Noise Control 2007
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Transcript of 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
115dBA for 15 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
98dBA for 30 minutes
101dBA for 15 minutes
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