Noise Exposure & Hearing Conservation Exam 1
Occupational noise can be any sound in any work environment. A textbook definition of sound is
"a rapid variation of atmospheric pressure caused by some disturbance of the air." Sound propagates as a wave of positive pressure disturbances (compressions) and negative pressure disturbances (rarefactions)
Question: Event 1- 100 dBA 2 hours Event 2- 97 dBA 6 hours Event 3- 91 dBA 7 hours Calculate the noise dose using OSHA and NIOSH criteria?
(2/2) + (6/3) + (7/7) x 100 = 400% OSHA (2/0.25) + (6/.50) + (7/2) x 100 = 2,350% NIOSH If it exceeds 100 it is hazardous (numbers from reference chart in slides)
There are 5 cardiovascular risk factors increasing noise susceptibility by altering blood flow in it
- H/o Coronary disease - Elevated BP - Elevated serum cholesterol - Elevated serum triglycerides - Elevated 2 hr glucose tolerance test
Example of Summation of Noise
-1 machine registers at 80 dB -Bring in second machine that registers at 80 dB -Will register a 3 dB increase in intensity -83 dB for both machines -Add a 3rd machine at 80 dB compare to the 83 dB. -Difference between two old machines and the new machine is 83-80 = 3. B/c the difference is 3 we will use an increase of 2 dB for the new machine. -Total dB level for all 3 machines is 85 dB 1 machine makes 100 dB. Another machines makes 100 dB. This will be 103. Another machine makes 100. It will be 105. 4 machines and they all make 100 dB of noise. 100 100 100 100 103 103 106
Summation of noise rules:
-2 sounds of equal intensity are put together +Increase in 3 dB intensity -2 sounds differ by 0-1 dB +Increase in 3 dB intensity 2 sounds differ by 2-3 dB +Increase in 2 dB intensity 2 sound differ by 4-7 dB +Increase in 1 dB intensity 2 sound differ >8 dB +The intensity difference will not count +The higher of the 2 will only register.
Hyperacusis & Uncomfortable loudness levels
-40% of the individuals with hyperacusis have positive occupational noise exposure history. -Serious impact on everyday like if the patient has ULL below 70 dB. -Important to identify workers with low ULLs and provide necessary support.
Acoustic Reflex Decay
-A tone presented for 10 sec. at 10 dB above ART. -Magnitude of AR either remains same or decreased over 10 sec. period. -Magnitude of reflex decreased by ≥ 50% during 10 sec. period -> Positive reflex decay (retrocochlear pathology)
The 6 major auditory effects of excessive noise exposure are;
-Acoustic Trauma -Tinnitus -Temporary Threshold Shift (TTS) -Permanent Threshold Shift (PTS) -Diplacusis (double hearing, echo. Inaccurate understanding of the pitch) -Hyperacusis (excessively sensitive hearing)
Neural Changes
-Afferent nerve fibers. -Excessive noise exposure causes IHCs to release high amounts of glutamate (excitatory neurotransmitter) into the synapses of type I fibers of the auditory nerve. -High concentration of glutamate at these synapses overstimulate the glutamate receptors on the post-synaptic cells. -Swelling and rupturing of post synaptic cell bodies and dendrites-> "Glutamate excitotoxicity" (more than required)
Audiometry
-Air Conduction Thresholds; -250-8000 kHz, mid octaves if thresholds at two adjacent octaves differ by 20 db.
NOISE DOSE:
-Amount of noise exposure experienced by the worker relative to the amount of exposure. -Noise exposure presented in PERCENTAGE. -Noise dose =C1/T1+C2/T2+C3/T3+C4/T4+⋯⋯+Cn/Tn ×100 Cn -> total time of noise exposure at specified levels Tn -> Allowable duration or reference duration above which noise exposure is hazardous
Gender:
-Animals studies -> among older CBA mice, males show higher thresholds (i.e., more AHL) than females Hearing sensitivity deteriorates more than twice as fast in men as in women at most ages and frequencies
Noise characteristics in general
-Audible -Erratic or randomness -Undesired or unwanted
Tinnitus Evaluation
-Case history -Assessment of impact of tinnitus and coping strategies. -Pitch and loudness matching (pitch and loudness matching. Present different sounds at different frequencies, ask them to match to their tinnitus. We can estimate the loudness and the frequency. Tinnitus is more prevalent in industrial workers).
Factors that affect measurements
-Changes in Temperature (heat) -Electromagnetic Field (electronic device used) -Person changes their routine (the shift changes)
Types of Noise
-Constant Continuous Sound +Type of Source: Pumps, electric mixers, gunshots, conveyors -Constant but intermittent Sound +Type of Source: air compressor, automatic machinery during a work cycle -Periodically fluctuating sound +Type of Source: mass production, surface grinding -Fluctuating non-periodic sound +Type of Source: manual work, grinding, welding, component assembly -Repeated impulses +Type of Source:automatic press, pneumatic drill, riveting -Single impulse +Type of Source: hammer blow, material handling, punch press, gunshot, artillery fire
Purpose of Noise/Sound level measurements
-Determine if noise levels meet or exceed regulatory standards. -Evaluate the threat to worker's safety and hearing. -Determine areas that are hazardous. -Identify workers who are exposed to hazardous noise. -Collect data for legal proceedings and workers' compensation. -Collect data for determine need for hearing conservation program. -Determine if hearing protection is necessary and the type of hearing protection. -Monitor noise changes within the environment. -Collect data to support development of engineering controls. -Test machines or equipment components to determine compliance with particular specifications. The manufacturer should have tested the noise produced -Research interaction of noise exposure with other exposures -Collect data on signal and speech perception and annoyance problems. -Quantify interior levels of audiometric booths.
Auditory Processing Skills Assessment in Industrial Workers Cont.
-Dichotic speech processing -> Dichotic digit -Workers exposed to chronic solvents -> poor performance in free recall dichotic digit task -Temporal Resolution -> GDT (gap detection tests) -Temporal order judgement -Workers exposed to chronic solvents -> poor performance in RGDT , pitch pattern sequence test -Temporal processing speed
Effect of frequency
-Effect of frequency composition of noise on site of lesion. -Noise comprised of high frequencies selectively damages basal portion of organ of Corti, while low frequency noise preferentially affects apical portion of organ of Corti. -Critical level of noise exposure = beyond a particular point, the damage becomes mechanical -Mechanism of damage shifts from metabolic to mechanical once noise level exceeds critical level
CSE
-Excessive exposure to solvents can cause Chronic Solvent Encephalopathy. -Symptoms of CSE: +Mild to severe cognitive impairment +Sleep difficulties +Diffuse pain -Studies showed association between dosage of solvent exposure and performance on task which requires attention and psychomotor speed.
Organic Solvents
-Exposure through alcohol, paints, adhesives, heating, and automotive fuels. -Chronic exposure to solvents -> pulmonary edema, damage to central and peripheral nervous system, liver & kidney failure, and cancer. -Solvent exposure increases the chances of HFHL. -Exposure to jet fuel increases the chances of SNHL when it is combined to noise exposure in the first 12 years of exposure.
Slow vs. Fast response
-For an abrupt increase in sound level -> SLM takes certain amount of time to respond. -> TIME CONSTANT. (Time needed to reach 63% of eventual max. reading). Two types of response: SLOW RESPONSE & FAST RESPONSE SLOW RESPONSE: time constant of 1 second. (it will take 1 second for the device to realize there is a change) Average out sound fluctuation -> easy to read. FAST RESPONSE: time constant of 0.125 sec. (1/8 of a second) Good for evaluating the variability of sound -> fluctuating readings on display make it difficult to determine the overall level. Use fast response
ROS
-Free radicals can cause damage to cells but they also play an important role in a number of important biological processes like intracellular killing of bacteria by white blood cells and some cell signaling processes. -If membranous layer is compromised/damaged then the ions can easily go in and out of the cell. This will eventually damage the HCs. -Reactive oxygen species (ROS) are oxygen based free radicals, which includes superoxide anion, O-2 , the hydroxyl radical .OH , peroxynitrite (ONOO-) and hydrogen peroxide H2O2. -Excessive noise exposure -> Calcium overload in mitochondria -> more production of nitric oxide and ROS.
Notched Audiogram
-HCs in the regions of 3-6 kHz are more vulnerable to damage from noise than those tuned to lower and higher frequencies -Thus, hearing thresholds gets affected at 3-6 KHz frequencies first. -Hearing thresholds reach max. between 3-6 kHz and then returned toward normal level at high frequencies. -A notched audiogram + positive history of noise exposure has been gradually accepted as clinical sign of NIHL
ABR
-Hearing loss resulting from noise exposure reflects damage or dysfunction of the cochlea, specially in the region of frequencies from about 3KHz to 6KHz. -Characteristic pattern for pure-tone audiometry in patients with chronic noise exposure or acoustic trauma is a 'notch' in the audiogram in the region of 4KHz. -Due to high frequency hearing loss, wave I may not be closely observed unless the ABR is recorded with ECochG type electrodes. -This eliminates the opportunity for Wave I-III, III-V and I-V analysis. -Some etiologies for NIHL such as acoustic trauma for one ear -> increase in interaural latencies and this can complicate the results. -Latency-intensity function for Vth peak is steep compared to normal slopes i.e., latency values are prolonged at low levels and approach normal values at high intensities.
Audiometric Tonal Thresholds in Nonorganic Hearing Loss Cases
-High variability in ascending and descending trials. -More than 10 dB of threshold differences during repeat testing. Check 1 kHz on repeat testing then one more frequency. -Absence of false positive and higher false negative -BC thresholds worse than AC thresholds -Absence of Shadow responses for unmasked thresholds in the impaired ear.
ROS cont.
-Higher free radicals and ROS -> breakdown lipid molecules located in membranes of outer hair cells, which affects channels of the cellular membrane. The channels allow for entry of Ca+ ions. -Lipid breakdown (lipid peroxidation) -> alter membrane permeability -> more influx of Ca+ in noise traumatized HCs. -OHC swelling and ultimately necrotic cell death. -Increased concentrations of ROS from noise exposure is not limited to OHCs. It can affect stria vascularis and structures in stria media. - Yamane reported elevation in superoxide levels in marginal cells of stria vascularis along with empty strial capillaries.
Noise Control Things to consider: •Spectral analysis of the noise
-In order to provide proper noise control we must know the spectral content of the sound source --This is why we perform an octave-band analysis
Cause of Pseudohypacusis
-Increased benefits before retirement. -Way of avoiding obligations or hiding failure. -Shock of being thrust in the strict military regimen.
Dosimeter
-Integrates noise samples over time. -Averages noise in discrete period of times and sums up all those averages to give to give a total. -Can be set at any parameters. -For OSHA compliance -> A weighting, 5 dB exchange rate, 80 dB criterion threshold, slow response. -For NIOSH compliance -> it is a 3 dB exchange rate -Good for personal noise exposure measurements. -Area sound exposure measurements is also possible. One mic at a ear, one at the collar, which is more accurate? Ear
Pre-existing HL
-It does increase the susceptibility in some individual whereas in some it does not. •People with impaired hearing prior to noise exposure show reduced TTS than those with normal hearing. Conductive hearing loss serves as ear protector thus reducing the amount of noise reaching the cochlea. • People with SNHL also show less TTS than those with normal hearing . This may be because, the existing permanent HL reduces the no. of sensory cells available to experience the adverse effect of noise The conductive hearing loss attenuates sound to the cochlea. If less amount of sound is reaching the cochlea, there is less damage
Disadvantages of dosimeter over slm
-Limited accuracy (type I/2 dependent). -Susceptible to nonintentional or intentional errors that may influence readings. -Body shielding may affect measurements. -Calibration may drift out of adjustment over long measurement periods. -Inaccurate measurement for impulse or impact noise.
Ways to reduce noise
-Make the machine quieter -barrier between the listeners and machines -Listener modification (hearing protection)
Phon lines
-Measure of loudness judgment -Analyzing persons perception of loudness -Compare loudness at different frequencies. -Phon is a unit of loudness level. 10 kHZ, is close to 93 -Is it possible to compare loudness at 40 and 60 phon. We cannot estimate, the purpose of phon scale was to show loudness is different than the physical unit. It is possible the physical unit might change, but they say the same equal loudness
Theory
-Measure stress hormone levels before and after noise exposure -May be able to determine who would be more likely to have NIHL
Smile example in slides
-Need pad under the vibrating machine to make it better -It is not realistic that the worker can be in an isolating chamber for all labor positions, but some could use the chamber to work at a lower level -Acoustic enclosure around the machine to reduce noise and vibration helps
Different Notch Definitions
-Niskar et al (2001) definition: The audiometric configuration should satisfy these three criteria: + Hearing threshold level values at 500 Hz and 1 kHz should be ≤15 dB HL, + The maximum threshold value at 3, 4, or 6 kHz should be at least 15 dB HL higher than the highest (poorest) threshold value for 0.5 and 1 kHz, and -Hearing threshold value at 8 kHz should be 10 dB better than the worst threshold at 3, 4, or 6 kHz. -Dobie & Rabinowitz (2002) refer to their NIHL definition as the Notch Index (NI), which is calculated by deducting the mean threshold of 2, 3, and 4 kHz from the mean threshold of 1 and 8 kHz. NI> 5 dB indicates the presence of a notch. -Coles, Lutman & Buffin (2000) defined a high-frequency notch as "the hearing threshold level (HTL) at 3 and/or 4 and/or 6kHz, is at least 10 dB greater than at 1 or 2 kHz and at 6 or 8 kHz. -McBride & Williams (2001) definition +Narrow or 'V' shape notch: only one frequency in depth of notch and depth is at least 15 dB. +Wide or 'U' shaped notch: more than one frequency in depth of the notch, depth of 20 dB, Threshold better by 20 dB at high frequency end.
Ototoxic Medications
-Noise exposed workers + ototoxic medication -> ? -HL due to ototoxic drugs begins at HF and then spreads to lower frequencies contingent upon duration drug ingestion. -Noise exposure+ opium -> increased chances of HL -Some individual are more susceptible to develop HL due to opioid abuse. -Dose and duration of treatment -> presence and degree of HL
Study
-Noorhashim, Kaga, & Nishimura (1996) examined relationship between pure-tone audiometry results and the auditory brainstem response wave abnormalities in 22 subjects (44 ears) with permanent threshold shift. -PTA were average thresholds in 3 different ways: 0.5 kHz, 1 kHz, and 2 kHz (PTA1); 2 kHz and 4 kHz (PTA2); and 4 kHz (PTA3) Results: Abnormal ABR wave patterns were detected in 72.7% of the ears. -prolonged ABR wave latencyà 20.5%, absent early wavesà 18.2%, prolong interpeak wave I-V latencyà21.1%. -Normal ABRs were recorded in 27.3% of the ears despite marked thresholds elevation of the PTA at high frequencies
Special features of SLM
-Octave band analyzer (Function: break down broad band noise into different frequency bands and see which are contributing the most. Establish noise controllers. If the high or low freq. noise is contributing the most) -Sound intensity analyzers
Interaction of Ototoxins and Noise
-Ototoxins+ Noise exposure -> worsening of hearing. -Industrial setup: Important to evaluate the interaction of work related ototoxic substances and noise exposure. -The interaction could be synergistic (exponential) or additive. (linear) -Additive effects -> predictable, obtained by adding effects of exposure to noise and toxins. -Synergistic effects are greater than additive effects
Asphyxiants
-Oxidative stress -Excessive glutamate release at the synapses of IHCs due to exposure to asphyxiants -Critical exposure level 200 ppm -CO poisoning -> SNHL (partial or full recovery) -Group of workers at risk? Coal miners, fire fighters
Sones
-Phon curves show -> equally loud relationships among different sounds. -Not adequate to show how loudness is related to intensity -We need a scale of loudness as a function of intensity. -Sone scale (Stevens, 1975): Expresses loudness as ratio. -Sone is a unit of loudness 1 sone is equal to 40 phons, 2 sone is equal to 50 sones, 4 sones is 60 phons, 8 sones is equal to 70 phons As they double, it goes up in 10 phons!!
Auditory Processing Skills Assessment in Industrial Workers
-Poor auditory processing skills in workers who are exposed to solvents -Patient reporting exposure to ototoxic substances/solvents -> possibility of damage to central auditory system -> use auditory processing test battery.
Word rec. scores
-Presentation level 40 dB above SRT. -Sometimes considered in awarding workers' compensation. (sometimes needed in report) -Better WRS and poorer AC thresholds -> does not make sense if PTA is 80 and they have 100% WRS
Stenger test
-Principle: 2 tones of same frequency are presented simultaneously to both ears, and only the tone with higher sensation level is perceived. -A difference of minimum 20 dB between the ears to be able to administer tonal or speech stenger test. Procedure: -Tone of desired frequency in better ear at 10 dB above threshold and 10 dB below threshold in poor ear. -If the loss is genuine? -> STENGER NEGATIVE - STENGER POSITIVE -A positive result on stenger test do not identify true hearing thresholds. -Way of obtaining threshold information -> Minimum Contralateral interference Level (MCIL). -MCIL should be within 20 dB of true thresholds.
