Evaluation of Work Positions used by Continuous Miner Operators in 

Underground Coal Mines

J. R. Bartels, Research Engineer, C. C. Jobes, PhD, Research Engineer J. P. DuCarme, Research Scientist, 

T. J. Lutz, Research Engineer, NIOSH, Pittsburgh, PA 

This work is not subject to U.S. copyright restrictions. 

ABSTRACT 

Operation of underground coal mine mobile equipment is usually done in a restricted workspace with 

reduced visibility. This work environment puts machine operators in awkward postures for tasks that 

require awareness of their surroundings and fast reactions to avoid hazardous situations. Using experienced 

equipment operators as a source, researchers conducted an investigation that developed a method to gather 

data on the needs and practices of machine operators while controlling the machine and the reasons for 

needing particular operational cues. The method used was an interview technique including a survey 

questionnaire and visual aids. The data gathered defined operator cues and work positions for the cutting 

and tramming phases of remote controlled continuous mining machines used in underground coal mines. 

Analysis techniques to determine which cues an operator sees from a variety of positions utilizing a 

computer simulation is shown to be potentially useful to the mining industry for design of work practices 

and workplace layout and could impact equipment design and selection for improved worker safety. 

Conclusions indicate that the survey was a good research tool to collect data and helped investigators 

understand important visual cues. Using this information, researchers were able to analyze the visual cues 

an operator can see from a given work position and posture. 

INTRODUCTION 

Operating large mobile equipment such as a continuous miner 

(Figure 1) is one of the most dangerous jobs that workers 

perform in underground coal mining.

Figure 1. Continuous miner 

 Throughout the mining 

sequence, whether cutting coal or tramming (moving 

equipment) to another location, the machine operator, helpers, 

crew boss, maintenance mechanics, and other equipment 

operators are put at risk from close proximity to the 

continuous miner machine and other hazardous situations 

associated with mining underground coal. Restricted 

workspace and reduced visibility of hazards compound the 

danger of operating a continuous miner. Mine Safety and 

Health Administration (MSHA) accident data from 2002-2007 

indicate that the coal industry averages 6,517 accidents per 

year in underground mines. 20% (1,362) of those total 

accidents per year involved mobile face equipment that 

includes continuous mining machines, roof bolters, and 

haulage vehicles for underground mines. An average of 4% 

(266, 2 fatal) of those total accidents per year occurred while 

operating continuous mining machines. 

Unfortunately, MSHA accident investigation reports do not 

contain sufficient information to aid in studying interactions 

between a machine and its operator. Experienced operators 

have a wealth of information on what is needed to operate 

equipment and why operators choose certain operating 

positions. Consequently, in-mine observations and a survey, 

consisting of a questionnaire and visual aids, were used to 

gather pertinent information about operating a continuous 

mining machine in underground coal mines. 

METHOD 

Investigators used a scripted interview survey method and 

visual aids to gather information on work positions and visual 

needs of the operator during both the cutting and tramming 

(moving to new location) phases of mining. Surveys were 

followed by direct observation of the operators during mining 

operations. The data gathered was compiled into a database 

and used to develop computer simulations of work positions 

and visual cues used by operators. This information was then 

used to develop computer-based analysis tools that could be 

used to develop or to identify new safety interventions. 

Survey Development 

The survey collected information on operator position and 

visual cues from 77 operators of continuous mining machines 

with experience ranging from 2 to 30 years. Operators 

representing 39 separate underground coal mine operations in 

Alabama, Colorado, Illinois, Kentucky, Maryland, New 

Mexico, Ohio, Pennsylvania, Virginia and West Virginia were 

interviewed. 

A survey using a scripted interview technique was the most 

efficient method of collecting and consolidating this sort of 

information. The survey was developed through a series of 

discussions with individuals having years of mining research 

and continuous miner operator experience, and by using pilot 
interviews to refine the survey questions. In addition, 

researchers determined which phases of the continuous miner 

work sequence should be studied by analyzing statistical 

information from MSHA’s annual mine accident database, 

from Sanders and Kelley's (1981) effort defining visual cues 

for mining machine cabs, and job task analyses for machine 

operators conducted by NIOSH. 

There are a number of visual cues and other machine feedback 

cues that operators must assimilate and process to safely 

control a continuous miner. The survey questions were 

designed to provide data on what the operator looks at and 

from what position, and on why the operator uses certain cues 

to make decisions on how to operate the equipment and select 

a work location. For example, questions addressed possible 

obstructions that might block the operator’s view of vital cues, 

such as dust, water spray, light housings, and the glare from 

light sources, and asked what the operator would do about 

these obstructions. Another series of questions dealt with 

initial work positions and postures of the operator and 

possible deviations from that initial position during the work 

sequence while operating the continuous miner. 

