ERGONOMIC AND EXISTING SEAT DESIGNS COMPARED ON UNDERGROUND MINE HAULAGE VEHICLES 

Alan Mayton, Dean Ambrose, Chris Jobes 

National Institute for Occupational Safety and Health (NIOSH), Pittsburgh Research Laboratory, Pittsburgh, PA 

N. Kumar Kittusamy 

NIOSH, Spokane Research Laboratory, Spokane, WA 

ABSTRACT 

NIOSH researchers conducted a study to compare seat designs on underground coal mine haulage vehicles. 

The objective of the study was to support prior findings that NIOSH-designed seats, which incorporated 

ergonomic design features (e.g., viscoelastic foam padding and low-back support), are improved designs. 

Based on measured levels of vehicle jarring/jolting and perceived discomfort, researchers evaluated four 

different designs - two in-use and two NIOSH-developed, ergonomic designs. Researchers collected data 

using a short questionnaire, a linear, visual analog scale, and accelerometers with a data recorder. Results 

showed that vehicle operators favored the NIOSH seats with added adjustability, low-back support, and 

improved seat padding over the existing seats. In addition, the measurements indicated all NIOSH seats 

performed better than the existing seat, under the no-load (worse of two) conditions, in reducing peak 

acceleration, crest factor, and RMS acceleration. The authors summarize the data collected and operator 

preferences for seat designs and different foam padding arrangements. 

INTRODUCTION 

Industrial equipment exposes individuals to whole-body 

vibration (WBV) and mechanical shock. This exposure can 

adversely affect their health, safety, comfort, as well as, 

working efficiency and performance. For many years, seat 

design was not a priority in vehicle design. Yet, proper seat 

design is a basic consideration in reducing the adverse effects 

of WBV exposure to vehicle operators. Since the human body 

is sensitive to low frequency WBV, ride quality has become 

an important need in seat design. This is especially true in the 

mining industry. When designing a suitable seat, it is prudent 

to answer two fundamental questions (Amirouche et al., 

1997): 1) What is the vibration environment that individuals 

are exposed to? 2) How well can they tolerate this 

environment? 

Mayton et al. (1 999) reported on a low-coal, mine shuttle 

car seat design with limited, yet successful, underground mine 

field trials. The current seat design comparison study, an 

extension of earlier work, was a more systematic evaluation of 

the low-coal shuttle car seat design and included a mid-coal 

shuttle car seat design. By gathering information with a larger 

sample of shuttle car operators, research supported earlier 

findings that NIOSH seats, with unique viscoelastic foam 

padding, are improved seat designs in isolating shuttle car 

operators fromjars and jolts. The NIOSH seat designs include 

viscoelastic foam that has properties similar to those found in 

a mechanical spring/damper suspension system. The NIOSH 

seats also include ergonomic features, such as, an adjustable 

lumbar support and fore-aft seat adjustment. This contrasts 

with some existing seats, which have limited adjustability, 

little or no lumbar support, and include inexpensive foam 

padding commonly used in furniture. 

THESIS 

- 

The authors assert that NIOSH seat designs offer better 

alternatives to some existing seat designs for mine shuttle cars 

in isolating operators from vehicle jarring/jolting and for 

reducing discomfort. This is demonstrated from both 

subjective and objective data collected through operator 

responses and recorded vibrations during production 

operations. The data indicate NIOSH seat designs are 

preferred by haulage vehicle operators and incorporate 

ergonomic features, such as viscoelastic foam padding, lowback support, and greater adjustability. 

MINE FIELD TRIALS 

Underground mine field trials for the study were 

performed at the Elk Run Coal Company’s Laurel Alma and 

Black King underground coal mines near the Beckley/ 

Charleston area of West Virginia. The coal seam thickness 

and mining height for the Laurel Alma mine averaged 183 cm 

(72 in) with a range of 152 to 244 cm (60 to 96 in) for seam 

thickness and 206 cm (81 in) with a range of 198 to 244 cm 

(66 to 96 in) for mining height. Black King mine averaged 124 

cm (49 in) with a range of 102 to 127 cm (40 to 50 in) and 142 

cm (56 in) with a range of 132 to 152 cm (52 to 60 in), 

respectively, for seam thickness and mining height. The study 

focused on two shuttle cars, a mid-coal-seam and a low-coalseam model. Eight vehicle operators performed their regular 

duty cycles (comprising no-load and full-load conditions) with 

the shuttle cars using four distinct seat designs that included 

seven different foam padding arrangements. Data were 

collected using three techniques: a short questionnaire; a 

linear, visual analog scale (VAS); and accelerometers 

connected to a data recorder. 

