Whole-body vibration - Guidelines for vibration hazards reduction - Part 2: Management measures at the workplace

This Technical Report outlines practicable measures for the reduction and control of exposure to whole-body vibration at workplaces in order to provide a practical professional aid to workplace managers and health and safety officers. It covers identification and reduction of health risks from exposure to hazardous machinery vibration at the particular workplace, corresponding to Articles 4, 5 and 6 in the EU Directive 2002/44/EC, including
-   identification of main sources of whole-body vibration at the workplace,
-   formulation of a strategy for minimising and control of vibration exposure and
-   implementation of the strategy.
NOTE   Although the term vibration covers continuous vibration and transient vibration (shocks), in this Technical Report shocks are referred to in special cases where they require special attention.
This Technical Report is not concerned with hand-arm vibration which is covered by CR 1030-2.

Ganzkörper-Schwingungen - Leitfaden zur Verringerung der Gefährdung durch Schwingungen - Teil 2: Organisatorische Maßnahmen am Arbeitsplatz

Dieses Dokument zeigt durchführbare Maßnahmen für die Verringerung und Beherrschung der Einwirkung
von Ganzkörper-Schwingungen, um Führungspersonal und Verantwortlichen für Gesundheit und Sicherheit
eine praktische professionelle Hilfe zu geben. Es behandelt die Feststellung und Verringerung gesundheit-
licher Risiken durch die Einwirkung von gefährdenden Schwingungen von Maschinen an einem bestimmten
Arbeitsplatz entsprechend Artikel 4, 5 und 6 der EU-Richtlinie 2002/44/EG, einschließlich
Erkennung der Hauptquellen von Ganzkörper-Schwingungen am Arbeitsplatz,
Formulierung einer Strategie zur Minimierung und Beeinflussung der Einwirkung von Schwingungen,
Umsetzung der Strategie.
ANMERKUNG Obgleich der Begriff Schwingungen Dauerschwingungen und transiente Schwingungen (Stöße)
umfasst, wird in diesem Dokument auf Stöße dann in besonderen Fällen Bezug genommen, in denen sie eine besondere
Aufmerksamkeit erfordern.
Dieses Dokument befasst sich nicht mit Hand-Arm-Schwingungen, die in CR 1030-2 behandelt werden.

Vibrations globales du corps - Guide pour la réduction des risques de vibrations - Partie 2: Mesures de prévention sur le lieu de travail

Le présent Rapport technique décrit brievement les mesures pratiques visant a la réduction et a la maîtrise de l'exposition a des vibrations globales du corps sur les lieux de travail afin de fournir un outil professionnel pratique aux dirigeants et aux agents de santé et de sécurité du lieu de travail. Il couvre l'identification et la réduction des risques pour la santé dus a l'exposition aux vibrations dangereuses des machines sur le lieu de travail individuel, correspondant aux articles 4, 5 et 6 de la Directive UE 2002/44/CE, y compris :
-   l'identification des sources principales de vibrations globales du corps sur le lieu de travail ;
-   l'élaboration d'une méthode de réduction au minimum et de maîtrise de l'exposition aux vibrations ; et
-   la mise en ouvre de la méthode.
NOTE   Bien que le terme « vibration » couvre les vibrations continues et les vibrations durant les transitoires (chocs), le présent Rapport technique fait référence aux chocs dans des cas spécifiques ou ils requierent une attention toute particuliere.
Le présent Rapport technique ne traite pas des vibrations main-bras qui sont couvertes par le CR 1030-2.

Tresenje celotnega telesa – Smernice za zmanjšanje tveganja zaradi vibracij – 2. del: Organizacijski ukrepi na delovnem mestu

General Information

Status
Published
Publication Date
30-Jun-2006
Technical Committee
Current Stage
6060 - National Implementation/Publication (Adopted Project)
Start Date
01-Jul-2006
Due Date
01-Jul-2006
Completion Date
01-Jul-2006

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SLOVENSKI STANDARD
SIST-TP CEN/TR 15172-2:2006
01-julij-2006
Tresenje celotnega telesa – Smernice za zmanjšanje tveganja zaradi vibracij – 2.
del: Organizacijski ukrepi na delovnem mestu

