Human Vibration

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Human Vibration

• Introduction, Legislation and Standards

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

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Legislation and Standards
EC Vibration Protection Directive 2002/44/EC
Measurement and evaluation of human exposure to
hand-transmitted vibration ISO 53492001
Evaluation of human exposure to whole-body
vibration ISO 26311997
Human Response to Vibration Measuring
Instrumentation ISO 80412005
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EC Directive 2002/44/EC
Since 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
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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
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EC Directive 2002/44/EC

• Once 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.

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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

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Hand-Arm Vibration Standard ISO 5349

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

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Hand-Arm Vibration Standard ISO 5349

• Interval 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.

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Hand-Arm Vibration Standard ISO 5349

• Total 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

for one dominating axis
for three similar axes
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Hand-Arm Vibration Standard ISO 5349

• Daily 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

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Hand-Arm Vibration Standard ISO 5349

• Combined 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

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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)

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Hand-Arm Vibration Standard ISO 5349

• Measuring 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

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Hand-Arm Vibration Standard ISO 5349

• Function 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

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Hand-Arm Vibration Standard ISO 5349

• Practical sensor locations for various machine
  tools

Chain saw
Angle grinder
Grinding machine
Straight handle
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.
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Whole-Body Vibration Standard ISO 2631-1

• General 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

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Whole-Body Vibration Standard ISO 2631-1

• Sensor
• 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.

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Whole-Body Vibration Standard ISO 2631-1

• Evaluation 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
yes
no
Crest factor lt 9?
Basic Evaluation Method (interval RMS)
Running RMS Method (MTVV)
Fourth Power Vibration Dose Method (VDV)
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Whole-Body Vibration Standard ISO 2631-1

• Basic Evaluation Method
• For vibration with low contents of shocks (crest
  factor lt 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.

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Whole-Body Vibration Standard ISO 2631-1

• Running 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
• aw(t) is the instantaneous frequency weighted
  acceleration
• ? 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

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Whole-Body Vibration Standard ISO 2631-1

• Fourth 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
• aw(t) is the instantaneous frequency weighted
  acceleration
• 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

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Whole-Body Vibration Standard ISO 2631-1

• Weighting 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
Wk Z 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)
Wd X / 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
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Whole-Body Vibration Standard ISO 2631-1

• Weighting Filters
• Additional weightings are Wc, We and Wj

Frequency Weighting Health Comfort Perception
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
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Whole-Body Vibration Standard ISO 2631-1

• Weighting Filters

Wk (Z standing and seated, vert. recumb.)
Wc (Seat back)
Wd (X/Y standing and seated, hor. recumb.)
Wj (head recumbent)
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Whole-Body Vibration Standard ISO 2631-1

• Vibration 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

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Whole-Body Vibration Standard ISO 2631-1

• Multiplying Factors for Vibration Total Value

Health Comfort Perception
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 Wd, seat surface) 1.0 (Filter Wd, standing) 1.0 (Filter Wk, recumbent)
ky 1.4 (Filter Wd, seat surface) 1.0 (Filter Wd, seat surface) 0.5 (Filter Wd, seat backrest) 0.25 (Filter Wk, seated, feet) 1.0 (Filter Wd, standing) 1.0 (Filter Wd, recumbent) 1.0 (Filter Wd, seat surface) 1.0 (Filter Wd, standing) 1.0 (Filter Wd, recumbent)
kz 1.0 (Filter Wk, seat surface) 1.0 (Filter Wk, seat surface) 0.4 (Filter Wd, seat backrest) 0.4 (Filter Wk, seated, feet) 1.0 (Filter Wk, standing) 1.0 (Filter Wd, recumbent) 1.0 (Filter Wk, seat surface) 1.0 (Filter Wk, standing) 1.0 (Filter Wd, recumbent)
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Whole-Body Vibration Standard ISO 2631-1

• Health 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

Health risk
Caution Zone
No known effects
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Whole-Body Vibration Standard ISO 2631-1

• Basic 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

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Instrumentation Standard ISO 8041

• Basic 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 lt 6
• Linear range gt 60 dB
• Cross-talk lt 0.5
• A battery indicator is required
• Measuring error at minimum battery voltage lt 3
• Environmental temperature range at least 10 to
  50 C waterproof design (IP42 to IP65)