Human Vibration - Introduction, Legislation and

Report
Human Vibration
Introduction, Legislation and Standards
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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
Hand-Arm Vibration:
• Hand-held powered tools used in
manufacturing: percussive metalworking tools, grinders and other rotary
tools, impact wrenches etc.
• Quarrying, mining and construction:
rock-drills, stone-hammers, pickhammers, 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.
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
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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 5349:2001
Evaluation of human exposure
to whole-body vibration
ISO 2631:1997
Human Response to Vibration –
Measuring Instrumentation
ISO 8041:2005
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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:
A 8
where
a hv
T
e
T0
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
Exposure Action Value
Exposure Limit
Hand-Arm Vibration
Whole-Body Vibration
2.5 m/s²
0.5 m/s²
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
10
1
0,1
0,01
Hz
0,001
1
10
100
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10000
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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:
a hw
n
1
T0
2
a hw i t i
i
1
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:
a hv
•
2
a wx
2
a wy
2
a wz
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:
a hv
1 .0 a w meas
for one dominating axis
a hv
1 .7 a w meas
for three similar axes
where
awmeas is the measured RMS value
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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:
A 8
a hv
T
e
T0
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:
A 8
n
1
T0
2
a hvi T i
i
1
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:
Ai 8
a hvi
Ti
T0
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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
Straight handle
Angle grinder
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.
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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:
C RE S T
PEAK
Evaluation Methods
RM S
yes
Basic Evaluation Method
(interval RMS)
•
Crest factor < 9?
no
Running RMS Method
(MTVV)
Fourth Power Vibration
Dose Method (VDV)
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.
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Whole-Body Vibration Standard ISO 2631-1
Basic Evaluation Method:
• For vibration with low contents of shocks (crest factor < 9)
• Measurand is the RMS of frequency weighted acceleration in m/s²
aw 
1
T
T
 a w ( t ) dt
2
0
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:
a w (t 0 ) 
1

t0
 a w ( t ) dt
2
t 0 
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:
MTVV  max a w ( t 0 ) 
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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
T
V DV
1
aw t
4
dt
4
0
•
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
V DV
V DV
total
4
1
4
i
i
•
Estimated Vibration Dose:
eVDV  1 . 4  a W  4 T
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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
Wk
Wd
Health
Comfort
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
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
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Perception
Z axis of seat surface
Z axis when standing
vertical recumbent
(except head)
X / Y axes of seat surface
X / Y axes when standing
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horizontal recumbent
24
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)
10
10
1
1
0,1
0,1
0,01
0,01
Hz
0,001
0,1
1
10
100
Hz
0,001
1000
0,1
1
10
100
1000
Wd (X/Y standing and seated, hor. recumb.) Wj (head recumbent)
10
10
1
1
0,1
0,1
0,01
0,01
Hz
0,001
0,1
1
10
100
1000
Hz
0,001
0,1
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10
100
1000
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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:
a hv
•
2
2
k x a wx
2
2
k y a wy
2
2
k z a wz
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:
kx
ky
kz
Health
Comfort
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)
1.4 (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 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)
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Perception
1.0 (Filter Wd, seat surface)
1.0 (Filter Wd, standing)
1.0 (Filter Wk, recumbent)
1.0 (Filter Wd, seat surface)
1.0 (Filter Wd, standing)
1.0 (Filter Wd, recumbent)
1.0 (Filter Wk, seat surface)
1.0 (Filter Wk, standing)
1.0 (Filter Wd, recumbent)
28
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:
Weighted acceleration (m/s²)
10
Health risk
1
No known effects
0,1
1
10
100
1000
10000
Exposure duration (min)
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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: < 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)
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