1. Human Vibration Human Vibration Human Vibration Human Vibration
Abstract
Human vibration is defined as the effect on the human body of mechanical vibration. The effect might be on the body as a whole, whole-body vibration, or on parts of the body. The hand-arm system is the most important of these. In many cases, vibration of the whole-body system arises from vehicles, land-based or otherwise, from vibrating floors in buildings, or from big machines where the operator is seated on the machine. Hand-arm vibration is produced by powered hand tools - chain saws, chipping hammers, grinders etc.
This lecture describes how to measure and evaluate the impact of vibration on the human body.
Copyright© 2002
Brüel & Kjær Sound and Vibration Measurement A/S
All Rights Reserved
Copyright© 2002
Brüel & Kjær Sound and Vibration Measurement A/S
All Rights Reserved
LECTURE NOTE
English BA

2. Hand-arm Vibration
Long-term exposure can cause white-finger or dead-finger syndrome
Symptoms:
Tingling
Numbness
Blanching
Over-reaction to coldness
Hand-arm Vibration
The harm done to the body is most pronounced in hand-arm vibration. The so-called white-finger or dead-finger syndrome is a well-known effect of long-term exposure. The symptoms are:
Tingling
Numbness
Blanching
Over-reaction to coldness
These symptoms are caused by capillary and nervous malfunctions.

3. Whole-body Vibration
Long-term exposure can cause severe damage especially to the lumbar region of the spine
Short-term symptoms:
Fatigue
Headache
Slower reactions
Nausea
Insomnia
Whole-body Vibration
The effects on the body as a whole are less specific. The most pronounced long-term effect is found in the lumbar region of the spine, where spine deformation, lumbago and sciatica can develop.
Short-term effects of whole-body vibration are those felt during or after the working day. They are:
Fatigue
Headache
Slower reactions
Nausea
Insomnia
These symptoms are caused by vascular disorders and nervous malfunctions.

4. Mechanical Models of the Human Body
Whole body
Hand-arm
Shoulder girdle
(4 - 5 Hz)
Eyeball,
intraocular
structures
(ca. 25 Hz)
Lung
volume
Chest wall
( Hz)
Head
(axial mode)
( Hz)
Lower
arm
Abdominal Mass (4 - 8 Hz)
Seated
person
Spinal column
(axial mode)
( Hz)
Hand grip
( Hz)
Legs
Mechanical Models of the Human Body
Mechanical models of the human body are attempts to make relatively simple models of an enormously complex system. The model on the right consists of mass, spring and damper elements. The figures in Hz are resonance frequencies for different components of the body system. Resonance frequency means the frequency, or narrow frequency band, at which the components oscillate.
The spinal column has a resonance at about 10 to 12Hz; the abdominal mass in the 4 to 8Hz frequency band; the head (axial) at about 25Hz. The body system is a heavily damped system. Resonances are therefore not “sharp”. They are felt over a wide frequency band.
(Variable from
ca. 2 Hz with knees flexing to
over 20 Hz with rigid posture)
Standing person

5. Standards for Human Vibration
ISO :1997
“Mechanical vibration and shock – Evaluation of human exposure to whole-body vibration,
Part 1, General Requirements”.
ISO
“Mechanical vibration - Guidelines for the measurement and the assessment of human exposure to hand-transmitted vibration.”
Standards for Human Vibration
To make an assessment of the effect of vibration on the body, the relative annoyance or danger of different types of vibration must be determined. There have been many such investigations, which have resulted in a number of standards and proposals from the ISO.
ISO2631 deals with whole-body vibration and ISO5349 deals with hand-arm vibration. ISO/DIS8041 specifies how the measurement instrumentation should be designed and classified.