Seat design trials were conducted on a mid-coal seam, 

side-saddle-style shuttle car operating at the Laurel Alma mine 

and a low-coal-seam shuttle car operating at the Black King 

mine. (The side-saddle-style refers to how the vehicle 

operator is positioned in the vehicle cab. In this case, the 

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

travel.) Four basic seat designs were compared on the shuttle 

cars. Mid-coal-seam vehicle seats were designated as M1 
(existing) and M2A and M2B (NIOSH), Figure la. Low-coalseam vehicle seats, shown in Figure 2a, were designated L1 

(existing) and L2A, L2B, and L2C (NIOSH). The viscoelastic 

foam padding arrangements distinguishing the different 

NIOSH seats are shown in Figures lb and 2b. 

Since they were in service for some time, the existing seats 

were more worn than the NIOSH seats, which were like new. 

The seats (after the NIOSH design) for the mid-coal-seam 

shuttle car, were designated according to viscoelastic foam 

arrangements as follows: 

0 Seat M2A - included a total thickness of 13 cm (5 in) 

Sun-Mate Extra-Soft (XSS) foam padding. 

0 Seat M2B - included padding with a combination of 

Pudgee (PU) and XSS and a total thickness of 13 cm (5 

in). 

For the low-coal-seam shuttle car, the seats (after the NIOSH 

design) were designated according to the viscoelastic foam 

arrangements as follows: 

0 

0 

0 

Seat L2A - included padding with a combination of PU 

and XSS and a total thickness of 8 cm (3 in). 

Seat L2B - included a total thickness of 13 cm (5 in) XSS 

foam padding. 

Seat L2C - included padding with a combination of PU 

and XSS and a total thickness of 13 cm (5 in). 

Figure la. Mid-coal-seam shuttle car seats - existing (left) 

and NIOSH/Ergonomic (right). 

METHODS 

Figure 1 b. Viscoelastic foam padding arrangements M2A 

(left - without pudgee) and M2B (right - with 

pudgee). 

Figure 2a. Low-coal-seam shuttle car seats - existing (left) 

and NIOSH/Ergonomic (right). 

Figure 2b. Viscoelastic foam padding arrangements left to 

right, L2A, L2C and L2B (without pudgee). 

Researchers interviewed shuttle car operators to obtain a 

major portion of subjective data. The interview guide was 

administered at the conclusion of each trial for each seat and 

took approximately 5 to 10 minutes to complete. The list of 

seven questions included on the quide is summarized as 

follows: 

How would you rate the seat in terms of comfort? 

How would you rate the seat relative to reducing shock 

and vibration? 

0 What do you like about the seat? 

0 What don’t you like about the seat? 

Rate seat padding, lumbar support, reclining seatback, 

seat-pan tilt, armrest, and fore-aft adjustment. 

0 What would you do to improve this seat? 

0 Compare the seats to each other. 

The remaining portion of the subjective data was 

collected using a linear, visual analog scale (VAS) and a brief 

questionnaire. The VAS 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. The shuttle car operator marked this 

scale after traveling with a full load of coal and with no load 

on the first, third, and sixth round trip of the trials for each 

seat. A round trip consisted of traveling to the coalface with 

no load and returning to the load discharge location with a full 

load of coal. 

Objective data gathering was done with a data recorder, 

accelerometers, signal conditioning amplifiers and in-line, 

low-pass filters. Researchers collected data to determine the 

acceleration and impact energy entering the seat through the 

floor from the vehicle frame. Triaxial accelerometers were 

placed on the floor of the operator’s compartment near the 

base of the seat (frame measurement) and on the seat at the 

subjectheat interface (seat measurement). Because of muddy 

conditions, the frame accelerometers were mounted to the 

frame of the shuttle car above the control panel. During the 
field trials, mine roadway conditions were noted as smooth, 

pothole-riddled, debris-strewn, rutted, dry, wet, and waterfilled. 

FINDINGS 

Questionnaire Data - Mid-Coal-Seam Shuttle Car 

Researchers used the numerical scales: 1 = very 

comfortable, 2 = comfortable, 3 = uncomfortable and 4 = very 

uncomfortable for operator assessments of comfort; and 1 = 

very good, 2 = good, 3 = fair and 4 = poor for operator 

assessments of reducing vibration or vehicle jarring/jolting. 

