Audition plays many important roles in our daily lives. Fromsound, we can identify and locate an object. Also, spoken languageand its auditory reception have become an extremely important meansof communication. A deficit in the ability to hear have tremendouseffects on a person physically and mentally. Hearing loss caused byoccupational noise is one of our biggest industrial diseases. It is adisease that has been recognized since the Industrial Revolution.According to Sataloff and Sataloff (1987) about 35 million Americanssuffer from hearing loss, and of those, eight million suffer fromoccupational hearing loss. Because of the sheer number of people andour neglect of the subject, almost every American may be affecteddirectly or indirectly.
It has certainly been technologically possible for many years toeradicate the problem of occupational hearing loss, but a delay hasbeen caused by legislative, economic, and political resistance. Also,because hearing loss does not impede your earning power as much asvision loss would, it has taken the back burner as far as industrialperceptual diseases are concerned. Because of the new laws onworker's compensation an estimated 20 billion dollars might have tobe paid out to those inflicted, which would make it the number oneenvironmental and medical-legal problem in the United States (Harris,1979).
Exposure to excessive noise for a sufficiently long period of timecan result in the destruction and eventual loss of the organ ofCorti. Harris (1979) has divided the effects of industrial noise onhearing into three categories. The first is acoustic trauma, theimmediate organic damage to the ear from excessive sound energy, itis restricted to the effects of a simple exposure at very high soundlevels. Such intense noise reaching the inner ear may exceed thephysiological limit of those structures, producing a completebreakdown of the organ of Corti. The second is a noise-inducedtemporary threshold shift that results in an elevation of heightenlevels following noise exposure. The loss is usually reversible. Thethird effect is a noise-induced permanent threshold shift, which isnot reversible. It may come from acoustic trauma or be produced bythe cumulative effect of repeated noise exposures over many periodsof years.
The structures most susceptible to noise damage are the sensoryreceptor cells, the hair cells, located in the cochlea. Damage fromrepeated noise is a physiochemical problem where the metabolic stressexerts pressure on the maximally stimulated cells. Depending on theamount of cellular damage, it could be permanent or temporary damage.In fact, cochlear damage is the number-one characteristic ofoccupational hearing loss. Sataloff and Sataloff (1987) namea fewothers. For one,the patient must have a history of long-term exposureto intense noise levels sufficient to cause the degree and pattern ofhearing loss evident in audiologic finding. The hearing loss musthave developed gradually over a period of years. The hearing lossmust have developed during the first eight to ten years of exposure.The hearing loss must initially have started in the higherfrequencies (generally 3000-6000 Hz) and be almost equal in bothears. Speech discrimination scores, even with substantial highfrequency losses, are generally good. Finally, the hearing lossshould stabilize if the patient is removed from noise exposure.Another characteristic of occupational hearing loss is that specificnoisy jobs produce a maximum degree of hearing loss. This is known asasymptotic hearing loss. For example, employees using jackhammersdevelop severe high-frequency, but minimal low-frequency hearinglosses. A diagnosis of occupational hearing loss must be based onspecific criteria. The potential medical, legal, and economicconsequences are likely to be very serious.
Because industrial noise does affect you hearing, it leaves manyresidual effects, mainly psychological. Dublins National Board forScience and Technology (1980) looked into the psychological effects.First, difficulties in hearing interfere with speech communication.When people are in environments where background noise is at 75 dB,normal conversation becomes unsatisfactory. After 80dB, just raisingones voice is not enough. Workers become hoarse by the end of theday. When people have problems hearing and communicating, it leads tomisunderstandings which result in waste and inefficiency, and in theworse situations, accidents. Industrial noise, and itsunpleasantness, is associated with a lower level of job satisfaction.According to Dublins National Board for Science and Technology(1980), some characteristics of noise lead to increased annoyance:noise which is highly variable, where there is a considerabledifference between background and peak intensities, noise in themiddle frequencies where the ear is most sensitive, noise with alarge component of pure tones or narrow wave-bands, and noise that isincreasing rather than decreasing.
