Kurtosis corrected sound pressure level as a noise metric for risk assessment of occupational noises

Abstract

Current noise guidelines use an energy-based noise metric to predict the risk of hearing loss, and thus ignore the effect of temporal characteristics of the noise. The practice is widely considered to underestimate the risk of a complex noise environment, where impulsive noises are embedded in a steady-state noise. A basic form for noise metrics is designed by combining the equivalent sound pressure level (SPL) and a temporal correction term defined as a function of kurtosis of the noise. Several noise metrics are developed by varying this basic form and evaluated utilizing existing chinchilla noise exposure data. It is shown that the kurtosis correction term significantly improves the correlation of the noise metric with the measured hearing losses in chinchillas. The average SPL of the frequency components of the noise that define the hearing loss with a kurtosis correction term is identified as the best noise metric among tested. One of the investigated metrics, the kurtosis-corrected A-weighted SPL, is applied to a human exposure study data as a preview of applying the metrics to human guidelines. The possibility of applying the noise metrics to human guidelines is discussed.

Figure 1

Scatter plots of the PTS₅₁₂₄ values against the metric values with the regressed lines. Each point represents the pair of the average PTS₅₁₂₄ of the chinchillas in the group exposed to one specific type of noise and the metric calculated for the noise. (A) against L_eq and _L^′eq, (B) against L_Aeq and _L^′Aeq, and (C) against L_eq,5124 and _L^′eq,5124. It is seen that adding the kurtosis correction term improves the correlation between the metric and PTS₅₁₂₄.

Figure 2

Effect of kurtosis correction on the measured human NIHL data. AHFNIHL is percentage of the subjects having a higher HTL by 30 dB or more than the control group. Solid line with filled diamond symbol represents the CNE-NIHL relationship of the group exposed to Gaussian noises, dashed line filled square symbol represents the CNE-NIHL relationship of the group exposed to complex noise, and dotted line with filled triangle symbol represents (kurtosis corrected CNE) CNE′-NIHL relationship of the group exposed to complex noises. CNE′-NIHL curve of the complex noise becomes much closer to the CNE-NIHL curve of the Gaussian noise, which the kurtosis correction reduces underestimation of the risk of complex noises.