Vibration

Vibration

Sean Mahar, PhD, CIH, CSP, PESean Mahar, PhD, CIH, CSP, PE

Vibration Vibration IntroductionIntroduction

• TypesTypes

• ProblemsProblems

• ControlsControls

• MeasurementsMeasurements

• StandardsStandards

Sean MaharSean Mahar

• BS, Sacred Heart UniversityBS, Sacred Heart University

• MS, Texas A&M UniversityMS, Texas A&M University

• PhD, University of IowaPhD, University of Iowa

• Certified Industrial HygienistCertified Industrial Hygienist

• Certified Safety ProfessionalCertified Safety Professional

• Professional EngineerProfessional Engineer

ExperienceExperience

• U of Wolverhampton, 4 yearsU of Wolverhampton, 4 years

• Ohio University, 3 yearsOhio University, 3 years

• Worksafe Iowa, 3 yearsWorksafe Iowa, 3 years

• US Navy, 9 yearsUS Navy, 9 years

• Tracor, 1 yearTracor, 1 year

Educational ObjectiveEducational Objective

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

Definitions and measurements unitsDefinitions and measurements units

Units of measurement - understanding of Units of measurement - understanding of acceleration amplitudeacceleration amplitude

Velocity amplitude displacement Velocity amplitude displacement amplitude amplitude

Definitions and measurements unitsDefinitions and measurements units

Choice of measurement parameters, Choice of measurement parameters, dynamic range and frequency dynamic range and frequency information requiredinformation required

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

Monitoring instrumentsMonitoring instruments

Vibration transducersVibration transducersPiezoelectric accelerometer. Also aware of Piezoelectric accelerometer. Also aware of

existence of proximity probes and velocity pick-existence of proximity probes and velocity pick-up.up.

MetersMetersElements of a general purpose vibration Elements of a general purpose vibration

meter.Also awareness of swept filter frequency meter.Also awareness of swept filter frequency analyser and fast Fourier transformanalyser and fast Fourier transform analyser.analyser.

Making a surveyMaking a survey

ISO Evaluation of human exposure to ISO Evaluation of human exposure to whole body vibrationwhole body vibration::

• Equivalent acceleration valueEquivalent acceleration value• Frequencies of the vibrationFrequencies of the vibration• Direction of excitement of the vibrationDirection of excitement of the vibration• Time of exposure to vibrationTime of exposure to vibration

Making a surveyMaking a survey

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

• Frequency weighted RMS acceleration Frequency weighted RMS acceleration valuevalue

• Probability of developing white finger Probability of developing white finger syndromesyndrome

Exposure limits for vibrationExposure limits for vibration

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

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

• HSG 88HSG 88 Hand -arm vibrationHand -arm vibration

Control of vibrationControl of vibration

Whole-body vibration dampingWhole-body vibration damping

• Use of suspension system for vehiclesUse of suspension system for vehicles• Use of suspension system for seats of Use of suspension system for seats of

vehicles with stiff suspensionsvehicles with stiff suspensions• Decrease operator's exposure time by Decrease operator's exposure time by

job rotatingjob rotating

Control of vibrationControl of vibration

Hand-arm vibration dampingHand-arm vibration damping

• Damping of tool internallyDamping of tool internally• Insertion of damping between tool Insertion of damping between tool

housing and handhousing and hand• Remote operation of toolRemote operation of tool• Decreasing operator's exposure by job Decreasing operator's exposure by job

rotationrotation

Vibration effects and limitsVibration effects and limits

Health effects of whole body vibration, Health effects of whole body vibration, vibration dosevibration dose

Sensitivity to vibration at different Sensitivity to vibration at different frequencies,frequencies,

Fatigue - decreased proficiency and Fatigue - decreased proficiency and exposure limits, reduced comfort exposure limits, reduced comfort


Sources of vibrationSources of vibration

Vibration in buildings, Vibration in buildings,

Segmental vibration, hand arm vibration Segmental vibration, hand arm vibration - neurological and vascular effects- neurological and vascular effects

Vibration from powered hand tools and Vibration from powered hand tools and other processesother processes


8-hour energy equivalent weighted 8-hour energy equivalent weighted acceleration acceleration

