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 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 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.

Ergo-Online Academy Ergo-Online, LLC Copyright 2007 Ergo-Online, LLC 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/s 2 or in/s 2 ) –Jerk (rate of change of acceleration – cm/s 3 or in/s 3 ) G – force of gravity (32.2 ft/s 2 or 9.81 m/s 2 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.

Ergo-Online Academy Ergo-Online, LLC Copyright 2007 Ergo-Online, LLC 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.

Ergo-Online Academy Ergo-Online, LLC Copyright 2007 Ergo-Online, LLC 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.

Ergo-Online Academy Ergo-Online, LLC Copyright 2007 Ergo-Online, LLC 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.

Ergo-Online Academy Ergo-Online, LLC Copyright 2007 Ergo-Online, LLC 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.

Ergo-Online Academy Ergo-Online, LLC Copyright 2007 Ergo-Online, LLC 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%.

Ergo-Online Academy Ergo-Online, LLC Copyright 2007 Ergo-Online, LLC 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

Ergo-Online Academy Ergo-Online, LLC Copyright 2007 Ergo-Online, LLC Biodynamic vs. Basicentric Coordinate Systems Biodynamic and Basicentric coordinate systems for the hand, showing the directions of the acceleration components (ISO 5349 and ANSI S ).

Ergo-Online Academy Ergo-Online, LLC Copyright 2007 Ergo-Online, LLC Whole-Body Vibration The frequency range of 0.5 Hz to 80 Hz is significant in terms of the body's response.

Ergo-Online Academy Ergo-Online, LLC Copyright 2007 Ergo-Online, LLC Whole-Body Vibraton Health Effects 1.Lumbar spinal disorders 2.Hemorrhoids 3.Digestive problems 4.Urinary problems

Ergo-Online Academy Ergo-Online, LLC Copyright 2007 Ergo-Online, LLC 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/ 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.

Ergo-Online Academy Ergo-Online, LLC Copyright 2007 Ergo-Online, LLC HAVS Hand Arm Vibration Syndrome Vibration White Finger (FWF) Traumatic Vasospastic Disease Occupational Raynaud’s Disease

Ergo-Online Academy Ergo-Online, LLC Copyright 2007 Ergo-Online, LLC 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.

Ergo-Online Academy Ergo-Online, LLC Copyright 2007 Ergo-Online, LLC HAVS Internationally Accepted Grading System

Ergo-Online Academy Ergo-Online, LLC Copyright 2007 Ergo-Online, LLC HAVS

Ergo-Online Academy Ergo-Online, LLC Copyright 2007 Ergo-Online, LLC HAVS Table 1 Stages of Vibration White Finger (Taylor-Pelmear System) StageCondition of FingersWork & Social Interference 00No tingling, numbness or blanching of fingersNo complaints OTIntermittent tinglingNo interference with activities ONIntermittent numbnessNo interference with activities TNIntermittent tingling and numbnessNo interference with activities 1Blanching of a fingertip with or without tingling and/or numbnessNo interference with activities 2Blanching of one or more fingers beyond tips, usually during winterPossible interference with activities outside work, no interference at work 3Extensive blanching of fingers; frequent episodes in both summer and winter Definite interference at work, at home, and with social activities; restriction of hobbies 4Extensive blanching of most fingers; frequent episodes in both summer and winter Occupation usually changed because of severity of signs and symptoms

Ergo-Online Academy Ergo-Online, LLC Copyright 2007 Ergo-Online, LLC Vibration Table 2 contains the American Conference of Governmental Industrial Hygienists (ACGIH) recommendations on the limits for exposure of the hand to vibration. Table 2 Threshold Limit Values for Exposure of the Hand to Vibration in Either X h, Y h, Z h, Directions Total Daily Exposure Duration a Values of the Dominant, b Frequency-Weighted, rms, Component Acceleration Which Shall Not be Exceeded a k, (a keg ) m/s 2 gcgc 4 hours and less than hours and less than hour and less than less than 1 hour a 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

Ergo-Online Academy Ergo-Online, LLC Copyright 2007 Ergo-Online, LLC 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

Ergo-Online Academy Ergo-Online, LLC Copyright 2007 Ergo-Online, LLC Topics of Interest Lever Systems –First-Class Levers –Second Class Levers –Third-Class Levers

Ergo-Online Academy Ergo-Online, LLC Copyright 2007 Ergo-Online, LLC Force

Ergo-Online Academy Ergo-Online, LLC Copyright 2007 Ergo-Online, LLC Gender, Age & Training Effects

Ergo-Online Academy Ergo-Online, LLC Copyright 2007 Ergo-Online, LLC Conclusion of Module 9 We have concluded discussing Module 9, Vibration.