Transcript Principles of Noise Analysis

Principles of Noise
GCA Safety Committee
March 22, 2005
Susan Geier Fahmy, CSP, CCC-A
Lovell Safety Management Co., LLC
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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 Noise



Lower reading scores
Lower quality of work
disturbs concentration
disruptive
fatigue
aggravation and frustration
Stress - “fight or flight response”
adrenalin surge
heart and breathing rate increases
muscles 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
 Home
 Air traffic
 Laundromats
 Entertainment
 Power tools
 People
 Emergency vehicles
 Animals
 Restaurants
 And…..
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Construction Sites
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 Sound
Frequency (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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Intensity
The Height of the Wave
Sound Pressure Level – Decibel
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How Do We Hear?
Outer Ear
Middle Ear
Inner Ear
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The Inner Ear
Sensori Neural
Hearing Loss
Noise Induced
Hearing Loss
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Effects of Noise
 Sensorineural Hearing Loss
Destruction of hair cells in the cochlea
Outer hair cells (high frequency receptors)
are first affected
Continued exposure collapses other hair
cells
**Damage is initially temporary and then
permanent!
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How Do We Measure All of This?
Measuring Pitch (Frequency)
Hertz or Cycles Per Second
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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 Decibel
Means Nothing Without a Reference
dB SPL – Sound Pressure Level
dB HTL – Hearing Threshold Level
20 micropascals = 0 dBSPL
Frequency Dependent
dB A Mimics Human Hearing
db C
Mimics Flat SPL
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‘Normal’ Hearing Frequency Range
Intensity:
0 dbHTL – 25 dBHTL
Frequencies: 500 Hz - 2 kHz
Noise Induced Hearing Loss
Loss of high frequency acuity
s’s, x’s, f’s difficult to distinguish
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Decibels are
Logarithmic
Cannot Add and Subtract - Are Not Linear
Difference between 5 dBSPL and 10 dBSPL
DOES NOT EQUAL
The Difference between 10 dBSPL and 15 dBSPL
Decibels
 Ear responds to logs (dB) as if the sound
pressure is a linear increment
 Doubling of perceived loudness is
approximately a 3 dBSPL increase
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Common Noise Levels - dBSPL
Barely Audible
Watch Ticking
Street With out Traffic
Normal Conversation
Heavy truck
Pneumatic chipper
Typical Rock Concert
Jet Engine (800 ft away)
Jackhammer
10 dB
20 dB
40 dB
60 dB
90 dB
100 dB
100 dB
120 dB
120 dB
Noise Levels for
Common Tools
Task/Tool
Mortising
Orb. Sand.
Table Saw
Planer
Belt Sander
Router
Metal Shear
Hand Drill
Circular Saw
Tile Saw
Impact Wrench
Miter Saw
Chop Saw
Chain Saw
Hammer Drill
75
80
85
90
95
100 105 110 115
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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 Sound
Measurements taken at a
comparable site in the
nearby area
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Noise Control
Source
Receiver
Path
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Source Control
 Quieter
Work Process
Internal damping
 Enclose Equipment
Walls with high Transmission Loss
Lead rubber fabric draperies
Noise jackets
 Alter/ modify equipment
Internal damping
Mufflers
Prevent/ reduce impact between machine parts
Replace metal parts with plastic parts
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Path Control
 Sound reduction by distance
Sound level is reduced 6 dBSP for
•
each doubling of distance from
noise source
 Sound Barriers
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Receiver
Employee
Hearing Protection
Reduce time exposed - HCP
Increase distance of nearby workers
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New York City Noise Code
Construction:
Work, Device and Material
New Definitions:
Extraneous Sound: intense, intermittent < 50% of sound
source – excluded when measuring sound
Impulsive Sound: Each peak of sound lasts < 2 seconds
Plainly Audible Sound: does not requirement measurement
Unreasonable 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….
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 sources
24-228 – Construction devices/exhausts
>85dBA measured 50’ or more outside
property line of source.
Impulsive: < 15dBA over ambient
24-229 – Containers and construction material
>7dBA over ambient – night
>10dBA over ambient – day
measured 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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