Download noise-induced hearing loss

Dr Mohammad Ghasemi
1
Occupational Hearing loss
It is estimated that over 22 million workers are
exposed to hazardous noise on the job and an
additional nine million are at risk for hearing loss
from other agents such as solvents and metals .
Noise-induced hearing loss is 100 percent
preventable but once acquired, hearing loss
is permanent and irreversible.
Occupational Hearing loss
Occupational hearing loss may be partial or
total unilateral or bilateral, and conductive,
sensorineural, or mixed .
In the workplace, hearing loss can be caused by
blunt or penetrating head injuries, explosions and
thermal injuries such as slag burns sustained when
a piece of welder's slag penetrates the eardrum.
Ear anatomy
•
0-120 dB is rang of faintest noise to painful
stimulation.
The normal human cochlea is capable of detecting
and encoding sound waves across the frequency
range extending from approximately 20 hertz (Hz)
to 20,000 Hz.
The most important range for human speech
reception is between 500 Hz and 3000 Hz .
Normal PTA
Conductive Loss
Sensorineural Loss
Mixed Loss
Effects of Excessive Exposure
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Primary Effects
Effects on Communication and Performance
Effects on Other Organs
Primary Effects
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Noise-induced temporary threshold shift
Noise-induced permanent threshold
shift
Acoustic trauma
Tinnitus
Effects on Communication and
Performance
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Isolation
Annoyance
Difficulty concentrating
Absenteeism
Accidents
Other Effects
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Stress
Muscle tension
Ulcers
Increased blood pressure
Sensorineural Hearing Loss
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"Sensory" hearing loss is associated with
irreversible damage to the inner ear.
The term "neural" suggests a degeneration
of the neural elements of the auditory
nerve.
ACUTE NOISE INDUCED HEARING
LOSS
Result from a brief exposure to extremely
loud noise (explosion)
May also occur following single periods of
exposure to continuous noise. (For example,
several hours of unprotected exposure to a jet
turbine producing sounds in the 120-140 dB )
Acute NIHL can result in temporary or permanent
damage
NOISE-INDUCED HEARING LOSS
Risk of permanent hearing impairment is related
to the duration and intensity of exposure as well
as genetic susceptibility to noise trauma.
prolonged exposure to sounds louder than
85 dBA is potentially injurious.
most severe around 4000 Hz, with extension toward
the "speech frequencies" (500-3000 Hz) occurring
only after prolonged or severe exposure.
Risk Factors for NIHL:
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Unprotected Exposure to Noise(>85dB)
Hyperlipoproteinemia
Diabetes
Solvents
Cigarette Smoking
Eye Color
Thyroid Abnormalities
Clinical Findings
Bilateral, predominantly high-frequency sensorineural hearing loss with a maximum drop of the
pure tone thresholds occurring at or around 4000
Asymmetry can exist
Frequently complain of gradual deterioration
in hearing
Clinical Findings
Difficulty in comprehending speech, especially
in the presence of competing background noise
vowel sounds are heard better than consonant
sounds
Frequently accompanied by tinnitus
1. High frq. Tonal (ringing)
2. Low frq. Tonal ( buzzing , blowing, hissing )
3. Non tonal (popping , clicking)
Clinical Findings
Tinnitus frequency matches the frequency of
the hearing loss seen on the audiogram and is
about 5 dB above that threshold in loudness.
SDS is normal in the early stages but may
deteriorate as the loss becomes more severe
NIHL as specified by :
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1. Always sensorineural.
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2. Nearly always bilateral and symmetric.
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3. Will not progress once noise exposure is stopped.
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4. The frequency is the most severely effected and the
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higher frequencies (3-6kHz) are more affected than the lower
frequencies (500Hz-2kHz).
6. Maximum losses typically occur after 10-15 years of chronic
exposure.
8. Continuous noise is more damaging than intermittent noise .
Audiogram Characteristics
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Always sensorineural and high-frequency
Usually bilateral and symmetric
Typically the first sign is a notching of the
audiogram at 3000,4000, or 6000 Hz, with
recovery at 8000 hz
Notch broaden over time with continuing
exposure
NIHL usually does not produce a loss >75 dB in
high frequencies and >40 dB in lower
frequencies
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NIHL does not progress ( in excess of
what would be expected from the
addition of age related threshold shift)
once the exposure to noise is
discontinued
The rate of hearing loss in NIHL is
greatest during the first 10-15 years of
exposure. After 10 years of exposure
further loss is negligible.
Other Characteristics
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NIHL characteristically develops in the first years of
exposure
Rarely will an employee working in consistent noise
have good hearing for 4-5 years and then develop
progressive hearing loss from occupational cause
unless condition has changed.
