P e r s

46 January 2008 ring

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 Paper number tP-07-002. original 

manuscript submitted january 2007. revised manuscript 

accepted for publication september 2007. discussion of this 

peer-reviewed and approved paper is invited and must be 

submitted to sme Publications dept. prior to april 30, 2008. 

 

 

 

 

 

 

 

 

 

 

 

 

Prevalence and cost of cumulative 

injuries over two decades of 

technological advances: a look at 

underground coal mining in the U.S. 

s.m. moore. e.r. bauer and l.j. steiner 

Abstract 

Technological advances in underground coal mining have 

reduced fatalities but may not have reduced worker exposure 

to cumulative injury risk factors. The objective of this study 

was to evaluate the prevalence of cumulative injuries before 

and after the implementation of technological advances in 

underground coal mining and to make a general cost estimate for these injuries. A previously published algorithm 

was utilized to identify cumulative injuries within the Mine 

Safety Health Administration (MSHA) database for two 

data sets: 1983-1984 and 2003-2004. For both, the following 

were determined: the number and percentage of cumulative 

injuries, the average days lost, the average age at the time 

of injury, the average years of experience and the general 

cost estimate by body part. The percentage of cumulative 

injuries remained largely unchanged (37 percent in the 

1983-1984 period and 33 percent in the 2003-2004 period). 

The average number of lost days due to cumulative injuries 

increased (36±55 days and 62±82 days, respectively), which 

may have been due to the increased worker age (~seven 

years older in the 2003-2004 period), increased length of 

employment (~seven years longer in the 2003-2004 period) 

or other factors such as changes in medical practices. Cumulative injuries to the back decreased by 10 percent, while 

cumulative injuries to the knee increased by 8 percent. The 

reduction in back injuries may be due to the implementation 

of assist devices, while the increase in knee injuries may be 

related to kneeling/crawling in low-seam mines. Cumulative 

injuries were found to remain a major financial burden on 

the industry. Recently, National Institute for Occupational 

Safety and Health (NIOSH) developed tools to assist mining 

companies with incorporating an ergonomics process into 

their existing health and safety programs. The participating 

companies have reported tremendous success. Therefore, it 

is recommended that ergonomics processes be implemented 

as a means to systematically identify and address the root 

causes to cumulative injuries and ultimately reduce costs. 

Introduction 

In the early 1900s, as many as 

3,000 underground coal mine work- S.M. Moore, E.R. Bauer and L.J. Steiner, members 

ers died annually. Since then, howev- sme, are research engineer, mining engineer and supervisor, 

er, there has been a decreasing trend respectively, with the national institute for occupational safety 

in mine worker fatalities. In fact, a and Health, Pittsburgh, Pa. 

low of 11 fatalities occurred in 2003 

(Mine Safety and Health Administration, 2006). This trend may be due to 

the fact that technological advances 

have provided for a safer work environment and have decreased the 

number of workers required to perform tasks.These technological advances have come in the form of machinery 

design, control and operation. 

As technology advances, it is important to consider 

the effects of these advances on mine workers, to avoid 

exposing them to cumulative injury risk factors (CIRFs) 

such as awkward postures, repetitive motions, jarring 

and jolting and vibration. During the past two decades, a 

series of technological advances have greatly changed the 

working conditions and requirements of mine workers in 

underground coal mines. These advances include but are 

not limited to: 

• implementing continuous mining machines with fan 

spray/scrubber systems and 

remote controls, 

•	 the use of automated roof 

supports and dual-boom roof 

bolters and 

•	 mechanization of supplydelivery tasks. 

The development of fan spray/ 

scrubber systems and remote control has allowed for 

increased productivity and has reduced the operator’s 

exposure to whole body vibration. However, with the operator no longer seated on the machine, extended cuts are 

utilized as the machine is controlled remotely. While the 

operator’s exposure to whole-body vibration may have 

decreased, the operator handles cables that are longer 

in length and, thus, more physically demanding (Gallagher et al., 2001). Thus, the operator’s overall exposure 

to CIRFs may not have been reduced. 

With the advent of the dual-boom roof bolter, the 

time spent by the operator tramming and manipulating 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

the boom is greatly reduced, and the helper installs bolts 

with one of the boom heads instead of providing supplies 

to the operator. It is also becoming more common for 

roof-bolter operators to install secondary supports such 

as pizza pans, straps and even screening. However, while 

the tasks performed by the operator and the helper have 

changed, both are still exposed to CIRFs, such as repetitive motions and awkward postures. 

