IC 9519 

INFORMATION CIRCULAR/2010 

Mine Roof Bolting Machine Safety: 

Investigations of Roof 

Bolter Boom Swing Velocity 

Department of Health and Human Services 

Centers for Disease Control and Prevention 

National Institute for Occupational Safety and Health 
Information Circular 9519 

Mine Roof Bolting Machine Safety: 

Investigations of Roof Bolter Boom Swing Velocity 

By Joseph H. DuCarme and August J. Kwitowski 

DEPARTMENT OF HEALTH AND HUMAN SERVICES
 Centers for Disease Control and Prevention
 

National Institute for Occupational Safety and Health
 

Office of Mine Safety and Health Research
 

Pittsburgh, PA • Spokane, WA
 

February 2010 
 

 

This document is in the public domain and may be freely copied 

or reprinted. 

Disclaimer 

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do not constitute NIOSH endorsement of the sponsoring organizations or their programs or 

products. Furthermore, NIOSH is not responsible for the content of these Web sites. All Web 

addresses referenced in this document were accessible as of the publication date. 

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DHHS (NIOSH) Publication No. 2010–126 

February 2010 

SAFER • HEALTHIER • PEOPLE TM
CONTENTS
	

Abstract............................................................................................................................................

Page

 1 

Introduction......................................................................................................................................2 

Background......................................................................................................................................3 

Phase 1 tests: NIOSH volunteer subjects........................................................................................5 

Study population.....................................................................................................................5 

Experimental design and measurements.................................................................................6 

Data analysis: NIOSH subjects.....................................................................................................10 

Methods ................................................................................................................................10 

Results ..................................................................................................................................10 

Discussion.............................................................................................................................19 

Phase 2 tests: mine worker subjects..............................................................................................19 

Study population...................................................................................................................19 

Experimental design and measurements...............................................................................20 

Data analysis: mine worker subjects.............................................................................................23 

Methods ................................................................................................................................23 

Results ..................................................................................................................................25 

Discussion.............................................................................................................................28 

Conclusions....................................................................................................................................28 

Acknowledgments..........................................................................................................................29 

References......................................................................................................................................29 

Appendix.—Mine worker data ......................................................................................................31 

ILLUSTRATIONS 

 1. Typical roof bolter posture........................................................................................................4 

 2. Overhead view of bolting environment ....................................................................................5 

 3. Slide mechanism used for NIOSH subject testing....................................................................6 

 4. Standing posture........................................................................................................................7 

 5. Stooping posture .......................................................................................................................7 

 6. Squatting posture ......................................................................................................................7 

 7. Kneeling posture .......................................................................................................................7 

 8. JACK markers, front.................................................................................................................8 

 9. JACK markers, back .................................................................................................................8 

10. NIOSH subject test fixture and artificial roof...........................................................................9 

11. Velocities for forward boom swing motions ..........................................................................12 

12. Velocities for backward boom swing motions........................................................................12 

13. NIOSH subjects: 72-in seam height, standing posture, forward motion ...............................14 

14. NIOSH subjects: 72-in seam height, standing posture, backward motion ............................14 

15. NIOSH subjects: 60-in seam height, stooping posture, forward motion ...............................15 

16. NIOSH subjects: 60-in seam height, stooping posture, backward motion ............................15 

17. NIOSH subjects: 60-in seam height, squatting posture, forward motion ..............................16 

18. NIOSH subjects: 60-in seam height, squatting posture, backward motion ...........................16 
CONTENTS—Continued Page

19. NIOSH subjects: 48-in seam height, squatting posture, forward motion ............................17 

20. NIOSH subjects: 48-in seam height, squatting posture, backward motion .........................17 

 21. NIOSH subjects: 48-in seam height, kneeling posture, forward motion .............................18 

 22. NIOSH subjects: 48-in seam height, kneeling posture, backward motion ..........................18 

 23. Mine worker subject in a stooping posture ...........................................................................21 

 24. Mine worker subject in a kneeling posture ...........................................................................21 

 25. Distance versus time plot for swing-out ...............................................................................24 

 26. Distance versus time plot for swing-in .................................................................................24 

 27. Mine worker subjects: standing 72-in results ......................................................................25 

 28. Mine worker subjects: stooping 60-in results ......................................................................25 

 29. Mine worker subjects: squatting 60-in results .....................................................................26 

 30. Mine worker subjects: squatting 48-in results .....................................................................26 

 31. Mine worker subjects: kneeling 48-in results ......................................................................27 

A-1. Actual mine worker data for standing posture, 72-in height ................................................31 

A-2. Actual mine worker data for stooping posture, 60-in height ................................................32 

A-3. Actual mine worker data for squatting posture, 60-in height ...............................................33 

A-4. Actual mine worker data for squatting posture, 48-in height ...............................................34 

A-5. Actual mine worker data for kneeling posture, 48-in height ................................................35 

TABLES 

 1. Detailed results of NIOSH subject testing............................................................................11 

 2. Mine worker subject anthropometric data ............................................................................20 

 3. Target swing velocities and times.........................................................................................22 

A-1. Results for standing posture, 72-in height ............................................................................31 

A-2. Results for stooping posture, 60-in height............................................................................32 

A-3. Results for squatting posture, 60-in height...........................................................................33 

A-4. Results for squatting posture, 48-in height...........................................................................34 

A-5. Results for kneeling posture, 48-in height............................................................................35 
ACRONYMS AND ABBREVIATIONS USED IN THIS REPORT
	

 ANSI American National Standards Institute 

 ASIS anterior superior iliac spine 

 DOE U.S. Department of Energy 

 MSHA Mine Safety and Health Administration 

 NIOSH National Institute for Occupational Safety and Health 

 PVC polyvinyl chloride 

 SD standard deviation 

UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT 

 ft foot 

 in inch 

 in/sec inch per second 

 lb pound 

 sec second 

 

MINE ROOF BOLTING MACHINE SAFETY:
	

INVESTIGATIONS OF ROOF BOLTER BOOM SWING VELOCITY
	 By Joseph H. DuCarme1 

1

Mechanical engineer.
	

and August J. Kwitowski2 

2

Civil engineer.
	

Office of Mine Safety and Health Research, National Institute for Occupational Safety and Health, Pittsburgh, PA.
	

ABSTRACT 

An analysis of accident/injury data for 2001 through 2005 from the Mine Safety and 

Health Administration (MSHA) revealed that powered machinery accounted for nearly 40% of 

the total underground coal injuries reported and 62% of all fatalities. Underground coal miners 

work in an environment with limited space for lateral movement and in awkward postures, 

including kneeling on one or both knees. During informal discussions, MSHA and the United 

Mine Workers of America expressed concerns about the velocity of appendages on machines 

used in such environments. 

This report describes a study of operator movement relative to the motion of a roof 

bolting machine boom arm. This work was aimed at reducing the risk of injury to underground 

coal mine workers from moving machinery. The study used motion capture technology to 

evaluate human movement in restricted heights and postures while controlling a mockup of a 

roof bolter boom. 

Results suggest that boom horizontal swing velocity is an important factor in determining 

operator safety from pinch point and crush hazards during the boom positioning phase of the 

bolting sequence. The working height where the machine is operating, the operator’s working 

posture, and the direction of the swing, toward or away from the operator, are also important in 

determining safe boom velocity. 
INTRODUCTION 

An analysis of the Mine Safety and Health Administration’s (MSHA) accident, injury, 

illness database for 2003–2007 shows there were 405 injuries involving worker-to-roof bolter 

contact. During those 5 years, roof bolting was the most hazardous machine-related job in 

underground mining. It accounted for nearly one-third of accidents involving powered 

machinery. 

Literature searches showed that worker activities involving boom arm movement during 

the bolting cycle [Klishis et al. 1993a,b] were associated with many of the accidents. A committee established by MSHA in 1993 composed of representatives from the West Virginia Board 

of Coal Mine Health and Safety, the U.S. Bureau of Mines, and roof bolter manufacturers 

identified 10 problems that may have contributed to or caused accidents. Seven of 

these were associated with movement of the boom arm. MSHA [1994] and Turin et al. 

[1995] revealed that there are no data on safe velocities for machine appendages operating close 

to workers in the confined work environment of underground mines. A prior NIOSH study 

investigated vertical boom velocity [Ambrose et al. 2005; Bartels et al. 2003]. During the course 

of that research, MSHA, bolting machine manufacturers, and all of the mine worker human 

subject participants in the study inquired as to when horizontal swing velocity would be studied. 

