1 principles of noise susan geier fahmy, csp, ccc-a lovell safety management co., llc gca safety...
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Principles of Noise
Susan Geier Fahmy, CSP, CCC-A
Lovell Safety Management Co., LLC
GCA Safety Committee
March 22, 2005
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Health Effects Attributed to Excessive Exposure to NoiseHealth Effects Attributed to Excessive Exposure to Noise Lower reading scores Lower quality of work
disturbs concentrationdisruptivefatigueaggravation and frustration
Stress - “fight or flight response”adrenalin surgeheart and breathing rate increasesmuscles tense
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Health Effects Attributed to Excessive Exposure to Noise Elevated blood pressure Irritability Fatigue Vasoconstriction of
peripheral blood vessels Sore throat
Gastrointestinal disorders Headaches Allergic reactions Sleeping disorders Damage to the brain stem
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Sources of Noise Motor vehicles Air traffic Entertainment People Animals
Home Laundromats Power tools Emergency vehicles Restaurants And…..
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What is Sound ? An oscillation in pressure in a medium
(such as air) The oscillation travels through the
medium at a certain speed and magnitude
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Frequency - Pitch # of cycles a wave passes by a point in
space per unit of time
Cycles/ second or Hertz (Hz)
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Effects of NoiseSensorineural Hearing Loss
Destruction of hair cells in the cochleaOuter hair cells (high frequency receptors) are first affectedContinued exposure collapses other hair cells
**Damage is initially temporary and then permanent!
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How Do We Measure All of This?
How Do We Measure All of This?
Measuring Pitch (Frequency)Hertz or Cycles Per Second
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Measuring Loudness
Measuring Loudness
Measure intensity or sound pressure Pressure = force/ area Unit of pressure is measured in “Pascals” 0.00002 Pascals 100,000 pascals
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The DecibelMeans Nothing Without a Reference
dB SPL – Sound Pressure Level 20 micropascals = 0 dBSPL
dB HTL – Hearing Threshold Level Frequency Dependent
dB A Mimics Human Hearing
db C Mimics Flat SPL
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‘Normal’ Hearing Frequency Range
Intensity: 0 dbHTL – 25 dBHTLFrequencies: 500 Hz - 2 kHz Noise Induced Hearing LossLoss of high frequency acuity
s’s, x’s, f’s difficult to distinguish
Decibels are LogarithmicDecibels are Logarithmic
Cannot Add and Subtract - Are Not LinearDifference between 5 dBSPL and 10 dBSPL
DOES NOT EQUAL
The Difference between 10 dBSPL and 15 dBSPL
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DecibelsEar responds to logs (dB) as if the sound
pressure is a linear incrementDoubling of perceived loudness is
approximately a 3 dBSPL increase
Common Noise Levels - dBSPLCommon Noise Levels - dBSPL
Barely Audible 10 dBWatch Ticking 20 dBStreet With out Traffic 40 dBNormal Conversation 60 dBHeavy truck 90 dB
Pneumatic chipper 100 dB
Typical Rock Concert 100 dBJet Engine (800 ft away) 120 dBJackhammer 120 dB
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Hammer DrillHammer DrillHammer DrillHammer DrillChain SawChain SawChain SawChain Saw
Chop SawChop SawChop SawChop SawMiter SawMiter SawMiter SawMiter Saw
Impact WrenchImpact WrenchImpact WrenchImpact WrenchTile SawTile SawTile SawTile Saw
Circular SawCircular SawCircular SawCircular Saw
Hand DrillHand DrillHand DrillHand DrillMetal ShearMetal ShearMetal ShearMetal Shear
RouterRouterRouterRouter
PlanerPlanerPlanerPlaner
Belt SanderBelt SanderBelt SanderBelt Sander
Table SawTable SawTable SawTable SawOrb. Sand.Orb. Sand.Orb. Sand.Orb. Sand.
MortisingMortisingMortisingMortising
75 80 85 90 95 100 105 110 115
Tas
k/T
ool
Noise Levels forNoise Levels forCommon ToolsCommon Tools
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A - Scale (dBA) Attenuation of low frequencies Enhances high frequency perception Human ears attenuate sounds below 1 kHz We perceive high frequency sounds to be louder
than low frequency sounds, though they might have equal sound pressure
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Measurement of Sound Sound Level Meters (type 1 or 2)
Measures continuous sound pressure instantaneously
A scale, slow response
Set to “max” or Lmax (for OSHA/NYC measurements)
Gives instantaneous readout
Measurement done in hearing zone
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Noise Dosimeters Will measure sound levels which are
constantly fluctuating Integrate sound pressure with time Worn by the worker for the entire shift Readout indicates percentage of the
permissible exposure limit (90 dBA @ 8 hours) to which employee was exposed
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Source Control Quieter Work Process
Internal damping
Enclose EquipmentWalls with high Transmission LossLead rubber fabric draperiesNoise jackets
Alter/ modify equipmentInternal dampingMufflersPrevent/ reduce impact between machine partsReplace metal parts with plastic parts
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Path Control Sound reduction by distance
Sound Barriers
•
Sound level is reduced 6 dBSP for
each doubling of distance from noise source
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ReceiverReceiverEmployee
Hearing ProtectionReduce time exposed - HCPIncrease distance of nearby workers
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New York City Noise CodeNew York City Noise Code
Construction: Work, Device and MaterialNew Definitions:
Extraneous Sound: intense, intermittent < 50% of sound source – excluded when measuring soundImpulsive Sound: Each peak of sound lasts < 2 secondsPlainly Audible Sound: does not requirement measurementUnreasonable Noise: >15’ from source; 7dBA over ambient 10 pm–7am; 10dBA over ambient 7am-10pm – Impulse 15dBA over ambient on fast scale - Not Construction!
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Construction….Construction….
New subchapter (24-219) will be added with new rules prescribing noise mitigation strategies (in addition to those already listed (Perimeter fences, blanket insulation etc.)
Noise Mitigation Plan – adopted at beginning of construction
After hours work cannot exceed 8dBA over ambient measured inside “residential receiving property”
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Subchapter 5 – standards for specific noise sources24-228 – Construction devices/exhausts
>85dBA measured 50’ or more outside property line of source.
Impulsive: < 15dBA over ambient24-229 – Containers and construction material
>7dBA over ambient – night>10dBA over ambient – daymeasured 15’ or more from source>15dBA over ambient – impulsive
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24-230 – Paving breakers
Not operated electrically or hydraulically
Must have pneumatic discharge muffler
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