Figures 3 and 4 represent average values for the eight shuttle 

car operators. 

reduction (Figure 3), seat padding and lumbar support; 

however, one-operator liked its comfort and another liked the 

way the body fit the seat frame. Broken (from weakness in 

seat mounting) and no comfort were the leading dislikes of 

Seat M1. Suggested improvements to Seat M1 included 

adding armrests and removing and replacing the seat. 

Seat M1 ranked the lowest in comfort, vibration 

24 

m3 

E2 

k1 

A 

C .- 

m 50 

Comfort Vi brat ion 

Reduction 

Figure 3. Mid-coal-seam shuttle car seat designs rated for 

comfort and vibration reduction 

Seat M2A was ranked most favorable. Operators liked 

the seats ability to absorb vibration and jars. The seat provided 

good support to the back and felt comfortable. The seat was 

apparently too low for good visibility and seat placement 

caused the controls to be too close. Adding armrests and 

improving seat location were the major suggestions to 

improve Seat M2A. 

comfort and vibration. Operators liked the seat comfort and 

firmness and disliked the way it absorbed shock and the stated 

that the back support was too stiff. Operators offered several 

suggestions to improve Seat M2B such as to make the seat 

softer, add armrests and improve lumbar supports. 

operator. Seat M2A was the favored. Seat padding rated well 

for both Seat M2A and SeatM2B. Seat M1 was the least 

favored in all ratings. Adding armrests was the improvement 

most often suggested for any of the seats. 

Seat M2B was ranked second in comparisons relative to 

In summary, the ratings reflect how the seats felt to the 

Questionnaire Data - Low-Coal-Seam Shuttle Car 

Seat L1 ranked the lowest in seat comfort and vibration 

reduction (Figure 4). Nevertheless, prior to using the NIOSH 

seats, the operators commented that they liked the way Seat 

L1 reduced jars and jolts; one operator even thought it was 

fairly Comfortable. However, operators disliked its durability 

and stated that the lumbar support 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. 

8 

Comfort Vibration 

Reduction 

Figure 4. Low-coal-seam shuttle car seat designs rated for 

comfort and vibration reduction 

Seat L2A and Seat L2C ranked well in comfort and 

vibration reduction. Operators liked how Seat L2A reduced 

lower back strain when the shuttle car traveled across large 

holes. Also, operator’s liked the thick cushion on Seat L2A 

and how the seat adjusts to the body. Operators liked Seat 

L2B for how comfortable it felt, how it reduced shocks, and 

for its thick cushion. Both seats were situated too close to the 

controls and did not fit the shuttle car confined area. 

Regarding Seat L2B, operators rode the shuttle car slower to 

avoid being bounced into the canopy. Suggested 

improvements for Seat L2A and Seat L2B were to make the 

lumbar support wider. An operator suggested improving the 

operator’s control panel envelope to accommodate better 

seats, such as Seat L2B. 

Seat L2C was favored. Operators liked the padding for 

its comfort and shock reduction properties and the lumbar 

support for reducing back strain. However, operators did not 

like the lumbar width. Also, the seat was too big for the 

confined area of the shuttle car. Operators’ suggested several 

improvements to Seat 2C: make lumbar support and seat 

wider and add a scaled down seat so as to fit better behind the 

controls. 

In summary, Seat L1 was the least favored in all ratings. 

Seat padding, lumbar support and seat-pan tilt were rated 

better in Seat L2B than any other seat. Reclining back is 

better on Seat L2B and surprisingly favored on Seat L1. 

Making the seat a better fit for the operator compartment was 

a suggested improvement. This could improve clearance 

between operator and controls and allow for better operator 

adjustability and visibility. 
VAS and Measured Data 

(Existing) 

M2A 

(NIOSH 5 in XSS) 

M2B 

NIOSH (5 in 

XSSiPU) 

Tables 1 and 2 present the results of the analysis for VAS 

and measured data. The VAS ratings showed that vehicle 

operators rated overall (on average from 3 trial ratings) the 

NIOSH-designed seats better than the existing seats. The 

ratings were transformed from the marked linear scale into a 

decimal value between 0 and 1 .O, which is interpreted as 

jarring/jolting or discomfort and extreme levels of the same, 

respectively. For the mid-coal-seam vehicle, under the noload (worse case of two) conditions, operators rated level of 

jarringijolting 3 1 to 66% !ewer and level of discomfort 40 to 

65% lower with the Seats M2A and M2B. (Data on Seat M2A 

was obtained with two fewer subjects than for Seat M1 and 

Seat 2B.) For the low-coal-seam, under no-load conditions, 

operators rated levels of jarring/jolting as 7 to 23% lower with 

the Seats L2A, L2B, and L2C. In addition, operators rated 

level of discomfort 7% lower with Seat L2C, but 2 to 7% 

higher with Seats L2A and L2B. Researchers determined the 

higher discomfort ratings with Seats L2A and L2B were 

largely due to mounting the NIOSH seats in existing bolt 

holes. This caused location of the NIOSH seats to be closer to 

the control panel and forced vehicle operators to assume a 

more awkward and slightly cramped posture when driving the 

vehicle. 

