0

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Underground Coal Production (tons)

Longwall Face

Continuous

Machine Loaded

Handloaded

Figure 1. Underground coal mining methods of the 20th Century.

THE INTRODUCTION OF ROOF BOLTING TO U.S. UNDERGROUND 

COAL MINES (1948-1960): A CAUTIONARY TALE

Christopher Mark, Chief, Rock Mechanics Section

National Institute for Occupational Safety and Health

Pittsburgh Research Laboratory

Pittsburgh, Pennsylvania USA

ABSTRACT

Perhaps the most significant development in coal mine ground

control during the last century was the introduction of roof bolting

during the late 1940’s and 1950’s. From an engineering standpoint,

roof bolts are inherently more effective than the wood timbers they

replaced. Roof bolts promised to dramatically reduce the number of

roof fall accidents, which then claimed hundreds of lives each year,

and they were initially hailed as “one of the great social advances of

our time.” Roof bolting also emerged at a time of rapid technologic

transformation of the coal industry, and greatly accelerated the

transition to trackless, rubber-tired face haulage.

The U.S. Bureau of Mines quickly became the new roof support’s

strongest advocate. Some state agencies and miners were skeptical

at first, but nearly everyone was soon won over. Case histories were

reported showing that roof falls could be largely eliminated while

productivity increased dramatically. Little wonder that, in the words

of one contemporary observer, “roof bolting has been adopted more

rapidly than any other new technology in the history of coal mine

mechanization.”

Yet by the end of the 1950’s, it was clear that roof fall fatality

incidence rates had actually increased. It would be another decade

before the superior ground support provided by roof bolts would

clearly save lives. The story of how roof bolting was implemented by

the mining industry, but took so long to live up to its promise, is a

fascinating example of the interaction between economics,

technology, regulation, and science. It still has important lessons for

today.

INTRODUCTION

The 20th century was a time of continuous revolution in

underground coal mining technology. At the beginning of the

century, traditional pick mining with hand loading was nearly

universal. Undercutting machines had largely replaced picks by

1930, when mechanical loading began the first great transformation

of mining (figure 1)1

. Other revolutionary developments included the

replacement of drilling and blasting by continuous miners during the

50’s and 60’s and the rapid growth of longwall mining during the

1980’s.

These technological changes were accompanied by equally

dramatic developments in work organization, government regulation,

and mine safety. Where the hand-loader worked independently and

seldom saw a foreman, today’s mines are highly organized and

supervised. Mine inspectors were rare 100 years ago, while today

many large mines are inspected nearly every day. And while coal

mines once claimed thousands of lives each year, annual fatalities are

now numbered in the tens.2

Yet at least one aspect of mining remained constant. Throughout

the century, falls of roof were the greatest single safety hazard in

underground coal mines. In fact, roof falls were responsible for

between one-third and one-half of mining fatalities in each decade.

To be sure, the same period saw a dramatic improvement in the

annual fatality record measured either by the total number or by the

rate per-hour per-million hours of miner exposure (figures 2 and 3).

One logical explanation for this reduction is the application of new

ground control technology.

Without a doubt, roof bolting has been the single most important

technological development in the field of ground control in the entire

history of mining. Bolting was substituted for timbering in U.S.

underground coal mines in the late 1940’s, and it was “accepted by

the mining industry with greater rapidity than any other mining

change since the inception of mechanization.”3

 It has generally been

assumed that roof bolting just as quickly reduced the toll taken by

roof falls. Yet the real story, as it emerges from careful analysis of
Figure 2. Roof fall fatalities in underground coal mines.

1

10

100

1000

1900 1920 1940 1960 1980 2000

Years

Roof Fall Fatalities 

(log scale)

Figure 3. Roof fall fatality rate for underground coal mines

(fatalities per million employee hours).

Figure 4. Hand loading with a safety post.

the accident data and the words of the participants, was far more

complex.

“Miner—Be Careful!”

ROOF CONTROL DURING THE HAND-LOADING ERA

At the turn of the century, roof support was considered the

responsibility of each individual miner. It was his duty to “examine

his working place before beginning mining work, to take down all

dangerous slate, and make it safe by properly timbering it before

commencing to mine coal.”4

 The mine operator was responsible for

delivering timbering materials to each working place, and the

foreman checked that it was installed properly on his daily visit.5

The miners often had considerable discretion about the amount of

support they installed. In weak shale roof, posts might be set 2.5 to

5 ft apart,6

 but where the roof rock was strong, no posts might be set

at all. An important element in early roof support systems were

“safety posts,” which were set at the end of the track to protect miners

while they loaded the coal or prepared the face for the next shot

(figure 4).7

 These temporary supports required extra time and effort,

and their use was often at the discretion of the miner.

Under these circumstances, it is understandable that much of the

blame for roof fall accidents was placed on the inexperience and

carelessness of the miners themselves.8

 In 1912, the US Bureau of

Mines (Bureau) asked: “How can you, the miner, escape harm from

roof falls?” The answer was: “Be careful...do not take the risk of

loading a car before putting up a prop...set extra posts, even though

they are in your way.”9

Over time, however, safety professionals began to recognize that

“a condition responsible for many fatalities from falls of roof is the

absence of any policy on the part of management with respect to

systematic methods of roof inspection and support.”10 Encouraging

mine managers to prepare, promulgate, and enforce a systematic

timbering plan became a key element in the Bureau’s roof control

efforts. Violations of the timbering plan would include:

• Timber too far from the face;

• Working under loose roof or loose roof not taken down;

• Props insecurely set;

• Spacing between posts too great, and;

• Safety post not set up.11

The Bureau also exhorted miners to “comply with systematic

methods of timbering, where such systems have been adopted, and

exercise judgment in placing additional posts for your own

protection.”12 But so long as the typical mine foreman was

responsible for about 80 miners, and seldom spent more than 5

minutes with each one during a shift, enforcing timber plans

presented a challenge.

