Jarring/jolting exposure and musculoskeletal symptoms

among farm equipment operators

* A.G. Maytona, , D.H. Ambrosea

, C.C. Jobesa,

a

NIOSH, Pittsburgh, PA, USA 


*Corresponding author. Tel.: +1 412 386 4657; fax: +1 412 386 6764.
 

E mail address: amayton@cdc.gov (A.G. Mayton).

N.K. Kittusamyb,

b

NIOSH, Spokane, WA, USA 


 M.L. Legaultc

c

Indiana State University, Terre Haute, IN, USA 


Abstract

Vehicle vibration exposure has been linked to chronic back pain and low back symptoms among agricultural tractor drivers. The

objectives of this study by the National Institute for Occupational Safety and Health (NIOSH) were to assess driver whole body

vibration (WBV) exposures and recommend interventions to reduce the risk of back related injuries, particularly relative to vehicle

jarring/jolting (the transient mechanical shock components of WBV). The methodology included collecting, from two independent

samples, field data and health and work history data of farm equipment operators. Data were collected during mowing, raking, baling,

chiseling, tilling, and road travel for different model tractors. Spraying using a sprayer and shrub removal with a skid steer loader were

also included. Based on ISO 2631 (1985), the American Conference of Governmental Industrial Hygienists, threshold limit values,

presents 0.5 m/s2 as the action level recommended by the Commission of European Communities for overall weighted total RMS

acceleration (vector sum for axes x, y, and z) [ACGIH, 2006. Threshold limit values and biological exposure indices. Cincinnati, OH].

WBV measured at the operator/seat interface exceeded this action level. The roughest rides and highest vector sum accelerations

occurred with small utility tractor mowers (3.3 and 2.8 m/s2

) and a skid steer loader (1.7 m/s2). Major findings from health and work

history data showed 96% of participants reported having to bend or twist their necks, although 24% reported neck symptoms. Sixty four

percent of participating operators reported experiencing back symptoms (e.g., pain, aching, stiffness, etc.). Recommendations included:

specifying a seat that ‘‘better’’ isolates operators from jars/jolts with new tractor purchases; maintaining the seat/seat suspension and

replacing worn or damaged cushions with NIOSH tested viscoelastic foam padding; using larger diameter tires with radial ply instead of

bias ply construction, particularly on small utility tractor mowers, to aid in attenuating ride ‘‘roughness’’; using a swivel seat to reduce

the stress on the neck from bending or twisting; and improving efforts to educate owner/operators of the adverse effects of WBV

exposures. Since the data presented in this paper were collected from two independent samples, the authors were unable to draw any

correlations or etiological inferences from the study. However, results were compared and contrasted with other studies which included

similar vibration measurements in agriculture.

Relevance to industry

Studies concerning agricultural tractor drivers have shown that vibration exposure and duration of exposure are associated with

lifetime, transient, and chronic back pain and low back symptoms. The results from the field measurements and health and work history

data are useful for the U.S. agricultural industry to help reduce back injury risk for farm equipment operators.

1. Introduction

Farm tractors and other earth-moving equipment contribute to some of the most common, prolonged, and

severe occupational exposures of vehicle vibration among
 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

equipment operators. The recognition of potential hazards

has resulted in standards concerned with the vibration

transmitted by the seats (ISO 5007, 2003) of these vehicles

and the vibration exposure (ISO 5008, 2002) of vehicle

operators (Griffin, 1990).

Exposure to whole-body vibration (WBV) and the

postural requirements of the job have been identified as

important risk factors in the development of musculoskeletal disorders (MSD) of the spine among workers exposed

to a vibratory environment (Kittusamy and Buchholz,

2004; Kittusamy, 2002, 2003; Bovenzi and Zadini, 1992;

Johanning, 1991; Bongers et al., 1988, 1990). Several

investigators (Wikstrom et al., 1994; Seidel, 1993; Hulshof

and van Zanten, 1987; Seidel and Heide, 1986) have

reported on the adverse health effects of WBV. NIOSH

compiled a comprehensive body of epidemiological research presenting risk factor exposures for MSD, such

as repetition, force, posture, and WBV (Bernard et al.,

1997). Acute health effects include loss of visual acuity,

postural stability and manual control; whereas chronic

health effects include low-back pain, early degeneration

of the spine, herniated discs, and digestive and circulatory

disorders. Long-term exposure to WBV may also contribute to disorders of female reproductive organs and

disturbances of pregnancy (Seidel, 1993; Seidel and

Heide, 1986). Furthermore, WBV may synergistically affect

the development of noise-induced hearing loss (Seidel,

1993).

