Illustrated in Figure 3-1 are possible clinical manifestations ofstress concomitant with noise. Not only might there be harmfulconsequences to health during the state of alertness, but researchalso suggests effects may occur when the body is unaware or asleep.
Hearing protectors can either be earplugs or muffs. Earplugs canbe made of many materials, such as soft flexible plastic, wax, paper,glasswool, cotton, and mixtures of these materials. To be effectivethey must provide a snug, airtight and comfortable seal. Muff-typeprotectors cover the entire external ear and generally providegreater protection than do earplugs. (23) Figure 2-10 depicts thesound attenuation characteristics of several representative types ofhearing protectors.
One factor that can lessen the effects of rock music on hearing isits intermittency. Rock music is characterized by on-times ofapproximately three to five minutes alternating with off-times ofapproximately one minute. (27) Another factor is the prominence oflow frequency sounds which are not as damaging as high frequencysounds.
Since the invention of television, adverse effects such as obesity and increased violence in the emulation of television acts has been displayed in children.
The threshold of hearing rises naturally (hearing becomes lesssensitive) with increasing age. This effect involves primarily thefrequencies above 3000 Hz. (14) Figure 2-7 presents data that depictthe progression of presbycusis with age and the degree of loss. Asage increases, losses at high frequencies become greater and hearingloss progresses farther down the scale to lower frequencies.
It has been determined that an outdoor Ldn value of 55dB (or an indoor Ldn of 45 dB) represents the lowerthreshold of noise jeopardizing the health and welfare of people. Inthe range above these levels, noise may be a cause of adversephysiological and psychological effects. These effects often resultin annoyance and community action. Noise above Ldn 75 dBmay, in time, cause hearing loss and the possibility of other severehealth effects.
It is not possible to provide a definitive answer to this questionat this time. However, EPA-sponsored primate research has shown thatsignificant and sustained elevations in blood pressure can beproduced as a result of exposure to noise levels which do not produceany significant permanent hearing loss in the subjects. (106) Thesedata would suggest that protecting against the auditory effects ofnoise does not necessarily prevent the nonauditory effects. Humandata confirming this conclusion are needed.
People with hearing losses require more favorable speech-to-noiseratios than do persons with normal hearing. (14) This means that thedifference between the level of speech and the background noise levelmust be greater for hearing impaired individuals than for people withnormal hearing. This can be achieved either by decreasing thebackground noise level or increasing the speech level. Increasedlevels of noise, in relation to the speech signal, tend to aggravatethe adverse effects of hearing loss. (48)
Not at the present time. In the past, EPA stated that noise levelsidentified to protect against hearing loss should be sufficient toprotect against the nonauditory effects of noise. However, growingevidence suggests that this assumption needs to be tested throughresearch. (5) In considering noise as a general stressor, the need toestablish quantitative criteria has now become evident, given thegrowing concern about these effects.
It is possible that repeated or constant exposure to noise cancontribute to a deterioration in health. Whether or not environmentalor industrial noise by itself can lead to chronic disturbances ishard to determine since there are so many other stresses to whichpeople are exposed. (41) This research is difficult to conduct andlittle has been done in this area, but research is accumulating whichsuggests a relationship between long-term noise exposure andstress-related health effects, particularly those related to thecardiovascular system.
Continuous noise may also interact with impulse noise and bodyvibrations to exacerbate hearing loss, although the magnitude of thiseffect is not exactly known.
High doses of ototoxic drugs such as quinine,dihydro-streptomycin, neomycin, and kanamycin can have toxic effectson the cochlea and cause subsequent sensori-neural hearing loss. (13)The use of these drugs is now restricted.
Diseases such as measles, mumps, scarlet fever, diphtheria,whooping cough, influenza, and certain other viral infections canlead to sensori-neural hearing loss. The processes of these diseasescan have a toxic effect on the sensitive nerve endings in thecochlea. Infections of the cerebrospinal fluid such as meningitis canalso cause damage to the cochlea. Tumorous growths near the auditorynerve can cause sensori-neural hearing loss due to pressure on thenerve. (13)