EVALUATION OF SEAT DESIGNS RELATIVE TO TRANSMITTED 

VEHICLE VIBRATION ON UNDERGROUND MINE TRANSPORT VEHICLES 

Christopher C. Jobes, Ph.D. and Alan G. Mayton, P.E. 

National Institute for Occupational Safety and Health (NIOSH) 

Pittsburgh Research Laboratory, Pittsburgh, PA 

ABSTRACT 

The National Institute for Occupational Safety and Health (NIOSH) researchers have investigated seat 

design issues for the occupants and operators of underground mine transport vehicles relative to wholebody vibration (WBV) and mechanical shock. Considering the ergonomic and engineering improvements 

made to underground mine shuttle car seats, this study has focused on reducing injury risk by improving 

seating on transport vehicles such as scoops, mantrips, personnel carriers, and rail-mounted locomotives. 

Similarly, proposed seat design improvements included layering of various types of viscoelastic foam 

padding to isolate vehicle occupants and operators from adverse health effects of jarring/jolting exposure. 

This paper discusses the results obtained from laboratory vibration testing of new seat padding materials in 

seven configurations at the NIOSH – Pittsburgh Research Laboratory (PRL) showing that careful use of 

configuration and materials can reduce the operator’s exposure to WBV. In addition, results for four mine 

transport vehicles are presented from field data collection efforts at a Southwestern Pennsylvania mine 

showing that a NIOSH based design does reduce the operator’s exposure to WBV. Finally, the authors 

discuss efforts to develop and field test seat padding interventions using new padding materials and 

configurations based on the laboratory test results [The findings and conclusions in this report are those of 

the author(s) and do not represent the views of the National Institute for Occupational Safety and Health.] 

INTRODUCTION 

 Mobile mining equipment can expose workers to wholebody vibration (WBV) and mechanical shock. This exposure 

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

working efficiency and performance. Remington et al. (1984) 

documented WBV exposure for operators of underground 

mining equipment. For mining equipment, proper seat design 

is an important consideration in reducing the adverse effects of 

WBV exposure to vehicle operators. 

 Mayton et al. (1999, 2003, and 2005) reported on 

improved seat designs for underground mine shuttle cars. 

Current research is an extension of this work and focuses on 

seat designs for underground mine transport vehicles. NIOSH 

developed seat designs include padding with selected 

viscoelastic foams that have undergone extensive laboratory 

vibration experiments. During vibration exposure, the unique 

qualities of these foams provide responses similar to those 

found in a mechanical spring/damper suspension system and 

thus, isolation for the seated occupant or operator. In contrast, 

many existing transport vehicle seats, which typically include 

inexpensive foam padding commonly used in furniture, 

provide minimal isolation from vibration. 

THESIS 

 Seat designs using viscoelastic foam padding offer better 

alternatives to existing seat designs for mine transport vehicles 

in isolating operators from vehicle jarring/jolting and for 

reducing discomfort. As demonstrated in prior mine shuttle 

car seat studies (Mayton et al. 1999, 2003, and 2005), 

researchers intend to show similar enhancements in isolating 

the seated vehicle operator/occupant from vehicle 

jarring/jolting and improving comfort. Seat padding 

improvements developed through NIOSH laboratory vibration 

testing are good interventions in reducing risk of back injuries 

on transport vehicles. This paper presents results of initial 

laboratory testing of seat padding options and configurations. 

It also presents results of field data collected on selected 

mining transport vehicles of vehicle vibration exposure for the 

seated occupants/operators. 

METHODS 

Laboratory vibration tests of different seat padding 

materials 

 In the laboratory, researchers conducted vibration testing 

with a MTS® shaker table [Mention of any company or 

product does not constitute endorsement by the National 

Institute for Occupational Safety and Health] and seven 

different seat/seat padding configurations (see Table 1). The 

objective was to ascertain which configuration provided the 

best damping of the seat/seat padding selections for the 

vibration test conditions. A SONY PC208 AX, 8-channel 

digital data recorder and PCB tri-axial accelerometers and 

signal conditioning amplifiers were used to measure and 

record accelerations on the shaker table, the seat/mass 

interface and on the mass itself. The seat designs included 

foam padding composites with different 1-in thick layers of 

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

viscoelastic foams and viscoelastic polymer materials. The 

sequence of foams was altered for some designs, whereas, all 

designs were assembled into a total seat pad thickness of 127 

mm (5 in) and incorporated into an off-the-shelf seat. 