Finally, supply tasks have been mechanized with 

scoops to reduce the manual tasks performed by the supply person, utility person and laborers. However, there is 

still a great deal of exposure to CIRFs because the rate 

at which supplies are needed has increased and the need 

to manually unload supplies still exists, resulting in lifting, 

twisting and awkward postures. Other CIRFs were also 

introduced with the changes in technology, such as jarring 

and jolting. Furthermore, pinch points were also introduced, which may result in an acute injury that eventually 

gives way to a cumulative injury because worker capabilities are decreased and the demands on the worker may 

not be fully adjusted for these limitations while the body 

heals. 

The primary concerns within the mining industry have 

been reducing fatalities, increasing productivity and decreasing the cost of equipment and replacement parts 

(McPhee, 2004). While the technological advances in the 

mining industry may have positively affected workers’ 

tasks and the efficiency of extracting coal, they may not 

have reduced cumulative injuries. Many jobs still expose 

mine workers to CIRFs such as awkward postures, exposure to whole body vibration, forceful exertions and 

repetitive motions (Zhuang and Groce, 1995; Cornelius 

and Turin, 2001; McPhee, 2004; Steiner et al., 2004). 

In the early 1980s, sprains and strains alone were 

shown to account for approximately 20 percent to 50 

percent of all underground mining injuries (Stobbe et al., 

1986). Despite the improvements in technology, workers are still exposed to CIRFs throughout their shift. 

Therefore, the high prevalence of cumulative injuries 

in underground mining may still exist. Thus, as a means 

of reducing cumulative injuries it would be necessary to 

have a drive towards the design of tasks, equipment and 

tools. However, the National Institute for Occupational 

Safety and Health’s (NIOSH’s) interactions with mining 

companies have indicated that many have not chosen to 

commit their resources to such an endeavor because a 

clear cost/benefit had not yet been shown. 

The objective of this study was to determine and compare the prevalence of cumulative injuries before and 

after the implementation of technological advances in 

underground coal mining and to make a general cost estimate for these injuries. It was hypothesized that a difference in the percentage of cumulative injuries reported in 

1983-1984 and 2003-2004 would not be observed because 

mine workers are still exposed to a host of CIRFs. It was 

assumed that using two time points separated by 20 years 

would allow a high likelihood that the data compared was 

from before and after major technological advances had 

been in place for an extended period of time. 

Methods 

While mining companies have rapidly employed some 

of the technological advances, there are others that the 

mining companies have been slow to implement. Therefore, data were obtained from periods representing two 

different decades to ensure that nearly all mine operations now implemented the major technological advances. To increase the sample size and avoid a local minima 

or maxima in the database, two years were evaluated for 

both decades instead of just one. Mine Safety and Health 

Administration (MSHA) injury databases were used for 

this study. All injuries listed in the MSHA databases for 

calendar years 1983 and 1984 were combined to form the 

first data set, which is referred to as the 1983-1984 data 

set. Similarly, all injuries listed in the MSHA databases 

for calendar years 2003 and 2004 were combined to form 

the second data set, which is referred to as the 2003-2004 

data set. Both the 1983-1984 and the 2003-2004 data sets 

were filtered such that only injuries occurring at underground coal operations were considered. The total number of underground coal injuries was then determined 

for each data set. 

To determine the number of cumulative injuries for 

each data set, a previously reported algorithm was utilized (Battelle Centers for Public Health Research and 

Evaluation, 1999). This algorithm identifies injuries that 

were cumulative in nature based on their “nature of injury” code. Cumulative injuries can be attributed to cumulative trauma or can be a reoccurring injury that was 

initially attributed to an 

acute trauma. Many injuries caused by an acute 

trauma result in a recurring injury.Therefore, the 

methodology utilized in 

this paper assumes that 

regardless of whether 

the injury was initiated 

by a cumulative trauma 

or an acute trauma, it is a 

cumulative injury. Under 

Table 1 

Average total incurred costs per claim by body part. 

	 

	 National	Safety	Council	Injury	Facts 

	 Part	of	body	 	 2004	Edition 

	 ankle	 	 	 $10,358 

	 arm/shoulder	 	 $16,564		 

	 Knee	 	 	 $16,966 

	 Lower	back	 	 $17,738 

	 Upper	back	 	 $11,533 

	 Neck	 	 	 $23,862 

Table 2 

Breakdown of cumulative injuries by incidence rate, days lost, age and length of 

employment. 

