Environmental Engineering Reference
In-Depth Information
DID YOU KNOW?
In 1983, the Occupational Safety and Health Administration (OSHA) adopted
a Hearing Conservation Amendment to 29 CFR 1910.95 requiring employ-
ers to implement
hearing conservation programs
in any work setting where
employees are exposed to an 8-hour, time-weighted average of 85 dB and above
(LaBar, 1989). Employers must monitor all employees whose noise exposure
is equivalent to or greater than a noise exposure received in 8 hours where
the noise level is constantly 85 dB. The exposure measurement must include
all continuous, intermittent, and impulsive noise within an 80-dB to 130-dB
range and must be taken during a typical work situation. This requirement is
performance oriented because it allows employers to choose the monitoring
method that best suits each individual situation (OSHA, 2002).
Audible range
—The frequency range over which individuals with normal
hearing acuity hear (approximately 20 to 20,000 Hz).
Audiogram—
A chart, graph, or table resulting from an audiometric test show-
ing an individual's hearing threshold levels as a function of frequency.
Audiologist
—A professional specializing in the study and rehabilitation of
hearing and who is certified by the American Speech-Language-Hearing
Association or licensed by a state board of examiners.
Background noise
—Noise coming from sources other than the particular
noise sources being monitored.
Baseline audiogram
—A valid audiogram against which subsequent audio-
grams are compared to determine if hearing thresholds have changed. The
baseline audiogram is preceded by a quiet period so as to obtain the best
estimate of the person's hearing at that time.
Continuous noise
—Noise of a constant level as measured over at least one sec-
ond using the “slow” setting on a sound level meter. Note that a noise that
is intermittent (e.g., on for over a second and then off for a period) would be
both variable and continuous.
Controls, administrative
—Efforts, usually by management, to limit workers'
noise exposure by modifying workers' schedules or location or by modify-
ing the operating schedule of noisy machinery.
Controls, engineering
—Any use of engineering methods to reduce or control
the sound level of a noise source by modifying or replacing equipment,
making any physical changes at the noise source or along the transmission
path (with the exception of hearing protectors).
dB (decibel)
—The unit used to express the intensity of sound. The decibel
was named after Alexander Graham Bell. The decibel scale is a logarith-
mic scale in which 0 dB approximates the threshold of hearing in the mid-
frequencies for young adults and in which the threshold of discomfort is
between 85 and 95 dB SPL and the threshold for pain is between 120 and
140 dB SPL.