Whole-body vibration - Guidelines for vibration hazards reduction - Part 2: Management

measures at the workplace
Ganzkörper-Schwingungen - Leitfaden zur Verringerung der Gefährdung durch
Schwingungen - Teil 2: Organisatorische Maßnahmen am Arbeitsplatz

Vibrations globales du corps - Guide pour la réduction des risques de vibrations - Partie

2: Mesures de prévention sur le lieu de travail
Ta slovenski standard je istoveten z: CEN/TR 15172-2:2005
ICS:
13.160 Vpliv vibracij in udarcev na Vibration and shock with
ljudi respect to human beings
SIST-TP CEN/TR 15172-2:2006 en

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST-TP CEN/TR 15172-2:2006
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SIST-TP CEN/TR 15172-2:2006
TECHNICAL REPORT
CEN/TR 15172-2
RAPPORT TECHNIQUE
TECHNISCHER BERICHT
November 2005
ICS 13.160; 17.160
English Version
Whole-body vibration - Guidelines for vibration hazards
reduction - Part 2: Management measures at the workplace

Vibrations globales du corps - Guide pour la réduction des Ganzkörper-Schwingungen - Leitfaden zur Verringerung der

risques de vibrations - Partie 2: Mesures de prévention sur Gefährdung durch Schwingungen - Teil 2: Organisatorische

le lieu de travail Maßnahmen am Arbeitsplatz

This Technical Report was approved by CEN on 25 July 2005. It has been drawn up by the Technical Committee CEN/TC 231.

CEN members are the national standards bodies of Austria, Belgium, Cyprus, Czech Republic, Denmark, Estonia, Finland, France,

Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Slovakia,

Slovenia, Spain, Sweden, Switzerland and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre: rue de Stassart, 36 B-1050 Brussels

© 2005 CEN All rights of exploitation in any form and by any means reserved Ref. No. CEN/TR 15172-2:2005: E

worldwide for CEN national Members.
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Contents Page

Foreword ..........................................................................................................................................................3

Introduction......................................................................................................................................................4

1 Scope ...................................................................................................................................................5

2 References...........................................................................................................................................5

3 Abbreviations ......................................................................................................................................5

4 Determination and assessment of health risks ................................................................................6

4.1 General ................................................................................................................................................6

4.2 Identification of main sources of whole-body vibration at the workplace......................................6

4.3 Relationships between whole-body vibration exposure and health risk........................................6

4.4 Legal requirements.............................................................................................................................7

4.5 Use of declared values .......................................................................................................................7

5 Formulation of provisions aimed at avoiding and reducing vibration exposure ...........................7

6 Minimising vibration exposure ..........................................................................................................8

6.1 Vibration reduction by task and process re-design .........................................................................8

6.2 Vibration reduction by selection of machinery, tools and seats.....................................................9

6.3 Vibration reduction by instructions and maintenance...................................................................13

6.4 Reduction of the exposure duration................................................................................................14

7 Information related to health risks for the operator .......................................................................14

Annex A (informative) Examples of machines and processes that may expose operators to

significant whole-body vibration above the exposure action and/or limit values of the EU

Directive 2002/44/EC.........................................................................................................................16

Annex B (informative) Assessment of health risks from whole-body vibration at the workplace .........19

Annex C (informative) A practical example of application of methods for limitation of vibration

exposure............................................................................................................................................26

Annex D (informative) Selecting mobile machinery for use at work.........................................................27

Annex E (informative) Questions to ask of suppliers ................................................................................31

Annex F (informative) Seating as a means of reducing risks from exposure to whole-body

vibration.............................................................................................................................................32

Annex G (informative) Health surveillance .................................................................................................37

Bibliography...................................................................................................................................................38

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Foreword

This Technical Report (CEN/TR 15172-2:2005) has been prepared by Technical Committee CEN/TC 231

“Mechanical vibration and shock”, the secretariat of which is held by DIN.
CEN/TR 15172 consists of the following parts:

CEN/TR 15172-1, Whole-body vibration — Guidelines for vibration hazards reduction — Part 1: Engineering

methods by design of machinery

CEN/TR 15172-2, Whole-body vibration — Guidelines for vibration hazards reduction — Part 2: Management

measures at the workplace
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Introduction

The EU Directive 2002/44/EC on the minimum health and safety requirements regarding the exposure of

workers to the risks arising from physical agents (vibration) requires those responsible for workplaces to

introduce measures protecting workers from the risks arising from vibration insofar as these affect the health

and safety of workers.