“Mining Companies Are Continuously Searching for Improved

Types of Roof Support”

THE IMPACT OF MECHANIZED MINING ON ROOF

CONTROL

Between 1930 and 1948 the portion of underground coal that was

loaded by machine rose from less than one-tenth to nearly twothirds.13 Mechanized mining allowed for increased supervision,

because “it was possible to obtain the desired production with a

smaller number of miners and fewer working places than hand

mining.”14 In addition, timbering often became the responsibility of

a special crew, paid by the day rather than the ton.15

Unfortunately, in many ways machine mining in fact made roof

support more difficult. Most importantly, loading machines required

a prop-free front in which to work. The machine operator was usually

protected by posts and crossbars, but the helper had to venture into

the unsupported face zone (figure 5).16 The Bureau summarized the

situation:
Figure 5. Machine loading with timber support. Figure 6. Shuttle car haulage with timbers.

Figure 7. A timbering machine.

Figure 8. Pins and timbers hitched to the ribs.

“In many mines the simple safety post offers effective protection

at the face with hand loading; after mechanical loading

equipment is installed, however, safety posts may interfere with

the efficiency of the equipment, and their effectiveness may be

destroyed because of frequent accidental dislodgement. Too

often the result is that either the safety posts are eliminated or are

used only when an official is present.”17 

Noise that prevented miners from hearing the warning sounds

from the roof also contributed to the hazards of machine mining.18

A detailed and widely reported Bureau of Mines study conducted

in 1951 concluded that “mechanical operations are, to a considerable

degree, more dangerous from the standpoint of roof falls” than hand

loading, “notwithstanding that much closer supervision is maintained

in such operations.” Particularly high-risk occupations cited in the

report included loading machine operator and helper, timberman, and

foreman. The study also found that 74% of roof fall fatalities

occurred within 25 ft of the working face, and that 3 out of 4 of these

took place inby the last permanent support (between the last support

and the face).19

The same study also attributed 89% of the roof fall fatalities to

“human failure,” and of these nearly two-thirds were considered the

responsibility of management. It concluded that:

“These facts very definitely indicate management failure in

providing sufficient roof support at working faces....Regardless

of roof conditions, minimum standards of roof support suited to

the conditions and mining system of each mine should be adopted

and followed....The judgment of the person should never be

substituted for the minimum support required in the systematic

roof support plan.” 20

The difficulties posed by traditional timber supports increased as

the early track-mounted loading machines were replaced by crawlermounted ones. When rubber-tired shuttle cars that carried coal away

from the face were introduced in the late 1930’s, “timbering resolved

itself into setting cross-bars, because the machines required the full

width of the place, leaving no room for posts.”21 The maximum span

without a post increased from the 9-10 ft over track to 15-20 ft and

even more (figure 6). Intersections were particularly difficult, and

mines with weak top that required narrow entries or close timbering

had particular problems. In fact, during this time the Bureau

maintained a separate category of fatalities from “roof falls due to car

or machine knocking out post.” In 1946, for example, 14 deaths were

attributed to this cause.22

Timbering began to be seen as a critical bottleneck in the

mechanical mining process. Simply moving the required quantities

of timber to the face was a major undertaking and caused many

injuries.23 Timber crews typically consisted of 4-5 men. To reduce

the burden, equipment manufacturers and individual mining

companies developed timbering machines (figure 7). These were

mobile units operated by a crew of 2-3, and could carry a supply of

timber posts and crossbars, cut them, and hoist them into place.24 By

1949, Coal Age reported that timbering machines were on their way

to becoming “standard loading unit equipment.”25

As crossbars became the primary roof support, a variety of

techniques were developed to install them without posts. Most

involved pins or timbers that were hitched into the ribs.26 It is

impossible to view photographs of these support systems today

without wondering how effective they could have been (figure 8).
Figure 9. A roof bolt.

Figure 10. Installing roof bolts with a hand-held stoper drill.

Certainly they had almost no vertical stiffness, and the amount of

deadweight that they could transmit to the ribs was limited,

particularly where the coal was friable or fractured. Little wonder,

then, the Bureau’s Edward Thomas wrote in 1948 that: 

“The more progressive mining companies are continually

searching for improved types of roof support that will give

maximum protection and at the same time offer minimum

interference with the preparation and loading of coal.”27 

“A Different and Possibly Advantageous

 Method of Supporting Roof”

FIRST TRIALS

Even as Thomas wrote those words, the roof bolt was emerging

as the leading candidate “temporary legless support” in machine

mining.28 Roof bolts are steel rods, normally 3-6 ft long and

5/8-1 inch in diameter, that are inserted into holes drilled in the mine

roof. The early bolts all used some kind of mechanical anchor at the

back of the hole (today a polyester resin grout is normally used

instead), and were tensioned between the anchor and the head

(figure 9). As a support, roof bolts are theoretically superior to

timbers because “timbers offer support after the strata they are

supporting have failed; whereas roof bolts reinforce the roof rock,

which contributes to its own support.”29

Roof bolts work best when they are anchored in a strong, selfsupporting rock layer. In such conditions, their role is to suspend any

underlying weak or loose rock. Where there is no self-supporting bed

within reach, the bolts must tie the roof together to create a “beam.”

In general, it is much more difficult for roof bolts to build a beam

than it is to suspend weak rock from one. Greater ground stresses and

wider roof spans also increase the requirements placed on roof bolt

systems.30

Some use of roof bolts was apparently recorded as early as

1905,31 and J. C. Baldwin was credited with installing bolts in the

Sagamore Colliery in southern WV in 1917.32 The St. Joe Lead

Company was the first major mining company to make extensive use

of roof bolts, beginning in the 1920’s.33

Early in 1947, C. C. Conway, Chief Engineer for the

Consolidation Coal Company in St. Louis, visited one of the St. Joe

mines near Bonne Terre, Missouri, and was impressed with the roof

bolts he saw there.34 He determined to try them at Consol’s Mine No.

7 near Staunton IL. The roof at Mine No. 7 was a common Herrin

No. 6 Seam sequence, with several feet of weak shale and “clod”

drawrock beneath the extremely competent Brereton limestone.