4. Oxidative Stress in Cochlea
-Production of free radicals -> byproduct of normal metabolic process. -Electron transport chain is an important part of metabolic process occurring within HCs. -Free radicals has unpaired electron which makes them highly reactive with other molecule. They are searching for something to reactive with because of the unpaired electron -The antioxidant system neutralizes the harmful effects of free radicals. -Increased production of free radicals due to noise exposure -> ? -High Levels of ROS aren't necessarily bad in all cases
Applications of acoustic reflex tests
-RCP; Elevated ARTs, absent ARTs, and positive reflex decay. -Auditory neuropathy; Often absent -Nonorganic hearing loss (Pseudohypacusis): ARTs within 85- 100 dB HL (faking it because of the presence of the reflex)
3. Changes in Blood Flow
-Reduced blood flow in cochlea due to noise exposure. -Amount of reduction in blood flow depend on intensity and duration. -Ischemic effect -Ischemia reduces the cochlear oxygen supply -> the phosphorylation process in mitochondria becomes more inefficient -> increase production of reactive oxygen species (ROS)
ASSR
-Relies on peak detection of amplitude and phases of response. -Elicited by amplitude or frequency modulated tones and usually measured in nano volts. -Multiple hertz ASSR technique allows evaluation of multiple frequencies simultaneously. (4) -Useful in Pseudohypacusis. -Mean difference in ASSR thresholds and behavioral thresholds can vary from 15 to 1 dB. (can get objectively, but reliability is not great)
Some ways of designing quiet machines are as follows:
-Selecting nonmetallic (e.g., plastic) materials -Adjusting the shape, thickness, and size of components to avoid resonance peaks -Damping vibrations through insertion of joints -Reducing the height of fall of parts -Regulating the flow of compressed air exhaust -Selecting power transmission that permits the quietest speed regulation (e.g., rotation-speed-controlled electric motors) -Including effective cooling flanges that reduce the need for air jet cooling and related noise -Reducing speeds gently between forward and reverse movements -Enclosing especially noisy parts of the machine -Providing proper transmission loss and seals for doors for machines
Advantages of Dosimeter over SLM
-Simple procedure -> Single unit of exposure (less than, equal to, or greater than PELs). -The device works well in varying noise levels. -The person making the determination of noise level need not be present during the whole measurement period. -The unit handles multiple determinations concurrently. -Cost effective.
•Selection of effective vibration isolator depends on following factors;
-Size and weight of machine •Sound spectra •Environmental conditions (some environments are not good for rubber- may get degraded quickly) •Selection of wrong vibration isolator not only be ineffective but may amplify the force vibration transmitted.
Acoustic Reflex Testing
-Softest stimulus level that cause minimal recordable change in ME admittance -> Acoutic reflex threshold. -ART should be established at 500, 1000, and 2000 Hz at 226 Hz probe tone. -ARTs can also be established using broadband stimuli and HF probe tones.
Pseudohypacusis/ Nonorganic Hearing Loss
-Some patient indicates a deficits in hearing which is greater than hearing loss due to an expected pathology -In certain situations -> Nonorganic HL superimposed on existing organic HL (realizes the hearing loss is not bad enough) -Higher prevalence of pseudohypacusis in industrial workers. -8% industrial workers who are applying for compensation had excessively high thresholds -34 % of medicolegal cases of industrial workers may exaggerate HL (sometimes from accidents, will dramatize)
•Attenuation provided by acoustic enclosure depends on following factors:
-Sound absorption coefficient of materials used in construction of machines. It varies from 0 to 1. It can also greater than 1 depending on mounting techniques (NIOSH, 1980). •Noise reduction Coefficient (NRC): Indicates overall ability to absorb noise. Arithmetic average of sound absorption coefficients at 250, 500, 1000, and 2000 Hz. •Tightness of seals. Isolation of enclosure from the equipment.
Does this loss of auditory nerve fibers exist in humans?
-Stamper & Johnson (2015) reported significant correlation between noise exposure background and ABR wave I amplitude at suprathreshold levels recorded using a mastoid electrode (p=0.015). Conducted with students -Bramhall et al. (2016) found reduced suprathreshold ABR wave I amplitude in veterans and non veterans reporting high noise exposure history than veterans and non veterans reporting low noise exposure. -Some studies have shown no association. The audiologist community is divided. Some believe the loss of somatic ribbons exist in humans (hidden hearing loss - not evident on audiogram or DPOAE, only on ABR at high levels) -The auditory nerve fibers get effected first, then the HC get effected with noise exposure. -Speech perception in noise ability may be reduced in those with NIHL history and lower ABR wave I
OAE
-Studies show that small duration of post exposure causes an SOAE to become extinct. -TEOAE and DPOAE are very sensitive to degeneration of normal hearing. -DPOAE can cover large range of frequencies by holding the primary levels and frequency ratio constant. -Probst (1993) found significant changes in amplitude of high frequency components of TEOAE even before damage could be detected with PTA. -In some industrial workers, TEOAEs can be absent in presence of normal hearing thresholds due to subclinical cochlear damage -Significant reduction id DPOAEs observed in half octave bands centered at 1.4 to 6 kHz following a 30 min. MP3 player music exposure 85 dBC in young adults in without any changes in hearing thresholds. -Hence, OAEs becomes an early indicator of NIHL and they are absent even when the hearing loss is not evident on the audiogram. -This makes OAE an integral part of early detection in NIHL. -Presence of OAEs in presence of AC thresholds above 50-60 dB HL -> presence of non-organic hearing loss
Ototoxin
-Substances which can cause HL. -Ototoxins can be classified into following categories +Asphyxiants (CO) (effects oxygen consumption, carbon monoxide) +Drugs (antibiotics, chemotherapeutic agents, aspirin, and loop diuretics) +Metals (Arsenic, organic tin, mercury, and manganese) +Solvents (Ethylbenzene, n-propylbenzene, toluene, styrene and methylstyrenes, trichloroethylene, p-xylene, ethyl benzene, and carbon disulfide).
Head phone issues in AC testing
-TDH 39, TDH 39P earphones & thresholds at 6 K -Presence of standing waves -> poor test-retest reliability and higher threshold at 6 kHz -Thresholds at 6 kHz can be worse by 6 dB when calibrated on the IE 303 coupler, compared with those obtained with TDH39 P earphones calibrated on IEC318 coupler. -Circumaural headphones are more reliable the supra-aural head phones. (try and use inserts when testing for noise induced)
TIME WEIGHTED AVERAGE (TWA)
-TWA always averages the sampled sound over an 8-hour period. -Calculation of overall exposure by considering different exposure levels over various duration during an exposure period. -Eight hour time weighted average Ltwa(8) = (Q/Log10(2)) * [Log10(D/100)] + LC = (Q/0.3) * [Log10(D/100)] + LC
Noise characteristics relevant to hearing
-Temporal Pattern -Level -Frequency -Overall Duration
Inverse square law
-The amount of intensity drops by one over the square of the change in distance. -Doubling of distance -> level of sound drops by 6 dB -Why it happens? Entire environment is a sphere, as the sound travels it is divided into a large area, it will decrease intensity in the different areas, this continues as the sound propagates from the sound source I = (P /4 pi r 2) The energy twice as far from the source is spread over four times the area, hence one fourth the intensity. I was standing at 40 m and then I was at 10 m. It is 16 x larger (I * 4^2) I was standing 10 m from the source then I was 20 m away so it decreases by 1/4 (I/(2^2))
Lavg (or LAVG)
-The average sound level measured over the run time of measurement. -The average does not include any sound below the threshold. -Sound is measured in the logarithmic scale of decibels, So......... -When averaging decibels, short duration of high levels can significantly contribute to the average level.
Conclusion
-The mechanism of NIHL is complex. -NIHL physiology is Multifaceted. -The mechanical, metabolic, and neural changes due to NIHL rarely occurs separately.
TIME WEIGHTED AVERAGE (TWA) cont. (in dB) -If a worker works in an environment with a steady noise level of 90 dB for 8 hrs, then what will be the TWA?
-This average starts at zero and grows. It is less than the Lavg for a duration of less than 8 hours, is exactly equal to the Lavg at 8 hours, and grows higher than the Lavg after 8 hours 90 = TWA
Otoscopy
-To examine ear canal & TM. -To confirm that ear canal is free from cerumen. -To check for condition like ear canal collapse.
Tympanometry
-To rule out any middle ear pathologies. -In presence of findings indicating reduced TM movement, TM perforation/rupture, acoustic reflex cannot be conducted. -In case of abnormal tympanogram: OAE results needs to interpreted with caution (OAE-echoes produced by the outer hair cells, DPOAE or TEOAE from sound. SPOAE - not from sound. The sound will not transfer to or from the cochlea and the responses may be affected by the blockage (minimized or eliminated).
Trying to solve problems with noise
-Try to fix the root of the problem -Then, use sound absorbing materials
The European Union Directive has established lower exposure action values of LEX, 8h = 80 dBA and peaks of 135 dB peak SPL, upper exposure action values of LEX,8h = 85 dBA and 137 peak SPL, and exposure limit values of LEX,8h = 87 dBA and 140 dB peak SPL. The Union requires elimination or reduction of noise exposure at the source by using all available technical resources. Some of the specified means of noise reduction are as follows:
-Use of alternative working methods that lead to less noise exposure -Provision of alternative work equipment with least possible noise emission -Restructuring the layout and design of work-places and work stations -Training workers in the appropriate use of equipment aimed at reducing noise exposure -Using methods such as shields, enclosures, and sound-absorbent materials to reduce airborne noise -Using methods such as damping and isolation to minimize structure-borne noise -Adequate maintenance of work equipment, the workplace, and workplace systems -Scheduling work to reduce the duration and intensity of exposure, including adequate rest periods
Speech reception threshold
-Usually within 8-10 dB of pure tone avg. of 500, 1000, and 2000 Hz. -Audiogram with steep slope -> SRT similar to average of 500 and 1000 Hz. -Workers with nonorganic hearing loss -> PTA-SRT difference more than 12 dB. -Pseudohypacusis; SRT using ascending procedure provides largest difference between SRT and PTA
One should not diagnose NIHL by just seeing the notch in the audiogram; Other causes of 4 KHz notch
-Viral infections -Skull trauma -Hereditary (genetic) hearing loss -Acoustic Neuroma -Sudden Hearing Loss -Multiple Sclerosis -Ototoxicity
Noise monitoring is necessary when:
-Workers complain of decreased hearing or tinnitus; -Employees report sounds to be too loud; -Employees are unable to carry on conversations without speaking loudly or shouting; -Loud sounds come from specific machines; and -Informal/formal measures suggest hazardous noise levels.
Leq
-represents a value known as Equivalent Continuous Sound Level. -Sound pressure level (SPL) varies in amplitude over time -An imaginary constant SPL that would produce the same energy as the fluctuating sound level you are measuring over a given time interval. -Says average of the fluctuating sound. Imaginary to tell you at what value it would have the same emphasis as the fluctuating sound
sts calculation
1. Calculate average threshold for current audiogram. 2. Calculate average threshold for baseline. 3. Subtract the two. If >10 dB there has been a STS.
INDIVIDUAL'S VARIABILITY IN SUSCEPTIBILITY OF NOISE There are 4 major factors:
1. Constitutional factors 2. Physiological factors 3. External factors 4. Miscellaneous factors
Bohne, Harding, and Lee (2006) identified three death pathways of OHCs in noise- exposed cochleas of chinchillas:
1. Oncotic death pathway -> swollen, pale staining cell with swollen nucleus 2. Apoptotic death -> Shrunken, dark staining cell with pyknotic nucleus (i.e. a degenerative condition of nucleus marked by clumping of chromosomes, hyperchromatism, and shrinking of nucleus) 3. A pathway characterized by cells with absent basolateral plasma membranes and a nucleus lacking in nucleoplasm.
Mechanical Changes
1. Reticular Lamina: -Damaged reticular lamina due to excessive noise exposure -> excessive influx of K+ into OHCs. -Excess influx of K+ leads to acute swelling of OHC and consequently results in apoptotic or necrotic OHC death 2. Plasma Membrane -Plays an important role in cell-cell adhesion, maintenance of intracellular homeostasis, and extra and intracellular communication. -Excessive motion of BM during noise exposure -> stretching injury/rupture to plasma membrane. OHC can change their length. 3. Stereocilia of OHCs and IHCs -Sterocilia remain in their shape from tip links connecting them together. The transduction channel is located in the sterocilia. -Noise exposure affects the permeability of protein transduction channels in the cell membrane covering the stereocilia -Morphological changes in stereocilia after noise exposure includes fused, bent, collapsed, and even missing stereocilia. -Loss of contact between stereocilia of OHCs and tectorial membrane) which results in loss of hearing sensitivity. The ionic fluid is also effected. -The stereocilia of the inner hair cells are free floating and the stereocilia of the outer hair cells are embedded -What is the role of stereocilia in TTS and recovery from TTS? After noise exposure, the stereocillia may be bent and the fused stereocilia may start functioning normally after awhile. 4. Pillar cells -High level continuous and impulse noise damages pillar cells -Loss of pillar cells affects local impedance of vibration of the organ of Corti. Loss of pillar cells may also trigger loss of OHCs. 5. Hair cells -Extent of HC damage depends on intensity and duration of exposure -HC damage in TTS and PTS are different -TTS -> increase in size and number of lysosomes and enlarged nuclei -> Swollen OHCs -PTS -> Severe HCs death
Procedures:
1.Notify the workers 2.Calibration 3.Instruct workers 4.Dosimeter 5. SLM Some say noise level measurements should be calculated in presence of workers or absence of workers. With workers there they will absorb some sound. Without it is a base level
•Loudest sound we can tolerate is .. million times larger than the softest one than can be heard.
10
•According to WHO, ...% of world population is exposed to hazardous sound levels that could cause NIHL. •Each day ... million US workers go to work in damaging noise •Approximately ... million US workers are exposed to hazardous noise levels at their work each year. •Approximately .... cases of occupational HL were reported in 2007 in USA. Amount of money spent annually on compensation for hearing loss disability
10 4 22 23000 $242 million
Log10 (10^2) Log10 (10^3)
2 3
Pairs of numbers with 2:1 ratio Linear vs. Logarithmic
2/1 Linear: 1 Logarithmic: 0.3 8/4 Linear: 4 Logarithmic: 0.3 20/10 Linear: 10 Logarithmic: 0.3 100/50 Linear: 50 Logarithmic: 0.3
Noise, or unwanted sound, is one of the most common occupational hazards in American workplaces. The National Institute for Occupational Safety and Health (NIOSH) estimates that .... workers in the United States are exposed to hazardous noise. Exposure to high levels of noise may cause hearing loss, create physical and psychological stress, reduce productivity, interfere with communication, and contribute to accidents and injuries by making it difficult to hear warning signals.
30 million
34 to 37 that is 3 dB apart so we add 2 to the highest number so.. 34 to 39 that is 5 dB apart so we add 1 to the highest number so.. 39 to 40 is 1 dB apart so we add 3 to the highest so...
39 40 43 DO THIS INSTEAD OF EQUATION
Table 2 CHABA Criteria
5 dB exchange rate and the pel is 90 SPL at 8 hours
NIOSH's sound level parameters
80 to 140 dBA, recommended exposure limit is 85 dBA. No protected or unprotected exposure to any sounds above 140 dBA
Permissible Exposure level of NIOSH
85
•The results of the study confirmed ... dBA as critical noise level for worker's exposure on a daily basis over a prolong period of time.
90
Fill in the blanks: OSHA uses a criterion level of ___ dB, a threshold level of 80 dB, and an exchange rate of ___ dB. An OSHA 100% noise dose is __ dB for 8 hours, 95 dB for __ hours, 100 dB for ____ hours. NIOSH: criterion level of __ dB, a threshold level of 80 dB, and an exchange rate of __ dB. A NIOSH 100% noise dose is ___ dB for 8 hours, ___ dB for 4 hours, 91 dB for___ hours,
90 5 90 4 2 85 3 85 88 2
OSHA's sound level parameters
90 to 140 dBA (levels above 90 dBA TWA require noise controls and hearing protection)
•One machine in a room creates sound measured to be 95 dB. What will be the predicted sound level if one more identical machine starts working in the same space?
