[Effect of noise and other factors damaging to hearing on hearing loss]

The goal of the present paper was to investigate the relationship between hearing loss and noise exposure. Moreover, the author also examined the question whether damaging factors detected in the case history (hereditary susceptibility, toxic and infectious-toxic factors, cerebral and acoustic trauma, war, tinnitus) and working conditions (ototoxic industrial substances, shift work, hearing protection) affect hearing loss in any way. A tone and speech audiogram of 1020 persons exposed to industrial noise in a power station and non-exposed persons was evaluated for this purpose. In addition to exposure at the respective place of work, the sound intensity and total period of employment were also taken into consideration. The noise exposure of the persons working in industrial noise exceeded the limits of hearing damage, although it generally amounted to levels of less than 95 dB (A). Hearing loss in persons exposed to industrial noise increases as the noise level increases. In the intensities we examined, however, the level of sound appears to be less decisive in its effect than generally assumed. The effect of time on the threshold of hearing, on the other hand, is of importance at evaluation levels of less than 90 dB (A). In addition to age and occupational noise exposure, the following factors are significantly correlated to the threshold of hearing: hereditary susceptibility, traumata, war, tinnitus and shift work. On the whole, the factors and working conditions recorded in the case history have a considerable effect on hearing loss and are approximately equivalent to the noise at sound levels up to about 90 dB (A).