Ergonomics 

Using Ergonomics to Enhance Safe

Production at a Surface Coal Mine —

A Case Study with Powder Crews

Column Editor 

Leo Old

Reported by 

Janet Torma-Krajewski,1,2 

1National Institute of

Occupational Safety and Health

(NIOSH), Pittsburgh Research

Laboratory, Arvada, Colorado

2Currently with the Colorado

School of Mines, Golden,

Colorado

Fred Turin,3 

and Richard Unger3 

William Wiehagen,3,4 

3NIOSH, Pittsburgh Research

Laboratory, Pittsburgh,

Pennsylvania

4Retired

Ann Etcheverry,5,6 

5Bridger Coal Company, Point of

Rocks, Wyoming

6Currently with EnCana, Rock

Springs, Wyoming

Job tasks that involve exposure to work-related musculoskeletal disorder (WMSD)

risk factors may impact both the risk of injury and production downtime. Common

WMSD risks factors associated with mining tasks include forceful exertions, awkward

postures, repetitive motion, jolting and jarring, forceful gripping, contact stress, and

whole body and segmental vibration. Mining environments that expose workers to

temperature/humidity extremes, windy conditions, and slippery and uneven walking

surfaces also contribute to injury risk. National Institute for Occupational Safety and

Health (NIOSH) researchers worked with powder crew members from the Bridger

Coal Company to identify and rank routine work tasks based on perceived exposure

to WMSD risk factors. This article presents the process followed to identify tasks

that workers believed involved the greatest exposure to risk factors and discusses risk

reduction strategies. Specifically, the proposed prill truck design changes addressed cab

ingress/egress, loading blast holes, and access to the upper deck of the prill truck.

INTRODUCTION 

From January 2001 to January 2005, personnel from NIOSH and Bridger Coal 

Company collaborated on a process to implement ergonomics as an element of 

the safety and health program at the Jim Bridger Mine, a surface coal mine located 

in southwest Wyoming. In general, the collaboration involved two approaches. For 

the first approach, Bridger, with support from NIOSH researchers, implemented a 

proactive process to identify and reduce WMSD risk factors before the risk factors 

resulted in discomfort and pain. This process has been described elsewhere.(1−3) As 

part of the process, a training program was developed and implemented by NIOSH 

and Bridger to impart skills within the Bridger work force that would help them 

identify WMSD risk factors associated with their work tasks. As part of this training, 

an interactive exercise was designed to present work scenarios, identify plausible 

WMSD risk factors, and explore options (e.g., engineering controls, work procedures) 

to reduce the frequency, level, or duration of risk factors. 

For the second approach, NIOSH, with support from Bridger employees, analyzed 

work tasks performed at the Jim Bridger Mine to identify and study equipment design 

interventions that could reduce exposures to WMSD risk factors. This article discusses 

the results of NIOSH’s work with the powder crews. 

Powder Crews and Work Tasks 

At the Jim Bridger Mine, two powder crews (six members each) worked 12-hr 

shifts, 7 a.m. to 7 p.m., on a straight 4-day rotation (4 days on, 4 days off). Table I provides age and experience data collected for the powder crews. The general functions 
12

of the powder crews were to use explosives to break up 

overburden and parting, which could then be removed by 

draglines and dozers to expose coal seams, and to break 

up coal seams so that the coal could be loaded into haul 

trucks. 

TABLE I. Demographic Information for Powder 

Crew Members 

Years Mining Years on

Age Experience Powder Crew

Average 41.6 14.4 .8 

Std Dev 9.4 8.7 9.1 

Min 24 1 1 

Max 51 25 25 

Note: Powder crew members (N = 11); one position vacant. 

Information obtained from mine management and the 

safety department indicated that powder crews performed tasks 

that were physically demanding, particularly when they were 

exposed to extremes in weather conditions. A general outline 

of powder crew tasks is shown in Table II. Work duties were 

rotated among crew members within each crew. 

Crew productivity was assessed using the number and 

depth of blast holes loaded and shot from January 2001 

through August 2002. The three types of holes loaded and 

shot included: 

1.	 Overburden. Mean depth was 26.2 m with a mean of 

835 holes loaded and shot per month. 

2.	 Parting. Mean depth was 11.5 m with a mean of 1552 

holes loaded and shot per month. 