65 66 16 13 * 23 

40 31 4 11 * 11 

(Existing) 

L2A 

(NIOSH 3 in 

XSS/PU) 

L2B 

(NIOSH 5 in XSS) 

L2C 

(NIOSH 5 in 

XSS/PU) 

l* I 22 IO 14 

23 14 1 8 * 

7 12 8 9 0 

The quantitative levels of vehicle jarring/jolting for noload conditions showed that NIOSH Seats M2A and M2B for 

the model mid-coal-seam performed better than the existing 

seat, in terms of peak acceleration and crest factor; whereas, 

L2A, L2B, and L2C performed better than the existing seat in 

terms of peak acceleration, RMS acceleration, and crest factor. 

(Data on Seat L2C was obtained with one less subject than 

Seats L1, L2A, and L2B.) Field trials included shuttle cars 

operating under full- and no-load conditions. 

provided primary damping or attenuation of jardjolts as a 

result of the extra mass from the load of coal. The 

performance of the seat in providing this attenuation of 

jardjolts 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 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, the NIOSH Seat 

M2A showed a 16% and 23% reduction in peak acceleration 

and crest factor. Seat M2A, however, showed a 13% increase 

for RMS acceleration. Similarly, Seat M2B showed a 4% and 

1 1% reduction in peak acceleration and crest factor and a 11% 

increase in RMS acceleration. Nevertheless, NIOSH 

researchers considered RMS acceleration the least significant 

of the three measurement parameters in terms of jarring/jolting 

levels for the vehicle operator. 

Even better results were obtained with NIOSHdesigned seats for the low-coal-seam vehicle. NIOSH Seat 

L2A showed a 22%, and 14% reduction in peak acceleration 

and crest factor. Moreover, Seat L2A reduced RMS 

acceleration by 10%. Similarly, Seat L2B showed 14% and 

8% reductions in peak acceleration and crest factor and also a 

7% reduction for RMS acceleration. Finally, Seat L2C 

showed 8% and 9% reductions in peak acceleration, and RMS 

acceleration with no change for crest factor. 

During full-load conditions, the foam- or air-filled tires 

DISCUSSION 

Research concerning underground coal mining has 

shown that equipment operators experience adverse levels of 

exposure to WBV, which includes vehicle jarring/jolting 

(identified as the higher-amplitude, peak component of WBV). 

Remington, et al. (1984) showed that shuttle car haulage 

vehicles are among the major sources of exposure to WBV 

and vehicle jarring/jolting in underground coal mines. These 

circumstances have changed some since 1984, yet there is still 

much room for improvement. 

Additional evidence exists to illustrate the serious health 

effects that can result from prolonged exposure of vehicle 

operators to jarring and jolting. A study, done in New South 

Wales, Australia, identified jarring/jolting as a significant 

concern to mobile equipment operators. Cross and Walters 

(1994) reviewed WBV and vehicle jarring as a contributing 

factor to back pain in the Australian mining industry. They 
examined 28,306 compensation claims for a 4-year period 

(July 1986 to March 1990) that included surface and 

underground mining environments. From the 8,961 claims 

relating to the head, back, and neck that they identified, 11% 

(986) were due to vehicle jarring. Underground transporters 

and shuttle cars accounted for 53% of all injuries attributed to 

vehicle jarring. 

In summarizing the results from the questionnaire data, 

the ratings reflect how the seats felt to the operator. For the 

mid-coal-seam shuttle car, Seat M2A is the favorite. Seat 

padding rated well for both Seat M2A and Seat M2B. Seat 

M1 is the least favorite in all ratings. Adding armrests is the 

improvement most often suggested for any of the seats. 

favorite in all ratings. Seat padding, lumbar support and seatpan tilt are rated better in 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 operator and controls and allow 

for better operator adjustability and visibility. 

