Ergonomics Considerations 

for Reducing Cumulative 

Trauma Exposure in 

Underground Mining 

K.M. Cornelius and F.E. Turin 

National Institute for Occupational Safety and Health (NIOSH), Pittsburgh 

Research Laboratory, Mining Injury Prevention, PO Box 18070, Pittsburgh, 

PA15236·0070,USA 

1. INTRODUCTION 

Underground mining in the USA has undergone significant change 

in the past 20 years. Two key elements have been increased 

mechanization and a more educated work force. In spite of these 

changes, many jobs continue to be labor-intensive and repetitive in 

nature. They entail tasks that, performed over time, can take a toll 

on the soft tissues and joints. The problem may be compounded by 

an aging mining workforce. In 1996, the mean age of the coal 

mining work force was 45 years and the median total years of 

experience was 20 (NMA 1998). As a person ages, the body’s 

resilience to chronic Wear and tear is reduced, which may cause a 

worker to pay an increasingly higher health price for performing 

the same task. Mining companies, like many others, are becoming 

more aware of cumulative effects to the worker as reports of these 

types of injuries rise. 

Conducting a job analysis is an important step when 

considering a job redesign or modification to reduce worker 

cumulative trauma exposure. A basic approach to job analysis is to 

examine the types of aches and pains reported, the tasks performed, 

and work site conditions. The US Bureau of Mines (USBM) 

conducted an evaluation of roof bolting tasks performed at an 

underground coal mine concerned about early warning signs of 

cumulative trauma. This evaluation will comprise the primary 

focus of this chapter. The approach used for the roof bolting case 

study may be applicable to other work environments. 

2. FUNDAMENTALS OF CUMULATIVE TRAUMA 

EXPOSURE 

Musculoskeletal injury is a term used to describe a wide range of 

soft tissue disorders that affect the nerves, tendons and muscles. 

Common examples include lower back pain, tendinitis and carpal 

tunnel syndrome. The majority of these injuries are not the result of 

sudden mishaps, but usually develop gradually from repeated wear 

and tear. Symptoms may not appear immediately, but can take 

weeks, months or even years. Symptoms may result from many 

types of activities, performed at work or at home, and it is often 

difficult to attribute them to a single event. In fact, it is more 

common to identify factors that may have contributed to the 

development of the condition. The terms repetitive strain injuries 

or cumulative trauma disorders (CTD) have been commonly used 

to refer to disorders that have occurred due to work-related 

activities. 

Three main risk factors contribute to CTD: force, repetition 

and awkward postures. Any one or combination of these may 

contribute to the development of CTD. Therefore, the design of 

equipment in conjunction with the required tasks should be 

evaluated when attempting to reduce these risk factors, Examining 

the layout of the work area to help identify tasks which may 

contribute to cumulative trauma is necessary. The following list 

(Putz-Anderson 1988), describes ergonomics concerns that, 

overall, should be minimized at the work area: 

 Crowding or cramping the worker: a work area layout may 

unnecessarily constrain movements of the worker. 

 Twisting or turning: placement of tools and materials may 

require the worker to twist the spine to fulfill the 

requirements of the job. 

 Repeated reaching motions: the layout of the work area may 

require the worker to lean to reach and grasp the necessary 

tools and controls. 

 Misalignment of body parts: the arrangement of the work area 

may require the worker to frequently have one shoulder 

higher than the other or have the neck or spine bent to one 

side. 

While many of these concerns are a function of equipment 

design and environmental conditions, making workers aware of 

these issues may help them to adapt their work habits to reduce risk 

of injury. Additionally, this information is useful when conducting 

an ergonomic evaluation of a work area and associated tasks. 

3. UNDERGROUND MINING ENVIRONMENT 

The underground mining environment is a unique challenge. It is 

more difficult to develop controls for an underground mine site as 

compared with a factory setting where equipment and facilities can 

be more easily designed to reduce worker force, posture and 

repetitive exposures. In an underground mine, workers are required 

to perform labor-intensive tasks that often cannot be avoided due to 

environment constraints. The dynamic nature of the environment 

does not allow easy implementation of mechanical assists to reduce 

force exposure. Many of the tasks performed by workers are 

repetitive. Restrictive work areas due to low ceiling height, low 

lighting levels and large pieces of equipment cause workers to 

perform these tasks in postures that are not desirable. Designers of 

underground mining equipment can control how a machine will 

function, but not the environment in which it will be used, Hazards 

in an underground mine cannot be completely removed by 

redesigning the system. There are many hazards and information 

sources that must be continually monitored by workers including 

their position in relation to large pieces of mobile equipment and 

unpredictable geological anomalies. Thus, immediate dangers may 

take priority over awareness of ergonomic considerations while 

performing a job. 

4. CASE STUDY OF UNDERGROUND ROOF 

BOLTING 

4.1. Roof Bolting and Cumulative Trauma 

Exposure 

In an underground coalmine, after an area is mined it is necessary 

to support the roof to keep it from collapsing. Since 1950, the 

primary method for supporting the mine roof has been installation 

of roof bolts. Long bolts installed into the roof compress the layers 

of strata. achieving a uniformly distributed support anchorage. 

