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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
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)

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.

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
slide39

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
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)
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 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 pain eg- 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
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

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
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

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
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)

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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