Pope et al. (1998) studied the relationship between WBV

and low-back pain. Their WBV data showed that the

human spinal system has a characteristic response to

vibration inputs in a seated posture. From experiments

using percutaneous pin-mounted accelerometers, they

determined resonances at fairly uniform frequencies for

all subjects tested, first within a band of 4.5–5.5 Hz and

subsequently in the 9.4–13.1-Hz range. They concluded

posture, seating, and seat-back inclination affected the

frequency response and that rocking of the pelvis

essentially determined the response.

This paper reports on the agricultural portion of a

research project done under the National Occupational

Research Agenda (NORA) sponsored by NIOSH. NORA

is a collaborative program to stimulate innovative research

in workplace safety and health. The main goal of the

overall research project was to quantify the extent and

effects of vehicle jarring/jolting to reduce injury risk for

operators of mobile equipment in agriculture and construction industries.

1.1. Relevance to Industry 

A substantial portion of the research gives evidence of a

strong association between WBV exposure and back

disorders. Studies concerning agricultural tractor drivers

have shown that vibration exposure and duration of

exposure are associated with lifetime, transient, and

chronic back pain and low-back symptoms (Bovenzi and

Betta, 1994; Boshuizen et al., 1990a, b). Thus, the field data

with the health and work history data are useful information for the US agricultural industry to help reduce MSD

injury risk for farm equipment operators.

2. Methods

Vibration data were measured at selected field sites.

Weighted vertical accelerations were calculated with the

results plotted and superimposed on the ISO 2631 (1985)

exposure time limit curves in hours. Health and work

history data were collected from farm equipment operators

at a major farming convention and served as a means for

describing the injury issues for these operators and for

identifying probable causes of these injuries. A body map

was used as a tool to help participants identify body

part locations where they experienced musculoskeletal

symptoms.

2.1. Field data collection 

For most of the field data collection, NIOSH collaborated with The Pennsylvania State University (Penn State)

in University Park, PA. Penn State offered a wide variety

of farms, farm operations, terrain conditions, and equipment from which to collect data on the effects of equipment

operator exposure to vehicle jarring/jolting. A jar or jolt

can be generally defined as the transient mechanical shock

component of WBV that occurs when vehicles travel over

irregular surfaces and can result in a ‘‘rough’’ ride. The

farm operations comprise: (1) Agronomy Farm, (2)

Operations and Services Farm, (3) Horticulture Research

Farm and (4) Animal Facilities Farm. Because of its tractor

inventory and different farm operations, the Agronomy

Farm was selected, primarily, and secondarily, the Operations and Services Farm to collect data.

Vibration exposure data were collected on class 1

tractors with an un-ballasted maximum weight of 3600 kg

and class 2 tractors with an unballasted weight range from

3600 to 6500 kg. Both classes are the most commonly used

sizes of agricultural tractors. In addition to tractors, data

were collected on a sprayer, and skid-steer loader. The

different operations included mowing, baling, chiseling,

ground working, raking, shrub removal, spraying, and

road travel with a transition from smooth surface to dirt or

gravel. Examples of various farming operations are shown

in Figs. 1–4.

