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Vibration. Sean Mahar, PhD, CIH, CSP, PE. Vibration Introduction. Types Problems Controls Measurements Standards. Sean Mahar. BS, Sacred Heart University MS, Texas A&M University PhD, University of Iowa Certified Industrial Hygienist Certified Safety Professional

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Vibration

Sean Mahar, PhD, CIH, CSP, PE


Vibration Introduction

  • Types

  • Problems

  • Controls

  • Measurements

  • Standards


Sean Mahar

  • BS, Sacred Heart University

  • MS, Texas A&M University

  • PhD, University of Iowa

  • Certified Industrial Hygienist

  • Certified Safety Professional

  • Professional Engineer


Experience

  • U of Wolverhampton, 4 years

  • Ohio University, 3 years

  • Worksafe Iowa, 3 years

  • US Navy, 9 years

  • Tracor, 1 year


Educational Objective

The student should have a basic understanding of the measurement and control of vibration, including what instruments are used, the relevant exposure limits, but they need not have the practical experience to enable them to carry out a vibrations survey.


Definitions and measurements units

Units of measurement - understanding of acceleration amplitude

Velocity amplitude displacement amplitude


Definitions and measurements units

Choice of measurement parameters, dynamic range and frequency information required

Relationship and implications of mass and stiffness and damping, natural frequency and static deflection


Monitoring instruments

Vibration transducers

Piezoelectric accelerometer. Also aware of existence of proximity probes and velocity pick-up.

Meters

Elements of a general purpose vibration meter.Also awareness of swept filter frequency analyser and fast Fourier transformanalyser.


Making a survey

ISO Evaluation of human exposure to whole body vibration:

  • Equivalent acceleration value

  • Frequencies of the vibration

  • Direction of excitement of the vibration

  • Time of exposure to vibration


Making a survey

ISO Guidelines for the assessment of human exposure to hand-arm vibration:

  • Frequency weighted RMS acceleration value

  • Probability of developing white finger syndrome


Exposure limits for vibration

  • ISO 2631:1997Guide for the eval. of human exposure to whole body vibration.

  • ISO 5349-1:2001 Guide to meas, and eval. of human exposure to vibration transmitted to the hand

  • HSG 88Hand -arm vibration


Control of vibration

Whole-body vibration damping

  • Use of suspension system for vehicles

  • Use of suspension system for seats of vehicles with stiff suspensions

  • Decrease operator's exposure time by job rotating


Control of vibration

Hand-arm vibration damping

  • Damping of tool internally

  • Insertion of damping between tool housing and hand

  • Remote operation of tool

  • Decreasing operator's exposure by job rotation


Vibration effects and limits

Health effects of whole body vibration, vibration dose

Sensitivity to vibration at different frequencies,

Fatigue - decreased proficiency and exposure limits, reduced comfort


Vibration effects and limits

Sources of vibration

Vibration in buildings,

Segmental vibration, hand arm vibration - neurological and vascular effects

Vibration from powered hand tools and other processes


Vibration effects and limits

8-hour energy equivalent weighted acceleration

Relationship between time to development of vascular symptoms and weighted vibration and exposure time


Vibration effects and limits

BSEN ISO 2631 4:2001

Fatigue - decreased proficiency and exposure limits, reduced comfort

BS 6472 1992

Vibration in buildings, 1-80 Hz


Vibration

  • oscillatory motion of a system


Vibration

  • oscillatory motion of a systemmotion - simple harmonic or otherwise system - gaseous, liquid, or solidair molecules vibrating 20 - 20,000 Hz is sound


Vibration


Vibration Parameters

  • Displacement

  • Frequency

  • Velocity

  • Acceleration


Displacement

x(t) = X sin (2 p t/T) = X sin w t

= X sin (2 p f t)

x = instantaneous displacement (m)

X = maximum displacement (m)

t = time (s),T = period of vibration (s)

f = frequency of vibration (Hz)

w = angular frequency (2 p f ) (radians/s)


Velocity

v = dx/dt = wX cos (wt) =

= V cos (wT) = V sin (w + p/2)