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


BSEN ISO 2631 4:2001 BSEN ISO 2631 4:2001

Fatigue - decreased proficiency and Fatigue - decreased proficiency and exposure limits, reduced comfort exposure limits, reduced comfort

BS 6472 1992BS 6472 1992

Vibration in buildings, 1-80 HzVibration in buildings, 1-80 Hz

VibrationVibration

• oscillatory oscillatory motionmotion of a of a systemsystem

VibrationVibration

• oscillatory oscillatory motionmotion of a of a systemsystem

motionmotion - simple harmonic or otherwise - simple harmonic or otherwise systemsystem - gaseous, liquid, or solid - gaseous, liquid, or solid

air molecules vibrating 20 - 20,000 Hz air molecules vibrating 20 - 20,000 Hz is soundis sound

VibrationVibration

Vibration Parameters

• DisplacementDisplacement

• FrequencyFrequency

• VelocityVelocity

• AccelerationAcceleration

DisplacementDisplacement

x(t)x(t) = = XX sin (2 sin (2 t/T) t/T) = X= X sin sin t t

= = XX sin (2 sin (2 f t) f t)

xx = instantaneous displacement = instantaneous displacement (m) (m)

XX = maximum displacement = maximum displacement (m) (m)

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

f = frequency of vibrationf = frequency of vibration (Hz) (Hz)

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

VelocityVelocity

v = dx/dt = v = dx/dt = X cos (X cos (t) =t) =

= V cos (= V cos (T) = V sin (T) = V sin ( + + /2)/2)

= V cos (2 = V cos (2 f t)f t)

v = instantaneous velocityv = instantaneous velocity (m/s) (m/s)

V = maximum velocityV = maximum velocity (m/s) (m/s)

AccelerationAcceleration

a = dv/dt = d²x/dt² = - a = dv/dt = d²x/dt² = - ²S sin (²S sin (t) t)

= - A sin (= - A sin (t + t + ) )

= - A sin (2 = - A sin (2 f t)f t)

a = instantaneous acceleration (m/sa = instantaneous acceleration (m/s22))

A = maximum acceleration (m/sA = maximum acceleration (m/s22))

Acceleration, rmsAcceleration, rms

)(1

= T

0)( dtta

Ta

2rms

Acceleration, rmsAcceleration, rms

2)(

2)(

2)()xyz( = rmszrmsyrmsxrms aaaa

Crest factorCrest factor

rms

peak =factor crest

Phase DifferencePhase Difference

Non-harmonic motionNon-harmonic motion

Non-harmonic motionNon-harmonic motion

Effects depend on:Effects depend on:

• frequency (Hz)frequency (Hz)• displacement (m)displacement (m)• accelerationacceleration (m/s(m/s22)) - a measure of the - a measure of the

intensityintensity• resonanceresonance - depends upon the natural - depends upon the natural

resonant frequency of either the source of resonant frequency of either the source of vibration or of the object being vibrated (the vibration or of the object being vibrated (the human body segments or organs).human body segments or organs).

VibrationVibration

Segmental or Hand-Arm VibrationSegmental or Hand-Arm Vibration

General or Whole Body VibrationGeneral or Whole Body Vibration

Segmental or Hand-Arm VibrationSegmental or Hand-Arm Vibration

Transmitted to handsTransmitted to hands

and arms from powerand arms from power

tools and other tools and other

vibrating equipment, vibrating equipment,

such as chain saws, such as chain saws,

chipping tools, drills, chipping tools, drills,

grinders, motor bikes.grinders, motor bikes.

General or Whole Body VibrationGeneral or Whole Body Vibration

Transmitted to theTransmitted to the

sitting or standing bodysitting or standing body

through transmittingthrough transmitting

surfaces such as insurfaces such as in

aircraft, ships,aircraft, ships,

vehicles or working onvehicles or working on

vibrating floors.vibrating floors.

