Marc J. Blair

Date of Award

3-2020

Document Type

Thesis

Degree Name

Master of Science in Industrial Hygiene

Department

Department of Systems Engineering and Management

First Advisor

Jeremy M. Slagley, PhD

Abstract

This retrospective cohort epidemiology study sought to establish the comparative risks and potential indicators of hearing loss associated with combinations of ototoxic substances, impulse noise, and continuous noise exposure. Currently, there is not an existing model or methodology in the Department of Defense (DoD) that joins occupational exposure data and pure tone audiometric data. After developing an integrated database model for Tinker Air Force Base, the largest of three depot installations within Air Force Material Command, 2,372 individuals were grouped into eight combinations of exposure groups with a minimum three years exposure duration to hazards. The incidence rates and relative risk of hearing loss indicators were calculated with five different pure tone audiometry evaluation methods. With the NIOSH Significant Threshold Shift criteria, a significant increase in risk occurred in the left ear at 2,000 Hz for the Metal/Solvent/Continuous exposure group (RR=2.44 CI 1.24-4.83) compared to a continuous noise only reference group. Further descriptive and inferential statistical analysis confirmed a significant difference (Bonferroni adjusted p-value= 0.023) in hearing threshold shifts in the left ear at 2,000 Hz between this exposure group and reference exposure group. In the presence of continuous noise exposure, ototoxic effects on hearing loss could only be observed in the 1,000 and 2,000 Hz frequencies. Due to data availability, researchers could not establish further confidence in results with descriptive statistical analysis or logistic regression. Results indicate the current DoD Hearing Conservation Program's significant threshold shift criteria potentially do not capture the increased risk of hearing changes from ototoxic substance exposure.

AFIT Designator

AFIT-ENV-MS-20-M-187

DTIC Accession Number

AD1102620

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