Impairment of hearing loss caused by exposure to noise is a problem of increasing importance in industrial countries. In attempt to know audiometrical patterns of noise deafness in relation to the duration of exposure to noise and age and then find some available factors to make less noise deafness, the author performed an audiometrical examination of 1603 workers who has worked at noisy industries above 85 dB. in Busan City area.
The following three types of noise deafness were classified based on the audiograms. Mild deafness (N type) was the type ire which the hearing loss of air conduction was greater than 15 dB and less than 20 dB in high or middle frequencies. High tone deafness (H type) was the type in which the hearing loss of air conduction was greater than 20 dB in high frequencies. Speech range deafness(S type) was the type in which the hearing loss of air conduction teras greater than 20 dB in high and middle frequencies.
The following conclusions were obtained:
1. The detective rate of noise deafness was 29. 1%, showing 932 ears among 3,206 ears. Of 932 ears, speech range deafness occurred in 533 ears with 57.2% which was most frequently observed and high tone deafness next in order.
2. Noise deafness was usually established by first nine years, and after that, further hearing loss seemed to be very slightly. It might be said to depend on the duration of exposure to noise until first nine years.
3. Noise-deafness was in general most profound at the age of 39 except same cases of speech range deafness. Further hearing loss was progressive and might depend on more physiological phenomenon of aging than the effect of noise itself.
4. The level of hearing loss was 20-49 dB loss in tyro-third of the cases of high tone deafness and 20-40 dB loss in majority of the cases of speech range deafness.
5. All cases of high tone deafness and almost cases of speech range deafness supposed to be completly established by the first nine years of exposure to noise and the age of 39, while same cases of speech range deafness was most profound between 10-14 years of noise exposure and at the age of 4 decade.
6. Audiograms of noise deafness could be devided into several different, patterns, which the descending form was seen in 286 ears or 34.0%, dip form in 229 ears or 27.0% and abrupt drop form in 186 ears or 22. 1%.
7. The dip form was seen most frequently at 4000Hz. In addition, the dip form was checked at the frequencies of 2,000, 3,000, and 6,000 Hz.
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