95 + (10log10(2)) = 98
Sound Level Meter (SLM)
=Consist of microphone, preamplifier, an amplifier with an adjustable calibrated gain, filters for frequency weighting, meter response circuits and a reading meter. -Used for measuring; +Overall sound levels in general settings +Weighted sound levels in dBA, dBB, and dBC. +Octave & third octave band levels with appropriate filters. -Used in calibrating a sound instrument also
Weighting Networks
A Based on the 40-phon equal-loudness contour B Based on the 70-phon equal-loudness contour C Based on the 100-phon equal-loudness contour Z (linear)
Some important facts
A 3-dB exchange rate is also used for noise dose calculation by the -American Conference of Governmental Industrial Hygienists (ACGIH) [ACGIH, 1996], -United States Environmental Protection Agency (EPA) [EPA, 1974] -International Standard Organization [IS0, 1990] OSHA's exchange rate i.e. 5 dB takes into consideration the interruptions in high sound exposures and assumes that some recovery from TTS occurs during these intermittences.
Diffuse Field
A diffuse field describes an acoustic field where sound waves reach the observer from all directions. The reflected sound is of similar magnitude to the direct sound when it reaches the observer, and as a result, does not appear to have a single source. A microphone in a diffuse field measures the same magnitude regardless of orientation or location; the sound level is the same everywhere. A reverberation room is designed to have reflective walls built at oblique angles so no walls are parallel to each other. This causes the sound waves to be reflected a maximum number of times around the room to help create a diffuse field. Often, hemi-spherical features are added to large walls to increase wave diffraction (spreading out), adding to the diffusivity of the chamber.
Tinnitus:
A subjective perception of ringing or buzzing in ear. This could be temporary or permanent.
Is TTS a harmless phenomenon?
ANIMAL STUDIES -Kujawa and Liberman (2009) and Lin, Furman, Kujawa, and Liberman (2011) induced TTS in mice and guinea pigs respectively. Results -Loss of auditory nerve fibers innervating inner hair cells (IHCs). -Despite complete recovery from TTS on DPOAE, approximately 50% reduction of suprathreshold Auditory Brainstem Response (ABR) wave I amplitude.
Permissible Exposure Level
Above this level feasible engineering and/or administrative controls must be used to reduce the exposure level. pel Someone is exposed to a sound for 90 minutes. You can calculate using Ti equation Criterion Exposure level (LC) 85 dBA for NIOSH 90 dBA for OSHA Criterion sound duration (TC) 8 hours for NIOSH Allowed exposure time or reference duration Ti=TC/2^((L-LC)/Q)
Acoustic Enclosure Advantages and limitations
Advantages of Acoustic Enclosure: • Can provide 20 to 40 dB of noise reduction. • Can be installed in a relatively short time frame. • Can be purchased and installed at a reasonable cost • Provides significant noise reduction across a wide range of frequencies •Problems with acoustic enclosures or feasibility of acoustic enclosures: •Some sound sources cannot be adequately enclosed due to their size and shape. (too big) •Many noisy devices are part of production process which cannot be enclosed completely •Some machines requires frequent modification or maintenance. •The panels become damaged or the internal absorption material simply deteriorates over time. •Heat factor (fires) •Internal lighting (need light to see the machine) and fire suppression may need to be incorporated into the design
Sound absorption materials Advantages and limitations
Advantages: -Provides a significant reduction in the reverberant sound buildup. -Very effective in small volume rooms or spaces (<10,000 ft2). -Minimal maintenance after initial installation. -Reasonable price (buying and installing). -Effective on middle- to high-frequency noise. (most noises are high frequency) Limitations -Does nothing to resolve the root cause of the noise problem. -Does not reduce noise resulting from direct sound propagation. -Absorption may deteriorate over years and may need periodic replacement -Need of hearing protection.
Reflective or Reactive Silencers Advantages and limitations
Advantages: •Good low-frequency attenuation. •Can be designed to minimize pure tones. •Can be used in high-temperature and corrosive environments. Limitations: •Usually there is a high cost when fabricated from corrosion-resistant materials. •Sensitive to particulate and moisture contamination. •Relatively narrow range of attenuation. •High-to-medium pressure loss. •They can be a difficult retrofit. •Expensive due to -> custom design
TTS Cont.
All sounds does not affect hearing. Equivalent or effective quiet level-> 76 dB for octave bands of noise centered at 250 and 500 Hz, and around 68 dB for those centered at 1000, 2000, or 4000 Hz. (safe) Weakest SPLs causing TTS -> ~ 75 to 80 dB (for BBN). These level changes with frequency, 77 dB for 250 Hz OB to 65 dB for 4 kHz OB. (lower in the high frequency region, higher for low frequency) TTS = TTS2 (sometimes referred as 2, because they would expose the individual for 2 minutes) Effect of duration and intensity on TTS2
PTS
Also called as Noise Induced Permanent Threshold shift (NIPTS) Progressive with duration Difficult to notice at the beginning for an industrial worker Permanent damage to peripheral hearing mechanism Gradually worsens in industrial workers as noise exposure continues Aging + NIHL-> Increase growth in degree of HL -If someone shows NIHL at 55 there will be a component of aging and NIHL
Auditory Effects
Although noise-induced hearing loss is one of the most common occupational illnesses, it is often ignored because there are no visible effects. It usually develops over a long period of time, and, except in very rare cases, there is no pain. What does occur is a progressive loss of communication, socialization, and responsiveness to the environment. In its early stages (when hearing loss is above 2,000 Hz), it affects the ability to understand or discriminate speech. As it progresses to the lower frequencies, it begins to affect the ability to hear sounds in general. The primary effects of workplace noise exposure include noise-induced temporary threshold shift, noise-induced permanent threshold shift, acoustic trauma, and tinnitus. A noise-induced temporary threshold shift is a short-term decrease in hearing sensitivity that displays as a downward shift in the audiogram output. It returns to the pre-exposed level in a matter of hours or days, assuming there is not continued exposure to excessive noise. If noise exposure continues, the shift can become a noise-induced permanent threshold shift, which is a decrease in hearing sensitivity that is not expected to improve over time. A standard threshold shift is a change in hearing thresholds of an average of 10 dB or more at 2,000, 3,000, and 4,000 Hz in either ear when compared to a baseline audiogram. Employers can conduct a follow-up audiogram within 30 days to confirm whether the standard threshold shift is permanent. Under 29 CFR 1910.95(g)(8), if workers experience standard threshold shifts, employers are required to fit or refit the workers with hearing protectors, train them in the use of the hearing protectors, and require the workers to use them. Recording criteria for cases involving occupational hearing loss can be found in 29 CFR 1904.10. The effects of excessive noise exposure are made worse when workers have extended shifts (longer than 8 hours). With extended shifts, the duration of the noise exposure is longer and the amount of time between shifts is shorter. This means that the ears have less time to recover between noisy shifts. As a result, short-term effects, such as temporary threshold shifts, can become permanent more quickly than would occur with standard 8-hour workdays. Tinnitus, or "ringing in the ears," can occur after long-term exposure to high sound levels, or sometimes from short-term exposure to very high sound levels, such as gunshots. Many other physical and physiological conditions also cause tinnitus. Regardless of the cause, this condition is actually a disturbance produced by the inner ear and interpreted by the brain as sound. Individuals with tinnitus describe it as a hum, buzz, roar, ring, or whistle, which can be short term or permanent. Acoustic trauma refers to a temporary or permanent hearing loss due to a sudden, intense acoustic or noise event, such as an explosion.
•Many medical and related societies like .... started showing great interest in conservation of hearing. •These societies established hearing conservation committees and sponsored research and conferences to answer major question in the area of hearing conservation.
American Medical Association (AMA), American Academy of Otolaryngology, American Audiological Association, Acoustical Society, and Industrial Hygiene Society
Industrial Noise Control
An omnidirectional microphone is used on all dosimeters. The microphone responds to dynamic pressure variations, with the output being an electrical signal proportional to the sound pressure. The output signal of the microphone is fed into an attenuator and A-weighted network.
Examples of the Use of Noise control Principles Principle: -Greater changes in pressure and force produce louder noises -Lowering the height at which objects are dropped can reduce impact noise -Use of sound-absorbing materials can reduce impact noise -Resonance increases noise but it can be damped Application?
Application: -Complete a task or process with smaller force over longer time to reduce noise as opposed to conducting the task with stronger force over shorter time. Example: a quiet way of bending a flat strip of metal is to use pliers as opposed to a hammer -When possible, reduce the height from which objects are dropped. Example: use a hydraulic system for raising or lowering the conveyor belt so that the height is reduced -Whenever possible, use sound-absorbing materials. Example: The bin can be made of soft rubber or plastic and can be lined with sound-absorbing material -Damp vibrating surfaces, sometimes damping only part of the vibrating surface can reduce noise. Example: clamp a urethane rubber coating to a saw blade to reduce intense resonance sound
Example LAVG
Assume the threshold is set to 80 dB and the exchange rate is 5 dB (the settings of OSHA's Hearing Conservation Amendment). Consider taking a 1-hour noise measurement in an office where the A-weighted sound level was typically between 50 dB and 70 dB (below the threshold). If the sound level never exceeded the 80-dB threshold during the 1-hour period, then the LAVG would not indicate any reading at all. If 80 dB was exceeded for only a few seconds due to a telephone ringing near the instrument, then only those seconds will contribute to the LAVG, resulting in a level perhaps around 40 dB (notably lower than the actual levels in the environment).
Potential for Reduction in Coronary Heart Disease
Chronic exposure to hazardous occupational noise is significantly associated with coronary heart disease (Gan, Davies, & Demers, 2011). Thus, noise control has the potential to reduce the incidence of chronic heart disease.
Anticarcinogenic drugs:
Cisplatin and Carboplatin (HC and spiral ganglion loss and damaged stria). Enhanced ototoxic and nephrotoxic effect if combined with noise exposure or other drugs like aminoglycosides or loop diuretics.
Physiological Changes Associated with PTS
Cochlear changes in PTS are similar to Presbyscusis such as loss of hair cells, nerve terminals, and damaged stria vascularis. Schuknecht (1964) classified presbycusis into four categories: Sensory, neural, metabolic (strial), and mechanical. Similarly, physiological changes due to excessive high level noise exposure can be grouped into three categories: -Metabolic -Mechanical -Neural
Types of recovery in TTS
Complete linear recovery: occur within first ~16 hours post exposure provided that the noise exposure was continuous lasting not more than 8-12 hours and TTS2 is less than approx. 40 dB. Delayed complete recovery: Intermittent noise exposure more than 8-12 hours. Incomplete recovery
Aging vs NIHL
Contribution due to aging may not be a lot. But it is possible someone may acquire age induced hearing loss faster. Some argue that it might be because of aging not noise.
Sound level measurement can help in understanding .... and it can assess ... and it uses. .... and it seeks to assess..
Dangers of Loud Sounds which have generated OSHA Workplace Standards Sound intensity in decibels referenced to the standard threshold of hearing Filter contours A,B,C which reveal shortcoming of decibel measurements loudness which depends on Ear's response curves express in phons or sones
Free field microphones
Designed to compensate for microphone itself. Measure sound as though the microphone is not there. Free field microphone should be pointed towards the sound source at a 0° angle of incidence. (perpendicular)
U.S. Department of Defense (DoD; Instruction 6055.12, DoD Hearing Conservation Program, March 5, 2004)
DoD specifies that engineering controls incorporating all possible engineering principles should be the primary means of eliminating potentially hazardous noise exposure, and the goal of such controls should be to reduce steady state levels to below 85 dBA regardless of the TWA exposure and to reduce impulse noise to below 140 dB peak SPL.
equal energy principle (EEP) & Exchange rate (ER)
EEP -> Amount of biological damage caused by noise exposure is determined by total amount of energy. The amount of gas consumed would be similar between a car driving 40 miles per hour for 2 hours and a car going 80 miles per hours for 1 hour Damage caused by noise exposure level of 85 dBA for period of 8 hrs = Damage caused by noise exposure level of 88 dBA for period of 4hrs. The duration and biologic damage is the same, but the intensities are different. This time intensity relationship -> Exchange rate/ time intensity trade off. EE= increase in dB exposure levels that requires halving of the exposure times. (85 - 88. 8 - 4. Went down to half for duration) (85 - 90. 8 - 4. 100 - 85. 8 - 2) Different exchange rates have been proposed: 3 dB (NIOSH, 1998), 4 dB ( DoD, 2004), 5 dB (OSHA, 1983).
Receiver Control
Ear plugs or ear muffs are considered highly economical methods for reasonably effective receiver noise control. However, employees are often uncomfortable having to constantly wear these devices. They also note their inability to detect changes in the sound of equipment and problems in communicating with other employees. In environments with a lot of material handling equipment, such as forklifts, the use of hearing protection devices can create unsafe working conditions because employees may not be able to hear equipment entering their work areas. Quiet zones or personnel enclosures are preferred to reduce the noise level that reaches the receiver.
Auditory Effects of Noise Exposure
Excessive exposure to noise can cause damage to inner ear structures and auditory nerve. The human ear has a tendency to recover from damage after an acute exposure to loud sounds. Prolong high level exposure -> permanent damage to inner ear and auditory nerve. The hair cells get damaged at different intervals. High frequency is first in the cochlea so it is damaged more often. That is why we see a notch
Federal Railroad Administration (FRA; 2008; 71 FR 63123, Oct. 27, 2006, as amended at 73 FR 79702, Dec. 30, 2008)
FRA encourages railroads to use noise operational controls by reducing the duration of exposure to excessive noise when the noise exposure for workers exceeds an 8-hour TWA of 90 dBA measured by integrating all continuous, intermittent, and impulse sound levels from 80 dB to 140 dB.
Individuals Responsible for Noise Controls
For engineering noise controls, noise control engineers may serve as the key personnel. However, collaboration of several professionals, including the workers, is likely to produce the most effective noise control measures. For example, the U.S. Navy requires collaboration between industrial hygienists, command leaders, facilities managers, and safety managers in reducing or eliminating noise.
Purchasing Quiet Equipment
For new manufacturing sites, the best strategy to control noise is to purchase quiet equipment. According to the European Union Directive (2006/42/EC), manufacturers have the responsibility to design and construct machinery so as to reduce the risks from the emission of airborne noise to the lowest possible level, using all available means.
•Acoustic or audio shock limiters
For telephone operators •Acoustic shock: Physiological or psychological symptoms that individuals can experience after hearing an unexpected , sudden, loud sounds through a telephone headset or handset.
Frequency
Frequency, f, is a measure of the number of vibrations (i.e., sound pressure cycles) that occur per second. It is measured in hertz (Hz), where one Hz is equal to one cycle per second. Sound frequency is perceived as pitch (i.e., how high or low a tone is). The frequency range sensed by the ear varies considerably among individuals. A young person with normal hearing can hear frequencies between approximately 20 Hz and 20,000 Hz. As a person gets older, the highest frequency that he or she can detect tends to decrease. Human speech frequencies are in the range of 500 Hz to 4,000 Hz. This is significant because hearing loss in this range will interfere with conversational speech. The portions of the ear that detect frequencies between 3,000 Hz and 4,000 Hz are the earliest to be affected by exposure to noise. Audiograms often display a 4,000-Hz "Notch" in patients who are developing the beginning stages of sensorineural hearing loss
Genetic and environmental factors interactive effect. Need to look and see if someone is more susceptible
Genetic makeup is different for individuals and environmental factors are unique (work, drugs, noise exposure) NIHL more prevalent in males because they used to work in environments with higher noise levels (50s and 60s) Estrogen plays a protective role in females in the context of susceptibility with hearing loss. Also another factor why males are more prone to NIHL Those who work with OSHA there will be 25% who get NIHL and NIOSH is 8%. Not every worker is protected
Aminoglycosides:
Gentamycin, kanamycin, streptomycin, amikacin, tobramycin, and neomycin. (About 20-30% of patients receiving these drugs develops HL). -Treats TB, ototoxic
Foundation of Hearing Conservation (different disciplines)
Group 1 Basic Scientists: Studied Physiology of hearing, acoustics, physical and perceptual aspects of sounds Group 2 Medical & Engineering: for diagnosing hearing loss, measuring hearing loss, manufacturing diagnostic, treatment and rehabilitation, developing standards and ear protective devices Group 3 Implementation group: Government and industries, legislators, hearing protection company personnel
Reduction in Absenteeism
High noise exposure levels are associated with increased absence due to sickness. Thus, reduction of noise levels has the potential for improving attendance.
Potential for Reduction in Accidents
High noise levels may be associated with higher accident rates by masking warning shouts, sirens, and machinery sounds suggesting dangerous malfunction. Reduction of noise exposure levels through the use of hearing protection devices can result in a significant reduction in the injury rate, suggesting that reduction of noise levels through noise controls may similarly reduce injuries.
Intensity Formula MKS CGS
I=P/A w/m2 w/cm2 (10-12 w/m2) (10-16 w/cm2)
Alternative to using sound booth
If a sound booth is not available: •Insert earphones •Provide more IA ( 75 dB for freqs ≤ 1 kHz) •Provide Noise reduction •Increase comfort •Reduce risk of disease transmission •Remove the problem of collapsed canal •Durable
Potential Elimination of Costs Related to the Implementation of a Hearing Conservation Program
If application of noise control measures reduces the noise below levels specified by standards (e.g., 80 or 85 dBA TWA) above which implementation of hearing conservation programs is required, then the need for hearing conservation programs and the related costs is eliminated.
