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.