Several studies in the robotics industries have provided data for setting safe machine 

appendage speeds for reducing injuries and developing numerous guidelines for the safety of 

workers close to production line robots. Etherton [1987] reported that 10 in/sec is a speed 

at which humans could recognize and react to a perceived hazard. In addition, the Occupational 

Safety and Health Administration [OSHA 1987] requires that robot speeds for teach-and-repeat 

programming sessions where the programmer is within the robot’s motion envelope conform to 

the American National Standards Institute (ANSI) slow speed recommendation. The current 

ANSI standard recommends that this slow speed should not exceed 10 in/sec. However, 

Karwowski et al. [1992] reported that test subjects can perceive potential hazards from a moving 

robot arm at a rate of motion from 8 to 16 in/sec. Their study suggests that the safe speed of 

robot motions for teaching and programming purposes lies somewhere between 8 and 10 in/sec. 

Moreover, the U.S. Department of Energy (DOE) recommends a restricted speed of 6 in/sec on 

any part of the robot when a teacher is within the robot’s motion envelope because mistakes in 

programming can result in unintended movement. This slower speed would reduce possible 

injuries to a teacher if an inadvertent movement occurred [DOE 1993]. 

A production line robot will move from point to point regardless of a human in its motion 

path. Unlike a robot, the motion of the boom arm on a roof bolting machine is under the control 

of its operator. Observations of operators during bolting operations show that they, when 

possible, attempt to move in unison with the swing motion of the boom arm. If the motion is too 

fast for them to follow in the confined environment, they need to release the control so that they 

may reposition themselves. The designs of most roof bolter controls are quite logical. Pushing 

the control handle away from the operator causes boom swing in that direction and vice versa. 

However, if an operator should stumble or slip while swinging the boom out (toward oneself), 

the natural reaction is to attempt to steady oneself. This could result in unintended motion of the 

boom arm and injury to the operator. 

The goal of this study is to increase the safety of bolting machine operators during horizontal boom swing operations. Boom swing usually occurs when the operator is repositioning the 

boom arm to a new bolt insertion location. It requires that the operator properly actuate the right 

2 
control(s) and then reposition his/her body to follow the moving boom arm. In low roof heights, 

operators may perform this task from a kneeling position, which hinders their ability to keep 

pace with the boom arm. The basic issue is that it is not known what boom swing velocity maximizes the operator’s chances of escaping injuries while still allowing the operator to perform 

bolting functions in a timely manner. Like the earlier vertical boom arm study, this work used 

motion capture technology to evaluate human motions while operating a bolting machine in 

various postures. 

Laboratory experiments were conducted in two phases. Phase 1 used NIOSH volunteer 

subjects to determine the velocities at which they could follow a predetermined path under three 

working heights. The predetermined path represented the movement required by a roof bolter 

operator during boom swing operation. In phase 2, experienced mine workers were recruited to 

measure human motion versus time in operator postures commonly used when operating a roof 

bolter. The phase 2 study used three boom swing rates: two velocities determined from phase 1 

data and the manufacturer’s normal swing rate. Analysis of phase 2 data defined the range of 

roof bolter boom swing velocities that provide the roof bolter operator with the best prospect of 

safety. 

BACKGROUND 

Support of the roof after coal extraction is essential to worker safety and ventilation of 

the mine. Roof bolts are long steel rods, at least 4 ft long, with expansion or resin anchors used to 

secure them into the roof. After the mining crew removes a section of the coal seam, roof bolting 

machine operators install these bolts to secure the areas of unsupported roof. The bolters must 

complete this task as quickly as possible to prevent sections of the roof from falling. The speed at 

which the bolting crew can work is critical to mine safety. Bolts are installed according to the 

mine’s MSHA-approved roof control plan. Typically, this calls for installation on 4-ft centers. 

A bolter operator’s usual work sequence includes moving the machine into position, setting up 

for the operation, drilling the hole into the roof, and installing the bolt [Klishis et al. 1993a]. 

The setup step of this sequence may include setting the automated temporary roof support 

system, scaling (manual removal of loose material from the roof and walls), handling ventilation 

material, performing a methane check, emptying the machine’s dust box, and other tasks. Drilling bolt holes involves inserting the drill steel in the chuck, adding extension steels if required, 

changing the bits, drilling the hole, and removing the steel. The bolt installation is accomplished 

by making up bolt assemblies, inserting resin cartridge into the bolt hole (if used), inserting the 

bolt into the hole and bending it if necessary, and spinning to mix resin or torque the installed 

bolt. The bolting sequence repeats until the unsupported area of the roof is secured and the 

requirements of the roof control plan are met. Then the operator moves the machine to a new 

location and begins the process again. 

Roof bolting is a fairly structured and repetitive process. Figure 1 shows an operator 

performing this task. Although there is an established work cycle, it is often altered due to 

external influences, such as changes in geology, interruptions by coworkers and supervisors, 

machine malfunctions, and supply problems. The roof bolter operator is under pressure to install 

bolts as required to keep up with the coal mining operations while remaining vigilant to all 

possible dangers. 

3 
Figure 1.—Typical roof bolter posture. 

Bolter operators must perform their tasks in an environment (Figure 2) confined vertically by the mine’s roof height and horizontally by the bolter machine and closeness to the rib. 

Although Figure 2 shows an older roof bolter controls configuration, the environment is the same 

on newer equipment. This environment typically has low visibility due to the protective canopy 

and low light. This restricted work environment forces the operator into awkward postures for 

tasks that require quick reactions to avoid contact with moving machine parts. The bolting task 

requires working near unsupported roof, which increases the risk of injury from falling debris. 

Other factors affecting the operator’s movement include wet or muddy conditions, uneven floor, 

and the required mining gear. In addition, the operator needs to maintain an arm’s reach distance 

of 20–30 in from the moving boom arm because of the need to reach the controls and handle drill 

steels and bolts near the drill head. This requirement and the work environment force the 

operator to remain close to the moving boom arm. 

Studies by MSHA [1994] and Turin et al. [1995] revealed there were no data for 

determining safe operating velocities for bolter arms operating close to workers in confined 

environments such as an underground coal mine. Ambrose et al. [2005] examined vertical boom 

velocity and provided valuable data and guidance. The results of this research provide the same 

information for horizontal roof bolter boom swing velocities. 

Klishis et al. [1993b] examined worker job performance, risks, and hazard exposures 

during bolting operations. More than 12 bolting-related problems were identified as situations 

leading to injury. This study gave suggestions on how to avoid these situations which were subsequently evaluated at mining operations. Turin et al. [1995] conducted an analysis of hazards related 

to the movement of the drill head boom of a roof bolting machine. They recommended the 

following short-term solutions to increase the safety of roof bolter operators: 

(1) Use an interlock device to cut off power to the controls when the operator is out of 

position. 

(2) Place fixed barriers at pinch points and other dangerous areas. 

(3) Provide better control guarding. 

(4) Reduce the fast-feed speed. 

(5) Use automatic cutoff switches for pinch points and other dangerous areas. 

(6) Redesign the control bank to enable the operator to select the desired control by feel. 

(7) Use resin insertion tools. 

4 
Figure 2.—Overhead view of bolting environment. 

PHASE 1 TESTS: NIOSH VOLUNTEER SUBJECTS 

Study Population 

Since no special skills were involved for phase 1, eight volunteers from the NIOSH 

Office of Mine Safety and Health Research in Pittsburgh, PA, were used for the testing. The 

group consisted of seven males and one female ranging from 22 to 57 years of age and from 3rd 

to 99th percentile [McDowell 2005] by stature for males. The desired study population was the 

5th through 95th percentile for males, representing 99% of the male target population. The objective 

of the laboratory tests was to ensure that the experimental design represented an accurate picture 

of the real world, not to duplicate the entire target population. Therefore, the small sample size 

including a female did not affect the goal of the tests. 

The volunteers were solicited through a site-wide e-mail. Exclusion criteria for the testing 

included cardiovascular illness, knee problems, recent surgery or ailments, and current medications, which could limit or adversely affect the required movements. 

5 
Experimental Design and Measurements 

The testing required that the subjects move along a 40-in-long arc path on the floor that 

simulated the movement of an operator during the boom swing function on a Fletcher Roof 

Ranger II bolting machine. Although a wooden mockup roof bolter of this make/model machine 

was available, it was not used because it was desired to have the subjects unencumbered by 

significant machinery in their environment. Instead, a test fixture (Figure 3) was designed and 

constructed of steel for the testing. It was a partial arc supported at both ends with a sliding lever 

and knob. The lever and knob moved an effective length of 50 inches in a pattern conforming to 

the motion of a roof bolter boom while swinging laterally. 