The frequencies below 3 khz are almost never
damaged by occupational noise without damage to
the higher frequencies.
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4 khz notch & abnormal SDS & good
thresholds in speech frequencies indicates
other etiologies
Exposure to noise less than 90 dBA ( TWA)
cannot cause hearing loss with speech
frequencies involvement even in susceptible
employees.
Periodic audiogram of a site
operator with noise exposure
91 dbA 6 hrs per day without
hearing protection
Periodic audiograms of a
repairman. Job change to
compressor operator with
98 dbA noise exposure 4
hrs per day from 1380.
hearing protection: yes
Unilateral or Asymmetric
Unequal or unilateral exposure to noise
source
 Truck drivers, tractor drivers,
 Unequal fitting of hearing protective
devices
 Anatomic
difference
earleft
canals
Maximal
asymmetry in
pure NIHL isbetween
15 dB between
and
right ear at 3 or 4 or 6 khz.
 Preexisting unilateral or asymmetrical
In morenotch
asymmetry other causes or preexisting hearing
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loss must be ruled out
Unilateral NIHL
( crane operators with left-sided noise source)
Is this audiogram due to continuous noise exposure?
( A 38 yrs old “ring operator” exposed to continuous noise 92 dBA for 13 years )
And this audiogram?
(another ring worker exposed to continuous noise 92 dBA for 13
years)
‫‪Compare with this audiogram‬‬
‫‪‬‬
‫ادیوگرام مربوط به کاهش شنوایی ناشی از‬
‫صوت زمانی که در فرکانسهای باال به‬
‫حداکثرافت می رسد ( ‪ 75‬دسی بل ) حتما‬
‫فرکانس های گفتاری نیز گرفتار هستند‬
‫چون ‪ NIHL‬یک سیر تدریجی پیشرونده‬
‫مشخص را طی می کند و در نتیجه‬
‫ادیوگرام های قبلی نمی توانند بطور خالص‬
‫ناشی از صوت باشند حتی اگر در یک‬
‫کارگر مواجه با صوت غیر مجاز با مدت‬
‫کافی مواجهه وجود داشته باشد‪.‬‬
Progressive course of NIHL
Periodic audiograms of 41year-old employee ( site
operator ) with unprotected
noise exposure of 95 dbA 4
hrs per day from 1374 .
Hearing protector have been
used from 1384.
Diagnosis of NIHL
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Greatest value in diagnosis:
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- History
- Noise exposure assessment (intensity &
duration)
- Serial audiograms
Differential Diagnosis of NIHL:
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Presbycusis
Hereditary Hearing Impairement
Metabolic Disorders
Sudden Sensorineural Hearing Loss
Infections
Central Nervous System Diseases
Meniere’s Disease
Nonorganic Hearing Loss
Key Points:
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Coductive hearing loss
Mixed hearing loss
Inconsistent tests
SRT 15dB>PTA
Unilateral hearing loss
History of exposure to gunfire/airplane
engine noise
Presbycusis
PRESBYCUSIS
hearing loss is a gradual, symmetric,
progressive high frequency sensorineural
associated with gradual deteriorating speech
discrimination.
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HEREDITARY HEARING IMPAIRMENT
Distinguished by a family history and early age
at onset; however, there are delayed-onset
forms of HHL .
can be conductive, mixed, or sensorineural .
Otosclerosis is an example of a progressive
autosomal dominant hearing loss that can be
conductive, mixed, or sensorineural hearing
loss.
METABOLIC DISORDERS
DM, thyroid dysfunction, renal failure,
autoimmune disease, hyperlipidemia, and
hypercholesterolemia.
May result in a sensorineural hearing loss that
is bilateral, progressive, and high frequency.
SUDDEN
SNHL
Sudden onset, usually within 1 or 2 hours, in
the absence of precipitating factors.
Almost always unilateral
Sensorineural hearing loss (SNHL)
Can be exhibited at low frequencies with
improvement in the high frequencies, flat, or
high frequency with good low-frequency hearing.
SUDDEN
SNHL
Ranging from mild to severe
The etiology of SNHL is unknown; speculation
as to viral, vascular insult, or inner ear
membrane rupture .
Infections
Meningitis and encephalitis
Syphilis and Lyme
Congenital syphilis sufferer may develop
symptoms in infancy or later in life that may
also be associated with vestibular symptoms
similar to Meniere syndrome; the hearing
loss is usually bilateral.
Infections
Late syphilis may present a slowly progressive
sensorineural hearing loss and may also exhibit
associated vestibular problems.
