Semester

Spring

Date of Graduation

2009

Document Type

Thesis

Degree Type

MS

College

Statler College of Engineering and Mineral Resources

Department

Industrial and Managements Systems Engineering

Committee Chair

Steven Guffey.

Abstract

Fit testing is frequently described as a solution to the problem of detecting ineffective hearing protection devices and thus reducing noise exposures in workers. This study evaluates the effectiveness of a fit-test conducted at mine sites with cap mounted ear muffs actually worn by the tested miners. The dependent variable was noise reduction, and the independent variables included subject, noise source frequency distribution, orientation to noise source, instruction, and earmuff brand.;A series of eight 30-second tests were conducted for each worker to evaluate the effects of the independent variables. The tests were not randomized due to time constraints. Each of 30 workers was tested once for each test condition. The noise reduction (NR) was determined by setting up four dosimeters with one microphone on each shoulder and one at the entrance to each ear.;NR values for the right ear were modestly (3.3 dBA) but significantly higher (p < 0.0002) than for the left ear. The average of left and right ear NR values from fit-testing in this study showed substantial between-subjects variability (8.5 dBA) and within-subjects variability (ranging from 1.1 to 12.3 dBA). As expected, NR values were significantly (p < 0.0001) but modestly higher (0.3 dBA) for pink noise than for simulated underground noise. The mean NR for different brands of muffs varied from 13.4 dBA to 25.6 dBA with the overall effect of brand being highly significant (p < 0.0004). The lowest and highest visual fit categories of a fit rating had no false positives but many false negatives. The middle categories were uncorrelated to NR values. The orientation of the subject to the source had modest effects on NR (<1 dBA) that were highly significant (p < 0.008) because of the large sample size. Brief instruction showed no significant benefits for these experienced users of earmuffs.;The findings here support multiple repetitions of individualized fit-testing for every employee.

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