Vibration measurements were recorded with an

8-channnel, digital data recorder (model PC208Ax, Sony

Manufacturing Systems America, Lake Forest, CA). Other

instrumentation (PCB Piezotronics, Inc. Depew, NY)

included triaxial accelerometers (models 356B18, 356B40),

signal conditioning amplifiers (model 480E09), and in-line,

150-Hz low-pass filters (model 474M32). The floor or

frame-mounted accelerometer featured a frequency range

of 0.3 Hz to 5 kHz and a charge sensitivity ranging from

949 to 1052 mV/g for the three directional axes. The seat
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

pad accelerometer featured a frequency range of 0.5 Hz to

1 kHz and a charge sensitivity ranging from 97.4 to

105 mV/g for the three directional axes. The frame

accelerometer was secured with magnetic mounts to the

floor of the operator’s compartment near the base of

the seat (frame measurement). The seat pad was secured to

the seat with duct tape and directly sat upon by the

equipment operator (seat measurement). Vibration data

were generally collected for about 30 min and were used to

quantify the vibration energy transmitted to the seat

through the workstation platform from the vehicle chassis

or frame.

The raw data were initially viewed in terms of rootmean-square (RMS) acceleration, peak acceleration (for

jars/jolts), and crest factor (ratio of peak acceleration/

RMS). Of these variables, peak acceleration and crest

factor were the most descriptive relative to jars and jolts,

although RMS acceleration is necessary to compute the

crest factor. Further, the data were analyzed according to

ISO 2631 (1985) exposure limit (weighted vertical or z-axis

direction) and total overall weighted RMS acceleration,

a single-value computation for all three directions of

vibration.

Fig. 1. Class 2 tractor baling hay.

Fig. 2. Class 2 tractor mowing a field.

2.2. Health and work history data collection 

The 2003 American Farm Bureau Federation (AFBF)

Annual Meeting and Convention provided the forum for

collecting health and work history data from attendees who

operated farm equipment. To recruit participants for this

study, an ad was placed in the AFBF convention newsletter

and a display booth was set up in the section designated for

exhibitors. Respondents were volunteers who passed by the

booth, signed up to participate, and were subsequently

organized into small focus groups. An instrument, adapted

from Kittusamy (2003), was used in focus groups to gather

general information, work information, job history,

information on currently or recently operated equipment,

medical history, exercise and hobbies information, injury

history, and history of injury symptoms. Historical

musculoskeletal symptoms (within the last 12 months)

were identified by body part location and collected using a

body map instrument (Fig. 5). Data were tabulated and

analyzed using SPSS software.

3. Results

3.1. Vibration field measurements 

Table 1 provides a summary of results for data analyzed

from the Penn State farms. The jars/jolts showing the three

largest peak (vertical) accelerations, were obtained for the

road travel (33.7 m/s2

), shrub removal (13.8 m/s2, Fig. 6),

and mowing (11.3 m/s2

, Fig. 7). These peak accelerations

were taken from the raw data and not weighted values.

Notably, high crest factors (peak amplitude divided by the

RMS value) were computed also for road travel (16.2),

shrub removal (14.2), and tilling (7.3). Exposure limit times

for all of the equipment and shows the lowest, 3 h, for the

two small utility-type, tractor mowers (class 1). The total

overall weighted RMS accelerations for all equipment

operations ranged from 0.9 to 3.3 m/s2 thus exceeding the

2 0.5 m/s recommended action level (ACGIH, 2006).

Among the highest total overall weighted RMS accelerations were those obtained for mowing (3.3 and 2.8 m/s2

),

shrub removal and raking (1.7 m/s2

), and road travel

(1.6 m/s2

).

3.2. Health and work history data 

Fifty of 61 potential respondents (80% return rate)

participated in the study. Forty-five (90%) of the

participants were owner/operators, along with two (4%)

workers and two (4%) managers. One person did not

identify their position. Participants included 44 (88%)

males and six (12%) females. The respondent’s age and

years of experience in operating farm equipment averaged

48 and 33, respectively. The participants operated farming

equipment, on average, 24 h per week.

Most operators indicated that the cab/workstation

design was satisfactory. Thirty-four (68%) responded
that the seat was adjustable and 48 (96%) could easily

reach and operate the pedals and levers. Moreover, 96%

reported that they have to bend or twist their necks. All

operators indicated that proper maintenance was performed and that repairs were performed when needed/

required.

Fig. 3. Class 2 tractor tilling a field.