Figure 3.—Slide mechanism used for NIOSH subject testing. 

The testing was intended to address these questions: 

(1) What is the maximum velocity an individual perceiving danger can move toward 

or away from the bolter arm along a specified path in various work postures and 

seam heights? 

(2) What effects do postures and seam heights have on an individual’s motion and 

velocity? 

The experiments were conducted using working heights of 72, 60, and 48 in. For the 

72-in working height, a standing posture was used. For the 60-in height, stooping and squatting 

postures were used. For the 48-in height, squatting and kneeling postures were used. These four 

postures (standing, stooping, squatting, kneeling) are depicted in Figures 4–7. The roof height 

was adjusted by moving a suspended panel covered with a mesh fabric that represented the mine 

roof. Based on in-mine observations, the posture and working height combinations were thought 

to represent realistically what is experienced in real-world roof bolting situations. 

6 
Figure 4.—Standing posture. Figure 5.—Stooping posture. 

Figure 6.—Squatting posture. Figure 7.—Kneeling posture. 

7
	
An optical motion tracking system by Motion Analysis Corp. was used to record the 

experimental data. This system is computer-based and is a highly accurate, repeatable, noncontact three-dimensional (3-D) measuring system that uses two-dimensional infrared camera 

views of reflective markers in a calibrated volume to calculate the relative positions of a suite of 

markers in three dimensions. This motion tracking system can be used to track humans, parts of 

equipment and machinery, and precision movements for human-task applications. The motion 

capture system uses an array of reflective markers that are placed on the subject and other items 

of interest. Although there are recommended arrangements of markers for human motion 

capture, this software is very flexible and allows use of any practical arrangement of markers. 

The array of markers used in this testing consisted of 41 markers called the JACK marker set. 

The locations and naming conventions for the 41 markers are shown in Figures 8–9. Using this 

marker set enabled compatibility with both the motion analysis software and a virtual environment program called JACK. This software analyzes human performance via modeling and 

virtual environment simulation. The marker set allows importation of motion capture data from 

test subjects into JACK and will enable future research to be conducted easily in virtual 

environments. 

8 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

1
	

4 3 1 – Top Head		

3 – Front Head 

4 – L.Head_Offset 

5 – R.Shoulder 6 6 – L.Shoulder 5 

9 – R.Bicep 

16 9 

12 – R.Radius 

13 – R.Ulna 

23 24 16 – L.Bicep 

19 19 – L.Radius 12		 20 13 20 – L.Ulna 

28 35 

23 – R.Asis 

24 – L.Asis 

29 36 28 – R.Thigh 

29 – R.Knee 

30 – R.Shank 

31 – R.Ankle 

30 37 33 – R.Toes 

34 – R.Foot 

35 – L.Thigh 

36 – L.Knee 

37 – L.Shank 31 38		 38 – L.Ankle 

34 41 

33 40		 40 – L.Toes 

41 – L.Foot 

Figure 8.—JACK markers, front. 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

1
	

4 2

1 – Top Head 

2 – Back Head 

4 – L.Head_Offset 

5 – R.Shoulder 6 7 5 6 – L.Shoulder 

7 – Neck 8 8 – L.Back_Offset 

9 – R.Bicep 16 9 10. R.Elbow 

11 – R.Forearm 

12 – R.Radius 10 17		 13 – R.Ulna 

14 – R.Thumb 

15 – R.Pinky 

18 26 27 25 16 – L.Bicep 11 17 – L.Elbow 

18 – L.Forearm 

19 12		 19 – L.Radius 

20		 20 – L.Ulna 13 21		 14 21 – L.Thumb 

22 15 22 – L.Pinky 

25 – R.Psis 

26 – L.Psis 

27 – V.Sacral 

29 29 – R.Knee 36 

31 – R.Ankle 

32 – R.heel 

33 – R.Toe 

34 – R.Foot 

36 – L.Knee 

40 38 31 33 38 – L.Ankle 

39 – L.Heel 39 32 41 34 40 – L.Toe 

41 – L.Foot 

Figure 9.—JACK markers, back.
	
At the start of testing, the subjects were instructed to position themselves next to the test 

fixture to simulate working with a Fletcher Roof Ranger II machine. For the selected posture and 

working height, the subject was asked to assume as natural a position as possible with the right 

hand grasping the knob of the test fixture (Figure 10). At the verbal instruction―be gin,‖ the test 

subjects moved themselves forward along an arced path that simulated the motion of the bolter 

boom. 

Figure 10.—NIOSH subject test fixture and artificial roof. 

The subjects were told to move at a quick but comfortable pace while keeping their 

arm/hand and control lever/knob in the same position relative to their bodies. At the end of the 

forward excursion of the test fixture (about 50 in), the subjects were asked to remain stationary 

for 2 sec until they were given the verbal command―ba ck.‖ Then they repeated the exercise 

while moving backward. This procedure allowed the capture of both the forward and backward 

movements to be done in one recording session. 

The sequencing of experimental conditions was randomized for each subject. Within each 

experimental condition, three repetitions of the tests were performed to obtain average values. 

Subjects were allotted 2 min of rest if desired between repetitions. These experiments were 

videotaped and photographed to ensure that the recorded data could be correlated with the events 

that occurred. 

Simulated roof 

Slide mechanism 

9 
DATA ANALYSIS: NIOSH SUBJECTS 

Methods 

An analysis of the motion data determined the velocity at which subjects could move 

along the specified path for given postures and working heights. This information became 

the basis to set the boom swing velocity for the phase 2 tests with mine worker subjects. The 

motion data were also analyzed to try to answer the design study questions and to 

extract other items of interest. 

As supplied by the manufacturer, a Fletcher Roof Ranger II bolting machine can swing 

its boom laterally from one extreme to the other (about 48 in) in 4 sec. This applies to the boom 

swinging both toward and away from the operator and is equal to a velocity of 12 in/sec. It was 

assumed that the subjects would be capable of moving along the bolter arm path at 12 in/sec for 

all of the posture and working height combinations. A primary goal of this testing was to 

determine an upper range of velocities, based on postures, working heights, and direction of 

movement, to be used in the second phase of experiments using the wooden mockup roof bolter 

and mine worker subjects. 

The computer program Motion Analysis EVa Real-Time was used to determine exactly 

when the subjects started and ended their forward and backward motions. This program is part of 

the software library supplied by the motion tracking system manufacturer and was used to record 

the test sessions. The program allows the user to simultaneously view a 3-D depiction of all of 

the markers; a video of the subject; and a graphical display of the x, y, and z coordinates of a 

specific marker. Using this combination of synchronized displays and being able to step through 

the captured motion frame by frame allowed a very precise determination of when significant 

events occurred, such as on what frame number the subject started to move and on what frame 

number the subject’s movement stopped. Since the frames were recorded at a constant rate of 

60 frames/sec, it was simple to calculate the velocities for each trial and subject. 

Results 

Detailed results of the phase 1 NIOSH subject testing are presented in Table 1. The mean 

velocity for all postures/height combinations was 24.5 in/sec, over twice that of the base velocity 

for the bolting machine of 12 in/sec. The overall mean velocity while moving forward was 

25.6 in/sec; the mean velocity while moving backward was 23.4 in/sec. Of the 120 tests conducted, there were only four instances of individual posture and height combinations where the 

subjects were not able to maintain the base velocity of the bolting machine at 12 in/sec. This 

occurred for the 72-in standing posture moving forward at 11.3 in/sec, the 72-in standing posture 

moving backward at 11.4 in/sec, the 48-in squatting posture moving backward at 9.4 in/sec, and 

the 48-in kneeling posture moving backward at 11.8 in/sec. Three out of four of these low 

velocities were for the 3rd-percentile subject, while the remaining one occurred with the 87thpercentile subject. Figures 11–12 are bar graphs depicting the statistical information contained in 

Table 1. 

