Field Evaluation of Seat 

Designs for Underground 

Coal Mine Shuttle Cars 

IC 9493 

INFORMATION CIRCULAR/2006 

Department of Health and Human Services 

Centers for Disease Control and Prevention 

National Institute for Occupational Safety and Health 
Information Circular 9493 

Field Evaluation of Seat Designs for 

Underground Coal Mine Shuttle Cars 

By Alan G. Mayton, Christopher C. Jobes, Ph.D., N. Kumar Kittusamy, Sc.D., 

and Dean H. Ambrose 

DEPARTMENT OF HEALTH AND HUMAN SERVICES 

Centers for Disease Control and Prevention 

National Institute for Occupational Safety and Health 

Pittsburgh Research Laboratory 

Pittsburgh, PA 

November 2006 
This document is in the public domain and may be freely copied 

or reprinted. 

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DHHS (NIOSH) Publication No. 2007–100 

November 2006 

SAFER • HEALTHIER • PEOPLETM 
CONTENTS
 

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

Page 

1 

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

Background......................................................................................................................................2 

Study approach.................................................................................................................................3 

Methodology....................................................................................................................................8 

Subjects......................................................................................................................................8 

Procedure for vibration data collection......................................................................................8 

Procedure for subjective data collection....................................................................................8 

Results..............................................................................................................................................9 

 Vehicle jarring/jolting measurement results ..............................................................................9 

 JOY 10SC mid-coal-seam shuttle car..................................................................................9 

 JOY 21SC low-coal-seam shuttle car ................................................................................11 

Subjective evaluation: VAS.....................................................................................................14 

Subjective evaluation: operator questionnaire.........................................................................16 

 JOY 10SC mid-coal-seam shuttle car................................................................................17 

 JOY 21SC low-coal-seam shuttle car ................................................................................18 

Comparison of ISO 2631 fatigue-decreased proficiency limits with recorded data and

 questionnaire data .......................................................................................................................21 

Discussion......................................................................................................................................26 

Limitations .....................................................................................................................................30 

Conclusions....................................................................................................................................30 

Acknowledgments..........................................................................................................................30 

References......................................................................................................................................31 

Appendix A.—Visual analog scale form.......................................................................................33 

Appendix B.—Operator questionnaire to compare seats on shuttle cars in underground coal 

 mines...........................................................................................................................................34 

Appendix C.—Measured jarring/jolting data ................................................................................37 

ILLUSTRATIONS 

1. JOY 21SC low-coal-seam shuttle car .......................................................................................4 

2. JOY 10SC mid-coal-seam shuttle car.......................................................................................4 

3. Existing low-coal-seam shuttle car seat....................................................................................5 

4. NIOSH low-coal-seam shuttle car seat.....................................................................................6 

5. Viscoelastic arrangements for the low-coal-seam shuttle car seat............................................6 

6. NIOSH mid-coal-seam shuttle car seat.....................................................................................7 

7. Viscoelastic arrangements for the mid-coal-seam shuttle car seat ...........................................7 

8. Instrument setup on the mid-coal-seam shuttle car seat .........................................................10 

9. Instrument setup on the low-coal-seam shuttle car seat..........................................................12 

10. Seat ratings of mid-coal-seam shuttle car operators on comfort and vibration reduction ......17 
11. Seat ratings of mid-coal-seam shuttle car operators on seat padding and lumbar support........17 

12. Mid-coal-seam shuttle car operators’ comparisons and ratings of seats for padding and 

 lumbar support .....................................................................................................................18 

13. Low-coal-seam shuttle car operators’ ratings of seat designs for comfort and vibration 

reduction ..............................................................................................................................19 

14. Low-coal-seam shuttle car operators’ ratings of seat designs for different seat features .......19 

15. Low-coal-seam shuttle car operators’ comparisons and ratings of seat designs for 

different seat features...........................................................................................................20 

16. Fatigue-decreased proficiency curves for mid-coal-seam shuttle car with NIOSH seat M2B

 during no-load vehicle operations........................................................................................24 

17. Fatigue-decreased proficiency curves for low-coal-seam shuttle car with NIOSH seat L2C

 during no-load vehicle operations........................................................................................25 

TABLES 

1. Organization of seat trial days, seats, and subjects.................................................................8 

2. Existing seat versus NIOSH seats M2A and M2B: no-load comparison ............................10 

3. Existing seat versus NIOSH seats M2A and M2B: full-load comparison...........................11 

4. Existing seat versus NIOSH seats M2A and M2B: overall comparison .............................11 

5. Existing seat versus NIOSH seats L2A, L2B, and L2C: no-load comparison ....................12 

6. Existing seat versus NIOSH seats L2A, L2B, and L2C: full-load comparison...................13 

7. Existing seat versus NIOSH seats L2A, L2B, and L2C: overall comparison......................13 

8. Total average ratings for mid-coal-seam JOY 10SC shuttle car operators...........................14 

9. Total average ratings for low-coal-seam JOY 21SC shuttle car operators...........................15 

10. Comparison of FDP limit values with crest factor and vehicle operator questionnaire 

 ratings relative to improved performance for no-load conditions .....................................22 

11. Comparison of FDP limit values with crest factor and vehicle operator questionnaire 

 ratings relative to improved performance for full-load conditions....................................23 

12. Comparison of FDP limit values with crest factor and vehicle operator questionnaire 

 ratings relative to improved performance for full- and no-load conditions combined ......23 

13. Perceived and measured reductions in discomfort and jarring/jolting levels for operators

 of the JOY 10SC mid-coal-seam shuttle car (no load) ......................................................27 

14. Perceived and measured reductions in discomfort and jarring/jolting levels for operators

 of the JOY 21SC low-coal-seam shuttle car (no load) ......................................................27 

C–1. Output/input ratios, peak/RMS accelerations for different seats and operators of the 

 JOY 10SC mid-coal-seam shuttle car................................................................................37 

C–2. Average ratios, peak/RMS accelerations for different seats and conditions on the 

 JOY 10SC mid-coal-seam shuttle car................................................................................38 

C–3. Total average ratios, peak/RMS accelerations for different seats and conditions on the 

 JOY 10SC mid-coal-seam shuttle car................................................................................38 

C–4. Output/input ratios, peak/RMS accelerations for different seats and operators of the 

 JOY 21SC low-coal-seam shuttle car ................................................................................39 

C–5. Average ratios, peak/RMS accelerations for different seats and conditions on the 

 JOY 21SC low-coal-seam shuttle car ................................................................................40 

C–6. Total average ratios, peak/RMS accelerations for different seats and conditions on the 

 JOY 21SC low-coal-seam shuttle car ................................................................................40 
 

 

 

 

DEFINITION OF TERMS 

Autopower spectrum: Distribution of the mean square value of a time history over a frequency 

range. 

Crest factor: Ratio of peak acceleration divided by root-mean-square (RMS) acceleration. 

Peak: Peak amplitude of a signal. 

Transmissibility: Ratio of output/input for acceleration, velocities, displacements, forces. 

UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT 

 Hz hertz

 in inch

 lb pound 

 m/s2 

 meter per second square 

r Pearson product moment correlation 

 

FIELD EVALUATION OF SEAT DESIGNS FOR 

UNDERGROUND COAL MINE SHUTTLE CARS 

By Alan G. Mayton,1

 1

Mining engineer, Pittsburgh Research Laboratory, National Institute for Occupational Safety and Health, 

Pittsburgh, PA.

Christopher C. Jobes, Ph.D.,2

 2

Mechanical engineer, Pittsburgh Research Laboratory, National Institute for Occupational Safety and Health, 

Pittsburgh, PA.

N. Kumar Kittusamy, Sc.D.,3 

 3

Biomedical/mechanical engineer, Spokane Research Laboratory, National Institute for Occupational Safety and 

Health, Spokane, WA. 

and Dean H. Ambrose4 

 4

Safety engineer, Pittsburgh Research Laboratory, National Institute for Occupational Safety and Health, 

Pittsburgh, PA. 

ABSTRACT 

Researchers with the National Institute for Occupational Safety and Health (NIOSH) 

conducted a systematic study to evaluate seat designs on low- and mid-coal-seam shuttle cars. 

The purpose was to gather additional data to support earlier findings that NIOSH seats, with 

unique viscoelastic foam padding, are indeed improved designs for coal mine shuttle cars. This 

study included a larger sample of shuttle car operators than a prior NIOSH investigation. 

Eight shuttle car operators participated in evaluating seat designs on the basis of 

perceived levels of vehicle jarring/jolting and discomfort. Researchers then compared the 

operators’ perceptions with field-measured levels of vehicle jarring/jolting. Seven seat designs 

were evaluated on low- and mid-coal-seam shuttle cars during production operations at two 

underground coal mines in southern West Virginia. These seat designs comprised the one 

already in use on each vehicle and five NIOSH designs. 

Experimental data were collected using accelerometers, signal conditioning amplifiers, 

and filters connected to a data recorder, whereas subjective data were gathered via a visual 

analog scale (VAS) and a questionnaire. Field trials included shuttle cars operating under fulland no-load conditions. VAS responses indicated that NIOSH-designed seats performed better 

relative to comfort and isolation from vehicle jarring/jolting than the existing seats used in the 

shuttle cars. Both mid- and low-coal-seam shuttle car operators, during no-load and full-load 

conditions, rated lower levels of jarring/jolting with the NIOSH seat design. Questionnaire 

responses indicated that shuttle car operators rated NIOSH seat designs as more comfortable. 

Vehicle operators most frequently suggested the addition of armrests as a way to improve 

the seats on the mid-seam shuttle car. The quantitative levels of vehicle jarring/jolting for the 

no-load condition (more severe condition for vehicle operation) showed that NIOSH seats for the 

mid-coal-seam shuttle car performed better than the existing seat in terms of peak acceleration 

and crest factor. Similarly, for the low-coal-seam shuttle car, NIOSH seats performed better than 

the existing seat in terms of peak acceleration, root-mean-square (RMS) acceleration, and 

crest factor. 
This research will provide the mining industry with better seat designs for isolating 

operators from vehicle jarring/jolting. Furthermore, equipment manufacturers are afforded the 

opportunity to refine and improve the NIOSH seat designs using information gathered from this 

research study. 

INTRODUCTION 

Modern transportation vehicles continually expose individuals to whole-body vibration 

(WBV) and mechanical shock. These include airplanes, ships, trains, and a variety of industrial 

and agricultural equipment. Exposing individuals to WBV and mechanical shock can negatively 

impact their health, safety, comfort, and working efficiency and performance. 

In designing a comfortable seat, it is important to understand the vibration environment 

to which individuals are exposed and how well they can tolerate this environment. Moreover, 

human sensitivity to low-frequency WBV has pointed to ride quality as an important need in seat 

design [Amirouche et al. 1997]. This is especially true in the mining industry. 

A study by Mayton et al. [1999] reported on a low-coal shuttle car seat design that 

underwent limited, yet successful underground mine trials. The intent of the seat design 

comparison study reported here was to build on earlier work by performing a more systematic 

evaluation of the low-coal shuttle car seat design and a second mid-coal shuttle car seat design. 