Analysis of the data included calculating the ratio of the seat 

pad root-mean-square (RMS) acceleration to the shaker table 

RMS acceleration. This ratio is commonly referred to as 

transmissibility and is an established way of expressing how 

well the seat suspension is isolating the occupant from vehicle 

vibrations. 

Researchers tested the seat/seat padding designs 

according to the ISO 5007 Standard section 10.1 that required 

a sinusoidal peak-to-peak amplitude vibration of ±15 mm (0.6 

in) at a test frequency range from 0.5 to 2 Hz at 0.05 Hz 

intervals. The ISO 5007 Standard test procedure was 

modified to include the frequency range from 2 to 8 Hz at 0.25 

Hz intervals and test masses (weights) of 40 and 80 kg (88 

and 176 lbs). The latter frequency was added to aid in 

developing transmissibility curves for each seat/seat padding 

configuration, whereas the 40-kg (88-lb) and 80-kg (176-lb) 

weights were specified in ISO 5007 and used to approximate 

the upper torso weights of the seated 5th percentile female and 

95th percentile male vehicle operators. After a few tests, the 

amplitude criteria was reduced by one-half to ± 7.5 mm (0.3 

in) instead of the ± 15 (0.6 in) mm due to researchers’ safety 

concerns. At certain test frequencies, the seat/mass system 

became extremely difficult to control because of forces 

generated by the shaker system. Subsequently, all tests were 

performed at the lower amplitude. This change from the ISO 

5007 standard did appear to modify the results in the 0.5 Hz to 

1 Hz range due to the low amplitudes in the acceleration data. 

For foam seat pads, the transmissibility in this range should be 

close to 1, but with the adverse signal to noise ratio in this 

range, the results in this range are inaccurate. 

The test run procedures included the following steps: 

1. With the loaded seat on the shaker table, researchers 

conducted the vibration tests in amplitude control mode 

with a displacement of ±7.5mm (0.3 in) loaded with 40 kg 

(88 lbs). The tests comprised frequencies from 0.5 Hz to 

2 Hz in 0.05 Hz intervals and from 2 Hz to 8 Hz in 0.25 

Hz intervals; each interval was recorded for 15 s. 

2. Using the same test setup in step number 1, researchers 

reversed the frequency order (8 – 2 Hz in .25 Hz intervals 

and 2 to .5 Hz in .1 Hz intervals) as specified by the ISO 

5007 standard and its modification for our use. 

3. Again with the loaded seat on the shaker table, 

researchers conducted the vibration tests in amplitude 

control mode with a displacement of ±7.5mm (0.3 in) 

loaded with 80 kg (176 lbs). Similarly, the tests 

comprised frequencies from 0.5 Hz to 2 Hz in 0.05 Hz 

intervals and from 2 Hz to 8 Hz in 0.25 Hz intervals; each 

interval was recorded for 15 s. 

4. Researchers ran the same test setup in step number 3 

reversing the frequency order. 

Mine field data collection 

 Underground mine field data were collected at a mine 

near the town of Washington in Southwestern Pennsylvania. 

The coal seam thickness and mining height for the mine 

averaged 183 cm (72 in) with a range of 152 to 244 cm (60 to 

96 in) for seam thickness. Seam height averaged about 66 

inches in the area in which tests were conducted. NIOSH 

researchers collected vibration data on three rail vehicles and a 

rubber tired scoop with the same instrumentation used for 

laboratory tests: a data recorder, tri-axial accelerometers, 

signal conditioning amplifiers and in-line 150-Hz, low-pass 

filters. Data were gathered on existing seat designs for two 

personnel carriers or “mantrips,” a locomotive, and a mine 

scoop (Fig. 1). One mantrip (designated mantrip #1 in the 

results section) featured a NIOSH-based seat design supplied 

by a company collaborating with NIOSH research, while the 

other seat designs on the other mantrip and other vehicles 

were supplied by the original equipment manufacturer (OEM). 

