| NIHL Definitions Noise refers to unwanted, undesirable, or excessively loud sound experienced by an individual. The effects of noise depend on various characteristics of the sound: (1) intensity (more intense sounds > less intense sounds); (2) spectrum (higher frequencies > lower frequencies secondary to the protective effect of the acoustic reflex at lower frequencies); (3) cumulative lifetime exposure (longer exposures > shorter exposures); and (4) pattern (continuous exposures > interrupted exposures for the same overall duration and intensity). Temporary threshold shifts (TTS) are changes in hearing after noise exposure which completely recover within 24 hours. Permanent threshold shifts (PTS) are hearing losses that are not recoverable with time. The noise exposure causes permanent loss of hair cell stereocilia with apparent fracture of the rootlet structures and destruction of the sensory cells, which are replaced by nonfunctioning scar tissue . Because TTS may mimic PTS, individuals should be given audiometric tests only after a recovery period of 24 hours following exposure to hazardous levels of noise. Acoustic trauma occurs when high-intensity impulse noises (eg, explosions) penetrate the cochlea before the acoustic reflex has been activated. Impulse noises refer to either single or multiple noise events lasting 1 second or less, and high-intensity impulse noises of > 140 dB may cause immediate and irreversible hearing loss. The acoustic reflex is a reflex contraction of the stapedius muscle in response to noise > 90 dB. This reflex dampens sound transmission and is particularly protective against low-frequency noise. The delay from noise exposure to onset of the reflex is 25150 ms, rendering it less effective against impulse noise compared with continuous noise. Pathogenesis NIHL results from trauma to the sensory epithelium of the cochlea. The sensory epithelium of the cochlea comprises one inner and three outer rows of stereociliated hair cells within the organ of Corti. In TTS, several potentially reversible effects include: - 1. Regional decrease in the stiffness of stereocilia secondary to the contraction of rootlet structures which are anchored to the cuticular plate of hair cells
- 2. Intracellular changes within the hair cells including metabolic exhaustion and microvascular changes
- 3. Edema of the auditory nerve endings
- 4. Degeneration of synapses within the cochlear nucleus
In PTS, the changes become irreversible and include breaks in the rootlet structures, disruption of the cochlear duct and organ of Corti causing mixing of endolymph and perilymph, loss of hair cells, and degeneration of cochlear nerve fibers. Acoustic trauma causes severe, irreversible hearing loss. High-intensity impulse noises can directly damage tympanic membrane, ossicles, inner ear membranes, and the organ of Corti. Clinical Findings Patients with NIHL frequently complain of a gradual, insidious deterioration in hearing. The most common complaint is difficulty in comprehending speech, especially in the presence of competing background noise. Background noise, which is usually low frequency in bias, masks the better-preserved portion of the hearing spectrum and further exacerbates problems with speech comprehension . Because patients with NIHL have a high-frequency bias to their hearing loss, they experience a distortion of speech sounds when listening to people with particularly high-pitched voices (eg, women and children) (Figure 581).
NIHL is frequently accompanied by tinnitus. Most often patients describe a high-frequency tonal sound (eg, ringing), but the sound is sometimes lower in tone (eg, buzzing, blowing, or hissing) or even nontonal (eg, popping or clicking). Often, the tinnitus frequency matches the frequency of the hearing loss seen on the audiogram and is approximately 5 dB above that threshold in loudness. Tinnitus in the absence of hearing loss is likely not related to noise exposure. The diagnosis of occupational NIHL has been summarized in an evidence-based policy statement by the American College of Occupational and Environmental Medicine (2002). The typical "4000 Hz notch " is thought to occur due to the (1) resonance frequency of the ear canal, (2) the acoustic reflex protecting the ear at lower frequencies, (3) intermittency protecting the ear at lower frequencies, and (4) outer hair cells being most susceptible at the base of the cochlea. Lower and higher frequencies become affected after many years of noise exposure, and a significant decrease in word recognition scores does not begin until frequencies < 3000 Hz are affected (Figure 582). Asymmetry can exist in the audiogram, particularly when the source of the noise is lateralized (eg, a rifle or shotgun firing). Evoked otoacoustic emissions (OAE) may be useful in detecting early NIHL in persons with normal audiograms. Outer hair cells are affected early in NIHL, and both transient-evoked OAE and distortion-product OAE have been shown to detect subtle changes in outer hair cell function. Predisposing Factors Susceptibility It has been observed that some individuals are able to tolerate high noise levels for prolonged periods of time, whereas others who are subjected to the same environment lose hearing more rapidly . The genetic basis of this variability has been studied in detail using a mouse model, and several strains have been found to be either susceptible or resistant to noise-induced damage. The risk is likely an interaction between genetic susceptibility and the duration and intensity of the noise exposure (Figure 583). Presbycusis NIHL and presbycusis often coexist in our aging population. Large studies have shown that the combined effect is additive over time, and attempts have been made to quantify this interaction. Ototoxicity Concurrent exposure to noise and ototoxic medications may potentiate hearing loss. These effects have been shown for both cisplatin and aminoglycosides. Loop diuretics and salicylates, however, have not been definitively shown to potentiate NIHL. Vibration There is recent evidence that vibration can interact with noise to cause both TTS and PTS. The mechanism of this interaction is not well understood . ACOEM Noise and Hearing Conservation Committee Evidence-Based Statement. Noise Induced Hearing Loss. American College of Occupational and Environmental Medicine, 2002. (Update of the previous 1989 position statement by the ACOEM outlining diagnostic criteria of noise-induced hearing loss and worker evaluation.)
