By

Dr. BASSMA ABD EL HADI IBRAHIM

Lecturer of Industrial Medicine & Occupational Health
Faculty of Medicine
Suez Canal University
 Learning objectives
 To identify the types of occupational hazards
 To discuss properties of sound.

 To define noise

 to discuss exposure to noise

 To recognize health effects of noise

 To recognize prevention and control measures of

noise
 Classes of occupational Hazards

Health hazard
The potential to cause
Physical harm to health Psychosocial

Chemical Biological Ergonomic Mechanical

 Physical hazards

• Agents that impart energy to the body by physical

means.
Examples:
• Noise
• Vibration
• Radiation
• Heat and cold
• Pressure changes (high and low pressure)
NOISE
 What is sound?

Sound is the result of pressure variations

in an elastic medium (e.g., air, water,
solids), generated by a vibrating surface.
 What is sound?

Sound propagates in the form of longitudinal

waves, involving a succession of
compressions and rarefactions in the elastic
medium
 How Sound Travels…
Air
molecules

3) These
1) An object 2) The vibrations pass vibrations are
makes a sound through air by making air picked up by the
by vibrating the molecules vibrate ear
air around it
 Properties of Sound

Frequency sound pressure

(Pitch) (Loudness)
 Sound frequency
• The number of waves passing a fixed point each
second. OR
• The number of complete cycles that occur in one
second
• one cycle = one compression and one rarefaction
• Frequency is measured in “Hertz” (Hz).
• 5 Hz = 5 waves per second
Wavelength
.

One cycle
 Sound frequency

• Frequency correlates with pitch.

• The normal human ear can detect sounds across

the frequency range from approximately

20–20,000 Hz.
• The most important range for human speech
communication is between 500 and 3000 Hz.
 Pitch and frequency
• Pitch is human perception of frequency
• Low frequency = low pitch

• High frequency = high pitch

 Frequency spectrum of a sound
A sound which consists of a single frequency is
called a pure tone
 Sound with various frequencies

Noise produced by
most mechanical
sources, such as
machines, is made
up of many
different unrelated
frequencies (wide
band noise)
 Sound pressure

• Sound is usually measured with microphones and

they respond (approximately) proportionally to the
sound pressure.

• Sound pressure is the extent (magnitude) of the

pressure fluctuations or the difference between
static atmospheric pressure (with no sound present)
and the total atmospheric pressure with sound
present.
• expressed in Pascal (pa).
 The higher the amplitude, the greater or louder the
sound level will be

low-amplitude High-amplitude
(soft) (loud)
Loud sounds carry more energy!
The pulses of air compressions are tighter!
 Sound pressure
• For the frequencies humans hear best,
pressures between 20 and 20,000,000 μPa can
be heard and tolerated.

• Because of the large dynamic range of normal

hearing, the logarithmic decibel (dB) scale is
used, compressing a million-fold pressure
variation into a range of 120 dB.
 Decibel
• The decibel (dB) is a logarithmic unit used to
describe a ratio of a measured quantity to a reference
quantity. .

• Where p is the sound pressure, and po is the reference

which is equal to the threshold of human hearing (i.e.,
0.00002 Pa or 20 uPa)
 Decibel (dB) Levels
• Human intensity range is 0-140
0 dB - Threshold of hearing

65 dB - Average human conversation

120 dB - Threshold for discomfort

140 dB - Threshold of pain

• 160 dB - Ear drum rupture

 How Does the Ear Hear?

1.Sound waves are 4.The small bones

collected by the (ossicles) amplify
ear lobe (or pinna). the vibrations. 6.The auditory nerve
takes the signals
to the brain.
4 6
1

2
3 5 5.The hair cells
in cochlea
2.The waves turns these
travel along the into electrical
ear canal. signals (nerve
impulses).
3.The waves reach the eardrum
and make it vibrate.
Operation of the Cochlea
 What is Noise?

 Unwanted or undesired sound.

 Classification of noise

According According
to To
Continuous
frequency duration (spinning)
High frequency

Interrupted
Low frequency (traffic)

Impulsive
(explosions)
 Exposure of noise

occupational Non occupational

▪Exposure to * Traffic noise
loud sound >
85 dB
*working in noisy places
as spining &waving * Noise recreational
industery activities as using
stero head sets &
* Fire arms Hunting
.