This Technical Report reviews measures of value in the efforts of workplace management to protect workers

from adverse health effects of whole-body vibration and shock. It is recognised that workplaces are very

different and that for a specific workplace only some of the measures are applicable.

Guidelines on engineering methods directed to designers and manufacturers of machinery transmitting

vibration to the human body are given in CEN/TR 15172-1.
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1 Scope

This Technical Report outlines practicable measures for the reduction and control of exposure to whole-body

vibration at workplaces in order to provide a practical professional aid to workplace managers and health and

safety officers. It covers identification and reduction of health risks from exposure to hazardous machinery

vibration at the particular workplace, corresponding to Articles 4, 5 and 6 in the EU Directive 2002/44/EC,

including
— identification of main sources of whole-body vibration at the workplace,
— formulation of a strategy for minimising and control of vibration exposure and
— implementation of the strategy.

NOTE Although the term vibration covers continuous vibration and transient vibration (shocks), in this Technical

Report shocks are referred to in special cases where they require special attention.

This Technical Report is not concerned with hand-arm vibration which is covered by CR 1030-2.

2 Normative references

The following referenced documents are indispensable for the application of this Technical Report. For dated

references, only the edition cited applies. For undated references, the latest edition of the referenced

document (including any amendments) applies.

EN 14253:2003, Mechanical vibration — Measurement and calculation of occupational exposure to whole-

body vibration with reference to health — Practical guidance

ISO 2631-1:1997, Mechanical vibration and shock — Evaluation of human exposure to whole-body vibration

— Part 1: General requirements

ISO 2631-5, Mechanical vibration and shock — Evaluation of human exposure to whole-body vibration —

Part 5: Method for evaluation of vibration containing multiple shocks
3 Abbreviations
In this Technical Report the following abbreviations are used:
r.m.s. acceleration root-mean-square acceleration and
VDV fourth power vibration dose value, both of which are defined in ISO 2631-1.
S daily equivalent static compression dose, which is defined in ISO 2531-5.
EAV daily exposure action value and

ELV daily exposure limit value, which both are defined in EU Directive 2002/44/EC.

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4 Determination and assessment of health risks
4.1 General

General knowledge about whole-body vibration, its effects on man and its assessment and control, is

important as a basis for the determination of health risks at the workplace.
It is necessary to know
 the main sources of whole-body vibration at the workplace,
 the relationships between whole-body vibration exposure and health risk and
 legal requirements including exposure action and limit values.
4.2 Identification of main sources of whole-body vibration at the workplace

The major sources of excessive vibration and shock are usually mobile machinery travelling over rough

surfaces and working with machine tools (loading, drilling, soil compaction, road milling, etc.). A list of the

more common machinery and processes that expose operators to whole-body vibration is given in Annex A.

Furthermore, it is necessary to know representative vibration values for each machine and process that create

the hazard and the corresponding patterns of vibration exposure in order that the exposure of operators can

be estimated.

Of special importance is to search for the following information about the machinery used:

 What are the whole-body vibration exposure values for typical operations of the machine?

 Which operational conditions can be expected to cause whole-body vibration exposures above the

exposure action value and/or above the exposure limit value?
 Which modifications of the machine could cause changes of the declared values?

 Which seats and tools can be considered as suited for the machine, i.e. without worsening the declared

values?

 Which effect will an incorrect adjustment of the seat have on the whole-body vibration exposure?

If an operation handbook does not provide this information, the manufacturer should be asked to provide

additional information.

A thorough knowledge of how the machines are used in practical work is essential. This requires studies at

work sites and collection of information from operators of the machines.
4.3 Relationships between whole-body vibration exposure and health risk

Disorder of the spine and related structures is the main health problem which may be caused by whole-body

vibration. General information on health risks from exposure to whole-body vibration can be found in the

literature.