Mumps may cause a severe, most typically
unilateral sensorineural hearing loss
CENTRAL NERVOUS SYSTEM DISEASE
Cerebellopontine angle tumors, especially
acoustic neuroma, may present progressive
sensorineural hearing loss that is unilateral
Demyelinating diseases (e.g., multiple sclerosis)
may present a sudden unilateral hearing
loss that typically recovers to some degree.
MENIERE DISEASE
(ENDOLYMPHATIC
HYDROPS)
Fluctuating low frequency or flat
unilateral sensorineural hearing loss
Fullness or pressure in the affected ear
Tinnitus
Episodic disabling vertigo
In early stage usually low frequency sensorineural but over time it may progress to a flat
severe hearing loss.
NONORGANIC HEARING LOSS
Functional hearing loss for purposes of
secondary gain is quite frequent.
Poor correlation between the SRT and the
average of the air conduction thresholds at 500,
1000, and 2000 Hz is the most common
indication of functionality .
Test-retest variability is also suggestive.
In cases of suspected unilateral functional
hearing loss, the Stenger test is useful .
prevention
85 dBA has been characterized as the approximate
biologic threshold above which permanent shifts in
hearing are possible.
OSHA : the presence of occupational noise at or
above an 8-hour TWA exposure of 85 dBA is the
threshold that triggers the need to HCP .
Hearing conservation program
(HCP)
A hearing conservation program (HCP) is the
recognized method of preventing noise induced
hearing loss in the occupational environment.
Hearing conservation program
(HCP)
1.
Noise monitoring
2.
Engineering controls
3.
Administrating controls
4.
Worker education
5.
Hearing Protection Devices (HPD)
6.
Periodic audiometric evaluation
NOISE MONITORING
The noise must be characterized :
1.Frequency (predominantly high, predominantly
Low, or mixed)
2.Intensity (how loud it is)
3.Type (continuous> intermittent, or impulse)
Anytime there is any change in production,
process, equipment, or controls, all noise
monitoring tests must be repeated .
Noise Measurement
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Sound level meter:
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measures ambient noise levels in decibels
Dosimeter:
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sound level meter that integrates constant
or fluctuating sound over time
Sound level meters
Noise dosimeter
Engineering controls
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Based on the information collected during
noise monitoring.
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Possible engineering solutions:
The source
The path
The receivers
Engineering controls
The noise controls may involve the use of
enclosures (to isolate sources or receivers),
barriers (to reduce acoustic energy along the
path), or distance
In general, engineering controls are preferred
but are not always feasible because of their
costs and limits In technology.
Administrative controls
Reducing the amount of time a given worker
might be exposed to a noise source in order to
prevent the TWA noise exposure from reaching
85 dBA, and establishing purchasing guidelines
to prevent introduction of equipment that would
increase worker noise dose
Workers educations
Workers must understand the potentially
harmful effects of noise .
In general, the use of HPDs by employee
exposed to TWA noise levels of 85 dBA or
greater is recommended.
Workers educations
A good worker education program describes
(1) Program objectives
(2) Existing noise hazards,
(3) Now hearing loss occurs,
(4) Purpose of audiometric testing, and
(5) What workers can do to protect themselves.
Hearing protection
devices
Although the HCP is triggered by the presence of
noise levels equal to or greater than an 8 hour
TWA of 85 dBA, HPDs must attenuate worker
exposure to an 8-hour TWA at or below 90 dBA
Hearing protection
devices
There are three basic types of HPDs :
(1)Ear plugs or "aurals" (premolded, formable,
and custom molded)
(2)Caps or "semiaurals" (with a band that
compresses each end against the entrance of
the ear canal)
(3) Ear muffs or "circumaurals"
Premolded ear plags
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(NRR)=23dB
5 color-coded sizes:
 White (Extra Small)
 Green (Small)
 Orange (Medium)
 Blue (Large)
 Red (Extra Large)
Formable ear plags
Custom molded earplags
‫‪Earplugs‬‬
‫معایب‬
‫‪‬‬
‫‪‬‬
‫‪‬‬
‫‪82‬‬
‫جایگذاري سخت تر‬
‫محدودیت در مشكالت‬
‫گوش و آناتومي‬
‫نیاز به معاینه قبل از‬
‫استفاده‬
‫مزایا‬
‫‪‬‬
‫‪‬‬
‫‪‬‬
‫‪‬‬
‫حمل راحت‬
‫ارزان‬
‫قابل استفاده با سایروسایل‬
‫فردي‬
‫حركت راحت سر و‬
‫گردن‬
‫‪‬‬
‫استفاده از ایرپالگ های اسفنجی در مشاغلی که امکان‬
‫آلودگی دستها وجود دارد مانند سوهان کاری‪ ،‬فرزکاری‬
‫و در محیطهایی که تماس با مواد سوزاننده و محرک‬
‫وجود دارد مناسب نمی باشد‪.‬‬
Ear muffs
Noise Reduction Rating (NRR)=23dB
Ear muffs
‫‪Earmuff‬‬
‫معایب‬
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‫‪‬‬
‫‪‬‬
‫‪86‬‬
‫گران‬
‫سنگین‬
‫ناراحتي در گرما و‬
‫رطوبت‬
‫مشكالت استفاده توام با‬
‫سایر وسایل‬
‫كم كفایتي در موارد وجود‬
‫موي بلند و ریش‬
‫مزایا‬
‫‪‬‬
‫‪‬‬
‫‪‬‬
‫حفاظت مناسب‬
‫كنترل مناسب‬
‫عدم نیاز به معاینه‬
‫‪‬‬
‫مواجهه با گاز ازن تولید شده توسط بعضی از‬
‫ژنراتورها و در جریان جوشکاری می توانند سبب‬
‫سفت شدن فوم موجود در ‪DOME‬ایرماف شوند ‪.‬‬
Noise Reduction Rating
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All HPD are assigned a standardized as NRR.