Measurement parameter 1983-1984 2003-2004 

average	days	lost	for	cumulative	injuries	 	 	 	 	36±55	 												62±82 

average	age	when	suffered	cumulative	injury	 	 	 			35±9	 												42±11 

average	years	of	mining	experience	when	suffered	cumulative	injury	 			10±6	 												16±11 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

this assumption, the following injury codes were isolated: 

260 (hernia, rupture), 270 (joint, tendon or muscle inflammation or irritation), 330 (sprain, strains), 370 (multiple 

injuries) and 400 (unclassified, not determined). Occasionally, injuries to the musculoskeletal system are classified in two other injury codes as well: 380 (occupational 

diseases, NEC) and 390 (other injury, NEC). However, 

many of the injuries classified under these two injury 

codes are not to the musculoskeletal system. Therefore, 

it was necessary to read the narratives of those injury 

records to ascertain whether or not the injury was to the 

musculoskeletal system. Using this algorithm, a total of 

8,083 and 3,266 cumulative injuries were identified from 

the 1983-1984 and 2003-2004 databases, respectively. 

For the 1983-1984 and 2003-2004 data sets, the number and percentage of cumulative injuries, with respect to 

the total number of injuries reported, was determined for 

underground coal miners. For both sets of data, the days 

lost due to the injury and the associated incidence rates 

(normalized to 200,000 hours worked) were then computed (mean±SD). The incidence rate was determined by 

 

 

 

 

(Total number of injuries ∗ 200,000 hrs) Incidence rate = Total hours worked (1) 

The total hours worked included surface and under

ground mine workers at underground coal mines, includ

ing both bituminous and anthracite operations. For the 

1983-1984 and 2003-2004 data sets, the average age of the 

mine workers who experienced cumulative injuries and 

their average length of employment in mining were then 

determined. For both data sets, the cumulative injuries 

were then further subdivided by the part of body injured. 

The body parts included in the analyses were the ankle 

(MSHA data base code: 520), arm/shoulder (MSHA data 

base codes: 310, 311, 313, 314, 450), knee (MSHA data 

base code: 512), back (MSHA data base code: 420) and 

neck (MSHA data base code: 200). The costs of cumula

tive injuries by body part based on data from the Nation

al Safety Council (Itasca, 2004) are presented in Table 1. 

The manner in which the National Safety Council report

ed these data has changed over the decades. Therefore, a 

direct comparison between the 1983-1984 and 2003-2004 

data sets is not possible. It should be noted that the cost 

data provided by the National Safety Council are not 

specifically for cumulative injuries. Rather, the cost data 

pertains to all types of injuries to these body parts. 

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Results 

The total number of injuries decreased from 1983­

1984 (21,792 total injuries) to 2003-2004 (10,046 total injuries). Cumulative injuries accounted for 8,083 and 3,266 

for the 1983-1984 and the 2003-2004 data, respectfully. 

Thus, despite changes in technology, the percentage of 

cumulative injuries remained nearly unchanged between 

the two decades (37 percent and 33 percent, respectively). 

Additionally, there was only a small decrease in the incidence rate, which dropped from five to four between the 

two decades, respectively. 

When evaluating the average days lost for cumulative 

injuries, there were 11 injury records in the 1983-1984 

data in which this information was unknown. These data 

were thus excluded from the analysis. For cumulative 

injuries, it was found that in the 2003-2004 period (62±82 

days) the average days lost was higher by 26 days than 

in the 1983-1984 period (36±55 days). This also corresponded to an increase in the average age of the mine 

workers that were injured. 

The average age of the injured mine workers was 

calculated based on the date of birth entered into the 

MSHA database.Therefore, occasionally this information 

is entered incorrectly or not at all. For the 1983-1984 and 

2003-2004 data sets, 307 of 8,083 and 64 of 3,266 injury 

records, respectively, were excluded due to missing information or ages that were likely incorrect (i.e., less than 

17 years or greater than 75 years). Using the remaining 

injury records, it was found that in 2003-2004 the average 

age of the mine workers that suffered a cumulative injury 

increased by seven years. 

When evaluating the average length of employment 

of mine workers at the time they suffered a cumulative 

injury, missing data was encountered for 624 injury records in the 1983-1984 data set and 207 injury records in 

the 2003-2004 data set. For the remaining injury records, 

it was observed that mine workers suffering cumulative 

injuries in 2003-2004 had been employed six more years 

than those in 1983-1984. 

These cumulative injuries were then evaluated with 

respect to body part (Table 3). It should be noted that, 

for the 1983-1984 data, five injuries were listed as “unclassified” for body part, while for the 2003-2004 data, two 

injuries were “unclassified.” Thus, these injury records 

could not be included in this analysis. 

