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Human

Vibration

Introduction, Legislation and Standards

Metra Mess- und Frequenztechnik Radebeul / Germany www.MMF.de

http://www.mmf.de/

Metra Mess- und Frequenztechnik Radebeul / Germany www.MMF.de 2

Effects of Vibration at Workplaces

Human Vibration

Hand-Arm Vibration Whole-Body Vibration

Working with hand-held machines or driving mobile work machines and vehicles may cause damage to bones, joints, muscles and circulatory problems in the hand-arm system as well as disk damage to the spine.


Activities with Potential Health Risk Whole-Body Vibration:

• Tractor driving• Armored fighting vehicles, e.g., tanks• Earth-moving machinery - loaders,

excavators, bulldozers, graders, scrapers, dumpers, rollers

• Forest machines driving• Mine and quarry equipment• Forklift trucks• Some trucks• Some bus and tram driving• Some helicopters and fixed-wing

aircraft• Some concrete production machinery• Some railway driving • Some sports activities etc.

Source: Michael J. Griffin / ILO

Hand-Arm Vibration:• Hand-held powered tools used in

manufacturing: percussive metal-working tools, grinders and other rotary tools, impact wrenches etc.

• Quarrying, mining and construction: rock-drills, stone-hammers, pick-hammers, vibro-compactors etc.

• Agriculture and forestry: chain saws, brush saws, barking machines, lawn mowers etc.

• Public utilities: road and concrete breakers, drill-hammers, hand-held grinders etc.


Legislation and Standards

EC Vibration Protection Directive

2002/44/EC

Measurement and evaluation of humanexposure to hand-transmitted vibration

ISO 5349:2001

Evaluation of human exposure to whole-body vibration

ISO 2631:1997

Human Response to Vibration –Measuring Instrumentation

ISO 8041:2005


EC Directive 2002/44/ECSince the implementation of the EC Vibration Protection Directive 2002/44/EC

there has been an obligation on companies throughout Europe to assess the risks of

jobs involving vibration.

The directive defines minimum requirements for employers and manufacturers of

machines.

For evaluation daily vibration exposure A(8) is used:

where

ahv is the total vibration value of the frequency weighted acceleration during the exposure, calculated on the basis of the standards ISO 5349 for hand-arm vibration and ISO 2631 for whole-body vibration

Te is the total duration of exposure during one work day

T0 is the reference duration of 8 hours

A 8 a h vT e

T 0


EC Directive 2002/44/EC

The directive lays down the following limit values for the daily vibration exposure A(8):

A(8) limit values Hand-Arm Vibration Whole-Body Vibration

Exposure Action Value 2.5 m/s² 0.5 m/s²

Exposure Limit 5 m/s² 1.15 m/s²


EC Directive 2002/44/ECOnce the exposure action value is exceeded, the employer shall establish and

implement a program of technical and and organizational measures intended to reduce to

a minimum exposure to mechanical vibration, taking into account in particular:• Other working methods that require less exposure to mechanical vibration• Appropriate work equipment of ergonomic design, producing the least

possible vibration • Provision of auxiliary equipment that reduces the risk of injuries, such as

protective gloves or special seats• Appropriate maintenance programs for work equipment• Design and layout of workplaces• Adequate information and training to instruct workers to use work

equipment correctly and safely• Limitation of the duration and intensity of the exposure• Work schedules with adequate rest periods• Provision of clothing to protect workers from cold and damp

In any event, workers shall not be exposed above the exposure limit value. If this should

be the case, the employer shall take immediate action to reduce exposure below the

exposure limit value.


