Centre for Human Factors and Ergonomics
No. 2, September 2004
FARM TRACTORS: WHOLE BODY VIBRATION
– reducing the risk of musculoskeletal conditions
Liz Ashby and Richard Parker
Exposure to whole body vibration is strongly associated with back disorders (Teschke et al, 1999) with those exposed demonstrating
higher prevalence of back pain than those not exposed (Boshuizen, Bongers and Hulshof, 1990, Bovenzi and Betta, 1994). The effects
of vibration are likely to be most significant when in combination with other factors associated with musculoskeletal conditions
(Helmkamp et al, 1984; Canadian Centre for Occupational Health and Safety, 2003). International standards exist which consider
extent and frequencies of vibration and offer recommended maximum exposure levels (ISO 2631, 1985; BS 6841): evidence from
a number of studies indicates that tractors (among other vehicles), typically expose their operators to vibration levels in excess of
those recommended by ISO 2631 (Teschke et al, 1999; Lines et al, 1995).
Given the variety of agricultural machines
and of tractors, it is difficult to suggest
specific design features that would be
appropriate for them all, especially as
some common controls such as seat
suspension seem to frequently be
ineffective (Teschke et al, 1999). However,
addressing some generic factors in
combination with some of the other
hazards associated with musculoskeletal
risk may help reduce injuries. These factors
have been considered here with respect
to design, methods of use of tractors
and organisation of work.
Design
The design of tractors has changed
significantly over recent years; modern
tractors tend to have good seat
suspension at least in the vertical plane
and in some cases horizontal too and
some models have built in suspension.
The tractor tyres act as the main means
of suspension but the extent to which
t h ey p rov i d e p ro te c t i o n va r i e s
considerably - so the vibration
experienced by the operator is still
significant. However, tractors are built to
last and it is not uncommon to see old
tractors, even 30 or 40 years old, still in
operation. These tractors expose workers
to many of the poor design features that
have since been eliminated in the newer
models, and the newer models whilst
improved still present design elements
associated with musculoskeletal risk.
To reduce risk of harm from vibration,
tractor operators should look for:
1. Good seat suspension, specifically
relative to the users size and weight.
2. Seat characteristics appropriate for
limiting exposure to other
musculoskeletal risk factors i.e.
appropriate depth, height, width etc.
3. A suspension system that is well
maintained and complete – do not
match existing seats to a system
designed for another seat, which may
actually increase vibration levels
(Golsse, 1990).
4. Cab design appropriate for use e.g.
allowing seat rotation, good visibility
without requiring constrained postures.
Individual methods
of work
The manner in which machines are
operated is likely to have significant
effects on the vibration levels the operator
is exposed to – for example Wegscheid
(1994) observed marked differences in
vibration levels between the most and
least “aggressive” skidder (forestry
machine) operators.
Combinations of postural risk factors,
particularly twisting, with vibration are
likely to increase risk of harm and
discomfort, and many of these factors
are ones that individual operators can
control to greater or lesser degrees.
Tractor drivers should aim to:
1. Avoid or reduce jolting and jarring
as much as possible.
2. Use steering strategies that limit
obstacles and sharp turns, and that
reduce the need to use
asymmetrical postures, for example
by having well placed and clean
mirrors.
3. Use slower speeds to limit vibration
levels and sudden movements.
4. Adjust seating to suit their own
physique and tasks: extreme
postures combined with vibration
are the most harmful.
5. Take frequent short breaks and make
postural changes to limit awkward,
extreme or constrained postures.
Organisation of work
Given the limitations of suspension and
other design methods in reducing
vibration, the systems and organisation
of the work conducted by tractor
operators must be considered. Tractor
drivers will in most cases have a variety
of tasks other than operating the tractor.
The degree to which the operator can
control their tractor driving and other
tasks will depend on their work situation;
the tractor driver or the manager of work
requiring tractor operation should
consider the following methods of risk
control:
1. Limit exposure – reduce the duration
of tractor driving, especially where
other risk factors are present such as
rough terrain, requirement for awkward
postures etc.
2. Limit intensity of work – encourage
frequent breaks and postural changes;
reduce time pressures and deadlines.
3. Ensure international standards are met
to ensure drivers are not over-exposed
to harmful or uncomfortable vibration.
4. Adequately maintain tracks and roads
to reduce potholes, ruts and
corrugations.
5. Organise tasks to reduce the
requirement for extreme, constrained
or harmful postures – for example
through rearranging the layout of
loading areas.
References
British Standards Institution. 1985. British Standard Guide to Measurement
and evaluation of human response to whole-body mechanical vibration and
repeated shock. BS 6841:1987.
Boshuizen, H.C., Bongers, P.M. and Hulshof, C.T.J. 1990. International Archives
of Occupational and Environmental Health. Volume 62,
109-115.
Bovenzi, M. and Betta, A. 1994. Low-back disorders in agricultural tractor drivers
exposed to whole-body vibration and postural stress. Applied Ergonomics, Volume
25 (4), 231-241.
Lines, J., Stiles, M. and Whyte, R. 1995. Whole Body Vibration during Tractor
Driving. Journal of Low Frequency Noise and Vibration,
Volume 14 No. 2.
Golsse, J-M. 1990. Evaluation of skidder seats for reducing whole-body vibration.
Forest Engineering Research Institute of Canada, technical report TR-99.
Helmkamp, J.C., Redmond, G.R. and Cottington, E. 1984. Whole Body Vibration
– a critical review. American Industrial Hygiene Association Journal, 45(3),
162-167.
International Standards Organisation. 1995. Evaluation of human exposure to
whole body vibration Part 1 General requirements. International Standard IS
2631/1.
Teschke, K., Nicol, A-M., Davies, H. and Ju, S. 1999. Whole body vibration and
back disorders among motor vehicle drivers and heavy vehicle operators: a review
of the scientific evidence. Workers’ Compensation Board of British Columbia.
Wegscheid,E. 1994. Another look at skidder ride vibration. Journal of Forest
Engineering, Volume 5 (2) January 1994.
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