The characteristics of pure tone audiograms in a sample of Royal Marines after Operation Herrick 9.

Introduction Estimation of the incidence of noise-induced hearing loss sustained in the course of current operations requires both preand post-deployment pure tone audiometry. In a study of reserve personnel who deployed to Operation Herrick 6, 10% of personnel had good audiometric evidence to support a diagnosis of noise-induced hearing loss and a further 32% had audiograms that suggested it1. A sample of personnel of 42CDO were the subject of a recent study2 which intended to compare pre-and postdeployment audiometry conducted by medical centre personnel as well as to validate the medical centre audiometry against formal audiometry by Defence Audiology Service audiologists. The former aim was not successful, because too few subjects had had adequate pre-deployment audiometry. Therefore any estimate of the extent of NIHL is limited to an estimate of the prevalence. This study aims to estimate the prevalence of NIHL based upon the DAS audiometry. The accepted criteria required for a diagnosis of NIHL are: (1) an high frequency impairment; (2) noise exposure; (3) an audiometric configuration of a notch or bulge3. It goes without saying that criteria (1) and (3) may be derived from analysis of the audiogram. Although data exist on the loudness of various military vehicles and weapons, no data were available for the exposure for individual personnel. The statutory4 daily peak exposure limit value is 140 dB(C), which is exceeded by a single SA80 round when fired without any form of protective equipment. Anecdotal evidence is that troops fire thousands of rounds of various types in a deployment. The current personal interfaced hearing protection was not available for Op Herrick 9. It is therefore considered reasonable to assume that all troops were exposed to an excessive amount of noise.