Reduced Worker Compensation and Related Legal Costs
If fewer workers have compensable hearing loss or if the amount of NIHL is less, then the related worker compensation costs will be reduced accordingly.
Action Level
If it goes beyond a level, the industry needs to take action to fix that
Identify the Cause of Noise
If the cause of noise can be identified, such as that caused by mechanical impacts, vibration of machine parts, or fluids or air flowing at high velocities, then appropriate modifications can be made to reduce the noise. For example, reducing the distance between impacting parts, changing the pump in hydraulic systems, dynamically balancing rotating equipment, or reducing the force driving the impacting parts can minimize noise caused by mechanical impacts. Damping or isolating different parts can reduce noise caused by vibration of machine parts.
Intensity and duration switch off
If you have a very loud noise you cannot be around it for long
2. Ionic Changes in Cochlea
Importance of ionic balance in normal hearing. -Two pathways of K+ cycling: one through OHCs and another through IHCs. - OHC -> (K+) Fibrocytes in the outer sulcus region ->(K+) SV (stria vascularis) -Loss of type II & IV fibrocytes in the region with max. OHC damage due to noise exposure -IHCs -> (K+) Phalangeal cells, inner sulcus cells, and interdental cells -> (K+) Stellate fibrocytes -> (K+) Intermediate cells OHC to the supporting cells to the fibrocytes to the endolymph with K+. Intermediate cells gets damaged then there will be more K+ in the intrastrial fluid
Identify the Noisiest Machines and Machine Parts
In modifying equipment, first the machines that are noisiest should be identified because the noise generated by these machines will contribute most to the noise exposure levels. This can be achieved by turning only one machine on and measuring the sound levels generated by the machine. The processes or parts of the machine that are noisiest should then be identified and targeted for noise control. A machine with a single purpose can have multiple noise sources.
Metabolic Changes
Include changes in stria vascularis, blood flow, ionic changes, and metabolic changes in hair cells. Stria Vascularis: -High level sound exposure -> acute swelling of Stria-> Loss of intermediate cells of stria -Result of Animal studies: Stria vascularis swelling gradually disappears but the loss of intermediate cells remains permanent in PTS -Role of Intermediate cells of Stria -Loss of Intermediate cells-> shrinkage of the stria vascularis and a short term decrease in endocochlear potential because the potassium cycling gets effected
Other special cases
Infrasonic noise Ultrasonic noise Headsets
Loop diuretics:
Inhibit Na+ and Cl- reabsorption. Used in treating congestive heart failure or renal failure. Reduce fluid overload in body. Ex. Ethacrynic acid, furosemide, and bumetanide.
Intensity vs SPL
Intensity level: 10log 1/10 SPL: 10log p2/p02 (we cannot use I it is intensity so we need to switch it out with p2) THEN to simplify it would be SPL: 10log (p/p0)2 THEN SPL: 10*2 log (p/p0) THEN SPL: 20 log (p/p0)
Which is more important intensity or frequency in noise exposure?
Intensity. We talk about the hearing loss and how it effects the different frequencies after
Economic Efficiency of Noise Control Measures
It is important to assess the economic efficiency of any technically advanced noise measures by considering both benefits and costs. Ineffective noise controls are costly and time-consuming, and they do nothing to save the worker′s hearing while creating a false impression of the presence of noise control. Costs of implementing noise control measures will depend on the targeted reduction in noise exposure levels and the specific noise control procedures used to achieve the target. During this process, the impact of reduced noise on worker safety and work efficiency, as well as the reduction of community noise, should be considered. OSHA (2010) has proposed an interpretation of the word feasible to mean "capable of being done" or to mean that the cost of implementation of such controls will not threaten the viability of the employer′s business. It should be noted that employers' claims of lack of economic feasibility can be rejected in courts. For example, in Manchester Timber Importers (FWM) Ltd v Deary, 1984, an employer claimed that the fitting of acoustic enclosures to noisy woodworking machines would reduce the productivity of the machines and would place the small business at risk for closure. An industrial tribunal in Manchester rejected the claim because it was possible to install the enclosures and still operate the machines without much loss of productivity after the workers became adapted to them (Ping, 1986).
Heavy Metals
LEAD: -Exposure: breathing workplace or air, contaminated water. -Source of lead release: burning of fossil fuels, mining, battery production, ammunition, & metal products. -Blood lead level > 7 µg/dL associated with SHL in 3-8 K region -Neuro and ototoxic, nephrotoxic, and affects reproductive system. MERCURY (and it derivatives) -Exposure: contaminated air, skin contact with mercury, and contaminated food (seafood). -Metallic mercury: in production of thermometers, caustic soda, chlorine gas, and mercuric batteries. -OSHA limit: 0.1 mg organic mercury for each cubic meter of workplace air &0.05 mg/m3 of metallic mercury vapor during 8 hr work shift. -Damage nervous system, brain, kidney, and developing fetus. -ABR abnormalities were found in Andean children who had history of exposure to mercury vapors from gold mining operations -Prolonged methyl mercury exposure -> delay ABR latencies with incomplete recovery TIN -Besser et al. (1987) reported acute limbic-cerebellar syndrome with HL in 6 industrial workers who had inhaled trimethyltin. GERMANIUM -Yamasoba et al.(2006) reported degeneration of stria vascularis and supporting cells in guinea pigs after administration of germanium dioxide. -Li, Chen,& Chen (2009) showed brain transmission changes in rats following administration of germanium dioxide.
Which ear is more vulnerable to NIHL?
Left ear is more susceptible. No exact reasoning. Maybe because more right handed
Figure 2 TTS2
Linear recovery is faster to make the threshold come back to normal range. Delayed recovery (complete) takes a longer time to come back to normal range. Delayed (incomplete) there is a permanent threshold shift because they did not come back to normal
1. Stria Vascularis damage
Loss of intermediate cells -> Changes in EP (permanent) -> Changes in Endocochlear P are limited to region of cochlea with max. HC and stereocilia damage
Attenuation
Loss of power in a signal as it travels from the sending device to the receiving device
Loudness and Weighting Networks
Loudness is the subjective human response to sound. It depends primarily on sound pressure but is also influenced by frequency. Three different internationally standardized characteristics are used for sound measurement: weighting networks A, C, and Z (or "zero" weighting). The A and C weighting networks are the sound level meter's means of responding to some frequencies more than others. The very low frequencies are discriminated against (attenuated) quite severely by the A-network and hardly attenuated at all by the C-network. Sound levels (dB) measured using these weighting scales are designated by the appropriate letter (i.e., dBA or dBC). The A-weighted sound level measurement is thought to provide a rating of industrial noise that indicates the injurious effects such noise has on human hearing and has been adopted by OSHA in its noise standards (OTM/Driscoll). In contrast, the Z-weighted measurement is an unweighted scale, which provides a flat response across the entire frequency spectrum from 10 Hz to 20,000 Hz. The C-weighted scale is used as an alternative to the Z-weighted measurement, particularly for characterizing low-frequency sounds capable of inducing vibrations in buildings or other structures. A previous B-weighted scale is no longer used. The networks evolved from experiments designed to determine the response of the human ear to sound, two men, who were asked to adjust the level of the test tone until it sounded as loud as the reference tone. These contours represent the sound pressure level necessary at each frequency to produce the same loudness response in the average listener. The nonlinearity of the ear's response is represented by the changing contour shapes as the sound pressure level is increased (a phenomenon that is particularly noticeable at low frequencies). Among healthy individuals, the actual threshold may vary by as much as 10 decibels in either direction.
Free radicals
Makes you old. An unpaired unstable molecule become free radicals. They are created when we are breathing, exercising, digesting food. The main problem is free radicals tend to injure the cell damaging the DNA so whens a cell's DNA changes the cells become mutated, leads to cancer. The free radical will steal an electron from a neighboring molecule then that molecule becomes a free radical This causes oxidative stress as the cycle continues
Sound Fields
Many noise-control problems require a practical knowledge of the relationships between: A sound field (a region in which sound is propagating) and two related concepts. Sound pressure (influenced by the energy [in terms of pressure] emitted from the sound source, the distance from the sound source, and the surrounding environment) (OTM/Driscoll). Sound power (sound energy emitted from a sound source and not influenced by the surrounding environment). Sound fields are categorized as near field or far field, a distinction that is important to the reliability of measurements. The near field is the space immediately around the noise source, sometimes defined as within the wavelength of the lowest frequency component. Sound pressure measurements obtained with standard instruments within the near field are not reliable because small changes in position can result in big differences in the readings. The far field is the space outside the near field, meaning that the far field begins at a point at least one wavelength distance from the noise source. Standard sound level meters (i.e., type I and type II) are reliable in this field, but the measurements are influenced by whether the noise is simply originating from a source (free field) or being reflected back from surrounding surfaces (reverberant field). A free field is a region in which there are no reflected sound waves. In a free field, sound radiates into space from a source uniformly in all directions. The sound pressure produced by the source is the same in every direction at equal distances from the point source. As a principle of physics, the sound pressure level decreases 6 dB, on a Z-weighted (i.e., unweighted) scale, each time the distance from the point source is doubled. Free field conditions are necessary for certain tests, where outdoor measurements are often impractical. Some tests need to be performed in special rooms called free field or anechoic (echo-free) chambers, which have sound-absorbing walls, floors, and ceilings that reflect practically no sound. In spaces defined by walls, however, sound fields are more complex. When sound-reflecting objects such as walls or machinery are introduced into the sound field, the wave picture changes completely. Sound reverberates, reflecting back into the room rather than continuing to spread away from the source. Most industrial operations and many construction tasks occur under these conditions. The net result is a change in the intensity of the sound. The sound pressure does not decrease as rapidly as it would in a free field. In other words, it decreases by less than 6 dB each time the distance from the sound source doubles. Far from the noise source--unless the boundaries are very absorbing--the reflected sound dominates. This region is called the reverberant field. If the sound pressure levels in a reverberant field are uniform throughout the room, and the sound waves travel in all directions with equal probability, the sound is said to be diffuse. In actual practice, however, perfectly free fields and reverberant fields rarely exist--most sound fields are something in between.
4 layers
Marginal, intermediate, basal, fibrocyte If the intermediate layer gets damage then the potassium cycling is effected
The Use of Enclosures
Maximum noise control is provided by quality sound enclosures because they normally include materials and design features that provide sound absorption, transmission loss, sealing, and ventilation in one system. Noise is blocked from either leaving or entering the enclosure. This provides the option of enclosing either the noise source or the noise receiver. Proper sealing is required for an enclosure to maintain its acoustical integrity. Access doors, windows, and ventilation systems can pose special problems. Doors, windows, and structural joints must be properly sealed and caulked to ensure no sound leakage, in or out, occurs to degrade an enclosure's performance. In cases where a manufacturing process requires materials to be constantly moved in and out of an enclosure, acoustic tunnels or shields must be incorporated into the design to ensure acoustical integrity. The enclosure's ventilation system also may require adequate silencing of the inlet and outlet paths.
Measuring threshold or hearing screening better?
Measuring threshold because you are measuring more frequencies and you need to track changes and see the whole range
3 prerequisites for sound
Medium (air, water) Source of energy (hit the table with my hand) Vibrating object (table vibrates)
Microphone use and location
Microphone 2 types used for noise measurements 1.Free field microphone calibrated to measure sounds perpendicularly incident to the microphone diaphragm. This type of microphone should be pointed directly at the source to be measured. Placed directly in front of the source. 2.Diffuse-field microphone. Sensitive to all directions
Filtering
Most noise is not a pure tone, but rather consists of many frequencies simultaneously emitted from the source. To properly represent the total noise of a source, it is usually necessary to break it down into its frequency components. One reason for this is that people react differently to low-frequency and high-frequency sounds. Additionally, for the same sound pressure level, high-frequency noise is much more disturbing and more capable of producing hearing loss than low-frequency noise. Engineering solutions to reduce or control noise are different for low-frequency and high-frequency noise. As a general guideline, low-frequency noise is more difficult to control. Certain instruments that measure sound level can determine the frequency distribution of a sound by passing that sound successively through several different electronic filters that separate the sound into nine octaves on a frequency scale. Two of the most common reasons for filtering a sound include 1) determining its most prevalent frequencies (or octaves) to help engineers better know how to control the sound and 2) adjusting the sound level reading using one of several available weighting methods. These weighting methods (e.g., the A-weighted network, or scale) are intended to indicate perceived loudness and provide a rating of industrial noise that indicates the impact that particular noise has on human hearing. The following paragraphs provide more detailed information.
NIOSH vs. OSHA PEL
NIOSH PEL = 85 dBA Exchange Rate = 3 dB OSHA PEL = 90 dBA Exchange Rate = 5 dB Action level= 85 dBA Ex: Exchange rate of 5 indicates that for every 5 dB increase in noise level the duration of time a person can be exposed to that noise is halved. Employee can work in a noise environment >90 dBA for 8 hours. If the exchange rate is 5, the employee can work in a noise environment of 95 dB A for 4 hours.
Excessive risk table
NIOSH has higher risk percentages compared to EPA and ISO. We do not follow EPA, OSHA is a compromise and is the power of law
Which guideline is more strict? NIOSH or OSHA
NIOSH, states smaller amount of hours they can be exposed to. OSHA is main body because it lets workers work for longer to do well with financial needs. NIOSH is better for the worker's ears Every individual's hearing is unique, some people may still be affected by the noise because we are physiologically unique. Some of us are more susceptible to NIHL NIOSH is safer than OSHA but it does not mean people will not have NIHL
•These two steps initiated numerous research programs... •To overcome this problem, govt. and industry established ... •These committee designed and published a •After 3 years of hard work, in .... the results of major investigation were published
No uniformity or agreement between the studies. an advisory committee and monitoring committee to sponsor research projects that would set a critical noise levels for American industries. protocol for future researchers. 1978
There is a big room that has 5 noisy machines, I did sound absorbing on the walls, roof, and floor. Will workers be safe?
No, Sound absorption helps with echos. If you are working next to the machine you will still be exposed to the loud sounds.
Noise dose cont.
Noise dose is cumulative Noise dose never decreases over time. Sound levels may increase and decrease over time, noise dose only increases or plateaus over time.
Decibels
Noise is measured in units of sound pressure called decibels (dB), named after Alexander Graham Bell. The decibel notation is implied any time a "sound level" or "sound pressure level" is mentioned. Decibels are measured on a logarithmic scale: a small change in the number of decibels indicates a huge change in the amount of noise and the potential damage to a person's hearing. The decibel scale is convenient because it compresses sound pressures important to human hearing into a manageable scale. By definition, 0 dB is set at the reference sound pressure (20 micropascals at 1,000 Hz, as stated earlier). At the upper end of human hearing, noise causes pain, which occurs at sound pressures of about 10 million times that of the threshold of hearing. On the decibel scale, the threshold of pain occurs at 140 dB. This range of 0 dB to 140 dB is not the entire range of sound, but is the range relevant to human hearing. Decibels are logarithmic values, so it is not proper to add them by normal algebraic addition. The decibel is a dimensionless unit; however, the concepts of distance and three-dimensional space are important to understanding how noise spreads through an environment and how it can be controlled.
ath Control
Noise is transmitted via sound waves through the space that separates the source from the receiver. Altering the path of this transmission to reduce the amount of acoustical energy that will reach a receiver is an effective approach to industrial noise control. Usually, this involves impeding the sound transmission by interfering with its reflected and direct paths. Reflected noise paths can be reduced by adding sound-absorbing panels to walls and by hanging sound-absorbing devices (unit absorbers) from ceilings. Direct noise paths can be disrupted by using enclosures or acoustical barrier walls between the source and receiver. These barriers are most effective when used in combination with materials designed to treat reflected sounds.
•"Long term exposure to very loud noise can cause hearing loss"- very old fact. •Industrial revolution in 19th century: •Hearing loss among certain group of workers or people , like boilers, soldiers etc.... •Beginning of Hearing Conservation
Noise pollution and noise-induced hearing loss became a serious issue. Boiler maker's deafness, gun shooting deafness. World War II
Source Control
Noise radiates from a source. For projects in the design stage, try to specify the quietest operating equipment you can. This may not eliminate all potential for a noise problem, but it will make the noise control project easier and less expensive to implement. Buyers should be aware of and consider the noise level when making new equipment purchases. When a noise problem already exists, it is unusual that the mechanisms or processes that generate the noise can be quieted. In these situations, adding acoustical materials to the noise-radiating surfaces may help reduce the noise strength at the source, either eliminating the noise problem or partially controlling the problem. The materials that are added in these situations may provide sound absorbing, sound blocking, or damping properties (or any combination of these three properties). Particularly in industrial noise problems, compressed air discharge noises are easily treatable with the addition of pneumatic silencers.