Hand-Arm Vibration Standard ISO 5349 General Requirements:

• The used measuring equipment must conform to ISO 8041

• Vibration should be measured in three orthogonal directions simultaneously

• The sensor must be capable of measuring the highest peak acceleration magnitudes

• The sensor should be mounted as close as possible to the center of the handle without affecting normal use of the machine

• In the case of machines which need to be held with both hands, measurements must be made on each hand. The exposure is determined by reference to the higher value of the two

• Measurand is the interval RMS of frequency-weighted acceleration in m/s²


Hand-Arm Vibration Standard ISO 5349Weighting Filter:

• The weighting filter Wh represents the relative health risk of certain vibration frequencies for the hand-arm system

0,001

0,01

0,1

1

10

1 10 100 1000 10000

Hz


Hand-Arm Vibration Standard ISO 5349Interval RMS:

• Interval RMS values awx, awy and awz should be measured and reported for X, Y and Z

separately

• To minimize variation, vibration should be measured, if possible, several times during a work day and averaged:

where

ahwi is the interval RMS of measurement i

n is the number of measurements

ti is the duration of measurement i

• The measuring time shall be sufficiently long to provide representative values for a machine or activity. The duration of one measurement should be more than 8 seconds. The total measuring time should be at least 1 minute.

a hw1T 0 i 1

n

a hw i2 t i


Hand-Arm Vibration Standard ISO 5349Total Vibration Value:

• Evaluation is performed on the basis of Total Vibration Value ahv, which is the square root of the sum of the squares (vector sum) of the interval RMS values awx, awy and

awz:

• In certain cases it may be not possible or not necessary to measure the RMS in three axes for the calculation of ahv. The results of uniaxial measurements must be multiplied with a correction factor. The factor can vary from 1.0, if there is only one dominating axis, to 1.7, if all three axes have simi lar values:

where

awmeas is the measured RMS value

a h v a w x2 a w y

2 a w z2

a h v 1.0 a w meas for one dominating axis

a h v 1.7 a wmeas for three similar axes


Hand-Arm Vibration Standard ISO 5349Daily Exposure:• The health risk depends on the duration of vibration exposure during a work day• Daily exposure A(8) is the equivalent continuous acceleration over an eight-hour work

period. For the determination of A(8) it is not necessary to measure over eight hours. It is sufficient to make short-term measurements during representative work steps. The results are normalized to eight hours. Daily exposure is calculated as follows:

where

ahv is the total vibration value of the frequency weighted acceleration during the exposure

Te is the total duration of exposure during one work day

T0 is the reference duration of 8 hours

A 8 a h vT e

T 0


Hand-Arm Vibration Standard ISO 5349Combined Daily Exposure:• If a daily exposure consists of more than one activity with different vibration

magnitudes, daily exposure is calculated:

where

ahvi is the total vibration value of the frequency weighted acceleration of activity i

n is the number of activities

Ti is the duration of activity i

• To compare the contributions of different activities, it may be useful to calculate partial exposure values:

A 81T 0 i 1

n

a hvi2 T i

A i 8 a hviT i

T 0


Hand-Arm Vibration Standard ISO 5349• Daily exposure should be measured for both hands separately• Since measurement uncertainty is usually relatively high (e.g. 20 to 40 %), not more

than two significant digits should be stated for A(8)


Hand-Arm Vibration Standard ISO 5349Measuring Report:The result of measurements to ISO 5349 shall be a report including the following data:• Names of company / contractor and operating person• Purpose of measurement• Date• Location• Temperature, humidity, noise• Description of activities• Work procedure (working time, interruptions, breaks)• Tested equipment (model, serial no., condition, age, weight, rotary speed, handle type),

tools and work pieces• Measuring equipment (type, serial no., calibration date, function chaeck• Sensor positions and directions, mounting method• Measured interval RMS in X / Y / Z direction for each activity• Total vibration value Ahv for each activity

• Duration Ti of each activity for one work day• Daily vibration exposure A(8)• Partial Daily vibration exposure Ai (8), if measured


Hand-Arm Vibration Standard ISO 5349Function Check and Calibration:

• It is recommended to perform a function check of the sensor and the measuring instrument before and after each measurement by means of a vibration calibrator

• Calibration should be performed in regular intervals, e.g. after 2 years, in order to check that the equipment is within the specification to ISO 8041


Hand-Arm Vibration Standard ISO 5349Practical sensor locations for various machine tools:

Chain saw Angle grinder

Straight handle

Grinding machine

Chipping hammer

Steering wheel

More examples of measuring points can be found in ISO 8662 for various hand-held machines, ISO 7505 for chain saws and ISO 7916 for portable brush saws.


