WORK SAMPLING APPLIED TO A HUMAN FACTORS ANALYSIS OF 

MINE WORKER POSITIONING 

Lisa Steiner 

Kim Cornelius 

Fred Turin 

Dara Stock 

NIOSH, Pittsburgh Research Laboratory 

Pittsburgh, PA 

Growing concern from labor unions, regulatory agencies, and industry about the 

safety of a prevalent underground coal mining method which utilizes remote control 

has prompted human factors field evaluation of mining activities. Remote control 

operations were implemented with little consideration given to human-system 

interactions. Ideally, collecting and analyzing information prior to implementing 

new technology would have helped to address potential problems. One such problem 

that operators and other mine personnel are faced with is the question of where they 

should safely position themselves to avoid injury while remotely operating 

machinery. To determine work methods employed by machine operators before and 

after implementation of the new method, work sampling techniques have been used 

to provide data about positioning of face crew members at different points in the 

mining cycle. This data provides information for optimal positioning, leading to safer 

operating procedures and identifying training shortfalls. 

INTRODUCTION 

As with many industries, mining companies 

implement new technologies as they are developed 

to increase productivity and reduce costs. These 

technologies require evaluation to determine what 

unintended effects these new methods, machinery 

and interfaces have on mine workers. Extended cut 

mining, the primary method for coal extraction and 

mine development, uses remote control technology 

to allow the operator of the cutting machine to cut 

up to twice the horizontal distance than was 

permitted by manual on-machine operation. The 

mining industry readily adopted widespread use of 

the new method due to its productivity 

enhancements and its promise to keep operators 

farther from the hazards of unsupported mine roof. 

As such, the mining machine operator is no longer 

exposed to the shock and vibrations of the machine 

and is free to move about the worksite to facilitate 

visibility of the task. This same freedom has at 

times, exposed the operator to new hazards such 

as moving equipment and unpredictable roof and 

rib conditions. 

Growing concern about extended cut 

mining was expressed by the United Mine 

Workers of America (UMWA), Mine Safety and 

Health Administration (MSHA), state regulatory 

agencies and mining companies due to its possible 

contribution to several mining fatalities occurring 

from 1988 to 1995 (Bauer et al., 1997). Since 

available data on non-fatal injuries is insufficient 

to provide information about root causes or details 

of operators’ actions, it was not possible to relate 

safety issues directly to extended cut mining and 

the specific tasks that were performed. Why 

operators choose to position themselves in 

particular areas that may increase the risk of injury 

could not be determined. Analysis of continuous 

miner operators/helpers/trainers fatalities from 
1988-1995 reveal that 33% are from roof falls and 

23% from being crushed by the machine and other 

moving equipment. These incidents are a result of 

poor operator positioning. 

THESIS 

This paper discusses the application of a 

quantitative engineering task analysis tool, work 

sampling, supplemented by qualitative interview 

data to determine whether operators position 

themselves in unsafe areas while operating 

machinery because of the length of cut permitted. 

Data from the sampling reveals the feedback 

operators need to effectively operate machinery 

remotely. This method could also be used to predict 

hazards associated with method and equipment 

changes in the design phase before implementation. 

SOURCES OF INFORMATION 

A previous work sampling study performed 

by Bureau of Mines researchers revealed that 

continuous miner operators were standing in 

positions that were not recommended by their 

standard operating procedures because of their 

inability to observe operations effectively from the 

recommended positions (Love and Randolph, 

1992). This study was not concerned with extended 

cut mining per se, but rather with remote control 

mining. The study suggested that in comparison to 

taking cuts straight on, there was more operator 

position variability when turning the machine to 

begin a crosscut. Unfortunately, the number of 

observations was insufficient to draw conclusions. 

The study clearly showed that there are substantial 

differences between operator’s actions and the 

company’s safe operating procedures (SOP). 

However, further investigation of SOPS developed 

by mine companies revealed that detailed operator 

location information was lacking and it was difficult 

to make more specific comparisons of the work 

sampling observations and the SOP. 

Interviews were conducted with 1.55 miners 

at 7 mines to examine general safety issues in 

extended cut mining (Steiner et al, 1994). The 

interview data revealed that most mine workers 

were in favor of extended cut mining. However, 

operators again expressed concern about the safety 

of their location (especially when turning the 

machine), their inability to see the machine’s 

cutting head in some situations, ineffective 

lighting on the machine, and difficulties with 

performing certain maintenance tasks. 

In order to determine the work methods 

employed by continuous mining machine 

operators and the effects of extended cut mining 

methods, more detailed work sampling techniques 

were developed. Work sampling or activity 

analysis was appropriate in this situation because 

the tasks were easily defined, not highly repetitive, 

and cycle times were of proper duration (Kirwan 

and Ainsworth, 1992). Fixed interval sampling 

was used to document work methods and 

exposure to hazards (Keyserling, 1997). Due to 

the inherent variable conditions in underground 

mining, direct task observation in the field was 

essential. To specifically determine what effects 

extended cut mining had on miner operators’ 

habits, mines were identified that had not yet 

implemented extended cut technology, but were 

preparing to start. It was determined that useful 

information could be collected using work 

sampling techniques by examining mines both 

before and after implementing the longer cuts. 

