To effectively implement an occupational hearing conservation program, employers must know the amount of attenuation (noise reduction) provided by the hearing protective devices used by their employees. Currently standardized test methods, performed under laboratory conditions, cannot be easily implemented in industrial settings, and previously proposed field methods have depended upon the use of special headphones which are not typically available in the workplace. These problems have led many occupational hearing conservationists to use standard audiometric headphones to evaluate the attenuation provided to employees using insert-type hearing-protective devices. There has, however, been little research into the validity of using standard audiometric headphones to determine attenuation values. The purpose of this study was to describe a procedure for determining the attenuation of insert-type hearing-protective devices using standard audiometric earphones, typical industrial audiometric equipment, and other easily obtainable materials.

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Thesis (M.S.)--Boston University / PLEASE NOTE: Boston University Libraries did not receive an Authorization To Manage form for this thesis or dissertation. It is therefore not openly accessible, though it may be available by request. If you are the author or principal advisor of this work and would like to request open access for it, please contact us at open-help@bu.edu. Thank you. / 2999-01-01

Thesis (Ed.D.)--Boston University / PLEASE NOTE: Boston University Libraries did not receive an Authorization To Manage form for this thesis or dissertation. It is therefore not openly accessible, though it may be available by request. If you are the author or principal advisor of this work and would like to request open access for it, please contact us at open-help@bu.edu. Thank you. / 2999-01-01