3.	 Coal. Mean depth was 3.4 m with a mean of 3983 holes 

loaded and shot per month. 

The monthly range of work completed (total depth of holes 

loaded and shot) was quite large—from 21,204 to 90,640 m 

per month. The monthly mean was 48,036 m loaded. 

Tools, Equipment, and Materials Used by the 

Powder Crews 

Powder crews were assigned four prill trucks and three 

powder trucks. The prill trucks were used to transport 

ammonium nitrate prills, fuel oil, and emulsion to the blasting 

site and then to mix and load the holes with a blend of these 

materials. These trucks varied appreciably in age, physical 

features, and performance, which influenced how the crew 

interfaced with the operating controls for driving the truck and 

dispensing the explosive fuel oil mixture. 

Powder trucks were four-wheel drive pickup trucks 

equipped with crew cabs, and all three trucks were very similar 

in design and operation. Powder trucks were used to transport 

the blasting components (e.g., detonating cord, primers, and 

delays) from the magazines to the blasting site and to transport 

crew members.	 

Blasting components were stored in several magazines 

at two locations on mine property. The components were 

typically packaged in boxes weighing from 30 to 60 lbs. 

Deliveries occurred about once per week, and crew members 

assisted the vendor in off-loading components. Ammonium 

nitrate prills and emulsion were stored in silos that were similar 

in design. 

METHODS 

NIOSH personnel observed members of both crews 

and had numerous informal conversations with crew 

members to determine the scope of their duties and derive a 

sequential listing of work tasks (Table II). From this listing, 16 

discrete tasks were identified that involved potential exposures 

to WMSD risk factors. 

The method used to select tasks for possible redesign 

was based on a process that maximized employee involvement through individual and group discussions with both 

powder crews. These crews were quite experienced and had 

excellent knowledge of their job tasks. NIOSH believed that 

involving the crews would result in more direct use of their 

knowledge and skills and build ownership of potential design 

changes. 

Individual Rating of Work Tasks 

To obtain individual ratings, NIOSH personnel interviewed 

each crew member. The crew members were asked to rate each 

of the 16 tasks using a five-point scale, with 1 being “very 

easy,” and 5 being “very difficult.” When numerically rating 

each task, the crew members were asked to think in terms of 

their exposure to WMSD risk factors (based on ergonomics 

and risk factor awareness training). For example, what tasks 

required the greatest physical effort, extreme postures, and/or 

many repetitions of the same movements. Crew members 

were also asked to comment qualitatively on the tasks— 

what did they dislike about doing a specific task. The mean 

individual ratings and the number of negative comments 

about a task were summed to obtain a combined score for 

that task. 

Group Rankings of Work Tasks 

A series of short meetings with each of the two powder 

crews provided an opportunity to present and discuss the 

results of the individual ratings. During the meetings, each 

crew was asked to rank the top six individually rated tasks 

in order based on exposure to WMSD risk factors, with 1 

being the most difficult task and 6 being the least difficult 

task. 

Crew Interviews — Prill Truck Designs 

A final meeting was held with each powder crew to 

discuss features of all four prill trucks. This session allowed 

individuals and the group to comment and discuss preferences 

concerning operator interface, such as the design of steps and 
handholds, the ladder, and other features involving seating and 

control layout. 

TABLE II. General Workflow for Shooting Overburden, Parting, and Coal 

Tasks Comments

Prepare assignments 

Pick-up components 

Inspect prill truck 

Survey site 

Tape holes 

Stem bottom of holes with shovel or skidder 

Prime holes 

Load holes 

Tape holes to check ANFO column for each 

overburden and parting hole 

Stem top of holes with shovel or skidder 

Examine loaded pattern – prepare for shot 

Tie off holes 

Insert delays 

Check tied off pattern 

Position crew members 

Prepare to shoot 

Shoot pattern 

Check shot for misfires 

All clear communication 

A planning task for determining and coordinating crew member 

responsibilities. 

Lead blaster gets components from the magazines. Inventory management. 

Crew members check out and, if okay, drive one or more prill trucks to site. 

Crew adds ammonium nitrate prills, fuel oil, and emulsion as necessary. 

Crew members examine site prior to loading holes. 