By gathering more information with a larger sample of shuttle car operators, researchers 

confirmed earlier findings that NIOSH seat designs, with unique viscoelastic foam padding, are 

more effective in isolating shuttle car operators from jars and jolts. The NIOSH seat designs 

include viscoelastic foam, which has properties similar to those found in a mechanical 

spring/damper suspension system. The seats also include an adjustable lumbar support and a 

fore-aft seat adjustment, whereas existing seats have little or no lumbar support and include 

inexpensive foam padding of the type commonly used in furniture. In view of the harshness of 

the mining environment and the space constraints of mining equipment, viscoelastic foam 

padding offers a viable alternative to passive mechanical seat suspensions that are difficult to use 

under these conditions. 

BACKGROUND 

Research has shown that underground coal mine equipment operators experience adverse 

levels of exposure to WBV and vehicle jarring/jolting (mechanical shock). This exposure is 

identified as the higher-amplitude, peak components of WBV. Shuttle car haulage vehicles are 

among the major sources of exposure to vehicle jarring/jolting in underground coal mines. 

Remington et al. [1984] showed that WBV was severe for these vehicles, as well as for loadhaul-dumps (LHDs) or scoops. These circumstances have changed little since 1984, as 

evidenced by injury statistics and operator testimonials about these vehicles. Injury statistics for 

mobile mining equipment operators from the Mine Safety and Health Administration (MSHA) 

showed incidences of exposure to WBV and mechanical shock (vehicle jarring or jolting). These 

injuries can be described as acute and chronic musculoskeletal disorders affecting the back, 

neck, and head. The total MSHA-reported injuries involving the back, neck, and head showed a 

general decline for the period 1999–2003, although vehicle jarring/jolting-related injuries 

averaged 77% per year of the total back, neck, and head injuries for mine shuttle car operators. 

2
 
Additional evidence exists to illustrate that serious health effects can result from 

prolonged exposure of vehicle operators to jarring and jolting. Critical surveys of the literature 

have concluded that exposure to long-term WBV and awkward postures can adversely affect the 

spine and can increase the risk of low-back pain [Kittusamy and Buchholz 2004; Bernard 1997; 

Wikström et al. 1994; Seidel and Heide 1986; Hulshof and van Zanten 1987]. 

In an Australian study, Cross and Walters [1994] identified WBV and vehicle jarring as a 

contributing factor to back pain in the mining industry and as a significant concern to mobile 

equipment operators. They reviewed 28,306 compensation claims for a 4-year period (July 1986 

to March 1990), including surface and underground mining environments. Of the 8,961 claims 

relating to the head, back, and neck, 11% (986) were related to vehicular jarring. Underground 

transporters and shuttle cars accounted for 53% of all injuries attributed to vehicle jarring. 

STUDY APPROACH 

Through cooperative agreements, this study was carried out with the support of Joy 

Mining Machinery, the leading manufacturer and supplier of underground mine shuttle cars in 

the world (more than 90% market share of mine shuttle cars), and Dynamic Systems, Inc., 

Leicester, NC, a manufacturer and supplier of viscoelastic seating foams. The study was 

performed at the Laurel Alma and Black King underground coal mines (mid- and low-seam coal, 

respectively) in southern West Virginia. The mines are affiliates of Elk Run Coal Co. Their 

selection resulted from a referral by Joy Mining Machinery, the cooperator in the 

aforementioned agreement. 

Seat design trials were conducted on a JOY 21SC low-coal-seam shuttle car (Figure 1) 

operating at the Black King Mine and a JOY 10SC mid-coal-seam, side-saddle-style5

 

5

The side-saddle-style refers to how the shuttle car operator is positioned in the vehicle cab. In this case, the 

operator is perpendicular to, instead of facing, the direction of travel. 

3
 

shuttle car 

(Figure 2) operating at the Laurel Alma Mine. Seven different seat designs were tested on the 

two shuttle cars. The existing seats were designated as “seat L1” (Figure 3) and “seat M1” 

for trials with low- and mid-coal-seam shuttle car models, respectively. The NIOSH seats 

were designated as follows according to the viscoelastic foam arrangement for the low-seam 

shuttle car: 

•	 Seat L2A – included padding with a combination of Pudgee (PU) and Extra-soft 

SunMate (XSS) and a 3-in total thickness. 

•	 Seat L2B – included a 5-in total thickness of XSS foam padding. 

•	 Seat L2C – included padding with a combination of PU and XSS and a 5-in total 

thickness. 
Figure 1.—JOY 21SC low-coal-seam shuttle car. 

Figure 2.—JOY 10SC mid-coal-seam shuttle car. 

4
 
Figure 3.—Existing low-coal-seam shuttle car seat. 

Figures 4–5 show the NIOSH seat and the padding arrangements for the low-seam shuttle 

car. The NIOSH seats for the mid-seam shuttle car were designated as follows according to the 

viscoelastic foam arrangement: 

•	 Seat M2A – included a 5-in total thickness of XSS foam padding. 

•	 Seat M2B – included padding with a combination of PU and XSS and a 5-in total 

thickness. 

Figures 6–7 show the NIOSH seat and the padding arrangements for the mid-seam shuttle 

car. The peak acceleration, root-mean-square (RMS) acceleration, and crest factor, in reference 

to the threshold limit values (TLVs) of the American Conference of Governmental Industrial 

Hygienists [ACGIH 2006], were used to quantitatively evaluate seat design performance relative 

to vehicle jarring/jolting. 

5
 
Figure 4.—NIOSH low-coal-seam shuttle car seat. 

6
 

 Figure 5.—Viscoelastic arrangements for the lowcoal-seam shuttle car seat. 
Figure 6.—NIOSH mid-coal-seam shuttle car seat. 

Figure 7.—Viscoelastic arrangements for the mid-coal-seam shuttle car seat. 

7
 
 

 

 

METHODOLOGY 

Subjects 

Eight shuttle car operators participated in the study; five operated the JOY 10SC and 

three operated the JOY 21SC. The operators were all males from 24 to 58 years of age and 

averaged about 39 years. They ranged in height from 69 to 73 inches (an average of 71 inches) 

and in weight from 160 to 200 lb (an average of about 191 lb). The subjects’ experience in 

operating a shuttle car varied from to 1⁄2 to 24 years and averaged about 9 years. Similarly, their 

underground mining experience varied from 1⁄2 to 37 years and averaged 14 years. Moreover, 

before participating, the shuttle car operators were briefed about the study. Further, study 

participants were not coached, trained, or given practice sessions before the trials. They were 

briefly instructed about how to record their responses on the data forms and asked if they 

understood the instructions. Table 1 shows how the study was organized on the basis of seats, 

subjects, and test days. 

Table 1.—Organization of seat trial days, seats, and subjects 

Seat trials for low-coal-seam shuttle car: 

JOY 21SC 

Seat trials for mid-coal-seam shuttle car: 

JOY 10SC 

Trial day 

No. 

Seat 

design 

No. 

Operator ID No., 

shift 1 

Trial day 

No. 

Seat 

design 

No. 

Operator ID No., 

shift 1 

1 .............. L1 O1 O2 O3

2 .............. L2A O1 O2 O3

3 .............. L2B O1 O2 O3

 1.................. M1 O1 O2 O3 O4 

2.................. M2A O1 O2 O3 O4 

3.................. M2B O1 O2 O3 O4 

O5 

O5 

O5 

4 .............. L2C O1 O2 O3 

Procedure for Vibration Data Collection 

Researchers gathered data to determine the acceleration and impact energy entering the 

shuttle car seats through the floor and vehicle frame. Data were gathered in operating sections at 

each mine using three different tools. Quantitative or objective data were collected using a Sony 

PC208Ax eight-channel digital recorder; PCB triaxial accelerometers – model Nos. 356B18 and 

356B40; PCB 480E09 signal conditioning amplifiers; and PCB in-line, 150-Hz low-pass filters. 

The triaxial accelerometers were placed on the floor of the operators’ compartment near the base 

of the seat (frame measurement) and on the seat at the subject/seat interface (seat measurement). 

 Because of muddy conditions, the frame accelerometers were mounted to the frame of the 

shuttle car above the control panel. Mine roadway conditions during the field trials included 

areas that were deeply rutted and pothole-riddled, dry, wet and water-filled, and marginally 

“smooth.” 

Procedure for Subjective Data Collection 

8
 

Half of the qualitative or subjective data were collected with the visual analog scale 

(VAS) (see Appendix A). This tool was used to obtain the operators’ immediate impressions of 
shock, vibration, and discomfort levels for the vehicle ride on each of the seats and viscoelastic 

foam configurations. Operators were observed while tramming the shuttle cars when fully 

loaded with coal and when they were empty (en route to obtain a load). Each shuttle car 

operator made six round trips with each vehicle seat. The shuttle car operator marked this scale 

after traveling with and without a full load of coal on the first, third, and sixth round trips of each 

seat design trial. These round trip selections were deemed representative of typical roadwayinduced vibration and lessened the influence of earlier ratings on the current rating. A round trip 

consisted of traveling to the coal face with no load and returning to the load discharge location 

with a full load of coal. 

As such, the final ratings for each operator were the average of three out of the six round 

trips for each condition (of no-load and full-load). After each segment of the trip, participants 

were asked to rate the vehicle ride in terms of the level of jarring and jolting experienced through 

the selected seat. 

The VAS consisted of a line about 315

16 inches long and terminated at each end by a 

vertical hash mark by two extremes of jarring/jolting level and level of discomfort. The two 

extremes were denoted as “zero or none” and “maximum.” Operators were asked to make a 

vertical mark on the line that represents their level of perceived discomfort or jarring/jolting 

level. The rating scale was scored by measuring the distance (from left to right) from the 

beginning of the line to the operators’ mark and dividing this value by the total length of the line. 

A decimal value was calculated for each rating and varied from 0.0 to 1.0. Each operator, unless 

otherwise indicated, rated levels of jarring and jolting and discomfort three times. These values 

were summed and averaged to obtain an average operator rating for the individual seats. In turn, 

the average operator ratings were summed and averaged to obtain a total average operator rating. 

The remaining qualitative data were collected using a brief questionnaire administered 

through interviews with shuttle car operators. Researchers administered the questionnaire at the 

conclusion of each trial for each seat, which took approximately 5–10 minutes to complete. The 

questionnaire is shown in Appendix B. 

RESULTS 

Vehicle Jarring/Jolting Measurements 

JOY 10SC Mid-coal-seam Shuttle Car 

Data were taken on the side-saddle-style, mid-coal-seam shuttle car at the Laurel Alma 

mine in West Virginia. Figure 8 shows the instrumentation setup on this shuttle car. Five 

operators were tested on three seats (the existing seat (M1) and two test seats (M2A and M2B)) 

and the data sets were separated into full-load and no-load conditions. No information was 

collected for operator Nos. 3 and 5 on seat M2A due to other mining operation duties of these 

test subjects. Thus, from a possible 30 data sets, researchers obtained and analyzed a total of 

26 data sets. 