Fig. 4. Sprayer working a field.

All subjects stated they could at least feel some vibration

either through the floor or seat and 27 (54%) could feel

vibration often or always. Even though 45 of 47 (96% of )

respondents stated they had ladders or stairs present on

equipment and of those 41 (91%) said the first step was

70 cm or less (ANSI/ASABE, 2006), 17 (38%) said they

had to jump off equipment to exit.

Seven (14%) participants stated they operated equipment on the farm a minimum of 50 h per week. The

reported types of equipment used by the participants were:

various configurations of tractors (front end loaders,

backhoes, etc.); forklifts; self-propelled mowers; skid-steer

loaders; combines; self-propelled forage harvesters; cotton

harvesters; excavators having both tracks and tires;

bulldozers; and large and small trucks with some having

dump beds or feeder beds. The predominant types of
 

 

 

 

 

 

 

 

 

 

 

 

 
 

 
 

 
 

 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

equipment operated were tractors, with or without attachments. The age of all of the equipment reported was

predominantly older than 5 years.

Seventy-two percent of 43 participants reported musculoskeletal symptoms in various body parts. The percentage

of participants who reported symptoms in a particular

body part is shown in Table 2. Thirty-six percent of 43

respondents stated they missed one or more days of work.

Seventeen of 43 respondents stated the injuries sustained to

them had caused them to change or modify their normal

activities. Twenty-eight percent had back pain that

radiated to the legs for the year preceding.

 
 

 

Fig. 5. Front and rear diagrams of a body map with numbered body part

location (adapted from Kittusamy, 2003).

Table 1

Peak acceleration (nonweighted) and crest factor in vertical (z direction), exposure limit in vertical or z direction, and overall total weighted RMS

acceleration (3 directionsal vector sum) for different farm equipment

 

 

 

 

 

 

 

 

 

 

 

 

 
 

 
 

 
 

 
 

 
 

Equipment Class Actual ballasted Operation Peak vertical Crest factora Exposure limitb (h) Vector sumc (m/s2

)

weight (kg) acceleration (m/s2

)

Tractor 1 746d Mowing 11.25 4.91 3 2.84

Tractor 2 5386 Mowing 2.93 3.88 24 0.87

Tractor 1 965 Mowing 10.13 4.43 3 3.26

Tractor 1 2395 Raking 9.20 6.06 5 1.70

Tractor 2 5386 Baling 3.72 6.07 24 0.86

Tractor 1 5691 Baling 2.41 3.42 12 1.03

Tractor 3e 6909 Chiseling 4.55 5.22 20 1.33

Tractor 2 5386 Tilling 7.88 7.25 11 1.51

Tractor 1 2395 Road 33.69 16.18 6 1.56

Sprayer 2 6773 Spraying 5.92 6.56 17 0.96

Skid steer 2 3932 Shrub removal 13.75 14.18 11 1.73

loader

a

Crest factor is dimensionless.
 b

ISO 2631 (1985).
 c

Vector sum represents overall total weighted RMS acceleration.
 d

No ballast.
 e

Data taken at privately owned farm near Pittsburgh, PA USA.
 

Fig. 6. Skid steer loader during shrub removal operation.

4. Discussion

The field data analysis showed vehicle operators

experienced peak vertical accelerations—indicative of

jars/jolts—that could reach accelerations as high as

3.4g’s. This particular event occurred at the transition of

two road surfaces with the vehicle traveling at a relatively

higher rate of speed. A power spectral density analysis of

the data reveals that this g-level corresponded to a

frequency lower than the sensitivity range of the seated

human body (4–8 Hz). Potentially, this magnitude could be

problematic, but it is unclear to what degree that it would

be. How often such events occur for the type and class of

vehicle is important to note when evaluating operator

exposure, severity of exposure, and needed isolation for the

seat and possibly other operator cab components. The

authors observed that these occurrences were not frequent

during data collection. However, owing to the complexities
of collecting data in the field, it is not clear how often these

conditions could occur and what the cumulative effects of

such exposure may have on injury risk.