Timbering requirements were extensive, and often the drawrock

collapsed before it could be supported, causing extensive dilution of

the ore and a major safety hazard.35

The first roof bolts were installed in Mine No. 7 using hand-held

stoper drills (figure 10). The anchors were expansion shells “similar

to those used to support trolley wire”, though slot-and-wedge type

anchors like the ones “ordinarily used in the metal mines” were also

employed. A section of channel iron was used as a plate. The DC air

compressor was powered by a trailing cable and mounted on a truck.

Two men constituted the bolting crew.36

For Conway, the most important feature of roof bolts was that

they could be placed “as near the face as possible.” Shuttle car turnouts were also improved by eliminating some of the props that

formerly supported crossbars. After placing hundreds of bolts in

more than a year of experimentation, Conway concluded that the

“practicality of supporting slate from a bed of limestone has been

demonstrated.”37

Conway’s enthusiasm was restrained, however. He introduced

roof bolting not as a panacea but as “a different and possibly

advantageous method of supporting roof.” At this point there was “no

intention to completely eliminate timbering,” though timbering

requirements might be reduced. “Props and other timber are the

miner’s barometer or measuring stick,” wrote Conway; roof bolting

should be considered as supplemental support “before adequate

timbering is possible.” He did, however, propose that roof bolts could

be used to “make laminated shale homogeneous,” and said that trials

were already underway in other Consol mines where no strong

limestone was present in the roof.38

“No Development in Modern Coal Mining Has Been as

Spectacular and Far-reaching”

ROOF BOLTING ACCEPTED 1948-1955

The U.S. Bureau of Mines (Bureau) was apparently involved in

the roof bolt trials at Mine No. 7 almost from the beginning. Early

Bureau reports included roof bolts as one of several “legless supports”

for mechanical loading, along with hitch timbering and peg

timbering.39 As it gained confidence in the technique, the Bureau

began to advocate roof bolting enthusiastically as an accidentprevention measure.40
Figure 11. Speakers at the 1949 Kentucky Mining Institute. Ed

Thomas is the second from right.

Figure 12. An early roof bolt machine.

Since the Bureau was without regulatory powers, it had since

1910 “mastered the art of prodding operators into implementing new

technologies that resulted from its scientific investigations.”41* The

point-man in the Bureau’s roof bolt campaign was mining engineer

Edward M. Thomas (figure 11). Thomas had graduated from the

South Dakota School of Mines in 1926, and had served as an

inspector of mines in North Dakota and an operating official in the

Pennsylvania anthracite mines before joining the Bureau in 1936. In

1949, he was selected to head the Bureau’s new Roof Control Section

in College Park, MD.42

The Bureau’s effort in encouraging roof bolting was twopronged. On the one hand, Thomas and his associates adopted a high

public profile, writing papers and giving presentations at many

industry meetings. These touted the advantages of suspension

supports from the standpoints of safety and efficiency. Listed safety

features included:

• A systematic support “within inches” of the working face;

• Can’t be dislodged by blasting or equipment;

• Improved ventilation (because of less air resistance), and;

• Reduced accumulation of explosive coal dust (because places

could be cleaned more thoroughly).

Economic advantages included:

• A reduction in the time required to load a place by 15-50%;

• Potential for widening rooms;

• Faster haulage, and;

• Reduced labor cost for roof support and material handling.43

 

*Probably the Bureau’s single most important achievement was rock dusting

to reduce the hazard of coal dust explosions. During a 30-year campaign, the

Bureau publicized both its research findings about the effectiveness of rock

dust and examples of explosions that rock dust could have prevented. The

Bureau was acutely aware that the expense was the primary barrier to the

industry’s acceptance of rock dust, and it tried to help by developing

mechanized equipment to reduce the cost of applying dust. Ultimately,

however, external economic incentives may have been more important than

either scientific data or new legislation to the success of the Bureau’s

campaign. By 1925, 11 states gave worker’s compensation premium credits

to mines that rock dusted, and mines that didn’t dust had difficulty obtaining

insurance (Aldrich, 1995).

Perhaps more important than publicity was the Bureau’s

involvement with roof bolt trials in mines across the country. The

Bureau’s policy was “not to sponsor or condone the adoption of roof

bolting at any mine unless it has been preceded by one or more

experimental installations.” In the test sites, the standard procedure

was to install the normal amount of conventional timbering together

with the roof bolts, and then withdraw the timber. Roof conditions

were then observed over a period of several months. The test sites

also “served to acquaint the workmen with the unfamiliar tools

required and enables them under supervision to become expert in

installing the bolts properly.”44 This cautious approach was credited

with making the progress of bolting possible, because it guarded

against careless installations that could have caused serious accidents

and “might well have stopped all further experiments in those critical

early days.”45

The Bureau’s campaign had to overcome two primary barriers to

the new technology. The first was the cost and availability of the

required equipment. The development of carbide alloy insert bits was

essential because it made it possible to drill holes cheaply in hard

rock.46 Hand-held stoper drills were already available at most mines,

but they now required a mobile source of compressed air. Many of

the first mines to install roof bolts built their own cars to carry the

drills, compressor, bolts, and other supplies from face to face

(figure 12). In some cases, timbering machines were modified to

double as roof bolters. The bolts themselves were not readily

available either. In some cases, they were fabricated in the mine’s

own shop. 

The second barrier was psychological. Miners were used to the

reassuring presence of heavy timbers, and roof bolting seemed to be

“reverse in principal to the old methods,”47 because it “appears at first

glance to approximate holding oneself up by one’s bootstraps.”48

Bethlehem Mines Corporation’s Idamay Mine provides one example

of the educational program that was required to make bolting a

success in 1948. It began with training of all mine supervisors in the

theory and practice of roof bolting. Top management “knew that

first-line supervisors had to be sold on roof bolting before it could be

tried in the mine.” When the trial began, the company “started a

program to sell all underground employees on the benefits of roof

bolting, particularly from the safety angle.”49 In mines where “one or

more officials of authority refused to accept roof bolting, the roof

bolting program did not succeed,”51 as happened at the Green Valley

Mine in Indiana in 1949.50

Between 1949 and 1955, numerous case histories of the

successful application of roof bolting from all over the coalfields were

reported in the mining press (figures 13 and 14). An early article

reported that three northern West Virginia mines of the Christopher
Figure 13. Shuttle car haulage with roof bolts.