OSHA and NIOSH REL
OSHA AL - Slow, 5 dB exchange rate, criterion level 90 dB, 80 dB threshold OSHA PEL - Slow, 5 dB exchange rate, 90 dB criterion level, 90 dB threshold NIOSH REL - Slow, 3 dB exchange rate, criterion level 85 dB, 80 dB threshold
What Is Noise?
Occupational noise can be any sound in any work environment. A textbook definition of sound is "a rapid variation of atmospheric pressure caused by some disturbance of the air." Sound propagates as a wave of positive pressure disturbances (compressions) and negative pressure disturbances (rarefactions). Sound can travel through any elastic medium (e.g., air, water, wood, metal). When air molecules are set to vibrate, the ear perceives the variations in pressure as sound (OTM/Driscoll). The vibrations are converted into mechanical energy by the middle ear, subsequently moving microscopic hairs in the inner ear, which in turn convert the sound waves into nerve impulses. If the vibrations are too intense, over time these microscopic hairs can be damaged, causing hearing loss. Noise is unwanted sound. In the workplace, sound that is intense enough to damage hearing is unwanted and, therefore, is considered to be noise.
Octave Bands (Frequency Bands)
Octave bands, a type of frequency band, are a convenient way to measure and describe the various frequencies that are part of a sound. A frequency band is said to be an octave in width when its upper band-edge frequency, f2, is twice the lower band-edge frequency, f1: f2 = 2 f1. Each octave band is named for its center frequency (geometric mean), calculated as follows: fc = (f1f2)1/2, where fc = center frequency and f1 and f2 are the lower and upper frequency band limits, respectively The width of a full octave band (its bandwidth) is equal to the upper band limit minus the lower band limit. For more detailed frequency analysis, the octaves can be divided into one-third octave bands; however, this level of detail is not typically required for evaluation and control of workplace noise. Electronic instruments called octave band analyzers filter sound to measure the sound pressure (as dB) contributed by each octave band. These analyzers either attach to a type 1 sound level meter or are integral to the meter.
Replacement of Equipment with Alternative Equipment with Lower Noise Emission
Often, other versions of the same equipment generate lower noise levels. For example, fans, gears, motors, and bearings are available in a variety of sizes, shapes, and operating speeds. As another specific example, new printers are quieter because of the use of laser beams or ink-jet drops instead of impacting print heads. When buying quiet machines, it is helpful to have clear specifications for noise with the condition that the low noise levels will be validated through measurements and that the machine will be replaced if the noise levels are not within the specified limits.
Noise control and Cars
Older cars make more noise than the new car. If you do not do proper servicing then the cars will make more noises. The doors in the cars have a rubber strip to create a seal. They have padding to absorb sounds. Cars are manufactured with such precision you can hardly hear any vibration
Antioxidants
Organic molecules that help protect the body from harmful chemicals called free radicals
Power Formula MKS CGS
P=W/t= Fd/t=Fv Joules/s or watt Ergs/s or watt 1 w = 1 j/s (Power=pressure2) (107 ergs/s)
NIOSH
PEL = 85 dBA Exchange Rate = 3 dB Significant Threshold Shift = 15 dB or more at any frequency b/w .5 and 6 kHz in either ear & it continues to be present on the next annual test
OSHA
PEL = 90 dBA Exchange Rate = 5 dB Significant Threshold Shift = >10 dB at 2, 3, and 4k Hz average
Our perception of sound is comprised of many pressure waves of varying physical attributes
Physical Attribute: Amplitude (dB) Psychological Correlate: Loudness (Sone) Physical Attribute: Frequency (Hz) Psychological Correlate: Pitch (Mel) Physical Attribute: Complexity (reflects spectral energy) Psychological Correlate: Timbre
Revised Baseline - Decrease
Pre-Employment Testing Job now exposes him to 85 dBA - Now has to have annual hearing tests
Revised Baseline -improvement
Pre-employment testing Job now exposes him to 85 dBA- now has to have annual hearing tests Threshold got better
Pressure vs Power
Pressure: small p Power: big P Intensity derived from pressure and power
•Decibel (dB) scale:
Ratio scale (Takes advantage of ratio and logarithm). •Ratio-> Physical magnitudes can be used in relation to reference value. Ratio: Compares two things (like height of one man to another man, he is 2x taller) •Equal ratio corresponds to different distance on linear scale •Equal ratio corresponds to same distance in logarithmic scale.
Which approach is the best approach to control noise out of the three categories?
Reduction of the source. Taking care of the root of the problem. Safe for workers and it will become a favorable environment.
Noise Exposure Diagram
Refer to slide 20 All pathways work towards causing NIHL. There are things that can prevent NIHL like antioxidants
•Sound pressure expressed in decibel ->
SPL = 20 log p2/p02
Organic Solvent types
STYRENE -Absorbed through skin or airways. -Damage mucosa, liver, kidney, CNS, and increases the risk of cancer. -Permissible exposure limit by OSHA 100 ppm, 8 hr work day. -Industries: plastic, glass fiber reinforced plastic, synthetic rubber, insulators, and few agricultural products. TOLUENE -Absorbed through airway, skin, and digestive tract. -Damage CNS, liver and irritate the Respiratory tract. -Permissible exposure level 27 ppm. -Industries: leather tanning and printing, painting, and industries where dyes and degreasing agents are used. -A HFHL can occur in industrial workers who are exposed to noise and styrene within permissible level for 5 years or more. N-hexane -Colorless volatile liquid -Absorbed through inhalation and then spread to tissues and organs like brain, spleen, liver, kidney, adrenal glands, and peripheral nerves. -Industries: textile, furniture, printing, shoe industries, adhesive. -Exposure to N-hexane can affect Hearing system beyond cochlea because of its neurotoxic effects -Delayed interwave latencies in N-hexane exposed workers. XYLENE -Absorbed through Inhalation or skin contact. -Industries: paint, metal, furniture, biomedical laboratories, and automobile garage. -OSHA permissible limit -> 100 ppm for work place air for 8 hr shift. -Draper & Bamiou (2009) reported abnormal acoustic reflex , ABR and normal OAE in subject with xylene exposure history. -Prevalence of HL in workers of LPG factory can be as high as 56.8 %
High Frequency sounds have shorter or longer wave length? Time period?
Shorter
When you are in the field you are asked to measure the intensity
Sometimes there will be more than one source
Sound Vs. Noise
Sound is a pressure change detectable by the human ear. •The pitch ranges between 20 to 20,000 Hz. •The volume ranges between 0 to 140 dB. Noise is a type of sound. •It carries no information. •It is random. •It is generally described as undesirable or unwanted sound.
Instruments for noise measurments:
Sound Level Meter Noise Dosimeter
Sound Power
Sound power, usually measured in watts, is the amount of energy per unit of time that radiates from a source in the form of an acoustic wave. Generally, sound power cannot be measured directly, but modern instruments make it possible to measure the output at a point that is a known distance from the source. Understanding the relationship between sound pressure and sound power is essential to predicting what noise problems will be created when particular sound sources are placed in working environments. An important consideration might be how close workers will be working to the source of sound. As a general rule, doubling the sound power increases the noise level by 3 dB. As sound power radiates from a point source in free space, it is distributed over a spherical surface so that at any given point, there exists a certain sound power per unit area. This is designated as intensity, I, and is expressed in units of watts per square meter. Sound intensity is heard as loudness, which can be perceived differently depending on the individual and his or her distance from the source and the characteristics of the surrounding space. As the distance from the sound source increases, the sound intensity decreases. The sound power coming from the source remains constant, but the spherical surface over which the power is spread increases--so the power is less intense. In other words, the sound power level of a source is independent of the environment. However, the sound pressure level at some distance, r, from the source depends on that distance and the sound-absorbing characteristics of the environment (OTM/Driscoll).
basic components of general noise system:
Source of noise, path of noise, and receiver Direct path: from sound source to ear Indirect path: reflected off the walls to the ear
Threshold/trigger level
Specifies at what level the noise would be picked up
The function of the ear is to gather, transmit, and perceive sounds from the environment. This involves three stages:
Stage 1: Modification of the acoustic wave by the outer ear, which receives the wave and directs it to the eardrum. Sound reaches the eardrum as variations in air pressure. Stage 2: Conversion and amplification of the modified acoustic wave to a vibration of the eardrum. These vibrations are amplified by the ossicles, small bones located in the middle ear that transmit sound pressure to the inner ear. The vibrations are then transmitted as wave energy through the liquid of the inner ear (the cochlea). Stage 3: Transformation of the mechanical movement of the wave into nerve impulses that will travel to the brain, which then perceives and interprets the impulse as sound. The cilia of nerve cells in the inner ear, called hair cells, respond to the location of movement of the basilar membrane and, depending on their position in the decreasing radius of the spiral-shaped cochlea, activate the auditory nerve to transmit information that the brain can interpret as pitch and loudness
•Calculate the total SPL that results from combining one source that produces 70 dB SPL with a second source that produces 90 dB SPL?
Step 1: 70= 10 log I/I0 70= 10 log Ix/"10^-12" -> 7 = log Ix/"10^-12" -> log 107 = log Ix/"10-12" -> 107 = Ix/"10-12" -> 10-5 = Ix70 90= 10 log I/I0 90= 10 log Ix/"10^-12" -> 9 = log Ix/"10^-12" -> log 10^9 = log Ix/"10^-12" -> 109 = Ix/"10^-12" -> 10-3 = Ix90 •Step 2: Ix70 + Ix90 -> 10^-5 + 10^-3 -> (10^-2 + 1) 10^-3 (took out 10^-3 because it was common) -> (0.01+1) 10-3 -> 1.01 x 10-3 •Step 3: dB= 10 log ("1.01x10^-" 3)/"10^-12" =10 log (1.01x "10^9")= 10 (0.0043+9)=90.04 EASIER METHOD
Acoustic Trauma:
Sudden damage to hearing due to short burst of extremely intense noise. Ex: Bomb blast, gun shots etc. There were hundreds of people that reported bleeding from ears, loss of hearing because the blast was so loud. Buildings had windows broken from 3 km away from the site. Soldiers after war reports acoustic trauma
•Criterion Exposure level (LC) •Criterion sound duration (TC) •Noise dose
Table 2.2
Noise characteristics relevant to hearing
Temporal Pattern (Continuous,/steady state, time varying, intermittent, impulse) Level (level of cont. steady noise, max. sound level, level of fluctuating noise, level of impulse noise) Frequency (Octave and one third octave) Overall Duration (Exchange rate or doubling rate)
TTS
Temporary change in hearing sensitivity following exposure to intense sounds or loud events. Commonly experienced High frequency noise exposure causes larger threshold shifts than low frequencies. Largest TTS occur at frequency that is about ONE HALF octave higher than the band of noise which an individual is exposed to. Suppose the noise frequency is 2 kHz. It is 1/2 octave higher so around 3 kHz
Worker Illness and Injury Reports
The U.S. Bureau of Labor Statistics (BLS) publishes annual statistics for occupational injuries (including hearing loss) reported by employers as part of required recordkeeping.
Far Field
The acoustic far field is defined as beginning at a distance of 2 wavelengths away from the sound source, and extends outward to infinity. As wavelength is a function of frequency, the start of the far field is also a function of frequency. In the far field, the source is far enough away to essentially appear as a point in the distance, with no discernable dimension or size. At this distance, the spherical shape of the sound waves have grown to a large enough radius that one can reasonably approximate the wave front as a plane-wave, with no curvature. At this distance, sound pressure level is governed by the inverse square law, and a single microphone sound recording will give reliable & predictable results. For each doubling of distance away from the source, the sound pressure will drop 6 dB in the far field. In many acoustic standards, measurements are often specified at a distance of at least one meter from the sound emitting object to ensure that the measurement is taken in the far field for the most critical frequencies.
Improved Communications
The amount of vocal effort required for speaking and the amount of attention required for listening to speech in noisy backgrounds increases with increase in noise levels. Reduction in noise levels can be expected to improve ease of communication. It can also be expected to reduce miscommunication and the resulting number of production errors, as well as any negative impact on the employer-employee relationship.
Frequency Weighting networks
The attenuation gets smaller as you get higher. Because of the higher attenuation you need more intensity at low frequencies to get the same loudness perception. The graph is less steep as you increase the intensity (30 vs 130) At high intensity levels, the sensitivity will change. The C rating is recommended if the sound levels are high. If they are not high, A is recommended
Reduction of Noise-Induced Hearing Loss
The degree of noise-induced hearing loss (NIHL) is directly related to the amount of noise exposure. Therefore, reduction in noise levels can be expected to reduce the amount of NIHL.
If the levels differ by 0 or 1 dB 2 or 3 dB 4 to 9 dB 10 dB or more
The following should be added to the higher value 3 dB 2 dB 1 dB 0 dB
Figure 1 on TTS2
The graph shows three hypothetical noise levels. It shows for how long, it will affect their threshold shift (dB). 100 dB leads to more of a drastic shift then 80 dB. There is a plateau, after some point there will no longer be an increase in TTS. This is referred to as an asymptotic threshold shift
If a sound measuring device treats all frequency equally?
The measurements will not be usual for human studies. It does not represent human hearing, because our hearing isn't sensitive to all frequencies equally
ABR reduction with TTS
The reduction of wave 1 amplitude at suprathreshold stimulus levels in exposed animals without loss of hair cells -> Possibility Selective auditory nerve fiber damage i.e. fibers with high thresholds and low spontaneous rate (every nerve fiber in absence of a stimulus will fire. The rate will change when there is a stimulsu) -> Furman, Kujawa, & Liberman (2013) hypothesized the selective degeneration of auditory nerve fibers with high threshold and low spontaneous rate in recovered ears from TTS
Inverse Square Law, Sound
The sound intensity from a point source of sound will obey the inverse square law if there are no reflections or reverberation. A plot of this intensity drop shows that it drops off rapidly. The energy twice as far from the source is spread over 4x the area, hence 1/4 the intensity
Speed
The speed at which sound travels, c, is determined primarily by the density and the compressibility of the medium through which it is traveling. The speed of sound is typically measured in meters per second or feet per second. Speed increases as the density of the medium increases and its elasticity decreases. For example: In air, the speed of sound is approximately 344 meters per second (1,130 feet per second) at standard temperature and pressure. In liquids and solids, the speed of sound is much higher. The speed of sound is about 1,500 meters per second in water and 5,000 meters per second in steel. The frequency, wavelength, and speed of a sound wave are related by the equation c = f λ Where c = speed of sound in meters or feet per second, f = frequency in Hz, and λ = wavelength in meters or feet.
Sound Pressure
The vibrations associated with sound are detected as slight variations in pressure. The range of sound pressures perceived as sound is extremely large, beginning with a very weak pressure causing faint sounds and increasing to noise so loud that it causes pain. The threshold of hearing is the quietest sound that can typically be heard by a young person with undamaged hearing. This varies somewhat among individuals but is typically in the micropascal range. The reference sound pressure is the standardized threshold of hearing and is defined as 20 micropascals (0.0002 microbars) at 1,000 Hz. The threshold of pain, or the greatest sound pressure that can be perceived without pain, is approximately 10 million times greater than the threshold of hearing. It is, therefore, more convenient to use a relative (e.g., logarithmic) scale of sound pressure rather than an absolute scale (OTM/Driscoll).
Wavelength
The wavelength (λ) is the distance traveled by a sound wave during one sound pressure cycle. The wavelength of sound is usually measured in meters or feet. Wavelength is important for designing engineering controls. For example, a sound-absorbing material will perform most effectively if its thickness is at least one-quarter the wavelength.
Acoustic Power Watt chart
There is a huge range that we can hear and that is why we have to use a logarithm scale instead of a linear one.
Dissipative or Absorptive Silencers
These types of silencers attenuate sound by use of porous sound-absorbing materials such as fiberglass. Typically, such silencers are arranged to create a parallel baffle (Fig. 3.1). The thickness of acoustical linings or baffles should be selected to dissipate the sound levels in the predominant frequency of the noise. The noise reduction provided by dissipative silencers varies across the frequency range, with usually more reduction apparent in the 1000 to 4000 Hz range. As an example, dissipative silencers are used in heating, ventilation, and air conditioning duct systems.
If a sound source with a sound power of wa in a given environment produces a sound pressure p, then 100 similar sources will increase the sound power 100 times, which is equivalent to 20 dB.
Thus Wb= 100wa or SWLb=SWLa+20dB. From the equation I ∞ p2 it is evident that the sound pressure will only increase ten times. This ten times increase again corresponds to 20dB. p2 = 10p1 or SPL2=SPL1+20dB. The use of the multiplier 20 instead of 10 in the sound pressure scale makes the two units compatible
Case History
To gather information about onset and description of different complaints and associated conditions.