10 
 

 

 

 

 

Table 1.—Detailed results of NIOSH subject testing 

Forward postures: 

velocity, in/sec 

Backward postures: 

velocity, in/sec 

Percentile by 

stature 

Subject Trial 

72 in, 

standing 

60 in, 

stooping 

60 in, 

squatting 

48 in, 

squatting 

48 in, 

kneeling Mean 

72 in, 

standing 

60 in, 

stooping 

60 in, 

squatting 

48 in, 

squatting 

48 in, 

kneeling Mean 

3 A 

1 11.3 17.9 20.7 18.1 14.9 14.5 18.9 19.3 13.6 11.8 

2 13.8 19.9 20.4 17.0 16.4 13.7 20.4 18.3 9.4 11.8 

3 17.3 20.1 20.1 18.7 19.3 15.2 22.7 23.6 16.5 12.3 

Average 14.2 19.3 20.4 18.0 16.9 17.7 14.5 20.7 20.4 13.2 11.9 16.1 

87 B 

1 14.8 16.0 18.6 21.3 17.6 13.3 14.7 16.2 19.2 20.3 

2 14.5 18.6 20.7 19.2 20.1 11.4 14.8 18.8 18.0 16.1 

3 14.6 16.4 20.3 19.1 17.1 13.2 17.0 16.6 16.6 17.5 

Average 14.6 17.0 19.9 19.9 18.3 17.9 12.6 15.5 17.2 17.9 17.9 16.2 

75 C 

1 35.6 30.6 25.7 22.2 15.2 33.9 29.7 24.8 24.2 18.3 

2 35.6 32.7 28.2 27.4 21.8 28.2 29.4 29.1 27.4 19.9 

3 42.4 25.9 33.9 26.4 20.1 35.1 28.5 26.2 30.6 13.5 

Average 37.8 29.8 29.3 25.3 19.0 28.2 32.4 29.2 26.7 27.4 17.2 26.6 

62 D 

1 20.6 24.4 24.6 26.9 17.5 18.5 26.2 22.2 22.9 12.5 

2 26.7 30.6 24.4 22.5 19.5 24.2 28.5 26.7 21.0 15.9 

3 26.4 25.9 21.3 26.7 17.3 26.7 25.9 26.2 15.8 17.1 

Average 24.6 27.0 23.5 25.4 18.1 23.7 23.1 26.9 25.0 19.9 15.2 22.0 

14 E 

1 39.5 29.4 38.9 27.7 21.7 31.3 28.8 33.5 31.3 19.6 

2 38.4 29.1 36.9 36.9 20.9 36.0 30.6 30.6 34.7 24.6 

3 41.1 32.0 40.0 38.9 31.0 35.1 30.3 31.0 34.7 17.3 

Average 39.7 30.2 38.6 34.5 24.5 33.5 34.1 29.9 31.7 33.6 20.5 30.0 

9 F 

1 21.3 25.3 28.5 18.9 25.3 19.5 26.2 24.4 23.6 13.6 

2 29.7 22.2 28.0 25.0 23.6 25.7 24.2 24.2 24.6 14.8 

3 29.1 26.9 26.7 25.0 18.1 28.0 25.7 26.9 25.3 14.3 

Average 26.7 24.8 27.7 23.0 22.3 24.9 24.4 25.4 25.2 24.5 14.3 22.7 

99 G 

1 32.0 36.9 33.9 31.6 27.2 38.4 35.6 27.4 31.6 23.2 

2 35.1 41.1 29.1 32.0 23.4 29.7 40.0 32.0 29.4 20.4 

3 37.9 43.0 34.7 38.9 26.2 34.7 43.6 29.4 33.1 28.5 

Average 35.0 40.4 32.6 34.2 25.6 33.5 34.3 39.7 29.6 31.4 24.1 31.8 

71 H 

1 23.2 21.3 25.5 23.8 16.9 17.0 22.2 24.4 22.0 16.8 

2 26.4 28.8 28.8 25.0 26.9 19.6 22.2 25.3 26.4 22.2 

3 22.2 23.6 29.1 28.2 25.3 18.7 25.0 23.8 22.2 15.7 

Average 23.9 24.6 27.8 25.7 23.0 25.0 18.4 23.1 24.5 23.5 18.2 21.6 

Statistics 

Mean 27.1 26.6 27.5 25.7 21.0 25.6 24.2 26.3 25.0 23.9 17.4 23.4 

SD 9.7 7.3 6.3 6.3 4.3 8.7 7.0 4.7 6.9 4.3 

Maximum 42.4 43.0 40.0 38.9 31.0 38.4 43.6 33.5 34.7 28.5 

Minimum 11.3 16.0 18.6 17.0 14.9 11.4 14.7 16.2 9.4 11.8 

SD Standard deviation. 

11 
0.0

5.0

10.0

15.0

20.0

25.0

30.0

35.0

40.0

45.0

72, stand 60, stoop 60, squat 48, squat 48, kneel

Seam Ht (in)/Posture

Velocity, in/sec

Mean

Maximum

Minimum

12 in/sec

Baseline

0.0

5.0

10.0

15.0

20.0

25.0

30.0

35.0

40.0

45.0

72, stand 60, stoop 60, squat 48, squat 48, kneel

Seam Ht (in)/Posture

Velocity, in/sec

Mean

Maximum

Minimum

12 in/sec

Baseline

Figure 11.—Velocities for forward boom swing motions. 

12
	

Figure 12.—Velocities for backward boom swing motions. 
For all of the subjects, the highest mean velocity was demonstrated at the 60-in 

squatting posture while moving forward (27.5 in/sec). The posture that showed the lowest mean 

velocity was the 48-in kneeling posture while moving backward at 17.4 in/sec. 

For the range of working heights and postures tested, there was a positive correlation 

between the subject’s height and average velocity. Graphs were prepared plotting subject height 

versus the average recorded velocity for all of the tested working height and posture combinations. Figures 13–22 show examples of these plots for all of the postures, with the forward and 

backward motions shown separately. Also shown is a line that is fitted to the data using regression analysis, the equation for the line, and the correlation coefficient. For all of the cases, 

the lines showed positive slopes. The correlation coefficients ranged from 0.009 to 0.552. 

Based on this testing, it was decided to conduct the phase 2 testing with the mockup roof 

bolting arm so that the velocity of the arm would be 12 in/sec, 16 in/sec, and 24 in/sec when 

moving away from the operator and 12 in/sec, 13.7 in/sec, and 16 in/sec when moving toward 

the operator. The manufacturer’s base velocity of 12-in/sec was selected as the slowest 

velocity for both directions of boom arm testing. As detailed above, of the 120 tests conducted, 

there were only four instances where the tested subjects were not able to maintain the 

manufacturer’s standard velocity of 12 in/sec. Therefore, test velocities below 12 in/sec were not 

deemed to be necessary. Although maximum velocities of over 30 in/sec were recorded for all 

tested postures for the swing-in (operator walking forward) direction, this velocity was tested 

with the mockup boom arm and it was determined that 30 in/sec would be excessive and 

hazardous to test subjects. Therefore, 24 in/sec was selected as a fast swing-out velocity as it 

proved to be a challenging velocity as supported by the previous analysis. The velocity 

of 16 in/sec was selected as a fast velocity for the backward motion because this was 

near the mean value calculated for the kneeling posture at 17.4 in/sec. The decision 

was made to limit the number of velocities to three, since changing the velocities on the 

test apparatus was a cumbersome and somewhat imprecise procedure that used a stopwatch to 

time the swing from start to stop. We chose the medium velocity to be halfway between the fast 

and normal velocities—13.7 in/sec or 3.5 sec for the swing-out and 16 in/sec or 3.0 sec for the 

swing-in. 

13 
Figure 13.—NIOSH subjects: 72-inseam height, standing posture, forward motion. 

Figure 14.—NIOSH subjects: 72-inseam height, standing posture, backward motion. 

y = 0.5786x - 13.24

R

2

 = 0.0554

0.0

5.0

10.0

15.0

20.0

25.0

30.0

35.0

40.0

45.0

62.0 64.0 66.0 68.0 70.0 72.0 74.0 76.0 78.0

Subject Height, in.

Velocity, in/sec

y = 0.5516x - 14.212

R

2

 = 0.0659

0.0

5.0

10.0

15.0

20.0

25.0

30.0

35.0

40.0

62.0 64.0 66.0 68.0 70.0 72.0 74.0 76.0 78.0

Subject Height, in.

Velocity, in/sec

14
	
Figure 15.—NIOSH subjects: 60-inseam height, stooping posture, forward motion. 

Figure 16.—NIOSH subjects: 60-inseam height, stooping posture, backward motion. 

y = 0.9368x - 38.426

R

2

 = 0.272

0.0

5.0

10.0

15.0

20.0

25.0

30.0

35.0

40.0

45.0

62.0 64.0 66.0 68.0 70.0 72.0 74.0 76.0 78.0

Subject Height, in.