Figure 14. Machine loading with roof bolts.

Coal Co. had reduced roof falls by 80%. Shuttle car intersections

were particularly improved. The bolts were even successful in

stopping “roof cutters” that “travel relentlessly and have always

caused the roof to fall when they hit an intersection area.”52

The results of a major Bureau study in five southern West

Virginia mines were more striking. These mines “produced over two

million tons of coal without a fatal accident and with only four losttime accidents, as compared with two fatal and 71 lost time accidents

over a similar period when conventional timbering methods were

used. Production increases ranged from 0.86 to 10.7 tons per man

shift.” That these results were achieved during the dangerous process

of pillar recovery made them even more impressive.53 In northern

WV, the success of roof bolting in pillar work allowed 7-10% more

coal to be recovered.54

Roof bolts could also conquer weak roof. Zeigler Mine No. 3

was notorious for the “most treacherous roof in the Middle West,”

consisting of 28 ft of soft claystone under only 160 ft of cover. The

mine was on the verge of shutting down because of the excessive

timber requirements and the mining delays they engendered. After

just three months of bolting the tonnage per manshift increased by

37%, to 22.6 tons, and accidents were also reduced.55

Encouraged by the Bureau of Mines, the Tennessee Coal and Iron

Division of U.S. Steel introduced roof bolting to their 5 Alabama coal

mines in 1948. During the next five years, 19% of their combined 66

million tons was produced beneath 3.3 million roof bolts. Roof falls

claimed 49 lives in the TCI mines during this period, only one of

which involved roof bolts. The fatality rate for bolted roof was,

therefore, approximately just 1/10 of that beneath timbers (although

129 non-injury falls of bolted roof were also reported, mainly in

intersections.)56*

Such figures led many safety professionals to concur with Joe

Bierer of the West Virginia Department of Mines, that:

“Herein lies a wonderful opportunity for the coal industry to

bring about an epochal advance in safety for the mineworker,

a humanitarian accomplishment to compare with the great

social advances of recent years...No such immediately

effective and readily confirmed benefit has derived from any

other measure ever conceived, or devised, for safety in coal

mines.”57

The industry did not lose sight of the economic advantages either.

In its 1950 Annual Review, the American Mining Congress (AMC)

reported that roof bolting continued its “phenomenal growth,” and

that “some rather awe-inspiring estimates have been made concerning

the percentage increase in production efficiency as a result of bolted

roof.” It concluded that a “realistic appraisal” averaged a “most

worthwhile” 10-20% increase.58 In 1954, the AMC’s Committee on

Roof Action wrote that:

“No development in the history of coal mining has been as

spectacular and far-reaching as roof bolting. Its first success

in converting “bad top” to “good top” soon brought the

further advantages of wider working places, fewer

interruptions from slate falls, and, in general, improved

mining efficiency and higher tonnage.”

Looking back in 1956, Robert Fletcher of J. H. Fletcher & Co.

wrote that “the art of roof bolting has been accepted by the coal

industry with greater rapidity than any other mining change since the

inception of mechanization.” He attributed its success to three

factors:

• Roof bolting increases safety as well as production;

• It was encouraged by the Bureau of Mines, and;

• It could be tried with a minimum of equipment.59

“Pressure Has Been Brought to Bear on this Department”

CHALLENGES IN PENNSYLVANIA 1949-1953

Not everyone was immediately impressed with the effectiveness

of roof bolting, however. Richard Maize, Secretary of Mines for

Pennsylvania, wrote to all mine inspectors and mine operators on

October 14, 1949 that:

“It has been brought to the attention of this Department that a

number of operators have adopted the new method of suspension

roof support recommended by the U.S. Bureau of Mines...As a

result, one man has been killed in Pennsylvania and several near

accidents have resulted...Under no condition will anyone be

permitted to experiment with roof suspension supports at the

working faces without using the standard method of timbering at

that mine....If you are now using the bolt suspension method of

support you must discontinue this method of control

immediately...”60

 

*Not all mines reported immediate success, however. Despite a “thorough

trial,” the Reels Cove mine in Tennessee abandoned roof bolting because the

disintegration of the roof shale over time “loosened the bolts and made them

useless.” Timber was also much cheaper there, at $0.10 per post against $1

per bolt. (Coal Age [1951]. “Continuous-Face Mining.” June, p. 80.)
That Fall, it was reported that PA inspectors had halted work on

the Porter Tunnel mine until some 500 ft of roof bolt supports could

be replaced with conventional timbering.61

A battle royale was soon in process. Pennsylvania operators

clearly did not want to be denied access to a new technology that

their competitors were rushing to adopt. Maize was also in an

awkward position because the Bureau, other state agencies, and

apparently even many of his own inspectors felt favorably towards

the technique. 

Maize did not give up easily, and he seemed to have the law on

his side. On April 11, 1950, he wrote another Circular Letter to his

inspectors: 

“Pressure has been brought to bear on this Department from

the Operators urging that we permit the new method of

suspension roof support recommended by the USBM without

the use of conventional timbering... The Bituminous Mining

Laws state: ‘The mine foreman shall direct and see that

every working place is properly secured by props or

timbers’....As the law states that the roof must be supported

by timber, it can logically be assumed that the securing of the

working place must be by timber.”62

A compromise was soon achieved, however. A procedure was

developed whereby a mine could be granted a roof bolting permit

following the favorable report of a Committee of inspectors. An

example was provided in the 1950 Annual Report of the PA Dept of

Mines. The Renton No. 6 Mine of Consolidation Coal Co. had been

bolting on an experimental basis since 1949. Nearly 3 miles of entry

had been bolted, fenced off, and the timbers were removed. The

entire area was reported to be standing without any roof falls or even

indications of weight, while many falls had occurred in the adjacent

timbered area. Based on these findings, roof bolting was approved

at Renton for a 4 ft by 4 ft pattern, and with restrictions on miners

going beyond supports.63 In August of 1951, the PA Attorney

General ruled that roof bolting was permissible in lieu of timbering,

but only if permission was obtained first from the Secretary of Mines.