Crew members check to see if hole depths match up with the specifications 

for a given work area and to determine the presence of water in the drill 

holes. De-water as necessary. 

Amount is dependent on results of taping holes. Actual hole depth should 

match depth of the specific blasting plan. 

Dependent on the specific blasting plan 

Use prill trucks – calculate and dispense specific amount of ANFO 

(ammonium nitrate and fuel oil) and/or ANFO emulsion blend to each 

hole in the pattern. 

Prill truck operators perform this task – exit truck, measure overburden or 

parting hole, add ANFO or blended product as necessary. 

Dependent on the specific blasting plan 

Determine blast area and set cones. 

Dependent on the specific blasting plan 

Dependent on the specific blasting plan 

Communicate among crew members while walking pattern. 

Strategic locations are chosen to prevent others from entering area. 

Follow established communication protocol. 

Following communication and warning protocols 

Lead blaster, crew members 

Lead blaster 

Physical Measurements and Videotaping of Tasks 

Physical measurements were obtained for each of the prill 

trucks to determine differences among the trucks and to 

identify designs that likely exacerbated exposure to WMSD 

risk factors. Video recordings of tasks were taken to identify 

postures associated with getting in and out of the truck cab, 

use of the ladder, and loading coal holes. The measurements 

and observations allowed NIOSH to describe the variability 

in truck design and to identify potential negative or positive 

consequences of this variability. 

RESULTS 

Rating and Ranking of Work Tasks 

Individual Ratings

The results of the individual numerical rating appear in 

Table III. The range of the mean ratings was from 1.5 to 2.9. 

In general, these numerical ratings were relatively low when 

compared with the maximum possible score of 5. Overall, 

combined scores, derived by adding the mean numerical rating 

with the number of negative comments about the task, ranged 

from 2.1 to 12.9. Six tasks received a combined score of 9 or 

greater. Five of these six tasks were routine tasks performed 

for every drilling and blasting pattern. NIOSH ranked these six 

tasks as the first priority for a more in-depth discussion with 

each powder crew. 

Group Rankings of Work Tasks

Table IV summarizes the results of the crew discussions. 

Both crews’ rankings were very similar. Two of the tasks were 

ranked the same by both crews, while the other four tasks were 

within one ranking of the other crew. 

The highest-ranked task, tying off coal holes, was discussed 

with each crew. To perform this task, crew members repeatedly 

stooped to tie off the shot at each blast hole. Discussions 

with the crews implied that this task did not lend itself to an 

engineering solution that could reduce the frequency, level, 

or duration of the primary risk factor (awkward postures). 

Therefore, this task was often performed by all crew members. 

This administrative control served to reduce the frequency, 

level, and duration of exposure for any one crew member. 
From the individual ratings and group rankings (Tables III 

and IV), three of the six tasks with the greatest exposure to risk 

factors involved the use of the prill trucks. Because the designs 

(and variability in design) of the prill trucks were suspected 

5

5

5

5

as contributing to the difficulty of these tasks, the prill trucks 

were selected as the subject for design interventions. 

TABLE III. Rating of Tasks by Individual Powder Crew Members (N = 11) 

Task Mean Rating Number of Negative Comments Combined Score Priority Ranking

Stemming bottom of holes 

Off-loading and stacking supplies 

in the magazine from the delivery 

truck 

Climbing in and out of the prill 

truck cab 

Climbing up and down the ladder to 

fill the prill truck 

Tying off holes 

Driving prill truck while loading 

holes 

Filling the prill truck with 

ammonium nitrate prills 

Taping holes 

Chocking truck wheels 

Stemming top of holes 

Priming holes 

Driving the prill truck to the site 

Pre-shift inspection of prill truck 

Loading holes with ANFO 

Driving supply (explosives) truck to 

site 

Loading supply truck 

2.9 

2.9 

2.5 

2.4 

2.4 

2.2 

1.9 

2.1 

2.1 

2.1 

2.0 

1.6 

1.6 

1.7 

1.5 

2.1 

10 

8 

8 

8 

7 

7 

5 

3 

3 

2 

2 

2 

2 

1 

1 

0 

12.9 

10.9 

10.5 

10.4 

9.4 

9.2 

6.9 

5.1 

5.1 

4.1 

4.0 

3.6 

3.6 

2.7 

2.5 

2.1 

1 

1 

1 

1 

1 

1 

2 

2 

2 

2 

2 

3 

3 

3 

3 

3 

TABLE IV. Group Ranking of Top Six Tasks According to Exposure to WMSD Risk Factors 