Table 3 

Breakdown of the number and percentage of injuries 

by body part for comparison with average costs for 

injury shown in Table 1. 

1983-1984 2003-2004
 

Part of body Number percent Number percent
 

ankle	 	 				376	 5	percent									118						4	percent 

arm/shoulder	 				355	 4	percent									305						9	percent 

Knee	 	 				752	 9	percent									568				17	percent 

Back	 	 3,348				41	percent						1,031			31	percent 

Neck	 	 			475					6		percent									192					6	percent 

Other	 	 5,306				66	percent						2,214			68	percent 

The true cost of cumulative injuries is difficult to 

determine because the initial indirect costs, such as de

creased work rate or capacity, are often unreported until 

the injury has progressed to the point of needing medical 

intervention. Thus, it should be noted that the cost data 

provided by the National Safety Council are not specifi

cally for cumulative injuries but rather for all injuries to 

the specified body part.Additionally,the manner in which 

these data are reported has changed over the decades. 

Therefore, a direct comparison between the 1983-1984 

and 2003-2004 data sets was not possible. Thus, the costs 

of injuries by body part are presented based on the same 

time point from the National Safety Council (Table 1). 

For example, in 2003-2004, 569 cumulative injuries to the 

knee were reported. Thus, one could estimate that this 

resulted in a cost of $9,636,688, or $16,966 per knee injury. 

Table 3 demonstrates that back injuries accounted for 

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the largest percentage of cumulative injuries.While there 

was nearly a 10 percent drop in the percentage cumulative back injuries between the 1983-1984 and 2003-2004 

data sets, there was also an increase of 8 percent in the 

percentage of cumulative injuries to the knee between 

the two data sets (Table 3). 

Discussion 

In this study, the prevalence of cumulative injuries 

across two decades of technological advances was compared and a means to make a general cost estimate for 

these injuries was provided. Additionally, differences in 

the incidence rate of injury, age of the miners injured, 

days lost and length of employment at mining facilities 

were evaluated to allow for a more detailed comparison. 

The data demonstrated that there was a decrease 

in the number of cumulative injuries between the two 

decades. This may have been due to the decrease in the 

average number of workers from 103,431 to 44,456 for 

the 1983-1984 and 2003-2004 periods, respectively (Itasca 2004). However, despite the decrease in the overall 

number of cumulative injuries, the percentage of cumulative injuries remained nearly unchanged (37 percent 

and 33 percent between 1983-1984 and 2003-2004, respectively). This difference was within the accuracy of 

the algorithm used to isolate cumulative injuries via 

the “nature of injury” code (Battelle Centers for Public Health Research and Evaluation, 1999). Therefore, 

the hypothesis that a difference in the percentage of 

cumulative injuries reported in the 1983-1984 and 2003­

2004 periods would not be observed was supported. For 

both periods, a large percentage of cumulative injuries 

were reported, which indicates a need to address these 

types of injuries.These data compare well with previous 

studies that have reported sprains and strains or other 

cumulative injuries to be a major contributor to injury 

rates (Stobbe et al., 1986). 

There was only a small drop in the incidence rate of 

cumulative injuries, which was within the accuracy of the 

algorithm used to isolate the cumulative injuries. This 

indicates that the ratio of cumulative injuries to hours 

worked has remained largely unchanged as well. Thus, 

while technological advances may have increased production and decreased fatalities (MSHA), cumulative 

injuries must still be addressed. 

Several other interesting facts were also observed. In 

2003-2004, a longer recovery time was required before 

mine workers could return to work, which was indicated 

by an increase of 68 percent in lost days compared to the 

1983-1984 data.This may have been due to many factors. 

Previous research has reported that recovery periods for 

older (>55 years) workers are typically twice as long as 

those for younger (<35 years) workers (Merchant et al., 

2000).Thus, the seven-year increase in the average age of 

the mine worker injured in 2003-2004 may have been a 

primary contributor to the increase in lost days.Another 

contributing factor may have been the longer length of 

employment for those injured in 2003-2004. While the 

injury occurred at a later point in the mine worker’s 

career, the cumulative effect of exposure to CIRFs may 

have been a prolonged recovery period. Additionally, 

changes in the area of rehabilitation practices may also 

have been responsible for the increased days. Other 

confounding factors, such as lifestyle changes, injuries 

outside the workplace or a combination of several factors, may have also played a role. It should also be noted 

that there are large individual differences between mine 

workers, whereby exposure to CIRFs may or may not 

affect them. Regardless of the root cause (age, exposure, 

lifestyle, etc.), increased recovery time plays a major role 

in the cost of cumulative injuries. As the number of lost 

days increase, costs associated with the injury would 

also increase due to maintaining replacement workers, 

workman’s compensation and continued rehabilitation 

and medical evaluations. MSHA provides a calculator 

that estimates the cost of an accident with lost days at 

$28,000, but it does not calculate the cost based on the 

number of lost days themselves. 