Relative level of common noises

Health Effects of Noise

Extra
auditory Auditory
 Extra - auditory effect
➢ Annoyance
➢ Speech interference
➢ Poor communication
➢ Sleep Disturbance
➢ Fatigue and impaired concentration
➢ Stress reactions
➢ Cardiovascular problems
➢ Endocrine problems
➢ Gastrointestinal problems
Auditory effect
Hearing loss
 TYPES OF HEARING LOSS

Conductive Sensorineural Mixed

•Impedance with • Damage of hair • Combination

the mechanical cells in the of conductive
transmission of organ of Corti. and SN loss.
sound to inner
ear • Causes:
•Causes : • Noise exposure
•Obstructed (NIHL)
external ear canal • Head trauma
• Ageing
•Perforated (Presbycusis)
tympanic
• Ototoxic drugs
membrane
 Acoustic Trauma
 Exposure to sudden intense levels of noise can cause
abrupt acute and subsequent permanent damage to the
middle and inner ear.

 Impulse sound, 130-140dB

 Acute acoustic trauma (AAT) may occur in any

setting where loud impulsive noise is present, though
military operations present the greatest risks for
suffering an acute injury to the ear.
 Acoustic Trauma
• The most common symptoms :
✓ Persistent hearing loss
✓ Tinnitus

• On physical examination:
✓ The ear is usually normal unless the tympanic
membrane is ruptured, which occurs in one third of
the cases of AAT.
✓ Damage to the cochlea, vestibular system, and
ossicles of the inner ear can also occur.
 • Noise-Induced Hearing Loss
❑ It is time-linked to the noise exposure

❑Usually bilateral

❑ Gradual progression over time

❑ High-frequency hearing loss (3000-6000Hz)

(Most severe loss at the 4000Hz)

❑ Appropriate symptoms
 Noise-Induced Hearing Loss
• 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

 Pathogenesis
• A combination of mechanical, metabolic, and
vascular factors are involved in the destructive
changes that lead to NIHL.

• The effects of noise occur in the organ of

Corti, within the cochlea of the inner ear
 Hearing and Frequencies
➢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)
Safe sound Levels

Low noise
Normal cochlea
At safe sound
levels, sound waves
move along the
cochlea without
damaging receptor
cells
Loud Noise Levels

High noise
Damaged cochlea
High noise levels
damage the first turn
of the cochlea –
where high
frequency sounds
are heard…and lost
Healthy Cochlea Damaged Cochlea

cilia are Loss of

normal
cilia
 Noise-Induced Hearing Loss
Temporary Threshold Shift Permanent Threshold Shift
(PTS)
(TTS)
• Temporary loss of hearing ▪ Exposure to a
shortly after Single moderate or high
exposure to high level noise level of noise over a
• May last for few minutes / long period of time
hours ▪ No recovery when
• Depends upon frequency, exposure is
intensity, and duration of terminated
the noise
• Recovery when noise is ▪ Permanent hearing
removed, usually complete loss due to damage of
sensory cells.
 Risk Factors for NIHL
• The major risk factor for NIHL is prolonged
unprotected exposure to levels of noise above 85 db.
• Avocations and recreation activities (hunting,
recreational shooting, metalwork, and music) may
produce significant hearing impairment.
• Presbycusis or age-induced hearing loss can
accentuate impairment already present from noise
exposure and other factors
• Industrial solvent exposures
• lipid and cholesterol abnormalities, diabetes, cigarette
smoking, and thyroid abnormalities
 Signs and symptoms
of hearing loss

Tinnitus (Ringing in the ears)

Difficulty with high pitched sounds
Problems with conversing with others
Raising the volume on the TV / radio
 Clinical Evaluation of Hearing Impairment

History and Physical Examination

The physician's role in the clinical evaluation of NIHL
is to:
• obtain an objective assessment of hearing
impairment,
• prevent further deterioration of hearing, and
• recommend patients for further evaluation and
treatment.
 Occupational history
• Evaluation of occupational noise exposures should
include an estimate of years of exposure in
conjunction with any information on noise levels in
the workplace.