Velocity, in/sec

y = 0.7598x - 26.387

R

2

 = 0.1821

0.0

5.0

10.0

15.0

20.0

25.0

30.0

35.0

40.0

45.0

62.0 64.0 66.0 68.0 70.0 72.0 74.0 76.0 78.0

Subject Height, in.

Velocity, in/sec

15
	
Figure 17.—NIOSH subjects: 60-inseam height, squatting posture, forward motion. 

Figure 18.—NIOSH subjects: 60-inseam height, squatting posture, backward motion. 

y = 0.1339x + 18.079

R

2

 = 0.0073

0.0

5.0

10.0

15.0

20.0

25.0

30.0

35.0

40.0

45.0

62.0 64.0 66.0 68.0 70.0 72.0 74.0 76.0 78.0

Subject Height, in.

Velocity, in/sec

y = 0.1396x + 15.261

R

2

 = 0.0144

0.0

5.0

10.0

15.0

20.0

25.0

30.0

35.0

62.0 64.0 66.0 68.0 70.0 72.0 74.0 76.0 78.0

Subject Height, in.

Velocity, in/sec

16
	
Figure 19.—NIOSH subjects: 48-inseam height, squatting posture, forward motion. 

Figure 20.—NIOSH subjects: 48-inseam height, squatting posture, backward motion. 

y = 0.588x - 15.32

R

2

 = 0.1587

0.0

5.0

10.0

15.0

20.0

25.0

30.0

35.0

40.0

62.0 64.0 66.0 68.0 70.0 72.0 74.0 76.0 78.0

Subject Height, in.

Velocity, in/sec

y = 0.571x - 15.878

R

2

 = 0.1051

0.0

5.0

10.0

15.0

20.0

25.0

30.0

35.0

40.0

62.0 64.0 66.0 68.0 70.0 72.0 74.0 76.0 78.0

Subject Height, in.

Velocity, in/sec

17
	
Figure 21.—NIOSH subjects: 48-inseam height, kneeling posture, forward motion. 

Figure 22.—NIOSH subjects: 48-inseam height, kneeling posture, backward motion. 

y = 0.2822x + 0.7645

R

2

 = 0.1289

0.0

5.0

10.0

15.0

20.0

25.0

30.0

62.0 64.0 66.0 68.0 70.0 72.0 74.0 76.0 78.0

Subject Height, in.

Velocity, in/sec

y = 0.6927x - 30.695

R

2

 = 0.5733

0.0

5.0

10.0

15.0

20.0

25.0

62.0 64.0 66.0 68.0 70.0 72.0 74.0 76.0 78.0

Subject Height, in.

Velocity, in/sec

18
	
Discussion 

The statistics generated for the forward and backward motions did not differ significantly. As shown in Table 1, the average mean velocities for the forward motions were 

consistently higher than the corresponding backward motions regardless of posture. However, 

the overall forward motions were only 9.3% faster than the overall backward motions. The 

biggest difference was noted for the kneeling posture, where the forward motion was 20% faster 

than the backward motion. The smallest difference was noted for the 48-in squatting posture, 

where the forward motion was 7.6% faster than the backward motion. 

The positive correlations between a subject’s height and average velocity, as presented 

above and shown in Figures 13–22, can be explained by the fact that the larger subjects tended to 

have longer legs and could move through the distance of the test arc in one or two steps. The 

smaller subjects had shorter legs and strides that required three or more steps to complete the 

motions. For the small distance used in this testing, taking one or two steps was more efficient 

and faster than three or more steps. 

Additional findings based on the subjects’ anthropometry were initially desired but were 

found to be beyond the scope of this testing. A significant number of additional subjects would 

be required, and these subjects would need to exhibit a wide range of anthropometric differences. 

PHASE 2 TESTS: MINE WORKER SUBJECTS 

Study Population 

Twelve mine worker volunteers participated in the study. Seven of the subjects were 

experienced bolter operators and two were mechanics. The remaining three listed their positions 

as general laborers. The volunteers were all males from 27 to 69 years of age and averaged about 

46 years old. Their heights ranged from 5'5" to 6'3" (average 5'10"), and they weighed 160– 

270 lbs (average 210 lbs). Table 2 lists the subjects’ anthropometric data. With one exception, 

the subjects were right-handed. There were no measurements of the subject’s physical strength 

or motor skills because operating a roof bolting machine does not require more than nominal effort 

and coordination. Although this sample size is small, we believe it to be representative of the 

mining population. Interviews revealed both mechanics and two of the bolter operators knew that 

the roof bolter swing velocity could be adjusted by altering the setting of hydraulic flow control 

valves at any time. All subjects stated they had noticed variations in the rates at which different 

equipment of the same model operated. 

19 
 

 

 

 

 

 

 

 

 

Table 2.—Mine worker subject anthropometric data 

Subject Height, 

in 

Weight, 

lb 

Age, 

years 

Operator 

percentile 

1 72.7 190 55 93 

2 68.4 236 55 36 

3 69.3 230 52 52 

4 68.2 200 57 35 

5 68.5 240 38 38 

6 68.7 160 57 43 

7 70.0 205 54 66 

8 72.4 185 49 91 

9 72.2 175 27 89 

10 75.4 270 52 99 

11 67.6 245 31 27 

12 65.3 178 69 10 

Experimental Design and Measurements 

The purpose of this study was to determine if the boom arm swing velocity, in combination with operator posture, is the most significant factor that affects the operator’s ability to 

perceive and avoid machine contact hazards. Motion data were collected for human subjects 

using a full-scale working mockup of a roof bolter boom. 

The test setup was a wooden mockup of a 72-in Fletcher Ranger II roof bolter left-hand 

arm. This make and model were chosen because of their overwhelming dominance in the 

industry. The arm was placed in full extension for all testing. To minimize risk to test subjects, 

various safety features were designed into the mockup. These included friction clutches on all 

actuators and laser proximity detectors. Figure 23 shows a subject at the start of a test in a 

stooping posture. Figure 24 shows a subject at the start of a test in a kneeling posture. 

Table 3 lists the target times for a full swing during a test. The target velocities were 

based on the phase 1 tests and manufacturer data. The velocities were all set as a time base 

(i.e., seconds for full swing). The Fletcher Roof Ranger II bolting machine, as supplied by the 

manufacturer, can swing its boom laterally from one extreme to the other in 4 sec. With the 72-in 

boom length and the sump cylinder fully extended, the operator’s station moves about 48 inches 

in an arc path during a full swing. This motion equates to a velocity of 12 in/sec and became the 

―normal‖ velocity used for the mine worker tests. Since the test had a fixed distance for the 

subject to move, time and velocity are transposable, as seen in Table 3. 

20 
Figure 23.—Mine worker subject in a stooping posture. 

Figure 24.—Mine worker subject inakneeling posture. 

21
	
 

 

 

 

 

 

Table 3.—Target swing velocities and times 

Swing-in Swing-out 

Target Actual 

(average) Target Actual (average) 

Normal: 

Time, sec 4.0 3.7 4.0 3.8 

Velocity, in/sec 12.0 12.8 12.0 12.6 

Medium: 

Time, sec 3.0 2.7 3.5 3.2 

Velocity, in/sec 16.0 17.6 13.7 14.9 

Fast: 

Time, sec 2.0 2.2 3.0 2.7 

Velocity, in/sec 24.0 21.5 16.0 17.5 

The target velocities were set before motion capture sessions using a stopwatch while 

adjusting flow controls built into the bolter arm mockup’s hydraulic system. At the time, it was 

thought this method provided sufficient accuracy. After testing with all mine worker subjects had 

been completed, analysis of the data showed that there was more-than-expected variance in the 

target swing velocities. So, rather than assuming the target velocities had been achieved, the data 

analysis had to take into account the velocity variances that had occurred from the desired target 

velocities. The actual times and velocities are also shown in Table 3. 

The same optical tracking hardware and software used for the NIOSH subject tests were 

used for the mine worker tests. Several markers were placed on the boom arm to record its 

motion in addition to the standard 41-marker set on the subject. These trials were conducted at 

the same working heights and postures as those used in the NIOSH tests. There was no provision 

for a suspended ceiling. Also, the protective canopy normally covering the operator had to be 

removed to allow a clear line of sight for the optical tracking system’s cameras. Instead, a small 

PVC tube was attached to the boom arm and thus moved with it. The tubing was used to simulate 

the obstruction created by the actual roof bolting machine’s protective canopy. The height of this 

was adjusted appropriately for each test. As with the NIOSH tests, the sequence of velocity, 

height, and posture combinations was randomized. The motion capture system recorded video 

as well as motion data. 