6. Evaluation Method: Weighting
Motion sickness
Whole body
Acceleration dB
x,y z
Hand-arm 5
- 5
- 10
- 15
- 20
Weighting Method
However, as an alternative method of evaluation, ISO2631 Part I indicates the weighting method. Furthermore, the ISO5349 for hand-arm vibration exclusively specifies this method. A weighting curve corresponds to an inverted rating curve. The figure shows examples of weighting curves for different categories of human vibration.
Whole-body lateral movement (x,y)
Whole-body longitudinal movement (z)
Hand-arm vibration.
- 25
- 30
- 35
0.02
0.05
0.1
0.2
0.5 1 2 5 10 20 50
100
200
500 1k Hz

7. Using the Weighing Method in Practice
Measurement
Weighting
Display
Frequency, Hz
In practice, the weighting method is easier to handle than the rating method, because no frequency analysis is required. An overall frequency weighting of the signal, carried out electronically by a weighting filter, produces after detection etc. a single figure for evaluation in a very direct way.
Result: One single figure to compare with the standard

8. Measurement Directions
Whole-Body
"Handgrip" position z zh y x xh zh
Measurement Directions
At this stage we must define the three orthogonal measuring directions used. (Orthogonal means at right angles). For the whole-body system, the longitudinal direction is called the Z direction. The lateral directions are called X and Y. X is back-and-front while Y is side-to-side. For the hand-arm system, similar definitions are used. However, ISO5349, the standard for measurement and assessment of hand-arm vibration, mentions two coordinate systems, a biodynamical and a basicentric system. The first is defined from the hand-arm anatomy. The second is defined from the handle or surface of the tool being investigated. yh
Basicentric coordinate system
Biodynamic coordinate system

9. Whole-Body Vibration Weighting
Acceleration dB
Whole body
x,y z 5
- 5
- 10
- 15
Combined filter
- 20
For whole-body vibration in vehicles or on platforms two weighting filters apply in the measurement of vibration: one for the Z direction, max. at Hz and another one for the X, Y-directions, max. at 1 – 2 Hz.
For whole-body vibration in buildings the same filtershapes as above apply, defined in the ISO2631 part 2. However, for unknown posture of the body, either the most stringent of z, y- and y-directions or a weighting characteristic obtained by the combination of the z-axis and x-, y-axes can be used. A German term, KB value, is used for evaluation of whole body vibration in buildings.
- 25
- 30
- 35
0.02
0.05
0.1
0.2
0.5 1 2 5 10 20 50
100
500 1k Hz
200

10. Measure in the Vertical Direction In Buildings
Again! Z Z Z Z Z Z
Since human beings in buildings are equally likely to in standing, sitting or lying posture, it makes little sense to prefer one body direction from another.
It makes therefore more sense to measure in the worst case direction for the house or room in question and then apply the combined weighting filter.
In houses of older construction the worst case direction is often the vertical. In high, concrete buildings it might be one of the horizontal direction.

11. Hand-Arm Vibration Weighting
Acceleration dB
8 Hz
16 Hz 5
- 5
- 10
- 15
- 20
Hand-Arm Vibration
For hand-arm measurements the weighting curve is the same for all directions. It is defined from 6,3 to 1250 Hz. It has its maximum sensitivity between 8 and 16 Hz.
The assessment of the vibration exposure should be based upon the directional component with the largest vibration acceleration.
- 25
- 30
- 35
0,02
0,05
0,1
0,2
0,5 1 2 5 10 20 50
100
500 1k Hz
200

12. Descriptive Parameters
Amplitude T
aPeak
aRMS t
aPeak-peak
Descriptive Parameters
To reduce the enormous amount of data in a vibration signal, some descriptive parameters must be defined. The parameters for human vibration are very similar to those used for noise: Current RMS value, a eq (or L eq) and Max. Peak value.
The simplest vibration is a pure tone which consist of a sinusoid with the frequency: f = 1/T. To characterise the magnitude of this vibration the RMS (root-mean-square) value is the most commonly used quantity because it has a direct relationship to the energy content of the signal.

