3-15. PERIODIC HEARING EVALUATION
a. Routine periodic audiograms made on all personnel working in areas having
high intensity noise are necessary to detect beginning changes in hearing acuity, since
the individual may be unaware of any hearing change. The first in this series of periodic
audiograms should be made at the beginning of the workday, approximately 90 days
after the beginning of the worker's exposure to high noise levels. If no significant
change in hearing acuity is noted, subsequent audiograms should be made every 12
months. Personnel exposed to excessively high-noise levels (that is, weapons instructors
and members of gun crews) should be tested more frequently.
b. All personnel should be encouraged to report for evaluation if symptoms of
progressive hearing loss or progressive tinnitus (ringing of the ear) develop. This is
imperative, since prompt action may prevent a permanent hearing loss.
Hearing loss caused by noise is difficult to differentiate from that resulting from
such other factors as systemic disease, toxicity from infection, effect of drugs, and
presbycusis. All reasonable methods of differential diagnosis should be used before
establishing the diagnosis of hearing loss caused by noise. This includes a careful
investigation of the worker's history with special references to any previous hearing
tests, a general physical examination, accurate pure tone and air conduction
audiometric tests, and complete speech and discrimination tests. Trained personnel
under the supervision of a physician or a qualified audiologist may measure hearing.
The physician, however, is responsible for determining and evaluating the degree of
Section III. SOUND MEASURING EQUIPMENT
In order to conduct accurate noise surveys, it is necessary to be able to operate
the instruments for measuring noise. It will be your job when you get to the field to
operate the equipment and take reliable readings and interpretations from them.
3-18. THE SOUND LEVEL METER
a. The standard sound level meter is the basic measuring instrument for the
industrial hygienist. It consists of a microphone, an amplifier with calibrated volume
control, and an indicating meter. It measures the sound pressure level in decibels,
which is proportional to intensity or sound energy flow.