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Industrial Lectures Page 1 Card number_____ 1 card fld "card field id 3" Ramazzini in 1700, "De Morbus Artificium Diatriba" morbus: "disease" artificium: a trade or profession diatriba: •a discourse or dispute •also, a wasting away "Those hammering copper had their ears so injured by that perpetual din that workers of this class became hard of hearing and, if they grow old at this kind of work completely deaf." -noise exposure results in hearing loss -damage is a function of exposure level and duration -correlation with aging Some terms: -NIHL: chronic exposure; most exposures are ≤ 100 dBA. Exposures. -tinnitus: common symptom associated with NIHL, often a symptom of temporarily or permanently damaged sensory or neural tissue. -acoustic trauma: brief duration exposure -occupational hearing loss: NIHL from employment, "boilermaker's deafness" -sociocusis: hearing loss from non-occupational noise exposure (music, airplanes, subways, firearms, lawnmowers, powertools, snowmobiles, etc.) -presbycusis: hearing in the elderly, hearing loss associated with aging; primary variable confounded with NIHL. The issue of ◊employer culpability ◊combination of factors affecting handicap -nosoacusis (GR nosos, disease): hearing loss from accident, trauma, ototoxicity, etc. Industrial Lectures Page 2 For an introduction to the main components of a hearing conservation program, click HCPs card fld "Info…" Towards the end of the semester, some concepts… •Be sure you are very familiar with the OSHA regulations for occupational noise exposure. ◊I will be picky & specific -go card Regulations •The story of the Mabaan tribe and presbycusis -regarding hearing loss: maybe its not growing old per se, but how we grow old -go card Mabaan •Calculating the fence (onset of material impairment) or %HL for each ear and binaural weighting (5:1) -go card Fence •Probability of crossing the fence from exposure to the PEL -29% without noise exposure ammendment, 5% risk with Jan '81 -go card Risk •Interaction of pre-existing permanent hearing loss with daily TTS -more hearing loss, less TTS -go card TTS •Cochlear electrophysiology and mechanics -go card Cochlea •Major theories regarding mechanism of hearing loss from noise exposure -go card Effects •Dose and TWA calculation -Done for you by the dosimeter -go card Dose •For a pink noise exposure, which formula, HPD attenuation, paragraph (j), predicts greater HPD attenuation (or estimated Alevel TWA exposure, Est-A)? ◊Est-A = A-weighted TWA - (NRR - 7) ◊Est-A = C-weighted TWA - NRR Industrial Lectures Page 3 -go card Regulations •Ambient noise in test suite can affect validity of the baseline audiogram -this limits ability of the annual audiogram to detect changes in threshold produced by noise exposure -go card Ambient card fld "HCPs" •Administration √Initial √Ongoing Evaluation & Re-evaluation •Exposure Measurements √Initial Survey √Noise Monitoring •Noise Controls √Administrative √Engineering •Hearing Protector Devices (HPDs) •Audiometry √Baseline √Annual •Training & Education •Medical Evaluation Card number_____ 2 card fld "Stressor" •increased noise levels produce peripheral vasoconstriction •resulting in increased heart action,causing increased blood pressure •increased secretion of corticosteroids (adrenal steroids, catecholamines) •fight or flight mechanism Industrial Lectures Page 4 card fld "Performance" •vigilance tasks boring, may help •hinders more complex tasks card fld "Absenteeism" •Noisy jobs generally less attractive, more dangerous Card number_____ 3 card fld "Elasticity" An elastic deformation: a deforming force causes a body to change shape. When the deforming force is removed, body returns to original size. •eg, a spring moving a distance when a mass is suspended from it •stiffness: the ratio of the applied force to the displacement •compliance: the inverse of stiffness card fld "Pascal" Blaise Pascal (1623-1662) French philospher and mathematician. Invented an adding machine, developed modern theory of probability, worked in field of hydrodynamics. •Physical unit, Pascal •Programming language card fld "Ambient" Ambient denotes "resting" or "initial" conditions, i.e., of the atmosphere which (usually) serves as the propagating medium… •The molecules of the atmosphere are uniformly distributed. Industrial Lectures Page 5 •Each molecule (particle) is connected to its neighbor. If one particle is disturbed, its neighbor is disturbed, as if they were connected by springs (i.e., elastic elements). Statistics about the atmosphere •The ambient density (ro) is… 1.21 kg/m^3 0.00121 gm/cm^3 •The ambient pressure is… 1 atmosphere (atm) 101,300 N/m^2 1,013,000 dyne/cm^2 14.7 psi 760 mm of Hg almost 30 inches of Hg •1 N/m^2 is 1 Pascal (Pa) •A Pascal is a relatively large unit. The softest sound we can hear is about 2*10^-5 Pa (0.00002 Pa), so units expressed in millionths of a Pascal are common (µPa) 2*10^-5 Pa = 20 µPa •Sound waves propagate as tiny fluctuations above and below atmospheric pressure •For example, the typical rms** pressure in average conversational level speech is about 0.036 Pa. ACL = 101,300 Pa ± 0.036 Pa **more about rms later •Fluctuations in atmospheric density (r) create fluctuations in pressure Pressure = r * c^2 •Fluctuations in atmospheric pressure (p) create fluctuations in sound intensity Intensity = p^2 / (ro* c) Industrial Lectures Page 6 card fld "Power" Sound Power •Power has the units of "Watts." is being used, or consumed. Power is the rate at which energy •1 Watt = 1 joule/s Sound Intensity •Intensity is measured in Watts/m^2. Intensity is the "rate at which energy is being radiated over a given surface area." Intensity = Power / m^2 Card number_____ 4 Card number_____ 5 card fld "Speed" The tine of the tuning fork moves to the right: •compressing the atmosphere (increasing density & pressure) pressure = r * c^2 Industrial Lectures Page 7 •when the tine moves to the left it expands or "rarefies" the atmosphere (decreasing density & pressure) •each molecule influences its neighbor •causing the area of compression (or rarefaction) to propagate away at the speed of sound, c Speed of sound is influenced only by the physical properties of the propagating medium (not by the characteristics of the vibrating body, such as frequency): •temperature -increased T increases c •density -increased density reduces c •elasticity -increased stiffness increases c •Generally, sound travels faster in solids, slower in liquids, slowest in gases -mainly due to differences in stiffness (not density) •At room temperature the speed of sound is about 344 m/s Sound waves are longitudinal •Each particle oscillates back & forth in the same direction that the wave travels; each particle… -moves very little -with a relatively small mean velocity Card number_____ 6 card fld "SHM" Simple harmonic motion… •Motion with one degree of freedom; repetitive, cyclical motion Examples… Industrial Lectures Page 8 •Tine of a tuning fork (produces a pure tone, a tone of a single frequency) •A swinging pendulum, a metronome, the pendulum on a cuckoo clock •A mass on the end of a spring •Beavis swinging a dead rat on a string about his head •The diaphragm of a headphone while its delivering a 1000 Hz tone during a hearing test •A spinning top, water swirling through a lavatory •The spinning wheel of a bicycle •The air inside your mouth while you are whistling Cycles, phase, period, frequency •After 1 complete cycle, the vibrations associated with SHM are repetitive, like going around a circle (0° to 360°) •Phase describes what part of the cycle the vibrating body is in… -or where in the cycle it begins, or -the difference between two bodies vibrating simultaneously •The duration of one complete cycle is defined as the period (T) -seconds -milliseconds (1000ths of a second) •Frequency (Hz, named after Heinrich Hertz) is defined as the number of cycles completed in 1.0 second (f) -Hz (cycles/sec) -kHz (1000nds of cycles/sec) Amplitude •Instantaneous amplitude is the displacement from the position of rest at any instant in time. •Peak amplitude (Ap) is the absolute value of the maximum deviation from the position of rest (to either the right or left, + or -). •Peak-to-peak amplitude (Ap-p) is the absolute value of the deviation between the maximum excursions (right to left, or + to ). Industrial Lectures Page 9 Card number_____ 7 card fld "Concepts" Harmonic Motion Stack •Illustrates SHM via a simple spring-mass system (a mass oscillating on the end of a spring) •Shows the linear projection of the SHM into a sine wave •Shows the analogy between projected SHM and circular motion — projected uniform circular motion •Describes why the waveform is called a sine wave — the anatomy of a triangle is defined. Oscilloscope Stack •This stack allows us to synthesize pure tones by defining the frequency, amplitude and phase. •We can define complex tones (i.e., sounds that have more than one frequency) •Illustrates how complex tones are built from simple tones by addition •Tones of the same frequency can be added, but phase is important -A 180° phase difference ("out of phase") causes cancellation. -A 0° phase difference ("in phase") causes reinforcement. •Periodicity, the repetitiveness of complex, periodic waves is illustrated. •Defines period and wavelength relative to the waveform •Describes the mathematical relationships between period, frequency, wavelength, and speed of sound •Defines peak amplitude (Ap), peak-to-peak amplitude (Ap-p), instantaneous amplitude (ai), and the rms amplitude (Arms) Industrial Lectures Page 10 •Defines the relationship between Ap and Arms. And… When complex sounds are composed of frequencies that bear simple numerical relationships to one another, the result is aesthetically pleasing. Nice visual and auditory patterns result, as in Leonardo da Vinci's ideas of beauty in symmetry. card fld "Ordinate" The ordinate of the graph can represent… •The instantaneous displacement of the vibrating body (relative to "0," its position of rest) •The corresponding changes in density, pressure, or intensity occurring in the propagating medium •A measured analog of these changes, like voltage on an oscilloscope) The abscissa of the graph, for example, when displaying density… •Can represent time. Changes in density occurring at a point in the atmosphere as a function of time (as the wave moves through). •Can represent distance. Strike the tuning fork, allow a few cycles to propagate, "freeze" time. Changes in density in the atmosphere can be plotted as a function of distance from the sound source. Card number_____ 8 Industrial Lectures Page 11 Card number_____ 9 Card number_____ 10 card fld "Info…" •A 10 volt peak sine wave delivered to a resistor, causes the resistor to generate heat (i.e., energy). •The same amount of heat would be generated by delivering a 7.07 volt dc signal to the same resistor. •The rms value measures the amount of energy contained within the signal. Card number_____ 11 Industrial Lectures Page 12 Card number_____ 12 card fld "Decibel" The decibel scale •Decibels are "dimensionless" units. In the process of calculating dB, the units cancel. So always specify the type of dB, i.e., dB SPL, dB IL, dB HL, etc. •All decibel scales have a reference. The reference defines what 0 dB is. The reference for the hearing level scale (dB HL) is the average sound pressure needed to reach threshold for normal hearing people. This pressure varies with frequency. •The reference for the SPL scale is… CGS MKS 0.0002 dyne/cm^2 2*10^-4 dyne/cm^2 0.00002 Pa 2*10^-5 Pa 20 µPa Note: These are the same pressures, just expressed in different units •The reference for the dB IL scale is… MKS 10^-12 Watt/m^2 Industrial Lectures Page 13 •A sound with a pressure of 20 µPa has an intensity of 10^-12 Watt/m^2. This means that the dB SPL for a sound will always equal its dB IL. Procedures for calculating decibels Sound pressure 1. Identify the sound pressure that you wish to convert to a sound pressure level. 2. Divide the pressure by the reference to obtain a ratio. the reference that has the same units. 3. Take the logarithm of the ratio. to get the dB SPL. Choose Multiply the logarithm by 20 Intensity 1. Identify the intensity that you wish to convert to an intensity level. 2. Divide the intensity by the reference (10^-12 Watt/m^2) to obtain a ratio. 3. Take the logarithm of the ratio. to get the dB IL. Multiply the logarithm by 10 Constant Proportions •Every time the pressure increases 10 times, the SPL increases by 20 dB. •Every time the sound pressure doubles, the SPL increases by 6 dB. •Every time the intensity increases 10 times, the IL increases by 10 dB. •Every time the intensity doubles, the IL increases by 3 dB. •Every time the sound pressure doubles, the intensity increases 4 times. The SPL increases by 6 dB, and the IL increases by 6 dB. Finding dB differences •You can find the dB difference between any two values, provided they have the same units. Industrial Lectures Page 14 •Example: What is the dB difference between a pure tone that has an Ap = 7 Volts, and one that has an Ap = 3.2 Volts? dB = 20*log( 7/3.2) = 6.8 dB Should I multiply by 10 or 20? •For pressure, force, voltage multiply the ratio by 20. •For intensity, power, energy multiply the ratio by 10. Card number_____ 13 Card number_____ 14 card fld "card field id 1" 0 Softest audible sound 10 Normal Breathing 20 Rustling leaves 30 Very soft whisper 40 Quiet residential community 50 Department store 60 Average speaking voice (65 dB) 70 Inside moving car 80 Loud music from radio 90 City traffic 100 Subway train 110 Loud thunder Industrial Lectures 120 130 140 180 Page 15 Amplified rock band Machine gun fire (close range) Jet engine at takeoff Space rocket at blastoff Card number_____ 15 card fld "Spectrum" The sound spectrum •The sound spectrum is… -a description of which frequencies are contained within a sound, and the dB level of each frequency -a plot of amplitude as a function of frequency (amplitude spectrum), phase is usually ignored •Given the waveform (a plot of amplitude as a function of time)… -the spectrum can be calculated using a mathematical procedure developed by Fourier -Fourier analysis, the FFT -the FFT converts the waveform into an amplitude spectrum -the inverse FFT converts the amplitude spectrum into the waveform •Spectrum analyzer: a device which determines and displays the spectrum of a sound Line spectrum •Complex periodic sounds are composed of discrete frequencies, their amplitudes can conveniently be graphed as lines Continuous spectrum •Complex aperiodic sounds are continuous in the frequency domain, they are graphed as a continuous spectrum Sonogram •The sonogram is useful for displaying sounds whose spectra change with time, such as speech Industrial Lectures Page 16 •The sonogram displays… -frequency along the ordinate -time along the abscissa -amplitude by the darkness (more intense) or lightness (less intense) of the display Card number_____ 16 Card number_____ 17 Card number_____ 18 Industrial Lectures Page 17 Card number_____ 19 card fld "Continuous" Noise… complex & aperiodic classified as continuous or impulse Continuous •steady state •fluctuating •intermittant Impulse •type A -Pmax (peak pressure) usually large -Tr relatively short -rapidly expanding gases •type B (impact) -Pmax lower -Tr longer -often contain more energy than type A -collision of two masses card fld "Noise" •Noise results from a vibrating body undergoing random motion. •The waveform is not repetitive; it is aperiodic. are present so noise is "complex and aperiodic." Many frequencies Industrial Lectures Page 18 •Completely random motion results in all frequencies being present at the same level (there are statistical fluctuations). -This is broad band noise, -white noise (by analogy with visible light), -Gaussian noise (the normal curve), -Thermal noise (from amplifying the random voltage fluctuations in a resistor) •Transient (temporally brief) sounds have a spectrum that is white. -clicks Card number_____ 20 Card number_____ 21 Card number_____ 22 Industrial Lectures Card number_____ 23 card fld "The Point" When you are in an environment that contains multiple sound sources, the overall SPL is determined primarily by the single source with the highest SPL. If you want to reduce the employee's exposure, identify the highest level source and eliminate it. Card number_____ 24 Card number_____ 25 card fld "card field id 1" Page 19 Industrial Lectures Page 20 A method for finding the total SPL resulting from the combination of two sources (A and B) 1. Identify a frequency from source A, display its waveform 2. Find the same frequency from source B 3. Add the two sine waves, taking into account amplitude and phase differences. Call the result p1 (p1 is the rms value of the pure tone that is the sum of the two waves). 4. pn Repeat #1 thru #3 for all frequencies. The result is p1 thru 5. Find the total sound pressure by summing p1 thru pn. pTotal. 6. Call it Find the dB SPL associated with pTotal. An alternative method 1. Find the intensity Ia associated with source A. 2. Find the intensity Ib associated with source B. 3. Find Itotal = Ia + Ib 4. Find the dB IL associated with Itotal Note: This method is much simpler. It simulates the process of combining all frequencies of complex sources. The procedure assumes: •There are many frequencies present •The average phase relationship is 90° The End Card number_____ 26 Industrial Lectures Page 21 Card number_____ 27 card fld "Dosimeters" Dosimeters… a lot like sound level meters •personal, wearable device •continuously samples the worker's environment (microphone on shoulder) •very useful when employee's exposure is -fluctuating, or intermittant -contains impulse noise •often has the capability to save samples -gives a time related profile (histogram) of worker's exposure -to identify "problem times" in the workday -accessible via personal computer •integrates dBA or dBC levels according to a formula •computes dose (and TWA), Leq •this information used in hearing conservation program Dosimeter 1 Dosimeter 2 Dosimeter 3 card fld "Ballistic" Industrial Lectures Page 22 •The fast and slow settings provide a more "sluggish" response to time varying sound, so the eye can follow the variations. •The fast setting has a time constant of 1/8 sec; the slow setting has a time constant of 1 sec. •For a rapid increase in dB level, the meter needle will reach 63%** of its steady state value in one time constant. The OSHA standard specifies dBA levels with a slow response. •Some SLMs have an impulse setting (rise time of 35 msec, decay time of 1.5 sec). This does not give the true peak SPL. ___________________________________ **The increase in amplitude (y) varies with time (t) according to: y = Yo*(1 - exp(-k*t)) where Yo is the steady state value, k is a constant, and k*t is the "time constant." For y/Yo = .63, k*t = 1. This is, coincidentally, the same formula for describing how TTS approaches ATS. Card number_____ 28 card fld "card field id 1" Frequency 50 63 80 100 125 160 200 A-Weight -30 -26 -22 -19 -16 -13 -11 C-Weight -1 -1 -1 0 0 0 0 Industrial Lectures 250 315 400 500 630 800 1000 1250 1600 2000 2500 3150 4000 5000 6300 8000 10000 Page 23 -9 -7 -5 -3 -2 -1 0 1 1 1 1 1 1 1 0 -1 -2 0 0 0 0 0 0 0 0 0 0 0 0 -1 -1 -2 -3 -4 Card number_____ 29 card fld "Filters" •The shape of the filter is given by its frequency response. Individual frequencies, all at the same level, are input to the filter. The output for each frequency is measured. The difference (dBout minus dBin) is plotted as a function of frequency. •The corner frequencies are defined as the "half-power" points, the output is 3 dB less than the input. f1 (or fl): low frequency cut-off f2 (or fh): high frequency cut-off fo (or fc): center frequency •The bandwidth (BW) is f2 - f1. 