13. Characteristics of Vibration – RMS
Max. Peak
Acceleration
Time
Root Mean Square:
Acceleration
Exponential average
Characteristics of Vibration – RMS
Mechanical vibrations are characterised by their frequency and their amplitude. The vibration has to be of a certain magnitude and the frequency has to be within certain limits in order for the body or the hand-arm system to perceive this.
Most vibration met with in daily are not purely sinusoidal vibrations. Very often they very with time, both in frequency and in magnitude. The RMS value is in fact obtained by exponential averaging as a current integration and which in many cases very much with time. It can be different to be assessed, when dealing with longer periods.
aRMS
Time Constant: 1s = slow, 1/8s = fast
Time

14. The “Energy Equivalent” Acceleration, aeq
Max. Peak
Acceleration
Time T
Energy Equivalent Acceleration:
aRMS
Acceleration
aeq
While the current RMS is an exponential average, the aeq - the “energy equivalent” acceleration - is a linear average taken over a longer time-period. Exponential average means that the most recent part of the signal has the greatest influence on the averaged level. Linear average means that each part of the signal has the same influence on the averaged level.
aeq
Time

15. Max. Peak and Crest Factor
Acceleration
Time
T = 60 s
Crest Factor
Acceleration
aRMS
Max. Peak
The max. peak value of a signal is the single highest acceleration during the measurement period considered.
Crest Factor
The crest factor is defined as the ratio between the peak value and the RMS value. When the RMS value is fluctuating the crest factor might be evaluated as the ratio between the peak value and an equivalent value. A suitable period for the equivalent value could be 60 s, but other periods might be chosen.
aeq
Time

16. The body reacts logarithmically
m/s2 or Decibels?
0.01
0.1 1 10
100 80
120
140
160
Acceleration dB
re m/s2
m/s2
m/s2 or Decibels?
When the measurement result is reported, we have two alternatives: to report it in the normal linear acceleration unit, m/s2 or in logarithmic, decibels, referred to the reference level 10-6m/s2. Decibels translate a given factor into a given increase. A multiplication by 2 is always +6dB while a multiplication by 10 is always +20dB. The body reacts logarithmically, perceiving a doubling as a constant rather than feeling a certain linear increment as a constant. The shift from 1 to 2 m/s2 is therefore perceived as a much larger change than the change from 10 to 11 m/s2.
The choice between between m/s2 and decibels is a matter of convention. The information content is exactly the same.
However, a convention states that values in decibels should be designated with an “L”, whereas values in m/s2 should be designated with an a. Thus, the symbol Leq is used for equivalent level in decibels and aeq for equivalent values in m/s2. In what follows the symbol aeq will be preferred since most countries prefer to work in m/s2.
Here are some examples of human vibration levels:
The range of interest for hand-arm vibration is 120 to 160dB, or 1 to 100m/s2.
The range of interest for whole-body vibration in vehicles is 100 to 140dB, or 0,1 to 10m/s2.
For whole-body vibration in buildings the range of interest is 60 to 100dB or 0,001 to 0,1m/s2.
The body reacts logarithmically

17. m/s2 or Decibels? Acc.dB 80 00.1 0.1 100 120 1 140 10 160 Hand-arm
(re m/s2) 80
00.1
0.1
100
120 1
140 10
160
Hand-arm
Whole body in
vehicles
m/s2 or Decibels?
When the measurement result is reported, we have two alternatives: to report it in the normal linear acceleration unit, m/s2 or in logarithmic, decibels, referred to the reference level 10-6m/s2. Decibels translate a given factor into a given increase. A multiplication by 2 is always +6dB while a multiplication by 10 is always +20dB. The body reacts logarithmically, perceiving a doubling as a constant rather than feeling a certain linear increment as a constant. The shift from 1 to 2 m/s2 is therefore perceived as a much larger change than the change from 10 to 11 m/s2.
The choice between between m/s2 and decibels is a matter of convention. The information content is exactly the same.
However, a convention states that values in decibels should be designated with an “L”, whereas values in m/s2 should be designated with an a. Thus, the symbol Leq is used for equivalent level in decibels and aeq for equivalent values in m/s2. In what follows the symbol aeq will be preferred since most countries prefer to work in m/s2.
Here are some examples of human vibration levels:
The range of interest for hand-arm vibration is 120 to 160dB, or 1 to 100m/s2.
The range of interest for whole-body vibration in vehicles is 100 to 140dB, or 0,1 to 10m/s2.
For whole-body vibration in buildings the range of interest is 60 to 100dB or 0,001 to 0,1m/s2.
Whole body in
buildings
Acc.m/s2