= V cos (2 pf t)

v = instantaneous velocity (m/s)

V = maximum velocity (m/s)


Acceleration

a = dv/dt = d²x/dt² = - w²S sin (wt)

= - A sin (wt + p)

= - A sin (2 pf t)

a = instantaneous acceleration (m/s2)

A = maximum acceleration (m/s2)


Acceleration, rms


Acceleration, rms


Crest factor


Phase Difference


Non-harmonic motion


Non-harmonic motion


Effects depend on:

  • frequency (Hz)

  • displacement (m)

  • acceleration(m/s2) - a measure of the intensity

  • resonance - depends upon the natural resonant frequency of either the source of vibration or of the object being vibrated (the human body segments or organs).


Vibration

Segmental or Hand-Arm Vibration

General or Whole Body Vibration


Segmental or Hand-Arm Vibration

Transmitted to hands

and arms from power

tools and other

vibrating equipment,

such as chain saws,

chipping tools, drills,

grinders, motor bikes.


General or Whole Body Vibration

Transmitted to the

sitting or standing body

through transmitting

surfaces such as in

aircraft, ships,

vehicles or working on

vibrating floors.


Segmental Vibration


Symptoms

  • finger blanching, particularly when exposed to the cold

  • tingling and loss of sensation in fingers

  • loss of light touch (difficulty fastening buttons and zippers)

  • pain and cold sensations between periodic white finger attack


Symptoms

  • loss of grip strength

  • bone cysts in fingers and wrists

  • carpal tunnel syndrome


Although segmental or local vibration almost always affects only upper limbs, legs can be affected if they come into contact with vibrating equipment.


Primary syndrome names

  • Raynaud's syndrome

  • Traumatic Vasospastic Disease

  • Vibration White Finger

  • Hand Arm Vibration Syndrome


Characteristics

  • sudden block in blood circulation to fingers

  • fingers become white, pale, cold, and sometimes painful

  • tactile sensitivity reduced

  • Symptoms last from minutes to hours, at first reversible


www.whitefinger.co.uk


Causes

  • vascular disturbance

    • (changes in blood vessel walls)

  • nervous disturbance

    • (reflex contraction of smooth muscles of blood vessels)

  • occurs naturally in ~ 1% of pop, 90% of which are female


Factors

  • Physical

  • Biodynamic

  • Individual


Physical Factors

  • Dominant frequencies & vibration direction

  • Years of employment & daily duration

  • Temporal exposure pattern

  • Non-occupational exposure


Biodynamic Factors

  • Grip forces

  • Surface area & mass of hand

  • Handle orientation & texture


Individual Factors

  • Susceptibility

  • Vasoconstrictive agents

    • (smoking, drugs)


Frequency dependence


Taylor-Pelmear Classification


Taylor-Pelmear Classification


Taylor-Pelmear Classification


Taylor-Pelmear Classification


Taylor-Pelmear Classification


Stockholm scale for vascular symptoms


Stockholm scale for vascular symptoms


Stockholm scale for sensorineuralstages


Control


Control Measures

  • Anti-vibration tools

  • Anti-vibration gloves

  • Safe work practices

  • Warm clothing, including gloves

  • Avoid holding the tool too tightly


Control Measures

  • Regular rest breaks

  • Rest the tool

  • Regular equipment maintenance

    • eg keeping cutting tools sharp

  • Reduce smoking


Whole Body Vibration


Whole Body Vibration

Vibration energy absorbed by body tissue and organs.


Whole Body Vibration

  • Spinal column disease

  • Digestive system problems

  • Cardiovascular effects

  • Motion sickness

  • Discomfort

  • Loss of balance and concentration

  • Fatigue


Whole Body Vibration

  • Energy absorbed by body tissue and organs muscles esp. important

  • Leads to

    voluntary/involuntary contraction causing fatigue esp. at resonant frequency


Whole Body Vibration

  • Reflex contractions reduce motor capabilities.increase risk of low back paineg- tractor, truck and bus drivers,

  • some studies have even shown radiographic changes


Whole Body Vibration

  • extremely strong vertical accelerations can cause spinal fractures (compression)


Resonance

  • 5-10 Hz range: thoracic-abdominal system

  • 20-30 Hz range: head-neck-shoulder system

  • 60-90 Hz range: eyeball


Very low-frequency 0.1 - 1 Hz

  • Cause motion sickness by upsetting the body's balance mechanism.

