Estimation of Occupational Noise-Induced Hearing Loss Using Kurtosis-Adjusted Noise Exposure Levels.

Abstract

Objectives:Studies have shown that in addition to energy, kurtosis plays an important role in the assessment of hearing loss caused by complex noise. The objective of this study was to investigate how to use noise recordings and audiometry collected from workers in industrial environments to find an optimal kurtosis-adjusted algorithm to better evaluate hearing loss caused by both continuous noise and complex noise.Design:In this study, the combined effects of energy and kurtosis on noise-induced hearing loss (NIHL) were investigated using data collected from 2601 Chinese workers exposed to various industrial noises. The cohort was divided into three subgroups based on three kurtosis (β) levels (K1: 3 ≤ β ≤ 10, K2: 10 <β ≤ 50, and K3: β > 50). Noise-induced permanent threshold shift at test frequencies 3, 4, and 6 kHz (NIPTS346) was used as the indicator of NIHL. Predicted NIPTS346 was calculated using the ISO 1999 model for each participant, and the actual NIPTS was obtained by correcting for age and sex using non-noise-exposed Chinese workers (n = 1297). A kurtosis-adjusted A-weighted sound pressure level normalized to a nominal 8-hour working day (LAeq,8h) was developed based on the kurtosis categorized group data sets using multiple linear regression. Using the NIPTS346 and the LAeq.8h metric, a dose-response relationship for three kurtosis groups was constructed, and the combined effect of noise level and kurtosis on NIHL was investigated.Results:An optimal kurtosis-adjusted LAeq,8h formula with a kurtosis adjustment coefficient of 6.5 was established by using the worker data. The kurtosis-adjusted LAeq,8h better estimated hearing loss caused by various complex noises. The analysis of the dose-response relationships among the three kurtosis groups showed that the NIPTS of K2 and K3 groups was significantly higher than that of K1 group in the range of 70 dBA ≤ LAeq,8h < 85 dBA. For 85 dBA ≤ LAeq,8h ≤ 95 dBA, the NIPTS346 of the three groups showed an obvious K3 > K2 > K1. For LAeq,8h >95 dBA, the NIPTS346 of the K2 group tended to be consistent with that of the K1 group, while the NIPTS346 of the K3 group was significantly larger than that of the K1 and K2 groups. When LAeq,8h is below 70 dBA, neither continuous noise nor complex noise produced significant NIPTS346.Conclusions:Because non-Gaussian complex noise is ubiquitous in many industries, the temporal characteristics of noise (i.e., kurtosis) must be taken into account in evaluating occupational NIHL. A kurtosis-adjusted LAeq,8h with an adjustment coefficient of 6.5 allows a more accurate prediction of high-frequency NIHL. Relying on a single value (i.e., 85 dBA) as a recommended exposure limit does not appear to be sufficient to protect the hearing of workers exposed to complex noise.