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Audition plays many important roles in our daily lives. From
sound, we can identify and locate an object. Also, spoken language
and its auditory reception have become an extremely important means
of communication. A deficit in the ability to hear have tremendous
effects on a person physically and mentally. Hearing loss caused by
occupational noise is one of our biggest industrial diseases. It is a
disease that has been recognized since the Industrial Revolution.
According to Sataloff and Sataloff (1987) about 35 million Americans
suffer from hearing loss, and of those, eight million suffer from
occupational hearing loss. Because of the sheer number of people and
our neglect of the subject, almost every American may be affected
directly or indirectly.
It has certainly been technologically possible for many years to
eradicate the problem of occupational hearing loss, but a delay has
been caused by legislative, economic, and political resistance. Also,
because hearing loss does not impede your earning power as much as
vision loss would, it has taken the back burner as far as industrial
perceptual diseases are concerned. Because of the new laws on
worker's compensation an estimated 20 billion dollars might have to
be paid out to those inflicted, which would make it the number one
environmental and medical-legal problem in the United States (Harris,
1979).
Exposure to excessive noise for a sufficiently long period of time
can result in the destruction and eventual loss of the organ of
Corti. Harris (1979) has divided the effects of industrial noise on
hearing into three categories. The first is acoustic trauma, the
immediate organic damage to the ear from excessive sound energy, it
is restricted to the effects of a simple exposure at very high sound
levels. Such intense noise reaching the inner ear may exceed the
physiological limit of those structures, producing a complete
breakdown of the organ of Corti. The second is a noise-induced
temporary threshold shift that results in an elevation of heighten
levels following noise exposure. The loss is usually reversible. The
third effect is a noise-induced permanent threshold shift, which is
not reversible. It may come from acoustic trauma or be produced by
the cumulative effect of repeated noise exposures over many periods
of years.
The structures most susceptible to noise damage are the sensory
receptor cells, the hair cells, located in the cochlea. Damage from
repeated noise is a physiochemical problem where the metabolic stress
exerts pressure on the maximally stimulated cells. Depending on the
amount of cellular damage, it could be permanent or temporary damage.
In fact, cochlear damage is the number-one characteristic of
occupational hearing loss. Sataloff and Sataloff (1987) namea few
others. For one,the patient must have a history of long-term exposure
to intense noise levels sufficient to cause the degree and pattern of
hearing loss evident in audiologic finding. The hearing loss must
have developed gradually over a period of years. The hearing loss
must have developed during the first eight to ten years of exposure.
The hearing loss must initially have started in the higher
frequencies (generally 3000-6000 Hz) and be almost equal in both
ears. Speech discrimination scores, even with substantial high
frequency losses, are generally good. Finally, the hearing loss
should stabilize if the patient is removed from noise exposure.
Another characteristic of occupational hearing loss is that specific
noisy jobs produce a maximum degree of hearing loss. This is known as
asymptotic hearing loss. For example, employees using jackhammers
develop severe high-frequency, but minimal low-frequency hearing
losses. A diagnosis of occupational hearing loss must be based on
specific criteria. The potential medical, legal, and economic
consequences are likely to be very serious.
Because industrial noise does affect you hearing, it leaves many
residual effects, mainly psychological. Dublins National Board for
Science 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 raising
ones voice is not enough. Workers become hoarse by the end of the
day. When people have problems hearing and communicating, it leads to
misunderstandings which result in waste and inefficiency, and in the
worse situations, accidents. Industrial noise, and its
unpleasantness, 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 considerable
difference between background and peak intensities, noise in the
middle frequencies where the ear is most sensitive, noise with a
large component of pure tones or narrow wave-bands, and noise that is
increasing rather than decreasing.
Because noise affects ones hearing, it indirectly affects your
performance. Dublins National Board for Science and Technology (1980)
looked at specific experiments. One experiment they spoke of dealt
with the film-processing industry, in which one room they reduced the
noise from 99 to 89 dB. Comparing this quieter room to another
room at the regular noise level, the workers in the quieter
room had a significant reduction of film breakage. Another study
found that the number of sorting errors made by the postal sorters
increased systematically with noise level.
In general, if people have a hard time communicating to one
another, attempts to interact will become less frequent, leading to
an increased sense of isolation. This in turn can lead to depression.
Also, in many cases, people who obtain hearing loss have problems
commuicating outside of the work place with communicating, causing
people to have problems in their marriages and friendships.
Fortunately, there are things that can be done to protect the
hearing of employees from the effects on industrial noise. First, if
possible a company can reduce the noise coming from the source. This
is the best way but cannot always be accomplished, so covering
surrounding surfaces with sound absorbent materials, using noise
barriers, or just moving the person or the source of noise to
different location can help. When none of the above mentioned ways
work, however, personal protective devices must be used. According to
Sataloff and Sataloff (1987) sound energy may reach the inner ears of
persons wearing protection by four ways. The first way is by passing
through bone and tissue around the protector. Another way is by
causing vibration of the protector, which in turn generates sound
into the external ear canal; or by passing through leaks in the
protector; or through leaks around the protector. They then goes on
to explain the rules that should be followed in order to minimize
losses due to the leaks. Hearing protectors should be made of
imperforate materials. The protector should be designed to conform
readily to the head or ear canal configuration. It should have a
support means or a seal compliance that will minimize protector
vibration. Finally, muff-type protectors should not be worn over long
hair, poorly fitted eyeglass, or other obstacles.
