Ergo-Online Academy Ergo-Online, LLC Copyright 2007 Ergo-Online, LLC Module 9 Vibration.

Ergo-Online Academy Ergo-Online, LLC

Copyright 2007 Ergo-Online, LLC

Module 9

Vibration



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, are called Motion Sickness 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.

• Finally, 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.



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.



Vibration• The primary quantity to

describe the magnitude of the vibration is acceleration which is normally expressed in meters per second per second (m/s²).

• The magnitude of the vibration is expressed as a root mean square (rms) acceleration value.



Vibration

• 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.



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.



Vibration

• 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.



Vibration

1. 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.

4. 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%.

5. Between 4 and 6 Hz resonance are set up in the trunk with amplification of up to 200%.

6. Vibrations between 20 and 30 Hz set up the strongest resonance between the head and shoulders with amplification of up to 350%.



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



Biodynamic vs. Basicentric Coordinate Systems

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



Whole-Body Vibration

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



Whole-Body Vibraton• Health Effects1. Lumbar spinal disorders

2. Hemorrhoids

3. Digestive problems

4. Urinary problems



Whole-Body Vibration

• In an attempt to consolidate the large number of parameters involved in WBV measurement (i.e. mechanical, biological and psychological) the International Standards Organization (ISO) developed a standard (ISO 2631) in 1985 for defining, measuring and analyzing WBV.

• Because of the roughness and intermittent nature of the ride, ISO 2631/1-1985 is not used since it is only applicable to vibration and repeated shock in the frequency range 1 to 80 Hz. Because of these shortcomings, a better and then more recent standard was the British Standard 6841 (1987) which is applicable to vibration and repeated shock in the frequency range 0.5 Hz to 80 Hz (repeated shock being predominantly of low frequency i.e. 0.5 to 2 Hz).

• ISO 2631 was revised in 1997 and now covers the same frequency ranges as the British Standard, with a slight difference on how the data is analyzed. ISO 2631 (1997) was recently adopted as a draft South African standard, and will most probably be accepted.

• For the analysis and measurement of WBV ISO 2631 (1997) should be used.



HAVSHand Arm Vibration Syndrome

• Vibration White Finger (FWF)• Traumatic Vasospastic

Disease• Occupational Raynaud’s

Disease



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.



HAVS

• Internationally Accepted Grading System



HAVS



HAVSTable 1

Stages 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



Vibration

• Table 2 contains the American Conference of Governmental Industrial Hygienists (ACGIH) recommendations on the limits for exposure of the hand to vibration.

Table 2Threshold Limit Values for Exposure of the Hand

to Vibration in Either X h, Yh, Z h, Directions

Total Daily ExposureDurationa

Values of the Dominant,b

Frequency-Weighted, rms, ComponentAcceleration Which Shall Not be Exceeded

ak, (akeg)

m/s2 gc

4 hours and less than 8 4 0.40

2 hours and less than 4 6 0.61

1 hour and less than 2 8 0.81

less than 1 hour 12 1.22a The total time vibration enters the hand per day, whether continuously or intermittently.

b Usually one axis of vibration is dominant over the remaining two axes. If one or more vibration axes exceeds the Total Daily Exposure then the TLV has been exceeded.

c g = 9.81 m/s . d



The Reduction of Vibration

• How can we reduce vibration?1. 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



Topics of Interest

•Lever Systems– First-Class Levers

– Second Class Levers

– Third-Class Levers



• Force



• Gender, Age & Training Effects



Conclusion of Module 9

• We have concluded discussing Module 9, Vibration.

Ergo-Online Academy Ergo-Online, LLC Copyright 2007 Ergo-Online, LLC Module 9 Vibration.

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