2. For an octave-band filter, f2/f1 = •The filter does not change the output frequency from what it was at the input or add additional frequencies. •The filter only changes the level (dB) of the frequency. Industrial Lectures Page 24 •The filter doesn't care what the absolute input level is or the absolute output level. It only controls the difference between the two. •Multiple frequencies at the input respond the same as if each were input individually. •A filter shapes the spectrum. If white noise was the input to the filter, the spectrum of the noise at the output of the filter would equal the frequency response of the filter. •By doing an octave-band analysis, you get an idea of where in the spectrum energy predominates. This could help with choosing engineering controls. Card number_____ 30 card fld "Bandwidth" Octave-band filters… •The bandwidth of each filter doubles as the center frequency of the filter doubles Consider the following experiment where white noise is being measured. The octave-band filter set of a SLM is set to 250 Hz. The octave band SPL is measured at 94 dB. •At a ◊at ◊at ◊at center frequency of 500 Hz, the octave band SPL is 97 dB 1000 Hz, 100 dB SPL 2000 Hz, 103 dB SPL 4000 Hz, 106 dB SPL •What is the overall level of the noise? level? What is the A-weighted •What would have been the result of this experiment if pink noise had been used? Card number_____ 31 Industrial Lectures Card number_____ 32 Card number_____ 33 card fld "Phon" Psychoacoustics •The study of our internal representation of external stimuli •Don't ask a guy who has been operating a jack hammer for 15 years — without HPDs — if he's exposed to loud noise. Loudness (phons & sones) Phon scale Page 25 Industrial Lectures Page 26 •Loudness level in phons (Lp) used for making relative loudness judgements √Compare loudness of a car horn to the loudness of a 1000 Hz tone, say 82 phon √Compare loudness of a door bell to the loudness of a 1000 Hz tone, say 63 phon √Compare loudness of a door bell to the loudness of a car horn (19 phon difference) •reference: A 1000 Hz tone at 40 dB SPL has a loudness level of 40 phons -a 57 dB SPL 1000 Hz tone = 57 phons -a 80 dB SPL 1000 Hz tone = 80 phons •Equal loudness contours (related to weighting networks on SLM) -The 80 phon contour, for example, shows all combinations of frequency/SPL judged to be equally loud -Loudness contours are like isobar maps used in meteorology, or elevation contours around mountains -The A-weight is a (inverse) 40 phon contour, the B-weight is a (inverse) 70 phon contour, the C-weight is a (inverse) 100 phon contour — approximately. -The C-weight is intended to provide a flat response from 25 to 8000 Hz •The 0 phon contour is usually described as the threshold sensitivity curve, assuming 0 dB SPL is threshold at 1000 Hz — but it isn't. •The 4.2 phon contour is approximately the threshold senstivity curve (binaural) in the sound field (MAF). The equivalent contour under headphone is the MAP curve. The MAP curve defines normal hearing and is used to calibrate audiometers. •One goal of a successful hearing aid fitting is to restore normal loudness perception for as large a frequency range as possible. card fld "Sone" Sones Industrial Lectures Page 27 •The sone scale is used for making absolute loudness judgements •The reference is… a 1000 Hz tone, 40 dB SL re: threshold for a normal hearing person has a loudness of 1 sone -SL is sensation level (the number of dB above threshold) •How does loudness change with SPL? -For every 10 dB increase in SPL the loudness doubles (approximately) ___________________________________ Loudness phons Loudness in sones Lp Ls ___________________________________ 20 0.25 30 0.5 40 1 50 2 60 4 70 8 80 16 90 32 100 64 Ls = 2^((Lp - 40)/10) •This is useful for performing a listening check of the calibration of an audiometer •Also notice how rapidly loudness is changing between 80 and 100 dB SPL (PEL = 90 dBA, AL = 85 dBA) Recruitment •Recruitment is usually described as an abnormal rate of loudness growth that is associated with cochlear pathology (i.e., damage to the hair cells) •For example, compare the results for a normal hearing person, a 40 dB HL conductive hearing loss, and a 40 dB HL cochlear hearing loss. Each person judges the tone to be equally loud Normal 80 dB HL Conductive 120 dB HL Cochlear 80 dB HL Industrial Lectures Page 28 •Ears with recruitment don't hear soft sounds very well, but hear more intense sounds normally -This makes it difficult to fit hearing aids. Amplification that makes the soft sounds audible makes the more intense sounds too loud. Card number_____ 34 card fld "Pitch" Pitch: the psychoacoustic analog of frequency •Pitch can be measured in units called "mels" •1000 mels is defined as the pitch associated with a 1000 Hz, 40 phon tone -a 2000 mel tone would be judged as being twice as high in pitch as the reference tone •Below pitch, -100 -500 1000 Hz there is a linear relationship between frequency and i.e. Hz ≈ 100 mels Hz ≈ 500 mels •Above 1000 Hz, the relationship is not linear -to increase the pitch of a 1000 Hz tone by a factor of 3 (3000 mels), the frequency must be increased to 9000 Hz) Card number_____ 35 Industrial Lectures Page 29 Card number_____ 36 card fld "card field id 1" Most Industrial noise exposures are: •red to pink to white, or "light blue" •riveting, chipping, planing, saws, steam or air hiss, grinders, welders, lathes, etc. So why is hearing loss usually localized to the octave band surrounding 4000 Hz? •For pure tone exposures, most of the hearing loss occurs about 1/2-octave above the stimulus frequency •Results are similar for complex stimuli, except there are more frequencies •The resonant characteristics of the external ear are primarily responsible for the 4 kHz notch Noise Control Techniques General principle: Energy flows most efficiently from one medium to another when the impedances of the two media are equal. So, reduce the efficiency of energy flow by making impedances unequal. √Source Control √Path Abatement √Receiver Abatement Industrial Lectures Page 30 Typical source control procedures: •maintenance •substitution of quieter machines/processes •check noise level specifications for new equipment •modify equipment •reducing vibration via damping material •decoupling vibrating equipment from surrounding structures •reducing fluid (or gas) flow noise (i.e., mufflers, reduce velocity) Path Abatement Procedures: •Sound absorbing material •Enclosures for equipment ◊reduced access to controls ◊generates heat •Segregate noisy operations from quiet •Barriers ◊reflections can increase other worker's exposures Receiver Abatement techniques: •HPDs (muffs, plugs, semi-aural) •Personal enclosures •Control rooms Card number_____ 37 card fld "Info…" Valsalva (Italian anatomist, 1666-1723) credited with dividing ear into 3 major divisions: •Outer (external): pinna & canal •Middle: eardrum, ossicles, middle ear spaces, Eustachian tube, middle ear muscles Industrial Lectures Page 31 •Inner ear: cochlea, vestibule, and semicircular canals Some points: •Outer ear/middle ear are the conductive portion of the system √funnels acoustic energy to drum √transduces acoustic energy to mechanical •Cochlear portion is the sensory system √Four rows of ≈3500 sensory cells (hair cells) each, over a distance of 35 mm √motion detectors, changing mechanical energy to electrical energy √an ADC •Vestibular system monitors linear and angular accelerations of the head √automatically controls eye movements, vestibulo-ocular reflex (VOR) √maintains posture (orientation relative to the gravitational field, while stationary or moving) √intense low frequency noise may produce vertigo Card number_____ 38 card fld "Info…" External Ear •Protective function √S-shaped curve keeps objects from directly hitting drum •External ear resonance √3.2 cm tube closed at one end √maximum of 17 dB at 2700 Hz √results in the 4 kHz notch (1/2 octave above 2700 Hz) •Cerumen √produced by apocrine and sebaceous glands located in cartilaginous portion of canal √dark and bitter tasting? √moistens and lubricates canal tissue Industrial Lectures Page 32 √probably has no insect repellent properties √normally externalized by TMJ movements, growth pattern of epidermis √motion of the condyle of the mandibule increases size of the anterior canal at the first bend, causes plugs to extrude •Otitis externa √accumulation of cerumen aggravated by HPDs (plugs defeat normal removal mechanism), increases moisture in canal √increased moisture, higher pH associated with fungal, bacterial infections √dirt, chemicals, etc. from hand while inserting can contribute to HPDs as a source of