Samar El-Sayed
Sound Sound isis Vibrational Energy Vibrational Energy
Travels in Waves Travels in Waves from a Sourcefrom a Source
FREQUENCYFREQUENCY INTENSITYINTENSITY Cycles per Second
Hertz (Hz)Hertz (Hz)
loudness of the sound
Decibels (dB)Decibels (dB)
How We HearSound waves enter the ear canal striking the eardrum.
When eardrum vibrates, ossicles conducts vibrations to the cochlea.
Tiny hairlike cells in cochlea respond to vibrations by generating nerve impulses.
Brain interprets nerve impulses as sound.
Acoustical
Mechanical
Hydraulic
Chem/Elec
What is Noise? Unwanted or undesired sound.
Sound that has potential to cause hearing impairment.
An intense sound capable of damaging the inner ear
Effects of NoiseAuditory
• Acute acoustic trauma Sudden, permanent SNHL caused by single exposure to an intense Impulse sound, 130-140dB
• Noise-induced hearing loss
Extra – auditory• Interfere with communication• Physiological effects• Annoyance
Auditory effects of NoiseTemporary threshold shift (TTS)
•Temporary loss of hearing shortly after exposure to noise.
•Resolves over a period of hours or days
Permanent threshold shift (PTS)•Permanent hearing loss due to damage of sensory cells.
• Nerve cells in the cochlea are tuned to specific frequencies
• Base of the cochlea is sensitive to high frequency sounds (red dots)
• Tip of the cochlea is sensitive to low frequency sounds (green dots)
Hearing and Frequencies
Safe Noise Levels
At safe noise levels, sound waves move along the cochlea without damaging receptor cells
Low noiseNormal cochlea
Loud Noise Levels
High noise levels damage the first turn of the
cochlea – where high frequency sounds are heard…
and lost
High noiseDamaged cochlea
• Causes no pain
• Causes no visible trauma
• Leaves no visible scars
• Is unnoticeable in its earliest stages
• Takes years to notice a change
Is Permanent + 100% Preventable
Noise-Induced Hearing Loss
Indicators of NIHL•Time-linked to noise exposure
•High-frequency hearing loss
•Usually bilateral (both ears)
•Gradual progression over time
•mostly irreversible
•Appropriate symptoms (tinnitus, muffled hearing)
Noise + Acoustics
Hearing Conservation Program
Action Level – 85 dB• Hearing Conservation Program implemented• Hearing protectors made available• Annual audiometric testing & training
85
dB TWA
90 95
Permissible Exposure Limit – 90 dB Hearing protectors required
Elements of Hearing Conservation Program
• Noise control measures•Engineering•Administrative
• Hearing Protectors
• Workers education
• Noise Monitoring
• Periodic audiometric evaluation
Hierarchy of Controls
ADMINISTRATIVE CONTROLS
•Rotate Workers
•Extended Breaks
•2nd/3rd Shift
ENGINEERING CONTROLS
•Vibration Pads
•Enclosures
•Barriers
•Isolation
PERSONAL PROTECTIVE EQUIPMENT
Time Weighted Average
Permissible Exposure Limits
Time Weighted Average
Permissible Exposure Limits
Hearing Protection SelectionEarplugs
Advantages• Comfortable for extended use• Free head movements• Good for tight work spaces• Worn with hats, eye protection, respirators
Disadvantages• Must be replaced periodically• Small and can easily be lost• Hygiene issues in dirty environments
Hearing Protection SelectionBands
Advantages• Very convenient for intermittent noise
• Readily available around neck when not in use
Disadvantages• Lower attenuation than most earplugs
• Some noise transmission through band
Hearing Protection SelectionEarmuffs
Advantages• Easy to get proper fit• Good for intermittent noise
Advantages• Can feel hot/heavy with extended wear
• Compatibility with other PPE
Comfort
Noise Reduction
Size
Communication
Job Requirements
Hygiene
Use with Other PPE
Hearing Protection Selection Factors
• The right hearing protector should feel comfortable
• One protector may not satisfy all workers
• Offer a variety of earplugs or earmuffs to meet varying worker needs and preferences
• Selecting HPDs with suitable attenuation for noise environment
• Avoid overprotection in marginal noise environments
• Consider banded earplugs for intermittent noise or electronic earmuffs for impact noise.
• Every ear canal has its own shape and size
• Ensure proper fit with variety of earplug sizes and shapes
• Sized multiple-use earplugs
• Low-pressure foam earplugs for smaller ear canals
• Keep workers connected to their environment
• Uniform attenuation allows speech/signals to be hear more naturally
• Sound amplification earmuffs for workers with hearing impairment
• Consider job requirements in HPD selection
• Detectable earplugs for process industries
• Hi-visibility earmuffs for dark/high traffic areas
• Dielectric HPDs for electrical environments
• Proper care and maintenance can extend life and performance of HPDs
• Examine and clean all multiple-use earplugs daily
• Clean and replace ear cushions on earmuffs every 4-6 months
• Select HPDs that can work with other PPE without compromise
• Cap-mounted earmuffs for hard hats
• Multiple-position earmuffs for full-brim hard hats
• Ultraslim neckband earmuffs with welding shields
How much protection?
0 dB 0 dB33 dB
EAR #1EAR #2
EAR #3
Workers education•Effects of noise on hearing•Purpose of hearing protectors•Advantages and disadvantages of different
types of hearing protectors•Attenuation of different types of hearing
protectors•Instructions on selection, fitting, use, and care
of hearing protectors•Purpose of audiometric testing
Noise Measurement Devices
SOUND LEVEL METER
Sound is measured immediately in a specific area
PERSONAL DOSIMETER
Sound “averaged” throughout day for sample employee/job
Pure tone audiometry •Basic test to find out if a hearing loss is present or not. •During the test the test person wears a headphone or insert ear phones through which pure tones at different frequencies are being presented.•level at which tones are barely audible is found, is the hearing threshold levels
.
Speech audiometry A speech reception threshold (SRT) • Two-syllable words like "hotdog," baseball," and "cupcake" are presented at various intensity levels and the worker repeats them or point to a picture. • SRT is determined by the lowest level of sound intensity needed for the patient to correctly identify 50% of these words.
Speech audiometrySpeech discrimination test • Evaluates the patient's ability to comprehend a list of single-syllable words presented at a comfortable listening level. • The percentage of words the worker is able to correctly repeat or identify is then recorded.
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