The data were initially examined according to RMS acceleration, peak acceleration, and 

crest factor. Ratios of input (frame) to output (seat) were used to normalize the data for different 

travel paths and operators. Averages were derived for each operator, load condition, and overall. 

Tables of these data are included in Appendix C. 

9
 
 Seat pad accelerometer 

Figure 8.—Instrument setup on the mid-coal-seam shuttle car seat. 

 

 

The data from Table C–1 (see Appendix C) were further reduced by overall averaging of 

the operators for the no-load condition, with the results shown in Table C–2. Table 2 below 

compares each test seat with the existing seat under the no-load condition. 

Table 2.—Existing seat versus NIOSH seats M2A and M2B: 

no-load comparison 

Average ratio Seat comparison 

Seat (output/input) 

Peak RMS Crest 

factor 

(1 vs. 2A or 2B) 

Peak RMS Crest 

factor 

M1.............. 2.54 1.66 1.47 — — — 

M2A ........... 2.13 1.88 1.13 0.84 1.13 0.77 

M2B ........... 2.44 1.85 1.31 0.96 1.12 0.90 

NOTE.—Peak and RMS are in m/s2

; crest factor is dimensionless. 

10

Viewing the data and comparing with seat M1: 

•	 Seat M2A showed a decrease in peak amplitude by 16% and crest factor by 23%, but 

an increase in RMS of 13%. 

•	 Similarly, seat M2B showed a decrease in peak amplitude by 4% and crest factor by 

10%, but an increase in RMS of 12%. 

The data from Table C–1 were further reduced by overall averaging of the operators for 

the full-load condition, with the results shown in Table C–2. Table 3 compares each test seat 

with the existing seat under the full-load condition. 
 

 

 

 

Table 3.—Existing seat versus NIOSH seats M2A and M2B: 

full-load comparison 

Average ratio Seat comparison 

Seat (output/input) 

Peak RMS Crest 

factor 

(1 vs. 2A or 2B) 

Peak RMS Crest 

factor 

M1.............. 1.64 1.49 1.10 — — — 

M2A ........... 2.13 1.78 1.20 1.30 1.20 1.09 

M2B ........... 2.48 1.89 1.32 1.52 1.27 1.20 

NOTE.—Peak and RMS are in m/s2

; crest factor is dimensionless. 

Viewing the data and comparing with seat M1: 

•	 Seat M2A showed increases in peak amplitude, RMS, and crest factor by 30%, 20%, 

and 9%, respectively. 

•	 Similarly, seat M2B showed increases in peak amplitude, RMS, and crest factor by 

52%, 27%, and 20%, respectively. 

The data from Table C–1 were further reduced by averaging over all the operators for 

both load conditions, with the results shown in Table C–3. Table 4 below compares each test 

seat with the existing seat overall. 

Table 4.—Existing seat versus NIOSH seats M2A and M2B: 

overall comparison 

Average ratio Seat comparison 

Seat (output/input) 

Peak RMS Crest 

factor 

(1 vs. 2A or 2B) 

Peak RMS Crest 

factor 

M1.............. 2.09 1.57 1.28 — — — 

M2A ........... 2.13 1.83 1.17 1.02 1.16 0.91 

M2B ........... 2.46 1.87 1.32 1.18 1.19 1.03 

NOTE.—Peak and RMS are in m/s2; crest factor is dimensionless. 

11
 

Viewing the data and comparing with seat M1: 

•	 Seat M2A showed an increase in peak amplitude and RMS by 2% and 16%, 

respectively, but a decrease in the crest factor of 9%. 

•	 Seat M2B showed increases in peak amplitude, RMS, and crest factor by 18%, 19%, 

and 3%, respectively. 

JOY 21SC Low-coal-seam Shuttle Car 

Data were taken on the JOY 21SC at the Black King Mine in West Virginia. Figure 9 

shows the instrumentation setup on this low-coal shuttle car. Three operators were tested on four 

seats (the existing seat (L1) and three test seats (L2A, L2B, and L2C)), and the data sets were 

separated into full-load and no-load conditions. No information could be salvaged from 

operator 1 on seat L2C owing to excessive battery bounce in the data recorder caused by a very 

rough ride. Thus, from a possible 24 data sets, researchers obtained and analyzed a total of 

22 data sets. 
 

 

 

Signal conditioning amplifiers 

Seat pad accelerometer 

Low-pass filters 

Seat pad accelerometer 

 Figure 9.—Instrument setup on the low-coal-seam shuttle car seat. 

 

 

The data were first examined by RMS acceleration, peak acceleration, and crest factor. 

Ratios of input (frame) to output (seat) were used to normalize the data for different travel paths 

and operators (see Table C–4 in Appendix C). The data were also examined using an autopower 

spectrum and transmissibility methods. 

The data from Table C–4 were further reduced by overall averaging of the operators for 

the no-load condition, with the results shown in Table C–5. Table 5 below compares each test 

seat with the existing seat under the no-load condition. 

Table 5.—Existing seat versus NIOSH seats L2A, L2B, and L2C: 

no-load comparison 

 

 

Average ratio Seat comparison 

Seat (output/input) 

Peak RMS Crest 

factor 

(1 vs. 2A, 2B, or 2C) 

Peak RMS Crest 

factor 

L1............... 1.29 1.27 1.02 — — — 

L2A ............ 1.00 1.14 0.88 0.77 0.90 0.86 

L2B ............ 1.11 1.18 0.94 0.86 0.93 0.92 

L2C ............ 1.19 1.16 1.02 0.92 0.92 1.00 

NOTE.—Peak and RMS are in m/s2

; crest factor is dimensionless. 

Viewing the data and comparing with seat L1: 

•	 Seat L2A showed decreases in peak amplitude, RMS, and crest factor by 23%, 10%, 

and 14%, respectively. 

•	 Seat L2B showed decreases in peak amplitude, RMS, and crest factor by 14%, 7%, 

and 8%, respectively. 

•	 Seat L2C showed decreases in both peak amplitude and RMS by 8% and no change 

in the crest factor. 

12
 
The data from Table C–4 were further reduced by overall averaging of the operators for 

the full-load condition, with the results shown in Table C–5. Table 6 below compares each test 

seat with the existing seat under the full-load condition. 

 

 

 

 

Table 6.—Existing seat versus NIOSH seats L2A, L2B, and L2C: 

full-load comparison 

Average ratio Seat comparison 

Seat (output/input) 

Peak RMS Crest 

factor 

(1 vs. 2A, 2B, or 2C) 

Peak RMS Crest 

factor 

L1............... 1.21 1.13 1.06 — — — 

L2A ............ 1.17 1.14 1.03 0.97 1.00 0.97 

L2B ............ 1.43 1.32 1.08 1.18 1.16 1.02 

L2C ............ 1.31 1.25 1.04 1.08 1.10 0.99 

NOTE.—Peak and RMS are in m/s2; crest factor is dimensionless. 

Viewing the data and comparing with seat L1: 

•	 Seat L2A showed decreases in both peak amplitude and crest factor by 3% and no 

change in RMS. 

•	 Seat L2B showed increases in peak amplitude, RMS, and crest factor by 18%, 16%, 

and 2%, respectively. 

•	 Seat L2C showed increases in peak amplitude and RMS by 8% and 10%, 

respectively, but a decrease in the crest factor of 1%. 

The data from Table C–4 were further reduced by overall averaging of the operators for 

both load conditions, with the results shown in Table C–6. Table 7 below compares each test 

seat with the existing seat overall. 

Table 7.—Existing seat versus NIOSH seats L2A, L2B, and L2C: 

overall comparison 

Average ratio Seat comparison 

Seat (output/input) 

Peak RMS Crest 

factor 

(1 vs. 2A, 2B, or 2C) 

Peak RMS Crest 

factor 

L1............... 1.25 1.20 1.04 — — — 

L2A ............ 1.08 1.14 0.95 0.87 0.95 0.91 

L2B ............ 1.27 1.25 1.01 1.02 1.04 0.97 

L2C ............ 1.25 1.21 1.03 1.00 1.00 0.99 

NOTE.—Peak and RMS are in m/s2; crest factor is dimensionless. 

Viewing the data and comparing with seat L1: 

•	 Seat L2A showed decreases in peak amplitude, RMS, and crest factor by 13%, 5%, 

and 9%, respectively. 

•	 Seat L2B showed increases in peak amplitude and RMS by 2% and 4%, respectively, 

but a decrease in the crest factor of 3%. 

•	 Seat L2C showed no change in peak amplitude and RMS and a slight decrease in the 

crest factor of 1%. 

13
 
 

 

 

 

 

 

 

 

 

 

 

Subjective Evaluation: VAS 

 Tables 8 and 9 illustrate the average and total average ratings for the shuttle car 

operators of the JOY 10SC mid-coal-seam and JOY 21SC low-coal-seam shuttle cars, 

respectively. 

Table 8.—Total average ratings for mid-coal-seam JOY 10SC shuttle car operators 

Average operator ratings Total 

Seat ID No. 1 ID No. 2 ID No. 3 ID No. 4 ID No. 5 average 

value 

NO LOAD 

M1 - Existing seat:

 Level of jar/jolt.............................. 0.869 0.769 0.788 0.825 0.457 0.742

 Level of discomfort....................... 0.866 0.750 0.859 0.859 0.358 0.738 

M2A - NIOSH seat (5-in XSS):

 Level of jar/jolt.............................. 0.093 0.115 ND 0.046 ND 0.085

 Level of discomfort....................... 0.112 0.140 ND 0.028 ND 0.093 

M2B - NIOSH seat (5-in XSS/PU):

 Level of jar/jolt.............................. 0.648 0.068 0.922 0.062 0.461 0.432

 Level of discomfort....................... 0.632 0.031 0.601 0.021 0.383 0.334 

FULL LOAD 

M1 - Existing seat:

 Level of jar/jolt.............................. 0.725 0.834 0.872 0.429 0.398 0.652

 Level of discomfort....................... 0.719 0.863 0.881 0.563 0.302 0.666 

M2A - NIOSH seat (5-in XSS):

 Level of jar/jolt.............................. 0.037 0.133 ND 0.012 ND 0.061

 Level of discomfort....................... 0.031 0.205 ND 0.025 ND 0.087 

M2B - NIOSH seat (5-in XSS/PU):

 Level of jar/jolt.............................. 0.598 0.115 0.934 0.050 0.423 0.424

 Level of discomfort....................... 0.595 0.034 0.810 0.009 0.380 0.366 

XSS Extra-soft SunMate. PU Pudgee. ND No data. 