• Area survey or individual monitoring data is

particularly useful in establishing the exposure
history.
 Occupational history
• In the absence of such data, a careful description of
the processes and equipment used in the workplace
may give estimation of exposure.

• A history describing personal protective equipment

and other measures to reduce noise in the workplace
should also be taken.

•
 Occupational history
• Contributory effects of solvent exposures should be
considered,

• An evaluation of concomitant exposures should be

made.

✓ non occupational causes such as target shooting,

hunting, loud music, and portable radios. Personal
stereos with headphones
 Physical examination
• Physical examination should be targeted toward the
assessment of the extent and possible contributing
causes of hearing loss.

- Otological examination
 Audiometry
• Pure tone audiometric testing, which assesses the
ability to hear various standardized frequencies, is the
mainstay of evaluation.
 Treatment
• There is no medical or surgical treatment
available to reverse the effects of NIHL.
• the physician should :
• counsel the patient on the likely consequences
of continued exposure to excessive noise and
• recommend techniques for avoidance of
further noise-induced damage.
• Hearing amplification is reserved for patients
with socially impaired hearing.
 Prognosis

• Hearing in patients with NIHL will stabilize if the

patient is removed from the noxious stimulus.

• If it does not stabilize, hearing will continue to

deteriorate, ultimately resulting in severe high-
frequency hearing impairment.

• Although adequate hearing protection is essential and

always should be recommended,
PREVENTION
&
CONTROL
 Hearing Conservation Program
• Noise control measures
• Engineering
• Administrative
• Hearing Protective Equipments
• Workers education
• Noise Monitoring
• Periodic audiometric evaluation
 Hearing Conservation Program (HCP)
Action Level – 85 dB
• Hearing Conservation Program implemented
• Hearing protectors made available
• Annual audiometric testing & training
Permissible Exposure Limit – 90 dB
▪ Hearing protectors required

dB TWA
 Engineering controls
Reducing noise at the source

Altering the noise path

Reducing reverberation

Reducing equipment vibration

 Engineering controls
❑ Isolation

❑ Enclosure

❑ Sound barriers (partial enclosure)

❑ Proper maintenance of equipment

 “Buy Quiet”
“Buy Quiet” is the initiative to purchase the quietest
noise emitting equipment, tools, and machinery in order
to reduce occupational noise and sound exposures.

Create a “Buy Quiet” agenda and program.

“Buy Quiet” may initially cost more in the beginning

but will ultimately save costs for the future.
 Administrative Controls

Rotate Workers through high-noise areas

Extended Breaks
Posting hazards signs and warnings in effected areas.
 Creating policies, procedures, rules, regulations, to
minimize noise and sound intensity or duration of
exposure.
Permissible Exposure Limits (TLV)
 • Time Weighted Average

Permissible Exposure Limits

 • Time Weighted Average

Permissible Exposure Limits

Permissible Exposure Limits

Exposure level Maximum exposure per

(dB) day (hr)
90 dB 8
95 dB 4
100 dB 2
105 dB 1
110 dB 30 min
115 dB 15 min
 Elements of Hearing
Conservation Program
• Noise control measures
• Engineering
• Administrative
• Hearing Protective equipments
• Workers education
• Noise Monitoring
• Periodic audiometric evaluation
 Personal Protective Equipments

• Purpose of hearing
protectors is Reduction
of sound waves traveling
to the inner ear
 Advantages and Disadvantages
of Hearing Protectors
Protector Advantages Disadvantages
•Inexpensive, •Requires a good fit
•Comfortable for extended •cannot be inserted with dirty
use hands
• Free head movements •cannot be worn with ear
Ear Plug • Good for tight work spaces infections
• Worn with hats, eye •Must be replaced
protection, respirators periodically (become loose
over time)

•Easy to get proper fit •Difficult to wear with eye,

• Good for intermittent noise head and breathing
•Can be worn despite ear protection
Ear Muff infections. •Bulky and can be
uncomfortable in warm
weather
 Attenuation of Hearing Protectors
(Noise Reduction Rate)

Reduce noise by as much as 20

Ear Plug
decibels

Reduce noise by as much as 15-30

Ear Muff decibels
0 dB
0 dB
20 dB

EAR #1
EAR #2
EAR #3

How much protection?

