HL1115 Influences on Health at Work

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Vibration

• Sean Mahar, PhD, CIH, CSP, PE

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Vibration Introduction

• Types
• Problems
• Controls
• Measurements
• Standards

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Sean Mahar

• BS, Sacred Heart University
• MS, Texas AM University
• PhD, University of Iowa
• Certified Industrial Hygienist
• Certified Safety Professional
• Professional Engineer

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Experience

• U of Wolverhampton, 4 years
• Ohio University, 3 years
• Worksafe Iowa, 3 years
• US Navy, 9 years
• Tracor, 1 year

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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.

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Definitions and measurements units

• Units of measurement - understanding of
  acceleration amplitude
• Velocity amplitude displacement amplitude

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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

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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 transform analyser.

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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

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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

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Exposure limits for vibration

• ISO 26311997 Guide for the eval. of human
  exposure to whole body vibration.
• ISO 5349-12001 Guide to meas, and eval. of human
  exposure to vibration transmitted to the hand
• HSG 88 Hand -arm vibration

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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

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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

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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

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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

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Vibration effects and limits

• 8-hour energy equivalent weighted acceleration
• Relationship between time to development of
  vascular symptoms and weighted vibration and
  exposure time

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Vibration effects and limits

• BSEN ISO 2631 42001
• Fatigue - decreased proficiency and exposure
  limits, reduced comfort
• BS 6472 1992
• Vibration in buildings, 1-80 Hz

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Vibration

• oscillatory motion of a system

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Vibration

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

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Vibration
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Vibration Parameters

• Displacement
• Frequency
• Velocity
• Acceleration

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Displacement
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Velocity

• v dx/dt wX cos (wt)
• V cos (wT) V sin (w p/2)
• V cos (2 p f t)
• v instantaneous velocity (m/s)
• V maximum velocity (m/s)

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Acceleration

• a dv/dt d²x/dt² - w²S sin (wt)
• - A sin (wt p)
• - A sin (2 p f t)
• a instantaneous acceleration (m/s2)
• A maximum acceleration (m/s2)

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Acceleration, rms
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Acceleration, rms
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Crest factor
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Phase Difference
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Non-harmonic motion
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Non-harmonic motion
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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).

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Vibration
Segmental or Hand-Arm Vibration General or Whole
Body Vibration
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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.

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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.

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Segmental Vibration
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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

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Symptoms

• loss of grip strength
• bone cysts in fingers and wrists
• carpal tunnel syndrome

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

• Raynaud's syndrome
• Traumatic Vasospastic Disease
• Vibration White Finger
• Hand Arm Vibration Syndrome

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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

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www.whitefinger.co.uk
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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

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Factors

• Physical
• Biodynamic
• Individual

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Physical Factors

• Dominant frequencies vibration direction
• Years of employment daily duration
• Temporal exposure pattern
• Non-occupational exposure

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Biodynamic Factors

• Grip forces
• Surface area mass of hand
• Handle orientation texture

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Individual Factors

• Susceptibility
• Vasoconstrictive agents
• (smoking, drugs)

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Frequency dependence
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Taylor-Pelmear Classification
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Taylor-Pelmear Classification
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Taylor-Pelmear Classification
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Taylor-Pelmear Classification
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Taylor-Pelmear Classification
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Stockholm scale for vascular symptoms
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Stockholm scale for vascular symptoms
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Stockholm scale for sensorineural stages
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Control
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Control Measures

• Anti-vibration tools
• Anti-vibration gloves
• Safe work practices
• Warm clothing, including gloves
• Avoid holding the tool too tightly

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Control Measures

• Regular rest breaks
• Rest the tool
• Regular equipment maintenance
• eg keeping cutting tools sharp
• Reduce smoking

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Whole Body Vibration
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Whole Body Vibration

• Vibration energy absorbed by body tissue and
  organs.

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Whole Body Vibration

• Spinal column disease
• Digestive system problems
• Cardiovascular effects
• Motion sickness
• Discomfort
• Loss of balance and concentration
• Fatigue

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Whole Body Vibration

• Energy absorbed by body tissue and organs
  muscles esp. important
• Leads to
• voluntary/involuntary contraction causing
  fatigue esp. at resonant frequency

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Whole Body Vibration

• Reflex contractions reduce motor
  capabilities. increase risk of low back
  pain eg- tractor, truck and bus drivers,
• some studies have even shown radiographic changes

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Whole Body Vibration

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

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Resonance

• 5-10 Hz range thoracic-abdominal system
• 20-30 Hz range head-neck-shoulder system
• 60-90 Hz range eyeball

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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

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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

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Frequency dependence
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Control
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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

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Assessment
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Assessment

• Vibration magnitude
• Daily exposure time
• Partial exposure
• 8 hour exposure

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Vibration Assessment

• Manufacturers data
• National Institute for Working Life
• http//umetech.niwl.se/Vibration/
• Measurements

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Measurement
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Vibration Pick-up

• Measures
• Displacement
• Velocity
• Acceleration
• Accelerometer normally used
• Parameters inter-related

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Accelerometer

• Electromechanical transducer
• Piezoelectric
• Piezioresistive

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Accelerometer

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

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Measurement
Frequency analyser
Level recorder
Pre-amplifier
Accelerometer
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Measurement
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Axis of Vibration
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Accelerator Mounting

• Good frequency response
• Not affected by surface temperature
• Contact surface must be flat
• Difficult to use on hand tools

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Accelerator Mounting

• Good frequency response
• Contact surface must be flat and clean

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Accelerator Mounting

• Rapid mounting
• Suitable for triaxial measurements
• Light
• No sharp edges
• Mainly limited to measurement on power tool
  handles

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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

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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

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Accelerometer placement
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Accelerometer placement
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Accelerometer placement
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Accelerometer placement
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Single tool, 8 hour TWA
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Multiple tools
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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)

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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)

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Exposure equivalents
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Exposure equivalents
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Whole Body Exposure limits

• Root Mean Square (RMS) or A8 method
• Vibration Dose Value Method (VDV)

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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

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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.

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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