external otitis √surprisingly, external otitis and cerumenosis do not seem to be a major problem with industrial workers √earplugs seem to help with cerumen management Card number_____ 39 Card number_____ 40 Industrial Lectures Page 33 Card number_____ 41 card fld "Protocols" Audiometric Test Protocols •Ascending procedure (Hughson-Westlake) + the level is decreased by 10 dB - the level is increased by 5 dB •Descending procedure + the level is decreased by 5 dB - the level is increased by 10 dB •Combined procedure alternate between ascending/descending Threshold is defined as lowest level where tone is detected 50% of the time, on at least three presentations. card fld "Procedures" Audiometric Test Procedures •History AMA criteria for medical referral… ◊visible congenital, traumatic deformity ◊history active drainage (90 days) ◊sudden, rapidly progressive loss (90 days) ◊acute/chronic dizziness Industrial Lectures Page 34 ◊unilateral loss of sudden, recent onset (90 days) ◊ABG ≥ 15 dB @ 500, 1000, 2000 Hz ◊significant cerumen accumulation, foreign body ◊pain or discomfort •Otoscopic exam ◊collapsed canal ◊cerumenosis, foreign body ◊perforation ◊inflammation, anything abnormal •Patient instructions (before putting headphones on) ◊tell them what they will hear (tone) ◊emphasize that tones will be soft, they must listen carefully ◊they should guess if necessary ◊indicate how they should respond (press button, raise hand, or finger, anything unambiguous) •Headphone placement ◊remove eyeglasses, ear rings if large ◊red on RE, blue on LE (during testing, stop to check, you will eventually make an error) ◊allign cone of loudspeaker with canal ◊put cords in back of patient •Patient placement ◊at right angles so you can see them, they cannot see you ◊do not allow them to watch you, people can pick up subtle cues •Select an ear to test ◊test better ear, or ◊test RE (for consistency) ◊test all frequencies for ear before moving on to next ear •Select a frequency to test ◊begin at 1000 Hz ◊then 2000, 3000, 4000, 6000, 500 Hz ◊order of frequencies tested will not affect validity of threshold, but consistency will avoid errors •Present tone Industrial Lectures Page 35 ◊first tone should be clearly audible ◊40 dB HL, or higher (60, 80 dB) if no response ◊this presentation defines what you meant by "tone" in your instructions ◊their response validates that they understand instructions •Choose a protocol (Hughson-Westlake) ◊see "Protocols" button ◊particular protocol does not affect validity of threshold, but consistency will avoid errors •Duration of tone ◊present tone for 1 second (0.5 to 1.5 sec is OK) ◊longer presentations will create more false positives (believing a random response was really heard) •Response characteristics ◊note response latency, this varies with patient, but is usually less than 1 second ◊latency increases slightly as you get nearer to threshold, but ◊do NOT accept a response longer than the normal latency •Stupid tendencies we all have ◊when close to threshold, you present the tone longer, and push the button harder (to squeeze out a few extra dB?) ◊when close to threshold, you wait too long for a response, thereby increasing false positive responses •Faking a hearing loss (pseudohypacusis) Malingerers… ◊usually have something to gain (money, or attention) ◊often feign a unilateral hearing loss ◊often give a flat audiogram configuration ◊may respond inconsistently over a wide range of presentation levels ◊may respond to conversation better (or worse) than their "audiogram" indicates ◊may make an exaggerated show of effort at listening ◊you can often "smell them a mile away" Industrial Lectures Page 36 •Inconsistent responses ◊abnormal behavior can be related to drugs, alcohol, etc. ◊FM modulation of tone, or presenting 3 beeps (tell the patient to respond when you hear 3) can be useful when tinnitus interferes with audibility of tone ----The End---card fld "Audiometers" Microprocessor-Based Audiometers •Utilize software that simulates the decision making a human would go through when using the Hughson-Westlake protocol. •Sometimes the software gives up with inconsistent responses, and you must intervene manually. The audiometers have a manual mode. •You must carefully monitor the equipment and patient to make sure the results are valid. Sometimes the software can be fooled. •Most audiometers interface with a PC (via the RS232 serial port) for maintaining an audiometric database, facilitating recordkeeping. Automatic (Self-Recording) Audiometers •Automatic audiometers sometimes called "Békésy audiometers," after the first one developed. •Automatic audiometers have a servo-mechanism that automatically controls the dB HL of the tone… ◊When the patient response button is pressed, the signal decreases in level. When the button is released, the tone increases in level. ◊The patient is instructed to "press the button when you hear, release when you don't." ◊A pen records the level changes on an audiogram form. Disadvantages of Automatic Audiometers Industrial Lectures Page 37 •They cost as much as 4 times what a manual audiometer will cost, and there are more parts to go wrong. Microprocessor audiometers seem to be replacing automatic audiometers. •It is easier to malinger with an automatic audiometer. In one study of a plant with poor worker morale, Gosztonyi et al. (1971) found that whereas all office worker audiograms were judged valid, only 27% of the shop employees were judged valid. ◊Company performed self-recorded audiograms vs. audiologist performed manual ranged from -18 dB to 53 dB. ◊Manual and self-recorded audiograms performed by the audiologist differed by only 10 dB. •Automatic has difficulties with older employees, those with physical limitations, limited education, language barriers, those lacking attention or motivation (drugs & alcohol). •The idea that "it takes care of itself," ◊people with little training perform the test ◊noise levels are not monitored ◊patient motivation is not monitored ◊quality of the audiogram is not monitored, amplitude of tracings Advantages of Self Recording •Speed, you can test up to 4 employees at one time (maybe more), but ◊Manual is quicker for testing one employee •It is easier on the tester, less fatigue at end of day. less likely to take shortcuts. Examiner •Applied properly, a valid audiogram can be obtained either manually, or automatically. Card number_____ 42 card fld "About Patient…" Patient History •21 yr old male •Handgun Industrial Lectures Page 38 •Head injury 2x, MVA, coma Card number_____ 43 card fld "About Patient…" Audiogram of Ruben Gonzales, a virtuoso violinist who has played with the Chicago Symphony Orchestra •He has played for 30-35 years, 60+ hours per week with a powerful Bergonzi which previously was owned by Itzaac Pearlman •The 8 hour Leq = 105 dBA •From Killion, "The parvum bonum, plus melius fallacy in earplug selection." -ER-15 flat attenuation, musician's earplug Card number_____ 44 Card number_____ 45 Industrial Lectures Page 39 Card number_____ 46 Card number_____ 47 card fld "Info…" •The middle ear serves as an impedance matching device •The stapedius muscle offers limited protection from noise exposure •Otitis media is a common cause of middle ear pathology •Otosclerosis is a common cause of conductive hearing loss in early to middle adult life •Conductive hearing loss serves roughly the same function as a HPD Industrial Lectures Page 40 Card number_____ 48 card fld "Info…" Cochlear electrophysiology & mechanics (in brief) •The stria vascularis generates a +80 mV potential in scala media. ◊This is the cochlear energy source or "battery." •Scala media contains endolymph, a fluid rich in potassium ion, K+. •Motion of the stapes footplate delivers energy to the fluid of the inner ear. This initiates a traveling wave which propagates from the basal end of the organ of Corti towards the apical end. ◊See the traveling wave movie. •The wave crests after traveling a certain distance. Higher frequencies crest sooner (toward the base); lower frequencies travel further and crest more toward the apex. Each frequency "has its place" along the organ of Corti. ◊The central auditory nervous system "knows" which frequencies are present in the stimulus by the place being "touched" — much like our body's surface area is mapped onto the somatosensory cortex. •As the wave moves down the organ of Corti, a shearing force is created between the tectorial membrane and the reticular lamina. The shear is maximum at the crest and causes bending of the cilia of the outer and inner hair cells (OHCs and IHCs). •Bending the OHC cilia causes K+ to flow into the interior of the cell, depolarizing the cell, causing a length change (shortening) of the OHC. This effectively amplifies the sound, generates additional shearing force, causing increased bending of the IHC cilia. ◊Typical industrial noise exposures damage the OHCs and their stereocilia, causing less stimulation of the IHCs (i.e., bending of their cilia). ◊The mechanism of the damage is related to "mechanical stress" and/or "metabolic exhaustion." ◊Completely eliminating the OHC amplifier results in a 40 - 50 dB HL hearing loss. Industrial Lectures Page 41 •Bending IHC cilia causes K+ current to flow into the hair cell, releasing the neurotransmitter (glutamate) onto the dendrites of the neurons of the auditory nerve. Depolarization of the neurons sends afferent information to the central auditory nervous system. Card number_____ 49 Card number_____ 50 Card number_____ 51 