Acceleration data were collected to determine the energy 

transmitted from the vehicle frame through the floor and 

entering the seat. Tri-axial accelerometers are typically placed 

on the floor of the operator 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 on a higher portion of 

the vehicle’s frame. Mine roadway and rail conditions were 

noted during data collection. 

Table 1. Test seat configurations. 

Seat Bottom  Top 

Design Spring Layer 1 Layer 2 Layer 3 Layer 4 Layer 5 

1 Yes XS XS XS PU XS 

2 Yes XS XS XS XS XS 

3 No XS XS XS PU XS 

4 No XS XS XS XS XS 

5 No YIM XS XS PU XS 

6 No YIM XS XS XS XS 

7 No BIM XS XS PU XS 

Materials Used: XS – Extra Soft Sunmate, PU – Pudgee, YIM – Yellow 

Impact Material, and BIM – Blue Impact Material 

Figure 1– A scoop traveling along mine roadway. 

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

RESULTS 

Laboratory Data 

Researchers created graphs of transmissibility versus 

frequency to aid in analyzing the seat design response to 

vibration test conditions. Figures 2 and 3 show the results of 

laboratory tests for the seven seat/seat padding configurations 

using 40- and 80-kg masses (88- and 176-lb), respectively. 

The curves represent the average of the ascending and 

descending frequency order of testing. The horizontal straight 

line represents transmissibility (output acceleration/input 

acceleration) equal to 1. 

 Values greater than 1 demonstrate amplification of the 

transmitted vibration, whereas, transmissibility less than 1 

indicates attenuation of vibration. Considering curves for the 

40-kg (88-lb) mass, peak amplitudes of vibration for seat 

designs 1 and 2 occur between 3.5 and 4.0 Hz, whereas peak 

amplitudes for the remaining seat designs 3 through 7 occur 

between 5.0 and 6.0 Hz. Similarly, for the 80-kg (176-lb) 

mass, peak amplitudes of vibration for seat designs 1 and 2 

occur between 3.25 and 3.5 Hz, whereas peak amplitudes for 

0

0.25

0.5

0.75

1

1.25

1.5

1.75

2

2.25

2.5

2.75

0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5 8

Frequency, Hz

Transmissibility

Seat 1 Seat 2 Seat 3 Seat 4 Seat 5 Seat 6 1 to 1 Ratio Seat 7

Figure 2 - Test results for the seat/seat padding configurations using the 40-kg (88-lb) mass. 

0

0.25

0.5

0.75

1

1.25

1.5

1.75

2

2.25

2.5

0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5 8

Frequency, Hz

Seat 1 Seat 2 Seat 3 Seat 4 Seat 5 Seat 6 1 to 1 Ratio Seat 7

Transmissibility

Figure 3 - Test results for the seat/seat padding configurations using the 80-kg (176-lb) mass. 

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

seat designs 3 through 7 occur between 4.5 and 5.5 Hz. Seat 

designs 1 and 2 included an internal horizontal spring, 

typically included in automotive seats. Attenuation of 

vibration seat designs 1 and 2, using the 40-kg (88-lb) mass, 

occurs at a frequency below 2.5 Hz (for seat design 2) and 

below 1.75 Hz (for seat design 1) and above 5.25 Hz (for both 

designs). For designs 3 through 7, attenuation occurs below 

2.5 and above 7.25 Hz. Attenuation of vibration for seat 

designs 1 and 2, using the 80-kg (176-lb) mass, occurs at a 

frequency below 2 Hz and above 4.75 Hz. For seat designs 3 

through 7, attenuation occurs 1.25 and 2.0 Hz and above 7.25 

Hz. Seat designs 1 and 2 show higher peak amplitudes or 

greater amplification that are just the reverse of each other 

when the 40-kg (88-lb) mass is used versus 80-kg (176-lb) 

mass. 