What about impulse noise like gunshots, blast etc.? Is fast response good enough for impulse noise?
True peak or Instantaneous response -> Type 0 SLM can respond to pulses of 50 ms duration. Noise measurements in army, DoD (2004) specifies the use of SLM which has peak hold circuit, a rise time not exceeding 35 ms, and ability to measure sound levels exceeding 140 dB SPL. Gunshots duration is very short, around 10 ms. Impulse response only available in type 0 or 1 SLM.
Types of SLM
Type 0: (Laboratory Std. SLM) -Have the most extracting tolerance, which require them to be correct within +/- 0.7 dB from 100 to 4000 Hz. -For calibration and references purpose under laboratory conditions Type 1: (Precision SLM) -Has an accuracy of +/- 1 dBA -For precise sound level measurement in the laboratory and in the field Type 2: (General Purpose) -A field measurement instrument -Accuracy of +/-2 dBA
Sones
Units of perceived loudness
Silencers/Mufflers
Use of silencers, which are devices inserted in the path of a flowing medium such as air, is an effective way of reducing the levels of the sounds propagating through the medium. As an example, a good muffler has the potential to reduce noise levels of an exhaust pipe as close as 1 ft to the operator′s ear by 3 dBA for diesel tractors and 6 dBA for gasoline tractors. There are different types of silencers, as described subsequently.
When close to a sound emitting object, the sound waves behave in a much more complex fashion, and there is no fixed relationship between pressure and distance.
Very close to the source, the sound energy circulates back and forth with the vibrating surface of the source, never escaping or propagating away. These are sometimes called "evanescent" waves. As we move out away from the source, some of the sound field continues to circulate, and some propagates away from the object This transition from circulating to propagating continues in an unpredictable fashion until we reach the threshold distance of 2 wavelengths, where the sound field strictly propagates (the far field.) This mix of circulating and propagating waves means that there is no fixed relationship between distance and sound pressure in the near field, and making measurements with a single microphone can be troublesome and unrepeatable. Typically, measuring in the near field requires the use of more than one microphone in order to accurately capture the energy borne by the circulating and propagating waves.
•Federal govt. showed their concern for OHL first time by publishing •1973, Department of labor appointed an OSHA ( Occupational Safety and Health Administration) Committee for ..
Walsh-Healy Act. establishing noise levels considered safe and above which noise might be considered as unsafe. OSHA took a long time to figure out what level was harmful. Because it was completely new, the people in research were following different guidelines and criteria while conducting their studies. Their findings couldn't correlate with other findings.
Free Field versus Diffuse Field
When sound radiates from an object, it can reach an observer directly by traveling in a straight line, or indirectly via reflections. Reflected sound waves can bounce off surfaces such as walls, the floor, ceiling, as well as other objects in the area. Often when we experience sound, we are receiving both direct and reflected sound waves. Under carefully controlled circumstances, however, we can experience the extreme ends of this continuum: 1) an acoustic field where zero reflections are present, and only the direct sound is observed, and 2) the opposite acoustic field, where zero direct sound is observed, and only reflected sound is present. The names given to these two extreme acoustic environments are FREE FIELD and DIFFUSE FIELD respectively
Mine Safety and Health Administration (MSHA; 1999; 30 CFR Part 62)
When workers are exposed to hazardous noise levels (measured by integrating all sound levels from 90 dBA to at least 140 dBA) above 90 dBA TWA (5 dB exchange rate), MSHA requires the use of all feasible engineering and administrative controls to reduce the miner′s exposure to the 90 dBA TWA level. Miners should not be exposed to any sounds exceeding 115 dBA with or without hearing protection devices. Thus, all noise exposures should be below 115 dBA TWA.
Occupational Safety and Health Administration (OSHA; 1983; 29 CFR 1910.95)
When workers are exposed to hazardous noise levels above 90 dBA time weighted average (TWA; 5 dB exchange rate), OSHA requires the implementation of feasible engineering or administrative controls. Impulse or impact noise should be controlled in such a way that it does not exceed 140 dB peak sound pressure level (SPL).
Microphone use and location
Where to make measurements Do Not: +Stand behind or in front of +Near reflective surfaces Controversial on whether to remove employees during measurements.
There are two sources that are making sound One is making 120 dB Another is making 130 dB What is the total?
You do not add like normal, it involves logarithms
Oxidative stress
a condition in which the production of oxidants and free radicals exceeds the body's ability to handle them and prevent damage -Oxidation causes free radicals to enter our body
Equal loudness contour
a curve showing the amplitude of tones at different frequencies that sound about equally loud Imagine an experiment where you are wearing headphones. In right ear 40 dB sound 1000 Hz, continuous reference sound. Whatever sound presented to left ear, will have different frequencies and intensities. Need to say when the loudness is equal. If I presented 40 Hz in left ear at 40 dB and you said its softer, when you move to 45 you say its softer, then move to 50, 55, 60 again softer. Then you move to 70 dB and you say it is similar at 40 Hz. With this experiment you get points and you connect them and that is where the curve comes from You need higher intensity at lower frequencies for it to be perceived at the same level Loudness (psychological) and intensity (physical attribute)
Miscellaneous Factors:
a) Exposure Intensity Level: For exposure to SPL of 85 to 105 dB for duration less than <8hrs. TTS shows linear increase with increasing SPL. b) Duration: TTS increases as duration of exposure increase up to certain time limits & later reaches plateau usual within 8-12 hrs. c) Frequency of exposed noise: Higher the freq. of exposed noise greater the threshold shift produce by it. d) Temporal pattern of exposure: Factors such as on & off time & overall temporal pattern and type of noise determine the TTS effect
Physiological Factors:
a) ME muscles: ¡ ME muscles control noise susceptibility by way of providing the method of attenuation of 20 dB noise. ¡The afferent auditory system provides 3 -5 dB protection from noise exposure. ¡The stapedius muscle acoustic reflex is dominant at low and high frequencies whereas the tensor tympani contraction is restricted to low frequencies. b) Vascular Factors: § Work by Rosen and Olin (1965) and others have suggested that cardiovascular disease and HL are related.
Constitutional Factors:
a) Species Difference ¨ Different species have different susceptibility to noise. ¨Humans are more prone to noise induced damage due to certain basic anatomical and pathophysiological features in the hearing mechanism. -Through animal studies we can learn more, that will help with humans, but they are not the same
External Factors:
a) Temperature: Clinical conditions like hypothermia increase TTS and PTS. b) Smoking: Individual who smoke are more susceptible. Smoking can increase the level of PTS by 3 dB. REASON: smoking decrease the supply of O2 to the inner ear by increasing carboxyhaemoglobin by 5-6% c) Drugs: Certain drugs such as salicyclates, aminoglycocides, antibiotics, quinine, dispartin have shown to be increase TTS and PTS & hair cell loss
What can cause free radicals
air pollutants, alcohol, cigarette smoke, stress, UV rays, diet. All massive free radical producers can overwhelm the body's natural defense system. Repeated or prolonged free radical damage which the body cannot stop can lead to increased risk of cancer, alzheimers, immune damage, and other diseases
Industrial audiologist
consults with companies that have potentially excessive noise levels and establishes appropriate hearing conservation programs they need to pick out those who are at risk for NIHL you can use case history and genetic analysis
Two sound sources each produce 100 dB of sound. Calculate overall intensity
dBN = dBi + 10 Log10 N = 100 + 10(Log10(2)) =103.3
Combining two sound intensities: Equal source intensities
dBN = dBi+ 10 Log10 N i= dB SPL or dB IL from one of the equal sources N= no. of sources -This is for only when the intensities are the SAME like both are making 90 dB sound. You CANNOT use this formula if there are two different intensities.
Diffuse field microphone
designed to respond in a uniform manner to any signal arriving on its measuring surface from any angle. Oriented at about 75° to the direction of the sound wave propagation in a free field.
If the frequency range is below 16 kHz and the accuracy of ± 2dB is acceptable then there is no
difference between these two types of microphones.
Important attributes in noise measurements
duration and intensity
If noise is •Low frequency output - will use •High frequency output - will use
equipment modification or barriers sound absorption
fill in the blanks: Sound field where the sound waves are free to expand outwards forever ___________ field. Sound field where the sound waves arrives equally from all directions________field. Fundamentally these microphones are same, these are transducers that are designed to sense pressure levels in air. Difference -> designs of microphone head. Microphones are supplied with calibration data sheet that will show the frequency response against transducer
free diffuse
Other consequences of excessive workplace noise exposure include
interference with communications and performance. Workers might find it difficult to understand speech or auditory signals in areas with high noise levels. Noisy environments also lead to a sense of isolation, annoyance, difficulty concentrating, lowered morale, reduced efficiency, absenteeism, and accidents. In some individuals, excessive noise exposure can contribute to other physical effects. These can include muscle tension and increased blood pressure (hypertension). Noise exposure can also cause a stress reaction, interfere with sleep, and cause fatigue.
The Noise Rating - NR - Curve
is developed by the International Organization for Standardization (ISO 1973) to determine the acceptable indoor environment for hearing preservation, speech communication and annoyance. The noise rating graphs for different sound pressure levels are plotted at acceptable sound pressure levels at different frequencies. Acceptable sound pressure level vary with the room and the use of it. Different curves are obtained for each type of use. Each curve is obtained by a NR number. 31.5 Hz : 40 dB 62.5 Hz : 40 dB 125 Hz : 50 dB 250 Hz : 55 dB 500 Hz : 60 dB 1000 Hz : 50 dB 2000 Hz : 55 dB 4000 Hz : 45 dB 8000 Hz : 45 dB
Leq calculation is performed on time domain data ->
it does not represent any specific band of frequencies!! Equivalent continuous A-weighted sound pressure level is a common measurement used in industry to characterize noise levels in loud environments.
Thick absorbents on the wall with a large space in between provides more ... frequency attenuation Thin absorbing baffles with small spaces in between provide more .... frequency attenuation Thick absorbing baffles with small spaces in between provide ..... frequency attenuation
low High Both high and low
Certain BIOCHEMICAL FACTORS like
low Mg++ diet, hyperlipoproteinemia, hypothyroidism etc increase noise susceptibility. d) Physical exercise also increase noise susceptibility -Breathing much faster, consume more oxygen, more free radicals produced. Environmental noise and physiological noise (heartbeat), play music louder while working out -> more detrimental to hearing
Example of TWA Think of a TWA as having a large 8-hour container that stores sound energy. If you run a dosimeter for 2 hours, your Lavg is the average level for those 2 hours— consider this a smaller 2-hour container filled with sound energy. For TWA, take the 2- hour container and pour that energy into the 8-hour container. The TWA level will be
lower. Again, TWA is always based on the 8-hour container. When measuring using OSHA's guidelines, TWA is the proper number to report if the full workshift was measured. Lavg is the mini version of TWA but can be for any period of time. TWA is always 8 hour period. If you do not measure for 8 hours you just measured the Lavg. The Lavg value will be much smaller when converted to TWA value
Excessive noise can affect
mental status: tired, angry, stressed, effects sleep
How to: Soundproofing & Noise Control in Factories & Industrial Facilities
noise is a huge concern in factories and industrial facilities not only is controlling it the law it's the right thing to do when people's health is involved. The acoustical blanket enclosures these highly effective custom-made enclosures both absorb noise and block it from entering or leaving they can enclose almost anything that makes noise and are available in interior grade exterior grade and even a silicone face for high-temperature applications. Similar to the blanket enclosure is the acoustical blanket usually used to create temporary walls these blankets can absorb sound block sound are both they can be hung from the ceiling framed in portable rolling screens or attached to existing walls Audio seal pipe and duct wrap which is made of foam insulation and a vinyl sound barrier that blocks most of the noise with which it comes into contact. Sealing banners and baffles are other products that can be very effective in industrial applications hung from the ceiling, these sound absorbing panels are very effective in large spaces their main function is to reduce reverberation and echo within a space by absorbing sound waves before they're reflected off the ceiling Acoustical wall panels are another product that accomplished reverberation and echo reduction To reduce structure born noise and vibration we use isolation mounts, these mounts are easy to attach and economical, they attach to casters up to 3 inches in diameter
inadequate maintenance, lubrication of parts, and worn out mufflers increase...
noise levels
Antioxidants are crucial for
our survival . Without them, oxidation would destroy our bodies. Antioxidants are molecules that can safely donate an electron to a free radical neutralizing it. You can find antioxidants in fruits, vegetables, seeds
Pressure Formula MKS CGS
p=F/A N/m2 Dynes/cm2 (2 x 10-5 N/m2 or 20 uPa) (2 x 10-4 dynes/cm2 or 20 uPa)
•Over the last few decades OSHA has achieved remarkable success in by ... •There are still many industries in US where workers are .. •Non-occupational noise exposure ->
preventing hearing of millions of industrial workers. exposed to hazardous levels of sound. (OSHA did not cover musicians in their guidelines) Awareness, research, and regulations. (NIOSH have been conducting more research and they are up to date. They have more strict/sensitive guidelines. The problem lies in the number of hours they can work because they cannot work over 8 hours at 90 dB so there is concern financially)
Stria Vascularis Function
produces the endolymph and supplies oxygen and other nutrients to the cochlea. Maintains ionic balance. Plays important role in potassium cycling.
Field of audiology is a mix of disciplines Normal hearing? How to measure normal hearing and HL accurately? How much noise is safe and how much is unsafe? Permissible duration of exposure? Instrument for measuring noise? Hearing impairment and handicap? Who will test hearing and how to test hearing? How to protect hearing ?
psychology, physics, electronics, pediatric, geriatric The professionals all worked together to develop an instrument to measure hearing -Engineers make the audiometer -Scientists look at the different areas of problems -Government needs to provide support so that laws can be passed
•Dr. Hallowell Davis... •World War II... •Military established 2 large medical centers ... •The field of Audiology started developing from this period along with professional Audiologists.
significant contributor in the area of hearing and hearing loss. OHL concerned for govt. and public due to rapid increase in incidence and prevalence -> Soldiers and veterans with HL. Post WWII, we had a large population of veterans with hearing loss. (The Walter reed Army Hospital & Philadelphia Naval Hospital) in 1943 for soldiers and veterans with HL.
Results:
significant reduction in synaptic counts for cochlear regions with CF> 4kHz (p<0.01) in animals from experimental group. -Higher loss of low spontaneous rate fibers in the region of noise exposed cochlea corresponding to high characteristic frequencies.
Endolymph contains
sodium (more in perilymph) potassium (more in endolymph) If the potassium decreases in the endolymph, the electrical gradient and the endocochlea potential will be off. Depolarization and hyperpolarization occur with the stereocilia. It will not be affected in the perilymph because there is a barrier?
In an acoustic free field there are no reflections;
sound waves reach an observer directly from a sound emitting object. The sound wave passes the observer exactly once, and never returns. Two common examples of acoustic free fields are: The sound source is far enough away that it appears as a single point source, far in the distance. Visualize an airplane flying high overhead on a clear day. An anechoic chamber is a special facility constructed to approximate an acoustic free field by using materials to absorb sound waves before they can be reflected A free field is a region in which there are no reflected sound waves. In a free field, sound radiates into space from a source uniformly in all directions
NRST test
speech perception in noise.
The acoustic terms "near field" and "far field" have to do with
the physical distance from the sound source. Depending on how far away an observer is from a sound emitting object, the acoustic energy produced by the sound source will behave quite differently.
Noise exposure leads to reduced O2 supply
this leads to an increase in free radicals production results in lipid oxidation and protein degradation. Then it damages cells/cell death. This results in NIHL
phons
unit of equal loudness
Comparison of NIOSH Noise Criteria and OSHA Hearing Conservation Criteria
§Aim: To compare the noise exposure measurements using revised noise exposure criteria recommended by NIOSH & OSHA hearing conservation amendment to the occupational noise standards. §Method: §5 Q400 noise dosimeters were used for noise measurements. §Dosimeters were programmed according to the NIOSH setting (85-dB criterion level, 3-dB exchange rate) and OSHA HCA setting (90-dB criterion level, 5-dB exchange rate). Noise measurement samples were collected from different group of workers shown in Table 2. §A total of 61 valid samples were collected from data analysis. Results & Discussion: §Noise exposure according to the NIOSH criteria ranged from 65.5-98.7 dBA with a mean of 85.8 dBA . §Noise exposure according to the OSHA criteria ranged from 52.2-93.9 dBA with a mean of 79.2 dBA . §Noise exposure using NIOSH criteria were on avg. 6.6 dB higher than OSHA. §The 3 dB ER increases the TWA + lower criterion level in NIOSH -> Increases the dose. §Use of NIOSH REL -> Classifying more workers as overexposed. -Increase in number of workers enrolled in HCP than the current HCP Conclusion of the study: Lower exchange rate + lower criterion level -> estimated 2.7-fold increase in the number of enrollments of workers in a HCP from 23% of the workers under OSHA-HCA criteria to 61% if the NIOSH criteria were applied. Will have to pay more for the programs and the hearing protection.