There was a shift between the percentage of knee 

and back injuries, with back injuries decreasing while 

knee injuries increased. However, this change in back 

and knee injuries may not be directly related. The 

change in back injuries may be attributed to advances 

the mining industry has pursued and implemented, such 

as the use of mechanical-assist devices and educating 

the mining population regarding back injuries. The increased percentage of knee injuries may be a result of 

awkward postures, such as kneeling and crawling, as well 

as uneven surfaces.Any increase in the rate of kneeling, 

crawling or duck walking may place additional stresses 

on the knee. 

In the future, there may also be a reduction in seam 

heights across the underground coal mining industry 

as technology allows for this coal to be extracted more 

economically (Petersen et al., 2001). This may increase 

the number of mine workers in low-seam mines and 

may also increase their exposure to CIRF’s associated 

with knee injuries (e.g., kneeling and crawling). This is 

a major concern because the cost of knee injuries was 

nearly identical to that for the back. 

At this time, tool and equipment design has been 

predominately focused on the cost of extracting coal because this has been the primary interest of their clients, 

the mine companies.Therefore, it is important to inform 

mine companies about the financial burden associated 

with equipment designs that do not fully complement 

the mine worker. If mine companies communicate with 

equipment manufacturers about the importance of ergonomics in equipment design, future technology improvements will include reductions in operating cost and in 

worker exposure to CIRFs. In addition to equipment 

design changes, other factors may also be considered, 

such as taking out extraneous matter to provide a working height that is larger than the seam height. 

The results of this study demonstrate the need to 

address the cost and prevalence of cumulative injuries. 

A proactive approach to this problem would be to implement an ergonomics process that would provide a 

systematic method to identify, prioritize and resolve the 

root causes of cumulative injuries. Ergonomics processes 

have already been shown to be successful in industries 

other than mining (Gjessing et al., 1997). In fact, ergonomics processes have even been implemented at some 

surface mines with the help of NIOSH personnel, and 

these are showing signs of success (Steiner et al., 2004; 

Porter et al., 2007; Torma-Krajewski and Hipes, 2007; 

Torma-Krajewski and Lehman, 2007). Many companies 
EEring

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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have been concerned with the resources necessary to 

implement an ergonomics processes. However, the resources required are often less than initially anticipated 

because it can frequently be integrated into already existing safety and health programs. 

In the current study, only underground coal mining 

injuries were evaluated. However, for all mining, technological advances were primarily focused on reducing 

fatalities while increasing production (McPhee, 2004). 

A limitation to this study was that the data presented 

were obtained from analyses of the MSHA database, 

which is an “injury” database. Thus, when mine workers 

experience the initial symptoms of cumulative injuries 

they often are not reported.Therefore, the results in this 

study should be considered a lower bound. Having only 

injury data also did not allow incidence rates to be ageadjusted, despite the fact that a substantial change in the 

age distribution of the population was noted between 

the two data sets evaluated. The data provided to perform a general cost should also be considered a lower 

bound, because the estimate did not include indirect 

costs such as those associated with finding a replacement 

mine worker or training new and existing mine workers. 

Other indirect costs include reduced efficiency/production, reduced quality, pain and suffering. Additionally, 

estimates for both decades were generated using cost 

data for only one time period. 

NIOSH intends to continue promoting and assisting 

mining companies in the implementation of ergonomics processes through Web-based training and “trainthe-trainer” guides, which will also provide solutions to 

common problems. Also, when redesigning equipment 

to reduce injuries, it is important to understand how 

mine workers are being injured. Different design characteristics may be warranted if an injury was caused by 

repetition, excessive force or if it is a recurring injury 

that initially occurred due to acute trauma. Therefore, 

in the future, the authors intend to investigate differences in injuries that are cumulative in nature to those 

that may become cumulative following an initial acute 

trauma. Additionally, an upcoming NIOSH project and 

consortium of mining community representatives will 

begin addressing issues associated with human interface 

and equipment design. 

Acknowledgment 

This research was supported by the National Institute 

for Occupational Safety and Health under the Implementing and Evaluating Ergonomic Interventions in 

Mining project. 

Disclaimer 

The findings and conclusions in this report are those of 

the authors and do not necessarily represent the views of 

the National Institute for Occupational Safety and Health. 

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