Variability of field-based hearing protection device attenuation measurements

Abstract

HPD attenuation is highly dependent on individual-specific fit. Prediction of an individual’s attenuation depends on measurement system accuracy and attenuation variability due to HPD refitting. This study compared attenuation measurements from two systems [one real-ear-attenuation-at-threshold (REAT) and the other microphone-in-real-ear (MIRE)] on workers using two earplugs (foam and custom-molded). Workers’ perceptions of the earplugs were also evaluated. Individual’s attenuation results were summarized as personal attenuation ratings (PARs). Variability in PARs from between-subject, between-day, and within-day differences was used to determine the lower confidence limit, or uncertainty factor (UF), of an individual’s attenuation. The custom-molded earplug PARs achieved a higher percentage of labeled attenuation than did the foam earplug with both test systems, and also had higher overall acceptance among workers. MIRE PAR levels were lower than REAT levels for both earplugs, but the relationship between the two test systems was highly variable. The MIRE system had lower within-day variability than the REAT system. One individual’s MIRE results were highly influential; removal of these results greatly reduced the UF for the custom-molded earplug/MIRE combination. UFs ranged from 8.8 to 13.5 dB. These findings highlight the importance of evaluating variability in individuals’ HPD attenuation, rather than relying on single measurements.