18. Basic Instrumentation for Weighted Measurements
Level
Analyzer
Accele-
rometer
DeltaTron
Amplifier
Input
Filter
Weighting
Amplifier
Channel
1(X)
Multiplexer
Channel
2(Y)
Basic Instrumentation for Weighted Measurements
We have now outlined the general definitions and principles which lie behind the weighting method for measuring human vibration. The illustration shows a general flow diagram for the measuring equipment. The transducer must either be a three-axis transducer, or a single transducer which is mounted in each of the three directions X, Y, Z successively. After the transducer signal has been preamplified, it passes through the appropriate frequency weighting filter.
After additional amplification comes a Peak, RMS or Leq/aeq detector; digital or analogue readout and output and finally a DC output for level recording. AC output for tape-recording or frequency analysis is taken out before the detectors. DC output means a voltage output proportional to the logarithmic readout in the meter or display. AC output means a voltage which varies with time exactly as the original transducer signal.
This basic measuring system applies both to whole-body and hand-arm vibration measurements. The basic difference lies in the frequency range and weighting filter being used.
Channel
3(Z)

19. Transducer for Whole-body Vibration
Rubber disc
WHOLE-BODY VIBRATION
Transducer
The transducer for whole-body vibration measurements (vehicles) is a triaxial accelerometer mounted inside a rubber disc. The disc is so flat that it can be fixed to a test subject without any inconvenience to the wearer. ISO standard 2631 states that the vibration should be measured where the signal enters the body.
The triaxial seat accelerometer contains three accelerometers, each covering one of the orthogonal directions X, Y, and Z.
Tri-axial Accelerometer

20. Mounting the Transducer – Whole Body
When the vehicle seat is the area through which most of the signal enters the body, the test subject simply sits on the transducer. When an appreciable component of the vibration signal enters the body through the back of the chair, the rubber disc is mounted on the test subject's back or chest by means of a strap. A third possible area of entry is where the feet touch the floor of a vehicle or a vibrating platform. The rubber disc can then be placed on the floor. With a small static load (e.g. 1kg), it will transmit the signal from the floor in the specified frequency band (up to 80Hz).

21. Whole-body Vibration in Buildings
Again! Z Z Z Z Z Z
Whole-body Vibration in Buildings
An accelerometer can be mounted in different ways, depending of the accessibility of the mounting surface and of the vibration characteristics. The most adedquate mounting method will generally be to stick the accelerometer on the measurement surface using a thin layer of special wax. Practical experiences have shown that for wooden floors it is advisable that a persons stands close to the accelerometer during measurements.

22. Directional Considerationsaz Lz ay Ly ax Lx
Directional Considerations
ISO 2631 part 1 states that measurements should be carried out in all three orthogonal directions. If the directional components ax and ay when multiplied by 1,4 are similar in magnitude to az, then the Weighted Acceleration Sum, WAS, defined as:
WAS= (1,4ax)2 + (1,4ay)2 + az2
Apply for determination of the limit. Thus the WAS is calculated from the three orthogonal accelerations by a simple squared addition with slight emphasis on the X and Y directions.
Weighted Acceleration Sum:

23. Exposure Evaluation m/s2 dB Whole body exposure limit 30 150
Whole body fatique dec. prof. 10
140
Whole body reduced comfort 3
130 1
120
110
0.3
Exposure Evaluation
To obtain a figure for allowed exposure, consult the transcription of the ISO-curve system shown here:
ISO 2631 operates with three criteria for the evaluation of whole-body vibration: Reduced Comfort, Fatigue-decreased Proficiency and Exposure Limit. Reduced Comfort is typically concerned with the comfort of passengers in a bus, train or car. Decreased proficiency is typically concerned with the ability of an operator of a vehicle or crane to function properly. This includes the important aspect of safety. The Exposure limit is concerned with direct health hazards, such as vertebral deformations, circulation disorders and lumbago syndromes.
Choose the proper criterion. After entering the proper curve with the measured WAS, or the worst direction aeq, read the allowed exposure time on the horizontal axis.
100
0.1
Allowed
Exposure
time
1min
0.1h
0.5h 2h 5h
10h
16h
24h

