Semester

Spring

Date of Graduation

2010

Document Type

Dissertation

Degree Type

PhD

College

Statler College of Engineering and Mineral Resources

Department

Industrial and Managements Systems Engineering

Committee Chair

Steve E Guffey

Abstract

It is not clear how effective hearing protective devices are during actual use, including during coal mining. A proposed solution is individual fit-testing, which is usually done in an office environment. However, it is not clear that fit-testing accurately represents protection while actually working. This research investigates both issues for coal miners for two hearing protectors (E-A-R earplug and Peltor earmuff). It consists of two related studies: lab studies of fit-testing and field studies relating fit-testing at coal mine offices to the actual noise reductions provided for the same coal miners during work.;The effects of several variables on fit-testing results were investigated in the lab studies. First, the necessity of using a reverberatory chamber for fit-testing was investigated by testing the same individuals in both a chamber and an ordinary university laboratory room. The overall A-weighted noise reduction (NRA) difference was found to be about 1 dBA, a modest difference of little practical importance, indicating that an ordinary room can be used as a substitute for a reverberatory chamber for fit-testing. As part of this study, each subject was tested while oriented at 0, 180, and 90 degrees to the noise source. The fit-testing results showed modest effects of orientation to the source on NRA values. Likewise, having each subject do various body movements during testing produced only modest differences from results found while sitting still. Finally, the effect of re-fitting was tested by having each of five subjects remove and then re-don his or her Peltor(TM) ear muff or E-A-R(TM) earplugs twelve times. The twelve refittings produced NRA variations of 10 to 34 dBA, suggesting that the average of multiple fit-tests may be required to determine a representative value for each individual. Finally, by comparing noise levels measured concurrently the study demonstrated that there were negligible differences due to the use of the dosimeters.;For the field study, the investigator fit tested seventeen coal miners in ordinary coal mine offices while they wore either their own cap-mounted muffs or investigator-supplied E-A-R ear plugs, depending on whether they normally used cap-mounted muffs or earplugs while working prior to the study. The fit-test setup and apparatus was identical to the fit-testing done in the university lab room, with the exceptions that an analyzer and two dosimeters were employed. The fit-testing results showed that the coal miners' NRA was highly variable among the twelve different fitting measurements. Most subjects' NRA values varied over a range of more than 10 dBA, suggesting that the average of many fit-testings are necessary to adequately represent the NRA for each miner, agreeing with the results of the lab study.;Either earlier or later the same day for the same fit-tested miners, NRA values were determined continuously during full shifts of work using two dosimeters, one measuring at the shoulder and the other measuring proximal to the ear plug or muff. The field study also showed that the minute-by-minute NRA values of the tested coal miners fluctuated widely (ranges = -15.9 to 44.6 dBA) during their tested work shifts. Using observations of HPD use and non-use during each miner's work shift, investigators developed an algorithm to determine whether an HPD was worn during unobserved periods. These determinations made it possible to estimate the total fraction of the work shift and of exposure dose for each worker that were attributable to failure to wear the HPD. The results showed that the percentage of the noise dose measured in the ear attributable to failure to wear the HPD ranged from 0 to 98% with an average across subjects of 58%. The fraction of minutes in which the HPD were not worn ranged from 0 % to 78%, with an average of 26% minutes across all subjects. Broken down by HPD type, the comparable figures for dose and time were 60% and 29% for the earmuff, and 57% and 24% for the earplug.;The correlation between fit-testing and work NRA average values for these miners differed between earplugs and ear muffs. For the earplug, there was a modest linear relationship (R2=0.53) between fit-testing and work experience. For the earmuff, a linear relationship was not found when all subject results were included.;In conclusion, failure to wear the HPD was a main cause of the low mean NRA values during work for these subjects. The relationship between the average of twelve fit-tests and the same worker's work NR A would be moderately strong only if a pair of invalid results were arbitrarily omitted and did not show prediction relationship for earmuff.

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