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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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“Vision relates people to nature.

Sound relates humans to each

other.”

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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…..

Construction SitesConstruction Sites

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Noise…Unwanted sound

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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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Properties of SoundFrequency (Pitch) Intensity (Loudness)

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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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IntensityIntensityThe Height of the Wave

Sound Pressure Level – Decibel

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How Do We Hear?How Do We Hear?

Outer EarMiddle EarInner Ear

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The Inner Ear

Sensori Neural Hearing Loss

Noise Induced Hearing Loss

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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

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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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Ambient SoundAmbient Sound

Measurements taken at a comparable site in the

nearby area

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Noise ControlSource Receiver

Path

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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

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                                                                                                                     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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