24. Calculation of the Working Day Dose
WAS1
WAS2
WAS3
or a1eq
or a2eq
or a3eq
or t1
or t2
or t3
If the total work period is composed of sub-periods with different types of work, find the WAS or worst direction aeq for each sub-period. By dividing the sub-period time by the allowed time given by the vibration of that sub-period, calculate the working day dose contribution from each sub-period. Then add the sub-period dose contributions together, and multiply by 100%. This gives the total working day dose as a percentage of the allowed dose.
t = Elapsed time
t = Allowed time

25. Example of Dose Calculation:
Work
Type
Elapsed
Time
t(hours)
aeq
m/s2
Allowed
Time
t (hours) 1 2
0.7
2.5 2
0.5
1.3
0.9 3 1
0.3 8
Example:
There are three different types of work in the working day of a truck operator. (The rest of the day is spent in vibration-free work.) For all three types a representative aeq for each direction X, Y and Z was measured. It was thereby found that the dominant vibration was in the z-direction, so the signal from the two other directions could be neglected.
Consult the relevant ISO criterion curve (here Fatigue-decreased Proficiency) with the three WAS's to find the sub-period dose contributions.
Then calculate the daily dose as a percentage of that allowed as shown. Thus the allowed daily dose was exceeded by 48%.

26. Mounting the Transducer – Hand Arm
HAND-ARM VIBRATION
Transducer Mounting
As for ISO 2631 for whole-body vibration, ISO 5349 for hand-arm vibration states that the measuring point should be where the signal enters the body (the hand). Thus the interface between the palm of the hand and the tool handle is the measurement point. The test subject should be using his normal grip force. And so the problem arises: How is a transducer mounted between handle and hand, without disturbing the subject's normal work procedure?
Accelerometers should be rigidly attached to the tool, but not interfering with normal operation

27. Mounting Adaptors – Hand Arm
Hand-adaptor
Handle adaptor
Handle adaptors and hand-adaptors are used when rigid mounting to the tool is not possible
Mounting Adaptors
One proposal is the so-called hand adaptor developed by Bruel&Kjaer. This consists of a base plate to be placed between the handle and hand, an extension going up between the third and fourth finger, when using the right hand, the beam terminating in a mounting block for up to three small accelerometers. In an alternative version of the adaptor, the mounting block is situated directly at one end of the base plate.

28. Coordinate Systems
Coordinate Systems
The two adapters are optimised for different purposes.
The hand adaptor measures in the biodynamic coordinate system. The handle adaptor measures in the basicentric coordinate system. Both systems are defined in ISO The biodynamic coordinate system is defined by the geometry of the hand. The basicentric system is defined by the geometry of the handle or tool surface. The hand adaptor has only three holes so that simultaneous measurement can be made in all three directions at a time. The handle adaptor has only two mounting holes to keep mass to a minimum. It must therefore be turned 90 to measure in the third direction.
The hand adaptor measures in the biodynamic coordinate system
The handle adaptor measures in the basicentric coordinate system

29. Directional Considerations for Hand-ArmZ Y X
Directional Considerations
In contrast to the WAS-value suggested by the ISO 2631, the ISO 5349 for hand-arm vibration suggest the worst direction philosophy. Thus, for a start, it is necessary to measure in all three directions to find the worst one. For subsequent measurements on the same tool and the same working process, the worst direction might be considered as known.
For hand-arm vibration it is often necessary to measure in all three directions to find the worst direction
ISO 2631: WAS
ISO 5349: ”Worst direction”

30. Type of Adaptor Handle adaptor Hand-adaptor Type of adaptor
The handle adaptor is optimized for use with percussive tools. It is mounted directly where the percussive forces couple into the hand. The hand adaptor is placed more centrally with respect to the hand. Thus it complies with the requirement of the ISO standard that measurements should ideally be made where the vibration enters the body. In the case of a resilient element between the hand and the vibrating structure, if might be preferable to make the transducers rigidly attached to the handle or structure and to record separately the type, thickness, physical properties and estimated attenuation achieved by the cushioning material.

