Post on 24-Dec-2015
1Dr Mohammad Ghasemi
Ear & WORK
Maryam Saraei
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 .
Occupational Hearing loss
Noise-induced hearing loss is 100 percent preventable but once acquired, hearing loss is permanent and irreversible.
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.
Occupational Hearing loss
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
Primary Effects Effects on Communication and
Performance Effects on Other Organs
Primary Effects
Noise-induced temporary threshold shift
Noise-induced permanent threshold shift
Acoustic trauma Tinnitus
Effects on Communication and Performance
Isolation Annoyance Difficulty concentrating Absenteeism Accidents
Other Effects
Stress Muscle tension Ulcers Increased blood pressure
Sensorineural Hearing Loss
"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: Unprotected Exposure to
Noise(>85dB) Hyperlipoproteinemia Diabetes Solvents Cigarette Smoking Eye Color Thyroid Abnormalities
Clinical Findings
Frequently complain of gradual deterioration in hearing
Bilateral, predominantly high-frequency sensori-neural hearing loss with a maximum drop of the pure tone thresholds occurring at or around 4000
Asymmetry can exist
Difficulty in comprehending speech, especially in the presence of competing background noisevowel sounds are heard better than consonant sounds
Clinical Findings
Frequently accompanied by tinnitus1.High frq. Tonal (ringing)2.Low frq. Tonal ( buzzing , blowing, hissing
)3.Non tonal (popping , clicking)
Clinical Findings
SDS is normal in the early stages but may deteriorate as the loss becomes more severe
Tinnitus frequency matches the frequency of the hearing loss seen on the audiogram and is about 5 dB above that threshold in loudness.
1. Always sensorineural. 2. Nearly always bilateral and symmetric. 3. Will not progress once noise exposure is stopped. 4. The frequency is the most severely effected and the
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 .
NIHL as specified by :
Audiogram Characteristics 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
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
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.
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 between ear
canals Preexisting unilateral or
asymmetrical notch
Maximal asymmetry in pure NIHL is 15 dB between left and right ear at 3 or 4 or 6 khz.
In more asymmetry other causes or preexisting hearing 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
شنوایی کاهش به مربوط ادیوگرامدر که زمانی صوت از ناشیمی حداکثرافت به باال فرکانسهای
( ( 75رسد حتما بل دسیگرفتار نیز گفتاری های فرکانس
چون سیر NIHLهستند یکطی را مشخص پیشرونده تدریجیهای ادیوگرام نتیجه در و کند میخالص بطور توانند نمی قبلیدر اگر حتی باشند صوت از ناشیغیر صوت با مواجه کارگر یکوجود مواجهه کافی مدت با مجاز
. باشد داشته
Progressive course of NIHL
Periodic audiograms of 41-year-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
Greatest value in diagnosis: - History - Noise exposure assessment (intensity &
duration) - Serial audiograms
Differential Diagnosis of NIHL:
Presbycusis Hereditary Hearing Impairement Metabolic Disorders Sudden Sensorineural Hearing Loss Infections Central Nervous System Diseases Meniere’s Disease Nonorganic Hearing Loss
Key Points:
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.
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 with in 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.
The etiology of SNHL is unknown; speculation as to viral, vascular insult, or inner ear membrane rupture .
Ranging from mild to severe
SUDDEN SNHL
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.
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
Infections
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 lossFullness or pressure in the affected ear
TinnitusEpisodic disabling vertigo
In early stage usually low frequency sensori-neural 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 uni lateral functional hearing loss, the Stenger test is useful .
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 .
prevention
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
Hearing conservation program (HCP)
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
Sound level meter: measures ambient noise levels in
decibels
Dosimeter: sound level meter that integrates
constant or fluctuating sound over time
Sound level meters
Noise dosimeter
Engineering controls
Based on the information collected during noise monitoring.
Possible engineering solutions:
The source
The path
The receivers
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.
Engineering controls
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 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.
Workers educations
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"
Hearing protection devices
Premolded ear plags
(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
مزايا راحت حملارزان با استفاده قابل
فردي سايروسايل و سر راحت حركت
گردن
معايب تر سخت جايگذاري در محدوديت
و گوش مشكالتآناتومي
از قبل معاينه به نيازاستفاده
82
در اسفنجی های ایرپالگ از استفادهدارد وجود دستها آلودگی امکان که مشاغلی
در و فرزکاری کاری، سوهان مانندو سوزاننده مواد با تماس که محیطهایی
. باشد نمی مناسب دارد وجود محرک
Noise Reduction Rating (NRR)=23dB
Ear muffs
Ear muffs
Earmuff
مزايا مناسب حفاظت مناسب كنترل معاينه به نياز عدم
معايبگرانسنگين و گرما در ناراحتي
رطوبت استفاده مشكالت
وسايل ساير با توام موارد در كفايتي كم
و بلند موي وجودريش 86
بعضی توسط شده تولید ازن گاز با مواجههمی جوشکاری جریان در و ژنراتورها از
موجود فوم شدن سفت سبب توانندشوند .DOMEدر ایرماف
Noise Reduction Rating
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
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 .
Example
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 .
Combining HPDs
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.
Audiometric evaluation
Audiometry
Baseline Audiogram Monitoring Audiograms Retest Audiograms Confirmation Audiograms Exit Audiogram
Baseline Audiogram 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 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 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 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 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 dBA24 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
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 >20 dB at 3000, 4000, and 6000 Hz. Other criteria: ear pain, drainage, dizziness, tinnitus,
fluctuating or rapidly progressive hearing loss, and …
Indications for Removal from Noise
Thanks