Noise Control

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Noise Control

• Text Reference 596-618

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Noise Control

• Defining noise
• Common definition Unwanted sound
• Information theory context Noise is that
  auditory stimulus or stimuli bearing no
  informational relationship to the presence of
  completion of the immediate task

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Noise level standard

• 5 of individuals exposed to 80dBA noise levels
  develop a significant hearing loss.
• 5-15 for 85dBA exposure
• 15-25 for 90dBA exposure

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Noise and Time (standards)
OSHA Regulations 5dB rule Allowable 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 Regulations 3dB rule Allowable levels 85dBA
for 8 hours 88dBA for 4 hours 92dBA for 2
hours 95dBA for 1 hour 98dBA for 30
minutes 101dBA for 15 minutes 115dBA for .5
minutes
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Dosimeter
Dose (Time/8)100
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A worker who is exposed to the following noise
during a shift of work (8 hours) 95 dBA
3.5h 105 dBA
0.5h 85 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 decibel quantities
For example, two 60 dB sources
60 dB 60 dB 120 dBInstead SPL 10 log10
(2P2/Pref2) SPL 10 log10
(P2/Pref2)10 log10 (2) SPL 10
log10 (P2/Pref2) 3Therefore New SPLOLD SPL
3dB
Every 3dB increase in sound intensity leads to a
doubling of sound pressure.
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Noise Contouring
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Summary of possible clinical manifestations of
stress concomitant with noise
Subjective response irritability Perception of
loudness
Dilation of pupil
Increased sugar cholesterol And adrenaline
Galvanic skin response
Changes in heart rate
Increased blood pressure
Increased activity related to ulcer formation
Increased adrenal
Changes in intestinal motility
Changes in skeletal muscle tension
Vasoconstriction
Movement of stomach and intestine
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Noise Control Methods
Best

• Source
• Isolation
• Vibration reduction or changing process
• Path
• Blocking, active interference, absorbing
• Receiver
• Hearing protection

Worse
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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 shields
• Effective for high frequency noise
• Low frequency noise requires a full enclosure
• Distance
• Doubling distance - 6 dB
• Absorption
• Passive and active (- 3 to 7 dB)

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Receiver Controls

• Required at levels above 85 dBA TWA
• Types
• Insert
• muff
• Noise Reduction Rating (NRR)
• Noise Exposure dBA 7 NRR
• Ideal conditions

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• Personal Hearing Protectors Attenuation
• Earplugs Earmuffs Both

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Noise Control Methods
Best

• Source
• Isolation
• Vibration reduction or changing process
• Path
• Blocking, active interference, absorbing
• Receiver
• Hearing protection

Worse