| Borg E et al. Effect of the acoustic reflex on inner ear damage induced by industrial noise. Acta Otolaryngol. 1983;96:361. (Animal study investigating the stapedial reflex and its protective effect against temporary and permanent threshold shifts in noise exposure.) [PMID: 6637452]
| Dobie RA. Noise-induced hearing loss. In: Baily BJ et al, eds. Head and Neck SurgeryOtolaryngology. Philadelphia: Lippincott Williams & Wilkins, 2001. (General chapter covering noise-induced hearing loss.)
| Grati MM et al. Rapid turnover of stereocilia membrane proteins : evidence from the trafficking and mobility of plasma membrane Ca(2+)-ATPase 2. J Neurosci. 2006;26:6386. [PMID: 16763047]
| Kim JJ et al. Fine structure of long- term changes in the cochlear nucleus after acoustic overstimulation: chronic degeneration and new growth of synaptic endings. J Neurosci Res. 2004;77:817. (Animal studying demonstrating synaptic degeneration in the cochlear nucleus following noise exposure.) [PMID: 15334600]
| Lonsbury-Martin BL, Martin GK. Noise-induced hearing loss. In: Cummings CW et al, eds. Cummings OtolaryngologyHead & Neck Surgery. Philadelphia: Elsevier Mosby, 2005. (Chapter covering noise-induced hearing loss with a good review of basic science research.)
| Oghalai JS. Cochlear hearing loss. In: Jackler RK, Brackmann DE, eds. Neurotology. Philadelphia: Elsevier Mosby, 2005. (Chapter on cochlear hearing loss and a sub-section on noise-induced hearing loss.)
| Palmer KT et al. Raynaud's phenomenon , vibration induced white finger, and difficulties in hearing. Occup Environ Med. 2002;59:640. (Study examining the association between vibration and hearing loss.) [PMID: 12205240]
| Sha SH et al. Differential vulnerability of basal and apical hair cells is based on intrinsic susceptibility to free radicals. Hear Res. 2001;155:1. (Study examining the viability of outer hair cells from the base and apex of guinea pig cochleas. It suggests that basal outer hair cells may be more susceptible to free- radical damage.) [PMID: 11335071]
| Tan CT et al. Potentiation of noise-induced hearing loss by amikacin in guinea pigs. Hear Res. 2001;161:72. (Study suggesting that subtoxic doses of amikacin are sufficient to impair recovery from noise-induced threshold shifts in guinea pigs.) [PMID: 11744283]
| Treatment No medical or surgical treatments are available to reverse the effects of NIHL; therefore, prevention is the foremost priority. This often requires a team consisting of otolaryngology, audiology, and audiologic engineers . After the diagnosis has been established by otologic examination and by the administration of an audiometric test battery, the physician should counsel the patient on the likely consequences of continued exposure to excessive noise, including recommending techniques for avoiding further noise-induced damage. Hearing amplification is reserved for patients whose hearing impairment is severe in social situations. Hearing aids must be carefully fitted to optimally meet the needs of the individual with regard to frequency bias and gain. In bilateral hearing losses, bilateral amplification usually provides more satisfactory rehabilitation . Although the decision to try hearing amplification is the patient's, a reasonable criterion for referral to a professional for hearing aid evaluation is a speech reception thresholds > 25 dB or a word recognition score < 80% when words are presented at a normal conversational level of 50 dB above threshold. There are some instances in which hearing aids may be recommended to assist the patient to hear in special circumstances, such as lectures or group situations. In patients with high-frequency hearing loss and relatively normal low-frequency hearing, hearing aids are generally the most helpful to those who have a significant hearing loss at 2000 Hz on a pure-tone audiogram. A borderline candidate may be a person with normal hearing through 1500 Hz, a mild hearing loss at 2000 Hz, and a moderate or greater hearing loss at 3000 Hz and above. The two basic hearing aids that are available are the analog hearing aid and the newer , more expensive digitally programmable hearing aids. Before purchasing