Industrial Lectures Page 42 Card number_____ 52 Card number_____ 53 card fld "card field id 1" The Effects of Noise on Cochlear Physiology Metabolic Exhaustion: damage to hair cells & nerve endings •Inability to convert nutrients to energy to match biologic demands •Vasoconstriction of strial capillaries •Accumulation of waste products Mechanical stress: damage to hair cells (outer to inner) •Loss of ciliary stiffness •Fusion of cilia Industrial Lectures Page 43 •Cilia dissolving into cuticular plate, occasional formation of a giant cilium •Microfractures in cuticular plate allowing entrance of endolymph into fluid bathing hair cells •Swelling of hair cell •Extrusion of cytoplasm, destruction of hair cell •Hair cell missing, phalangeal scar •At high levels, rips & tears in organ of Corti, entire organ missing for large distances Card number_____ 54 Card number_____ 55 card fld "card field id 1" Hearing and Hearing Loss The ear is composed of three systems: •outer or external ear •middle ear •inner ear -contains hair cells which act as biologic transducers, converting mechanical to electrical energy: damaged from noise exposure NIHL is temporary and permanent •TTS: recovers in about 14 hours Industrial Lectures Page 44 •ATS: reached within about 6-8 hours, or sooner •PTS (NIPTS) -ATS approximates future PTS (5 to 10 years) NIHL is a sensorineural hearing loss; "nerve damge" •SN hearing loss is (with some execptions) not reversible •contrary to conductive lesions, it cannot be helped medically, or surgically -rehabilitation is the main option -the hearing aid •hearing aids offer much benefit, but there are limitations… •they do not simulate normal hearing in the same way that eyeglasses simulate normal vision •SN hearing loss is not just an attenuation, but a distortion •speech is audible, but loses clarity •hearing aids amplify speech, but also (unwanted) noise Estimating magnitude of damaging effect caused by noise •impairment…change in structure or function •handicap…disadvantage imposed by impairment on activities of everyday living •disability…loss in earning power The 25 dB HL fence…onset of material impairment •.5, 1, 2 KHz: AAOO, 5:1 weight for binaural -created for medico-legal purposes (compensation) –never intended for preventative purposes •.5, 1, 2, 3 KHz: AAO, 5:1 weight for binaural •1, 2, 3 KHz: NIOSH fence adopted by OSHA Effects of NIHL on speech perception •there is a difference between hearing and understanding speech •vowel sounds… lower frequencies •consonant sounds… higher frequencies •NIHL, by removing higher frequencies, reduces intelligibility of speech, not its audibility Other effects of hearing loss •depression, isolation, suspicion, withdrawal from social contacts •feelings of inadequacy, insecurity from constant misunderstanding Areas often mentioned •self •family •social •vocational Industrial Lectures Page 45 Ramsdell's psychological levels of hearing •symbolic… speech communication •warning… sounds signaling danger •primitive… fundamental attachment to real world Presbycusis… major variable confounded with noise exposure •hearing loss is a function of age •there is a gender effect, race effect •There are different types: strial, sensory, central •factors other than pure physiological aging may be confounded with presbycusis Exposure and Hearing Loss •Hearing loss builds rapidly and is almost complete within the first 10 years (5 years, actually) -protect people early •Hearing loss is a positively accelerated function of exposure level -increasing exposure by 5 dB (95 to 100 dBA) can produce 20 dB extra hearing loss Who is exposed, and at what levels? •over a third of the workers receive significant exposures (doses exceeding .5) •most people have exposures ≤ 100 dBA •Are HPDs capabable of providing protection? -yes and no, depending upon how they are used Card number_____ 56 card fld "The model" About the model… The buildup and decay of TTS at each frequency is calculated according to a combination (that I have made) of the mathematical models described by John Mills (The Effects of Noise on Hearing) and John Macrae (JSHR 34, 661-670, 1991). There is also an ISO standard 1999 which deals with this issue. Industrial Lectures Terms: L: Page 46 a frequency dependent level (dB SPL) that needs to be exceeded before TTS will occur: L= 500 Hz 93 dB 1000 Hz 2000 Hz 4000 Hz 89 dB 80 dB 75 dB (see note at end) SPL: ATS: the octave-band SPL for each frequency asymptotic threshold shift (dB) ATS = 1.7 * (SPL - L) T: TTS: the duration of the exposure (or post exposure) in hours temporary threshold shift (dB) at a frequency. The ear begins with normal hearing (0 dB HL) a constant used for calculating buildup of TTS= 0.476 where T is duration of exposure in hours: TTS = ATS * (1 - exp(-k1 * T) a constant used for calculating recovery of TTS= 0.141 where T is duration following exposure in hours: TTS = ATS * exp(-k2 * T) k1: k2: HTL: the threshold for an ear with pre-existing hearing loss, and also exposure to noise (dB HL). HTL, as calculated, represents the hearing loss that occurs from a combination of noise exposure and pre-existing hearing loss NIPTS: the noise induced permanent threshold shift (estimated by using calculated TTS) SNHL: pre-existing sensorineural hearing loss (dB HL) P: a power used in calculating HTL= 0.15 HTL = 10*LOG( ( (10^(NIPTS/10))^P + (10^(SNHL/10))^P - 1)^1/P) Note… •The model predicting TTS is essentially the one developed by Mills. I have substituted Mills values for L with those given by Macrae. •The method for calculating HTL is from Macrae. I use TTS in place of NIPTS when calculating HTL. •With regard to the relationship between TTS and NIPTS. I assume that, very nearly, one can substitute "years of exposure" for "hours of exposure" and use TTS to predict NIPTS. The ATS is essentially NIPTS after 10 years of exposure. ------The End------ Industrial Lectures Card number_____ 57 Card number_____ 58 card fld "Info…" To compute binaural hearing loss… Let BE = %HL for better ear PE = %HL for poorer ear BHL= binaural hearing loss BHL = (BE*5 + PE)/6 If BE is 50% and PE is 100% then BHL = (50*5 + 100)/6 = 58.33% Card number_____ 59 Page 47 Industrial Lectures Card number_____ 60 Card number_____ 61 Card number_____ 62 Page 48 Industrial Lectures Card number_____ 63 Card number_____ 64 Card number_____ 65 Page 49 Industrial Lectures Card number_____ 66 Card number_____ 67 Card number_____ 68 Page 50 Industrial Lectures Card number_____ 69 Card number_____ 70 Card number_____ 71 Page 51 Industrial Lectures Page 52 Card number_____ 72 card fld "1910.95" 1910.95 - Occupational noise exposure. * Standard Number: 1910.95 * Standard Title: Occupational noise exposure. * SubPart Number: G * SubPart Title: Occupational Health and Environmental Control Produced by USDOL OSHA - Directorate of Safety Standards & Directorate of Health Standards Maintained by USDOL OSHA - OCIS -----------------------------------------------------------------(a) Protection against the effects of noise exposure shall be provided when the sound levels exceed those shown in Table G-16 when measured on the A scale of a standard sound level meter at slow response. When noise levels are determined by octave band analysis, the equivalent A-weighted sound level may be determined as follows: FIGURE G-9 - Equivalent A-Weighted Sound Level (Figure G-9 is not shown, see card "Weighting Networks") Equivalent sound level contours. Octave band sound pressure levels may be converted to the equivalent A-weighted sound level by plotting them on this graph and noting the A-weighted sound level corresponding to the point of highest penetration into the sound level contours. This equivalent A-weighted sound level, which may Industrial Lectures Page 53 differ from the actual A-weighted sound level of the noise, is used to determine exposure limits from Table 1.G-16. ..1910.95(b) (b)(1) When employees are subjected to sound exceeding those listed in Table G-16, feasible administrative or engineering controls shall be utilized. If such controls fail to reduce sound levels within the levels of Table G-16, personal protective equipment shall be provided and used to reduce sound levels within the levels of the table. (2) If the variations in noise level involve maxima at intervals of 1 second or less, it is to be considered continuous. TABLE G-16 - PERMISSIBLE NOISE EXPOSURES (1) ______________________________________________________________ | Duration per day, hours | Sound level dBA slow response ____________________________|_________________________________ | 8...........................| 90 6...........................| 92 4...........................| 95 3...........................| 97 2...........................| 100 1 1/2 ......................| 102 1...........................| 105 1/2 ........................| 110 1/4 or less................