Task

Crew A

Ranking

Crew B

Ranking

Average

Ranking

Tying off (coal) holes 

Driving prill truck while 

loading (coal) holes 

Stemming bottom of 

overburden holes 

Climbing in and out of the 

prill truck cab 

Climbing up and down the 

ladder to fill the prill truck 

Off-loading the delivery truck 

and stacking components in 

the magazines 

1 

2 

3 

4 

5 

6 

1 

3 

2 

4 

6 

5 

1 

2.

2.

4 

5.

5.

Description of Top Ranked Work Tasks 

Loading Blast Holes

To complete this task, the operator must align the auger, 

which delivers a pre-set amount of explosive mixture, directly 

above the blast hole. Because the auger is located on the left 

rear of the prill truck, the operators have to twist and look over 

their left shoulder each time a blast hole is loaded. For each 

hole, the operator twisted twice to look over the left shoulder. 

The first time was to spot the auger over the hole; the second 

time was to make sure the ANFO was completely dispensed 

before moving onto the next hole. Side-view mirrors were not 

useful in accurately spotting the auger over the holes. 

Meanwhile, the controls for delivering the explosive 

mixture were located in the cab, behind the operator, to the 

right of the driver’s seat. Because the locations of the auger 

and the positioning controls were behind the operator, this task 

resulted in exposures to extreme awkward postures. 

Considering all three types of blast holes, this short duration 

(twisting and reaching) task was done an average of 12,740 

times per month (6370 holes loaded per month). The awkward 

twisting posture averaged 1062 times per month per crew 

member. Coal holes were more difficult to spot accurately 
due to the relatively small diameter hole, which took a few 

seconds longer. The monthly average was 3983 holes, or 664 

awkward postures per month per crew member. 

Climbing In and Out of the Cab

Throughout the shift, crew members needed to climb 

in and out of the prill truck cab to complete work tasks. 

Entering and exiting the cab was done most frequently when 

the crew members loaded overburden and parting holes and 

while placing additional blasting components into the holes. 

These tasks could not be completed from inside the cab, since 

the level of the ANFO column had to be measured to ensure 

the correct amount was loaded into each hole. 

The crews estimated they climbed in and out of the cab from 

10 to 90 times per day, with 30 being the daily average. The 

physical exertion required to climb in and out of the cab was not 

measured but likely contributed to the overall difficulty of this 

task. The design of the prill truck steps and handholds, which 

varied among the trucks, also increased the overall difficulty 

of this task. Problematic design features specific to one or 

more of the prill trucks included (1) the first step was too high; 

(2) handholds were not located within easy reach, or too few 

handholds resulted in operators using the steering wheel as 

a handhold; and (3) the steps were fairly narrow, which did 

not allow for secure footing when entering or exiting the cab. 

In effect, the design of the prill trucks increased the level of 

physical exertion and resulted in the use of awkward postures 

in performing this short-duration but frequent task. 

Climbing Up and Down the Ladder

To fill the trucks with ammonium nitrate and emulsion, the 

driver climbed the ladder located at the back of the truck to 

open and close the covers and fill the bins. When climbing 

up and down the ladder, the crew members faced toward the 

truck. The risk factor exposure associated with this task was 

the physical exertion required to climb up and down, as well 

as the ability to maintain balance while climbing. Specific 

design features that added difficulty or risk factor exposures in 

performing this task included (1) the angle of the ladders, (2) 

location and spacing of the handrails, (3) a high first step from 

the ground to the platform supporting the ladder, and (4) the 

transition from the top of the ladder to the upper work deck. 

Prill Truck Design Issues 

Crew Interviews Regarding Prill Truck Designs

Table V summarizes the results of the crew meetings. As 

expected, all of the trucks had some negative design features 

as assessed by crew members. Prill Truck D, which was the 

newest truck, was considered the best (far better ride and 

comfort) of the four prill trucks. Of note, Truck D also had a 

few negative comments, and some features on the older trucks 

(e.g., the ladder design on the Truck B) were rated a superior 

design in comparison with the newer Truck D. 