31. Accelerometers Cables
Because the adaptor is located between fingers, it is attached to the hand. During measurements the cable is led through a wrist strap and may be led further up through the operator's sleeve. The handle adaptor is attached to the tool. It may be taped to the handle before operation. The cable may be taped to the power cable of the tool (if there is one).
Cables are fixed down, often with tape, so that there is minimal cable-induced vibration in the measurement system

32. Exposure Evaluation
Risk of getting vascular disorders (White finger syndrome)
Years of
exposure 20
50 th percentile 15
40 th percentile 10
30 th percentile
20 th percentile 5
10 th percentile 4 3 2
1.5
Exposure Evaluation
For hand-arm measurements, ISO5349 does not set limits for allowed doses. The standard, in fact, leaves this to the national standardization boards. What the ISO standard does, besides specifying the measurement technique as such, is to provide a table of consequences for different exposures. Thus the curves show the risk of getting white-finger syndrome from a daily exposure in a certain number of years. If, for example, a group of workers are exposed to a 4h daily energy-equivalent acceleration of 5 m/s2, then 10 % of the group will probably develop vascular disorders in 6 years. 1
0.5 1
1.5 2
2,5 3 4 5 6 7 8 9 10 15 20 25 30 40 50
a [m/s2]

33. The 4-hour Energy Equivalent Acceleration, aeq (4)
m/s2 dB
The entrance value to the family of curves is the 4h energy equivalent acceleration aeq (4) . If the energy equivalent acceleration is measured over a period other than 4h, then the 4h energy equivalent can be calculated.
The Integrating Human-Vibration Unit automatically displays aeq (T) and the elapsed time T as well. The unit fots directly to the bottom of the sound level meter, which in this case is used as a vibration meter. It can store up to 99 records containing both the measurements parameters and the data. The system features a standard serial digital interface allowing connection to personal computer.

34. Exposure from Several EventsdB
If the working day is composed of different types of work involving exposure to vibration and no integrating instruments is at hand, then it is still possible to find the energy equivalent acceleration from the individual events.

35. Example of Exposure Calculations
Work
Type an
m/s2
Effective time
Hours 1
5.6
0.7 2
10.3
0.5
= 2.2 3
2.5
1.0
Example:
A working day is composed of three different processes, of duration and acceleration as shown. The combined aeq(T) and the corresponding four-hour aeq(4) is calculated. The 8h aeq(8) is also shown.

36. Example: Wheel-loader
Level dB
140
Health
135
Proficiency
130
125
120
115
Examples of Measurements and Analysis of Whole-Body Vibration
Wheel-loader
The illustration shows measurements on a tracked bulldozer under different conditions. The Z direction is known to be dominant.
The bulldozer vibration varies between 0,6m/s2 and 1.0m/s2. If 0,9m/s2 is taken as the aeq, the allowed exposure time using the ISO proficiency curve is about 1,5 h, whereas the allowed exposure time using the health risk curve is about 5h. If, therefore, the ISO system is followed, proficiency, and hence safety, is very well catered for, since the allowed exposure is exceeded quite early in the working day. Health is also affected, but only after five hours of effective work.
This 1/3-octave spectrum is the z direction vibration from a wheel-loader operator’s seat shows the characteristics suspension resonance which is seen in nearly all vehicles on wheels.
This truck has a rather stiff suspension system producing a resonance at 6 – 8 Hz. Other vehicles have suspension resonance as low as 1,5 – 2 Hz.
The components at 40 – 60 Hz come from the engine.
110
105
Allowed time
Hours
0,5 2 5 10 24
1,5

37. Example: Wheel-loader
1/3 Octave Spectrum dB
m/s2
Z-direction 1
120
Suspension
0,315
110
0,1
100
This 1/3-octave spectrum is the z direction vibration from a wheel-loader operator’s seat shows the characteristics suspension resonance which is seen in nearly all vehicles on wheels.
This truck has a rather stiff suspension system producing a resonance at 6 – 8 Hz. Other vehicles have suspension resonance as low as 1,5 – 2 Hz.
The components at 40 – 60 Hz come from the engine. 90
1,0
2,5
6,3 16 40 63
100 Hz