| 115 ____________________________|________________________________ Footnote(1) When the daily noise exposure is composed of two or more periods of noise exposure of different levels, their combined effect should be considered, rather than the individual effect of each. If the sum of the following fractions: C(1)/T(1) + C(2)/T(2) C(n)/T(n) exceeds unity, then, the mixed exposure should be considered to exceed the limit value. Cn indicates the total time of exposure at a specified noise level, and Tn indicates the total time of exposure permitted at that level. Exposure to impulsive or impact noise should not exceed 140 dB peak sound pressure level. ..1910.95(c) (c) "Hearing conservation program." (1) The employer shall administer a continuing, effective hearing conservation program, as described in paragraphs (c) through (o) of this section, whenever employee noise exposures equal or exceed an 8-hour time-weighted average sound level (TWA) of 85 decibels measured on the A scale (slow response) or, equivalently, a dose of fifty percent. For purposes of the hearing conservation program, employee noise exposures shall be computed in accordance with appendix A and Table Industrial Lectures Page 54 G-16a, and without regard to any attenuation provided by the use of personal protective equipment. (2) For purposes of paragraphs (c) through (n) of this section, an 8-hour time-weighted average of 85 decibels or a dose of fifty percent shall also be referred to as the action level. (d) "Monitoring." (1) When information indicates that any employee's exposure may equal or exceed an 8-hour time-weighted average of 85 decibels, the employer shall develop and implement a monitoring program. (i) The sampling strategy shall be designed to identify employees for inclusion in the hearing conservation program and to enable the proper selection of hearing protectors. ..1910.95(d)(1)(ii) (ii) Where circumstances such as high worker mobility, significant variations in sound level, or a significant component of impulse noise make area monitoring generally inappropriate, the employer shall use representative personal sampling to comply with the monitoring requirements of this paragraph unless the employer can show that area sampling produces equivalent results. (2)(i) All continuous, intermittent and impulsive sound levels from 80 decibels to 130 decibels shall be integrated into the noise measurements. (ii) Instruments used to measure employee noise exposure shall be calibrated to ensure measurement accuracy. (3) Monitoring shall be repeated whenever a change in production, process, equipment or controls increases noise exposures to the extent that: (i) Additional employees may be exposed at or above the action level; or (ii) The attenuation provided by hearing protectors being used by employees may be rendered inadequate to meet the requirements of paragraph (j) of this section. ..1910.95(e) (e) "Employee notification." The employer shall notify each employee exposed at or above an 8-hour time-weighted average of 85 decibels of the results of the monitoring. (f) "Observation of monitoring." The employer shall provide affected employees or their representatives with an opportunity to observe any noise measurements conducted pursuant to this section. (g) "Audiometric testing program." (1) The employer shall establish and maintain an audiometric testing program as provided in this paragraph by making audiometric testing available to all employees Industrial Lectures Page 55 whose exposures equal or exceed an 8-hour time-weighted average of 85 decibels. (2) The program shall be provided at no cost to employees. (3) Audiometric tests shall be performed by a licensed or certified audiologist, otolaryngologist, or other physician, or by a technician who is certified by the Council of Accreditation in Occupational Hearing Conservation, or who has satisfactorily demonstrated competence in administering audiometric examinations, obtaining valid audiograms, and properly using, maintaining and checking calibration and proper functioning of the audiometers being used. A technician who operates microprocessor audiometers does not need to be certified. A technician who performs audiometric tests must be responsible to an audiologist, otolaryngologist or physician. ..1910.95(g)(4) (4) All audiograms obtained pursuant to this section shall meet the requirements of Appendix C: "Audiometric Measuring Instruments." (5) "Baseline audiogram." (i) Within 6 months of an employee's first exposure at or above the action level, the employer shall establish a valid baseline audiogram against which subsequent audiograms can be compared. (ii) "Mobile test van exception." Where mobile test vans are used to meet the audiometric testing obligation, the employer shall obtain a valid baseline audiogram within 1 year of an employee's first exposure at or above the action level. Where baseline audiograms are obtained more than 6 months after the employee's first exposure at or above the action level, employees shall wearing hearing protectors for any period exceeding six months after first exposure until the baseline audiogram is obtained. (iii) Testing to establish a baseline audiogram shall be preceded by at least 14 hours without exposure to workplace noise. Hearing protectors may be used as a substitute for the requirement that baseline audiograms be preceded by 14 hours without exposure to workplace noise. (iv) The employer shall notify employees of the need to avoid high levels of non-occupational noise exposure during the 14-hour period immediately preceding the audiometric examination. ..1910.95(g)(6) (6) "Annual audiogram." At least annually after obtaining the baseline audiogram, the employer shall obtain a new audiogram for each employee exposed at or above an 8-hour time-weighted average of 85 decibels. (7) "Evaluation of audiogram." (i) Each employee's annual audiogram shall be compared to that employee's baseline audiogram to determine if the audiogram is valid and if a standard threshold shift as defined in paragraph (g)(10) of this section has occurred. Industrial Lectures This comparison may be done by a audiogram shows that an employee shift, the employer may obtain a the results of the retest as the Page 56 technician. (ii) If the annual has suffered a standard threshold retest within 30 days and consider annual audiogram. (iii) The audiologist, otolaryngologist, or physician shall review problem audiograms and shall determine whether there is a need for further evaluation. The employer shall provide to the person performing this evaluation the following information: (A) A copy of the requirements for hearing conservation as set forth in paragraphs (c) through (n) of this section; (B) The baseline audiogram and most recent audiogram of the employee to be evaluated; ..1910.95(g)(7)(iii)(C) (C) Measurements of background sound pressure levels in the audiometric test room as required in Appendix D: Audiometric Test Rooms. (D) Records of audiometer calibrations required by paragraph (h)(5) of this section. (8) "Follow-up procedures." (i) If a comparison of the annual audiogram to the baseline audiogram indicates a standard threshold shift as defined in paragraph (g)(10) of this section has occurred, the employee shall be informed of this fact in writing, within 21 days of the determination. (ii) Unless a physician determines that the standard threshold shift is not work related or aggravated by occupational noise exposure, the employer shall ensure that the following steps are taken when a standard threshold shift occurs: (A) Employees not using hearing protectors shall be fitted with hearing protectors, trained in their use and care, and required to use them. (B) Employees already using hearing protectors shall be refitted and retrained in the use of hearing protectors and provided with hearing protectors offering greater attenuation if necessary. (C) The employee shall be referred for a clinical audiological evaluation or an otological examination, as appropriate, if additional testing is necessary or if the employer suspects that a medical pathology of the ear is caused or aggravated by the wearing of hearing protectors. ..1910.95(g)(8)(ii)(D) (D) The employee is informed of the need for an otological examination if a medical pathology of the ear that is unrelated to the use of hearing protectors is suspected. (iii) If subsequent audiometric testing of an employee whose exposure to noise is less than an 8-hour TWA of 90 decibels indicates that a standard threshold shift is not persistent, the employer: Industrial Lectures Page 57 (A) Shall inform the employee of the new audiometric interpretation; and (B) May discontinue the required use of hearing protectors for that employee. (9) "Revised baseline." An annual audiogram may be substituted for the baseline audiogram when, in the judgment of the audiologist, otolaryngologist or physician who is evaluating the audiogram: (i) The standard threshold shift revealed by the audiogram is persistent; or (ii) The hearing threshold shown in the annual audiogram indicates significant improvement over the baseline audiogram. (10) "Standard threshold shift." (i) As used in this section, a standard threshold shift is a change in hearing threshold relative to the baseline audiogram of an average of 10 dB or more at 2000, 3000, and 4000 Hz in either ear. ..1910.95(g)(10)(ii) (ii) In determining whether a standard threshold shift has occurred, allowance may be made for the contribution of aging (presbycusis) to the change in hearing level by correcting the annual audiogram according to the procedure described in Appendix F: "Calculation and Application of Age Correction to Audiograms." (h) "Audiometric test requirements." (1) Audiometric tests shall be pure tone, air conduction, hearing threshold examinations, with test frequencies including as a minimum 500, 1000, 2000, 3000, 4000, and 6000 Hz. Tests at each frequency shall be taken separately for each ear. (2) Audiometric tests shall be conducted with audiometers (including microprocessor audiometers) that meet the specifications of, and are maintained and used in accordance