Noise, Vibration and Hearing Conservation

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Noise, Vibration and Hearing Conservation

• 2001 Annual Western Pulp and Paper Worker Safety
  and Health Conference, Portland OR
• Sue Swan, MS
• Rick Neitzel, MS
• University of Washington
• Department of Environmental Health

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Vibration Overview Scientific

• Im no physics instructor, so I apologize for
  these crude explanations
• Vibration description of object motion
• Vibration is a vector quantity
• Motion described by magnitude intensity
  (acceleration, velocity, or displacement) AND
• Motion described by direction

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Vibration - Acceleration

• Measures how fast speed changes over time
• Units meters per second, per second, or m/s2
• Difference between acceleration and velocity
• Velocity constant (m/s)
• Acceleration change in velocity (m/s2)
• Acceleration goes from 0 to a maximum in each
  vibration cycle
• Acceleration increases as object moves from
  stationary position slows stops reverses

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Vibration - Frequency

• Complete cycle of vibration
• From one extreme position to other, back
• Frequency
• Number of cycles completed in one second
• Units hertz (Hz)
• 1 Hz equals one cycle per second
• 1 kilohertz (kHZ) 1000 cycles/second
• Notes on piano different frequency
• Low freq low note, high freq high note

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Vibration - Frequency
Higher Frequency
Lower Frequency
Single Frequency
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Vibration - Amplitude

• Vibrating object moves to certain maximum
  distance on either side of stationary position
• Amplitude
• Distance from stationary position to either
  extreme position
• Measured in meters (m)
• Intensity of vibration depends on amplitude
• Strength you hit notes on piano with determines
  the amplitude

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Vibration Overview Understandable
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Vibration Example
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Factors that Affect Vibration
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Types of vibration exposure

• Whole Body (WBV) (head-to-toe)
• Heavy equipment run by a seated or standing
  operator
• Truck, earthmoving equipment, forklift, crane
• Hand Arm (HAV) (segmental)
• Vibrating pneumatic, electrical, hydraulic,
  gasoline powered hand tools
• Chipping tools, grinders, chainsaws, drills

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Vibration - Resonance

• Every object vibrates at specific frequency
• Factors comp, size, structure, weight, shape
• Natural vibration freq resonant frequency
• Seems unusual, but in all physical structures
• Example bridges
• Soldiers never march in synch across bridge
• Bridge could absorb vibration excitation from
  marching, then internally amplify vibration
• Bridge can sway, eventually collapse

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Vibration - Resonance
If resonance from marching seems like too
abstract a concept...
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Human Resonance Consequences

• Human WBV resonance vertical, 4-8 Hz
• What's the concern? Depends on two IFs...
• IF exposure includes 4-8 Hz frequencies AND
• IF exposure reaches operator's spine via seat
• THEN body will amplify effects of exposure
• Body selects, accepts, amplifies certain
  frequencies
• May affect major part of body, or certain organs
• In doing so can worsen vibration effects

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Human resonance
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Hand Arm Vibration Syndrome

• Discovered, described in US 80 yrs ago
• Alice Hamilton, pioneering occupational physician
  
• Early investigation of hand-arm problems
  associated with pneumatic hand tool use
• Stone quarrying, cutting, carving workers

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HAVS - Major Symptoms

• Initially characterized by
• Tingling and/or numbness in fingers (not CTS)
• With continuing exposure
• Appearance of single "white" (blanched) fingertip
  
• Usually, but not always, in cold
• White finger start of irreversible process
• Often mistaken for frostbite
• Initial attacks last 5-15 minutes, widely spaced

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HAVS

• With additional exposure (especially in cold)
• Attacks ? number, intensity, duration, pain
• Later stages all seasons, on/off job
• Combination of vibration, cold, nicotine bad
• All vasoconstrictors, close down blood vessels
• Extreme conditions loss of blood to fingers can
  lead to gangrene, amputation
• Months, years before HAVS symptoms noticed

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Potential Effects of HAV
Bone cysts
Tingling
Cold sensation
Worse over time
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HA Vibration Syndrome (HAVS)
Vibration White Finger/Raynauds Phenomenon
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Consequences of WBV Exposure

• Effects of WBV poorly understood
• Heavy vehicle operator studies problems in
• Bowel
• Circulatory/resp (heart rate, resp rate, O2
  uptake)
• Musculoskeletal and back
• Genitourinary
• Neurological (decreased performance)
• Fatigue, insomnia, headache, shakiness"
• Possible contrib posture/postural fatigue, diet
• Motion sickness if 0.1-0.6 Hz

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WBV research (not at UW, though)
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Vibration factors influencing health

• Threshold value
• Amount of vibration exposure that results in no
  adverse health effects
• Dose-response relationship
• How severity of ill health effects relates to
  amount of exposure
• Latent period
• Time from first exposure to appearance of
  symptoms

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How do we measure vibration?

• Most agencies use acceleration to measure
  vibration exposure because
• Several types of instruments measure acceleration
• Measuring acceleration gives information about
  velocity and amplitude
• Degree of harm related to magnitude of
  acceleration

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Vibration Measurement

• Typical measurement system includes
• Device to sense vibration (accelerometer)
• Possibly a tape recorder
• Freq analyzer/freq-weighting network
• Display (meter, printer or recorder)
• Memory for storing measurements

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Vibration Instrumentation

• Accelerometer makes electrical signal
• Signal size proportional to acceleration
• Frequency analyzer determines acceleration in
  frequency bands
• Some sound level meters measure vibration

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Vibration Weighting

• Freq-weighting mimics human sensitivity
• One number for vib exposure
• Freq-weighted level in m/s2

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HAV Axes
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WBV Axes
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Measurement of HAV