FACTORS CONTRIBUTING TO HIGHER NOISE EXPOSURE VALUES AND NOISEDOSE
§Exchange rate: most significant parameter in noise dose and TWA. Ti=TC/2^((L-LC)/Q)
Who governs hazardous noise exposure?
§Guidelines or regulations for noise exposure levels were established by OSHA (1983) and NIOSH (1998). §Both OSHA & NIOSH were created by Occupational Safety & Health Act (1970).
Time Weighting :
§If there are impulsive noise components in the measured noise spectrum -> Slow time weighting can have significant impact. §Slow time weighting -> Slows the instruments ability to react to fast changing noise levels. Results -> lower reported noise exposure §Threshold level -> If larger proportion of noise is below the threshold then obtained TWA and dose values will be lower.
Noise Dose
§Noisedose is expressed as a percentage of a predetermined maximum, defined by the OSHA or NIOSH criteria. -Noise dose calculation includes criterion level, threshold level and exchange rate
NIOSH
§Part of the Centers for Disease Control and Prevention (CDC) in the U.S. Department of Health and Human Services. §It conducts research and provides information, education, training, and recommendations regarding occupational safety and health. § NIOSH is in a position to recommend standards and best practices. §However, it is not in a position to regulate or enforce standards.
OSHA
§Part of the U.S. Department of Labor. §Responsible for developing and enforcing workplace safety and health regulations. § The OSHA standard (29CFR1910.95) carries behind it the force of law. §Employers in the industrial sector are bound to comply with it. § Those employed in mining, railroad, coast guard, military, and construction are bound by their own standards.
Noise exposure levels for musicians during rehearsal and performance times
§Purpose: To determine daily noise doses and 8-hour TWAs for rock band musicians, crew members, and spectators during a typical rehearsal and performance using both OSHA and NIOSH criteria. §Method: §Personal dosimetry measurements was completed on 5 rock band members during one 2-hrs rehearsal and one 4-hrs performance. (difference between rehearsal and performance. Put more effort into the performance. Play louder when there are spectators. more driven to play loud.) §TWA and noise dose were calculated using OSHA & NIOSH criteria. §TWA & noise dose values were compared to industry guidelines for enrollment in HCP and the use of HPDs. Conclusion of the study: §Rock band members are exposed to dangerously high levels of sounds and should be enrolled in HCP. §Use of HPDs especially during performance. §NIOSH criteria is more strict and more protective as far as hearing of musicians is concerned.
Occupational noise exposures among three farm families in northwest Ohio
§Purpose: To evaluate occupational noise exposures of three families living and working on farms in Northwest Ohio. §Method: §Noise measurement conducted for 7 consecutive days for every participant for 1 week each during planting, growing and harvesting period. §Dosimeters were programmed according to OSHA & NIOSH criteria. §One family was evaluated per year and a total of nine family members (six adults and three children) participated. §6 out of 45 exposures among the adults and none of the 11 exposures among the children exceeded the OSHA action level. 10 out of 45 exposures among the adults and 1 of 11 exposures among the children exceeded the NIOSH
§The difference in NIOSH & OSHA?
§The less strict OSHA values allow for higher exposures for longer durations and the more strict NIOSH values recommend lower exposures for shorter durations §The NIOSH recommended exposure limit is based on scientific data relating NIPTS to the level and duration of noise exposure. §The OSHA Permissible Exposure Limit (PEL) was the result of debate and compromises that are a part of enacting any legislation (OSHA, 1983). §Both standards are not completely protective in nature. -Looking at profit and working safety with the compromise. If they go for the most protective option, they lose profit §The NIOSH & OSHA guidelines allow for some NIPTS based on their individual definitions of material hearing impairment and the percentage of the population for whom this risk is deemed acceptable. §These guidelines are based on average risk (rather than individual susceptibility) so certain individuals may be at greater or lesser risk for developing NIHL .
Excess risk
§The percentage of people in a noise‑exposed population who develop a material hearing impairment (as defined by OSHA or NIOSH) above and beyond the percentage of people in a non‑noise‑exposed population who develop a material hearing impairment. §It is calculated based on the exposure level and assumes an8‑hour work day, 5 days per week, over a 40‑year working lifetime
Damage Risk Criteria (DRC)
§The term damage-risk criteria refers to the risk of hearing impairment from various levels of noise. Many factors enter into the development of these criteria and standards in addition to the data describing the amount of hearing loss resulting from a certain amount of noise exposure. §One approach to DRC is to protect just about everybody from just about any degree of NIHL . This notion is illustrated by the "Levels Document" issued by the Environmental Protection Agency (EPA) which suggested that NIPTS could be limited to less than 5 dB at 4kHz in 96% of the population by limiting noise level to 75 dB Leq over a 40 year period. §Changing the criterion to 77 dB Leq would protect 50% of the population §The DRC from Committee of Hearing & Bioacoustics and Biomechanics (CHABA) intended to limit the amount of NIPTS to 10 dB ≤ 1000Hz, 15dB at 2kHz, and 20 dB≥3kHz in among 50% of workers exposed to steady or intermittent noise for 10 yrs. §It is based on amount of TTS that occurs after an 8 hr noise exposure, and relied on the notion that this value seems to correspond to the amount of NIPTS after 10 years of occupational noise exposure. §The CHABA DRC required noises to be measured in third octave or octave bands and expressed maximum exposure levels for durations up to 8 hrs per day. Damage‑risk criteria provide the basis for recommending noise exposure limits based on noise level and exposure time
Material Hearing Impairment
§The time/intensity criteria for OSHA and NIOSH are in part based on each organization's definition of material hearing impairment and the excess risk of developing that impairment. §OSHA's definition of material hearing impairment: average hearing thresholds exceeding 25 dB HL at 1k, 2k and 3k Hz, bilaterally. §NIOSH's definition of material hearing impairment: average hearing thresholds exceeding 25 dB HL at 1k, 2k, 3k and 4k Hz, bilaterally. -Averaging of thresholds across 3 or 4 frequencies and ears means that significant hearing loss can occur before either formula labels it as hearing impairment. -The flaw from both of the definitions is they are not taking into account the sloping hearing loss, low frequencies are traditionally better. If someone has unilateral hearing loss that could affect it, since you are averaging bilaterally
Noise Susceptibility:
¨ Also depends on maturation & aging eg. Heavy noise exposed mothers have a higher proportion of neonates with HL. ¨ As age progresses the noise induced damage tends to reach a plateau.
Pigmentation;
¨Decreased pigmentation is related to higher degree of susceptibility to noise. Studies showed larger TTS in cases of albinism & also in individuals with less pigmentation.
Genetic Factors:
¨Different genetic strains have different noise susceptibility. ¨Any gene that weakens the ear functionally or structurally would make it more susceptible to noise damage. ¨Several genetic mutations in group of oxidative stress genes, inner ear potassium recycling pathway genes, and monogenic deafness genes have been associated with increased susceptibility to NIHL There are a lot of genes that can help protect people from certain diseases
Sound
• A vibration that typically spread as an audible wave of pressure through a medium like air, water or other materials. •Vibration-> Pressure changes in air-> Pressure waves -> Perception of pressure wave by ear. •Sound always transmitted as compression wave, but in solid medium other types of wave for transmission are possible.
A number of factors determine the best noise control measure. They are:
• Financial and technical feasibilities • Safety • Maintenance accessibility • Minimum allowable disruption time for a particular production operation or process
Psychological Effects: Annoyance
•A response to noise: SUBJECTIVE •It is an outcome when noise interferes with work, feeling, thoughts, and sleep. -It includes fear, anger, displeasure, and tiredness. •Traffic and aircrafts studies showed association between noise levels and annoyance (dose response). •High frequency noises are more annoying than low frequency noises
Active noise cancellation
•A sound minimization technique that utilizes the generation of an out-of-phase signal (called the active source) to "cancel out" unwanted noise. (it has to be at the same frequency or else the out of phase signal would not be able to work. This technique is not independently used) •Usually used in combination with standard passive silencers. •The pressure loss by this technique is much less than pressure loss by silencers. •Provide excellent low frequency attenuation and eliminates pure tone. •Work well in moisture or particle laden air. •Ineffective for frequencies >1000 Hz and requires periodic maintenance.
Sound Intensity
•A sound wave transfer energy and so energy is needed to produce a wave. •The sound power of source will decide the intensity of the waves produced.
•3 types of Silencers
•Absorptive or dissipative silencers •Reflective or reactive silencers •Combination silencers (absorptive + reflective)
Effect of Noise Exposure on Cardiovascular System
•Acute exposure of different types of noises -> Arousal of ANS & Endocrine system •Noise exposure -> increases systolic and diastolic blood pressure, changes in heart rate, and peripheral vasoconstriction •Individuals with high exposure level (at least 85 dBA) have high blood pressure than controls
Combination Silencers
•Addition of layer of fiberglass or other absorptive material to the outer shell of reflective silencer •Efficient reduction of noise levels over wide frequency range. •Limited application in environment with high temperature or contaminated air stream.
Overview
•Advantages of noise control measures -Prevent HL -Workers will be happier -Prevent law suits -Better conversations in workers -Workers would not have to wear hearing protection if it was quiet enough •Sound transmission •Strategies for noise Control •Reduction of noise at the source •Purchasing quiet equipment •Modification of equipment •Maintenance of equipment •Silencers •Vibration damping •Interrupt the pathway between source and receiver •Acoustic enclosures •Acoustic barriers •Vibration isolation •Enclose the receiver •Active Noise cancellation •Remove the receiver
Absorptive or Dissipative Silencers advantages and limitations
•Advantages: • Low-to-medium pressure loss. • Standard design. •Limitations: • Poor LFs (<500 Hz) attenuation. • Very sensitive to moisture and the material can degrade under certain circumstances such as high heat condition.
Absorptive or Dissipative Silencers
•Attenuate sound by porous sound absorbing material like fiberglass. •Parallel baffle •The thickness of baffles should be selected with reference to the predominant frequency of the noise. •Used in heating, ventilation, AC duct system. •More attenuation in 1000- 4000 Hz range
OSHA Occupational noise exposure - 1910.95
•Audiometric Monitoring Summary: Audiometric Calibration •Calibration will be checked before use by a person with known and stable hearing. •Acoustic calibration -> annually. Exhaustive calibration -> every 2 years.
Revised Baseline
•Baseline can be revised if: •STS persists •10 dB change over 2 consecutive annual tests (need to revise to update to current hearing, if it is consistent for 2 years, then that individual has developed a permanent threshold shift, that is the new hearing) •Improvement in hearing •Improves 5 dB over 2 consecutive annual tests •Revise for both ears •Use the better of the 2 consecutive audiograms as the revised audiogram. •If no difference use the earlier test.
Reduction of Noise at the Source: Purchase Quiet Instruments
•Best way to control noise for new industries. •Ways of designing quiet machines -Use of non-metallic materials (metal vibrates- more noises) -Adjusting shape thickness and size of components (noise level changes based on the size of the machines) -Damping vibration through insertion joints -Reducing the height of fall (object falling at higher is louder) -Regulating the flow of compressed air (vacuum has 3 levels (superficial, moderate, deep cleaning. Louder when you are using the third mode. The more power, the louder) -Reducing the power or speed of the equipment -Enclosing specially noisy parts -Providing proper seals and insertion loss
•Biological check
•Check the equipment output using the hearing of a non-noise exposed person. • If threshold checks shows deviation of 10 dB or more, acoustic calibration is required by OSHA
Non Auditory effects of noise exposure on Children
•Chronic noise exposure affects cognitive functions like central processing and language comprehension. •Deficits in sustained and visual attention •Difficulty in concentrating among children with noise exposure history •Children with high level environmental noise exposure -> poor auditory discrimination, poor memory and speech perception.
Children study
•Cohen, Glass, And Singer (1977) studies children from 32 floor apartment building which was adjacent to a busy road. •Results: Children living in lower floor showed great impairment in auditory discrimination and reading than children living in higher floors. •Bronzaft and McCarthy (1975) compared children from classroom with high noise (due to railways noise) to children from quieter classroom on reading task. •Mean reading age was 3-4 month lower in children with noise exposure -Children's education and learning can be affected from noise.
Evaluation of Audiogram:
•Comparison of Annual and baseline audiogram to determine significant threshold shift (STS). •STS = change in PTA of ≥ 10 at 2000, 3000, 4000 Hz in either ear. If STS: •Re-evaluate in 30 days. •Notify the employee in writing of the STS within 21 days. •Must be fitted with HPD or retrained on HPD. (hearing protection devices) •Age factors can be taken into consideration. •If further testing indicates the STS is not persistent and the employee's noise exposure is < 90 dB, the employee is not required to wear HPDs.
•Exhaustive: Every 2 years
•Comprehensive calibration •Frequency •Attenuator dial linearity •Tone distortion •Signal rise-fall time.
Vibration Isolation Cont.
•Connection to vibrating machines. Other than mounting points must also be properly designed. •The connection to the machine should be made where the vibration amplitudes are at a minimum, and the other end of the connection should be made on the most solid and massive support available. (it cant be at maximum or it would be worse)
Audiometric Calibration
•Daily functional check •Check the equipment prior to use •Visual Check: Examine headphones, cables, and controls •Listening check at soft and loud intensity : •Signal should be steady and undistorted. •Bend the cords to check for static or intermittency •Appropriate plugging of jacks, test crosstalk
Acoustic Enclosures
•Decision to control the noise reaching a worker using acoustic enclosures depend on spectral content. •Effectiveness of sound isolation by an enclosure is a function of mass. •Just placing an acoustic enclosure is not enough. •Physics law " Energy can neither be created nor be destroyed". (It gets transformed into heat energy and the temperature needs to be regulated or else it will catch fire) •Sound absorption -Not a good idea for a machine that needs to be opened everyday. That enclosure will not function effectively
Frequency
•Definition: the number of complete wavelengths that pass a point in a given time •Unit: Hz •Wavelength (λ)= c/f •Time period of wave f=1/t As frequency increases, time period decreases
Noise Criterion Curves
•Developed by American Acoustic consultancy firm of Bolt, Beranek, and Newman. •Commonly used in USA •Based on broadband noises and curves obtained by plotting individual band ratings. •The lowest of these contour curves which does not intersect or touched the measured spectrum is referred as NC level of the noise. Ex: Nc-45 is the last line that is not intersected by the black line. People aren't commonly using this anymore
Noise Rating Curves
•Developed by International Organization of Standardization (ISO 1973). •Purpose: To determine acceptable indoor noise for annoyance, hearing conservation, and communication. •Commonly used in Europe. • The noise rating graphs for different sound pressure levels are plotted at acceptable sound pressure levels at different frequencies. •Each curve is obtained by NR number. •Similar to NC curves but differ slightly at low frequency end of graph.
Enclose the Receiver
•Effective and practical to place workers in a sound-treated control rooms or isolated offices with windows from which instruments can be operated. •Ex. Printing press rooms. Saw mills, and paper making plants. •Absorption chambers can be created by covering walls of the space with sound absorbing material •Such arrangement provides receiver a comfortable environment for work and prevent receiver from exposure to noise, fumes, and dust
Silencers/Mufflers
•Effective way of reducing sound levels propagating through the medium. Ex.: Motorbike silencers •A good silencer attached to a exhaust pipe of diesel tractor -> reduce noise by 3 dB
Occupational noise exposure - OSHA 1910.95
•Employees will be protected from noise exposure when the sound levels are greater than the following: -Duration per days, hours: 8. Sound Level dBA Slow: 90 -Duration per days, hours: 6. Sound Level dBA Slow: 92 -Duration per days, hours: 4. Sound Level dBA Slow: 95 -Duration per days, hours: 3. Sound Level dBA Slow: 97 -Duration per days, hours: 2. Sound Level dBA Slow: 100 -Duration per days, hours: 1.5. Sound Level dBA Slow: 102 -Duration per days, hours: 1. Sound Level dBA Slow: 105 -Duration per days, hours: 0.5. Sound Level dBA Slow: 110 -Duration per days, hours: 0.25 or less. Sound Level dBA Slow: 115 -Measurements were made with a standard SLM using A scale and at a slow response.
Effect of Noise Exposure on Endocrine System
•Exposure to high level of noise-> Increase level of stress hormones (cortisol, adrenaline, and noradrenaline). •Pattern of hormonal response to noise exposure -> Noise as a stressor. -THE TYPE OF NOISE WILL HAVE DIFFERENT EFFECTS ON THE ENDOCRINE SYSTEM. Music vs. White noise. When you enjoy the noise, like the music at a concert, you can listen to the noise that exceeds the 100 dB. The cortisol will be different than the 100 dB white noise
•Two types of damping
•Extensional damping: damping material brushed directly on the surface. •Constrained layer damping: Damping material sandwiched between 2 sheets of stiff material that lack sufficient damping. (vibration should not make it to the next layer)
Study example
•Fields (1992) reported that noise annoyance increases with fear of danger from the sound source, sensitivity to noise, belief that he has no control over noise , and awareness about non-noise impact of the source after controlling noise levels.