Segmental VibrationSegmental Vibration

SymptomsSymptoms

• finger blanching, particularly when finger blanching, particularly when exposed to the coldexposed to the cold

• tingling and loss of sensation in fingerstingling and loss of sensation in fingers

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

• pain and cold sensations between pain and cold sensations between periodic white finger attackperiodic white finger attack

SymptomsSymptoms

• loss of grip strengthloss of grip strength

• bone cysts in fingers and wristsbone cysts in fingers and wrists

• carpal tunnel syndromecarpal tunnel syndrome

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

Primary syndrome namesPrimary syndrome names

• Raynaud's syndromeRaynaud's syndrome

• Traumatic Vasospastic DiseaseTraumatic Vasospastic Disease

• Vibration White FingerVibration White Finger

• Hand Arm Vibration SyndromeHand Arm Vibration Syndrome

CharacteristicsCharacteristics

• sudden block in blood circulation to sudden block in blood circulation to fingersfingers

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

• tactile sensitivity reducedtactile sensitivity reduced

• Symptoms last from minutes to Symptoms last from minutes to hours, at first reversiblehours, at first reversible

www.whitefinger.co.ukwww.whitefinger.co.uk

CausesCauses

• vascular disturbance vascular disturbance

– (changes in blood vessel walls) (changes in blood vessel walls)

• nervous disturbance nervous disturbance

– (reflex contraction of smooth muscles (reflex contraction of smooth muscles of blood vessels) of blood vessels)

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

FactorsFactors

• PhysicalPhysical

• BiodynamicBiodynamic

• IndividualIndividual

Physical FactorsPhysical Factors

• Dominant frequencies & vibration Dominant frequencies & vibration directiondirection

• Years of employment & daily durationYears of employment & daily duration

• Temporal exposure patternTemporal exposure pattern

• Non-occupational exposureNon-occupational exposure

Biodynamic FactorsBiodynamic Factors

• Grip forcesGrip forces

• Surface area & mass of handSurface area & mass of hand

• Handle orientation & textureHandle orientation & texture

Individual FactorsIndividual Factors

• SusceptibilitySusceptibility

• Vasoconstrictive agents Vasoconstrictive agents – (smoking, drugs) (smoking, drugs)

Frequency Weighting Curve

0.01

0.10

1.00

1.0 10.0 100.0 1000.0

Frequency, HZ

We

igh

tin

g F

ac

tor

Frequency dependenceFrequency dependence

Taylor-Pelmear Taylor-Pelmear CClassificatiolassificationn

StageStage Signs andSigns and

symptomssymptoms

InterferenceInterference

wwith activitiesith activities00 NoneNone NoneNone

0T0T Intermittent Intermittent tinglingtingling

NoneNone

0N0N Intermittent Intermittent numbnessnumbness

NoneNone

0TN0TN Tingling and Tingling and numbnessnumbness

NoneNone



symptomssymptoms


wwith activitiesith activities11 Blanching of one Blanching of one

or more fingertips or more fingertips wwith or without ith or without tingling and tingling and numbnessnumbness

NoneNone



symptomssymptoms


wwith activitiesith activities22 Blanching of one Blanching of one

or more fingers or more fingers with numbness, with numbness, usually during usually during winter onlywinter only

Slight interference with Slight interference with home and social home and social activities; no activities; no interference with workinterference with work



symptomssymptoms


wwith activitiesith activities33 Extensive Extensive

blanching with blanching with frequent episodes frequent episodes during both during both summer and summer and winterwinter

Definite interference Definite interference with work, home, and with work, home, and social activities;social activities;restricted hobbiesrestricted hobbies



symptomssymptoms


wwith activitiesith activities44 Extensive Extensive

blanching of most blanching of most fingers; frequent fingers; frequent episodes during episodes during summer and summer and winter; finger winter; finger ulcerationulceration

Occupation change Occupation change required to avoid required to avoid further vibration further vibration exposureexposure

Stockholm scale for vascular symptoms

StageStage DescriptionDescription

00 NNo attackso attacks

11 Occasional attacks that affect only the Occasional attacks that affect only the tips of one or more fingerstips of one or more fingers

22 Occasional attacks that affect the distal Occasional attacks that affect the distal and middle (rarely also proximal) and middle (rarely also proximal) phalanges of one or more fingersphalanges of one or more fingers

Stockholm scale for vascular symptoms


33 Frequent attacks affecting all phalanges Frequent attacks affecting all phalanges of most fingersof most fingers

44 As in stage 3, with trophic skin changes As in stage 3, with trophic skin changes in the finger tipsin the finger tips