Whole-Body Vibration Standard ISO 2631-1General Requirements:• ISO 2631-1 covers methods for the measurement of periodic, random and transient

vibration with regard to health, comfort and perception• The considered frequency range is 0.5 to 80 Hz• Measurand is frequency weighted acceleration• Applicable for vibrations transmitted to the body as a whole through the supporting

surfaces: the feet of a standing person, the back and the feet of a seated person, the buttock or the supporting surface of a recumbent person

• Vibration is measured triaxial with a coordinate system originating at the point from which vibration enters the body. The Z axis always runs along the spine :


Whole-Body Vibration Standard ISO 2631-1Sensor:• A commonly used sensor design for seat vibration measurement is given in

ISO 10326-1. A flat triaxial accelerometer is built into a semi-rigid rubber disk:

• Sensors shall be located at the interface between the body and the supporting surface• Most common sensor locations for seated and standing persons are the principal

support areas of the seat surface, the seat back and the feet. For recumbent persons the supporting surfaces under the pelvis, the back and the head are used.


Whole-Body Vibration Standard ISO 2631-1Evaluation Methods:• The selection of appropriate evaluation methods depends on the amount of shocks

and transient vibration in the measured signal, defined as the crest factor:

• The basic evaluation method shall be used for evaluation. In cases where one of the alternative methods is used, both the basic and the alternative evaluation value shall be reported.

Evaluation Methods

Basic Evaluation Method(interval RMS)

Crest factor < 9?yes no

Running RMS Method(MTVV)

Fourth Power Vibration Dose Method (VDV)

C RE STPEAKRM S


Whole-Body Vibration Standard ISO 2631-1Basic Evaluation Method:• For vibration with low contents of shocks (crest factor < 9)• Measurand is the RMS of frequency weighted acceleration in m/s²

where

aw(t) is the instantaneous frequency weighted acceleration

T is the duration of measurement (integration time)

• In the presence of occasional shocks or transient vibration, i.e. high crest factors, the basic evaluation method may underestimate the effects of whole-body vibration.

T

ww dttaT

a0

2 )(1


Whole-Body Vibration Standard ISO 2631-1Running RMS Method:• Takes into account occasional shocks and transient vibration by use of running RMS

with a short integration time constant of preferably 1 second:

where


is the integration time constant for running averaging

t is the time

t0 is the time of observation

• The result is given as the highest magnitude of the running RMS during the measurement period called maximum transient vibration value MTVV:

0

0

)(1

)( 20

t

t

ww dttata

)(max 0taMTVV w


Whole-Body Vibration Standard ISO 2631-1Fourth Power Vibration Dose Method (VDV):• More sensitive to peaks than the basic evaluation method by using the fourth power

instead of the second power of acceleration• The result is called Vibration Dose Value (VDV) which has the unit m/s1,75

where


T is the duration of measurement• When the vibration exposure consists of periods with different VDV, the total vibration

dose is calculated from the fourth root of the sum of the fourth power partial vibration dose values

• Estimated Vibration Dose:

VDV0

T

a w t 4 dt14

VDV to tali

VDV i4

14

44.1 TaeVDV W


Whole-Body Vibration Standard ISO 2631-1Weighting Filters:• Health, comfort and perception are dependent on the vibration frequency content• Different frequency weightings are required for the different directions• Two principal weightings are Wk and Wd:

Frequency Weighting

Health Comfort Perception

WkZ axis of

seat surface

Z axis of seat surface

Z axis when standing

vertical recumbent (except head)

X / Y / Z axes of feet

when sitting

Z axis of seat surface

Z axis when standing

vertical recumbent (except head)

WdX / Y axes of

seat surface

X / Y axes of seat surface

X / Y axes when standing

horizontal recumbent

Y / Z axes of seat back

X / Y axes of seat surface

X / Y axes when standing

horizontal recumbent


Whole-Body Vibration Standard ISO 2631-1Weighting Filters:• Additional weightings are Wc, We and Wj:

Frequency Weighting


Wc X axis of seat back X axis of seat back X axis of seat back

We -rx / ry / rz axes

(rotational) of seat surface

rx / ry / rz axes (rotational) of seat surface

Wj - vertical recumbent head vertical recumbent head


Whole-Body Vibration Standard ISO 2631-1Weighting Filters:

0,001

0,01

0,1

1

10

0,1 1 10 100 1000

Hz

Wk (Z standing and seated, vert. recumb.)