14
 
 

 

 

 

 

 

 

 

Table 9.—Total average ratings for low-coal-seam JOY 21SC 

shuttle car operators 

Average operator ratings Total 

Seat ID No. 1 ID No. 2 ID No. 3 average 

value 

NO LOAD 

L1 - Existing seat:

 Level of jar/jolt.............................. 0.769 0.152 0.264 0.395

 Level of discomfort....................... 0.451 0.189 0.476 0.372 

L2A - NIOSH seat (3-in XSS/PU):

 Level of jar/jolt.............................. 0.460 0.056 0.458 0.325

 Level of discomfort....................... 0.040 0.831 0.442 0.438 

L2B - NIOSH seat (5-in XSS):

 Level of jar/jolt.............................. 0.274 0.012 0.224 0.170

 Level of discomfort....................... 0.009 0.959 0.221 0.396 

L2C - NIOSH seat (5-in XSS/PU):

 Level of jar/jolt.............................. 0.619 0.025 0.174 0.273

 Level of discomfort....................... 0.056 0.657 0.189 0.301 

FULL LOAD 

L1 - Existing seat:

 Level of jar/jolt.............................. 0.560 0.297 0.442 0.433

 Level of discomfort....................... 0.135 0.127 0.408 0.223 

L2A - NIOSH seat (3-in XSS/PU):

 Level of jar/jolt.............................. 0.230 0.046 0.233 0.170

 Level of discomfort....................... 0.028 0.869 0.233 0.377 

L2B - NIOSH seat (5-in XSS):

 Level of jar/jolt.............................. 0.068 0.025 0.068 0.054

 Level of discomfort....................... 0.012 0.968 0.053 0.344 

L2C - NIOSH seat (5-in XSS/PU):

 Level of jar/jolt.............................. 0.407 0.031 0.130 0.189

 Level of discomfort....................... 0.025 0.959 0.108 0.364 

XSS Extra-soft SunMate. PU Pudgee. 

15
 

From Tables 8–9, the following observations were made: 

Ratings from VAS responses indicate that the NIOSH-designed seats performed better 

than the existing seats used in the shuttle cars. 

•	 For both no-load and full-load conditions, mid-coal-seam shuttle cars operators rated 

lower levels of jarring/jolting and discomfort with the NIOSH seat using two 

different 5-in viscoelastic foam pad arrangements. 

•	 The viscoelastic foam arrangement with five 1-in layers of XSS foam padding was 

the most preferred by operators of the mid-seam shuttle car. 

•	 Similarly, for no-load and full-load conditions, low-seam shuttle car operators rated 

jarring/jolting as lower with the NIOSH seat using three different viscoelastic foam 

pad arrangements. The viscoelastic foam arrangements, in order of operator 

preference, were the 5-in XSS, 3-in PU/XSS, and 5-in PU/XSS padding. 

•	 However, under no-load and full-load conditions for the low-seam shuttle car, 

operators rated discomfort levels as lower with the existing seat versus the NIOSH 

seat using three different viscoelastic foam pad arrangements. Because researchers 

had to use existing bolt holes to install the NIOSH seat, the seat was closer to the 

control panel and made the shuttle car operators feel awkward and cramped. 
Moreover, a strong positive correlation for jarring/jolting and discomfort was determined 

for the different seats tested on the mid-seam JOY 10SC shuttle car. The following results were 

obtained: 

•	 A strong positive correlation (between jar/jolt and discomfort) was obtained for seat 

M1 (no load, r = 0.89; full load, r = 0.93). 

•	 A strong positive correlation (between jar/jolt and discomfort) was obtained for seat 

M2A (no load, r = 0.71; full load, r = 0.90). 

•	 A strong positive correlation (between jar/jolt and discomfort) was obtained for seat 

M2B (no load, r = 0.94; full load, r = 0.97). 

All of the above correlations for the mid-seam shuttle car showed a significant relationship 

between the variables of jolting/jarring and discomfort (P ≤ 0.05). 

A weak-to-strong positive correlation (for jar/jolt and discomfort) was realized for the 

different seats tested on the low-seam JOY 21SC shuttle car (P ≤ 0.05). The following results 

were obtained: 

•	 A weak positive correlation (between jar/jolt and discomfort) was obtained for seat 

L1 (no load, r = 0.29; full load, r = 0.66). 

•	 A strong positive correlation (between jar/jolt and discomfort) was obtained for seat 

L2A (no load, r = 0.84; full load, r = 0.88). 

•	 A strong positive correlation (between jar/jolt and discomfort) was obtained for seat 

L2B (no load, r = 0.88; full load, r = 0.69). 

•	 A moderate positive correlation (between jar/jolt and discomfort) was obtained for 

seat L2C (no load, r = 0.58; full load, r = 0.73). 

Subjective Evaluation: Operator Questionnaire 

Appendix B contains the questionnaire used to collect the data. The questions investigate 

the shuttle car operators’ comfort in relation to vibration or shock; operators’ opinions about seat 

padding and lumbar support; operators’ likes, dislikes, and suggested improvements concerning 

each seat; and the operators’ summary comparison of the seats. The questions are listed as 

follows: 

1. How would you rate this seat in terms of comfort? 

2. How would you rate this seat relative to reducing shock and vibration? 

3. What do you like about this seat? 

4. What don’t you like about this seat? 

5. Rate the following: seat padding, lumbar support, reclining seatback, seat-pan tilt, 

 armrest, fore-aft adjustment 

6. What would you do to improve this seat? 

7. Compare seat No. 1 with seat No. 2. 

Figures 10–15 present graphical displays of the operators’ responses to these questions. 

16
 
JOY 10SC Mid-coal-seam Shuttle Car 

Figure 10 shows seat ratings regarding comfort and jarring/jolting (shock/vibration) 

reduction. Figure 11 shows seat ratings for seat padding and lumbar support. Both figures show 

that seat M2A was rated highest in comfort, vibration reduction, seat padding, and lumbar 

support. 

17
 

Comfort Vibration 

Seat Seat Seat M2B 

Better 

Ratings 

 Figure 10.—Seat ratings of mid-coal-seam shuttle car operators 

on comfort and vibration reduction.

 

Seat Padding Lumbar Support 

Seat M1 Seat M2A Seat M2B 

Better Ratings 

 Figure 11.—Seat ratings of mid-coal seam shuttle car operators on 

seat padding and lumbar support. 
Seat M1 ranked the lowest in comfort, vibration reduction, seat padding, and lumbar 

support; however, one operator liked its comfort and another liked the way the body fit the seat 

frame. “Partly broken,” “weak,” and “no comfort” were the leading dislikes expressed for seat 

M1. Suggested improvements to seat M1 included adding armrests and removing and replacing 

the seat with the original one. 

Seat M2A was ranked most favorable. Operators liked the seats ability to absorb 

vibration/jars and its good support to the back, and the seat felt comfortable. The seat was 

apparently too low for good visibility, and seat placement caused the controls to be too close. 

Adding armrests and improved seat location were the major suggestion to improve seat M2A. 

Seat M2B was ranked second (see Figures 10–11). Operators liked the seat comfort and 

firmness, but disliked the way it absorbed shock and found the back support too stiff. Operators 

offered several suggestions to improve seat M2B, such as making the seat softer, adding 

armrests, and improving the lumbar support. 

Figure 12 shows the seat comparisons. The ratings reflect how the seats felt to the 

operator in comparison to each other. Seat M2A was the favorite. Seat padding rated well for 

both seats M2A and M2B. Individual ratings in Figures 10–11 compare favorably to the 

findings in Figure 12. Seat M1 (the existing seat) was the least favorite in all ratings. Adding 

armrests was the improvement most often suggested for all of the seats. 

 

 

Better 

Ratings 

Seats Seats Seats 

M2A vs. M2A vs. M2B vs. 

Overal 

Seats 

M2B vs. M1 

Seat Padding Lumbar Support 

 Figure 12.—Mid-coal-seam shuttle car operators’ comparisons and 

ratings of seats for padding and lumbar support. 

JOY 21SC Low-coal-seam Shuttle Car 

Figure 13 shows seat ratings regarding comfort and shock/vibration reduction. Figure 14 

shows seat ratings for seat padding and lumbar support. Both figures show that seat L2B was 

rated highest in comfort, vibration reduction, seat padding, lumbar support, and seat-pan tilt. 

18
 
Seat L1 (the existing seat) ranked the lowest in seat comfort and vibration reduction. 

Operators liked how the seat reduced jars and jolts, and one operator thought it was fairly 

comfortable. However, operators disliked its durability and the lumbar was too thick. 

Suggestions to improve the seats were to make the back support better, improve adjustments for 

better visibility, and improve padding. Seat L1 did not have seat-pan tilt or fore-aft adjustment. 

 

Comfort Vibration Reduction 

Seat L1 Seat L2A Seat L2B Seat L2C 

Better Ratings 

 Figure 13.—Low-coal-seam shuttle car operators’ ratings of 

seat designs for comfort and vibration reduction.

Ratings 

Better 

Seat Lumbar Support Reclining Seatpan Fore-aft Adjustment 

Seat Seat Seat Seat 

 Figure 14.—Low-coal-seam shuttle car operators’ ratings of 

seat designs for different seat features. 

19 
Seats L2A and L2B ranked well in comfort and vibration reduction. Operators liked how 

seat L2A took the strain off the lower back when the shuttle car traveled across large holes. 

Also, operators liked the thick cushion on seat L2A and how the seat adjusts to the body. For 

seat L2B, operators liked how comfortable it felt, how it reduced shocks, and its thick cushion. 

However, both seats were too close to the controls and did not fit the confined space of the 

shuttle car. Regarding seat L2B, operators found that they drove the shuttle car slower to avoid 

being bounced into the canopy. Suggested improvements for seats L2A and L2B were to make 

the lumbar seat wider. One operator suggested improving the operators’ control panel envelope 

to accommodate better seats, such as seat L2B. 

Seat L2C was the favorite. Operators liked the padding, how well it reduced shock, how 

well the lumbar support took the strain off the back, and how comfortable the seat was. 

However, operators did not like the lumbar width. Also, the seat was too large for the confined 

space of the shuttle car. Suggested improvements for seat L2C were to make the lumbar support 

and seat wider and to add a scaled-down seat to fit better behind the controls. 

Figure 15 shows the seat comparisons. Individual ratings in Figures 13–14 favor seat 

L2C, while the comparison ratings favor seat L2B. Seat L1 is the least favorite in all ratings. 

Seat padding, lumbar support, and seat-pan tilt are rated better for seat L2B than any other seat. 

The reclining back is better on seat L2B and surprisingly favored on seat L1. Making the seat a 

better fit for the operator compartment is a suggested improvement. This could improve 

clearance between the operator and controls and allow for better operator adjustability and 

visibility. 

 

 

 

 

Seats 

L2A vs. L1

 Seats 

L2B vs. L2A

 Seats 

L2B vs. L1 

Seats 

L2C vs. L2B

 Seats 

L2C vs. L2A

 Seats 

L2C vs. L1 

Overall Seat Lumbar Support Reclining Back Seatpan Tilt

 Better 

Ratings 

 Figure 15.—Low-coal seam shuttle car operators’ comparisons and ratings of seat designs 

for different seat features. 