By 1954, the Pennsylvania Department of Mines had joined the

ranks of the true believers: 

“From the reports of our inspectors it has been learned that

neither a serious or a fatal roof fall accident has occurred

under 885 miles of area that has been roof bolted. This is a

remarkable achievement considering the fact that 70% of all

fatal accidents in PA mines were caused by falls of roof. We

realize that roof bolting may not be a cure all, however, we

cannot overlook experience, and this experience convinces us

that roof bolting has materially aided roof control. More and

more people are becoming roof bolt conscious and we hope

the trend will continue.”64

By this time, 72 of the largest PA mines, representing more than

half of the tonnage produced in the state, were using roof bolts for at

least some of their production.

“Roof Bolts Are Not Sky Hooks”

DISAPPOINTMENT 1955-1960

By the mid-50’s, it was clear that timber supports would soon go

the way of the pick and shovel. In 1957, the Bureau estimated that

more than 50% of all underground bituminous tonnage was produced

beneath roof bolts.65 The spread of roof bolts should have been

accompanied by an equally dramatic drop in roof fall fatalities. As

late as 1954 the Bureau had estimated that the fatality rate on sections

supported by conventional timber was 51⁄2 times higher than on roof

bolted sections.66

Yet overall fatality rates stubbornly refused to go down.

Responding to the 1955 statistics, Thomas wrote:

“Roof bolting’s influence on the over all roof fall injury picture

was disappointing when one considers that the use of bolts in coal

mines increased by 1/3 during the year...There were as many

fatalities (five) from failures in bolted roof in 1955 as the total for

1948-1954.”67

Thomas advanced two explanations for the frustrating lack of

progress. The first was that when miners go beyond the last support

they are unprotected, regardless of what type of support is used. A

1954 Bureau study had again found that more than 50% of roof fall

fatalities occurred in the unsupported space between the last row of

supports and the face.68 The following year, Thomas found that an

even higher percentage of the fatalities on roof bolted sections took

place in what he called the “danger zone.” One obvious solution was

the safety post:

 

“No responsible mining official would suggest that safety

props or jacks be eliminated as long as there is any chance

that anyone will enter it [the danger zone] to perform his

work.” 69 

Thomas also advocated work practices that kept workers out of

the danger zone, and endorsed the use of automatic safety supports on

roof bolting machines.

The second explanation for the lack of progress was that “many

mines are now bolting where the method is marginal in the sense that

perfect anchorage cannot be obtained.”70 Here Thomas was returning

to a warning he had sounded as early as 1951, when he wrote:

“In many instances the increase in productivity [with roof

bolts] has been almost incredible and has led many mining

men to conclude that through some hocus-pocus they can

now cast aside many or all of the time-proven rules of good

mining practice. If this tendency is not counteracted, it could

easily result in an increase of roof fall accidents...”71

Elsewhere, he said that “Roof bolts are not ‘sky hooks’ and they

do not eliminate the weight of the roof.”72

Looking back, it seems clear that simply replacing timbers with

bolts would not be sufficient to substantially reduce roof fall rates.

The success of any support system in a particular application depends

not just on the type of support, but also on the density of the pattern,

the capacity of each unit, when they are installed, the quality of the

installation, and many other factors including the span, the rock

quality, and the ground stress.73

Simply stated, roof bolts can only prevent roof falls if enough of

them are installed. That costs time and money. The mine operator’s

natural tendency was to adjust the expenditure to achieve an

acceptable level of roof fall risk. Unless the mining culture was

changed to reduce the acceptable level of risk, competitive pressures

would mean that the new technology would be adapted to obtain the

same results as before.
Figure 15. Materials from the 1960 Campaign to Prevent

Injuries from Roof Falls in Coal Mines.

Leon Kelly, a Bureau engineer in Vincennes IN, described this

process perfectly in remarks he made to the 1950 Annual Meeting of

the IL Mining Institute. He cited examples from three mines in his

own experience in which the level of support had been reduced:

• Four-ft bolts had originally anchored in limestone, suspending

2-ft of weak mudstone. The mudstone thickened to 5 ft, but the

mine kept using 4-ft bolts.

• Very weak roof was originally supported by 5-ft bolts in a 4-bolts

per row pattern. When that proved successful, the mine reduced

the bolt length to 4-ft on a 3-bolt pattern. Approximately 6% of

the newly bolted roof now collapsed, but the operator judged that

acceptable.

• A mine operator reduced the number of bolts per row from 3 to

2, because “in most cases the bolts held the roof long enough for

them to work the place out, and he didn’t feel justified in

spending the additional money.”

Kelly summed up:

“The important thing [the cases] show is the deliberate trend. In

each case, when bolts were first used at the mine, everyone was

more or less afraid of them and the pattern that was adopted was

followed religiously. As time went on, and none of the bolts fell

out, they were taken for granted and it was assumed that bolts

would hold up the roof as long as there were bolts in the roof.

Some operators are beginning to tell me that we are all

overbolting, and naturally when they feel that way they will

reduce either the number of bolts or the length of the bolts they

use.... If failures are accepted as a calculated risk, it is only a

matter of time until a serious accident occurs...”74

By 1960, roof bolting was no longer expected to perform

miracles. A Campaign to Prevent Injuries from Roof Falls in Coal

Mines was initiated that year under the auspices of the National

Safety Council, and was sponsored by Federal and State agencies, the

United Mine Workers of America, coal associations, safety

organizations, and others.75 Full-page articles on how to reduce the

number of roof falls were published in the Mining Congress Journal

during each month of that year, yet the strategy of abandoning

timbers in favor of roof bolts was never suggested. Instead, the

campaign focused on a number of older themes: Systematic roof

support plans, enforcing compliance with the plans, use of safety

posts, and not going inby supports (figure 15).76 As Coal Age

magazine said:

“Few are the mines that cannot cut accidents from falls of

roof, face, and ribs more than 50% by the intensive,

continuous application of well-known basic principles. All

that is necessary is to do it.” 77

Despite the campaign, the roof fall fatality rate climbed to its

post-war peak in 1960.