Hearing Protection Selection Factors

• Keep
The
Selecting
Every right
earhearing
HPDs
workers
Detectable canal
earplugs with
has
Worker’s Comfort protector
suitable
connected
its
for own attenuation
should
shape
process to their
and feel
industries
comfortable
for noise environment
environment
size
Noise Reduction Rate •• One protector may
(NRR) Hi-visibility earmuffs
• not
Avoidsatisfy
Uniform
Ensure
for all traffic
workers
overprotection
attenuation
proper
dark/high fit with
Size • areas
Offer
in marginal
allows
variety aspeech/signals
variety
of noise
earplug of
earplugs
environments
to andor
be hear
sizes earmuffs
more
shapes
Communication to meet varying
naturally
worker needs and
Job Requirements preferences
 Elements of Hearing
Conservation Program
• Noise control measures
• Engineering
• Administrative
• Hearing Protective equipments
• Workers education
• Noise Monitoring
• Periodic audiometric evaluation
 Workers education

• Topics must include:

 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
 Elements of Hearing
Conservation Program
• Noise control measures
• Engineering
• Administrative
• Hearing Protective equipments
• Workers education
• Noise Monitoring
• Periodic audiometric evaluation
 Noise Monitoring

• Used to identify work locations where hazardous

noise levels exits.
• Employee exposures to noise monitored
periodically with:

❑ Sound Level Meter

❑ Noise Dosimeter
 • Noise Measurement Devices

SOUND LEVEL METER PERSONAL DOSIMETER

Measure area noise level personal noise exposure level

Sound is measured immediately Sound “averaged” throughout

in a specific area day for sample employee/job
 Elements of Hearing
Conservation Program
• Noise control measures
• Engineering
• Administrative
• Hearing Protective equipments
• Workers education
• Noise Monitoring
• Periodic audiometric evaluation
 Periodic audiometric evaluation
• Pre-employment (Baseline Audiogram)

• periodic assessment as long as the employee is

assigned to a noisy job ( a time-weighted average
exposure level equal to or greater than 85 dBA)
(Monitoring Audiogram)

• At the termination of employment (Exit Audiogram)

 Pure Tone Audiometry
• The examiner measures The Threshold of hearing for different
• frequencies, 250 Hz, 500, 1000, 2000, 4000 and 8000 Hz
• The sound is delivered through
- HeadPhone For AIR CONDUCTION and,
- Bone Vibrator for BONE CONDUCTION
- The results are recorded on a graph (pure tone audiogram)
 Pure tone audiometry
• Why Do Audiometric Testing?
▪ Degree of Hearing Loss (mild, moderate, severe or,
profound)

▪ Diagnosis of Type of Hearing loss,( CD, SNHL Or

Mixed)

▪ Obtain a Baseline Audiogram for future comparison

▪ Identify Standard Threshold Shifts (STS) (a change
in hearing threshold relative to the baseline
audiogram of an average of 10 dB or more).
 Pure tone audiometry
❑The employee must spend 14
hours without exposure to
workplace noise before being
tested
❑Worker sits in a quiet booth
❑Masking
❑Pure tones used
• 500, 1000, 2000, 3000, 4000,
6000, [8000] Hz
Degree of Hearing Loss

Normal: Up to 25 dB

Mild: 25 - 40 dB
Moderate: 40 - 55 dB

Moderately Severe:55-70

Severe: 70 to 90 dB

Profound:> 90 dB
 Hierarchy of Controls

ENGINEERING
CONTROLS

ADMINISTRATIVE
CONTROLS
PERSONAL
PROTECTIVE
EQUIPMENT
 References
• Joseph LaDou, Robert J. Harrison. CURRENT
Diagnosis & Treatment: Occupational &
Environmental Medicine. Hearing loss.
• Rom, William N. Environmental and Occupational
Medicine, 4th Edition. Occupational Exposure to
Noise.
• Hunter’s Diseases of Occupations. Peter J Baxter,
Tar-Ching Aw, Anne Cockcroft, Paul Durrington
andJ Malcolm Harrington. Noise. Tenth edition.