The activity analysis was adapted to collect data 

regarding the face crew’s location at different 

points in the mining cycle, since operators and 

other crew members are faced with the question of 

where they should safely position themselves 

while machinery is being operated remotely. The 

most important factors influencing position were 

visibility, geological conditions, ventilation, 

positions of other mine workers, and moving 

machinery. The optimum location for an operator 

to stand may differ depending on the length of cut, 

type of cut, and a number of other variables. 

The goal of the work sampling method 

was to identify differences in operator positioning 

in standard versus extended cuts providing insight 

to the habits of the operator and reasons for 

differences in habits. In particular, it was 

necessary to determine what cues and information 

were used by operators to decide where to stand at 

what point in the mining cycle. The locations of 

workers and equipment at the face area were 
recorded along with the direction the operators were 

looking and at what stage they were in the mining 

process. Based on the observations made, verbal 

descriptions from the operator were recorded 

immediately following the observations to explain 

any unusual actions or safety discrepancies the 

operator performed during the observation periods. 

Case studies were conducted at two mines 

identified by MSHA as having applied for extended 

cut approval but were still in the approval process. 

The work sampling process was applied both before 

and after extended cut operations were approved 

and implemented. Observations were taken over 

several days with the same continuous miner 

operators and helpers for each condition so data 

were comparable. This reduced operator variability 

and the observer effects. Observations every three 

minutes prompted by a programmable beeping 

source. Fixed interval sampling was used at this 

rate due to the relatively slow changes in operator 

position and the extensive amount of data being 

collected. Videotaping of operator activities is 

virtually impossible 

in this environment 

due to low lighting 

and visual 

obstructions by 

machinery and 

people. Data was 

collected on graph 

paper pre-drawn 

with mine 

dimensions and 

machines. Operator 

positioning was 

recorded with 

respect to the 

mining machine. 

Zones were defined 

before field 

evaluations to make 

Figure 1. Miner Operator 

Zones Defined With Respect to 

recorded Mining Machine. 

positioning less 

vague (Figure 1). The type of data collected 

included: who was in the activity area, where they 

were located with reference to the machines, what 

they were doing according to previously defined 

activity codes, operator’s direction of view, and any 

discrepancies or violations observed. Data was 

collected over a four-day period for mines both 

before approval was granted for extended cut and 

again several months after approval was granted to 

allow for sufficient learning time. The sampling 

covered 30 cycles in the pre-approval status (15 

cycles at each mine) and 24 cycles in the post 

approval status (10 and 14 cycles at each mine). 

Researchers were also interested in whether 

management would provide training or institute 

additional safety precautions as a result of their 

change to extended cut mining. 

FINDINGS 

Several comparisons were made including 

operator differences between mines both before 

and after extended cut approval, operator 

positioning differences within mines but based on 

extended lengths of cuts and shorter lengths of 

cut, and operator positioning during the first 

twenty feet of the cut and the final twenty feet of 

the cut. These comparisons are made to determine 

whether taking an extended cut changes the 

actions of the operator and if it is necessary for 

operators to stand in particular positions in order 

to effectively operate equipment. 

Large differences were not evident among 

individual operators between the before and after 

extended cut approval conditions. In fact, 

operators preferred to stay in the same position, 

#lo, with reference to the machine during the first 

twenty feet of the cut regardless of the permitted 

length of cut. Zone #lO is an area 7’ by 8’ located 

at the right rear corner of the machine (Figure 2). 

During turning operations, operators stay in zone 

#lO unless they are in the first cut of turning the 

machine towards the left (with the cable and 

ventilation set up on the right side of the entry). 

In this case, one mine’s operators stand in zones 9 

and 11, sacrificing fresh air and visibility of the 

mining cable for better visibility of the cutting 

head when aligning the first cut. Turning a 

crosscut appears to be the most variable and 

difficult task for operators regardless of length of 
cut. The first two cuts of the crosscut were critical 

and required the most skill. Operators tended to 

stay further behind the machine during longer cuts. 

Operators are not allowed by law to go past the last 

row of roof supports. The longer cuts place the 

Figure 2. Continuous Mining Machine in Cut Two of 

a Right Crosscut 

machine away from the operator but the operator is 

not allowed to follow the machine into the cut. In 

this case, he has no choice but to operate from a 

further distance. Several safety discrepancies were 

observed including backing out the equipment while 

standing too close, failure to check for methane, 

standing in pinch points between the machine and 

the rib, and accidently going beyond roof supports. 

DISCUSSION 

The observations helped to define the 

preferred location of operators while mining straight 

ahead and while turning. Operators prefer zone #lO 

when the mine is set up with the ventilation and 

mining cable on the right side. The mirror image is 

also true. Operators tend to place themselves in one 

particular spot for the entire sequence unless there 

are unusual tasks that need to be performed. 