“A Health Hazard Is Created While Attempting to Eliminate

the Hazard from Rock Falls”

SILICA DUST AND ROOF BOLTING

Drilling creates dust. While the health dangers of coal dust had

been disputed for more than a century, there was no question about

the hazard of silica dust. The Bureau of Mines had identified silicosis

as a major hazard for metal miners as early as 1917.78 Nearly 2000

tunnel workers, many of them ex-miners, had been killed or disabled

by silicosis at Hawks Nest Mountain in WV during the 1930's.79 By

the late 1930’s, most states recognized silicosis in their workmen’s

compensation laws.80

The Bureau of Mines recognized the need for dust control when

drilling for roof bolts from the very beginning. Their studies showed

that coal mine roof strata contained an average of 31% free silica,

with typical values of 26% in shale and 55% in sandstone.81 The

accepted technique for controlling drilling dust in metal mines was to

force water up the drill steel to the bit. The Federal Mine Safety Code

specifically required the use of water where rock was drilled with

percussion drills.82 Wet drilling was enforced so rigidly in metal

mines that “it was taken as a matter of course, even though drilling

vertical holes is a sloppy, disagreeable task.”83

Many in the coal industry clearly understood the risks as well. At

a panel on roof bolting at the 1949 Annual Meeting of the Kentucky

Mining Institute, engineers from the Berwind-White Coal Company,

the West Kentucky Coal Company, and the National Coal Association

joined the Bureau’s Thomas in urging mine operators to give wet

drilling serious consideration.84

The Bureau publicized research that showed dry drilling, with

either pneumatic stoper or electric rotary drills, could result in silica

dust concentrations up to 200 times the recommended level of 5

million particles per cubic ft of air. Such concentrations were a

serious menace to not just the drill operators, but also anyone working

downwind in the return air. Wet drilling, on the other hand, was

found to result in acceptable levels of dust.85

Wet drilling never caught on, however. In a bluntly honest

assessment, Thomas explained how the Bureau’s decision to allow

dry drilling in the initial roof bolting trials had contributed to the

problem: 

“In the first installations of roof bolts in coal mines the

possibility of failure was of great concern to mine officials.

Frankly, we considered it more important to prove the

practicability of the method, leaving dust control a secondary

consideration. When roof bolting became popular, it was

difficult to convince new users that dust control measures

should be adopted, especially when the original installations

had not considered such provisions....The coal miner,

regardless of any explanation that wet drilling is standard

practice in metal mines, is unimpressed and wants no part of

such a sloppy, disagreeable task. It is difficult for him to

visualize the silicosis hazard or to take it seriously”86. 
Figure 17. Dry drilling using respirators for dust protection.

In an address to the 1950 Illinois Mining Institute, J.J. Forbes, the

Bureau’s Chief of Health and Safety, said that “without some means

of controlling dust a health hazard is created while the attempt is

being made to eliminate the hazard from falls of rock.” He reported

on a meeting held in Washington DC in which representatives of

machinery manufacturers, coal-mine operators, and mine workers had

discussed dust control measures in connection with roof bolting.87

Following this meeting, the Bureau began an extensive program of

testing dust collecting systems for performance. Yet as late as 1957,

the Bureau reported that of the 424 mines using roof bolts, just 8%

employed water to allay dust, 35% employed dry dust collectors, and

nearly half employed no means of dust control other than respirators

(figure 16).88 An industry consultant provided one explanation for the

lack of progress: “The application of dust control to bolt drilling

operations generally adds to the time and cost of the bolting and often

delays the mining cycle.”89

There is little doubt that the prevalence of occupational lung

disease among the generation of miners who worked in the dusty,

mechanizing mines of the postwar period was higher than among

most others in the past.90 Unfortunately, it seems that silica dust from

roof bolting must have contributed to this terrible human toll.

EPILOGUE

What is the verdict on roof bolting during the 1950’s? Certainly

it was a success, if it is judged by the speed with which it was

adopted or the effect that it had on the economics of mining. But

those were not the criteria used by technology’s most public

advocates:

“Safety has been the principal consideration of the inspection

and other accident-prevention agencies that have endorsed

and promoted roof bolting during the past several years.”91

On these grounds, the results are mixed. Certainly bolting did not

live up to its early high expectations. The total number of roof fall

fatalities declined, but three out of five mining jobs also disappeared

between 1948 and 1960. Each of the remaining miners actually had

a greater chance of being killed in a roof fall than his counterpart in

1948. Moreover, roof bolting had introduced a vicious new hazard,

silica dust.

However, it would be unreasonable to lay the blame for the

erosion of safety at roof bolting’s door. The 1950’s were a time of

severe economic stress for the mining industry. The coal boom that

began during WWII had ended, and production was decreasing and

prices were declining as competition from strip mining and other

fuels was growing. The UMWA under John L. Lewis collaborated

with the largest coal companies to raise miner’s wages, forcing the

pace of mechanization.92 Subjected to such extreme competitive

forces, the mining industry was unlikely to radically improve its

safety culture on its own. Little external pressure to improve safety

was applied either, as the 1952 Federal Coal Mine Safety Act was a

weak law that did little to stiffen regulation.93

The 1960’s saw stability return to the mining industry. America’s

demand for electric power was increasing, and coal was the fuel of

choice for new generating stations.94 Roof fall fatality rates fell back

to the levels of the late 1940’s.

Then, on Nov. 20,1968, the Farmington Mine was destroyed in a

massive gas and dust explosion. 78 miners died, and coal mining was

changed forever. When Richard Nixon signed the Federal Coal Mine

Health and Safety Act of 1969, federal inspectors were given much

expanded enforcement powers, and a detailed set of health and safety

standards was made mandatory for all mines.95 Systematic roof

support plans were finally required, with strict guidelines regarding

bolt spacing, bolt length, entry width, and other ground control

parameters. Working under unsupported roof without safety posts

was banned.