Stockholm scale for sensorineural stages


0SN0SN Exposed to vibration but no symptomsExposed to vibration but no symptoms

1SN1SN Intermittent numbness, with or without Intermittent numbness, with or without tinglingtingling

2SN2SN Intermittent or persistent numbness, Intermittent or persistent numbness, reduced sensory perceptionreduced sensory perception

3SN3SN Intermittent or persistent numbness, Intermittent or persistent numbness, reduced tactile discrimination and/or reduced tactile discrimination and/or manipulative dexteritymanipulative dexterity

ControlControl

Control MeasuresControl Measures

• Anti-vibration tools Anti-vibration tools

• Anti-vibration glovesAnti-vibration gloves

• Safe work practicesSafe work practices

• Warm clothing, including glovesWarm clothing, including gloves

• Avoid holding the tool too tightly Avoid holding the tool too tightly


• Regular rest breaksRegular rest breaks

• Rest the toolRest the tool

• Regular equipment maintenanceRegular equipment maintenance

– eg keeping cutting tools sharpeg keeping cutting tools sharp

• Reduce smokingReduce smoking

Whole Body VibrationWhole Body Vibration


Vibration energy Vibration energy absorbed by absorbed by body tissue and body tissue and organs.organs.


• Spinal column diseaseSpinal column disease• Digestive system problemsDigestive system problems• Cardiovascular effectsCardiovascular effects• Motion sicknessMotion sickness• DiscomfortDiscomfort• Loss of balance and concentrationLoss of balance and concentration• FatigueFatigue


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

• Leads to Leads to

voluntary/involuntary voluntary/involuntary contraction contraction causing fatiguecausing fatigue

esp. at resonant frequency esp. at resonant frequency


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

• some studies have even shown some studies have even shown radiographic changesradiographic changes


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

ResonanceResonance

• 5-10 Hz range: 5-10 Hz range: thoracic-abdominal systemthoracic-abdominal system

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

• 60-90 Hz range: 60-90 Hz range: eyeballeyeball

Very low-frequency 0.1 - 1 HzVery low-frequency 0.1 - 1 Hz

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

• Motion sickness appears to be worst at Motion sickness appears to be worst at about 0.3 Hzabout 0.3 Hz

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

Low-frequency 1 - 80 HzLow-frequency 1 - 80 Hz

• Short term (acute effects):Short term (acute effects):

– fatigue, insomnia, headache and fatigue, insomnia, headache and "shakiness""shakiness"

• Long term (chronic effects):Long term (chronic effects):

– circulatory, bowel, respiratory, muscular circulatory, bowel, respiratory, muscular and back disordersand back disorders

– Vibration, lifestyle, and posture Vibration, lifestyle, and posture contributecontribute

Frequency Weighting Curve

-55.0

-45.0

-35.0

-25.0

-15.0

-5.0

5.0

0.1 1.0 10.0 100.0 1000.0

Frequency, Hz

We

ight

ing

, dB

Frequency dependenceFrequency dependence

ControlControl


• Move machine controls away from vibrating Move machine controls away from vibrating surfacessurfaces

• Mechanically isolate the vibrating sourceMechanically isolate the vibrating source

• Maintain vibrating machineryMaintain vibrating machinery

• Reduce exposure timeReduce exposure time

Much of these efforts will also reduce noise Much of these efforts will also reduce noise exposure exposure

AssessmentAssessment

AssessmentAssessment

• Vibration magnitudeVibration magnitude

• Daily exposure timeDaily exposure time

• Partial exposurePartial exposure

• 8 hour exposure8 hour exposure

Vibration AssessmentVibration Assessment

• Manufacturer’s dataManufacturer’s data

• National Institute for Working LifeNational Institute for Working Life– http://umetech.niwl.se/Vibration/http://umetech.niwl.se/Vibration/

• MeasurementsMeasurements

MeasurementMeasurement

Vibration Pick-upVibration Pick-up

• MeasuresMeasures– DisplacementDisplacement– VelocityVelocity– AccelerationAcceleration

• Accelerometer normally usedAccelerometer normally used– Parameters inter-relatedParameters inter-related