Field Data 

 Table 2 presents the results of the measured data. The 

input acceleration data was obtained by a tri-axial 

accelerometer attached to the vehicle frame and was low-pass 

filtered at 150 Hz. The output acceleration data was obtained 

from a tri-axial accelerometer built into a seat pad upon which 

the operator sat and was also low-pass filtered at 150 Hz. The 

output to input ratios were obtained for both RMS and peak 

accelerations and the crest factor was generated as a ratio of 

the Peak to RMS accelerations. Several ISO metrics 

pertaining to the output acceleration data were also generated: 

exposure limit (EL), fatigue decreased proficiency limit 

(FDP), and reduced comfort boundary (RCB) as well as a 

vector sum generated using a total weighted RMS acceleration 

for all three axes according to ACGIH (2006). 

 The results show that the NIOSH based seat design 

exhibits greater attenuation of vehicle jarring/jolting levels for 

the seated operator/occupant. Of the rail vehicles tested 

(mantrips and locomotive), the NIOSH based design seat 

shows a performance in the peak and RMS transmissibility 

metrics almost an order of magnitude better than the OEM 

seat designs tested. Also, the vector sum (a measure of the 

operator’s exposure to WBV) is significantly lower showing 

improved performance in isolating the operator from WBV. 

DISCUSSION 

 The laboratory vibration tests were analyzed by plotting 

transmissibility against vibration frequency. The two leftmost curves in Figures 1 and 2 represent data for seat designs 

that incorporated an internal horizontal spring upon which the 

foam padding rests. The presence of this spring in the seat 

shows a shift to the left or reduction in frequency for seats 1 

and 2. Although all of the seat foam configurations show 

amplification for a large portion of the frequency range tested, 

the single seat foam showing the lowest amplitude was the 

foam used in seat design 3. 

The foam padding configurations of all seven seat 

designs tested in the laboratory show amplification of 

vibration as indicated by transmissibility values greater than 1. 

Amplification of the vibration levels may or may not 

adversely affect health. The effect of vibration exposure on 

the seated vehicle occupant depends not only on the 

frequency, but also on the exposure time and magnitude of 

vibration. Thus, the authors, in view of the test results and past 

experience, conclude that any use of the tested seat foam 

padding configurations should not negatively affect the health 

of seated vehicle occupants. Nevertheless, PRL researchers 

are committed to determining the seat padding foam(s) and 

configuration(s) that would provide the best seat padding 

option for occupants and operators of mine transport vehicles 

in terms of attenuating vibration and comfort. Furthermore, 

the seats on the mine transport vehicles for which vibration 

levels were measured should also have no negative effects in 

view of the Threshold Limit Value (TLV) guidelines (ACGIH, 

2006). 

 The quantitative levels of vehicle jarring/jolting for rail 

vehicles was generally larger than that of the rubber tired 

scoop being tested. In general, this is due to the floor 

conditions for the scoop (being soft and muddy without 

significant potholes) and the rail and switch conditions 

(typical of any mine) experienced by the man trips and the 

locomotive. The crest factor is designed to take this into 

account by dividing the peak ratios by the RMS ratios to 

generate a unit-less number which represents how well a seat 

design handles jolting/jarring. As can be seen from the data, 

the crest factors in all tests are comparable. There has been 

Table 2. Overall averages of measured jarring/jolting levels for operators of various mine transport vehicles. 

RMS Peak Crest Factor ISO Metrics 

Equipment Frame 

(m/s2) 

Seat 

(m/s2) Ratio Frame (m/s2) 

Seat 

(m/s2) Ratio Frame (m/s2) 

Seat 

(m/s2) Ratio EL (min.) 

FDP 

(min.) 

RCB 

(min.) 

Vector 

Sum 

(m/s2) 

Mantrip #1 0.71 0.47 0.66 5.81 3.38 0.58 8.49 7.65 0.89 7680 2380 460 0.38 

Scoop 1.94 1.08 0.56 47.14 22.93 0.49 24.26 21.19 0.87 2880 930 180 0.73 

Locomotive 7.93 1.49 5.31 4.75 1.17 4.06 0.60 0.78 0.77 960 420 60 0.83 

Mantrip #2 10.86 1.99 5.46 7.13 1.53 4.66 0.66 0.77 0.85 960 360 60 1.19 

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

9
 

much discussion amongst researchers as to whether the crest 

factor is the best measure of jarring/jolting and many are now 

looking to the ISO criteria previously mentioned. The ACGIH 

(2006) using the ISO (1985)-based criteria indicate 6 as the 

value above which the effects of WBV will be underestimated. 

