Noise Control 2007

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Noise ControlText Reference 596-618


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Defining noise

oCommon definition: Unwanted sound

oInformation theory context: Noise is that auditory

stimulus or stimuli bearing no informational

relationship to the presence of completion of theimmediate task

Noise Control


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5% of individualsexposed to 80dBAnoise levels

develop asignificant hearingloss.

5-15% for 85dBAexposure

15-25% for 90dBA

exposure

Noise level standard


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OSHA Regulations

5dB ruleAllowable levels

90dBA for 8 hours

95dBA for 4 hours

100dBA for 2 hours

105dBA for 1 hour

110dBA for 30 minutes


125dBA for 3.75 minutes

135dBA for .94 minutes

ACGIH Regulations3dB rule

Allowable levels

85dBA for 8 hours

88dBA for 4 hours

92dBA for 2 hours95dBA for 1 hour



115dBA for .5 minutes

Noise and Time (standards)

3/)85(2

480(min) LT

5/)

90(2480(min)

L

T


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Dose %=(Time/8)

100

Dosimeter


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A worker who is exposed to the following noise during a shift ofwork (8 hours): 95 dBA 3.5h

105 dBA 0.5h85 dBA 4.0h

100[(3.5h/4)+(.5/1)+(4/16)]=163.

5

163.5 93.5


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We can not add and subtract decibelquantities For example, two 60 dB sources:

Every 3dB increase insound intensity leads toa doubling of soundpressure.

60 dB+ 60 dB 120 dB

Instead: SPL = 10 log10 (2P2/Pref

2)SPL = 10 log10 (P

2/Pref2)+10 log10 (2)

SPL = 10 log10 (P2/Pref

2)+3

Therefore: New SPL=OLD SPL + 3dB


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Noise

Contouring


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Summary of possible clinical manifestations

of stress concomitant with noise

Galvanic skin response

Increased activity related

to ulcer formation

Changes in intestinal

motilityChanges in skeletal

muscle tension

Subjective response irritability

Perception of loudness

Increased sugar cholesterol

And adrenaline

Changes in heart rate

Increased blood pressure

Increased adrenal

Vasoconstriction

Dilation of pupil

Movement of stomach

and intestine


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Noise Control Methods

Source

Isolation

Vibration reduction or changing process

Path

Blocking, active interference, absorbing

Receiver

Hearing protection Worse

Best


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cont


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cont


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Less annoyance


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Avoid resonance


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Perforated

Panels


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Path Controls

Enclosures and shieldsEffective for high frequency noise

Low frequency noise requires a fullenclosure

DistanceDoubling distance = - 6 dB

AbsorptionPassive and active (- 3 to 7 dB)


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Receiver ControlsRequired at levels above 85 dBA TWA

Types

Insertmuff

Noise Reduction Rating (NRR)

Noise Exposure = dBA + 7

NRRIdeal conditions


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Personal Hearing ProtectorsAttenuation

Earplugs Earmuffs Both


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Noise Control Methods

Source

Isolation

Vibration reduction or changing process

Path

Blocking, active interference, absorbing

ReceiverHearing protection Worse

Best

Documents

Noise Control 2007