Previous studies of deck mounted operator cabs in continuous 

mining machines, shuttle cars, and scoops by Sanders and 

Kelley (1981) and Eger, Salmoni, and Whissell (2004) contain 

cue data from machine operators. Despite the change in 

operating method from inside a cab to remote control, Sanders 

and Kelley's work contains a number of cues that are still 

valid for today’s remote control operation of continuous 

mining machines. Information from the new survey (an 

example question dealing with cues is shown in Table 1) 

would provide information such as operator’s work positions 

and reason(s) for choosing a position. 

Table 1. Example questions 

Guides you look at.... How often.... 

Always Sometimes Never

 Edge of the machine on the 

side you are on 

 

Center line of the machine 

Back end of the boom 

Cutting head bits 

 How far the boom swings 

Spray nozzles 

Right edge of drum 

Left edge of drum 

Center or other point on the 

drum 

 

Haulage vehicle inby bumper 

Haulage vehicle operator 

Floor at the face 

Roof at the face 

Ribs on left side of miner 

Ribs on right side of miner 

Laser beam/spot 

 Center line of entry 

*partial list for one of the three studied configurations 

The survey evolved through a series of discussions with 

individuals having years of mining research and continuous 

miner operation experience. Experienced machine operators 

are a valuable source of information on machine job tasks. 

They have a wealth of knowledge, skills, and abilities gained 

from years on the job. The interview approach was the best 

method of compiling this knowledge. Researchers conducted 

three pilot interviews with machine operators. After 

completing the pilot interviews, the responses were examined 

for possible adjustments to the survey. Only during these pilot 

interviews were minor adjustments made to the survey such as 

rewording a question, changing the question sequence, and 

clarifying visual aids. These adjustments were not likely to 

have changed the responses obtained from the pilot 

interviews, but would contribute to clarity in future 

interviews. 

Survey Structure 

The survey covered two components of the work sequence: 

(a) cutting phase (15 questions) and (b) tramming phase (16 

questions). Illustrations representing 1 of 3 possible mining 

configurations were employed as visual aids. Each illustration 

showed a section layout of a mining work area. The mining 

configurations illustrated were mobile haulage, continuous 

haulage, and full face layouts. Each component of the survey 

was field tested at 7 mine operations to evaluate the relevance 

of the questions to mining machine operators. 

Continuous mining machine (CM) operators were interviewed 

one-on-one or in groups of up to 4. Meeting locations varied 

and included underground near the working face area, above 

ground in a conference room, or in the maintenance shop. 

Interviews took approximately 1-1.5 hours to complete. The 

participants were asked to respond to the questions verbally 

and to mark certain answers on a series of illustrations 

representing the mining configuration at their mine. In 

addition, researchers arranged with the mine management to 

go underground after the interview to observe the operator 

doing their job. The positions the operator used and areas 

frequently looked at during an 8-hour shift were noted by the 

researcher on illustrations identical to those used during 

interviews. These observations of the CM operator were used 

to validate the responses researchers obtained during the 

interview. 

DATA ANALYSIS 

Cue Ranking 

Operator cues, operator position location, and their frequency 

of use were tabulated for each mining configuration using data 

from the interviews. Cue ranking was based on rankings 

provided by operators combined with the frequency of the 

cue's occurrence in the answers to open-ended questions. An 

example of the rankings for the various mining configurations 

is presented in Table 2, which shows a partial list for the 

mobile haulage configuration. There is significant overlap in 

the top six cues for all three mining configurations. 

Overlapping important cues include roof at the face, edge of 

drum, ribs, center line of entry, center line of entry, and 

cutting head bits. 
Table 2. Example of cue ranking for a mobile haulage 

configuration 

Importance Mobile Haulage Configuration 

1 Roof at the face 

2 Right edge of drum 

3 Ribs on right side of miner 

4 Edge of the machine on the side you are on 

5 Center line of entry 

6 Cutting head bits 

7 Floor at the face 

8 Laser beam/spot 

9 Back end of the boom 

10 Center or other point on the drum 

11 Center line of the machine 

12 Left edge of drum 

13 Ribs on left side of miner 

14 Spray nozzles 

15 Haulage vehicle inby bumper 

16 How far the boom swings 

17 Haulage vehicle operator 

*partial list for one of the three studied configurations 

Figure 2 illustrates the operator positions and their frequency 

of use for the mobile haulage layout. 

Figure 2. Available operator positions in cutting mobile 

haulage configuration. 

The most frequent 

operator positions are 4, 5, and 6, which together account for 

48% of the positions taken. Positions 9 and 10, on the left side 

of the miner, provide the best viewing. They are not regularly 

used because they are located in return air, not in fresh air. 

They are used only when ventilation layout dictates. Position 

8, in the center of the entry, was used primarily to determine 

how the mining machine lined up with the center of the entry. 

Position 8 cannot be used while a haulage vehicle is present. 

Similar results were found for the other mining configurations 

and various postures at these positions, depending on the 

height of the coal seam. 