The testing consisted of having the subject perform the swing function under various 

working height and posture combinations. The following simulated working heights and 

associated postures were tested: 72-in standing, 60-in stooping, 60-in squatting, 48-in squatting, 

and 48-in kneeling. 

22 
DATA ANALYSIS: MINE WORKER SUBJECTS 

Methods 

Analysis of the motion capture data determined a rate of change of the distance between 

the operator and the moving boom arm through its 48-in swing. This analysis developed a visual 

picture of positional changes between the subject and the boom arm during the boom swing 

motion. A custom computer program was written in Visual Basic .NET to perform the initial 

analysis of the data. For each session, the motion capture system created an ASCII delimited file 

that contained the 3-D positions of each marker over the course of the observation. The program 

first identified the start and stop points for the boom while swinging out toward the operator and 

while swinging in, away from the operator. 

 Statistical information was calculated for each trial that included the average distance between two markers during a swing-in or swing-out operation, the standard deviation, 

the minimum, the maximum, and the range. The markers used for this were the boom arm 

marker closest to operator and the marker on the left hip of the subject, identified as the left 

ASIS marker (L.Asis - marker 24) in Figure 8. The program also calculated a linear regression 

for the distances versus time, with a record made of the resulting slope and the coefficient of 

correlation. The program calculated and compiled this information for all of the 45 data files that 

comprised the complete motion capture session for an individual subject. This information was 

placed in another delimited text file that was then imported into an Excel spreadsheet for further 

analysis. 

The following is a simplified explanation of the statistical methods. Plotting the data in 

Excel showed a graphical representation of the distance between the two markers versus time. If, 

on average, this distance increased during the range of the boom swing, it meant that the boom arm 

tended to move away from the subject. If it decreased, it meant that the boom arm moved closer 

to the subject. Of prime importance was calculating the rate of change of distance between the 

operator and the boom arm. This rate of change is analogous to the velocity of the boom arm 

approaching or moving away from the moving operator. This is easily expressed as a slope, 

where the slope would be zero if the subject tended to keep an even pace with the moving boom 

arm. 

By plotting this distance calculation versus time, graphs were produced using Excel, such 

as those shown in Figures 25–26. For these graphs, the slope of a line (the X coefficient) fitted to 

the data was associated with the tendency of the subject to move toward or away from the boom 

arm during a swing motion. A positive slope indicated that the subject and boom arm tended to 

separate. A negative slope indicated that the distance between the subject and boom arm closed. 

As a slope became more positive or negative, the rate of separation or closure increased. 

Although Excel was used to calculate the line slope in this explanation, the actual slopes and 

regressions used in the analysis were calculated by the custom computer program. 

During this analysis, it was realized that the time intervals from the selected start and stop 

points of the swing motions varied between operators. This meant that the desired target velocities had not been exactly set during testing. To take this into account, the actual velocities were 

extracted from the data files, and the slope data were plotted against the extracted velocities 

instead of using target velocities for the x-axis of the final result graphs. 

23 
Figure 25.—Distance versus time plot for swing-out. 

y = -3.1998x + 27.771

0

5

10

15

20

25

30

0 0.5 1 1.5 2 2.5 3

Time, sec

Distance, in

y = 7.0748x + 13.762

0

5

10

15

20

25

30

35

0 0.5 1 1.5 2 2.5

Time, sec

Distance, in

Figure 26.—Distance versus time plot for swing-in. 

24
	
Results 

The slope and swing velocity values from the custom software were imported into Excel 

for plotting and further analysis. The data are shown in the Appendix. Those results are depicted 

as X-Y scatter charts for each of the five working postures. To generate the final results, data for 

all 12 subjects were averaged together. Figures 27–31 show the results for each operating 

posture. The velocities are expressed as a slope to enable normalization of the data for individual 

operator physical characteristics. When the value of slope is positive, the subject-to-boom arm 

distance was increasing. Conversely, a negative slope indicates the subject-to-boom arm distance 

was decreasing or closing. As the absolute value of the slope increased from zero, the rate of 

change in distance between operator and boom arm increased. 

-3.0

-2.0

-1.0

0.0

1.0

2.0

3.0

4.0

5.0

6.0

12.0 14.0 16.0 18.0 20.0 22.0 24.0

Velocity, in/sec

Slope

Swing In

Swing Out

Figure 27.—Mine worker subjects: standing 72-in results. 

-3.0

-2.0

-1.0

0.0

1.0

2.0

3.0

4.0

5.0

6.0

12.0 14.0 16.0 18.0 20.0 22.0 24.0

Velocity, in/sec

Slope

Swing In

Swing Out

Figure 28.—Mine worker subjects: stooping 60-in results. 

25
	
Figure 29.—Mine worker subjects: squatting 60-in results. 

Figure 30.—Mine worker subjects: squatting 48-in results. 

-3.0

-2.0

-1.0

0.0

1.0

2.0

3.0

4.0

5.0

6.0

12.0 14.0 16.0 18.0 20.0 22.0 24.0

Velocity, in/sec

Slope

Swing In

Swing Out

-3.0

-2.0

-1.0

0.0

1.0

2.0

3.0

4.0

5.0

6.0

12.0 14.0 16.0 18.0 20.0 22.0 24.0

Velocity, in/sec

Slope

Swing In

Swing Out 26
	
Figure 31.—Mine worker subjects: kneeling 48-in results. 

Obviously, the direction of the swing must be taken into account when deciding whether 

a positive or negative slope is desired. During boom swing-out, the boom is moving toward the 

operator, and a positive slope value would indicate the operator is moving faster than the boom. 

This situation should be a benign case and may indicate the operator can safely interact with a 

greater boom swing velocity. However, a negative slope value during boom swing-out would 

indicate the operator-to-boom arm distance is decreasing. This means the boom arm motion 

is greater than that of the operator. For boom swing-in events, the opposite is true. 

In all postures except one, the trend is quite clear. As boom swing velocity increases, the 

velocity of the boom arm approaching or receding relative to the operator increases. For a fast 

swing-out motion, the boom arm approaches the operator faster than he/she can back away, 

so the boom arm-to-operator distance decreases during the motion. For the fast swing-in motion, 

the reverse happens. The boom arm moves away from the operator faster than he/she can follow, 

so the boom arm-to-operator distance increases during the motion. The lone outlier to this trend 

is the medium velocity data point for the swing-out motion, 72-in standing posture. Results for 

the 48-in kneeling posture show that for the slowest velocity tested, ~12 in/sec, the operators 

were unable to keep pace with the moving boom arm for both swing directions. During 

swing-out motion, the average slope value for the 48-in kneeling posture is always negative, 

meaning the operator-to-boom arm distance decreased at all velocities. 

-3.0

-2.0

-1.0

0.0

1.0

2.0

3.0

4.0

5.0

6.0

12.0 14.0 16.0 18.0 20.0 22.0 24.0

Velocity, in/sec

Slope

Swing In

Swing Out 27 
Discussion 

All mine worker study volunteers expressed an inability to keep pace with the fast 

velocity, as described in Table 3. About 30% commented that the medium velocity was 

satisfactory to work with for these trials, but felt they would have tired during a longer 

trial. All of the mine worker volunteers stated they had noticed different operating velocities on equipment of the same model they had used. Most stated that the equipment they were 

using moved at a rate higher than the slow velocity (the manufacturer’s standard) that we used. 

The boom arm swinging toward the operator (swing-out) was deemed the more 

hazardous situation, since the possibility of operator-to-boom arm contact and exposure to pinch 

point and crush hazards was increased. In some cases, inadvertent control activation may be a 

contributor to accidents. However, one manufacturer has added a strip stop switch protruding in 

front of the valves to provide some protection so that in case the operator contacts the strip, the 

machine shuts down. During swing-in events, the boom arm is moving away from the operator, 

forcing him/her to follow it. If the boom arm is moving faster than the operator can follow, the 

distance between the arm and operator will naturally increase. The increased distance and 

relative motions should provide a safety cushion from the hazards described above. Consider the 

extreme case where the control lever moved away from the operator rapidly enough so that grasp 

of the control was lost. The hydraulic actuator would become disengaged, the boom arm would 

stop, and the operator could catch up with it and regain control. 