Roof bolts, typically 6-8 feet long, are installed by workers using 

large roof bolting machines. There are different types of machines 
used for high, medium and low coal seams. Typically in medium 

and low seams, the operator works in a small area between the 

machine and walls of coal called ribs. A roof bolter operator 

working in a low seam mine is illustrated in Figure 1. In high seams 

workers often work from a platform on the bolting machine. This 

case study evaluates workers roof bolting in a high seam mine. In 

general, bolting machine operators work in tight spaces. 

Figure 1. Roof bolting in a low seam mine often requires workers to maintain awkward postures. 

Roof drilling and bolt installation in underground coal mines is 

labor intensive, repetitive and exposes operators to many hazards 

that can result in injury. In response to cumulative trauma exposure 

concerns at an underground coal mine, a case study was conducted 

to examine roof bolter tasks that performed over time could put 

workers at risk. For this study, the three data collection activities 

were analysis of lost time incident descriptions, interviews and 

observation of roof bolting tasks. 

4.2. Evaluation Approach 

Researchers analyzed 43 lost time incident descriptions to identify 

roof bolting activities and operator injuries having characteristics 

consistent with cumulative trauma exposure. Second, researchers 

conducted a series of interviews with the roof bolter operators, 

supervisors and the staff nurse. The objective of the interviews was 

to learn about bolting tasks and working conditions, to identify 

safety hazards and to discuss the details of injuries. The interview 

data were analyzed to identify similarities in injuries and pains; 

tasks that may contribute to cumulative trauma; and aspects of the 

working environment that may contribute to cumulative trauma. 

Finally, roof bolter operators were observed performing tasks, 

bolting activities were videotaped, still photographs were taken

of bolting equipment and mine conditions, and an experienced 

bolter operator discussed the layout and operation of a roof bolting

machine. 

4.3. Results 

From the injury analysis, 14 incident descriptions were identified 

as describing injuries that could have occurred from cumulative 

exposure and contained the following characteristics: 

 Five of the 14 incidents involved pain in the back, neck, 

shoulder or elbow, 

 Two incidents occurred while putting a roof bolt into a 

drilled hole. 

 Two incidents occurred while lifting bolting supplies. 

 One incident occurred while torqueing a roof bolt. 

Nine of the 14 incidents involved a strain or sprain injury to 

the ankle, knee or hip resulting from a slip, trip or misstep. Seven 

incidents involved stepping or kneeling on uneven floor, loose 

materials on the floor or equipment cable. Two incidents involved 

an operator stepping into or out of the bolting machine platform. 

Interviews were conducted with12 roof bolter operators. 

The most common injuries cited were: 

 face and arm lacerations and cuts; 

 shoulder, neck, and arm strains and pains; 

 ankle sprains and twists, back pain and strains, and knee 

strains; and 

 leg numbness. 

Operators said that roof bolting tasks require a lot of lifting, 

carrying, bending, reaching and stretching. Common activities 

cited as contributing to their pain and discomfort included: leg 

pains while leaning out to see the drill hole; hand and elbow pain
from using the controls; sore knees, back and shoulders from bending 

and twisting to install bolts or lift and position drill steels, wrenches 

and bolts; shoulder and elbow aches from picking up and holding drill 

steels; and knee and back aches at the end of the shift from standing all 

day. 

The layout of the work area was examined and taken into 

consideration to minimize crowding the worker, twisting and turning, 

repeated reaching motions, and misalignment of body parts. After 

reviewing observation notes, videotape, and still photographs, key 

items were identified and are listed in Table 1. 

Table 1. Observations and Issues concerning high seam roofbolting machines. 

Observation

Confined operator platform 

causes operators to twist and 

stretch to get drill steels, bolts, 

plates and wrenches. 

Supply trays are positioned at 

heights well above the 

operators' waists 

Tops of control levers are 

positioned well above waist 

height.

Operators lean against the 

back rail of operator 

compartment and out from 

under the canopy while 

performing drilling and 

bolting tasks. 

Operators shift their weight to 

the side of the body 

corresponding to the hand 

which places the drill steel into 

the drill chuck. 

Operators frequently extend 

their arm up and out to hold onto 

steels while drilling, and onto 

bolts while installing them. 

Drill steels are being inserted 

into the drill chuck usually at 

knee level or lower. 

Transfer of supplies from the 

back of a bolting machine to 

supply trays involves frequent 

lifting, carrying, and twisting.

Issue

This places operator in 

awkward postures creating 

stress to the muscles and joints, 

particularly in the back and the 

knees. 

Lifting and retrieving tools and 

bolts is stressful to the neck. 

arm and shoulder. 

The operator must work with 

the arm and wrist in awkward 

postures.

This places the operators in 

awkward postures. Also, it is 

putting them at risk of being hit 

by falling rocks. 

The muscles on the opposite 

side of the body, particularly 

the low back muscles, are 

stressed and may become 

fatigued. 

This is stressful to the neck, 

arm and shoulder muscles. 

The operator must do more 

bending which stresses the 

low back muscles. 