A big fallacy about the use of hearing protective devices is that
it will be even harder to communicate. Wearing hearing protectors in
high-level noise environments can improve communication for normal
ears because speech-to-noise ratios are kept nearly constant and the
protected ear does not distort from overdriving caused by the high
speech and noise levels. The two basic types of protectors are the
insert-type and the muff type, and there are advantages and
disadvantages to both. For the insert type the advantages are that
they are small, easy to carry, and cost efficient. The disadvantages
are that they can get dirty when removed and inserted with dirty
hands, and that they take time to get familiar. Muff-type protectors
are technically better for reducing noise levels. Unfortunately, that
they are more expensive that opts the employer to get the plugs.
According to Harris (1979) the federal government showed its first
real concern about industrial noise by including a noise standard in
the Occupational Safety and Health Act of 1972. The standard makes it
mandatory for industries to reduce noise by every feasible means
where employees are exposed to 90dB or more for an eight-hour
workday. If the noise cannot be reduced adequately, a hearing
conservation program has to be established. Before 1948, gradual
partial hearing loss caused by industrial noise was not included in
state workers compensation laws. Little or no mention was made of
partial hearing loss caused by long exposure to occupational noise.
Law makers were unaware of the consequences of hearing loss because
it did not seem to cause loss of wage or earning power. The original
basic objective of workmens compensation was to provide payment for
loss of earning and for medical costs of injury related to
employment. Now under the system of laws in the United States, a
person who suffers hearing loss from occupational noise exposure or
traumatic injury may be entitled to an award for damages. In most
states, noise-induced hearing impairment is treated as an
occupational disease with scheduled awards based on degree of hearing
loss.
Research in the area of industrial noise and its effects on
hearing has been abundant. Sataloff and Sataloff (1987) have done a
review of some of the basic research done in the past. In 1952 James
H. Sterner, M.D. conducted an opinion poll among a large number of
individuals working with noise and hearing as to the maximum
intensity level of industrial noise they considered safe to hearing.
The wide range of estimates demonstrated clearly the lack of
agreement. Some studies were based on a very small number of subjects
exposed to continuous steady state noise, particularly in the 82-92
dBA range. Workers were included who change position from time to
time using noisy hand tools that hardly constitute a continuous or
steady state. Around 1970, individuals from industry, labor,
government, and scientific organizations got together for the purpose
of gathering data on the effects of steady-state noise in the range
of 82-92dB. The basic purpose was for scientific rather than
regulatory reasons. They found that difference in noise intensity had
observable effects on hearing levels. Age was a more important factor
than duration on the job. Levels in the noise-exposed group
significantly exceeded those in the control group at 3000, 4000, and
6000Hz by approximately six to nine dB. At 8000Hz, differences again
became not significant. There was no real evidence of a difference
between noise exposed workers and their controls with respect to the
changes in hearing level during the course of their follow-up one and
two years after initial audiograms.
The following is some current research done on the effects of
hearing. Investigators from the National Institute for Occupational
Safety and Health analyzed data collected during the 1971 and 1977
National Health Interview surveys. Self-reported hearing loss was
higher among adults working in industries with potential exposures to
industrial noise than among those working in industries without such
potential exposures. They found that self-reported hearing loss
increases with age, and that, within age groups, it is consistently
greater for noisy industries. Industries in the manufacturing sector
had the highest prevalence of noise exposure. Bauer, Kopert, Raber,
and Schwetz (1991) looked at the risk factors for hearing loss at
different frequencies. They examined how audiometric frequency was
affected by sex, noise emission level, ear disease, tinnitus, and
wearing protector usage. The age factor is at any observed frequency
the most important predictor for the wearing threshold. Persons who
did not use hearing protectors had better hearing. They suggested
that workers with a beginning hearing malfunction tend to use the
protection. Dryter (1991) found that industrial noise is deduced to
cause about half as much overall increase in male population hearing
levels as that caused by exposure to gun noise.
In a study done by Hetu and Getty (1993), they found that
employees who have developed occupation hearing loss will many times
not advance in their careers because of the stigma attached to
hearing loss. Employees with this infliction tend to avoid areas
where frequent communication is held. Also, they looked at
engineering problems, such as making regulatory emergency sirens more
stimulating to those that are hearing impaired. Research in the
medico-legal areas is starting to rise; and because this is a very
expensive disorder in terms of worker's compensation, much more
research in this area is needed. Some research done by Simpson,
Stewart, and Blakley (1995) reflects this need. They looked to see
how reliable audiometric retesting is in identifying false-positive
referral flags. They found that when second audiograms were used to
confirm initial findings they had lower referral rates, which could
save a lot of money in the long run. Finally, since there has been an
increase in the knowledge of industrial noise and its effects on
hearing, much attention has been given the hearing aid. Dolan and
Maurer (1990) found that hearing aids use can do more damage the ear
if worn around sufficient levels of industrial noise.
In conclusion, future research is necessary in the area of occupational hearing loss. This disease afflicts millions of people and costs society a good deal of money. For a short term solution to the problem, more research needs to be done in the areas of hearing protection devices, but for a long term solution a great deal more research needs to be done in the area of making the machines more quiet.
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F. (1991). Risk factors for hearing loss at different frequencies in
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Dolan, T. & Maurer, J. (1996). Noise exposure associated with
hearing aid use in industry. Journal of Speech and Hearing
Research, 48, 251-260.
Harris, C.M. (Ed.). (1979). Handbook of Noise Control (2nd
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Hetu, R. & Getty, L. (1993). Overcoming difficulties
experienced in the work place by employees with occupational hearing
loss. The Volta Review, 95, 391-402.
Kryter, K. (1991). Effects of nosocusis, and industrial and gun
noise on hearing of U.S. adults. Journal of Acoustical Society of
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(1980). Noise and the environment. U.S. Department of
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National Institute for Occupational Safety and Health. (1988).
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