hearing aids, the patient should have a hearing aid evaluation and a trial period, with the patient wearing the aids in various circumstances. Numerous assistive listening devices are available (FM and infrared) to enhance comprehension in specific situations. Aural rehabilitation classes designed to enhance the patient's ability to comprehend speech may also be helpful and are usually available in urban areas. There is no cure for tinnitus resulting from NIHL, although numerous amelioration measures are available. With no further inner ear injury , tinnitus gradually diminishes, usually over a course of weeks to months. A subtle degree of tinnitus often persists and is especially obvious when the patient is in a quiet room. For the few patients who find this to be extremely troublesome , masking the tinnitus with music or some other form of pleasant sound is often helpful. In those with significant hearing loss, the most successful treatment may be appropriate hearing amplification. Modified hearing aids (tinnitus maskers) designed to produce masking noises have generally been of limited success. The use of biofeedback has helped some patients suppress their tinnitus. Patients should be informed of various support groups available and psychiatric referral may be necessary to medically manage associated depression and anxiety. Prognosis In patients with NIHL, hearing generally stabilizes if the patient is removed from the noxious stimulus. NIHL does not progress after the worker is removed from the source of the hazardous noise. If there has been further progression of hearing loss after a person has been removed from the source of noise, the progression of further hearing loss is the result of some other degenerative, congenital, or metabolic process (eg, presbycusis). Although adequate noise protection is essential and should always be recommended, even with adequate hearing protection, other factors may play a role in the patient's prognosis. Presbycusis can add to NIHL as the patient grows older, and coexisting NIHL may cause the patient to be more susceptible to the adverse effects of ototoxic substances such as aminoglycoside antibiotics, loop diuretics, and antineoplastic agents used in the treatment of other disorders (see Ototoxic Hearing Loss, which follows ). Prevention Occupational Safety and Health Administration (OSHA) Regulations Noise has been measured by a number of governmental agencies, private corporate entities, and academic institutions. A list of common noise examples is included (Table 581). | Table 581. Examples of Noise in Industry and Noise in the Environment.
| | | Jet Engines-Flight Line | | FA-18E engine at 80% (rear) < 50 ft | 130 dBA | | FA-18E engine at idle (rear) < 50 ft | 105 dBA | | FA-18 after burner test (rear) < 50 ft | 139 dBA | | F104 engine at idle from 200 ft | 91 dBA | | Diesel hydraulic Jenny | 107 dBA | | Heavy Mobile Equipment | | Scrapers-loaders | 117 dBA | | Road graders | 95 dBA | | Tool Operations (Metal) | | Pneumatic grinders on aluminum | 100102 dBA | | Chipping weld on large aluminum structure | 120 dBA | | Cut-off grinder cutting aluminum pipe | 100 dBA | | Cut-off grinder cutting galvanized pipe | 9698 dBA | | Needle gun on 1/4-in. steel plate | 108 dBA | | Punch press 3/8-in. flat bar steel | 118 dBA | | Tool Operations (Woodworking) | | Cut-off saw | 112 dBA | | Radial arm saw | 98 dBA | | Router | 93 dBA | | Planer | 106 dBA | | Socioacusis | | Normal conversation | 5060 dBA | | Motorboats | 74114 dBA | | Motorcycles | up to 110 dBA | | Snowmobiles | 85109 dBA | | Lawnmowers | up to 96 dBA | | Hunting weapons | 143173 dBA | |
| The maximum permissible OSHA dB standard for nonimpulse noise is a time-weighted average of 90 dBA for 8 hours, with every increase of 5 dB halving the exposure time to a maximum of 115 dBA for 15 minutes (Table 582). OSHA has allowed for a maximum of 140-dB peak sound pressure for impulse noise. To protect against these maximal allowable exposures, workers exposed to 85 dBA or more require hearing protection and trigger the need to implement a hearing conservation program. | Table 582. Permissible Noise Exposure in the Workplace.
