Literature review of metrics for risk of hearing damage from impulse noise

This report contains a literature review with an aim to find the best available metric to evaluate impulse-noise-induced risk of hearing loss, especially for shooting activities in the Norwegian Armed Forces. Our recommendation is 𝐿𝐿𝐴𝐴𝐴𝐴𝐴𝐴,8ℎ𝑟𝑟. No perfect damage risk criterion currently exists. In other words, there is no single damage risk criterion that can accurately evaluate the hazard in all exposure conditions: for impulse and continuous noises, for small and large weapons, for protected and unprotected ears, and for the statistical variation of people and the situations they are in, including the individual fit and performance of hearing protection. We nonetheless recommend that the metric adopted for evaluation of impulse-noise-induced risk of hearing damage will be 𝐿𝐿𝐴𝐴𝐴𝐴𝐴𝐴,8ℎ𝑟𝑟. This metric is peer reviewed and has the best correlation with available test data. Moreover, the damping effect of hearing prediction devices can be included in this metric. We recommend that the maximum C-weighted peak level for impulse noise exposure in the Norwegian Armed Forces should be 140 dB, at the ear (protected or unprotected). Currently, the Norwegian noise regulations have a limit of 130 dB. 140 dB would be more in line with current international regulations and standards for impulse noise. One can apply the following method to include the damping effect of a hearing protection device in the metric, including a measurement method: • For 𝐿𝐿𝐴𝐴𝐴𝐴𝐴𝐴,8ℎ𝑟𝑟 , we apply Impulsive Spectral Insertion Loss (ISIL). The measurements are partly based on ANSI/ASA S12.42. • For maximum C-weighted peak level, we apply the method of Impulse Peak Insertion Loss (IPIL), based on ANSI/ASA S12.42-2010.