stable size of mine openings 

depends greatly on the geology. The back in some 

stone and salt mines is so competent that it can 

routinely maintain spans of 15 m (45 ft), while 5 m 

(15 ft) spans may be unstable in the weak, 

fractured ground found in some coal and hard rock 

mines. 

 U.S. mines use more than 100 million roof 

bolts every year. Only mines with exceptionally 

competent country rock can do without pattern 

roof bolting, and even they require some spot 

bolting. A wide variety of rock bolts are available, 

but matching the proper bolt type and pattern with 

the ground conditions remains as much an art as a 

science (Mark, 2000). 

Controlling Catastrophic Failures in 

Underground Mines: Catastrophic failures that 

create hazards for miners in coal, metal, and 

nonmetal underground mines include coal mine 

bumps, hard rock bursts, large collapses, and 

outbursts. Hazards to miners range from injuries 

associated with flying rocks to complete burial in 

ejected rock. Pressure waves from large collapses 

can throw miners into natural and manmade 

structures. When large quantities of gas are 

instantaneously released, gas ignition or 

asphyxiation can occur. 

Coal mine bumps have presented serious 

mining problems since the early 1900's. In 1996, 3 

miners were killed in two different bump events. 

Two Kentucky miners were fatally injured when 

six pillars suddenly failed violently during pillar 

recovery operations. The second event claimed the 

life of a Utah miner when coal along a longwall 

face violently ejected into the shields. Both of 

these events occurred in characteristic settings for 

coal bumps, with elevated overburden, proximity 

to a gob area, and a strong hanging roof. 
127 

Hard rock bursts have been occurring in deep 

metal mines for as long as records have been kept 

(White et al., 1995). Federal regulations have been 

developed mainly in the form of administrative 

controls (subsection 57.3461). When a rock burst 

causes miners to withdraw, impairs ventilation or 

impedes passage, MSHA must be notified. A rock 

burst control plan should then be developed and 

implemented. This plan is required to reduce the 

occurrence of rock bursts through monitoring and 

minimizing exposure. Monitoring can range from 

simple deformation measurements to mine-wide 

microseismic monitoring systems. Minimizing 

exposure can range from administrative controls to 

the use of remote controlled equipment. 

 A pillar collapse is a sudden, violent event 

that can pose a serious hazard in a room and pillar 

mine. A collapse occurs when one pillar in a 

mining layout fails, transferring its load to 

neighboring pillars, causing them to fail, and so on 

in a domino fashion. A pillar collapse can induce a 

devastating airblast which can disrupt the 

ventilation system and send flying debris that can 

injure or kill miners. In recent years, at least 13 

coal mines and 6 metal/non-metal mines in the 

U.S. have experienced pillar collapses. 

Fortunately, only one fatality has resulted, 

following a collapse of hundreds of pillars at a 

Wyoming trona mine (Zipf and Mark, 1997). 

Outbursts of gas and rock have occurred 

mainly in evaporite and to a lesser degree coal 

mines. With the occurrence of the multiple fatal 

explosion at the Belle Isle Salt Mine in 1981, 

domal salt mines in Louisiana and Texas were 

recognized as potential locations for large 

outbursts. Modifications to mining regulations 

were made in 1984 creating special levels of gassy 

metal/nonmetal mines (Subcategory II-A and II-B, 

57.22003). Each advance in the gassy level 

requires additional operational safeguards. 

Outbursts in Canadian bedded salt and New 

Mexico potash mines have periodically created 

serious safety hazards. 

Roof Monitoring. Roof falls seldom occur 

entirely without warning. Often, however, miners 

are not aware of the warning signals until it is too 

late. Most underground mines use observational 

techniques, primarily visual inspection, as a means 

of determining roof stability. Traditionally, miners 

have sounded the rock, listening for the drummy 

sounds that signal loose rock. Also the act of 

drilling exploration roof bolt or blast holes can 

provide much information about the rock. During 

drilling, blasting, and scaling operations, 

additional knowledge related to roof conditions 

can be gained. For example, a driller preparing to 

bolt may notice a sudden increase in the 

penetration rate, and then realize that possibly a 

gap or clay seam was encountered. Much of this 

“hands-on” information provides an overview of 

the general conditions related to roof stability. 