| | | Hours Per Day | Sound Levels dBA (Slow Response) | | 16 | 85 | | 8 | 90 | | 6 | 92 | | 4 | 95 | | 2 | 100 | | 1 | 105 | | 0.5 | 110 | | 0.25 | 115 | |
| In 1998, the National Institute for Occupational Safety and Health (NIOSH) recommended limiting occupational noise exposure to a time-weighted average of 85 dBA for 8 hours, with a 3-dB exchange rate, although this has yet to become the enforced standard. Even with a time-weighted average of 85 dBA, the risk of impairment may be 1015%. Each country uses its own standards and many have adopted programs similar to the revised criteria of the NIOSH. Hearing Conservation Program The hearing conservation program is the recognized method of preventing NIHL in the occupational environment. Although there is a tendency to think of "hearing conservation" as the provision of audiometric tests and hearing protection, much more effort is required. An effective hearing conservation program integrates the following program elements: (1) noise monitoring, (2) engineering controls, (3) administrative controls, (4) worker education, (5) selection and use of hearing protection devices, and (6) periodic audiometric evaluations. Record keeping is important, and record-keeping requirements are described in the OSHA standard. Records should show a notation of NIHL on the OSHA log of injuries and illnesses. Noise Monitoring If there is reason to believe that worker noise exposure equals or exceed a time-weighted average of 85 dBA, then noise monitoring is required. A sampling strategy must be designed to identify all workers who need to be included in the hearing conservation program. Using the appropriate noise-monitoring instrumentation, noise must be characterized in terms of the following: (1) frequency (predominantly high, predominantly low, or mixed); (2) intensity (how loud the sound is); and (3) type (continuous, intermittent, or impulse). Any time there is a change in production, the process, equipment, or controls, noise monitoring must be repeated. Engineering Controls The information collected during noise monitoringparticularly octave band analysis, which indicates the sound level at selected frequenciesmay be used to design engineering controls. Designers conceptualize possible engineering solutions in terms of (1) the source (what is generating the noise), (2) the path (the route or routes the generated noise may travel), and (3) the receivers (the noise-exposed workers). To reduce noise exposure to workers, such controls may involve (1) enclosures (to isolate sources or receivers), (2) barriers (to reduce acoustic energy along the path), and (3) distance (to increase the path and ultimately reduce the acoustic energy at the receiver). In general, engineering controls are preferred but are not always feasible because of both their costs and the limits of technology. Administrative Controls Administrative controls include (1) reducing the amount of time a given worker might be exposed to a noise source to prevent a time-weighted average of noise exposure from reaching 85 dBA, and (2) establishing purchasing guidelines to prevent the introduction of equipment that would increase the dose of noise to which workers are subjected. Though simple in principle, the implementation of administrative control requires management commitment and constant supervision, particularly in the absence of engineering or personal protection controls. In general, administrative controls are used as an adjunct to existing noise control strategies within a hearing conservation program rather than as an exclusive approach for controlling noise exposure. Worker Education Workers and management must understand the potentially harmful effects of noise in order to satisfy OSHA requirements andmost importantto ensure that the hearing conservation program is successful in preventing NIHL. A good worker education program describes (1) program objectives, (2) existing noise hazards, (3) how hearing loss occurs, (4) the purpose of audiometric testing, and (5) how workers can protect themselves . In addition, the roles and responsibilities of the employer and the workers should be clearly stated. Training is required to be provided annually to all workers included in the hearing conservation program. Opportunities for maintaining awareness occur during periodic safety meetings, as well as during audiometric testing appointments, when testing results are explained. Hearing Protection Devices Hearing protection devices are available in a variety of types from a number of manufacturers. There are three basic types of hearing protection devices: (1) ear plugs or "aurals" (eg, premolded, formable, and custom molded); (2) canal caps or "semiaurals" (with a band that compresses each end against the entrance of the ear canal); and (3) earmuffs or "circumaurals" (which surround the ear). Each type of device has advantages and disadvantages that vary according to worker activity, noise characteristics, and the work environment. The selection of appropriate hearing protection devices should include input from the industrial hygienist, the audiologist, the physician of occupational medicine, and the workers who will use the device(s). Although hearing conservation programs are triggered by the presence of noise levels  an 8-hour, time-weighted average of 85 dBA, hearing protection devices must attenuate worker exposure to an 8-hour, time-weighted average of 90 dBA, which is the 8- hour level of permissible noise exposure mandated