AccelerometerAccelerometer

• Electromechanical transducerElectromechanical transducer

• PiezoelectricPiezoelectric

• PiezioresistivePiezioresistive


• PiezoelectricPiezoelectric– Two piezoelectric discs produce a Two piezoelectric discs produce a

voltage on their surfaces due to a voltage on their surfaces due to a mechanical strain on asymmetric mechanical strain on asymmetric crystalscrystals

– Robust and sensitiveRobust and sensitive



Frequency analyserFrequency analyser

Pre-amplifierPre-amplifier Level recorderLevel recorder


Axis of VibrationAxis of Vibration

Accelerator MountingAccelerator Mounting

• Good frequency Good frequency responseresponse

• Not affected by Not affected by surface surface temperaturetemperature

• Contact surface Contact surface must be flatmust be flat

• Difficult to use on Difficult to use on hand toolshand tools


• Good frequency Good frequency response response

• Contact surface Contact surface must be flat and must be flat and cleanclean


• Rapid mountingRapid mounting

• Suitable for triaxial Suitable for triaxial measurementsmeasurements

• LightLight

• No sharp edgesNo sharp edges

• Mainly limited to Mainly limited to measurement on measurement on power tool handlespower tool handles


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

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


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

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

Accelerometer placementAccelerometer placement




Single tool, 8 hour TWASingle tool, 8 hour TWA

88 usedta)A(

Multiple toolsMultiple tools

222

21 8...888 )(A)(A)(A)A( i

HAVS Exposure limitsHAVS Exposure limits

HSE Action Level Recommendation:HSE Action Level Recommendation:

2.8 m/s2.8 m/s22 A(8) A(8)

Physical Agents Directive:Physical Agents Directive:

Exposure Action Value (EAV):Exposure Action Value (EAV):

2.5 m/s2.5 m/s22 A(8) A(8)

Exposure Limit Value (ELV):Exposure Limit Value (ELV):

5.0 m/s5.0 m/s22 A(8) A(8)

HAVS Exposure limitsHAVS Exposure limits

HSE Action Level Recommendation:HSE Action Level Recommendation:

2.8 m/s2.8 m/s22 A(8) A(8)

• Based on magnitude of vibration in the Based on magnitude of vibration in the dominant axisdominant axis

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

4 m/s4 m/s22 A(8) A(8)

Exposure equivalentsExposure equivalents

Total exposure Total exposure duration (hours)duration (hours)

1616 88 44 22 11 ½½

Average (rms) Average (rms) vibration vibration magnitude (m/smagnitude (m/s22) ) to give to give daily exposure of daily exposure of 2.5 (m/s2.5 (m/s22) A(8)) A(8)

1.81.8 2.52.5 3.53.5 55 77 1010

Exposure equivalentsExposure equivalents

Total exposure Total exposure duration (hours)duration (hours)

1616 88 44 22 11 ½½

Average (rms) Average (rms) vibration vibration magnitude (m/smagnitude (m/s22) ) to give to give daily exposure of daily exposure of 5.0 (m/s5.0 (m/s22) A(8)) A(8)

3.53.5 5.05.0 77 1010 1414 2020

Whole Body Exposure limitsWhole Body Exposure limits

Root Mean Square (RMS) or A8 methodRoot Mean Square (RMS) or A8 method

Vibration Dose Value Method (VDV)Vibration Dose Value Method (VDV)

Root Mean Square (RMS) or A8 Root Mean Square (RMS) or A8 methodmethod

Uses units of metres per second squared Uses units of metres per second squared normalised to 8 hours [m/snormalised to 8 hours [m/s22A(8)] A(8)] or A(8) or A(8)

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

Vibration Dose Value Method Vibration Dose Value Method (VDV)(VDV)

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

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

Whole Body Exposure limitsWhole Body Exposure limits

Root Mean Square (RMS) or A8 methodRoot Mean Square (RMS) or A8 method• EAV 0.5 m/sEAV 0.5 m/s22, ELV 1.15 m/s, ELV 1.15 m/s22

Vibration Dose Value Method (VDV)Vibration Dose Value Method (VDV)• EAV 9.1 m/sEAV 9.1 m/s1.751.75 , ELV 21 m/s , ELV 21 m/s1.751.75

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