Wd (X/Y standing and seated, hor. recumb.)

0,001

0,01

0,1

1

10

0,1 1 10 100 1000

Hz

0,001

0,01

0,1

1

10

0,1 1 10 100 1000

Hz

0,001

0,01

0,1

1

10

0,1 1 10 100 1000

Hz

Wc (Seat back)

Wj (head recumbent)


Whole-Body Vibration Standard ISO 2631-1Vibration Total Value:• Combining vibrations of three orthogonal directions by calculating the square root of

the sum of the squares (vector sum) of the interval RMS values awx, awy and awz:

• The values of the multiplying factors kx, ky and kz depend on the selected frequency weighting

a h v k x2 a w x

2 k y2 a w y

2 k z2 a w z

2


Whole-Body Vibration Standard ISO 2631-1Multiplying Factors for Vibration Total Value:


kx 1.4 (Filter Wd, seat surface)

1.0 (Filter Wd, seat surface)

0.8 (Filter Wc, seat backrest)

0.25 (Filter Wk, seated, feet)

1.0 (Filter Wd, standing)

1.0 (Filter Wk, recumbent)



1.0 (Filter Wk, recumbent)

ky 1.4 (Filter Wd, seat surface)


0.5 (Filter Wd, seat backrest)



1.0 (Filter Wd, recumbent)




kz 1.0 (Filter Wk, seat surface)

1.0 (Filter Wk, seat surface)

0.4 (Filter Wd, seat backrest)


1.0 (Filter Wk, standing)


1.0 (Filter Wk, seat surface)

1.0 (Filter Wk, standing)



0,1

1

10

1 10 100 1000 10000

Exposure duration (min)

Wei

gh

ted

acc

eler

atio

n (

m/s

²)Whole-Body Vibration Standard ISO 2631-1Health Guidance Zones:• There are not sufficient data to establish a quantitative relationship between vibration

exposure and health risk• The following health guidance zone diagram can be used as a rough orientation:

No known effects

Health riskCaution Zone


Whole-Body Vibration Standard ISO 2631-1Basic Requirements for Human Vibration Meters:• The instrument shall at least display the following quantities:

- The interval RMS of frequency weighted acceleration over the averaging time- The interval RMS of unweighted, but bandpass filtered acceleration over the averaging time- The averaging time

• The instrument shall display an overload condition which occurred during the averaging time. Overload shall be indicated for all relevant points of the signal path.The overload message must be held during the entire averaging time.

• A calibration function for transducer sensitivity must be available• The instrument may also measure Maximum Transient Vibration Value (MTVV)• The instrument may also measure Vibration Dose Value (VDV)• The instrument may also measure Total Vibration Value Ahv• The selected vibration quantity shall be identifiable, preferably by displaying the

physical unit• The display shall allow reading with a resolution of better than 1 %• Settling time shall not exceed 2 minutes• The delay between starting a measurement and the acquisition of valid data must not

exceed 0.5 seconds


Instrumentation Standard ISO 8041Basic Requirements for Human Vibration Meters (continued):• The instrument has one ore more weighting filters calculated by the product of

- band limitation- transition acceleration / velocity- step function

• Most important weighting filters are Wh for hand-arm, Wd and Wk for whole-body• Maximum errors:

- Mechanical reference signal (80 Hz / 10 m/s² for H/A and 16 Hz / 1 m/s² for W/B) under reference conditions (23 °C, 50 % rel. Hum.) ± 4 %- Deviation between the measured acceleration with weighting filter and the acceleration measured only with band limiting filter after multiplication with a correction factor: ± 3 %- Deviation between the measured interval RMS and running RMS: ± 2 %

• Linearity error: < 6 %• Linear range: > 60 dB• Cross-talk: < 0.5 %• A battery indicator is required• Measuring error at minimum battery voltage: < 3 %• Environmental: temperature range at least –10 to 50 °C

waterproof design (IP42 to IP65)