It is well known that the workers exposed to high level nosie slowly but inevitably developed a hearing disturbance.
This survey was carried out to evaluate the characteristics of exposed noise and noise-induced hearing disturbance of workers in one air-base and 15 industries.
For this survey, 1,345 male workers (370 air-base servicemen, 368 industrial workers and 607 workers for control group) were investigated, and their hearing acuities were measured by Individual Pure Tone Threshold Determination Test(air
conduction).
1. The characteristic of F-4D Jet aircraft noise was broad band which comprised a relatively flat frequency spectrum and the intensity was varied by the kind of maneuver, e. g., take-off or landing.
2. The intensity of background noise in the air-base was highest in Engine Test Cell, 128 dB(A) and band components distributed in high frequencies, from 2.000 to 8,000 hertz, but in industries, highest in boiler rooms, 102 dB(A), chiefly
distributed mid frequencies, from 250 to 1,000 hertz.
3. Average exposure duration per day in the air-base was 3.1 hours but in the industries, it was 8.0 hours.
4. The type of noise in the air-base was intermittent noise(64%), but in the industries, it was chiefly steady-state noise(89%)
5. Hearing threshold levels by frequencies were highest in the 4,000 hertz(air-base group; 24.8 dB, industrial group; 26.1dB) and followed by 6,000, 8,000, and 3,000 hertz.
6. Hering threshold levels of the 8,000 hertz were varied by groups of examinees, e. g., 23.2dB in the airbase group but 18.3dB in the industrial group.
7. The mean hearing loss of control, air-base and industrial group was 12.0±4.8, 16.2±7.1 and 16.6±8.1 dB respectively.
8. The mean hearing loss of Engine Test Cell technicians was highest among the air-base group, 17.6±7.4dB and among the industrial group, that of boilermakers was highest, 17.5±8.4dB.
9. Degree of mean hearing losw correlated with duration of service years(the longer the period of work, the more increase), but the increasing rate was varied by group of examiness, e. g. increasing level in airbase group was 3.8dB between
the
group of under 5 years service and from 5 to 9 years service, but in industrial group, the difference was only 1.5dB.
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