ISO 2631-1 and ISO 2631-5 provide guidance on health risks from whole-body vibration as well as limits at

which a health risk can be expected. Postures with bending and or twisting of the spine can significantly

increase the health risk at these exposures. Since the strength of the matured spine decreases with age, the

risk of injury due to a particular exposure can essentially increase with age.
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There are indications of an exponential rise of the risk with an increasing intensity. Therefore, the integrated

values (e.g. r.m.s. values) will severely underestimate the health risk if daily exposures contain segments with

a high magnitude or transients with high peak acceleration (shocks, bumps). The more sophisticated

procedures described in ISO 2631-5 will be required for an adequate evaluation in such cases. For the same

reason, averaging of r.m.s. values for different days can lead to an underestimation of the health risk. This is

the case if days with significantly different daily exposure values are averaged.

EN 14253 describes how to measure and calculate the daily vibration exposure in various situations. Annex A

of EN 14253:2003 includes calculation of daily exposure for the cases where the daily work consists of long

uninterrupted operations and for the cases where the daily work consists of operations or work cycles with

different vibration magnitudes over short periods.

NOTE Research is continuously going on in various places and it is important for the management to follow the

development and be aware of revisions of the applicable standards.
4.4 Legal requirements

The EU Directive 2002/44/EC includes requirements on vibration exposure values that shall not be exceeded

(limit values) and exposure values above which actions for reduction of the vibration shall be taken (exposure

action values).

The vibration exposures should be determined for a workday that is representative for the most pronounced

vibration conditions. Averaging over workdays should not be made.

It should be noted that the limit values given by the EU Directive 2002/44/EC are not "safe" values. According

to ISO 2631-1:1997, Annex B, a significant health risk can be expected at levels below the limit values of the

EU Directive 2002/44/EC. Although exposures below the action value do not generally generate significant

health risks, there are cases where exposures below the action value can cause health problems. This is, for

example, the case when the exposure contains shocks or at unfavourable postures.
Guidance on strategies for assessment of a workplace is given in Annex B.
4.5 Use of declared values

The Machinery Directive 98/37/EC requires a declaration of the vibration emission value at operator’s position

in case this value is above 0,5 m/s . According to EN 1032, the declared value is representative of the

75-percentile of vibration values experienced in typical intended use of the machinery in the mode of operation

causing the highest vibration. It also states that the emission values should not be used for assessment of the

health risk. However, the declared emission values can be useful in comparison of machinery and in selection

of a machine for a certain task. If declared emission values are used, together with exposure duration, in order

to get a rough and conservative estimate of the daily exposure that can be expected, it should be kept in mind

that the declared value may be temporarily exceeded.
5 Formulation of provisions aimed at avoiding and reducing vibration exposure

In case the daily vibration exposure for an individual operator can exceed the action value of the EU Directive

2002/44/EC, a strategy for reduction and control of the vibration exposure should be formulated and

implemented. If the exposure action value is not exceeded but risk is demonstrated to exist (e.g. because of

exposure to high level of shocks), the strategy should include control of this risk. Elements of a strategy for the

control of vibration and shock exposure may include one or more of the following activities:

 work task re-design, especially with regard to the main contributor to the vibration exposure;

 machinery or process modification, e.g. use of low-vibration machinery;
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 modification of means for reduction of vibration transmission from source to operator, e.g. selection of

machine with cab suspension, appropriate seats, etc.;

 limitation of individual exposure durations, especially with regard to the main contributor to the vibration

exposure (including job rotation);

 control of that the tyre inflation pressure is maintained according to the manufacturer's manual;

 selection of manufacturer’s options for wheels and tyres appropriate for the conditions of use;

 maintenance of road surface.
Annex C provides a practical example of application of the various methods.
6 Minimising vibration exposure
6.1 Vibration reduction by task and process re-design

Detailed information should be gathered concerning the usage of the various machines, processes and tools

that have been identified as sources of whole-body vibration hazard.

In considering a particular process or task, the first step would be to define its purpose in broad terms, i.e.

what is to be achieved or done. The second step is to split up the process into its key elements, highlighting

those stages that are the principal contributors to the vibration exposure. Actions for limitation of the vibration

exposure may be concentrated to these contributors.
Work tasks should be designed so that
 whole-body vibration exposures are as low as practicable,
 the daily period of exposure to excessive vibration is as short as possible,
 the exposure to severe shocks is avoided and

 the working posture is one which imposes the least adverse health effects of the vibration.