Fig. 7. Class 1 utility tractor mowing a field.

Table 2

Summary of respondents reporting musculoskeletal symptoms according

to affected body part

 

 

 

 

Body part Respondents reporting symptoms (%)

Low back 38

Wrist/hand 28

Knee 28

Ankle/foot 28

Middle/upper back 26

Neck 24

Shoulder/upper arm 24

Elbow/forearm 16

Hip 12

Crest factors exceeding six were noted for raking, baling,

tilling, spraying, shrub removal and road travel. In the

latter two cases, the crest factors were more than double

the ACGIH (2006) TLV guideline based on ISO 2631

(1985). The guideline states 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 ywhen crest factors

exceed 6.’’ ISO 2631 (1997) stipulates that the crest factor

may not always indicate severity of vibration and refers to

a crest factor of nine as compared to six noted above.

The data analysis for the two small, utility-type, mower

tractors (class 1) showed the lowest recommended exposure

times of 3 h (based on an 8-h day); whereas the class 2

vehicles showed the highest peak accelerations. It is

believed that the lower ISO 2631 (1985) recommended

exposure time limit of 3 h for the class 1 compared to the

class 2 vehicles results from the class 1 vehicle having: a

lower mass and shorter wheel base 142–165 cm; smaller

diameter tires with, e.g., radial- versus bias-ply tire

construction; and a lower grade/cost seat with fewer

features (e.g., small displacement from seat suspension)

for isolating against vehicle vibration and jars/jolts. These

factors contribute to a generally rougher ride for the class 1

vehicle. Also, the class 2 vehicles (with greater mass and

usually better seating) are intended for use in more ‘‘heavy

duty’’ service (raking, baling, tilling, etc.) over generally

rougher ground.

The total overall weighted RMS accelerations for all

equipment 2 operations exceeded the 0.5 m/s 8-h action level

recommended by the European Commission (ACGIH,

2006). The order of magnitude ranged from 1.7 to 6.5

times. These values show the potential for adversely

affecting the long-term health of these machinery operators

performing the selected dynamic activities.

Several studies have investigated WBV exposure in

farming for tractor drivers (Lines et al., 1995; Sorainen et

al., 1998; Kumar et al., 1999, 2001; Muzzammil et al., 2004;

Scarlett et al., 2007). Scarlett et al. (2007) quantified WBV

levels and estimated operator exposure for a range of

modern state-of-the art tractors under controlled ‘‘in-field’’

conditions and actual ‘‘on-farm’’ use. The operations

studied included ploughing, plough transport, cultivating,

and trailer transport. Farm equipment included a range of

medium to large (90–130 kW) four-wheel drive tractors

that were characterized as unsuspended, suspended cab,

suspended front axle and cab, and fully suspended (front

and rear axle). The ISO 5008 (2002) methodology was used

for the controlled test conditions. They considered

European Physical Agents Directive: 2002 in the study

from the premise of potential consequences of operator

WBV limitations. Results of the controlled tests showed

greater differences in WBV levels between target operations

than between different tractors (i.e., suspension systems)

performing the operations. Magnitude of WBV, cultivating

generated high WBV levels (RMS of 1.50 m/s2

) opposed to

spraying which generated low levels (RMS of 0.75 m/s2

).

Tractors in the NIOSH study were considerably smaller in
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

size, particularly the utility tractor mowers, although the

tasks concerning cultivating and spraying were similar.

NIOSH results, though not directly comparable using ISO

2631 (1985) method, showed similar indications of WBV

levels with higher vector sum values 1.50–1.60 m/s2 for

chiseling and tilling (cultivating) operations and lower

(o1.0 m/s2

) for spraying.

As in this NIOSH study, Lines et al. (1995) measured

tractors and other farming vehicles during a range of

normal field operations. Using both the ISO 2631 (1985)

and BS 6841 (1987) methods of analysis, they concluded

that most drivers were exposed to WBV levels that

exceeded the safe limit for an 8-h day. Only baling and

combine harvesting operations were considered safe with

exposure limits of 16 and 24 h, respectively. This compares

to the NIOSH study using ISO 2631 (1985) where results

for the two small, utility-type, mower tractors showed the

lowest recommended exposure times of 3 h, and for the

larger tractors (class 1 and above), raking and road travel.