NRRs are based on laboratory attenuation data and
achieved under ideal conditions.
Adjustment of the assigned NRR based on:
A- Weighting scale adjustment
B- Derating
C- Combining HPDs
Example
If a device has an NRR of 21 and workplace noise
measurements were made using the "A" scale,
then the predicted field attenuation or "relative
performance" of the device would be (21 – 7) / 2
= 7 dBA. Such a device would be expected to
provide protection where 8-hour TWA noise
levels up to 97 (90 + 7) dBA are present .
Combining HPDs
OSHA advises its inspectors that 5 dB are to be
added after the weighting scale adjustment is
applied to the device with the higher NRR .
Audiometric evaluation
Only quantitative means of assessing the overall
effectiveness of a hearing conservation program.
Results of audiometric testing must be shared
with employees to ensure effectiveness.
Audiometry
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Baseline Audiogram
Monitoring Audiograms
Retest Audiograms
Confirmation Audiograms
Exit Audiogram
Baseline Audiogram
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The baseline audiogram should be
obtained within 30 days of enrollment in
the HLPP
It shall be preceded by a minimum of 12
hr of unprotected quiet.
Use of hearing protectors should not be
considered a substitute for an actual 12-hr
quiet period.
Monitoring Audiograms
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Monitoring audiometry shall be conducted
no less than annually.
Unlike baseline audiometry, these annual
tests should be scheduled at the end of,
or well into, the work shift.
The results should be compared
immediately with the baseline audiogram
Retest Audiograms
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Audiometry be repeated immediately after
any monitoring audiogram that indicates a
threshold shift of 15 dB or more at 500,
1000, 2000, 3000, 4000, or 6000 Hz in
either ear.
The worker should be reinstructed and the
headphones refitted before conducting the
retest.
Confirmation Audiograms
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Audiometry should be conducted again
within 30 days of any monitoring or retest
audiogram that continues to show a
significant threshold shift.
A minimum of 12 hr of quiet shall
precede the confirmation audiogram to
determine whether the shift is a
temporary or permanent change in
hearing sensitivity
Exit Audiogram
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Audiometry should be conducted when a
worker leaves employment or is
permanently rotated out of an
occupational noise exposure at or above
85 dBA as an 8-hr TWA.
This exit audiogram, like the baseline,
should be performed after a minimum of
12 hr of quiet.
8- hour time-weighted average
(TWA)
Duration / Day hours
Slow response dBA
24
80
16
82
8
85
4
88
2
91
1
94
0.5
97
1/4
100
calculation of impairment
(AAO-79 method)
Criteria for referral to
otolaryngologist
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Baseline audiogram:
a- Average HL at 500, 1000, 2000, and 3000 Hz > 25 dB in either ear.
b- Difference in average HL between the better and poorer ears > 15
dB at 500, 1000, and 2000Hz or > 30 dB at 3000, 4000, and 6000.

Periodic audiogram:
- Change for the worse in average HL in either ear compared to the
baseline audiogram >15 dB at 500, 1000, and 2000Hz or
3000, 4000, and 6000 Hz.

>20 dB at
Other criteria: ear pain, drainage, dizziness, tinnitus, fluctuating
or rapidly progressive hearing loss, and …
Indications for Removal from Noise
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