with, American National Standard Specification for Audiometers, S3.6-1969. (3) Pulsed-tone and self-recording audiometers, if used, shall meet the requirements specified in Appendix C: "Audiometric Measuring Instruments." (4) Audiometric examinations shall be administered in a room meeting the requirements listed in Appendix D: "Audiometric Test Rooms." (5) "Audiometer calibration." {i} The functional operation of the audiometer shall be checked before each day's use by testing a person with known, stable hearing thresholds, and by listening to the audiometer's output to make sure that the output is free from distorted or unwanted sounds. Deviations of 10 decibels or greater require an acoustic calibration. [Image] ..1910.95(h)(5)(ii) {ii} Audiometer calibration shall be checked acoustically at least annually in accordance with Appendix E: "Acoustic Calibration of Audiometers." Test frequencies below 500 Hz and above 6000 Hz may Industrial Lectures Page 58 be omitted from this check. Deviations of 15 decibels or greater require an exhaustive calibration. {iii} An exhaustive calibration shall be performed at least every two years in accordance with sections 4.1.2; 4.1.3.; 4.1.4.3; 4.2; 4.4.1; 4.4.2; 4.4.3; and 4.5 of the American National Standard Specification for Audiometers, S3.6-1969. Test frequencies below 500 Hz and above 6000 Hz may be omitted from this calibration. (i) "Hearing protectors." (1) Employers shall make hearing protectors available to all employees exposed to an 8-hour timeweighted average of 85 decibels or greater at no cost to the employees. Hearing protectors shall be replaced as necessary. (2) Employers shall ensure that hearing protectors are worn: (i) By an employee who is required by paragraph (b)(1) of this section to wear personal protective equipment; and (ii) By any employee who is exposed to an 8-hour time-weighted average of 85 decibels or greater, and who: ..1910.95(i)(2)(ii)(A) (A) Has not yet had a baseline audiogram established pursuant to paragraph (g)(5)(ii); or (B) Has experienced a standard threshold shift. (3) Employees shall be given the opportunity to select their hearing protectors from a variety of suitable hearing protectors provided by the employer. (4) The employer shall provide training in the use and care of all hearing protectors provided to employees. (5) The employer shall ensure proper initial fitting and supervise the correct use of all hearing protectors. (j) "Hearing protector attenuation." (1) The employer shall evaluate hearing protector attenuation for the specific noise environments in which the protector will be used. The employer shall use one of the evaluation methods described in Appendix B: "Methods for Estimating the Adequacy of Hearing Protection Attenuation." (2) Hearing protectors must attenuate employee exposure at least to an 8-hour time-weighted average of 90 decibels as required by paragraph (b) of this section. ..1910.95(j)(3) (3) For employees who have experienced a standard threshold shift, hearing protectors must attenuate employee exposure to an 8-hour time-weighted average of 85 decibels or below. (4) The adequacy of hearing protector attenuation shall be reevaluated whenever employee noise exposures increase to the extent that the hearing protectors provided may no longer provide adequate Industrial Lectures Page 59 attenuation. The employer shall provide more effective hearing protectors where necessary. (k) "Training program." (1) The employer shall institute a training program for all employees who are exposed to noise at or above an 8-hour time-weighted average of 85 decibels, and shall ensure employee participation in such program. (2) The training program shall be repeated annually for each employee included in the hearing conservation program. Information provided in the training program shall be updated to be consistent with changes in protective equipment and work processes. (3) The employer shall ensure that each employee is informed of the following: (i) The effects of noise on hearing; ..1910.95(k)(3)(ii) (ii) The purpose of hearing protectors, the advantages, disadvantages, and attenuation of various types, and instructions on selection, fitting, use, and care; and (iii) The purpose of audiometric testing, and an explanation of the test procedures. (l) "Access to information and training materials." (1) The employer shall make available to affected employees or their representatives copies of this standard and shall also post a copy in the workplace. (2) The employer shall provide to affected employees any informational materials pertaining to the standard that are supplied to the employer by the Assistant Secretary. (3) The employer shall provide, upon request, all materials related to the employer's training and education program pertaining to this standard to the Assistant Secretary and the Director. (m) "Recordkeeping" - (1) "Exposure measurements." The employer shall maintain an accurate record of all employee exposure measurements required by paragraph (d) of this section. (2) "Audiometric tests." (i) The employer shall retain all employee audiometric test records obtained pursuant to paragraph (g) of this section: ..1910.95(m)(2)(ii) (ii) This record shall include: (A) Name and job classification of the employee; (B) Date of the audiogram; (C) The examiner's name; (D) Date of the last acoustic or exhaustive calibration of the audiometer; and (E) Employee's most recent noise exposure assessment. Industrial Lectures Page 60 (F) The employer shall maintain accurate records of the measurements of the background sound pressure levels in audiometric test rooms. (3) "Record retention." The employer shall retain records required in this paragraph (m) for at least the following periods. (i) Noise exposure measurement records shall be retained for two years. (ii) Audiometric test records shall be retained for the duration of the affected employee's employment. (4) "Access to records." All records required by this section shall be provided upon request to employees, former employees, representatives designated by the individual employee, and the Assistant Secretary. The provisions of 29 CFR 1910.20 (a)-(e) and (g)-(i) apply to access to records under this section. ..1910.95(m)(5) (5) "Transfer of records." If the employer ceases to do business, the employer shall transfer to the successor employer all records required to be maintained by this section, and the successor employer shall retain them for the remainder of the period prescribed in paragraph (m)(3) of this section. (n) "Appendices." (1) Appendices A, B, C, D, and E to this section are incorporated as part of this section and the contents of these appendices are mandatory. (2) Appendices F and G to this section are informational and are not intended to create any additional obligations not otherwise imposed or to detract from any existing obligations. (o) "Exemptions." Paragraphs (c) through (n) of this section shall not apply to employers engaged in oil and gas well drilling and servicing operations. (p) "Startup date." Baseline audiograms required by paragraph (g) of this section shall be completed by March 1, 1984. (Approved by the Office of Management and Budget under control number 1218-0048) card fld "STS" From Federal Register 2-2-96 (c.) Hearing loss. Employers would record any work-related case resulting in an average shift of15 decibels or more at 2000, 3000 and 4000 hertz in one or both ears as measured from the employee's original baseline established under 29 CFR Part 1910.95 Occupational Noise Exposure. The hearing test may be adjusted for aging and the recorded case may be removed if a retest performed within 30 days does not confirm the original shift. A presumption Industrial Lectures Page 61 of work-relatedness is used for hearing loss occurring to employees covered by the Occupational Noise Exposure standard, i.e. those who are exposed to noise levels in excess of an 85 dB 8 hour time weighted average. The lowest action level in the noise standard is an average shift of 10 decibels or more at 2000, 3000 and 4000 hertz. OSHA is proposing the 15 decibel criteria for recordkeeping purposes to account for variations in the reliability of individual audiometric testing results. OSHA asks for input on which level of a shift in hearing should be used as a recording criteria; 10 decibels? 20 decibels? 25 decibels? For each level, what baseline should be used? Preemployment (original) baseline? Audiometric zero? Is adjusting for presbycusis appropriate? Card number_____ 73 card fld "card field id 1" 1935 •Congress passes the Walsh-Healey Public Contracts Act •DOL now has authority to impose regulations on companies having contracts with the federal government 1969 •DOL issues a standard requiring noise exposures to be limited to 90 dBA, or less •Engineering controls, feasible administrative controls must be employed. •HPDs used as a last resort 1970 •Occupational Safety and Health Act passed by congress 1971 •Walsh-Healey noise standard becomes OSHA standard 29 CFR 1910.95 (a)-(b) 1981 Industrial Lectures Page 62 •Hearing Conservation Amendment to standard was issued: 29 CFR 1910.95 (c)-(p) •this outlined an effective hearing conservation program •"January version" of the standard 1981 •in August, due to industry lobbying, an administrative stay was issued on several paragraphs (and portions of paragraphs) of the standard •"August version" of the standard 1983 •In March the final rule went into effect •"March version" of the standard 1984 •November 8, 1984 the United States Court of Appeals for the Fourth Circuit issued an opinion in the Forging Industries Association and National Arborist Association v. Secretary of Labor vacating the hearing conservation ammendment Allegations: •OSHA had exceeded its authority √hearing loss is an effect or result, not a hazard; therefore OSHA cannot regulate it √the standard requires the employer to take action when the cause may not have been in the workplace •December 28, 1984 DOL petitioned for a rehearing and eventually the ammendment was reinstated ------The End?