The results were quick and dramatic. In the eight years following

1968, roof fall fatality rates plummeted by two-thirds, and they

maintained that level for the next decade. The improvement might

have been due to regulatory enforcement, or to changes in safety

standards implemented by the operators themselves. But there can be

little doubt that the tidal wave generated by Farmington transformed

the safety culture of underground mining. 

Today, roof bolting is the universal primary roof support. Indeed,

it is hard to imagine modern coal mining, in the U.S. or

internationally, without it. Modern roof bolting machines efficiently

collect nearly all the silica dust. Yet, roof fall fatality and accident

rates seem to have reached another plateau.96 New types of bolts and

other supports continue to be introduced and adopted by the mines,

with little overall effect on safety. Perhaps the lesson from the

introduction of roof bolting is that improved technology is not

enough, it must be accompanied by a change in the way safety is

viewed. Much technology for preventing roof falls and protecting

miners is already available. The challenge now for the mining

community is to decide that the current risk of roof falls is

unacceptable. 

ENDNOTES

1

Data collated by Deno Pappas from a variety of sources, as follows:

1900-1922 from U.S. Geological Survey; 1923-1976 from USBM

Mineral Handbooks; 1977-1998 from DOE/EIA Coal Industry

Annuals.

2

Pappas DM, Bauer ER, and Mark C [2000]. Roof and Rib Fall

Incidents and Statistics: A Recent Profile. Paper in Proceedings:

New Technology for Coal Mine Roof Support, NIOSH IC 9453, p. 4.

3

Fletcher R [1956]. Roof Bolting Equipment and Practices. Mng.

Cong. J., Nov., pp. 80-82.

4

Pennsylvania Mining Law, 1911

5

Paul JW and Geyer JN [1928]. State Laws Related to Coal Mine

Timbering. USBM Technical Paper 421, 57 pp.

6

Paul JW, Calverly JG, and Sibray DL[1930]. Timbering Regulations

in Certain Coal Mines of Pennsylvania, West Virginia, and Ohio.

USBM Technical Paper 485, 40 pp.

7

Paul et al [1930]. Ibid, p. 3.Dix K [1977]. 
8

Work Relations in Hand-Loading Era, 1880-1930. WVU Press,

126 pp.

9

Rice GS [1912]. Accidents from Falls of Roof and Coal. USBM

Miner’s Circular 9, 1912, 15 pp.

10Paul JW[1927]. Stop, Look, and Listen! The Roof is Going to Fall.

USBM IC 6032, 1927.

11Paul JW[1930a]. What the Mine Foreman Can Do to Prevent Injury

from Falls of Roof in Coal Mines. USBM IC 6344, 1930, 7 pp.

12Paul JW[1930b]. What the Coal Miner Can Do to Prevent Injury

from Falls of Roof. USBM IC 6315.

13Dix K [1988]. What’s a Coal Miner to Do? The Mechanization of

Coal Mining. Univ. Pgh. Press, 1988

14Forbes JJ, Thomas E, and Barry AJ [1951a]. Questions and

Answers on Roof Support in Bituminous Coal Mines. USBM

Handbook, p. 63.

15Paul [1930b, p. 1.

16Coal Age [1945]. Timbering for Safety in Mechanical Mining.

March, p. 92.

17Thoms E, Seeling CH, Perz F, and Hansen MV [1948]. Control of

Roof and Prevention of Accidents from Falls of Rock and Coal:

Suggested Roof Supports for use at Faces in Conjunction with

Mechanical Loading. USBM IC 7471, p. 1.

18 Dix [1988], p. 101; Forbes et al., [1951a], p. 61.

19Forbes JJ, Back TL, and Weaver HF [1951b]. Falls of Roof: The

No. 1 Killer in Bituminous Coal Mines. USBM IC 7605, pp. 1-3.

20Ibid, p.3 and p. 9

21McElroy DL and Schroder JL Jr. [1941]. Shuttle Car Haulage in

West Virginia. Transactions of the Institute of Mining Engineers

(US), p. 62.

22 Thomas E, Barry AJ, and Metcalfe A [1949]. Suspension Roof

Support: Progress Report 1. USBM IC 7533, p. 3.

23 Edwards JH [1947]. Machine Timbering Promotes High Efficiency

at Gay Mines. Coal Age, April, p. 102.

24 Edwards [1947], p. 104; Burchart RB [1947]. Timbering

Machines Cut Cost and Promote Safety at Isabella. Coal Age, Feb.,

pp. 102-105.

25Coal Age [1949], Feb., p. 89.

26Thomas et al. [1948], pp. 2-9.

27Ibid., p. 2.

28Ibid., p. 6.

29Thomas E [1951]. Suggestions for Inspection of Roof Bolt

Installations. USBM IC 7621, p. 2.

30Mark C [2000]. Design of Roof Bolt Systems. Paper in

Proceedings: New Technology for Coal Mine Roof Support, NIOSH

IC 9453, p. 112.

31Weigel WW [1943]. Channel Irons of Roof Control. Eng. Mng. J.,

v.144, n. 5, May, pp. 70-72.

32Gibson AV [1960]. A Practical Look at Progress in Roof Control.

Coal Age, Dec, p. 53.; Coal Age [1952]. Roof Bolts Still Hold After

34 Yr. Aug., p. 152.

33Weigel [1943]. Eng. Mng. J., May, pp. 70-92.

34Jamison W [2001]. Telephone interview with the author.

35Conway CC [1948]. Roof Support With Extension Rods. Proc. IL

Mng. Inst., pp. 59-60. Also republished in Mng. Cong. J., June 1948.

36Ibid., pp. 63-65.

37Ibid.

38Ibid.

39Thomas et al. [1948]

40Thomas [1951], p. 1.

41Aldrich M [1995]. Preventing ‘the Needless Peril of the Coal

Mine’: The Bureau of Mines and the Campaign against Coal Mine

Explosions, 1910-1940. Technology and Culture, Society for the

History of Technology, pp. 483-518. 