In many cases, travelling over rough ground is the main contributor to the vibration exposure. This exposure

may be managed by the following activities:

 Minimising the travelling distance by organisation of the work, including (if applicable) travelling to and

from breaks. This is also positive for the work efficiency.

 Limitation of the travelling speed. Travelling speed has a very pronounced effect on the vibration value as

shown by the examples in Figure 1. Effective management of the work and information of the operator on

the health risks are prerequisites for getting speed limitation rules followed in practice.

 Maintenance of the ground surface by removing obstacles, filling potholes, levelling of transport roads, etc.

 Information to the operator of the health importance of correct adjustment of the seat and seat back (in

case this is adjustable) and of the driving posture.

For some machines, other operations than travelling can involve excessive vibration and shocks. An example

is tree harvesting, where the main effect of vibration exposure can be from shocks originating from felling

operation and movement of the stem in the harvesting head as delimbing occurs.
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To reduce the risks the work should be organised in such a way that unnecessary climbing out from the cabin

in slippery conditions is reduced to a minimum. The management of the workplace should make sure that

sufficient support for feet and hands is provided and that footwear is provided with adequate anti-slipping

device (at least under heals). The operators should be trained for safe manners in choosing the place and

position of the machinery for climbing out.
Key
Y ratio between vibration values d soil compactor

a hauler (dumper with an articulated frame for steering) e agricultural transporter

b heavy wheel loader f agricultural tractor
c light wheel loader g small dumper

NOTE Figure 1 shows the ratio between the vibration values at the lowest speed, twice the lowest speed and three

times the lowest speed, and the vibration value at the lowest speed. The measurements were made in the z-direction in

the seat cushion, underneath the driver, at travelling over more or less rough surfaces. Similar measurements on industrial

trucks show that a doubling of speed increases the vibration value by a factor of two.

Figure 1 — Influence of driving speed on vibration value
6.2 Vibration reduction by selection of machinery, tools and seats
6.2.1 General

The management of a workplace should be careful in selection of machinery and working equipment and give

enough priority to freedom of excessive vibration and possibilities to operate the machine and working

equipment without attaining an undesirable posture.
6.2.2 Selection of machinery

The supplier should be asked to provide well-founded information on vibration emission and also an

assessment of exposure values during intended use of the machine.

In practice, some difficulty may be experienced in choosing low-vibration machine because of a lack of

appropriate test codes and the current inadequacy of available information on machine vibration emissions.

The declared vibration value provided in accordance with the requirements of the Machinery Directive

98/37/EC is useful for comparison of machines from different manufacturers.
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Proper training and experience of use of the machinery are important factors for controlling vibration exposure

and avoid inappropriate postures. It is also important that the maintenance of the machinery is clear and easy.

More detailed guidance for selecting mobile machinery is provided in Annex D.

Annex E provides a list of the most important questions with regard to whole-body vibration that potential

buyers of machinery should ask suppliers.
6.2.3 Selection of working equipment or tools for the machine

When selecting working equipment or tools for the machine, soft movements of the working equipment and its

coupling to the machine should be aimed at. A check should be made to investigate to which extent the tool

influences the vibration level at the operator's position.

One important factor is to provide the right tool for the job. The machinery producer/manufacturer/supplier

should be asked for guidance on what tools to use and how to operate the tools in order to minimising the

vibration without loosing in efficiency. Also the tool maintenance instructions are important.

Machines that have suspensions of booms or buckets should have these suspensions in operation when

travelling.

A check should be made so that the control levers of the working equipment or tools are placed so that the

operator will maintain an upright posture and avoid unnecessary twisting of the body when using the

equipment or tools.
6.2.4 Selection of seats

The machine supplier should give detailed information on appropriate seat selection. It is important that there

is no conflict between the resonance frequencies of the tyre-machine system, chassis suspension system or

cab suspension system on one side and of the seat suspension system on the other side. It is further

important that there is enough room for the seat suspension to avoid topping and bottoming of the suspension

system. In order to avoid dangerous shocks when driving across an unexpected, severe obstacle, it is also

important that there is a protection from very hard topping and bottoming (reasonably soft end stops).

