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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

Vibration

Sean Mahar, PhD, CIH, CSP, PE


Vibration introduction

Vibration Introduction

  • Types

  • Problems

  • Controls

  • Measurements

  • Standards


Sean mahar

Sean Mahar

  • BS, Sacred Heart University

  • MS, Texas A&M University

  • PhD, University of Iowa

  • Certified Industrial Hygienist

  • Certified Safety Professional

  • Professional Engineer


Experience

Experience

  • U of Wolverhampton, 4 years

  • Ohio University, 3 years

  • Worksafe Iowa, 3 years

  • US Navy, 9 years

  • Tracor, 1 year


Educational objective

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

Definitions and measurements units

Units of measurement - understanding of acceleration amplitude

Velocity amplitude displacement amplitude


Definitions and measurements units1

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

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

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 survey1

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

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

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 vibration1

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

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 limits1

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 limits2

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 limits3

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


Vibration1

Vibration

  • oscillatory motion of a system


Vibration2

Vibration

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


Vibration3

Vibration


Vibration parameters

Vibration Parameters

  • Displacement

  • Frequency

  • Velocity

  • Acceleration


Displacement

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

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

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


Acceleration rms1

Acceleration, rms


Crest factor

Crest factor


Phase difference

Phase Difference


Non harmonic motion

Non-harmonic motion


Non harmonic motion1

Non-harmonic motion


Effects depend on

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).


Vibration4

Vibration

Segmental or Hand-Arm Vibration

General or Whole Body Vibration


Segmental or hand arm 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

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

Segmental Vibration


Symptoms

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


Symptoms1

Symptoms

  • loss of grip strength

  • bone cysts in fingers and wrists

  • carpal tunnel syndrome


Vibration

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

Primary syndrome names

  • Raynaud's syndrome

  • Traumatic Vasospastic Disease

  • Vibration White Finger

  • Hand Arm Vibration Syndrome


Characteristics

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


Vibration

www.whitefinger.co.uk


Causes

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

Factors

  • Physical

  • Biodynamic

  • Individual


Physical factors

Physical Factors

  • Dominant frequencies & vibration direction

  • Years of employment & daily duration

  • Temporal exposure pattern

  • Non-occupational exposure


Biodynamic factors

Biodynamic Factors

  • Grip forces

  • Surface area & mass of hand

  • Handle orientation & texture


Individual factors

Individual Factors

  • Susceptibility

  • Vasoconstrictive agents

    • (smoking, drugs)


Vibration

Frequency dependence


Taylor pelmear c lassificatio n

Taylor-Pelmear Classification


Taylor pelmear c lassificatio n1

Taylor-Pelmear Classification


Taylor pelmear c lassificatio n2

Taylor-Pelmear Classification


Taylor pelmear c lassificatio n3

Taylor-Pelmear Classification


Taylor pelmear c lassificatio n4

Taylor-Pelmear Classification


Stockholm scale for vascular symptoms

Stockholm scale for vascular symptoms


Stockholm scale for vascular symptoms1

Stockholm scale for vascular symptoms


Stockholm scale for sensorineural s tages

Stockholm scale for sensorineuralstages


Control

Control


Control measures

Control Measures

  • Anti-vibration tools

  • Anti-vibration gloves

  • Safe work practices

  • Warm clothing, including gloves

  • Avoid holding the tool too tightly


Control measures1

Control Measures

  • Regular rest breaks

  • Rest the tool

  • Regular equipment maintenance

    • eg keeping cutting tools sharp

  • Reduce smoking


Whole body vibration

Whole Body Vibration


Whole body vibration1

Whole Body Vibration

Vibration energy absorbed by body tissue and organs.


Whole body vibration2

Whole Body Vibration

  • Spinal column disease

  • Digestive system problems

  • Cardiovascular effects

  • Motion sickness

  • Discomfort

  • Loss of balance and concentration

  • Fatigue


Whole body vibration3

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 vibration4

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 vibration5

Whole Body Vibration

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


Resonance

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

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

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


Vibration

Frequency dependence


Control1

Control


Control measures2

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


Assessment1

Assessment

  • Vibration magnitude

  • Daily exposure time

  • Partial exposure

  • 8 hour exposure


Vibration assessment

Vibration Assessment

  • Manufacturer’s data

  • National Institute for Working Life

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

  • Measurements


Measurement

Measurement


Vibration pick up

Vibration Pick-up

  • Measures

    • Displacement

    • Velocity

    • Acceleration

  • Accelerometer normally used

    • Parameters inter-related


Accelerometer

Accelerometer

  • Electromechanical transducer

  • Piezoelectric

  • Piezioresistive


Accelerometer1

Accelerometer

  • Piezoelectric

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

    • Robust and sensitive


Measurement1

Measurement

Frequency analyser

Level recorder

Pre-amplifier

Accelerometer


Measurement2

Measurement


Axis of vibration

Axis of Vibration


Accelerator mounting

Accelerator Mounting

  • Good frequency response

  • Not affected by surface temperature

  • Contact surface must be flat

  • Difficult to use on hand tools


Accelerator mounting1

Accelerator Mounting

  • Good frequency response

  • Contact surface must be flat and clean


Accelerator mounting2

Accelerator Mounting

  • Rapid mounting

  • Suitable for triaxial measurements

  • Light

  • No sharp edges

  • Mainly limited to measurement on power tool handles


Accelerator mounting3

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 mounting4

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 placement1

Accelerometer placement


Accelerometer placement2

Accelerometer placement


Accelerometer placement3

Accelerometer placement


Single tool 8 hour twa

Single tool, 8 hour TWA


Multiple tools

Multiple tools


Havs exposure limits

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 limits1

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


Exposure equivalents1

Exposure equivalents


Whole body exposure limits

Whole Body Exposure limits

Root Mean Square (RMS) or A8 method

Vibration Dose Value Method (VDV)


Root mean square rms or a8 method

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

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 limits1

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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