-----Card number_____ 74 Industrial Lectures Page 63 January 1981 (Original) Version 29 CFR 1910.95, March 1983 a) same as original adopted in May of 1969 a) Permissable Exposure Limit (PEL) •TWA of 90 with a 5 dB timeintensity trade; Dose = 1 •See next card for sample calculations •Impulses shall not exceed 140 dB peak pressure. Otherwise impulse noise is integrated into the dose same as other noise. (b) same (b)(1) Controls •when PEL is exceeded, "feasible" engineering or administrative controls shall be utilized •exposure reduced to ≤ PEL •when controls fail, use HPDs (b)(2) Fluctuations •when time interval between successive peaks is ≤ 1 sec, it's continuous noise (c) same (c) Hearing Conservation Program Industrial Lectures Page 64 •provided (free) for all employees with exposures exceeding action level (AL) •TWA = 85 (Dose= .5) (d) major compromises •used to have an initial determination (d) Monitoring (1) Do it when "any information" indicates exposures exceed AL •more precise definition of how to sample, how to use SLM or dosimeter •a "sampling strategy" should identify employees with significant exposures √help in selecting HPDs •area monitoring is Ok •use personal (dosimeter) measurements when area sampling in not appropriate √fluctuating noise levels √high worker mobility •all sound between 80-130 dBA should be included in exposure •no precise statements for calibrating dosimeters/SLMs •all equipment used in taking exposure measurements should be calibrated •no time limit within which monitoring has to be done, used to be 60 days •repeat monitoring when there is a change that could √increase number of employees exposed ≥ AL √render HPDs inadequate •no provisions for repeat monitoring, used to be every 2 years •goal is to obtain an exposure measurement for each employee (e) similar (e) Employee Notification •employer must notify each employee exposed to levels ≥ AL (f) similar (f) Observation of Monitoring •employee, or their representative can observe Industrial Lectures Page 65 monitoring (g) major changes (g) Audiometric Test Program (1) for all exceeding AL (2) no cost (3) tests performed by •licensed/certified audiologist •ENT, other physician •certified technician •anyone who has demonstrated competency √audiometric testing √calibration (4) audiometer must meet appendix C requirements •specifications for selfrecording audiometers •baseline had to be taken within 4 months (5) Baseline audiogram •obtained within 6 months of first exposure ≥ AL •no exemption for van •obtained within 1 year if using mobile van √HPDs used for last 6 months •HPDs were no substitute for quiet •preceded by 14 hours of "no exposure to workplace noise" √HPDs may substitute for quiet √employer must tell employee to avoid non-occupational noise (6) Annual audiogram •for each employee ≥ AL •STS was "significant" not "standard" •audiologist/ENT/physician had to evaluate audiograms for STS (7) Evaluate audiograms for STS •the technician can do this •if STS the employer can redo audiogram within 30 days •audiologist/ENT/physician shall review "problem" audiograms Industrial Lectures Page 66 √copy of 29 √baseline & √background √audiometer records CFR 1910.95 annual audio noise levels calibration (8) Follow-up regarding STS. •notify employee in writing (21 days) -->If STS, (assuming a physician has not determined it to be non-work related) •fit employee with HPD •train them in their use & care •they are required to use HPD •already using HPD? √re-train √re-fit, perhaps with HPD with greater attenuation •possible medical pathology? √refer for ENT evaluation, or √audiologic evaluation √even if unrelated to HPD use, or occupational exposure •STS was "permanent" not "persistent" (9) Revise baseline when •STS is persistent, or •hearing has improved •used to have objective criteria for baseline revision •audiologist/ENT/physician should make subjective decision •STS used to have a more stringent definition, especially as hearing became poorer •You don't have to report STS until it is ≥ 15 dB (10) Standard threshold shift •STS exists when annual changes ≥10 dB (relative to baseline) for (2K + 3K + 4K)/3 (h) same except for quiet environment (h) Audiometric test requirements (1) minimum frequencies .5, 1, 2, 3, 4, 6 kHz •you can correct for presbycusis using appendix F Industrial Lectures •used to use ANSI standard, now too much background noise is allowed Page 67 (2) ANSI S3.6-1969 (3) appendix C (self-recording) (4) Quiet test environment, appendix D (5) How often to calibrate? •biologically, daily, with a stable hearing person, deviations ≥ 10 dB then do acoustic calibration •acoustic calibration annually √SPL (audiometric zero) √linearity if deviations ≥ 15 dB then do exhaustive calibration •exhaustive calibration every 2 years √complete ANSI calibration (i) same, basically •used to require warning signs where TWA = 85, HPDs required (i) Hearing protectors •for everyone who wants one, regardless of exposure (no cost) •employer ensures they are worn by √everyone ≥ PEL √all who ≥ AL if -STS been documented -waiting for the van (baseline) •employee has a the right to a choice in selecting HPD •employer must ensure √HPDs worn properly √employee trained in use & care (j) same (j) HPD attenuation •estimated A-weighted TWA = TWA - (NRR - 7) = TWA (C-weighted) - NRR Industrial Lectures Page 68 •reduce exposure to: √PEL, or √AL if STS exists •re-evaluate HPD if dose changes (k) different •used to have to include a lot more, almost too much (k) Training program •all people in HCP •repeated annually •areas covered √effects of noise on hearing √purpose of HPDs, advantage, disadvantages, attenuation of various types, instructions on selecting, fitting, use & care √purpose of audiometric testing (l) same •they eliminated a paragraph requiring posting warning signs √AL exceeded √PEL exceeded √HPDs required (l) Access to information & training materials •the employer should make copies of standard available, post in workplace •make available anything supplied by assistant secretary •assistant secretary can have access to your training materials (m) similar, but •details of how exposure measurement were taken are not included, used to have to keep track of who the representative individual was •most records had to be retained longer √audiograms, employment duration plus 5 years (m) Recordkeeping •all exposure measures (2 years) •audiograms (keep for duration of employment) including √date √examiner's name √date of last calibration √employees last noise exposure √background noise levels •access to records by employee, former employee, his representative, asst. secretary Industrial Lectures Page 69 (n) similar, left out a horrendous one dealing with SLM sampling strategies, fine with me (n) Appendicees •mandatory √exposure computation √HPD attenuation √audiometers √test room √acoustic calibration •informational √presbycusis √monitoring noise levels (o) no oil & gas exemptions (o) Exemptions •oil & well drilling/servicing (p) startup date had to change (p) Startup date •baseline audiograms completed by March 1, 1984 ------The End------ card fld "Table G-16" Table G-16 — Permissable Noise Exposures. Duration per day, 8 . . . . . . . . 6 . . . . . . . . 4 . . . . . . . . 3 . . . . . . . . 2 . . . . . . . . 1.5 . . . . . . . 1 . . . . . . . . 1/2 . . . . . . . 1/4 or less . . . hours . . . . . . . . . . . . . . . . . . . . . . . . . . . Card number_____ 75 Sound Level, dBA slow response . . . 90 . . . 92 . . . 95 . . . 97 . . . 100 . . . 102 . . . 105 . . . 110 . . . 115 ------The End------ Industrial Lectures Page 70 Card number_____ 76 Card number_____ 77 card fld "Standards" All the standards define what is meant by "normal hearing," audiometric zero (0 dB HL), or RETSPL (reference equivalent threshold SPL) Industrial Lectures Page 71 •The ASA-1951 standard was based upon a US Department of Public Health survery (late 1930s). It describes hearing of the "typical man on the street." Test booths were set up at state and county fairs. ◊geographically diverse ◊people of different ages, gender ◊may have included individuals with ear pathology, noise exposure ◊testing environment was not optimal (noisy) •The ISO-1964 standard was a "laboratory standard." compiled from European and US researchers. Results were ◊Young (18-24 yo), otologically normal adults. ◊Well-defined test protocols ◊Quiet conditions •ANSI-1969 standard is the ISO-1964 standard using a different set of headphones (TDH-39 vs. WE 705A). Current revision is ANSI-1996. Points: •Hearing is about 10 dB better using ANSI-1969 as compared to the ASA-1951 standard. A 30 dB HL threshold (ANSI-1969) is a 20 dB HL threshold (ASA-1951). •Some compensation laws reference the older standard, reducing the magnitude of hearing loss. Card number_____ 78 Industrial Lectures Card number_____ 79 Card number_____ 80 Card number_____ 81 Card number_____ 82 Page 72 Industrial Lectures Card number_____ 83 Page 73