[The development of occupational perceptual deafness in blacksmiths]

Analysis of hearing of 140 blacksmiths from three workships (280 ears) revealed considerable differences in the development of occupational perception deafness between different individuals and also as regard the affection of the right and left ear. The author worked out the decibel increment and average audiogram after 40 years exposure to noise after dividing the aers into five groups with regard to the affection on the main four frequencies. In the majority of ears the audiometric curve is not higher than 60 dB which is due to the numerical atrophy of the external ciliated cells. A drop of the audiometric curve below 60 dB was recorded in 13 ears (4.6%); in the group during the subsequent development of deafness a decline of the audiometric curve was recorded also at lower frequencies which suggests affection of the inner ciliated cells in the course of development of progressive necrosis. For investigation of hearing during preventive examinations ensues that occupational deafness develops after a prolonged period of exposure to noise typically at a frequency of 4 kHz to 60 dB on the audiogram. A drop of the audiometric curve below 60 dB in the area of a frequency of 4 kHz and concurrently below 20 dB at lower frequencies means that the hearing of the person is threatened due to overexposure.