Thesis (MAud)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: In developing countries, like Namibia, there is limited data pertaining to the number of individuals with hearing loss and its associated factors. This study aimed to determine the prevalence of potential hearing loss in Namibian Class A mines and to describe the extrinsic and intrinsic factors associated with hearing loss. A cross-sectional design was utilised and data were collected from 132 respondents (mining employees) from five different Class A mines throughout the country. A questionnaire and a retrospective review of respondents’ medical records were utilised to determine the risk factors. The most recent audiogram found in the respondents’ records was used to determine the presence of potential hearing loss. Three definitions of potential hearing loss were used in this study and included all major frequency hearing loss (AFHL), high frequency hearing loss (HFHL) and low frequency hearing loss (LFHL). Potential hearing loss was identified when the pure tone average (PTA) of 0.5, 1, 2, & 4kHz, 0.5, 1 & 2kHz and 4 & 8kHz respectively was greater than 25dBHL in either one or both ears. Chi-square measurements or, where necessary, Fisher’s exact tests, as well as Odds Ratios were used for the analysis of data. In general a significance level of 5% was applied for all analyses. Results indicated the prevalence of potential hearing loss in Namibian mining employees to be 27% and that both extrinsic and intrinsic factors were associated with hearing loss. The extrinsic factors significantly associated with potential hearing loss were both occupational and medical. The occupational factors found to be significant were the number of years employed in whole life >10 years (p=0.012; OR=3.1, 95% CI=1.3-7.9), the number of years employed in current job > 10 years (p=0.01; OR=3.9, 95% CI1.7-8.8) and the non-availability of formal training in prevention of hearing loss (p=0.022; OR=0.3, 95% CI (0.1-0.9). Diabetes was the sole significant extrinsic medical factor (p=0.035, OR=5, 95% CI 1.1-22.1). The only intrinsic factor which was found to be significantly associated with hearing loss was Age, specifically being older than 40 years (p=0.002; OR=3.5, 95% CI 1.6-7.8) and 50 years (p=0.001, OR=5.5, 95% CI1.9-15.8). A multiple logistic regression model of all significant factors found that only no formal training of prevention of hearing loss was found to be significant in the presence of all other factors (p=0.036, OR=0.036, 95% 0.1-0.92). Findings from this study suggest that multiple factors may be associated with potential hearing loss and not just the exposure to hazardous occupational conditions. Recommendations for future research and clinical practice should, therefore, include thorough investigations into the aetiology of hearing loss. As this study focused on Class A mines, it is recommended that future research be conducted in other mines that are not categorised as Class A mines. Keywords: prevalence, extrinsic factors, intrinsic factors, extrinsic occupational factors, extrinsic social factors, extrinsic medical factors, potential hearing loss, mining industry, Class A mine, Namibia. / AFRIKAANSE OPSOMMING: In ontwikkelende lande, soos Namibië, is daar beperkte data met betrekking tot die aantal individue met gehoorverlies en sy verwante faktore. Hierdie studie het gepoog om die voorkoms van gehoorverlies in Namibiese Klas A myne te bepaal en die ekstrinsieke en intrinsieke faktore wat verband hou met potensiale gehoorverlies te beskryf. 'n Deursnee-ontwerp is gebruik en data is ingesamel uit 132 respondente (mynbou werknemers), uit vyf verskillende Klas A myne regdeur die land. 'n Vraelys en 'n retrospektiewe oorsig van die respondente se mediese rekords is gebruik om die risiko faktore te bepaal. Die mees onlangse oudiogram wat in die respondente se rekords gevind is, is gebruik om die teenwoordigheid van potensiale gehoorverlies te bepaal. Drie definisies van potensiale gehoorverlies is gebruik in hierdie studie, ingesluit al die groot frekwensie gehoorverliese (AFHL), hoë frekwensie gehoorverlies (HFHL) en 'n lae frekwensie gehoorverlies (LFHL). ‘n Gehoorverlies was teenwoordig wanneer die suiwer toon gemiddelde (PTA van 0.5 , 1 , 2, & 4kHz , 0.5, 1 & 2kHz en 4 & 8kHz onderskeidelik , groter was as 25dBHL in een of albei ore. Chi -square metings of, waar nodig, Fisher se presiese toetse, asook kans verhoudings is gebruik vir die ontleding van data. In die algemeen is 'n beduidendeidsvlak van 5% gebruik en toegepas vir al die ontledings. Resultate het aangedui die voorkoms van gehoorverlies in Namibiese mynbouwerknemers tot 27 % was en dat beide ekstrinsieke en intrinsieke faktore ‘n verband toon met potensiaal gehoorverlies. Die ekstrinsieke faktore wat ‘n beduidende verband getoon het met gehoorverlies was albei beroeps- en mediese faktore. Die beroepsfaktore wat betekenisvol was, was die aantal jare diens in hele lewe > 10 jaar ( p = 0,012 ; OR = 3.1 , 95 % CI = 1.3-7.9) , die aantal jare in huidige pos> 10 jaar diens (p = 0,01 ; OF = 3.9 , 95 % CI1.7-8.8 ) en die onbeskikbaarheid van formele opleiding in die voorkoming van potensiaal gehoorverlies (p = 0,022 ; OF = 0,3 , 95 % CI ( 0,1-0,9 ). Diabetes was die enigste beduidende ekstrinsieke mediese faktor (p = 0,035 , OR = 5 , 95 % CI 1,1-22,1 ). Die enigste intrinsieke faktor watbeduidend was en verband hou met gehoorverlies was ouderdom, spesifiek om ouer as 40 jaar ( p = 0,002 ; OF = 3.5 , 95 % CI 1,6-7,8 ) en 50 jaar ( p = 0.001 , OR = 5.5 , 95 % CI1.9-15.8 ) te wees. 'n Veelvuldige regressie model van alle beduidende faktore het bevind dat slegs geen formele opleiding in die voorkoming van gerhoor verlies beduidende was in die teenwoordigheid van al die ander faktore ( p = 0,036 , OR = 0,036 , 95 % 0,1-0,92 ) . Bevindinge van hierdie studie dui daarop dat verskeie faktore geassosieer kan word met gehoorverlies en nie net die blootstelling aan gevaarlike beroepstoestande nie. Aanbevelings vir toekomstige navorsing en kliniese praktyk moet dus 'n grondige ondersoek na die etiologie van gehoorverlies uitvoer. Aangesien hierdie studie gefokus het op die Klas A- myne , word dit aanbeveel dat toekomstige navorsing gedoen word in ander myne wat nie gekategoriseer is as Klas A myne nie. Sleutelwoorde: Voorkoms, ekstrinsieke faktore, instrinsieke faktore, ekstrinsieke beroepsfaktore, ekstrinsieke sosiale faktore, ekstrinsieke mediese faktore, potensiale gehoorverlies, Klas A myn, Namibië.

published_or_final_version / Environmental Management / Master / Master of Science in Environmental Management