Title page for ETD etd-02062013-040020
|Type of Document
||Laboratory investigation of in-field influences on spectral noise attenuation and comfort of insert and circumaural hearing protectors
||Master of Science
||Industrial Engineering and Operations Research
|Casali, John G.
|Kemmerling, Paul T. Jr.
|Kroemer, Karl H. E.
|Date of Defense
Laboratory-obtained, manufacturer—supplied hearing protector attenuation ratings typically
overestimate the workers’ protection level In the workplace. ln addition, several work-related
in-field factors often degrade protection performance ofthe hearing protection devices (HPDs),
posing the threat of underprotection for industrial workers. This research investigated the
effects of HPD wearing time, subject activity movement, and HPD fltting procedure on the
frequency~specIflc attenuation and user-rated comfort achieved with a popular foam cushion
earmuff, two types of earplugs (user-molded foam and pre-molded, triple-flanged polymer),
and an earmuff over foam earplug combination. Both attenuation and comfort data were collected
from 40 naive but audiometrically normal subjects. Using a psychophysical real-earattenuation-
at—threshoId measurement procedure, attenuation data were obtained before,
during, and after the activity movement tasks, which induced typical worker movements, so
that the influence of wearing time and activity movement could be determined. Bipolar comfort
rating data were also collected before and after the activity movement tasks, The results
of statistical analyses indicated that achieved attenuation and user comfort signiflcantly decreased
over a two-hour wearing period and that training to achieve better lltting markedly
improved protection, although these changes were device- and frequency-specific. Loss in
frequency-specific attenuation over the wearing period was up to 6.3 dB for all HPDs except the foam plug, and attenuation Improvement due to training ranged from 4 to 14 dB for all
HPDs except the earmuff at 1000 Hz and below. Almost no difference In achieved attenuation
or comfort was found between the two activity (head/torso and temporomandibular) movements, but the earmuff tended to slip during highly kinematic head/torso movement. In general,
out of the four different HPD conligurations used in the study, the foam plug was very
resilient to either type of activity movement but did benetit more than the other devices from
the training for proper tilting; it was also perceived as the most acceptable and stable HPD
by the subjects. ln summary, the research illuminated the strong influence of in-field factors
on HPD effectiveness.
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