Tractors performing transport tasks exhibited the highest

vibration levels, whereas the NIOSH study showed highest

levels for these same class 1 utility mower tractors. Crest

factors from the NIOSH study were for the vertical

acceleration (z) generally were lower than those recorded

by Lines et al. (1995).

Health and work history data revealed musculoskeletal

symptoms in various body parts for the respondents.

Nearly all farm equipment operators reported having to

bend or twist of the neck showing it is an essential part of

pulling equipment and other machinery behind it. Whether

or not performing this awkward posture leads to injury or

injury symptoms would depend on how often operators

assume this posture and the angular extent of turning the

head. More than a third of the respondents reported

jumping off equipment to exit, which may contribute to

back-related and knee/ankle/foot symptoms that respondents reported with relatively high incidence. Jumping

from the cab of a tractor presents a significant health risk

with potentially damaging effects when considering that

the impact force may be as high as 11 times the operator’s

body weight for a jump from cab level of a commercial

farm tractor (Fathallah and Cotnam, 2000). Pain, along

with stiffness, may begin after lifting a heavy object, a fall

(equivalent to jumping off equipment), standing or sitting

for a long time, e.g., all-day operation of farm vehicles

(Bovenzi et al., 2002). Unfortunately, the data was limited

in that it did not permit the authors to correlate the various

injury symptoms with high-risk work practices, awkward

postures, and vehicle jarring/jolting. Nonetheless, control

measures or interventions to reduce the amount or degree

of neck bending/twisting (e.g., a swivel seat) and educating

operators to avoid jumping off equipment would be

positive steps toward reducing the incidences of musculoskeletal symptoms and injury risks.

Kumar et al. (1999, 2001) investigated the effect of WBV

on the low back in northern India using a retrospective

cohort study of 50 tractor-driving farmers (TDF), the

study group, and fifty non-tractor-driving farmers

(NTDF), the control group. Subjects in the control group

were matched for age, gender, generic/ethnic group,

land-holding, and work routines. In addition to clinical

investigations, magnetic resonance imaging (MRI) was

used to assess WBV exposure and degenerative changes

in the spine, while vibration measurements were done to

assess vibration severity. TDF showed self-reported back

pain (for last 12 months) at 24% and NTDF at 14%. This

compares similarly to the NIOSH study of self-reported

back symptoms at 64%-although these may not all be

work-related. MRI results revealed no significant differences between the study and control groups concerning

degenerative changes of the spine (P40.050). Considering

the area of the back, in the North India study for TDF

lower back results were 75% versus 56% for NTDF

compared to 38% in the NIOSH study; concerning the

upper back was 13% for NTDF and 4% for TDF

compared to 26%. Kumar et al. (1999, 2001) concluded

that TDF reported more frequent backache than NTDF,

but clinical MRI evaluations revealed no significant

differences between these two groups.

NIOSH researchers noted that study participants were

generally not aware of the potential effects of WBV

exposure from operating farm equipment. The authors

believe that knowledge of these effects may help the

equipment operators to avoid or minimize injury risk and/

or discomfort. Examples of this would be recognizing when

attenuating properties of a seat suspension or seat padding

has deteriorated or what postures should be avoided or

altered during vibration exposure. Consequently, educating

owners/operators to increase awareness of how WBV may

affect the body and health during farm equipment

operation would be a simple, yet important part in

lessening injury risk.

Finally, it is helpful to comment briefly about tractor age

for this study. The age distribution of the tractors was not

unlike the Myers and Snyder (1995) findings that showed,

in 1993, the national average age of tractors in operation

was 22.870.53 years with model years that ranged from

1924 to 1994. Similar results were found in New York State

(West and May, 1998).