Because noise affects ones hearing, it indirectly affects yourperformance. Dublins National Board for Science and Technology (1980)looked at specific experiments. One experiment they spoke of dealtwith the film-processing industry, in which one room they reduced thenoise from 99 to 89 dB. Comparing this quieter room to anotherroom at the regular noise level, the workers in the quieter room had a significant reduction of film breakage. Another studyfound that the number of sorting errors made by the postal sortersincreased systematically with noise level.
In general, if people have a hard time communicating to oneanother, attempts to interact will become less frequent, leading toan increased sense of isolation. This in turn can lead to depression.Also, in many cases, people who obtain hearing loss have problemscommuicating outside of the work place with communicating, causingpeople to have problems in their marriages and friendships.
Fortunately, there are things that can be done to protect thehearing of employees from the effects on industrial noise. First, ifpossible a company can reduce the noise coming from the source. Thisis the best way but cannot always be accomplished, so coveringsurrounding surfaces with sound absorbent materials, using noisebarriers, or just moving the person or the source of noise todifferent location can help. When none of the above mentioned wayswork, however, personal protective devices must be used. According toSataloff and Sataloff (1987) sound energy may reach the inner ears ofpersons wearing protection by four ways. The first way is by passingthrough bone and tissue around the protector. Another way is bycausing vibration of the protector, which in turn generates soundinto the external ear canal; or by passing through leaks in theprotector; or through leaks around the protector. They then goes onto explain the rules that should be followed in order to minimizelosses due to the leaks. Hearing protectors should be made ofimperforate materials. The protector should be designed to conformreadily to the head or ear canal configuration. It should have asupport means or a seal compliance that will minimize protectorvibration. Finally, muff-type protectors should not be worn over longhair, poorly fitted eyeglass, or other obstacles.
A big fallacy about the use of hearing protective devices is thatit will be even harder to communicate. Wearing hearing protectors inhigh-level noise environments can improve communication for normalears because speech-to-noise ratios are kept nearly constant and theprotected ear does not distort from overdriving caused by the highspeech and noise levels. The two basic types of protectors are theinsert-type and the muff type, and there are advantages anddisadvantages to both. For the insert type the advantages are thatthey are small, easy to carry, and cost efficient. The disadvantagesare that they can get dirty when removed and inserted with dirtyhands, and that they take time to get familiar. Muff-type protectorsare technically better for reducing noise levels. Unfortunately, thatthey are more expensive that opts the employer to get the plugs.
According to Harris (1979) the federal government showed its firstreal concern about industrial noise by including a noise standard inthe Occupational Safety and Health Act of 1972. The standard makes itmandatory for industries to reduce noise by every feasible meanswhere employees are exposed to 90dB or more for an eight-hourworkday. If the noise cannot be reduced adequately, a hearingconservation program has to be established. Before 1948, gradualpartial hearing loss caused by industrial noise was not included instate workers compensation laws. Little or no mention was made ofpartial hearing loss caused by long exposure to occupational noise.Law makers were unaware of the consequences of hearing loss becauseit did not seem to cause loss of wage or earning power. The originalbasic objective of workmens compensation was to provide payment forloss of earning and for medical costs of injury related toemployment. Now under the system of laws in the United States, aperson who suffers hearing loss from occupational noise exposure ortraumatic injury may be entitled to an award for damages. In moststates, noise-induced hearing impairment is treated as anoccupational disease with scheduled awards based on degree of hearingloss.
Research in the area of industrial noise and its effects onhearing has been abundant. Sataloff and Sataloff (1987) have done areview of some of the basic research done in the past. In 1952 JamesH. Sterner, M.D. conducted an opinion poll among a large number ofindividuals working with noise and hearing as to the maximumintensity level of industrial noise they considered safe to hearing.The wide range of estimates demonstrated clearly the lack ofagreement. Some studies were based on a very small number of subjectsexposed to continuous steady state noise, particularly in the 82-92dBA range. Workers were included who change position from time totime using noisy hand tools that hardly constitute a continuous orsteady state. Around 1970, individuals from industry, labor,government, and scientific organizations got together for the purposeof gathering data on the effects of steady-state noise in the rangeof 82-92dB. The basic purpose was for scientific rather thanregulatory reasons. They found that difference in noise intensity hadobservable effects on hearing levels. Age was a more important factorthan duration on the job. Levels in the noise-exposed groupsignificantly exceeded those in the control group at 3000, 4000, and6000Hz by approximately six to nine dB. At 8000Hz, differences againbecame not significant. There was no real evidence of a differencebetween noise exposed workers and their controls with respect to thechanges in hearing level during the course of their follow-up one andtwo years after initial audiograms.