Physical Measurements

The trucks varied significantly in the design features used 

to drive the vehicle, dispense the explosive fuel oil mixture, 

enter or exit the cab, and gain access to the storage tanks. 

These design differences required operators to adopt different 

postures when (1) climbing into or out of the cab, (2) ascending 

or descending the access ladder to storage tanks, and (3) 

locating (spotting) the auger over the hole (target) to be loaded. 

Table VI provides measurements affecting cab ingress and 

egress and ladder use. 

Proposed Design Changes

NIOSH proposed three design changes for the prill trucks 

used at the Jim Bridger Mine. A summary of the proposed 

interventions is provided in Table VII. The anticipated benefits 

of the proposed interventions included reduced risk for slips 

and falls, decreased physical exertion, reduced number of 

awkward postures, and improved ease of use. 

DISCUSSION 

I

n this case study with the Bridger powder crews, employee 

participation was critical, as the proposed prill truck 

interventions involved not only the equipment and tools used 

but also how the crews used the tools and equipment to perform 

the tasks. Participatory ergonomics, promoted by NIOSH as a 

significant element in successful ergonomic processes, can 

take several different approaches, ranging from individual 

employee input to membership on formal companywide 

committees.(4) In many cases of participatory ergonomics, employee involvement has been at the committee and workgroup 

level. While the ergonomic process implemented at Bridger 

followed this model, participatory ergonomics was taken a 

step further in determining interventions for the powder crew. 

The powder crew members were involved in many steps 

of the process followed to select appropriate interventions. 

Employees (1) identified tasks that involved exposure to 

WMSD risk factors, (2) ranked these tasks based on perceived 

level of risk factor exposure, and (3) identified critical design 

features that impacted the risk associated with performing 

these tasks. The main advantage of following this approach was 

to enhance the acceptance level of interventions. The success of 

ergonomic interventions often is determined not by the efficacy 

of the design alone but also by the acceptance and proper 

use of the interventions by employees. In this case, every 

member of both powder crews had multiple opportunities to 

provide input. 

Involving employees can also provide access to a wealth of 

information about the work tasks and equipment, particularly 

when the employees are experienced. In the case of the powder 

crews, the average work experience on the powder crew was 

13 years. Employees provide a perspective that may be missed 

if they are not involved in the process. 

Individual employee participation at multiple steps also has 

a few disadvantages. First, this approach is workable only 

when the number of employees affected by the intervention is 
TABLE V. Crew Discussions Regarding Positive and Negative Features of the Prill Trucks 

Prill Truck Ingress/Egress Ladder Loading Coal Holes Control Location Mirrors Seats

A + – – – 

–

– – 

Year of mfr. 1992 Steps are even, good Vertical climb, easy Longest truck, more “T” handle controls Concave mirrors Cab not roomy 

location of to hit your butt difficult to maneuver, are opposite in too small enough handholds, steering when you climb or PTO control outside, different trucks + wheel is easily descend auger switch and + Ride comfortable 

accessible computer controls are good “T” handle 

in a difficult position design 

B – 

+ + – + and – – 

Year of mfr. 1999 Too high to climb Once you get to the PTO inside, easier to Button fixture, fixed Mixed within Seat belt does not 

bumper, it is easy run, toggle switch for position above arm and across the move at seat, to climb due to the throttle set control crews poor suspension, slanted ladder and hard ride, rough good rungs and ride when full or handrails empty 

+ Good ride when 

fully loaded 

C –– – – – 

–

– – 

Year of mfr. 1995 Steps are too narrow, Vertical climb Reset, cannot monitor “T” handle controls Mirrors old and Poor suspension 

poor location and fuel% from inside are opposite in too small –– 

narrow door + different trucks Not very adjustable, 

Outside auger control + no adjustment for 

Good “T” handle the seat back 

design 

D – 

– – + 

+ + 

Year of mfr. 2002 Would be better if it had Slanted ladder, but Throttle set control not Button shifter Good types of Cab bigger, more 

outside handholds bad handrails and easy to use or reset, console mounted mirrors, larger comfortable, 