42Coal Age [1949]. Bureau of Mines Sets Up Roof Control Unit.

Sept., p. 152.

43Thomas et al. [1949], pp. 3-5

44Thomas E [1951], p. 2.

45Bierer J [1952]. Roof Bolting for Safety. WV Dept of Mines, p. 1.

46Thomas E [1956]. Roof Bolting Finds Wide Application. Mng.

Eng., Nov., p. 1080

47Alexander AJ [1950]. The First Year of Roof Bolting in West

Virginia Mines. WV Dept. of Mines, p. 10.

48Thomas E [1951], p. 3.

49Flowers AE [1953]. Successful Roof Bolting at Idamay. Coal Age,

Oct., p. 76

50Kelly LW [1952]. Economic Benefits of Systematic Roof Bolting

in Zeigler No. 3 Mine, Williamson County, IL. USBM IC 7633, p. 8.

51Kirk N [1955]. Roof Bolting Reduces Accidents and Costs. Mng.

Cong. J., p. 38.

52Coal Age [1949]. Small Bolts Hold Bad Top. Sept., pp. 92-94.

53Gilley JL, Thomas, E [1951]. Pillar Extraction with Roof Bolts.

Mng. Cong. J., Nov., p. 68.

54Flowers AE [1953], p. 79.

55Kelley LW [1952], pp. 1-8.

56Young HC [1954]. Roof Bolting in Alabama Coal Mines and Iron

Ore Mines. USBM IC 7678, pp. 4 & 14; Broughton HJ, Johnson LH

[1952]. Roof Bolting. Mng. Cong. J., p. 124; Coal Age [1955].

Investigating Bolted Roof Falls. Oct., pp. 55-57.

57Bierer J [1952]. Roof Bolting for Safety. WV Dept. of Mines, no

document or page numbers.

58Hamilton JL [1951]. Modern Mechanical Coal Mining. Mng.

Cong. J., Feb, p. 38.

59Fletcher R [1956], p. 80.

60Maize, R [1949]. Circular Letter No. 185-B, published in PA Dept

of Mines Annual Report for 1949.

61Coal Age [1950]. WV Bureau Requires Roof-bolting Permits. Jan,

p. 132.

62Maize, R [1950]. Circular Letter No. 203-B, published in PA Dept

of Mines Annual Report for 1949.

63Cortis, S et al [1950]. Letter to R. Maize, Dec 20. Published in PA

Dept of Mines Annual Report for 1950.

64PA Dept of Mines [1954]. Annual Report for 1953.

65Coal Age [1958]. News Item, Sept., p. 28.

66Sall GW [1955]. Four Years of Roof Fall Accidents. Mng. Cong.

J., Sept., p. 79.

67Thomas E [1956]. Progress and Problems in Roof Support. Coal

Age, Aug., p. 87. 

68Sall GW [1955], p. 79.

69Thomas E [1956], p. 87.

70Thomas E [1956], p. 87.

71Thomas E [1951], p. 1.

72Coal Age [1950]. Report on the 1950 Annual Meeting of the

American Mining Congress. June, p. 91.

73Mark C [2000], pp. 114-121; Mark C and Barczak TM [2000].

Fundamentals of Coal Mine Roof Support. Paper in Proceedings:

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pp. 23-42.

74Kelly LW [1951]. Discussion on “Progress in Roof Bolting.” Proc.

of the 1950 Annual Meeting of the IL Mng Inst., pp. 27-30.

75Williams RRJr [1960]. Progress in Mine Safety. Mng. Cong. J.,

Feb, p. 36.

76Mining Congress Journal [1960]. Series of articles pertaining to the

1960 National Campaign to Prevent Injuries from Roof Falls in Coal

Mines. Jan, p. 41; Feb. p. 126; Mar. p. 78; Apr. p. 89; May, p. 69;

Jun., p. 72; Jul., p. 69; Aug., p. 39; Sep. p. 63; Oct., p. 57; Dec. p. 47.

77Coal Age [1960]. Unless... Mar., p. 86.

78Rosner D and Markowitz G [1991]. Deadly Dust: Silicosis and the

Politics of Occupational Disease in 20th Century America. Princeton

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79Cherniack, M. The Hawks Nest Incident: America`s Worst

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80Smith BE [1987]. Digging Our Own Graves: Coal Miners and the

Struggle Over Black Lung Disease. Temple Univ. Press, p. 103.

81Westfield J, Anderson FG, Owings CW, Harmon JP, and Johnson

L [1951]. Roof Bolting and Dust Control. USBM IC 7615, pp. 1-3.

82Westfield J [1951]. Roof Drilling With Dust Control Equipment.

Proc. of the Illinois Mining Institute, p. 28.

83Thomas E [1950]. How You Can Get More From Roof Bolting.

Coal Age, April, p. 73.

84Coal Age [1950]. Kentucky Mining Institute. Feb., pp. 160-161.

85Wefield et al. [1951], p. 3.

86Thomas E [1950], p. 73.

87Forbes JJ [1950]. Progress in Roof Bolting. Proc. of the Illinois

Mining Institute, p. 22.

88Coal Age [1957]. Roof Bolting in 1956. Apr., p. 88.

89Auchmuty RL and Summers MW [1954]. Mechanical Coal Mining

Progress. Mng. Cong. J., Feb., p. 81.

90Smith BE [1987], p. 107.

91Thomas E [1957]. Coal Age.

92Dubosfsky M and Van Tine WV [1977]. John L. Lewis: A

Biography. Chap. 20, “Prisoner of Change.”

93Lewis-Beck ML and Alford JR [1980]. Can Government Regulate

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pp. 751-752.

94Curran DJ. Dead Laws for Dead Men: the Politics of Federal Coal

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95Lewis-Beck ML and Alford JR [1980], p. 752.

96Pappas et. al [2000], p. 6-7; Dolinar DR and Bhatt SK [2000].

Trends in Roof Bolt Application. Paper in Proceedings: New

Technology for Coal Mine Roof Support, NIOSH IC 9453, p. 45-46.