Operators prefer zone #lO because it allows them to 

receive the vibratory and auditory feedback they 

need to determine if the cutting head is in rock or 

coal. Also, because operators were used to riding 

on the deck of the machine, and they may prefer to 

stay rather close to that original location. The 

lighting scheme on the machine influences 

operator positioning since the lighting is still 

designed for on-deck operation. This is a major 

problem for the operator. If the lighting were 

redesigned to illuminate the necessary visual 

attention locations, the operator would have more 

freedom for positioning. The operator also likes 

to stand in fresh air and be able to attend to the 

miner power cable. If the miner or the haulage 

operator runs over the cable, power can be cut off 

to the machine causing production delays. 

Though operators have chosen this position for 

many reasons, it is not necessarily the safest with 

respect to human factors considerations. While 

operators have definite position preferences, those 

preferences may be based mostly on habit. In 

several mines visited after the work sampling 

study was completed, operators were observed 

standing two to three feet behind the machine 

(zones 18, 19, 20 and beyond) when cutting coal, 

and said they were able to operate effectively. In 

this work sampling study, operators were 

effectively operating from behind the machine 

when they were legally required to do so. This 

suggests that it may be possible for more skillful 

operators to stay further back from the machinery 

and unsupported top and still operate effectively. 

It also suggests that less skillful operators can be 

trained to stand in safer zones thus reducing the 

exposure to crushing injuries and roof falls. 

Since most fatalities occur when the 

operator goes beyond the last row of roof supports 

or when the operator is pinned between the 

machine and the rib, it is critical that operators 

avoid those locations. The injury data show that 

operators of remote control machines are more 

likely to be injured by being struck by the machine 

than by roof falls. Being struck by the machine 

usually happens while taking the first twenty feet 

of the cut. Being struck by unsupported roof 

usually occurs while taking the next 20 feet of the 

cut. The main threat to safety in extended cut 

mining resides in the use of remote control 

technology. The majority of injuries occur during 

the turning operations, i.e., during the first twenty 

feet of the cut. This study highlights the difficulty 
of taking turns, the danger of using remote control 

while in close proximity of the machine, the types 

of sensory feedback operators need, and suggests 

reasons for operator preferences and habits. 

The data collected has prompted some 

changes to be implemented and others are in the 

research phase. The information has been used at 

these mines to develop more explicit safe operator 

procedures for continuous miner operators and 

helpers. NIOSH is currently using this data to 

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Figure 3. HASARD Two-Zone Operator Warning 

System 

develop and test a device, HASARD (Hazardous 

Area Signaling and Ranging Device), to warn 

operators when they get too close to mining 

equipment (Figure 3). HASARD is an electronic 

warning system that warns operators at three levels: 

a safe zone, a caution or warning zone, and a danger 

zone. In the warning zone, operators can make a 

decision to step back into the safe zone or continue 

moving closer to the mining machine into the 

danger zone which will shut down the tramming 

function of the machine. The feasibility and 

practicality of this system from a human factors 

perspective is being determined at this time. 

HASARD can also be used to train new equipment 

operators to form safe habits and learn to rely on 

feedback while staying a safe distance from the 

machine. Although HASARD will not prevent 

miner operators and helpers from going under 

unsupported top, it will address the issue of being 

pinned between the rib and the mining machine. 

Also, the machine’s lighting scheme needs to be 

redesigned to improve illumination of critical 

areas. Some of the pinning/crushing injuries and 

roof fall injuries are a result of operators trying to 

see what they need to see. Improved illumination 

could help to reduce these injuries as well. The 

engineering technique adapted to identify risk 

factors in mining could be applied in many 

manufacturing situations where a change in work 

methods and equipment is forthcoming. This 

information could help to predict problems and 

prevent injuries before implementation of the 

proposed change. 

REFERENCES 

Bauer, E.R., Chekan, G.J., and Steiner, L.J. 

(1997). Stability Evaluation of Extended 

Cut Mining in Underground Coal Mines. 

Int J. Rock Mech. & Min. Sci., 34, 3-4, 

Paper No. 302. 

Love, A.C. and Randolph, R. F., (1992). Radio 

Remote Control Continuous Miner 

Operator Positioning. In Proceeding of 

Symposium of Annual SME Meeting (pp. 

124- 132). Society of Mining Engineers. 

Keyserling, W.M., (1997). Sampling Strategies 

for Ergonomic Job Analysis. In 

Ergonomics: Job Analysis and Field 

Studies Handbook. University of 

Michigan, Center for Occupational Health 

and Safety Engineering. 

Kirwan, B. and Ainsworth, L.K. (Eds.). (1992). 

A Guide to Task Analysis. London: Taylor 

and Francis Ltd. 

Steiner, L.J., Turin, F.C., and Hamrick, C.A. 

(1994). Ergonomic and Statistical 

Assessment of Safety in Deep-Cut Mining. 

In Improving Safety at Small Underground 

Mines (pp. 124- 132). Special Publication 

18-94. U.S. Department of Interior, 

Bureau of Mines. 

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