Simulation Modeling 

Researchers used computer simulation tools to determine what 

was blocked from the operator’s view at any of the work 

positions and postures. The operator position and posture data 

was used to define virtual human operator positions in a 

simulated environment. In the computer simulation, a matrix 

of points was used to define the desired visual area. Visual 

cues could be represented as individual points for a cue that 

represented a specific location on the machine, or as multiple 

points for cues associated with a general area such as a rib. By 

representing areas as a matrix of points, the percentage of the 

area seen or blocked from the operator's view, from any 

perspective, could be determined. The virtual operator could 

then be placed in any of the work positions and postures, and 

the matrix scanned by the simulation software (Figure 3). 

Figure 3 Simulated operator with visual cue matrix 

The 

scanning automatically determines which visual cues are seen 

or blocked from any position, and allows a numerical means 

of comparing one work position to another. The positions can 

then be compared to MSHA's data on accident injury 

locations. 

Perspective views from the digital human’s eyes of what the 

operator might see from a given position (Figure 4) allowed 

researchers to analyze the positions and postures of CM 

operators. The perspective views reveal how limited an 

operator’s field of view can be in various positions, postures, 

and mining configurations. For example, the operator’s field 

of view improves the further into the section he or she moves. 

This creates the temptation to move forward for a better view, 

even though doing so may place the operator in an unsafe and 

illegal position, such as underneath unsupported roof. By 

comparing the operator’s view at different operator positions, 

researchers gained insight into the cues CM operators need to 

control the machine safely, as well as positions where 

operators may place themselves at greater risk. 
Figure 4. Perspective view of simulated operator 

Data tables showing (a) the visible percentage of the areas an 

operator wants to see from the operator positions in standing, 

kneeling, or squatting postures and (b) the average percentage 

of individual visual cues visible from all of the operator 

positions were developed for each of the individual mining 

configurations. Comparing the survey and observation data 

with visibility data from the simulations shows that CM 

operators most frequently selected positions that provided 

access to the cues they most wanted to see. The most blocked 

visual cues are the left edge of the cutting drum and the floor 

at the face, while the least blocked visual cues are the haulage 

vehicle operator and the center line of the machine. 

Interventions need to be concentrated at the most blocked cue 

locations. 

From a safety standpoint, the safest positions to stand are 

farthest from the mining equipment, under supported roof, in 

fresh air, not near the ribs, and out of the way of tripping 

hazards and haulage equipment. Positions 2 and 6 best fit 

these requirements, but are only used 30% of the time (Figure 

2). 

DISCUSSION 

The main thrust of this research is to identify the cues that are 

most significant to the operators. Interventions can then be 

developed to enhance these cues so that operators are more 

likely to choose a safe working position. 

The methods of data collection and analysis used in this study 

successfully identify both the work positions and the quality 

of information available to a continuous miner operator. With 

the help of research tools such as computer models and 

simulations to evaluate visual data, the results of this study 

reveal that knowing the work positions and visual needs of 

operators in performing their job can have the potential to 

improve equipment design, machine operating procedures, 

and the areas where interventions would be the most effective. 

Eger et al. (2004) report that the use of the operator’s specific 

locations and visual perspectives as a training tool could assist 

operators in making better decisions on safe work positions. 

Operators should be trained to position themselves in safe 

locations, but they must be able to operate the equipment 

effectively from those locations. Operator position selection 

was determined to be based on the need for operational cues 

and by the dictates of the mining environment. The safest 

positions were only selected 30% of the time, which implies 

that improving other factors could make safer positions more 

attractive to operators. Data comparing the most important 

operator cues with the frequency of a selected operator 

position can now be compared to accident frequency and 

location. 

The ranking of the visual and machine feedback cues allowed 

improved evaluations of each job phase for the most common 

mining configurations, and helped better define the complex 

relationships between visual cues and operator positions. The 

improved understanding of cues used by operators can further 

help the development of interventions. 

The database of survey and observation information provides 

a good representation of operators and mining configurations 

from a cross-section of underground mine operations in both 

eastern and western states. The generated database of position 

frequency allows a comparison of the operator-selected work 

positions with a map of injuries derived from the MSHA 

injury database. How the relationships between cues, position 

selection, and injury occurrences apply in different phases of 

the mining cycle can be used to propose changes to machines 

to enhance operator safety and effectiveness. 

Based on the promising results of this initial study, an indepth study to develop interventions to improve safety of 

operators is underway. Results indicate that the survey and 

underground observations were a good combination and 

technique to develop a database of important visual cues and 

locations an operator wants to see from a given work position 

and posture. An analysis technique that determined how much 

of a particular area an operator sees from a variety of positions 

and postures in a computer simulation was shown to be 

potentially useful. The mining industry now has a tool to 

design work practices and section layout. The study could also 

influence equipment design or selection for improved worker 

safety through training. 

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