The most hazardous situations depicted in Figures 27–31 are when the slopes are more 

negative than −0.5 and the boom arm swing was toward the subject (swing-out). This meant that 

the distance between the subject and the boom arm was decreasing rapidly and subject-toboom arm contact could occur. At this slope, the closing velocity between the boom arm and the 

operator is 50% of the arm’s velocity. The target fast swing-out velocity was 16 in/sec. Due to 

inaccuracies in setting this velocity during human subject testing, the actual average velocity was 

about 17.5 in/sec. Therefore, the closing velocity between operator and boom arm would be 

about 9 in/sec. This velocity is similar to the limiting velocities reported by Etherton [1987], 

OSHA [1987], Karwowski et al. [1992], and DOE [1993]. 

All tests conducted with the boom swing-out velocity set to the target of 16 in/sec had 

slopes equal to or less than −0.5. Thus, the rate of 16.0 in/sec for swing-out seems to be too fast 

for all of the postures tested. The medium rate tested for swing-out averaged 14.7 in/sec and 

resulted in satisfactory slope values for all postures tested except for the 48-in kneeling posture. 

However, caution must be exercised because swing velocities at this rate could induce operator 

fatigue over time. 

CONCLUSIONS 

Recent MSHA statistics indicate that roof bolter operators are being injured by contact 

with the boom arm during the bolting cycle. In this study, the subjects were able to keep pace 

with the manufacturer’s standard boom swing rate of 12 in/sec for all of the postures tested 

except the 48-in kneeling posture. Additional research needs to be conducted for this working 

height and posture to provide adequate data for conclusions. The data show that subjects are able 

to keep pace with horizontal boom swing velocities in excess of the manufacturer’s standard in 

some working heights and postures. The data should be viewed with caution because these trials 

were of a limited duration and the subjects were permitted rest periods as needed. Operator 

28 
fatigue might be a significant factor in interacting with the higher velocity settings detailed in 

this research. In addition, other environmental and human factors that were not feasible or within 

the parameters of this laboratory study, such as floor conditions and operator fatigue may 

affect safe working velocities. 

The hypothesis of this project was that boom arm horizontal swing velocity is an 

important factor in determining operator safety from pinch point and crush hazards during the 

boom positioning phase of the bolting sequence. We believe that the data and results support this 

hypothesis. 

ACKNOWLEDGMENTS 

We thank the following engineering technicians with the NIOSH Office of Mine Safety 

and Health Research, Pittsburgh, PA: George F. Fischer (retired) for his efforts in constructing 

the bolter arm mockup; and Albert H. Cook, Mary Ellen Nelson, and William E. Rossi (retired) 

for assisting with experiment setup, data collection, and human subject testing. We also express 

our appreciation to Dean H. Ambrose (retired) and John R. Bartels for helping with mine worker 

subject scheduling and testing. 

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Administration, Coal Mine Safety and Health, Safety Division, pp. 1–28. 

OSHA [1987]. Guidelines for robotic safety. OSHA directive STD 01-12-002 (instruction 

pub 8-1.3). Washington DC: U.S. Department of Labor, Occupational Safety and Health 

Administration, Office of Science and Technology Assessment, September 21. 

Turin FC, et al. [1995]. Human factors analysis of roof bolting hazards in underground 

coal mines. Pittsburgh, PA; U.S. Department of the Interior, Bureau of Mines, RI 9568. NTIS 

No. PB95-274411. 

30 
 

 

 

 

 

 

 

 

 

 

 

 

-4.00

-3.00

-2.00

-1.00

0.00

1.00

2.00

3.00

4.00

5.00

6.00

11.00 13.00 15.00 17.00 19.00 21.00 23.00 25.00

Velocity, in/sec

Slope

Swing Out, Normal Velocity

Swing In, Normal Velocity

Swing Out, Medium Velocity

Swing In, Medium Velocity

Swing Out, Fast Velocity

Swing In, Fast Velocity

APPENDIX.—MINE WORKER DATA 

This appendix contains tables and figures for each of the mine worker subject tests. 

Custom software extracted the data from the motion capture files. The analysis was completed 

by importing the information into Excel. There are five table and figure pairs, each corresponding to a working height/posture combination. Comparison of the actual velocities in the 

tables below and the target velocities listed in Table 3 shows the variance that occurred during 

the testing. The slope value represents the rate of change of distance between the operator and 

boom arm as described in the ―Results‖ section under ―Data Analysis: Mine Worker Subjects.‖ 

The figures are an X-Y scatter plot of the data contained in the associated table. 

Table A-1.—Results for standing posture, 72-in height 

Subject 

Normal velocity Medium velocity Fast velocity 

Swing-out Swing-in Swing-out Swing-in Swing-out Swing-in 

Velocity, 

in/sec Slope Velocity, in/sec Slope Velocity, in/sec Slope Velocity, in/sec Slope Velocity, in/sec Slope Velocity, in/sec Slope 

1 12.61 −2.91 12.95 2.22 14.85 −1.49 18.91 2.36 17.65 −2.30 22.56 1.75 

2 13.53 −1.31 13.20 −0.88 15.10 −3.19 18.95 2.33 17.79 −1.84 23.48 1.16 

3 13.19 −1.91 12.95 0.70 16.86 1.96 17.25 −0.92 17.37 0.85 23.05 2.77 

4 12.75 2.05 13.64 −0.10 15.03 0.50 19.43 1.30 17.36 −0.55 22.59 5.42 

5 11.89 0.77 12.96 −1.58 15.33 3.02 16.60 −1.88 17.55 −1.91 20.97 0.73 

6 12.34 −2.45 12.60 1.01 14.33 −3.13 17.36 2.48 17.27 −3.36 20.82 2.56 

7 12.40 −2.41 13.04 0.93 14.65 0.54 17.59 −1.21 17.79 −0.82 21.55 −2.37 

8 12.27 −1.01 12.20 0.45 14.02 1.03 17.90 1.27 17.78 −0.12 21.90 2.86 

9 12.40 −1.11 12.21 0.30 14.55 0.21 17.14 −0.13 16.67 −1.20 21.07 −0.09 

10 12.91 0.18 12.85 −0.05 14.94 0.16 18.37 0.76 18.20 −0.07 20.22 −0.07 

11 12.40 1.60 12.83 −1.95 14.84 0.15 16.48 −0.47 17.79 −1.24 22.04 2.29 

12 12.57 −0.54 12.17 −0.50 14.25 1.07 16.42 −0.51 16.65 0.92 19.07 −1.14 

31 

Figure A-1.—Actual mine worker data for standing posture, 72-in height. 
 

 

 

 

 

 

 

 

 

 

 

 

-4.00

-3.00

-2.00

-1.00

0.00

1.00

2.00

3.00

4.00

5.00

6.00

11.00 13.00 15.00 17.00 19.00 21.00 23.00 25.00

Velocity, in/sec

Slope

Swing Out, Normal Velocity

Swing In, Normal Velocity

Swing Out, Medium Velocity

Swing In, Medium Velocity

Swing Out, Fast Velocity

Swing In, Fast Velocity

Table A-2.—Results for stooping posture, 60-in height 

Subject 

Normal velocity Medium velocity Fast velocity 

Swing-out Swing-in Swing-out Swing-in Swing-out Swing-in 

Velocity, 

in/sec Slope Velocity, in/sec Slope Velocity, in/sec Slope Velocity, in/sec Slope Velocity, in/sec Slope Velocity, in/sec Slope 

1 12.61 −2.53 12.95 1.93 14.85 −1.31 18.91 0.46 17.65 −1.49 22.56 2.27 

2 13.53 −0.97 13.20 −0.83 15.10 −1.46 18.95 −1.43 17.79 −2.56 23.48 3.80 

3 13.19 −0.40 12.95 0.03 16.86 0.58 17.25 0.18 17.37 1.20 23.05 1.81 

4 12.75 2.09 13.64 −0.52 15.03 1.26 19.43 −0.87 17.36 0.15 22.59 2.41 

5 11.89 −0.01 12.96 −1.27 15.33 0.37 16.60 −1.24 17.55 −0.83 20.97 1.44 

6 12.34 −2.34 12.60 1.31 14.33 −2.60 17.36 1.70 17.27 −3.35 20.82 3.33 

7 12.40 0.92 13.04 −1.01 14.65 0.50 17.59 −1.62 17.79 −0.02 21.55 −1.19 

8 12.27 0.67 12.20 −1.19 14.02 −0.03 17.90 0.43 17.78 0.63 21.90 1.74 

9 12.40 −0.32 12.21 0.37 14.55 −0.19 17.14 0.29 16.67 −1.00 21.07 0.92 

10 12.91 0.50 12.85 −0.10 14.94 0.43 18.37 0.51 18.20 0.77 20.22 1.71 

11 12.40 1.82 12.83 −1.80 14.84 −1.56 16.48 0.91 17.79 −1.88 22.04 3.13 

12 12.57 −1.75 12.17 −0.20 14.25 1.19 16.42 −0.30 16.65 0.91 19.07 −0.68 

32 

Figure A-2.—Actual mine worker data for stooping posture, 60-in height. 
 