20 
COMPARISON OF ISO 2631 FATIGUE-DECREASED PROFICIENCY LIMITS 

WITH RECORDED DATA AND QUESTIONNAIRE DATA 

21
 

Researchers compared the International Organization for Standardization (ISO) 2631 

fatigue-decreased proficiency (FDP) limits from the ACGIH [2006] for the objective and 

subjective data discussed above. Again, it is important to note that the shuttle car operator 

receives the roughest ride when traveling with no-load. Acceleration levels tend to be higher 

during no-load conditions since the shuttle car has less mass while maintaining the same spring 

rate and damping. The natural frequency of the vehicle shifts higher in the no-load condition 

and lower in the full-load condition, as shown by the equation— 

ω = k / m (1) 

where ω = natural frequency; 

 k = spring constant; 

and m = mass. 

Researchers compiled Tables 10–12 to show how the FDP limits correlated with the 

results obtained from measured levels of vehicle jarring/jolting and questionnaire responses for 

the different vehicle operators and seats designs. Table 10 provides data for the JOY 10SC and 

JOY 21SC shuttle cars when operating under no-load conditions. For the JOY 10SC, seat M2A 

showed 57% better performance in FDP, 30% better performance in crest factor, and 47% better 

overall performance when rated by the operators. Seat M2B showed 60% better performance in 

FDP, 12% better performance in crest factor, and 17% better overall performance when rated by 

the operators. Figure 16 is an example of FDP curves for the JOY 10SC mid-coal-seam shuttle 

car during no-load operation with NIOSH seat M2B. 

For the JOY 21SC, seat L2A showed 45% better performance in FDP, 16% better 

performance in crest factor, and 9% better performance overall when rated by the operators. 

Seat L2B showed 46% better performance in FDP, 9% better performance in crest factor, and 

25% better overall performance when rated by the operators. Seat L2C showed 77% better 

performance in FDP, no change in crest factor, and 9% better overall performance when rated by 

the operators. Figure 17 is an example of FDP curves for the JOY 21SC low-coal-seam shuttle 

car during no-load operation with NIOSH seat L2C. 

Table 11 lists data for the JOY 10SC and JOY 21SC shuttle cars when operating under 

full-load conditions. For the JOY 10SC, seat M2A showed 143% worse performance in FDP, 

8% worse performance in crest factor, and 47% better overall performance when rated by the 

operators. Seat M2B showed 194% worse performance in FDP, 17% worse performance in crest 

factor, and 17% better overall performance when rated by the operators. 

For the JOY 21SC, seat L2A showed 31% better performance in FDP, 3% better 

performance in crest factor, and 9% better overall performance when rated by the operators. 

Seat L2B showed 63% better performance in FDP, 2% worse performance in crest factor, and 

25% better overall performance when rated by the operators. Seat L2C showed 57% better 

performance in FDP, 2% better performance in crest factor, and 9% better overall performance 

when rated by the operators. 
Overall data for both full- and no-load conditions are shown in Table 12. For the JOY 

10SC, seat M2A showed 4% worse performance in FDP, 9% better performance in crest factor, 

and 47% better overall performance when rated by the operators. Seat M2B showed 3% worse 

performance in FDP, 3% worse performance in crest factor, and 17% better overall performance 

when rated by the operators. 

For the JOY 21SC, seat L2A showed 37% better performance in FDP, 9% better 

performance in crest factor, and 9% better overall performance when rated by the operators. 

Seat L2B showed 59% better performance in FDP, 3% better performance in crest factor, and 

25% better overall performance when rated by the operators. Seat L2C showed 67% better 

performance in FDP, 1% better performance in crest factor, and 9% better overall performance 

when rated by the operators. 

Table 10.—Comparison of FDP limit values with crest factor 

and vehicle operator questionnaire ratings relative to 

improved performance for no-load conditions 

Seat 

Fatigue 

decreased, 

min 

Crest 

factor 

Questionnaire

(rating)

NO LOAD - JOY 10SC 

M1............... 

M2A ............ 

M2B ............ 

76.00 

175.67 

190.40 

1.47 

1.13 

1.31 

2.00
 

3.75
 

2.40
 

NO LOAD - JOY 21SC 

L1................ 

L2A ............. 

L2B ............. 

L2C............. 

32.33 

59 

59.33 

139.5 

1.02 

0.88 

0.94 

1.02 

3
 

3.3
 

4
 

4.3
 

NO-LOAD COMPARISON - JOY 10SC 

(percent better than seat M1) 

M1............... 

M2A ............ 

M2B ............ 

— 

56.74 

60.08 

— 

30.09 

12.21 

— 

46.67 

16.67 

NO-LOAD COMPARISON - JOY 21SC 

(percent better than seat L1)
 

L1................ 

L2A ............. 

L2B ............. 

L2C............. 

— 

45.20 

45.51 

76.82 

— 

15.91 

8.51 

0.00 

—
 

9.09
 

25.00
 

9.09

 NOTE.—Crest factor is dimensionless. Higher values for 

"questionnaire" and "fatigue decreased" indicate better results, 

whereas lower values for "crest factor" indicate better results. 

22
 
Table 11.—Comparison of FDP limit values with crest factor 

and vehicle operator questionnaire ratings relative to 

improved performance for full-load conditions 

Seat 

Fatigue 

decreased, 

min 

Crest 

factor 

Questionnaire

(rating)

FULL LOAD - JOY 10SC 

M1............... 

M2A ............ 

M2B ............ 

185 

76 

63 

1.1 

1.2 

1.32 

2
 

3.75
 

2.4
 

FULL LOAD - JOY 21SC 

L1................ 

L2A ............. 

L2B ............. 

L2C............. 

60.33 

88 

165 

139.5 

1.06 

1.03 

1.08 

1.04 

3 

3.3 

4 

3.3 

FULL-LOAD COMPARISON - JOY 10SC 

(percent better than seat M1) 

M1............... 

M2A ............ 

M2B ............ 

— 

–143.42 

–193.65 

— 

–8.33 

–16.67 

— 

46.67 

16.67 

FULL-LOAD COMPARISON - JOY 21SC 

(percent better than seat L1) 

L1................ 

L2A ............. 

L2B ............. 

L2C............. 

— 

31.44 

63.44 

56.75 

— 

2.91 

–1.85 

1.92 

— 

9.09 

25.00 

9.09

 NOTE.—Crest factor is dimensionless. Higher values for 

"questionnaire" and "fatigue decreased" indicate better results, 

whereas lower values for "crest factor" indicate better results.
 

Table 12.—Comparison of FDP limit values with crest factor and 

vehicle operator questionnaire ratings relative to improved 

performance for full- and no-load conditions combined 

Seat 

Fatigue 

decreased, 

min 

Crest 

factor 

Questionnaire

(rating)

OVERALL - JOY 10SC 

M1 ............... 

M2A ............. 

M2B ............. 

130.8 

125.83 

126.7 

1.28 

1.17 

1.32 

2
 

3.75
 

2.4
 

OVERALL - JOY 21SC 

L1 ................ 

L2A .............. 

L2B .............. 

L2C.............. 

46.33 

73.5 

112.17 

139.5 

1.04 

0.95 

1.01 

1.03 

3
 

3.3
 

4
 

3.3
 

OVERALL COMPARISON - JOY 10SC 

(percent better than seat M1) 

M1 ............... 

M2A ............. 

M2B ............. 

— 

–3.95 

–3.24 

— 

9.40 

–3.03 

— 

46.67 

16.67 

OVERALL COMPARISON - JOY 21SC 

(percent better than seat L1)
 

L1 ................ 

L2A .............. 

L2B .............. 

L2C.............. 

— 

36.97 

58.70 

66.79 

— 

9.47 

2.97 

0.97 

—
 

9.09
 

25.00
 

9.09

 NOTE.—Crest factor is dimensionless. Higher values for 

"questionnaire" and "fatigue decreased" indicate better results, 

whereas lower values for "crest factor" indicate better results. 

23 
 Figure 16.—Fatigue-decreased proficiency curves for mid-coal-seam shuttle car with 

NIOSH seat M2B during no-load vehicle operations. 

24
 Figure 17.—Fatigue-decreased proficiency curves for low-coal-seam shuttle car with 

NIOSH seat L2C during no-load vehicle operations. 

25
DISCUSSION 

26
 

Average ratings from VAS responses indicated that the NIOSH-designed seats were 

superior to the existing seats used in the shuttle cars. For both no-load and full-load conditions, 

average ratings by operators of mid-coal-seam shuttle cars indicated lower levels of 

jarring/jolting and discomfort with the NIOSH seat using two different 5-in viscoelastic foam 

pad arrangements. The 5-in XSS viscoelastic foam arrangement (seat M2A) was most preferred 

by operators of the mid-coal-seam shuttle car. 

Similarly, for no-load and full-load conditions, average ratings by low-coal-seam shuttle 

car operators showed lower jarring/jolting with the NIOSH seat using three different viscoelastic 

foam pad arrangements. The viscoelastic foam arrangements, in order of operator preference, 

were the 5-in XSS (seat L2B), 3-in PU/XSS (seat L2A), and 5-in PU/XSS foam padding (seat 

L2C). Nevertheless, with regard to overall levels of discomfort, the average operator rating 

favored the existing seat over the NIOSH seat with the three different viscoelastic foam pad 

arrangements under both full-load and no-load conditions. Researchers had to install the NIOSH 

seat using existing bolt holes, which caused the seat to be closer to the control panel and made 

the shuttle car operators feel awkward and cramped. Also, seats L2B and L2C (the 5-in foam 

pads) caused the operators to be closer to the canopy. 

With regard to the mid-coal-seam vehicles, according to Table 13, NIOSH seat M2A 

showed 16% and 23% reductions in peak acceleration and crest factor, respectively. Seat M2A, 

however, showed a 13% increase for RMS acceleration. Similarly, seat M2B showed 4% and 

11% reductions in peak acceleration and crest factor, respectively, and an 11% increase in RMS 

acceleration. Nevertheless, NIOSH researchers consider RMS acceleration the least descriptive 

of the three measurement parameters in terms of jarring/jolting events for vehicle operators. The 

reason is that RMS acceleration reflects a greater time period and includes acceleration levels 

far lower than those of peak acceleration, which includes a very short time period and a much 

higher level of energy. With its short time period and higher level, the peak acceleration (the 

jar/jolt) is perceived by vehicle operators as having a more profound impact on them in terms of 

comfort and health. 

Better results were obtained with NIOSH-designed seats for the low-coal-seam vehicle. 

NIOSH seat L2A showed 22% and 14% reductions in peak acceleration and crest factor, 

respectively. Moreover, seat L2A reduced RMS acceleration by 10%. Similarly, seat L2B 

showed 14% and 8% reductions in peak acceleration and crest factor, respectively, and a 

7% reduction for RMS acceleration. Finally, seat L2C showed 8% and 9% reductions in peak 

acceleration and RMS acceleration, respectively, with no change in crest factor. 

With regard to the mid-coal-seam shuttle car, seat M2A showed 57% better performance 

in FDP, 30% better performance in crest factor, and 47% better overall performance when rated 

by the operators. Seat M2B showed 60% better performance in FDP, 12% better performance in 

crest factor, and 17% better overall performance when rated by the operators. 