5. Recommendations

From observations and conversations with tractor

operators and farm conference attendees, the following

recommendations are offered. First, whenever possible,

specify the ‘‘better’’ seat for new tractor purchases or seat

replacement (i.e., a ‘‘better’’ seat with transmissibility

characteristics that attenuate jars/jolts and thereby, isolate

equipment operators from them). The purchaser should

consult with the equipment dealer for seat manufacturer

specifications on seats with good vibration attenuating

characteristics. Also, farmers should keep the seats/seat

suspensions well-maintained and replace worn or damaged

seat padding. One consideration for replacement padding is
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

NIOSH tested viscoelastic foam padding which has proved

effective in mining applications (Mayton et al., 2003, 1999)

with vibration environments similar to those found in

farming. In reviewing field data results, operators of small,

class 1 utility tractor-mowers can experience rough rides

with peak vertical accelerations of 11.3 m/s2 and an ISO

2631 (1985) exposure time limit of 3 h. As practical, farm

equipment operators are encouraged to vary tasks to

reduce exposure time for tasks where higher vibration

levels are encountered. In addition, a slow 10-min walk is

recommended after exiting the vehicle and before performing other physical tasks to permit the low-back motion

segments to reorient themselves (Wilder, 1993).

Another recommendation, particularly for the small

utility tractor-mowers, is to use larger diameter tires with

radial—instead of bias-ply construction to aid in attenuating ride ‘‘roughness.’’ Intuitively speaking, larger diameter

tires have greater tire height (tread to rim) that allows for

greater flexing (larger travel) and more damping. Moreover, they can more easily span the distance across surface

irregularities in which smaller diameter tires are prone to

‘‘bottom out.’’ Furthermore, radial-ply, in contrast to biasply, tires generally possess a more flexible sidewall leading

to a softer ride and show a decrease in force amplitude for

frequencies below 15 Hz (Gillespie, 1992). Tire pressure is

also an important factor. Given the manufacturer’s

recommended range of tire pressures, a ‘‘harder’’ tire

(higher pressure) supplies less damping than a ‘‘softer’’

(lower pressure) one.

From health and work history data, 24% of participants

indicated symptoms for the neck. Ninety-six percent of

tractor operators bend or twist their neck during operations such as tilling, plowing, raking, etc. Consequently, a

seat that swivels is recommended to reduce the stress on the

neck caused by frequent bending and turning of the head.

Finally, health and work history and field data collection

efforts revealed that study participants lacked awareness

about the potential adverse effects of WBV exposure on

farm equipment operators. Consequently, educating owners/operators of the effects of WBV on the operator during

farm equipment operations is recommended. This can be

done with safety training sessions during industry conferences and trade shows and by including such information

in the owner’s manual or CD for the equipment provided

by the manufacturer.

6. Limitations

This study provides useful information and results in

quantifying WBV exposure and musculoskeletal symptoms

for farm machinery operators. However, it includes various

limitations. Field data collection occurred at just three

farms with a small sample size of farm equipment. The

study was also limited by the difficulties and constraints

that accompany field data collection and the individual

driving differences among equipment operators. The

measured data at the seat may not be representative of

the vehicle or the task, since different vehicles generally

employ seats that differ in design, construction, age and

suspension and cushion properties. The health and work

history results provided an initial step of basic information

about musculoskeletal symptoms for farm equipment

operators. Different population samples were used for

measured field data and the health and work history data

collection; this did not allow for cross-sectional correlation

of the data. The latter data of musculoskeletal symptoms

were collected at a conference and reflect ‘‘current’’

symptoms (within the last 12 months) that may not

necessarily relate to work since participants were not at

work. Since the data presented in this paper were collected

from two independent samples, the authors were unable to

draw any correlations or etiological inferences from the

study. Moreover, it is likely that results of the health and

work history include selection and recall biases. Furthermore, comparisons of NIOSH data with other similar

vibration studies have limitations that include national and

cultural differences associated with, among others, farming

methods, tractor make, model, age, size, and ground

surface, as well as individual driver preferences in driving

speed, posture, and steering technique.

Acknowledgments

The authors thank Pennsylvania State University for use

of their farms for data collection. They also thank PRL

employees: Tim Matty and Larry Scott for their contributions in field data collection.

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