 

 

 

 

 

 

 

 

 

 

 

-4.00

-3.00

-2.00

-1.00

0.00

1.00

2.00

3.00

4.00

5.00

6.00

11.00 13.00 15.00 17.00 19.00 21.00 23.00 25.00

Velocity, in/sec Slope

Swing Out, Normal Velocity

Swing In, Normal Velocity

Swing Out, Medium Velocity

Swing In, Medium Velocity

Swing Out, Fast Velocity

Swing In, Fast Velocity

Table A-3.—Results for squatting posture, 60-in height 

Subject 

Normal velocity Medium velocity Fast velocity 

Swing-out Swing-in Swing-out Swing-in Swing-out Swing-in 

Velocity, 

in/sec Slope Velocity, in/sec Slope Velocity, in/sec Slope Velocity, in/sec Slope Velocity, in/sec Slope Velocity, in/sec Slope 

1 12.61 −2.16 12.95 1.07 14.85 −0.57 18.91 0.21 17.65 −1.84 22.56 3.40 

2 13.53 −1.59 13.20 −0.02 15.10 −2.58 18.95 −2.32 17.79 −1.71 23.48 −0.25 

3 13.19 0.11 12.95 0.07 16.86 0.05 17.25 0.37 17.37 −0.03 23.05 2.58 

4 12.75 0.91 13.64 0.05 15.03 0.02 19.43 1.22 17.36 0.63 22.59 1.86 

5 11.89 −0.78 12.96 −0.33 15.33 −0.35 16.60 −0.15 17.55 −0.87 20.97 0.77 

6 12.34 −1.69 12.60 0.72 14.33 −1.63 17.36 2.29 17.27 −2.48 20.82 2.14 

7 12.40 1.16 13.04 −1.19 14.65 −0.13 17.59 −1.62 17.79 −0.05 21.55 −0.83 

8 12.27 0.49 12.20 −0.55 14.02 0.28 17.90 1.02 17.78 −0.74 21.90 3.43 

9 12.40 0.38 12.21 −0.23 14.55 0.28 17.14 −0.66 16.67 −0.41 21.07 −0.48 

10 12.91 1.28 12.85 −0.17 14.94 −0.06 18.37 −0.05 18.20 −0.04 20.22 −0.32 

11 12.40 2.30 12.83 −1.87 14.84 −1.08 16.48 1.60 17.79 −1.03 22.04 1.87 

12 12.57 −0.15 12.17 –0.91 14.25 −0.54 16.42 −0.48 16.65 0.12 19.07 −0.09 

33 

Figure A-3.—Actual mine worker data for squatting posture, 60-in height. 
 

 

 

 

 

 

 

 

 

 

 

 

-4.00

-3.00

-2.00

-1.00

0.00

1.00

2.00

3.00

4.00

5.00

6.00

11.00 13.00 15.00 17.00 19.00 21.00 23.00 25.00

Velocity, in/sec Slope

Swing Out, Normal Velocity

Swing In, Normal Velocity

Swing Out,Medium Velocity

Swing In,Medium Velocity

Swing Out, Fast Velocity

Swing In, Fast Velocity

34 

Table A-4.—Results for squatting posture, 48-in height 

Subject 

Normal velocity Medium velocity Fast velocity 

Swing-out Swing-in Swing-out Swing-in Swing-out Swing-in 

Velocity, 

in/sec Slope Velocity, in/sec Slope Velocity, in/sec Slope Velocity, in/sec Slope Velocity, in/sec Slope Velocity, in/sec Slope 

1 12.61 −1.18 12.95 0.02 14.85 −0.68 18.91 −1.59 17.65 −0.72 22.56 1.17 

2 13.53 −2.14 13.20 0.42 15.10 −2.86 18.95 2.78 17.79 −3.52 23.48 4.71 

3 13.19 0.45 12.95 −0.53 16.86 −0.42 17.25 0.80 17.37 0.24 23.05 0.46 

4 12.75 0.28 13.64 −0.70 15.03 0.82 19.43 0.87 17.36 0.24 22.59 1.72 

5 11.89 −0.33 12.96 −0.43 15.33 −0.74 16.60 −0.35 17.55 −1.59 20.97 0.94 

6 12.34 −1.93 12.60 1.62 14.33 −3.25 17.36 3.19 17.27 −4.24 20.82 4.91 

7 12.40 1.36 13.04 −1.31 14.65 1.05 17.59 −1.63 17.79 1.55 21.55 −1.51 

8 12.27 0.26 12.20 −0.69 14.02 1.28 17.90 0.83 17.78 −1.12 21.90 1.76 

9 12.40 0.07 12.21 −0.65 14.55 −0.99 17.14 0.20 16.67 −1.26 21.07 1.13 

10 12.91 1.89 12.85 −0.68 14.94 0.33 18.37 1.15 18.20 0.18 20.22 1.88 

11 12.40 0.89 12.83 −1.95 14.84 2.12 16.48 −1.24 17.79 −0.34 22.04 2.61 

12 12.57 0.59 12.17 −1.45 14.25 −0.02 16.42 −1.33 16.65 0.88 19.07 −0.65 

Figure A-4.—Actual mine worker data for squatting posture, 48-in height. 
 

 

 

 

 

 

 

 

 

 

 

 

-10.00

-5.00

0.00

5.00

10.00

15.00

11.00 13.00 15.00 17.00 19.00 21.00 23.00 25.00

Velocity, in/sec

Slope

Swing Out, Normal Velocity

Swing In, Normal Velocity

Swing Out, Medium Velocity

Swing In, Medium Velocity

Swing Out, Fast Velocity

Swing In, Fast Velocity

Table A-5.—Results for kneeling posture, 48-in height 

Subject 

Normal velocity Medium velocity Fast velocity 

Swing-out Swing-in Swing-out Swing-in Swing-out Swing-in 

Velocity, 

in/sec Slope Velocity, in/sec Slope Velocity, in/sec Slope Velocity, in/sec Slope Velocity, in/sec Slope Velocity, in/sec Slope 

1 12.61 −3.38 12.95 2.21 14.85 −2.93 18.91 3.54 17.65 −2.34 22.56 6.37 

2 13.53 −4.40 13.20 1.72 15.10 −4.92 18.95 4.96 17.79 −7.25 23.48 11.23 

3 13.19 −2.02 12.95 1.95 16.86 −2.26 17.25 2.83 17.37 −2.55 23.05 5.83 

4 12.75 −1.61 13.64 4.03 15.03 −1.41 19.43 7.25 17.36 −0.98 22.59 9.73 

5 11.89 −0.01 12.96 0.32 15.33 −0.37 16.60 1.07 17.55 −0.72 20.97 4.06 

6 12.34 −3.36 12.60 2.00 14.33 −4.06 17.36 2.96 17.27 −6.46 20.82 4.27 

7 12.40 −1.86 13.04 −0.74 14.65 −2.92 17.59 −0.58 17.79 −4.90 21.55 1.66 

8 12.27 −1.59 12.20 1.09 14.02 −0.50 17.90 5.60 17.78 −1.10 21.90 8.75 

9 12.40 −0.43 12.21 0.59 14.55 −0.22 17.14 0.20 16.67 −1.43 21.07 3.73 

10 12.91 1.37 12.85 0.42 14.94 −0.30 18.37 2.04 18.20 0.97 20.22 2.19 

11 12.40 −2.89 12.83 2.38 14.84 −2.92 16.48 3.20 17.79 −2.74 22.04 5.27 

12 12.57 −2.57 12.17 0.07 14.25 −2.51 16.42 1.85 16.65 −3.49 19.07 2.20 

35 

Figure A-5.—Actual mine worker data for kneeling posture, 48-in height. 
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