Noise Exposure and Hearing Impairment in the Shipbuilding Industry

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Abstract
The purpose with the present work is to illustrate the dose-response relationship for the effects of noise on hearing within the shipbuilding industry. Special problems are involved in retrospective studies of this kind, due mainly to the difficulty of determining each person's total noise dose. In evaluating the results, therefore, we have concentrated on the question whether the noise at a shipyard is less or more harmful than continuous noise of the same equivalent level. Results: Registering of the noise exposure with microphone and tape recorder and subsequent analysis at the laboratory gave an accurate description of the exposure. It shows that about 2500 impulses with peak levels between 110 and 135 dB occur daily and that these impulses are superimposed on a high, fluctuating background level. The results from individual noise dosimetry show that the daily or weekly noise dose follows the rhythm of the production and is also a function of the employee's occupation. As an arithmetic average the measured equivalent level for the near field was found to be 94 dB(A) and 88 dB(A) for the reverberant field. Despite the fact that hearing protectors were worn in most cases, the hearing measurements demonstrated that noise-induced hearing losses were common. The pure tone audiogram showed the typical noise dip. Only 41.9% of the 1492 employees examined have normal hearing, while 58.1% have some type of hearing impairment. 20.4% of the employees have severe NIHL. A comparison between the hearing-damage hazard when exposed to continuous noise according to ISO R 1999 and the risk when exposed to shipyard noise indicates that shipyard noise is definitely more harmful to hearing than is continuous noise.

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