Observational techniques can be extended by 

monitoring the movement of the mine roof in 

boreholes using mechanical tools (Figure 5). 

 A comprehensive ground control plan not only 

includes the basic observational, visual, and handson components, but also uses supplemental 

observational and monitoring techniques and 

regularly reads, analyzes and displays information 

gained from these efforts. Mines that follow these 

practices and promote open communication and 

participation from everyone at the site are the 

mines with the most pro-active approaches towards 

ground control safety. 
128 

SURFACE HIGHWALLS AND SLOPES 

 Surface mines have relatively few serious falls 

of ground, with 6 fatalities in the period 1996 to 

1998. However, six additional fatal falls of 

highwalls and slopes fatalities occurred in the first 

half of 1999. Two of these six were initially 

classified as Powered Haulage, but they were 

actually caused by slope failure beneath haulage 

equipment. The large jump in fatalities in 1999 is 

hopefully an aberration, but it may signal a new 

safety issue caused by a change in mining method 

or equipment, different enforcement practices, or a 

social issue such as the experience level of the 

mining workforce. 

 Most highwall injuries occur when loose 

pieces of rock fall on workers located below. 

Small pieces of rock can be dangerous when they 

fall from great height; even a fist-sized rock 

caused one recent fatality. At the other extreme, an 

entire section of a highwall or spoil pile may 

collapse, endangering miners working either on or 

beneath it. 

 Good basic design is essential to highwall 

safety. The height should be limited for stability 

and to allow scaling. Where the pit is deep, 

benches should be used to limit the slope height. 

Angling the highwall back from vertical also 

increases stability. Good blasting practices make 

for a smoother wall and reduce the need to scale. 

Drainage ditches should be used to divert springs 

and groundwater away from slopes. 

 Geologic features have contributed to many 

rockfall injuries from highwalls. Faults or 

“hillseams” (weathered joints) can create wedges 

of unstable ground that can slide into the pit. In 

dipping strata, the rock can also be prone to slide 

along bedding planes. Freeze-thaw action acts to 

loosen rocks, and has been cited in several fatality 

reports. A review of accident records indicates that 

 highwall accidents are twice as likely to occur in 

December and January than they are in the summer 

months. The presence of abandoned underground 

mine openings in the highwall has contributed to 

three of the recent fatalities. 

Figure 5. - Four techniques used for roof monitoring 
129 

 Rock faces should be monitored frequently to 

check for loose rocks, and scaling should be 

conducted as needed. As highwalls age, 

weathering may cause additional loosening. The 

surface at the top of the highwall should also be 

checked for tension cracks that could indicate 

pending massive slope failure. In very large pits, 

various kinds of electronic surveying and 

monitoring systems are in use to provide early 

warning. 

CONCLUSIONS 

 This paper has presented an overview of the 

most significant ground control hazards facing 

today’s mineworkers. Underground miners, 

particularly in coal mines, are at the greatest risk 

from ground falls. The six highwall and slope 

fatalities that occurred in the first half of 1999 

show that surface miners are at risk as well. 

 The analysis of recent fatality investigations 

and accident statistics identified certain job 

categories, mining techniques, and geologic 

environments that appear to pose the greatest 

hazards. Best Practices have been developed 

through experience and research to reduce these 

risks. They combine engineering design, roof 

support, equipment, mining methods, and human 

factors to create safer workplaces and work 

practices. The Roof Control Plan is another 

valuable tool in this effort. 

 Unfortunately, recent trends indicate that 

ground fall injury rates have stopped decreasing, 

and may even be on the increase. A renewed effort 

by the entire mining community will be necessary 

to finally eradicate the groundfall hazard.

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