Similarly, with regard to the low-coal-seam shuttle car, seat L2A showed 31% better 

performance in FDP, 3% better performance in crest factor, and 9% better overall performance 

when rated by the operators. Seat L2B showed 63% better performance in FDP, 2% worse 

performance in crest factor, and 25% better overall performance when rated by the operators. 

Seat L2C showed 57% better performance in FDP, 2% better performance in crest factor, and 

9% better overall performance when rated by the operators. 
Tables 13–14 show the results of the analysis for VAS and unweighted measured data. 

Table 13.—Perceived and measured reductions in discomfort and jarring/jolting levels 

for operators of the JOY 10SC mid-coal-seam shuttle car (no load) 

Perceived reduction in— Measured reduction in

jarring/jolting 

Seat Discomfort, 

% 

Jarring/ 

jolting, 

% 

Peak 

a, 

%

RMS 

a, 

%

Crest

factor,

% 

M1 - Existing seat .................................. 

M2A - NIOSH seat (5-in XSS)................ 

M2B - NIOSH seat (5-in XSS/PU).......... 

— 

65 

40 

— 

66 

31 

— 

16 

4 

— 

1

13 

1

11 

— 

23 

11 

a = acceleration 

1

Increase instead of reduction. 

Table 14.—Perceived and measured reductions in discomfort and jarring/jolting levels 

for operators of the JOY 21SC low-coal-seam shuttle car (no load) 

Perceived reduction in— Measured reduction in

jarring/jolting 

Seat Discomfort, 

% 

Jarring/ 

jolting, 

% 

Peak 

a, 

%

RMS 

a, 

%

Crest

factor,

% 

L1 - Existing seat ................................... 

L2A - NIOSH seat (3-in XSS/PU)........... 

L2B - NIOSH seat (5-in XSS)................. 

— 

1

7 

1

2 

— 

7 

23 

— 

22 

14 

— 

10 

7 

— 

14 

8 

L2C - NIOSH seat (5-in XSS/PU)........... 7 12 8 9 0 

a = acceleration 

1

Increase instead of reduction. 

27
 

The percentages in these tables were obtained from averages and, consequently, as in the case of 

the measured data, they may not necessarily result in the same values that are computed from a 

single set of the stated measured parameters. The VAS ratings showed that vehicle operators 

rated overall (on average from three test trial ratings) the NIOSH-designed seats better than the 

existing seats. For the mid-coal-seam shuttle car, under no-load (worse case of two) conditions, 

operators rated the level of jarring/jolting 31%–66% lower and level of discomfort 40%–65% 

lower with the M2A and M2B seats. For the low-coal-seam shuttle car, under no-load conditions, 

operators rated the level of jarring/jolting 7%–23% lower with the L2A, L2B, and L2C seats. 

In addition, operators rated the level of discomfort 7% lower with seat L2C, but 2%–7% higher 

with the L2A and L2B seats. 

The quantitative levels of vehicle jarring/jolting for no-load conditions showed that the 

NIOSH M2A and M2B seats for the mid-coal-seam shuttle car performed better than the existing 

seat in terms of peak acceleration and crest factor, whereas the L2A, L2B, and L2C seats 

performed better than the existing seat in terms of peak acceleration, RMS acceleration, and crest 

factor. During full-load conditions, the foam- or air-filled tires provided primary damping or 

attenuation of jars/jolts as a result of the extra mass from the load of coal. The performance of 

the seat in providing this attenuation of jars/jolts is thus secondary. However, the extra mass is 

lacking under no-load conditions and allows for more severe levels of jarring/jolting for the 
shuttle car operators. Consequently, it is significant that the NIOSH-designed seats performed 

better than the existing seats when comparing average values for peak acceleration, RMS 

acceleration, and crest factor. 

With the mid-coal-seam vehicles, NIOSH seat M2A showed 16% and 23% reductions in 

peak acceleration and crest factor, respectively. Seat M2A, however, showed a 13% increase for 

RMS acceleration. Similarly, seat M2B showed 4% and 11% reductions in peak acceleration 

and crest factor, respectively, and an 11% increase in RMS acceleration. Again, NIOSH 

researchers consider RMS acceleration the least descriptive of the three measurement parameters 

in terms of jarring/jolting events for vehicle operators. The reason is that RMS acceleration 

reflects a greater time period and includes acceleration levels far lower than those of peak 

acceleration, which includes a very short time period and a much higher level of energy. With 

its short time period and higher level, the peak acceleration (the jar/jolt) is perceived by vehicle 

operators as having a more profound impact on them in terms of comfort and health. 

Even better results were obtained with the NIOSH-designed seats for the low-coal-seam 

vehicle. NIOSH seat L2A showed 22% and 14% reductions in peak acceleration and crest 

factor, respectively. Moreover, seat L2A reduced RMS acceleration by 10%. Similarly, seat 

L2B showed 14% and 8% reductions in peak acceleration and crest factor, respectively, and also 

a 7% reduction for RMS acceleration. Finally, seat L2C showed 8% and 9% reductions in peak 

acceleration and RMS acceleration, respectively, with no change in crest factor. 

The concepts of peak acceleration, RMS acceleration, and crest factor as a means for 

assessing vehicle jarring/jolting exposure were used in the data analysis. These analytical 

parameters, although descriptive as presented in ISO 2631 (1985)- and American National 

Standards Institute (ANSI) (1979)-based TLVs of the ACGIH [2006], do not seem to completely 

address the true impact on the body sustained by seated vehicle operators when they are 

subjected to vehicle jarring and jolting. The method assesses the effects of environmental 

vibration on the human body relative to health, efficiency, and comfort. Human exposure to 

vibration is described relative to three broad criteria: health and safety (exposure limit), working 

efficiency (FDP), and comfort (reduced-comfort boundary) (ISO 2631–1 [ISO 1985], 

ANSI S3.18 [ANSI 1979]). The ACGIH [2006] points out that the TLVs are not adequate for 

evaluating a vibration environment characterized by high-amplitude mechanical shocks (jars or 

jolts) and it will “underestimate the effects of WBV...when crest factors exceed 6.” 

Some optional methods of analysis concerning the impact of jars and jolts on the body 

are worth considering and include those presented in ISO 2631–1 [ISO 1997] and ISO 2631–5 

[ISO 2004]. The ISO [1997], which stipulates a crest factor of 9 as compared to 6 noted above, 

no longer includes exposure boundaries or limits and FDP. The standard cites that exposure 

duration of various effects on people (assumed to be the same for different effects—health, 

working proficiency, and comfort) was not supported by laboratory research. ISO 2631–1 

[ISO 1997] offers health guidance caution zones based on the RMS value of the frequencyweighted acceleration. In cases where the crest factor exceeds 9, the running RMS method 

featuring the maximum transient vibration value and the fourth-power vibration dose value 

method are suggested. On the other hand, ISO 2631–5 [ISO 2004] presents a method for 

evaluating vibration containing multiple shocks (jars and jolts) using the spinal response 

acceleration dose. This is determined by calculating the human response of the spine, counting 

the number and magnitudes of peak accelerations, and calculating acceleration dose using a dose 

model that applies the Palmgren-Miner fatigue theory. 

28
 
Griffin [1990, 1998] discusses the evolution of ISO 2631–1 from its inception and points 

out its various shortcomings through the 1997 revision. Griffin suggests that ISO 2631–1 

[ISO 1997] may cause unneeded confusion relative to the measurement, evaluation, and 

assessment of human shock and vibration exposures. 

Another method of analysis is the absorbed power method investigated by Pradko et al. 

[1965]. Lee and Pradko [1968] discussed the analytical use of absorbed power to determine how 

humans would respond to vibration in periodic and random environments. They described this 

method in the time and frequency domains. According to Lee and Pradko [1968], the method of 

absorbed power is important in that it has physical significance; it can be measured and 

computed analytically. In addition, absorbed power is a scalar quantity and thus can be summed 

to assess the human response in complex systems with multidegrees of freedom. 

More recently, Amirouche et al. [1991] and Tong et al. [1999a] reported on analytical 

computer models for optimizing the energy absorption during exposure to human body 

vibration and for evaluating the distribution of absorbed power and how the body reacts to 

roadway-induced vibration. Using their model to study the energy absorption and work 

done by the human body’s muscles (represented as springs and dampers) during a rough ride, 

Tong et al. [1999a] discussed how energy is transmitted to different parts of the body and what 

happens when input conditions change. Understanding the energy flow among the body’s parts 

can provide valuable input for the design of a seat and its suspension. The application of this 

approach to mining vehicle seats requires further study. 

As Mayton et al. [2003] reported relative to Tables 13–14, quantitative levels of vehicle 

jarring/jolting for no-load conditions showed that NIOSH seats M2A and M2B for the mid-coalseam performed better than the existing seat (M1) in terms of peak acceleration and crest factor, 

whereas L2A, L2B, and L2C seats performed better than the existing seat (L1) in terms of peak 

acceleration, RMS acceleration, and crest factor. Furthermore, Mayton et al. [2005] compared 

the NIOSH seat designs according to the absorbed power method discussed by Amirouche et al. 

[1991] and Tong et al. [1999a,b]. The results concurred with the aforementioned analytical 

results of this NIOSH study in showing lower energy absorption to the body. 

Joy Mining Machinery has been marketing the NIOSH seat designs and includes the 

improved seat design in its current product line. The company independently tested the new 

design and affirmed the results of the NIOSH studies. Between two shuttle car models, Joy has 

sold more than 510 of the newly designed seats from 1999 to 2005 and estimates that about 

2,600 shuttle cars are in operation worldwide (about 1,500 in the United States). This translates 

to approximately 15% of the global population of shuttle cars that are equipped with the new seat 

design or padding design. In terms of the U.S. market for low-seam shuttle cars, 26% of shuttle 

cars are equipped with the improved seat design. Extrapolating further, the new seat design is 

positively impacting the health and safety of approximately 1,140 shuttle car operators.6 

 

6

Assumptions include: one operator per shuttle car per shift, three shifts per day; 380 shuttle cars with new seat 

designs – 130 low-seam models (two seats per vehicle) and 250 mid- to high-seam models (one seat per vehicle); 

and 500 total shuttle cars in U.S. low-seam operations in 2005. 

29
 
LIMITATIONS 

This study provides useful results and information regarding shuttle car seat designs for 

two models of underground coal mine shuttle cars. Nevertheless, it was limited in various ways. 

The primary limitations of the study included: the small sample size of eight subject shuttle car 

operators, the constraints of conducting field trials during coal mining production operations, the 

driving differences among individual subjects, two underground coal mines and no noncoal 

mines, the exact same driving route was not possible although the same roadway was used, the 

worn existing seat versus the virtually new NIOSH seats, the short period of time that subjects 

used the NIOSH seats, and the durability and the reliability of the NIOSH seat designs could not 

be determined within the test period. 