by OSHA. An OSHA standard threshold shift occurs if the hearing level has changed by 10 dB or more in either ear in the average hearing thresholds of 2000, 3000, and 4000 Hz. If an employee has not had a baseline audiogram or is exposed to noise with a time-weighted average of 85 dBA and has a demonstrated standard threshold shift, then hearing protection devices must be provided and must attenuate noise levels to below an 8-hour time-weighted average of 85 dBA. Audiometric Evaluations Audiometric testing provides the only quantitative means of assessing the overall effectiveness of a hearing conservation program. A properly managed audiometric testing program supervised by either a certified audiologist or a physician trained and experienced in occupational hearing conservation can detect changes in the response to environmental noise that might otherwise be overlooked. The results of audiometric testing must be shared with employees to ensure effectiveness. The overall results or trends noted in an audiometric testing program can be used to fine-tune the hearing conservation program, including determining what types of hearing protection devices to offer to employees and the location where additional employee training is needed. If a standard threshold shift occurs, the individual employee is notified and further action is required that may necessitate both modifying the hearing conservation program and notifying the appropriate authorities (eg, the employer or the appropriate government agency). In some cases, a referral to an otologist is indicated to determine the change in the hearing level from the previous audiogram or baseline audiogram. Noise Reduction Ratings & Selection of Hearing Protection Devices All hearing protection devices sold in the United States are assigned a standardized value known as the noise reduction rating. The manufacturers of hearing protection devices are required by the Environmental Protection Agency to have their products tested to obtain a noise reduction rate before placing these products on the market. Though useful in making preliminary purchasing decisions, assigned noise reduction ratings must be viewed and applied cautiously. Noise reduction ratings (measured in decibels) are based on laboratory attenuation data and achieved under ideal conditions. Actual noise reduction achieved under field conditions using any hearing protection device is much lower than the assigned rating. The adjustment of an assigned noise reduction rating may be required before a device is prescribed for field use. Weighting Scale Adjustment Depending on the monitoring method used to determine the noise exposure, an initial adjustment to the noise reduction rating of a selected device may be required. Noise levels can be measured using either the "A" scale (dBA) or "C" scale (dBC). The A scale approximates the response of the human ear to speech frequencies and discounts much of acoustic energy from the low and high frequencies that are present in the work environment. Therefore, the A scale is often an underestimation of the total acoustic energy present. In contrast, the C scale is essentially flat across the frequency spectrum, and all of the acoustic energy present is integrated into the measurement. If workplace noise levels are determined using the C scale (dBC) on the monitoring instrumentation, the assigned noise reduction rating may be subtracted directly from the actual measured time-weighted average noise levels to determine the legal "adequacy" of the device selected relative to the regulatory criterion of a time-weighted average of 90 dBA. If workplace noise levels are determined using the A scale (dBA) on the monitoring instrumentation, the assigned noise reduction rating must be reduced by 7 dB before being subtracted from the actual measured time-weighted average noise levels in order to determine the legal "adequacy" of the device selected relative to the regulatory criterion of 90 dBA. For employees who have either a demonstrated standard threshold shift or have not yet had a baseline audiogram, the criterion of a time-weighted average of 85 dBA is enforced regardless of which scale is used. Fifty Percent De-Rating Levels Although the effectiveness of hearing protection devices depends on whether they are properly used, noise reduction ratings are obtained in the laboratory under ideal conditions and reflect "best-case" attenuation. To predict more accurately (and conservatively) the noise reduction rating of hearing protection devices during actual use, the noise reduction rating of a product should be de-rated. In calculating the noise exposure to an individual using a hearing protection device in the work environment, OSHA de-rates the assigned noise reduction rating (after scale adjustment) by one half (50%) for all hearing protection devices. This is done to determine the "relative performance" of the device. As a typical example, if a device has a noise reduction rating of 21 and workplace noise measurements were made using the A scale, then the predicted field attenuation (or relative performance) of the device would be 7 dB [(21 7) 2]. Such a device would be expected to provide protection (per the legal OSHA permissible exposure level of 90 dBA) when an 8-hour, time-weighted average noise level of up to 97 dBA [90 + 7] was present. As a worst-case example, the failure to make an adjustment for A scale noise measurements along with the failure to apply a 50% de-rating level could lead