ergo-online academy copyright 2007 ergo-online, llc 1 vibration

Ergo-Online Academy

Copyright 2007 Ergo-Online, LLC1

Vibration

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Types of Vibration• Motion Sickness Vibration

– Vibrations with high amplitude and low cycle frequency (i.e. < 1 Hz) such as those encountered on a boat at sea, or in a high cab on a slow moving vehicle.

• Hand-Arm Vibration– Vibration levels with higher frequency levels (i.e. 6.5 -

1250 Hz) affecting the upper body limbs, such as those transmitted by a chain saw's engine and chain motion, are called Hand-Arm Vibration.

• Whole-Body Vibration– Vibration levels with a frequency range between 0.5

and 80 Hz, as sensed by the entire body, are known as Whole-Body Vibration. Such vibrations are commonly associated with moving vehicles.

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Describing Vibration• Frequency of vibration (cycles/second) measured in

Hertz (Hz)• Intensity of vibration measured in:

– Amplitude/displacement (cm or in)– Velocity (cm/s or in/s)– Acceleration (cm/s2 or in/s2)– Jerk (rate of change of acceleration – cm/s3 or in/s3)

• G – force of gravity (32.2 ft/s2 or 9.81 m/s2)• Power Spectral Density (PSD) – the power at discrete

frequencies within a selected bandwidth.• Root mean square acceleration (RMS) – the total

energy across the entire frequency range.

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Describing Vibration

• The Crest Factor is equal to the peak amplitude of a waveform divided by the RMS value.

• Crest Factor (CF) helps to define the roughness of a particular ride. This is the ratio of the weighted peak acceleration level to its corresponding weighted RMS value.

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Describing Vibration

• Weighted Maximum Peak Acceleration levels provide information on shock loads which would otherwise be lost in the RMS acceleration levels. This is particularly significant with equipment which often encounter obstacles in their pathways, and usually have inadequate suspensions or poor seating.

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Resonance Frequency• Every object (or mass) has

a resonant frequency in somewhat the same sense that a pendulum has a natural frequency.

• When an object is vibrated at its resonance frequency, it will vibrate at a maximum amplitude which is larger than the amplitude of the original vibration.

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Resonance of the Human Body1. In the human body, individual body

members and organs have their own resonant frequencies and do not vibrate as a single mass, with its own natural frequency.

2. This causes amplification or attenuation of input vibrations by certain parts of the body due to their own resonant frequencies.

3. The most effective exciting frequency for vertical vibration lies between 4 and 8 Hz.

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Resonance Frequencies1. Vibrations between 2.5 and

5 Hz generate strong resonance in the vertebra of the neck and lumbar region with amplification of up to 240%.

2. Between 4 and 8 Hz resonance are set up in the trunk with amplification of up to 200%.

3. Vibrations of 25 Hz generate the strongest resonance between the head and shoulders with amplification of up to 350%.

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Hand-Arm Vibration

• Standards (ISO 5349 : 1986 and BS 6842 : 1987) exist that provide guidance on measuring and evaluating hand-arm vibration exposure in three orthogonal axis over the frequency range 5.6 to 1400 Hz.

• The hand-arm vibration is measured in three orthogonal directions.– z axis corresponds to the percussion axis– y corresponding to the axis of the handle– x corresponding to an axis perpendicular to the palm of

the hand

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Biodynamic vs. Basicentric Coordinate Systems

Biodynamic and Basicentric coordinate systems for the hand,showing the directions of the acceleration components (ISO 5349 and ANSI S3.34-1986).

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Whole-Body Vibration

• The frequency range of 0.5 Hz to 80 Hz is significant in terms of the body's response.

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Whole Body Vibration Coordinate System

• Axes of vibration used to measure exposure to whole-body vibration.

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Health Effects of Whole-Body Vibration

1. Lumbar spinal disorders

2. Hemorrhoids

3. Digestive problems

4. Urinary problems

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Hand Arm Vibration Syndrome (HAVS)

• Vibration White Finger (FWF)• Traumatic Vasospastic Disease• Occupational Raynaud’s Disease

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HAVS• Typically, the syndrome begins

with sensorineural symptoms – episodes of numbness and tingling precipitated by exposure to cold or damp conditions, or the use of vibrating tools.

• With ongoing exposure, the vascular symptoms become more apparent.

• Blanching initially affects the distal parts of the digits but will progress proximally if exposure is not reduced or discontinued.

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HAVSTable 1 Stockholm Workshop Scale

For Vascular Symptoms in HAVSStage Grade Description

0 - No Attacks

1 Mild Occasional attacks affecting only the tips of one or more fingers

2 Moderate Occasional attacks affecting distal and middle (rarely also proximal) phalanges = 1 finger

3 Severe Frequent attacks affecting all phalagnes of most fingers

4 Very Severe As in Stage 3, with trophic skin changes in the fingertips

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HAVSTable 2 Stockholm Workshop Scale For

Sensorineural Symptoms In HAVS

Stage Description

0SN Exposed to vibration, but no symptoms

1SN Intermittent numbness, with or without tingling

2SN Intermittent or persistent numbness, reduced sensory perception

3SN Intermittent or persistent numbness, reduced tactile discrimination, and/or manipulative dexterity

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HAVSStages of Vibration White Finger

(Taylor-Pelmear System)

Stage Condition of Fingers Work & Social Interference

00 No tingling, numbness or blanching of fingers No complaints

OT Intermittent tingling No interference with activities

ON Intermittent numbness No interference with activities

TN Intermittent tingling and numbness No interference with activities

1 Blanching of a fingertip with or without tingling and/or numbness

No interference with activities

2 Blanching of one or more fingers beyond tips, usually during winter

Possible interference with activities outside work, no interference at work

3 Extensive blanching of fingers; frequent episodes in both summer and winter

Definite interference at work, at home, and with social activities; restriction of hobbies

4 Extensive blanching of most fingers; frequent episodes in both summer and winter

Occupation usually changed because of severity of signs and symptoms

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The Reduction of Vibration1. Tools should be regularly maintained to keep

vibration to a minimum 2. Workers using vibrating hand-held tools

should wear multiple layers of warm gloves and should wear anti-vibration gloves whenever possible.

3. A worker using a vibrating hand-held tool should let the tool do the work by grasping it as lightly as possible.

4. The tool should be operated only when necessary and at the minimum speed (and impact force) to reduce vibration exposure.

5. Dampen at the source of the vibration

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Vibration Standards

• ISO• ANSI• EU

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