This places operator in 

awkward postures creating 

stress to the muscles and joints, 

particularly in the back and the 

knees.

4.4. Issues and Recommendations 

The following cumulative trauma exposure issues were identified from 

the analysis: materials handling, operator orientation in workspace, 

vision obstruction, equipment design, and slipping and tripping 

hazards. Recommendations were categorized within each issue. 

Recommendations focused on reducing the three main risk factors that 

contribute to cumulative trauma disorders: force, repetition and 

awkward postures. They also addressed the three elements that define a 

system: human, equipment and environment. Recommendations 

directed at the human element are intended to increase worker 

awareness of risk factors. This knowledge can then be motivation for 

workers to modify their behavior to reduce exposure, Equipment 

recommendations address modifications to existing equipment, which 

can be performed at the mine site or retrofitted by the manufacturer and 

more significant modifications that should be addressed in 

the design of future roof bolting machines. Environmental factors play 

an important role in human-machine interfaces. Environmental 

conditions addressed in the recommendations included space 

restrictions, visibility restrictions, and housekeeping.

The following is a sampling of the recommendations provided:

 Increase worker awareness of the risk factors associated with 

developing CTD. 

 Examine activities that require high force, high repetition and 

awkward postures to determine if the task or equipment can be 

modified.

 Modify materials handling tasks to carry supplies as close to 

the body as possible, restrict the size of the load and minimize 

lifting distances. 

 Eliminate barriers in the path that require operators to lift 

supplies up and over. 

 Improve supply tray design and position, and method for 

stacking and retrieving supplies. 

 Design bolter tasks and equipment to minimize shoulder 

abduction. 

 Design operator work areas considering reach and visibility 

requirements. 

 Reduce force required to activate controls. 

 Increase spacing of controls to accommodate a gloved hand. 

 Improve height of control bank in relation to operator, 

 Consider a height adjustable, padded rail at back of operator 

platform. 

 Evaluate the threshold between the bolting machine walkway 

and the operator platform with special consideration given to 

slipping and tripping hazards. 

 Improve housekeeping practices and implement an active 

program to evaluate, 

 Increase worker awareness of slipping and tripping hazards. 

Recommendations were intended to be used as a guide for more 

comprehensive examination of roof bolting activities. A mine-specific 

evaluation should be conducted at any mine concerned about 

cumulative trauma exposure due to varying conditions, equipment, 

and workforce. An evaluation team with diverse members including 

roof bolter operators, first line supervisors, engineers and safety 

personnel is an effective approach for developing solutions (Hamrick 

1992, Carson 1993). 

5. ROOF BOLTING HAZARDS AND HUMAN 

FACTORS DESIGN PRINCIPLES 

The presented case study does not cover all issues associated with 

underground roof bolting. Some issues presented are common acrossvariations mining conditions; however, the case study presented

focused on a high seam mine where workers operate from an attached 

compartment. There have been several published reports that have 

examined hazards associated with underground roof bolting. In 

particular, one USBM report examined hazards associated with the 

movement of the drill head boom (Turin et al. 1995). A human factors 

analysis approach similar to the case study approach presented here 

was used. Report recommendations focused oil equipment design 

issues and the need to conform to accepted ergonomic design 

principles. One of the primary recommendations was to redesign the 

control bank to reduce the likelihood of accidental activation and 

improve 
Figure 2. Knob shapes that can be recognized by touch by 

operators wearing gloves. 

ease of use. Current control handles are identical in shape and color 

and are mounted close together. Controls should be coded by 

sequence, location and shaped so that they can easily be 

distinguished and operated. Figure 2 illustrates examples of control 

shapes. 

To redesign the control bank properly, it is important to 

examine the operation of the roof bolting machine overall. For 

example, issues identified in the case study such as materials 

handling, ability, and operator orientation in workspace must 

be examined when equipment redesign is considered. A thorough 

task analysis would provide information critical to effective 

equipment redesign and resulting changes to roof bolting tasks. A 

useful resource, Human Factors Recommendations for Underground 

Mobile Mining Equipment contains information on human factors 

design considerations and can be accessed at http:/ 

/www.cdc.gov/niosh/mining: This web page addresses issues on 

system design, task analysis, aging, layout, controls, visibility, 

seating and maintenance for underground mining equipment. Links 

are available on this web page to access additional ergonomics and 

mining safety topics. 

REFERENCES 

CARSON, R., 1993, How to start a successful ergonomics program. 

Occupational Hazards, 122-7. 

HAMRICK, C., 1992, Ergonomics in mining: ergonomic intervention 

strategies. Applied Occupational Environmental Hygiene, 14-16. 

NATIONAL MINING ASSOCIATION, 1998, Facts About Coal 1997-98 

(Washington, DC: NMA). 

PUTZ-ANDERSON, V, 1988, Cumulative Trauma Disorders: A Manual for 

Musculoskeletal Diseases of the Upper limbs (Bristol, PA: Taylor & 

Francis). 

TURIN, F. et al., 1995, Human Factors Analysis of Roof Bolting Hazards in 

Underground Coal Mines (Rhode Island: US Bureau of Mines).