The manufacturer/supplier should be asked for proper mounting instructions. It is important to check and

assure that the seat mounting surface is rigid enough to avoid resonance problems. This is important also in

lateral directions where the vibration can be amplified and become dominant in certain mobile machinery with

current seats.

In selection of seats, it is also important that the seat suspension is easy to adjust according to the operator's

weight and body size. Height, forward-backward and backrest adjustments are especially important. The seat

cushions should be ergonomically well designed with width and height according to the needs of the operator.

The seat supplier should be asked to provide information on the life of the resilient materials included in the

seat suspension. This is especially important if the resilient material is organic (e.g. elastomers).

For more detailed guidance on selection of seats, see Annex F.
6.2.5 Selection of type of tyres

Tyres are usually selected according to their rolling resistance, grip, stability, cost, resistance to collision

damage, acceptability to the driver, etc.

Most all-terrain vehicles are fitted with pneumatic tyres because they filter out the small ground surface

irregularities. An exception to this are off-road machines fitted with caterpillar tracks and industrial trucks

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which are often mounted on solid tyres for stability reasons and for puncture resistance. These tyres should

only be used on perfectly smooth ground.

Other parameters, such as damping and stiffness, have to be taken into account in order to absorb obstacle

impact. However, even large tyres cannot absorb vibration energy as well as a shock absorber. Therefore,

vibration builds up even on relatively smooth surfaces. Tyres are normally much stiffer than a suspension

system. Excessively soft tyres may induce low-frequency motions, including pitching. In general, changes in

tyre pressure do not result in a simple increase or decrease in vibration, but rather have an effect which is

dependent on other vehicle characteristics, such as load and dimension.

Figure 2 compares r.m.s. acceleration values measured for an unloaded 1,5 t counterbalance truck fitted with

solid or pneumatic tyres and running over an obstacle at different speeds. Acceleration variations resulted

from phase interference between the free vibration of the counterbalance truck after the front tyres had run

over the obstacle and the impact of the rear tyres when hitting the obstacle. In some cases, it may be

judicious to select solid tyres with a carefully selected internal filling, which would offer optimised damping of

the vibration induced by impact with an obstacle. However, research is required to develop a suitable design.

6.2.6 Widening track width or use of dual wheels

Measurements of vibration in agricultural tractors show that widening track width or use of dual wheels

reduces transverse vibration (in the y-direction) significantly. An example of the effects on the frequency-

weighted r.m.s. acceleration value in the seat of an agricultural tractor when using dual wheels is shown in

Figure 3.
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Key
X speed, km/h solid tyres (measured)
Y r.m.s. acceleration, m/s pneumatic tyres (measured)
solid tyres (numerically calculated)
pneumatic tyres (numerically calculated)

Figure 2 — Comparison of acceleration values measured on an unloaded 1,5 t counterbalance truck

fitted with two tyre types and running over an obstacle at various speeds
Key
Y frequency-weighted r.m.s. acceleration, m/s
a single tyre
b dual tyre

Figure 3 — Example of effects of dual wheels on the frequency-weighted r.m.s. acceleration in the seat

of a small agricultural tractor, measured during harrowing in the x-, y- and z-direction

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6.3 Vibration reduction by instructions and maintenance
6.3.1 Adjustment of tyre inflation pressure

The tyre inflation should be adjusted and kept within the range specified by the manufacturer. Tyre inflation

pressure has an influence on the vibration from the contact between ground and tyre. Lower inflation pressure

normally results in lower vibration levels. However, for less heavy machines the resonance frequency

produced by the tyre resilience may be higher than the resonance frequencies caused by the chassis, cab or

seat suspension system. In such case a lowering of the inflation pressure may increase the vibration at the

operator's position due to conflict with the resonance frequency of the suspension of the chassis, cab or seat.

The influence of inflation pressure on vibration is shown in the following example.

EXAMPLE For many categories of machinery, especially fork-lift trucks, the tyre pressure is very high (around 5 bar

to 10 bar) to provide good stability with high loads. However, for all-terrain machines, much lower tyre pressures may be

used according to the use of the machinery.

To assess the effects of changes in tyre pressure, measurements have been made on three all-terrain machines at two

tyre pressures: the machinery manufacturer's recommended tyre pressure and a reduced pressure. The

...

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