If the noise exposure is prolonged...
•Habituation (not complete habituation, you cannot get completely used to it) to the noise. •Noise exposure during sleep -> increased blood pressure, heart rate, body movements, and finger pulse amplitude. •Cortical arousal due to noise exposure depends on +Noise events & their acoustic properties (intensity, frequency) + Individual noise susceptibility +Stage of sleep •Noise reduction studies: Decrease in amount of indoor noise level -> amount of REM sleep and slow wave sleep increased
Application of Age Correction in calculating STS
•Hearing loss due to aging should be taken into consideration when evaluating for a STS. •Appendix F of 1910.95 includes correction values.
Common applications of Silencers:
•High-pressure gas pressure regulators, air vents, and blow downs •Internal combustion engines •Reciprocating compressors •Centrifugal compressors •Rotary positive displacement blowers •Rotary vacuum pumps and separators •Industrial fans
•Need of personnel to assess occupational hearing loss at;
•Hospitals •Industries •Military •Scientific institution •Need resulted in new group of specialists -> Hearing testing technicians & hearing conservationists.
•From previous equations -> I ∞ p2
•I= p2 / Zc (P 0s) •Thus, if the intensity increases by 16:1, pressure increases by 4:1 •Intensity increases by 10:1, pressure increases by 3.16 •If sound intensity doubled, pressure increases by only 1.414
Modification of Equipment
•Identification of the noisiest machine •Identify the noisiest part of the noisiest machine •Identify the cause of the noise -Reducing the distance between the impacting parts -Damping and isolating different parts -Reducing the force driving the impacting parts -Changing pumps in hydraulic systems -Size of the component of machine -> small -> noise won't radiate efficiently
Record Keeping
•If it wasn't documented, it wasn't done. •Noise exposure records must be kept for 2 years. •Audiometric test results are to be kept the duration of employment. •If an employer stops doing business, the employer will transfer the records to the new employer. Graphic Audiogram -What we typically use everyday -Good when training employees and showing them the implications of their HL Tabular Audiogram •Most widely used •Less likely to make errors when reading thresholds. •Calculations for STS easier. •Keeps information compact. •Some use electronic spreadsheet. Make calculations for you.
Octave bands
•Impact of LF and HF sounds are different. •When dealing with noise issue-> It is important to divide sounds into bands of frequency. •Octave bands: Frequency bands which cover two to one range of frequencies ex. The 1 kHz (range from approximately 710 Hz to 1420 Hz). Noise is normally a broad band signal Frequency bands 2:1 range of frequencies
Frequency Weighting Cont.
•Industrial noise measurements -> "A" weighted decibels. •Advantage -> Single reading of the meter for assessment. •Disadvantage -> ?? Energy Concentration/ Detail design and calculations •Solution: OCTAVE BANDS •How? 1. Applying weighting network effect on individual octave bands 2. Comparing octave band sets of standard rating curves
Audiometric Monitoring
•Industrial workers are part of audiometric monitoring when sound exposure levels are ≥ TWA of 85 dBA. •Free to industrial workers (paid by industry) •Audiometric tests completed by audiologist, ENT, PCP, technician w/ CAOHC training under an Aud, ENT or PCP. •Baseline -> w/in 6 mo. of employee's first exposure to the action level. •OSHA allows additional 6 months for baseline if testing is completed using a mobile van and workers are using hearing protection for at least 6 out of the 12 months. •No noise exposure 14 hours prior to the baseline test. Hearing protection may be used if cannot be out of noise for 14 hours. (TTS could happen. Temporary shift component if measured immediately after shift) •Annual audiogram can obtained from any worker if exposure levels ≥ TWA of 85 dBA. (if below that, not required to go to hearing evaluation)
Intensity; Inverse Square Law
•Intensity= P/A •Intensity decreases with increase in distance (Inverse Square Law) •The range of sound amplitude that we can perceive is huge. •In other words " The sound energy per unit area received at any point is inversely proportional to the square of distance from the source." Intensity perceived at 10 m will be 1/4 the intensity as compared to 5 m a) The intensity at a point 10m away from source is one quarter of its intensity at 5m b) The intensity at a point 15m away from source is one ninth of its intensity at 5m
Remove the Receiver
•It can be called administrative noise control •Rotating the workers in and out of noisy areas -> reduces the noise dose of each worker. •Not feasible in all circumstances. •Provide adequate rest periods for recovery.
Octave Bands Cont.
•It is possible to calculate dBA values from Octave bands and one third octave bands. •Apply appropriate weighting factors to each individual octave band. •Combining the octave band values
Things to remember
•It is the energies or powers or intensities which should be added not the pressures. •Hence, it does not matter whether the question (for calculating sound intensities) is stated by reference to dB IL or dB SPL. •dB Il = dB SPL
•Barrier penetration:
•LF sounds penetrates barrier more readily than HF sounds. (LF can penetrate better because it is a longer waveform, heavier objects can vibrate better) Apartment walls: high tones are reflected or absorbed
Leq = 10 log [ 1/(t2 - t1) S (PA^2)/(PO^2) dt]
•Leq= equivalent continuous sound pressure level in dB •p0 = reference pressure level (typically 20 µPa) •pA = acquired sound pressure •t1 = start time for measurement •t2 = end time for measurement
Vibration Damping
•Materials used in manufacturing machines have varying degrees of internal damping. •Damping effectiveness is greater for specially developed damping materials than internal damping. •Compounded damping material is more effective. air filled spaces/rubber mats
Sound Transmission Loss (STL) materials
•Materials which are used to block noise or attenuate propagating noise •Typically heavy and dense, with poor sound transmission properties •Typical applications include barriers, enclosure panels, windows, doors, and building materials for room construction -Movie theaters use this material to make sure there is no interference from the other screens
Effect of Noise Exposure on Sleep
•Most deleterious non-auditory effect •Level of alertness, performance, health, and quality of life could be affected by disturbances in sleep. •Sound pressure level of 33 dBA can cause physiological reactions during sleep Ex. Body movements, awakening, and blood pressure •Sleep disturbances due to noise exposure is proportional to amount of noise. •Number of awakenings and rapid rate of changes in sleep stages.
•The audiometric test documents must include
•Name •Job classification •Date of the audiogram •Examiner •Audiometer model and serial number •Date of calibration (acoustic & exhaustive), •A record of biological checks •Record of background SPL levels in the booth •Number of hours the employee was away from noise prior to the test •Any personal noise exposure data •Audiogram classification code (military personal) •Results of follow-up examinations/recommendations
Noise Control Things to consider: •Location of the sound source and the location of the employee is also important to consider.
•Near field Far field
2 Sets of Rating Curve
•Noise Criterion (NC) Curves •Noise Rating (NR) Curves
OSHA Occupational noise exposure - 1910.95 Components to a HCP
•Noise Exposure Monitoring •Audiometric Testing •Recording Keeping •Hearing Protection •Training
Standard Threshold Shift
•OSHA freqs. : 2, 3, & 4 kHZ •PTA OSHA = (〖HL]]2k+〖HL〗3k+〖HL〗4k)/3 •STS -> If PTA of 234 kHz gets worse by 10 dB or more compare to baseline
Psychological Problems due to Noise Exposure
•Occupational noise exposure -> increased post work irritability. •Increased aggressiveness. •Impact on interpersonal relationship. •Decrease in tendency to help others.
Referral Criteria
•Other conditions may want to refer. •Based on American Academy of Otolaryngology •Employer does not have to pay. •Severity •> 25 dB average loss at 500, 1000, 2000 and 3000 Hz. •Difference b/w ears of: •>15 dB average at 500, 1000, 2000 Hz or •>30 dB average at 3000, 4000, 6000 Hz. •Change in hearing of: •>15 dB average at 500, 1000, 2000 Hz or •>20 dB average at 3000, 4000, 6000 Hz. •Medical Condition •H/o otalgia, otorrhea, fullness or discomfort, sudden or rapid loss, severe persistent tinnitus and dizziness. •Excessive cerumen or foreign body in the ear canal.
•Annual calibration
•Output calibration •Measure the coupler SLP at 70 dB from 500-6000 Hz . •Sound pressure levels shown by SLM should be within tolerance range shown in table 1 •Linearity Check •Purpose: To check attenuator is working properly •Measure at 1000 Hz the intensity from 70 down to 10 dB. •Can also be performed using voltmeter
Example with airport
•People who work at the airport at the ground level are exposed to a lot of noise. Even with the hearing protection, their hearing can be affected. Aircraft noise exposure study showed association between high noise exposure and more medical treatment for heart conditions, hypertension, high blood pressure, and more cardiovascular drug use •Summary -> Noise exposure is associated with hypertension and increases the risk of coronary heart disease.
•General decibel formula expressed in terms of power;
•Power Level (PL)= 10 log P/P0 •Intensity expressed in decibel-> Intensity level = 10 log I/I0 (reference intensity) •Power of fire & Power of sound •Acoustic impedance (opposition presented by a medium, air and liquid are different: that is why the speed of sound is different) of a progressive sound wave (Zc )= ambient density x speed of sound = =ρ0s •Intensity= ratio of the square of rms pressure to the characteristic impedance= prms2/ ρ 0s
TL Rating
•Products sold for noise control should have a TL rating that is determined by ASTM standard •TL rating varies with frequency. TL values generally range from 20 to 60 dB, with the higher number indicating superior attenuation properties (it avoids transmission a lot)
Acoustic or audio shock limiters •2 ways to control
•Proper maintenance of equipment. Use of sound shields to filter narrow bands. •Inclusion of acoustic limiter into the headset
Noise Control Through Servicing of Machines/Equipment
•Properly scheduled maintenance and servicing of equipment. •Acoustic enclosure removed during equipment should be properly placed back. If not placed back properly, there will be more noise because it will leak •Proper maintenance of acoustic enclosures: may get damage due to contamination from oil or other particles
Audiometric Test Requirements
•Pure tone hearing threshold measurement for both ears at 500, 1000, 2000, 3000, 4000 & 6000 Hz for each ear. •Finding thresholds; not a screening procedure •Audiometers must meet ANSI, S3.6-1969. •Hearing evaluations must be completed in a room meeting "Audiometric Test Room" requirements
Advantages of Noise Control
•Reduction of cost related to a implementation of HCP. (hearing conservation program) •Reduction of NIHL •Reduction of workers compensation and legal costs •Reduction in absenteeism •Improved communication •Reduction in accident rates •Reduction in coronary heart disease among workers.
Noise Exposure Monitoring
•SLM •Noise dosimeters •Measurements of noise and application of OSHA/ NIOSH guidelines for calculating sound levels, TWA, and noise dose.
•Acoustic pipe lagging:
•Situations when external wall of pipes radiates more energy and inline silencer is not feasible. •Exterior surface covered with sound absorbing material. •Sound absorbing material is covered with barrier material with high sound transmission loss properties. (it is a sound barrier, it prevents transfer to the environment or surrounding material)
Sound Transmission
•Sound originates from the source, travels via a path to a receiver. •Complex event (many sound source, paths, and receiver) (a lot of different sources) •Need to assess the concentration of sound energy •Low frequency noise -> treatment using equipment modification and massive barriers •High frequency noise -> sound absorption approaches
Age correction
•Steps: •Find the age correction values for the most recent audiogram •Find the age correction values for the baseline •Subtract the age correction values for the recent age and the baseline age. •The difference represents that amount of hearing loss that may be attributed to aging within this time period. •Subtract the age correction values from the most recent audiogram. •Determine if there is a STS.
•Permissible Exposure Level
•The level in dB to which an employee can be exposed for a specified duration of time and still meet occupational safety guidelines. •Above this level feasible engineering and/or administrative controls must be used to reduce the exposure level. Exchange Rate
Basics of sound measurement
•Thermometer measures temp not the heat output. •SLM measures sound pressure not the sound power. •Is our ear equally sensitive to all frequencies? •If a sound measuring instrument treats all frequency equally then? •Ex 70 db of sound ........
Training
•Those exposed to an the AL (action level) (TWA of 85 dBA) must receive annual training on hearing conservation. •Employer must ensure the employees participate in a training program. •The training can be in any format (video, PowerPoint....) Must however include: •Effects of noise on hearing •Hearing protection (adv/disadv, types, attenuation, instructions on use and care) •Audiometric testing (purpose and information on the test procedure)
Importance of detailed case history
•To meet record keeping requirement of agencies like OSHA •To monitor changes in noise levels and use of HPDs. •Tool for health surveillance •To determine contributing factors •To provide insight into the factors that increase the risk of HL
Sound absorption materials
•To reduce the buildup of sound in the reverberating environment •Effect of reverberating noise + noise from the source -> elevated noise level •Important to know and apply principles of room acoustics before starting any treatment using sound absorbing material. It would be hard to cover warehouses and large rooms •Application of sound absorption on a room's surfaces has both advantages and disadvantages.
•What if the strategies for reducing noise by working on source doesn't work?
•Treat sound transmission path or modify the listener
Interrupt the Pathway between Source & Receiver / Path Treatment:
•Typical path treatments include •Adding sound-absorption materials to the room or equipment surfaces •Installing sound transmission loss materials between the source and receiver(s) •Using acoustical enclosures or barriers, or any combination of these treatments.
NC and NR
•Unfortunately the NC and NR system are less reliable than A weighted reading on SLM. •Common broadband noises -> dBA level= NC/NR + 5 to 7 dB. • Do you think that we can extract frequency information from dBA reading? Yes, neither the NC and NR curves are used. We use dBA because you can extract frequency information.
Reflective or Reactive Silencers
•Use large impedance or sound reflective properties to reduce noise in a pipe. •Efficient in reducing LF noise. Commonly used to reduce the exhaust noise generated by internal combustion engine.
Noise Control
•Usually left up to other professionals like engineers. •Hearing conservation personnel are often not trained in noise control. •Need to be able to discuss control needs and to evaluate recommendations made by the noise control engineer.
Vibration Isolation
•Vibration of machines transmits to floor, ceiling, walls, or other structures -> generates noise. •Vibration isolators are made up of numerous different materials. Ex. Gas or liquid filled devices, pads made from rubber, cork, felt, or fiberglass.
Frequency Weighting Network
•What we want from measuring instrument? •Solution: Frequency weighting network. •3 principal weighting network -A weighting: 1 kHz at 40 dB should be used for SPLs up to 55 dB. -B weighting: For SPLs 55 to 85. -C weighting: For high sound levels •It was found that there is good agreement between subjective reaction & A weighted sound levels ->A weighting is used for all sounds
Acoustic barriers between source and receiver
•When equipment cannot be fully covered. •A barrier's capability to block transmission is indicated by transmission loss (TL) rating. •Measurement of TL over 16 freqs. between 125 - 4000 Hz is needed to determine barrier sound transmission class (STC). •Higher STC -> more sounds blocked. •To increase STC rating -> Add mass, increase or add air space (acts same as absorbing material) or add absorbing material. 3 inches of air space -> 3 dB improvement in STC. 6 inches -> 8 dB. •Effective when placed closest to the source or receiver and should have largest possible width and height. •Acoustic barriers + Acoustic treatment of walls and nearby surfaces-> better noise control •Low frequency: sound shadow -> barrier must be 5 wavelength high
Vibration Damping Effective in 2 cases:
•When forced vibration frequencies correspond with the resonant frequencies in component parts of attached equipment. •When impact type shocks are applied to thin surfaces.
When to report HL to OSHA?
•When the hearing loss is work related and current average threshold is 25 or worse in presence of an STS. •Detailed case history is a tool to determine if the hearing loss is work related
•Audiologist, ENT, or PCP can review audiograms and determine the need for further evaluation. •Employer will pay for follow-up if:
•You suspect audiogram is not valid -The HPD causing a medical problem.
Leq - Equivalent Continuous sound level
•represents a value known as Equivalent Continuous Sound Level. •Sound pressure level (SPL) varies in amplitude over time •An imaginary constant SPL that would produce the same energy as the fluctuating sound level you are measuring over a given time interval.
High Frequency Audiometry
►It refers to AC testing between 2K to 8KHz. ►Extended high frequency audiometry: ►It refers to AC testing between 8K to 20 kHz. ►Impulse noise exposure: high incidence of asymmetric & extensive threshold shift above 8kHz & raising configuration (most common). ►Steafan et.al 1981, reported that 8KHz to 12Khz was poorer for subjects expose to noise. Clinical applications: ►Early detection of NIHL. ►Differentiating NIHL & other high frequency SNHL e.g. Presbycusis, ototoxicity .
