Noise in Industry - Fundamentals and Assessment Tools for Occupational Ergonomics - page 617

0

10

20

30

40

EXPOSURE

50

5 - 9 Yr
15 - 19 Yr
25 - 29 Yr
35 - 39 Yr
40 - 52 Yr

60

70

250 1000 2000 3000 4000

125 500 6000

Frequency in Hertz

FIGURE 31.3 Cumulative auditory effects of years of noise exposure in a jute weaving industry. (Adapted from
Taylor, W., Pearson, J., Mair, A., and Burns, W., (1964). Journal of the Acoustical Society of America, 38, 113-120.
With permission.)

31.3.3.2.3 Concomitant Auditory Maladies
Following exposure to high-intensity noise, some individuals will notice that ordinary sounds are per-
ceived as “muffled,” and in some cases, they may experience a ringing or whistling sound in the ears,
known as tinnitus. These manifestations should be taken as serious indications that overexposure has
occurred, and that protective action should be taken if similar exposures are encountered in the
future. Tinnitus may also occur by itself or in conjunction with NIPTS, but in any case it is thought
to be the result of otoacoustic emissions, which are essentially acoustic outputs from the inner ear that
are audible to the victim, apparently resulting from mechanical activity or microphonics of the neural
cells. Some individuals report that tinnitus is always present, pervading their lives. It thus has the poten-
tial to be quite disruptive and, in severe cases, debilitating.
More rare than tinnitus, but typically quite debilitating is the malady known as hyperacusis, which
refers to hearing that is extremely sensitive to sound. Hyperacusis can manifest in many ways, but a
number of victims report that their hearing became painfully sensitive to sounds of even normal
levels after exposure to a particular noise event. Therefore, at least for some, hyperacusis can be directly
traced to noise exposure. Sufferers typically must use hearing protectors when performing normal activi-
ties, such as walking on city streets, visiting movie theaters, or washing dishes in a sink, because such
activities produce sounds that are painfully loud to them. It should be noted that hyperacusis sufferers
often exhibit normal audiograms; that is, their thresholds are not typically better than those of “normal
hearers,” even though their reaction to sound is one of hypersensitivity.
It is important that the industrial hearing conservationist be aware of these hearing-related maladies
that may or may not arise as a result of on-the-job noise exposure, but which may influence the worker's
ability to perform certain jobs or work in certain environments.

31.4 Measurement and Quantification of Noise Exposures

31.4.1 Basic Instrumentation
Measurement and quantification of sound exposure levels provide the fundamental data for assessing
hearing exposure risk, speech and signal masking effects, hearing conservation program needs, and
engineering noise control strategies. A vast array of instrumentation is available for sound measurement;
however, for monitoring and assessment of most noise exposure situations, a basic understanding of