CONCLUSIONS 

The objective of this study was to gather additional data to support earlier findings that 

NIOSH seats, with unique viscoelastic foam padding, are indeed improved designs for coal mine 

shuttle cars. A larger sample of shuttle car operators was included in this work compared to a 

prior NIOSH investigation. 

Both objective and subjective data from this study indicate that NIOSH seat designs are 

more effective in reducing levels of jarring and jolting and generally enhancing operator 

comfort, considering the limitations indicated with the seat installations for the low-coal-seam 

shuttle car. The researchers realize that the use of seat foam padding alone is not the ultimate 

answer in providing optimum isolation for vehicle operators. Nevertheless, the NIOSH seat 

designs showed definite improvements over the existing seat designs for the shuttle car models 

studied. Future research should study the effects of combining viscoelastic foam seat padding 

with passive, semiactive, or active seat suspension system, such as that described by Tong et al. 

[1999a,b]. 

These results can provide the mining industry with additional evidence that NIOSH seat 

designs are improvements relative to existing designs for isolating operators from vehicle 

jarring/jolting. Moreover, the equipment manufacturer with these study results has the 

opportunity to further refine and improve the NIOSH seat designs from the added input of shuttle 

car operators. Furthermore, the results of this study may have potential application for the seats 

of other heavy off-road vehicles used in surface mining, construction, and agriculture. 

ACKNOWLEDGMENTS 

The authors thank the following engineering technicians with the NIOSH Pittsburgh 

Research Laboratory: Albert H. Cook – for his work in constructing foam pads for the NIOSH 

seats and assistance with mine field trials; and George F. Fischer (retired) and Mary Ellen 

Nelson – for their efforts in constructing the NIOSH seats for the shuttle car field trials. The 

authors also express their appreciation to Wayne Persinger, Safety Director, his staff, and the 

mine management and hourly workers at the Laurel Alma and Black King Mines of Elk Run 

Coal Co. (an affiliate of A. T. Massey Corp.) for their cooperation in the mine field trials. 

In addition, the authors thank Joy Mining Machinery of Harnischfeger Industries, Inc., for its 

help and support in this work. Finally, the authors thank Dynamic Systems, Inc., for supplying 

the viscoelastic foams used as seat padding for the various padding configurations in the 

NIOSH seat designs. 

30
 
REFERENCES 

ACGIH [2006]. Threshold limit values (TLVs) for chemical substances, physical agents, 

and biological exposure indices (BEIs). Cincinnati, OH: American Conference of Governmental 

Industrial Hygienists, pp. 132–139. 

Amirouche FML, Xie M, Patwardhan A [1991]. Energy minimization to human body 

vibration response for seating/standing postures. In: Advances in Bioengineering. Vol. 20. 

New York: American Society of Mechanical Engineers, Bioengineering Division, pp. 539–542. 

Amirouche FML, Xu P, Alexa E [1997]. Evaluation of dynamic seat comfort and 

driver’s fatigue. Warrendale, PA: Society of Automotive Engineers, Inc., technical paper 

971573. 

ANSI [1979]. ANSI S3.18: guide for the evaluation of human exposure to whole-body 

vibration. New York: American National Standards Institute. 

Bernard BP, ed. [1997]. Musculoskeletal disorders and workplace factors: a critical 

review of epidemiologic evidence for work-related musculoskeletal disorders of the neck, upper 

extremity, and low back. Cincinnati, OH: U.S. Department of Health and Human Services, 

Public Health Service, Centers for Disease Control and Prevention, National Institute for 

Occupational Safety and Health, DHHS (NIOSH) Publication No. 97–141. 

Cross J, Walters M [1994]. Vibration and jarring as a cause of back injury in the NSW 

coal mining industry. Saf Sci 17(4):269–274. 

Griffin MJ [1990]. Handbook of human vibration. London: Elsevier Ltd., pp. 417–430. 

Griffin MJ [1998]. A comparison of standardized methods for predicting the hazards of 

whole-body vibration and repeated shocks. J Sound Vib 215(4):883–914. 

Hulshof C, van Zanten BV [1987]. Whole-body vibration and low-back pain: a review of 

epidemiologic studies. Int Arch Occup Environ Health 59(3):205–220. 

ISO [1985]. Mechanical shock and vibration: evaluation of human exposure to wholebody vibration. Part 1. Geneva, Switzerland: International Organization for Standardization. 

ISO 2631–1. 

ISO [1997]. Mechanical shock and vibration: evaluation of human exposure to wholebody vibration. Part 1. Geneva, Switzerland: International Organization for Standardization. 

ISO 2631–1. 

ISO [2004]. Mechanical shock and vibration: evaluation of human exposure to wholebody vibration. Part 5: method for evaluation of vibration containing multiple shocks. Geneva, 

Switzerland: International Organization for Standardization. ISO 2631–1. 

Kittusamy NK, Buchholz B [2004]. Whole-body vibration and postural stress among 

operators of construction equipment: a literature review. J Saf Res 35(3):255–261. 

Lee RA, Pradko F [1968]. Analytical analysis of human response to vibration. 

Warrendale, PA: Society of Automotive Engineers, Inc., technical paper 680091. 

Mayton AG, Merkel R, Gallagher S [1999]. Improved seat reduces jarring/jolting for 

operators of low-coal shuttle cars. Min Eng 51(12):52–56. 

Mayton AG, Ambrose DH, Jobes CC, Kittusamy NK [2003]. Ergonomic and existing 

seat designs compared on underground mine haulage vehicles. In: Proceedings of the Human 

Factors and Ergonomics Society 47th Annual Meeting (Denver, CO, October 13–17, 2003). 

Santa Monica, CA: Human Factors and Ergonomics Society, pp. 1256–1260. 

31
 
Mayton AG, Amirouche F, Jobes CC [2005]. Comparison of seat designs for 

underground mine haulage vehicles using the absorbed power and ISO 2631–1(1985)-based 

ACGIH threshold limit methods. Int J Heavy Vehicle Syst 12(3):225–238. 

Pradko F, Orr TR, Lee RA [1965]. Human vibration analysis. Warrendale, PA: Society 

of Automotive Engineers, Inc., technical paper 650426. 

Remington PJ, Andersen DA, Alakel MN [1984]. Assessment of whole-body vibration 

levels of coal miners. Vol. 2: Whole-body vibration exposure of underground coal mining 

machine operators. Bolt, Beranek, and Newman, Inc. U.S. Bureau of Mines contract No. 

J0308045. NTIS No. PB 87–144119. 

Seidel H, Heide R [1986]. Long-term effects of whole-body vibration: a critical survey 

of the literature. Int Arch Occup Environ Health 58(1):1–26. 

Tong RT, Amirouche FML, Nishiyama S [1999a]. Analysis of absorbed power 

distribution in ride dynamics: evaluation of driver’s comfort. In: Proceedings of the ASME 

Symposium: Innovations in Vehicle Design and Development. Vol. 101. New York: American 

Society of Mechanical Engineers, pp. 53–60. 

Tong RT, Amirouche FML, Palkovics L [1999b]. Ride control: a two-state suspension 

design for cabs and seats. In: Proceedings of the 16th Symposium of the International 

Association for Vehicle System Dynamics (Pretoria, Republic of South Africa, August 31­

September 4, 1999), Vol. 33, suppl. 1, pp. 578–589. 

Wikström BO, Kjellberg A, Landström U [1994]. Health effects of long-term 

occupational exposure to whole-body vibration: a review. Int J Ind Ergon 14:273–292. 

32
 
APPENDIX A.—VISUAL ANALOG SCALE FORM 

Shuttle Car Model: 

Operation: No Load 

Jarring/Jolting Level: 

Instructions: For the travel that you just completed, please rate the amount of jarring and jolting 

you felt from the vehicle through the seat by placing a straight line on the rating scale. 

| | 

No High 

Jarring/Jolting Jarring/Jolting 

Jarring/Jolting Discomfort: 

Instructions: For the travel that you just completed, please rate the amount of jarring and jolting 

you felt from the vehicle through the seat by placing a straight line on the rating scale. 

| | 

No Extreme 

Discomfort Discomfort

****************************************************************************** 

Operation: Full Load 

Jarring/Jolting Level:
 

Instructions: For the travel that you just completed, please rate the amount of jarring and jolting 

you felt from the vehicle through the seat by placing a straight line on the rating scale. 

| | 

No High 

Jarring/Jolting Jarring/Jolting 

Jarring/Jolting Discomfort:
 

Instructions: For the travel that you just completed, please rate the amount of jarring and jolting 

you felt from the vehicle through the seat by placing a straight line on the rating scale. 

| | 

No Extreme 

Discomfort Discomfort

33
 
 

APPENDIX B.—OPERATOR QUESTIONNAIRE TO COMPARE SEATS 

ON SHUTTLE CARS IN UNDERGROUND COAL MINES 

Date: 

Study ID No.: 

Name: 

Gender: Male Female ______ 

Age: (yrs) _________ 

 

Height: Ft _________ In _________ 

Weight: ___________ Lbs 

Experience as Shuttle Car Operator (yrs): 

Underground Mining Experience (yrs): 

Underground Experience At This Mine (yrs): 

 

 

34
 
1. How would you rate this seat in terms of comfort? 

1 = very comfortable 2 = comfortable 3 = uncomfortable 

4 = very uncomfortable Comments: 

2. How would you rate this seat relative to reducing shock and vibration? 

1 = very good 2 = good 3 = fair 4 = poor Comments: 

3. What do you like about this seat? 

4. What don’t you like about this seat? 

5. On a scale from 1 to 5, where 1 = poor, 2 = fair, 3 = good, 4 = very good, and 

5 = excellent, rate the following: 

o seat padding _____ 

o lumbar support _____ 

o reclining seatback _____ 

o seatpan tilt _____ 

o armrest _____ 

o fore-aft adjustment _____ 

6. What would you do to improve this seat? 

7. Compare Seat No. 1 with Seat No. 2 for the items below using this scale: 

1 = much worse, 2 = worse, 3 = same, 4 = better, 5 = much better. 

a. Overall _________________ 

Explain ___________________________________________________________ 

_________________________________________________________________ 

_________________________________________________________________ 

b. Seat padding _____________ 

Explain ___________________________________________________________ 

_________________________________________________________________ 

_________________________________________________________________ 

35
 
c. Lumbar support __________ 

Explain ___________________________________________________________ 

_________________________________________________________________ 

_________________________________________________________________ 

d. Reclining seatback ________ 

Explain ___________________________________________________________ 

_________________________________________________________________ 

_________________________________________________________________ 

e. Seatpan tilt ______________ 

Explain ___________________________________________________________ 

_________________________________________________________________ 

_________________________________________________________________ 

f. Armrest ________________ 

Explain ___________________________________________________________ 

_________________________________________________________________ 

_________________________________________________________________ 

36
 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

APPENDIX C.—MEASURED JARRING/JOLTING DATA 

Table C–1.—Output/input ratios, peak/RMS accelerations for different seats and operators of the 

JOY 10SC mid-coal-seam shuttle car
 

Input (frame) Output (seat) Ratio (output/input) 

