3 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 lossis permanent and irreversible.
4 Occupational Hearing loss Occupational hearing loss may be partial ortotal 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.
6 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 .
13 Effects on Communication and Performance IsolationAnnoyanceDifficulty concentratingAbsenteeismAccidents
14 Other EffectsStressMuscle tensionUlcersIncreased blood pressure
15 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.
16 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 dB )Acute NIHL can result in temporary or permanent damage
17 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" ( Hz) occurring only after prolonged or severe exposure.
18 Risk Factors for NIHL: Unprotected Exposure to Noise(>85dB) HyperlipoproteinemiaDiabetesSolventsCigarette SmokingEye ColorThyroid Abnormalities
19 Clinical FindingsBilateral, predominantly high-frequency sensori-neural hearing loss with a maximum drop of the pure tone thresholds occurring at or around 4000Asymmetry can existFrequently complain of gradual deterioration in hearing
20 Clinical FindingsDifficulty in comprehending speech, especially in the presence of competing background noisevowel sounds are heard better than consonant soundsFrequently accompanied by tinnitusHigh frq. Tonal (ringing)Low frq. Tonal ( buzzing , blowing, hissing )Non tonal (popping , clicking)
21 Clinical FindingsTinnitus 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
22 NIHL as specified by : 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 thehigher frequencies (3-6kHz) are more affected than the lowerfrequencies (500Hz-2kHz).6. Maximum losses typically occur after years of chronic exposure.8. Continuous noise is more damaging than intermittent noise .
23 Audiogram Characteristics Always sensorineural and high-frequencyUsually bilateral and symmetricTypically the first sign is a notching of the audiogram at 3000,4000, or 6000 Hz, with recovery at 8000 hzNotch broaden over time with continuing exposureNIHL usually does not produce a loss >75 dB in high frequencies and >40 dB in lower frequencies
24 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 discontinuedThe rate of hearing loss in NIHL is greatest during the first years of exposure. After 10 years of exposure further loss is negligible.
25 Other Characteristics NIHL characteristically develops in the first years of exposureRarely 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.
26 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.
27 Periodic audiogram of a site operator with noise exposure 91 dbA 6 hrs per day without hearing protection
28 Periodic audiograms of a repairman Periodic audiograms of a repairman. Job change to compressor operator with 98 dbA noise exposure 4 hrs per day from hearing protection: yes
29 Unilateral or Asymmetric Unequal or unilateral exposure to noise sourceTruck drivers, tractor drivers,Unequal fitting of hearing protective devicesAnatomic difference between ear canalsPreexisting unilateral or asymmetrical notchMaximal 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
30 Unilateral NIHL ( crane operators with left-sided noise source)
31 Is this audiogram due to continuous noise exposure Is this audiogram due to continuous noise exposure? ( A 38 yrs old “ring operator” exposed to continuous noise 92 dBA for 13 years )
32 And this audiogram? (another ring worker exposed to continuous noise 92 dBA for 13 years)
35 Compare with this audiogram ادیوگرام مربوط به کاهش شنوایی ناشی از صوت زمانی که در فرکانسهای بالا به حداکثرافت می رسد ( 75 دسی بل ) حتما فرکانس های گفتاری نیز گرفتار هستند چون NIHL یک 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.
47 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.
48 metabolic disordersDM, thyroid dysfunction, renal failure, autoimmune disease, hyperlipidemia, and hypercholesterolemia.May result in a sensorineural hearing loss that is bilateral, progressive, and high frequency.
49 sudden SNHLSudden onset, usually within 1 or 2 hours, in the absence of precipitating factors.Almost always unilateralSensorineural hearing loss (SNHL)Can be exhibited at low frequencies with improvement in the high frequencies, flat, or high frequency with good low-frequency hearing.
50 sudden SNHL Ranging from mild to severe The etiology of SNHL is unknown; speculation as to viral, vascular insult, or inner ear membrane rupture .
51 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.
52 InfectionsLate 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
53 central nervous system disease Cerebellopontine angle tumors, especially acoustic neuroma, may present progressive sensorineural hearing loss that is unilateralDemyelinating diseases (e.g., multiple sclerosis) may present a sudden unilateral hearing loss that typically recovers to some degree.
54 (endolymphatic hydrops) meniere disease(endolymphatic hydrops)Fluctuating low frequency or flat unilateral sensorineural hearing lossFullness or pressure in the affected earTinnitusEpisodic disabling vertigoIn early stage usually low frequency sensori-neural but over time it may progress to a flat severe hearing loss.
55 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 .
56 prevention85 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 .
57 Hearing conservation program (HCP) A hearing conservation program (HCP) is the recognized method of preventing noise induced hearing loss in the occupational environment.
59 noise monitoring The noise must be characterized : 1.Frequency (predominantly high, predominantlyLow, 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 .
65 Engineering controlsBased on the information collected during noise monitoring.Possible engineering solutions:The sourceThe pathThe receivers
66 Engineering controlsThe noise controls may involve the use of enclosures (to isolate sources or receivers), barriers (to reduce acoustic energy along the path), or distanceIn general, engineering controls are preferred but are not always feasible because of their costs and limits In technology.
67 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 guidelinesto prevent introduction of equipment that would increase worker noise dose
68 Workers educationsWorkers 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.
69 Workers educations A good worker education program describes Program objectivesExisting noise hazards,Now hearing loss occurs,Purpose of audiometric testing, andWhat workers can do to protect themselves.
71 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
72 Hearing protection devices There are three basic types of HPDs : Ear plugs or "aurals" (premolded, formable, and custom molded)Caps or "semiaurals" (with a band that compresses each end against the entrance of the ear canal)Ear muffs or "circumaurals"
86 Earmuff مزايا معايب حفاظت مناسب كنترل مناسب عدم نياز به معاينه گران سنگينناراحتي در گرما و رطوبتمشكلات استفاده توام با ساير وسايلكم كفايتي در موارد وجود موي بلند و ريش
87 مواجهه با گاز ازن تولید شده توسط بعضی از ژنراتورها و در جریان جوشکاری می توانند سبب سفت شدن فوم موجود درDOME ایرماف شوند .
88 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 adjustmentB- DeratingC- Combining HPDs
89 ExampleIf 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 .
90 Combining HPDsOSHA advises its inspectors that 5 dB are to be added after the weighting scale adjustment is applied to the device with the higher NRR .
91 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.
93 Baseline AudiogramThe baseline audiogram should be obtained within 30 days of enrollment in the HLPPIt 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.
94 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
95 Retest AudiogramsAudiometry 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.
96 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
97 Exit AudiogramAudiometry 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.
98 8- hour time-weighted average (TWA) Duration / Day hoursSlow response dBA248016828854882911940.5971/4100
100 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 …