High-frequency audiometry in the evaluation of critical noise intensity.

We investigated a total of 537 subjects (68 men, 469 women) working in the textile industry to ascertain their hearing level in the conventional hearing range as well as in the high-frequency (HF) range. The persons we tested work at three different noise-levels [80-84, 85-89, 90-94 dB (A), measured as leq). The differences in the hearing thresholds between this three groups mentioned were checked by means of discriminant analysis. The first hearing level changes at a noise-level below 90 dB (A) leq develop mainly in the HF range. In the conventional hearing range, however, the hearing levels remain unchanged even over long exposure times. Noise-induced hearing loss in the conventional range occurs only in the sound level group of 90 to 94 dB (A) leq without attaining any social importance. The tests show that, if the noise-level 90 dB (A) leq is not exceeded, no noise-induced hearing impairments involving social hearing loss are to be observed. Thus we assume that an auditory risk criterion of 85 dB (A) leq is sufficient to prevent hearing loss of any social importance.