Seat Peak RMS Crest 

factor Peak RMS Crest factor Peak RMS Crest factor 

FULL LOAD 

Seat M1:

 ID No. 1............ 10.88 1.79 6.09 17.96 2.70 6.64 1.65 1.51 1.09

 ID No. 2............ 5.37 1.03 5.20 9.09 1.57 5.79 1.69 1.52 1.11

 ID No. 3............ 4.04 0.80 5.08 7.00 1.18 5.94 1.73 1.48 1.17

 ID No. 4............ 3.93 1.14 3.44 7.20 1.90 3.79 1.83 1.66 1.10

 ID No. 5............ 14.00 1.60 8.74 17.83 2.01 8.87 1.27 1.25 1.02 

Seat M2A:

 ID No. 1............ 10.76 2.26 4.76 23.27 3.97 5.86 2.16 1.76 1.23

 ID No. 2............ 4.35 0.98 4.44 9.03 1.77 5.11 2.08 1.80 1.15

 ID No. 3............ ND ND ND ND ND ND ND ND ND

 ID No. 4............ 5.66 1.22 4.64 12.12 2.17 5.59 2.14 1.78 1.20

 ID No. 5............ ND ND ND ND ND ND ND ND ND 

Seat M2B:

 ID No. 1............ 7.39 1.54 4.79 18.98 3.07 6.18 3.07 1.99 1.29

 ID No. 2............ 5.41 1.09 4.97 11.13 2.03 5.48 2.06 1.87 1.10

 ID No. 3............ 7.10 1.38 5.16 16.05 2.64 6.08 2.26 1.92 1.18

 ID No. 4............ 5.65 1.40 4.04 11.23 2.60 4.32 1.99 1.86 1.07

 ID No. 5............ 7.54 1.65 4.56 26.64 2.97 8.97 3.53 1.80 1.97 

NO LOAD 

Seat M1:

 ID No. 1............ 7.31 1.81 7.31 37.04 3.88 37.04 3.88 2.14 2.36

 ID No. 2............ 9.96 1.49 6.68 17.54 2.27 7.72 1.76 1.53 1.16

 ID No. 3............ 7.61 1.53 4.98 18.47 2.33 7.94 2.43 1.52 1.59

 ID No. 4............ 5.99 1.64 3.66 11.57 2.85 4.07 1.93 1.74 1.11

 ID No. 5............ 8.54 1.56 5.48 13.00 2.13 6.09 1.52 1.37 1.11 

Seat M2A:

 ID No. 1............ 5.45 1.08 5.06 11.84 2.00 5.91 2.17 1.86 1.17

 ID No. 2............ 2.62 0.66 3.94 5.43 1.28 4.24 2.08 1.93 1.08

 ID No. 3............ ND ND ND ND ND ND ND ND ND

 ID No. 4............ 5.58 1.36 4.11 11.97 2.51 4.77 2.14 1.85 1.16

 ID No. 5............ ND ND ND ND ND ND ND ND ND 

Seat M2B:

 ID No. 1............ 8.19 1.31 6.27 22.66 2.71 8.37 2.71 2.07 1.34

 ID No. 2............ 2.61 0.60 4.36 6.05 1.09 5.53 2.31 1.82 1.27

 ID No. 3............ 3.43 0.80 4.26 10.17 1.52 6.71 2.97 1.88 1.57

 ID No. 4............ 5.94 0.91 6.56 12.91 1.73 7.48 2.18 1.91 1.14

 ID No. 5............ 5.91 1.05 5.62 11.65 1.65 7.04 1.97 1.57 1.25 

ND No data. 

NOTE.—Peak and RMS are in m/s2; crest factor is dimensionless.
 

37
 
 

 

 

 

 

 

 

 

 

 

 

 

Table C–2.—Average ratios, peak/RMS accelerations for different seats and conditions on the 

JOY 10SC mid-coal-seam shuttle car
 

Input (frame) Output (seat) Ratio (output/input) 

Seat Peak RMS Crest 

factor Peak RMS Crest factor Peak RMS Crest factor 

Seat M1:

 Full load ........... 7.64 1.27 5.71 11.81 1.87 6.21 1.64 1.49 1.10

 No load............. 7.88 1.60 4.97 19.53 2.69 7.07 2.54 1.66 1.47 

Seat M2A:

 Full load ........... 6.92 1.49 4.61 14.81 2.64 5.52 2.13 1.78 1.20

 No load............. 4.55 1.03 4.37 9.75 1.93 4.97 2.13 1.88 1.13 

Seat M2B:

 Full load ........... 6.62 1.41 4.71 16.80 2.66 6.21 2.48 1.89 1.32

 No load............. 5.22 0.93 5.41 12.69 1.74 7.03 2.44 1.85 1.31 

NOTE.—Peak and RMS are in m/s2

; crest factor is dimensionless. 

Table C–3.—Total average ratios, peak/RMS accelerations for different seats and conditions on the 

JOY 10SC mid-coal-seam shuttle car
 

Seat Input 

RMS 

Output Ratio Input 

Peak 

Output Ratio Input 

Crest factor 

Output Ratio 

Seat M1.............. 1.44 2.28 1.57 7.76 15.67 2.09 5.34 6.64 1.28 

Seat M2A ........... 1.26 2.28 1.83 5.74 12.28 2.13 4.49 5.25 1.17 

Seat M2B ........... 1.17 2.20 1.87 5.92 14.75 2.46 5.06 6.62 1.32 

NOTE.—Peak and RMS are in m/s2; crest factor is dimensionless. 

38
 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Table C–4.—Output/input ratios, peak/RMS accelerations for different seats and operators of the 

JOY 21SC low-coal-seam shuttle car
 

Input (frame) Output (seat) Ratio (output/input) 

Seat Peak RMS Crest 

factor Peak RMS Crest factor Peak RMS Crest factor 

FULL LOAD 

Seat L1:

 ID No. 1............ 10.08 2.07 4.87 10.30 2.12 4.87 1.02 1.02 1.00

 ID No. 2............ 8.14 1.58 2.00 10.54 1.92 2.00 10.54 1.92 2.00

 ID No. 3............ 9.58 1.92 4.99 12.44 2.23 5.57 1.30 1.16 1.12 

Seat L2A:

 ID No. 1............ 7.42 1.56 4.76 8.69 1.77 4.92 1.17 1.13 1.03

 ID No. 2............ 7.07 1.44 4.90 8.40 1.63 5.14 1.19 1.13 1.05

 ID No. 3............ 10.35 1.49 6.96 11.91 1.71 6.95 1.15 1.15 1.00 

Seat L2B:

 ID No. 1............ 7.30 1.18 6.21 10.17 1.50 6.79 1.39 1.27 1.09

 ID No. 2............ 7.46 1.15 6.46 11.86 1.55 7.67 1.59 1.34 1.19

 ID No. 3............ 13.43 1.58 8.49 17.34 2.11 8.22 1.29 1.33 0.97 

Seat L2C:

 ID No. 1............ ND ND ND ND ND ND ND ND ND

 ID No. 2............ 4.18 0.86 4.88 5.92 1.10 5.39 1.10 1.28 1.10

 ID No. 3............ 9.68 1.61 6.02 11.57 1.95 5.93 1.20 1.21 0.98 

NO LOAD 

Seat L1:

 ID No. 1............ 7.89 1.82 4.35 9.99 2.34 4.27 1.27 1.29 0.98

 ID No. 2............ 11.19 1.68 2.00 13.72 2.18 2.00 13.72 2.18 2.00

 ID No. 3............ 13.47 2.79 4.83 18.69 3.40 5.50 1.39 1.22 1.14 

Seat L2A:

 ID No. 1............ 13.21 1.91 6.90 12.38 2.11 5.87 0.94 1.10 0.85

 ID No. 2............ 14.11 1.73 8.18 15.99 2.11 7.59 1.13 1.22 0.93

 ID No. 3............ 7.34 1.56 4.70 6.75 1.69 3.99 0.92 1.08 0.85 

Seat L2B:

 ID No. 1............ 8.78 2.12 4.14 9.33 2.60 3.58 1.06 1.23 0.86

 ID No. 2............ 6.45 1.47 4.40 8.57 1.98 4.33 1.33 1.35 0.98

 ID No. 3............ 10.09 1.97 5.11 9.59 1.93 4.98 0.95 0.98 0.97 

Seat L2C:

 ID No. 1............ ND ND ND ND ND ND ND ND ND

 ID No. 2............ 7.92 1.36 5.83 10.59 1.73 6.13 1.34 1.27 1.05

 ID No. 3............ 7.67 1.36 5.63 8.02 1.44 5.57 1.05 1.06 0.99 

ND No data. 

NOTE.—Peak and RMS are in m/s2

; crest factor is dimensionless.
 

39
 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Table C–5.—Average ratios, peak/RMS accelerations for different seats and conditions on the 

JOY 21SC low-coal-seam shuttle car
 

Input (frame) Output (seat) Ratio (output/input) 

Seat Peak RMS Crest 

factor Peak RMS Crest factor Peak RMS Crest factor 

Seat L1:

 Full load ........... 9.27 1.86 5.01 11.09 2.09 5.31 1.21 1.13 1.06

 No load............. 10.85 2.10 5.27 14.13 2.64 5.35 1.29 1.27 1.02 

Seat L2A:

 Full load ........... 8.28 1.50 5.54 9.67 1.71 5.67 1.17 1.14 1.03

 No load............. 11.55 1.73 6.59 11.71 1.97 5.82 1.00 1.14 0.88 

Seat L2B:

 Full load ........... 9.40 1.30 7.05 13.12 1.72 7.56 1.43 1.32 1.08

 No load............. 8.44 1.85 4.55 9.16 2.17 4.30 1.11 1.18 0.94 

Seat L2C:

 Full load ........... 6.93 1.23 5.45 8.75 1.53 5.66 1.31 1.25 1.04

 No load............. 7.80 1.36 5.73 9.31 1.58 5.85 1.19 1.16 1.02 

NOTE.—Peak and RMS are in m/s2

; crest factor is dimensionless. 

Table C–6.—Total average ratios, peak/RMS accelerations for different seats and conditions on the 

JOY 21SC low-coal-seam shuttle car
 

Seat Input 

RMS 

Output Ratio Input 

Peak 

Output Ratio Input 

Crest factor 

Output Ratio 

Seat L1............... 1.98 2.37 1.20 10.06 12.61 1.25 5.14 5.33 1.04 

Seat L2A ............ 1.62 1.84 1.14 9.92 10.69 1.08 6.07 5.74 0.95 

Seat L2B ............ 1.58 1.94 1.25 8.92 11.14 1.27 5.80 5.93 1.01 

Seat L2C ............ 1.30 1.55 1.21 7.36 9.03 1.25 5.59 5.75 1.03 

NOTE.—Peak and RMS are in m/s2

; crest factor is dimensionless. 

40
 
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DHHS (NIOSH) Publication No. 2007 –0 10

SAFER ● HEALTHIER ● PEOPLE tm