Moreover, this ISO criteria includes the use of third octave 

analysis of the seat acceleration experienced by the operator 

(typically in the vertical direction) over-plotted on an ISOcurves graph. The vector sum (the overall total weighted 

RMS acceleration) alternatively attempts to take into account 

the weighted RMS accelerations experienced by the operator 

in all three axes. The limiting value of crest factor has been 

updated to 9 in ISO (1997), which also recommends use of the 

fourth power vibration dose value procedure when the 

calculated crest factor exceeds 9. When considering the 

vector sum values computed for the recorded field data, the 

NIOSH-based seat design indicated the most positive result. 

 An example of a potential seat padding intervention for 

transport vehicles is the “throw pad” (Fig. 4) which was 

developed by RM Wilson Company in collaboration with 

management at the mine. It is a 35.6-cm (14-in) square and 

6.4-cm (2-1/2-in) thick folding pad (covered in a black vinyl 

material) with a handle that workers could carry around with 

them. It was originally intended for maintenance workers, 

who needed the flexibility of a portable pad that can be used 

not only for sitting, but kneeling and lying down depending on 

the work task performed. NIOSH researchers are considering 

the “throw pad” as an intervention applicable for a variety of 

transport vehicles and optimizing the padding selection and 

configuration through laboratory vibration investigations. 

Limitations 

The ISO 5007 procedure was developed for testing 

mechanical seat suspension systems, thus demonstrating the 

need for researchers to modify the procedures for testing the 

different foam configurations. Field data was limited to only 4 

vehicles and a small number of samples. A meaningful 

comparison of field test seat transmissibility and laboratory 

test transmissibility results isn’t feasible due to resolution 

issues inherent in the third octave analysis performed on the 

field test data. 

 Other limitations that may affect the results include, but 

are not limited to, the use of a solid weight instead of a human 

body during laboratory testing, and use of the sine wave 

excitation function instead of random vibration that would 

approximate vehicle jarring/jolting. Nonetheless, researchers 

believe the results of this work show careful selection of seat 

padding materials and configurations can provide greater 

vibration attenuation and positively effect mine workers that 

are exposed to vehicle jarring/jolting when riding or operating 

mine transport vehicles. 

The testing of foam padding materials continues in order 

to determine the optimum padding and configuration. Future 

effort will include completing laboratory testing of the 

different and new seat padding foams and the selection of best 

configuration for use in the vibration environment of the 

aforementioned vehicles. The optimum foam padding will be 

incorporated in the “throw pad” or other intervention and 

tested in the field during actual coal mining operations. 

 

ACKNOWLEDGMENTS 

 The authors thank Joseph DuCarme, mechanical 

engineer and Tim Matty, electronics engineer, for their 

assistance in collecting the laboratory data on the 

different seat/seat padding configurations. They also 

thank Jim Manuel of Consol Energy and Mike Demchak 

of RM Wilson Company for their assistance in collecting 

underground mine field data. 

REFERENCES 

American Conference of Governmental Industrial Hygienists (ACGIH) 

(2006). Threshold Limit Values (TLVs) for Chemical Substances and Physical 

Agents and Biological Exposure Indices (BEIs). Cincinnati, OH, pp. 132-139. 

ISO (1997) ISO 2631/1 – Mechanical Shock and Vibration – Evaluation of 

Human Exposure to Whole-Body Vibration, Part 1. International Organization 

for Standardization, Geneva, Switzerland. 

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. 

Mayton AG, Ambrose DH, Jobes CC, and NK Kittusamy (2003) ‘Ergonomic 

and existing seat designs compared on underground mine haulage vehicles’, 

Proceedings of the Human Factors and Ergonomics Society 47th Annual 

Meeting, Human Factors and Ergonomics Society, Santa Monica, CA, 

pp.1256–1260. 

Mayton AG, Amirouche F, and CC Jobes (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 

Systems, Vol. 12, No. 3, pp.225–238. 

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

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

underground coal mining machine operators (contract JO308045, Bolt, 

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

144-119 

Figure 2 - The portable “throw pad” features connected seat 

and backrest pads with loop handle. 

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

0