an uninformed evaluator to falsely believe that the hearing protection device would provide protection in environments with 8-hour, time-weighted average noise levels up to and including 111 dBA [90 + 21]. Workers in this situation would have an increased risk of sustaining an NIHL. NIOSH has recommended a variable scheme for de-rating noise reduction ratings. For example, earmuffs are de-rated 25%; formable earplugs are de-rated 50%; all other earplugs are de-rated 70%. This scheme more accurately reflects the attenuation in actual work environments. It is important to remember that the de-rating level of hearing protection devices is not required; however, it does provide a conservative estimate of the attenuation in the working environment. Combined Hearing Protection Devices Hearing protection devices may be combined (eg, earplugs and earmuffs used together) to provide more protection in high-noise environments. However, the noise reduction ratings of combined devices are not added together to determine the total noise reduction. Under such circumstances, OSHA advises its inspectors that 5 dB are to be added after the weighting scale adjustment is applied to the device with the higher noise reduction rating (OSHA does not require 50% de-rating levels in this circumstance). This is a conservative approach to determining the combined attenuation and actual field attenuation (and protection) is probably higher. As a practical matter, double protection is inadequate for noise levels over 105110 dBA. Hearing Protection Device Enforcement For 8-hour, time-weighted average noise levels 85 dBA (a 50% noise dose) but < 90 dBA (a 100% noise dose), it is only requested that hearing protection devices be made available to the workers. However, for 8-hour, time-weighted average noise levels 90 dBA, hearing protection devices must be provided to workers. A suitable variety of hearing protection devices must be provided, and the employer is responsible for enforcing their proper use. The weighting scale adjustment of the noise reduction rating must be performed, and it is suggested that a 50% de-rating of the adjusted noise reduction rating be applied to ensure adequate protection of workers. Very few randomized controlled trials have been performed to assess interventions to promote the wearing of hearing protection. A large review by Daniell revealed that current prevention and enforcement strategies in the United States may be inadequate. On average, 38% of employees did not routinely wear hearing protection when exposed to noise, and most companies relied primarily on hearing protection rather than noise control to prevent hearing loss. Axelsson A. Scientific Basis of NIHL. New York: Thieme Medical Publishing, 1996. (Book covering the proceedings of the 5th International Symposium on the effects of noise on hearing.)
| Berger EH et al. The Noise Manual, 5th ed. Fairfax, VA: American Industrial Hygiene Association Press, 1999. (Comprehensive textbook covering noise effects on hearing and hearing conservation.)
| Berger EH et al. The naked truth about NRRs in Earlog. In: Berger EH et al, eds. The Noise Manual. Revised 5th ed. Fairfax, VA: American Industrial Hygiene Association Press, 2000. (Article examining noise reduction ratings and OSHA's 50% derating guidelines.)
| Daniell WE et al. Noise exposure and hearing loss prevention programmes after 20 years of regulations in the United States. Occup Environ Med. 2006;63:643. (A study in Washington that reveals poor hearing protection by employees and inadequate enforcement and noise control by companies.) [PMID: 16551755]
| El Dib RP et al. Interventions to promote the wearing of hearing protection. Cochrane Database Syst Rev. 2006;2:CD005234. (Cochrane review finding that tailored interventions were not more effective than general interventions; however, school-based hearing loss prevention programs may be effective.) [PMID: 16625628]
| Mansdorf SZ. Complete Manual of Industrial Safety. Fort Lee, NJ: Prentice Hall, 1993. (Book covering various aspects of industrial safety including hearing conservation strategies.)
| National Institute of Health Consensus Development Conference: Noise and Hearing Loss. Consensus Statement 1990; 8:1. (Examines various aspects of noise-induced hearing loss, prevention strategies, and directions for future research.) [PMID: 2202895]
| Royster JD, Royster LH. Hearing Conservation Programs: Practical Guidelines for Success. Albany, GA: Lewis Publishers, 1990. (Covers various aspects of designing and implementing cost-effective hearing conservation programs in the workplace.)
| Sataloff RT, Sataloff J. Occupational Hearing Loss. New York: Marcel Dekker, 1987. (Comprehensive textbook covering all aspects of occupational hearing loss including etiology , diagnosis, and testing.)
| US Department of Health and Human Services. Occupational Noise ExposureRevised Criteria 1998. National Institute for Occupational Safety and Health, 1998. (Criteria proposed by the NIOSH for permissible noise levels. Proposed criteria include reducing the maximum permissible noise exposure to 85-dB time-weighted average and reducing the exchange rate to 3%.)
| US Department of Labor, Occupational Safety, and Health Administration. Occupational Noise Exposure: Hearing Conservation Amendment Final Rule. Fed Reg. 1983;48:9738. (29CFR1910.95). (Federal regulations regarding noise exposure, hearing conservation programs, and reporting.)
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