Hearing Conservation
Presented by QBE
Loss Control Services
External Ear
• Pinna- Cartilaginous sound wave collector
• External Auditory Canal- Leads to ear
drum
Middle Ear
• Eardrum
• Ossicular Chain- 3 bones that transmit
sound
• Oval and Round Windows- membranes
separating middle & inner ear
• Eustachian Tube- connected to throat
equalizes air pressure in out and inner
ear
Inner Ear
• Vestibular System- fluid filled canals
• Cochlea- tubular structure filled with fluid
and lined with hair cells and nerve endings
Sound
• Changes in air pressure
• Weakest sound heard is a few millionths of
a lb/in2
• Pain threshold 10 million times higher
Decibels
• dB- Logarithm of the ratio of a sound
pressure level to a reference pressure level
• dB = 20 log P/P0
P0 is 20µPA (micopascals) at 1000 Hz (0 dB)
• Increase of 3 dB doubles sound energy
• dBA- Decibels using “A” scale weighting
which reflects how the ear responds to
speech frequencies
Sound Levels
Pressure Pa
100,000
200
6.3
2
0.2
0.02
0.006
0.0002
0.00006
0.00002
dBA Level Source
194
140
110
100
80
60
50
20
10
0
Rocket
Pain Threshold
Punch Press
Passing Truck
Noisy Office
Normal Speech
Private Office
Whisper
Good Hearing
Excellent Hearing
Sound Frequency
• Frequency- number of times per
second air molecules are displaced by
sound wave
• Hertz (Hz)- cycles per second
• Human audible range20- 20,000 Hz
• Speech frequency
500- 2,000 Hz
Noise
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Sound that bears no information
Unwanted by listener
Continual- constant level and frequency
Impact- sharp outbursts less than 0.5
seconds in duration
• Intermittent- Wide frequency range
several times per day
Noise Effects
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Masks wanted sounds
Interferes with speech
Causes auditory fatigue
Damages hearing
Annoyance/stress
Non-Noise Induced Impairments
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Physical blockage
Traumatic damage
Disease- infections, tumors, degenerative
Heredity damage
Drugs- streptomycin, quinine
Presbycusis- loss due to aging
Tinnitus- head noises
Types of Hearing Loss
• Conductive- external and middle ear mechanical
• Sensorineural- inner ear- nerves and hair
cells
• Mixed- conductive and sensorineural
Effects of Noise
• Temporary Threshold Shift
• Permanent Threshold Shift
Threshold Shift Variables
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dBA level
Frequency
Duration of exposure
Number and length of rest periods
Type of sound- continuous or impact
Individual differences
Purpose of Audiometric Testing
• Test hearing acuity before exposure to
noise (baseline)
• Annually check hearing acuity against
baseline
• Check effectiveness of Hearing
Conservation Program
• Record significant threshold shifts
Audiometric Testing
• Measure hearing ability at 500, 1000,
2000, 3000, 4000 and 6000 Hz
• Standard Threshold Shift- average
change in hearing threshold greater than
10 dB at 2000, 3000 and 4000 Hz in either
ear
Audiogram
Noise-Induced Hearing Loss
• Higher frequency loss usually first
• Permanent damage to cochlea
• Insidious- gradual with no pain effect
OSHA Noise Standard
• OSHA Action Level- 85 dBA average
noise level for an eight hour shift or 50%
dose
• OSHA Permissible Exposure Limit- 90
dBA average noise level for an eight hour
shift or 100% dose
Noise Monitoring
Noise Dose
• A measure of noise as a percentage of the
permissible limit.
• Dose=100 C1+ C2+ C3+... Cn
T1 T2 T3
Tn
Where Cn is the duration of exposure to a
noise level and Tn is the allowable time for
exposure to that noise level. (See Tables in
OSHA Noise Standard).
Other Shift Lengths
Shift Length 50% Dose 100% Dose
14 hr
81.0
86.0
12 hr
82.1
87.1
11 hr
82.7
87.7
10 hr
83.4
88.4
9 hr
84.2
89.2
8 hr
85
90
7 hr
86
91
6 hr
87.1
92.1
Action Level Exceeded
Implement Hearing Conservation Program
• Noise monitoring
• Provide hearing protectors
• Audiometric testing
• Training
• Recordkeeping
Permissible Exposure Level Exceeded
• Implement Hearing Conservation Program
• Use engineering and administrative controls
to reduce noise levels
• Require use of hearing protectors
Choosing Hearing Protection
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Ease of use
Fit and comfort
Hygienic considerations
Retainability within ear canal or over ears
Heat/cold/moisture
Noise Reduction Rating (NRR)
• EPA required noise attenuation factor for
all hearing protection devices
• Maximum noise attenuation of hearing
protectors about 35 dBA
• Optimal attenuation under laboratory
conditions
OSHA NRR Determination
• Subtract 7 dB from NRR
• Take %50 for a safety factor
Example: 100 dBA noise exposure
NRR for ear Muff= 19 dBA
1. 19 dBA - 7 dBA = 12 dBA
2. 12 dBA x 0.50 = 6 dBA
100 dBA- 6 dBA = 94 dBA. This is above
90 dBA limit so pick more protective
protection.
Ear Plugs
• Formable
• Custom-molded
• Must fit tightly in ear
canal
• Hands must be clean
• Must be checked and
readjusted
Ear Muffs
• Must seal around ear
• Hair must be pushed
aside
• Glasses may interfere
• Use with plugs if over
105 dBA
Use of Protectors
• Inspect before use
• Worn, loose, stiff or deformed protectors should
be discarded
• Do not use soiled plugs
• Make sure fit is snug
• Wash and clean frequently according to
manufacturer’s requirements
• Wash hands before inserting plugs
• Don’t use “homemade” protectors
Employee Training
• Effects of noise on hearing
• Company Hearing Protection Program and
policies
• Specific noise hazards in the workplace
• Purpose of hearing protectors
• Proper use of hearing protectors
• Audiometric testing
• Individual employee responsibilities
Noise Controls
• Engineering controls
• Administrative controls
Engineering Controls
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Enclosures
Control booths
Shields
Sound absorbing materials and coatings
Reduce vibrations
Change noise frequency
Reduce speeds
Reduce air pressures
Install mufflers on air devices
Increase distances
Provide proper maintenance of equipment
Reduce part dropping distances
Noise Controls
Administrative Controls
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Change way work is performed
Reduce number of workers in noisy areas
Minimize duration of exposure
Rotate between noisy and quiet areas
Provide quiet lunch/break areas