• 1-3 miniatureaccelerometers
• Small mount to hold accelerometers
• Cable to carry signal to vibration meter

Range 6.3-1500 Hz
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Measurement of WBV

• 3 miniature accelerometers
• Flat rubber mat to mount accelerometers
• Cable to carry signalto vibration meter

Range 0.5-80 Hz
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HAV Exposure Standards

• Am Conf of Gov Ind Hygienists (ACGIH) -Threshold
  Limit Value (TLV) for HAV

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HAV Exposure Standards

• International Organization for Standardization

ISO 5349 - 1986
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HAV Exposure Standards

• WA Ergonomics Rule -
• High HAV (gt10 m/s2 for 8 hrs)
• Impact wrench, chainsaw, percussion tool gt30
  min/day
• Grinder, sander, jig saw, other hand tool gt2
  hr/day
• Moderate HAV (2.5-10 m/s2 8 hrs)
• Grinder, sander, jig saw lt 2 hrs/day
• Tools lt 2.5 m/s2 for 8 hrs not covered
• Based on ANSI S3.34- 1986

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HAV Exposure Standards
WISHA
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WBV Exposure Standards

• ACGIH TLV for WBV (yuck!)

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WBV Exposure Standards

• Commission of the European CommunitiesFramework
  Directive COM-92-560

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Interpretation of ISO WBV std

• Reduced-comfort boundary for traveling in planes,
  boats, trains
• Exceeding limits reading, eating, writing
  difficult
• Fatigue-decreased proficiency boundary for
  effects that impair performance
• Fatigue affects flying, driving, operating heavy
  vehicles
• Exposure limit used to assess maximum possible
  WBV exposure allowed

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ISO WBV exposure standard
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UW Vibration Research Goals

• Characterize noise, vibration exposure (in
  forestry industry) by
• Task, tool, trade, operation
• No existing heavy equip WBV or HAV levels
• Measure noise and vibration level correlation
• Possible to use noise as HAV substitute? SO much
  easier to measure
• Identify areas forcontrol strategies

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UW Exposure Focus

• Whole-body vibration (WBV)
• Heavy equip seats
• Earthmoving/logging equipment, trucks
• Hand-arm vibration (HAV)
• Heavy equip controls, saws, axes
• Noise exposure

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Summary HAV Levels by Equipment
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WBV Exceedances by Operation
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Exceedances by Vibration Type
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Noise/Vibration Correlation
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Health Effects/Recommendations

• High overexposures by ACGIH, CEC
• HAV vascular sympt in 10-6 yr, 50-14 yr
• WBV health effects likely after yrs exposure
• No signif assoc between noise, HAV/WBV
• Cant use noise as vibration substitute
• All vehicles gtCEC WBV AL (0.5 m/s2)
• Detailed info on equipment makesimplementation
  of controls easier

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Thats great, but what should I DO?

• Inventory vibration sources in mill
• Assign exposure values to each
• Make measurements (via consultant)
• Examine existing databases
• Assume that certain tool types high exposure
• Take steps to prevent vibration-related health
  problems
• Implement controls where necessary

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Vibration Controls

• Vibration frequency, magnitude determine
  difficulty of implementing controls

Harder - Low freq
Easier - Higher freq
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Vibration Control Example
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WBV Controls

• WBV controls for equipment, machinery
• Air-ride seats
• Designed for maximum vertical 4-8 Hz vibration
• Some offer vertical, front-to-back, side-to-side
  control
• Also consider suspended cabs, properly inflated
  tires, and good shock absorbers
• Seats alone NOT a panacea

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WBV Controls

• In plants with vibrating machinery
• Air-ride/vibration-damping seats
• Limit time spent by workers on vibrating surface
• Insure equipment well maintained to avoid
  excessive vibration
• Mechanically isolate equipment from floor/worker
• Remote operation via inexpensive CCTV

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Administrative Controls

• Dont let heavy equip operators sit on wallets
• Dont let heavy equip operators twist or bend
  immediately after WBV
• Dont let heavy equip operators jump from cabs
• Consider vibration free breaks, ?10 min/vibration
  hr
• Symptoms medical help, switch to no-vibration
  job
• Employee education (training programs)
• Should include proper use, maintenance of
  vibrating tools

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HAV Controls

• HAV controls for rotating, impact equipment
• Grip tool lightly as safely possible
• Wear clothing, including gloves, for
  warmth/dryness
• Dont use tool more than necessary
• Rest tool whenever practical
• Dont smoke
• Sharpen cutting tools no faulty tools
• Keep tool exhaust away from hands

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HAV Controls

• Replace tools with antivibration (A/V) tools
• Ergonomically designed power tools
• NOT necessarily vibration reduced!
• Handles allow neutral hand-wrist position
• Lower Carpal Tunnel Syndrome, NOT HAVS, risk
• Tool handle wraps NOT recommended
• Increase handle diameter, increase other CTD
  risk
• Dont attenuate enough low freq HAV

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HAV Controls

• Use ONLY full-finger A/V gloves
• HAVS begins at finger tips, moves towards palm
• Properly fitted A/V gloves
• Reduce vibration, keep warm, dry
• Help prevent cuts, lacerations
• Anti-Vibration Gloves
• Cotton, leather gloves do not reduce HAV
• A/V uses layer of viscoelastic material
• Gloves not good for low-freq HAV
• Low-freq major contributor to HAVS

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Online Vibration Databases

• Swedish National Institute for Working Life
• http//umetech.niwl.se/vibration/HAVHome.html
• http//umetech.niwl.se/vibration/WBVHome.html
• Allows you to find vibration levels by
• Manufacturer
• Equipment type
• Model
• Weight, power supply, etc
• ANSI http//web.ansi.org/default.htm

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Vibration Database Sample