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 of mid-coal-seam shuttle cars operators 

showed levels of jarring/jolting and discomfort as lower with 

the NIOSH seats using the two different 13-cm (5-in) 

viscoelastic foam padding arrangements. Seat M2A with 13 

cm (5 in) of XSS foam padding was most preferred by 

operators of the mid-coal-seam shuttle car. Similarly, for 

shuttle car no-load and full-load conditions, average ratings of 

low-coal-seam shuttle car operators showed lower 

jarring/jolting with the NIOSH seat using three different 

viscoelastic foam pad arrangements. The seats and 

viscoelastic foam padding arrangements, in order of operator 

preference, were Seat L2B with 13 cm (5 in) of XSS foam, 

Seat L2A with 8 cm (3 in) of PU/XSS foam, and Seat L2C 

with 13 cm (5 in) of PU/XSS foam. Nevertheless, concerning 

levels of discomfort, the average operator rating favored the 

existing seat slightly better than the NIOSH seat with the three 

different viscoelastic foam pad arrangements seat, under fullload and no-load conditions. The explanation for this is the 

closer proximity of the NIOSH seats to the control panel 

which made the shuttle car operators feel awkward and 

slightly cramped. Researchers had to use existing bolt holes 

when mounting the NIOSH seats in the shuttle car. In 

addition, the NIOSH seats L2B and L2C with 13-cm (5-in) 

thick foam padding elevated operators nearer to the canopy. 

Results from recorded levels of jarring/jolting showed 

NIOSH-designed seats performed better than the existing seats 

when comparing average values for peak acceleration, RMS 

acceleration, and crest factor under no-load conditions with 

more severe levels ofjarring/jolting for the shuttle car 

For the low-coal-seam shuttle car, Seat L1 is the least 

operators. Concerning model mid-coal-seam shuttle car, the 

NIOSH Seat M2A featuring the 13-cm (5-in) XSS foam pad 

smoothed out bumps better than the Seats M1 and M2B with 

a 16% and 23% reduction in peak acceleration and crest 

factor. Seat M2A, however, showed a 13% increase for RMS 

acceleration, the least significant of the three measurement 

parameters in terms of jarring/jolting levels for the vehicle 

operator. Similarly, Seat M2B with the 13-cm (5-in) PU/XSS 

foam pad showed a 4 ?h and 11% reduction in peak 

acceleration and crest factor and a 11% increase in RMS 

acceleration. Results for NIOSH-designed seats on the model 

low-coal-seam vehicle were even better than those obtained on 

the model mid-coal-seam vehicle. NIOSH Seat L2A with the 

8-cm (3-in) viscoelastic XSS/PU foam pad provided 

significantly larger reduction in values of peak 

acceleration (22%) and crest factor (14%). Moreover, Seat 

L2A reduced RMS acceleration by 10%. Similarly, Seat L2B 

with the 13-cm (5-in) XSS foam pad showed 14% and 8% 

reductions in peak acceleration and crest factor and also a 7% 

reduction for RMS acceleration. Finally, Seat L2C, featuring 

the 13-cm (5-in) PU/XSS foam pad showed 8% and 9% 

reductions in peak acceleration and RMS acceleration with no 

change for crest factor. 

industry with supportive information that NIOSH ergonomic 

seat designs are improvements over some existing designs for 

isolating operators from vehicle jarring/jolting and for 

providing comfort. In particular, researchers have provided 

this important information to Dynamic Systems, lnc., a seat 

foam manufacturer, and JOY Mining Machinery, a mining 

equipment manufacturer, who is already incorporating seat 

design recommendations from earlier NIOSH research 

(Mayton et al., 1999). Furthermore, the additional data 

collected from shuttle car operators provided the opportunity 

to refine and improve the NIOSH seat designs. 

Finally, the findings of this study provides the mining 

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comfort and driver’s fatigue. SAE 971573, 12 pp. 

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

the NSW coal mining industry. Saf Sci 17(4):269-274. 

International Standards Organization (ISO) (1997). IS0 263111 - Mechanical 

shock and vibration - evaluation of human exposure to whole-body vibration, 

Part 1. Geneva, Switzerland: International Organization for Standardization 

Mayton A, Merkel R, and S Gallagher (1999). Improved Seat Reduces 

Jarring/Jolting for Operators of Low-Coal Shuttle Cars. Min. Eng. vol. 51, 

no.12, pp. 52-56. 

Remington P, Andersen D, and M Alakel(1984). Assessment of whole body 

vibration levels of coal miners. Volume 11: Whole-body vibration exposure of 

underground coal mining machine operators (contract 50308045, Bolt, 

Beranek, and Newman, Inc.), BuMines OFR 1B-87, 114 pp.; NTIS PB 87- 

144-1 19.