[Longitudinal audiometric studies concerning progression of noise induced hearing loss (author's transl)].

The development of occupational hearing loss is very important for the recommendation to change the work place. 1960 Dieroff has described a phasic development of noise induced hearing loss. After ten years in noisy environment no further development of hearing impairment was determinable. Recent investigations point to a logarithmical respectively linear dependence of noise induced permanent threshold shift on the duration of exposure to noise. During our observation over a period of two years of employees working on noisy jobs, no stay of noise induced permanent threshold shift proceeding could be stated after ten or twenty years. As the raiting sound level of the working places, which we have studied, had only approx. 60 to 100 dB(A), it can be assumed, that under these conditions the noise induced hearing loss developes delayed and the noise induced permanent threshold shift increases as long as it must be worked under noisy conditions. The noise induced hearing loss depends on the intensity of noise exposure of the different groups. Also the group of storehouse- and court personnel as well as the drivers, being exposed only to a raiting sound level of approx. 65-75 dB(A), showed a significant higher noise induced permanent threshold shift than the group of administrative employees.