  • Motion sickness appears to be worst at about 0.3 Hz

  • If pitch and roll are present as well as vertical displacement, tolerance to the vibration is lowered


Low-frequency 1 - 80 Hz

  • Short term (acute effects):

    • fatigue, insomnia, headache and "shakiness"

  • Long term (chronic effects):

    • circulatory, bowel, respiratory, muscular and back disorders

    • Vibration, lifestyle, and posture contribute


Frequency dependence


Control


Control Measures

  • Move machine controls away from vibrating surfaces

  • Mechanically isolate the vibrating source

  • Maintain vibrating machinery

  • Reduce exposure time

    Much of these efforts will also reduce noise exposure


Assessment


Assessment

  • Vibration magnitude

  • Daily exposure time

  • Partial exposure

  • 8 hour exposure


Vibration Assessment

  • Manufacturer’s data

  • National Institute for Working Life

    • http://umetech.niwl.se/Vibration/

  • Measurements


Measurement


Vibration Pick-up

  • Measures

    • Displacement

    • Velocity

    • Acceleration

  • Accelerometer normally used

    • Parameters inter-related


Accelerometer

  • Electromechanical transducer

  • Piezoelectric

  • Piezioresistive


Accelerometer

  • Piezoelectric

    • Two piezoelectric discs produce a voltage on their surfaces due to a mechanical strain on asymmetric crystals

    • Robust and sensitive


Measurement

Frequency analyser

Level recorder

Pre-amplifier

Accelerometer


Measurement


Axis of Vibration


Accelerator Mounting

  • Good frequency response

  • Not affected by surface temperature

  • Contact surface must be flat

  • Difficult to use on hand tools


Accelerator Mounting

  • Good frequency response

  • Contact surface must be flat and clean


Accelerator Mounting

  • Rapid mounting

  • Suitable for triaxial measurements

  • Light

  • No sharp edges

  • Mainly limited to measurement on power tool handles


Accelerator Mounting

  • Can be used in cases where a fixed coupling is inapplicable, e.g. on soft or resilient materials

  • Only suitable for fixed hand position and where the handle is always being held


Accelerator Mounting

  • The presence of the adaptor may change tool operation and the vibration magnitude

  • Additional fixing (e.g. adhesive) is required for transverse measurements


Accelerometer placement


Accelerometer placement


Accelerometer placement


Accelerometer placement


Single tool, 8 hour TWA


Multiple tools


HAVS Exposure limits

HSE Action Level Recommendation:

2.8 m/s2 A(8)

Physical Agents Directive:

Exposure Action Value (EAV):

2.5 m/s2 A(8)

Exposure Limit Value (ELV):

5.0 m/s2 A(8)


HAVS Exposure limits

HSE Action Level Recommendation:

2.8 m/s2 A(8)

  • Based on magnitude of vibration in the dominant axis

  • Basing it on total value increases value by a factor of 1.4 on average to:

    4 m/s2 A(8)


Exposure equivalents


Exposure equivalents


Whole Body Exposure limits

Root Mean Square (RMS) or A8 method

Vibration Dose Value Method (VDV)


Root Mean Square (RMS) or A8 method

Uses units of metres per second squared normalised to 8 hours [m/s2A(8)] or A(8)

Produces a cumulative exposure using an average acceleration adjusted to represent an 8 hour working day


Vibration Dose Value Method (VDV)

Ues metres per second to the power of 1.75 and is known as Vibration Dose Value or VDV

Sensitive to individual high acceleration events and produces a cumulative dose over a (working) day.


Whole Body Exposure limits

Root Mean Square (RMS) or A8 method

  • EAV 0.5 m/s2, ELV 1.15 m/s2

    Vibration Dose Value Method (VDV)

  • EAV 9.1 m/s1.75 , ELV 21 m/s1.75


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