The following is some current research done on the effects ofhearing. Investigators from the National Institute for OccupationalSafety and Health analyzed data collected during the 1971 and 1977National Health Interview surveys. Self-reported hearing loss washigher among adults working in industries with potential exposures toindustrial noise than among those working in industries without suchpotential exposures. They found that self-reported hearing lossincreases with age, and that, within age groups, it is consistentlygreater for noisy industries. Industries in the manufacturing sectorhad the highest prevalence of noise exposure. Bauer, Kopert, Raber,and Schwetz (1991) looked at the risk factors for hearing loss atdifferent frequencies. They examined how audiometric frequency wasaffected by sex, noise emission level, ear disease, tinnitus, andwearing protector usage. The age factor is at any observed frequencythe most important predictor for the wearing threshold. Persons whodid not use hearing protectors had better hearing. They suggestedthat workers with a beginning hearing malfunction tend to use theprotection. Dryter (1991) found that industrial noise is deduced tocause about half as much overall increase in male population hearinglevels as that caused by exposure to gun noise.
In a study done by Hetu and Getty (1993), they found thatemployees who have developed occupation hearing loss will many timesnot advance in their careers because of the stigma attached tohearing loss. Employees with this infliction tend to avoid areaswhere frequent communication is held. Also, they looked atengineering problems, such as making regulatory emergency sirens morestimulating to those that are hearing impaired. Research in themedico-legal areas is starting to rise; and because this is a veryexpensive disorder in terms of worker's compensation, much moreresearch in this area is needed. Some research done by Simpson,Stewart, and Blakley (1995) reflects this need. They looked to seehow reliable audiometric retesting is in identifying false-positivereferral flags. They found that when second audiograms were used toconfirm initial findings they had lower referral rates, which couldsave a lot of money in the long run. Finally, since there has been anincrease in the knowledge of industrial noise and its effects onhearing, much attention has been given the hearing aid. Dolan andMaurer (1990) found that hearing aids use can do more damage the earif worn around sufficient levels of industrial noise.
In conclusion, future research is necessary in the area ofoccupational hearing loss. This disease afflicts millions of peopleand costs society a good deal of money. For a short term solution tothe problem, more research needs to be done in the areas of hearingprotection devices, but for a long term solution a great deal moreresearch needs to be done in the area of making the machines morequiet.
Bauer, P., Korpert, K., Neuberger, M., Raber, A., & Schwetz,F. (1991). Risk factors for hearing loss at different frequencies ina population of 47 3888 noise-exposed workers. Journal ofAcoustical Society of America, 90(6), 3086-3097.
Dolan, T. & Maurer, J. (1996). Noise exposure associated withhearing aid use in industry. Journal of Speech and HearingResearch, 48, 251-260.
Harris, C.M. (Ed.). (1979). Handbook of Noise Control (2nded.). New York: McGraw-Hill.
Hetu, R. & Getty, L. (1993). Overcoming difficultiesexperienced in the work place by employees with occupational hearingloss. The Volta Review, 95, 391-402.
Kryter, K. (1991). Effects of nosocusis, and industrial and gunnoise on hearing of U.S. adults. Journal of Acoustical Society ofAmerica, 90(6), 3196-3201.
National Board for Science and Technology, Dublin (Ireland).(1980). Noise and the environment. U.S. Department ofCommerce Springfield, VA. (NTIS No. PB84-108638)
National Institute for Occupational Safety and Health. (1988).Self-reported hearing loss among workers potentially exposed toindustrial noise- United States. Journal of America MedicalAssociation, 259(15), 2213-2217.
Sataloff, R. T., & Sataloff, J. (1987). OccupationalHearing Loss. New York: Marcel Dekker, INC.
Simpson, T., Stewart, M., & Blakley, B. (1995). Audiometricreferral criteria for industrial hearing conservation programs.Arch Otolaryngol Head Neck Surgery, 121, 407-411.