+ hook at the top auger too short, to seat, cab bigger and wider, adjustable seat Good steps and height (where you cannot monitor fuel% broader ++ 

transition to the from inside visibility Good suspension upper deck) + 

Good control, outside 

auger control 

Comments Frequency of ingress Mirrors have 

and egress estimated improved with between 10–90 times each new per day. An average truck of 30 times per day 

Notes: Comments were qualitatively rated by NIOSH as either a positive or negative statement. If multiple workers repeated the same comment, that comment was rated as either a double negative or double positive (+ is a positive, – a negative, – – is a double negative, and ++ a double positive). PTO = power take off. 
limited. As the number of employees increases for a particular 

work activity, the amount of data gathered and processed could 

become unmanageable without applying more sophisticated 

statistical methods. Another disadvantage is the amount of 

time required to collect and process the input received from the 

employees. Obtaining employee input added several steps to 

the process, and because of rotating work schedules, additional 

visits to the mine site were needed to coincide with specific 

crews being on duty and accessible to participate in the 

interviews and meetings. 

Using prill trucks to load blasting holes was considered by 

the powder crews to be far superior to hand loading. However, 

the prill trucks, as designed, resulted in exposures to WMSD 

risk factors. Obviously, some risk will always be present. New 

equipment and tools often reduce risk but can bring a different 

set of problems and exposures. 

TABLE VI. Prill Truck Measurements Relevant to Cab Ingress/Egress and Ladder Use 

Task	 Truck Feature

Prill Truck

A B C D

Climbing in and out 

of truck cab 

Climbing ladder 

Size of steps 

Location of steps 

relative to truck door 

Distance from ground 

to first step 

Distance from first step 

to second step 

Distance from second 

step to floor of truck 

Offset between steps 

Angle of ladder 

Distance from ground 

to first step/rung 

Distance between first 

and second 

steps/rungs 

129.5 × 10.2 

63.5 cm to right 

of door 

50.8 

43.8 

43.2 

2.5 

82◦ 

43.2 

28.6 

83.8 × 12.7 

20.3 cm to right 

of door 

55.9 

45.7 

45.7 

6.4 

68◦ 

63.5 

57.2 

100.3 × 11.4	 

61.0 cm to right	 

of door	 

44.5	 

43.2	 

35.6	 

2.5 

90◦ 

34.3	 

36.8	 

91.4 × 12.1 

27.9 cm to right of door 

(top) 33.0 cm to right 

of door (bottom) 

42.5 

48.9 

34.9 

7.6 

75◦ 

62.2 

31.8 

Note: All measurements are in centimeters unless labeled otherwise. 

TABLE VII. Proposed Prill Truck Design Interventions 

Proposed Intervention Design Considerations Anticipated Benefits

Redesign the ladders used to access the top of Tread type, size and spacing, Reduced slip and fall risk, and 

the prill truck handrail design, mounting and improved ease of use 

dismounting, and vertical angle 

Redesign handholds for getting in and out of Location and size Reduced slip and fall risk, 

cab decreased shoulder and arm 

exertion, and improved operator 

comfort 

Redesign steps for getting in and out of the cab Location, size, and type of tread Reduced slip and fall risk and 

reduced exertion 

Use remote camera for verifying the alignment Complexity, ease of use, and utility Reduced twisting of the neck, upper 

of the prill boom and spout torso, and back 

To prevent unnecessary risk, changes in equipment design 

should be tested to see if they reduce risk, add new risk, or 

complicate the work process. One method for testing design 

changes is to incorporate the changes into one truck, thus 
providing an opportunity to further refine the redesigns and 

gather additional input from the crew members. When new 

trucks are bought or when trucks are modified in-house, 

the design changes suggested during this study should be 

considered for reducing the level, duration, and frequency of 

exposures to key WMSD risk factors. These design changes 

could likely reduce the risk of developing a musculoskeletal 

disorder, as well as help to prevent acute injuries such as those 

that may result from a slip or fall. 

REFERENCES 

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J. Torma-Krajewski: Initiating an ergonomics process at a surface coal 

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Safety and Research, Roanoke, Va., Aug. 27–30, 2002. Blacksburg, Va.: 

Virginia Polytechnic Institute and State University, Department of Mining 

and Minerals Engineering (2002). pp. 39–47. 

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