38. Example: Helicopter FFT Spectrum dB Main rotor Main blades Tail rotor
shaft
130
etc.
10,5 43 71
120 33 22 53
110
100
5,25 97 64 75 27 86
Helicopter
This is a narrow band analysis from a helicopter pilot's seat.
The spectrum is dominated by rotor blade frequencies and their harmonics. The main rotor has its basic blade passing frequency at about 10,5Hz. The second harmonic at 22Hz, the third harmonic at 33hz, fourth harmonic at 43, etc., are clearly recognised. The tail rotor blades are just about recognised at 55Hz, and the long shaft from the motor to the tail rotor has its main bending mode at 71Hz. 90 80 Hz 10 20 30 40 50 60 70 80 90
100

39. Example: Chipping Hammer
Examples of Measurements and Analysis of Hand-Arm Vibration
Chipping Hammer
The chipping hammer, together with a whole family of percussive pneumatic tools, is among the most harmful of hand tools. At the same time, the tools of this family present the greatest challenge to the measuring equipment.
The transducer mounting problems have already been mentioned above.
Very high peak acceleration levels are found at the handle of the chipping hammer. Even higher levels are found at the chisel (and the operator often uses his left hand to control the chisel).
Very high peak acceleration levels are found at the handle of the chipping hammer. Even higher levels are found at the chisel (and the operator often uses his other hand to control the chisel)

40. Chipping Hammer Vibration
1/3 - Octave Acceleration dB
m/s2
180
1000
Tool body resonance
170
315
Left Hand Resonance
100
Blow frequency
160
Subharmonic
150
31.5
This 1/3-octave spectrum shows how chipping hammer vibration are dominated by very high acceleration levels above the measurement frequency range (1500Hz). This represents a measurement problem since these very high peak levels sometimes overload the measuring instrumentation.
The blow rate - here at 63Hz - will normally be the dominating component after weighting, but in this case the subharmonic of the blow rate is even more pronounced (after weighting). The subharmonic is produced by the interaction between the blow rate and the tool reaction which is different for every single blow.
140 10
130 4 16 63
250 1k 4k
16k
63k Hz
861953/1

41. Chipping Hammer Risk Evaluation
Years of
exposure 20
50 th percentile 15
40 th percentile 10
30 th percentile
20 th percentile 5
10 th percentile 4 3 2
1.5
The weighted acceleration value for the signal above is 10m/s2. By consulting the consequence curves from ISO 5349, it is seen that on a four-hour energy equivalent per day there is a probability that this level will produce the white-finger syndrome in about 4 years at 20% of the workers.
If, however, the effective working time at the same vibration value with the chipping hammer is only 2.5h, then the corresponding aeq(4) can be calculated by using the formula
aeq(4) = aeq(T) T/4
= ,5 / 4 = 7,9 m/s2 (H-A)
Thus a somewhat lower risk is found. 1
0.5 1
1.5 2
2,5 3 4 5 6 7 8 9 10 15 20 25 30 40 50
a [m/s2]

42. Example: Grinders Z Y X Weighted 1/3-octave Spectrum Oscillation
frequency dB
m/s2
140 10
2thh
4thh
8thh
130
120 1
Random
distortion
products
Weighted
1/3-octave
Spectrum
110
Grinder
Grinders, too, are among the hard tools, especially the so-called orbital grinders or sanders.
The measurement directions are defined from the tool as illustrated for the left-hand grip surface.
The 1/3-octave spectrum is from the X direction of the left hand. The spectrum is dominated by the oscillation frequency at 80 Hz plus its even harmonics. The second, fourth and eighth harmonics are clearly seen. At the low frequency end other distortion products are found. They are produced by the interaction of the machine oscillation and the varying counterforces supplied by the hand
100
0.1 4 16 63
250 1k 4k Hz

43. Conclusion Central Issue:
Avoid breaking occupational health legislation at lowest cost
Monitoring and Risk assessment checklist:
Is there a problem?
How big is the problem?
What causes the problem?
How do we reduce the problem?
How do we prevent the problem?
Vibration + Time = Vibration Exposure
Vibration Exposure + Time = Tissue Damage
Vibration exposure is measured according to national and international standards for Hand-Arm Vibration and Whole-Body Vibration.
Conclusion