[Effects on hearing in exposure to impulsive and high frequency noise]

Audiometric tests performed on 41 workers at a metal engineering factory producing tools for the wood manufacturing industry showed hearing loss at 6 kHz in 45.9% of the cases. A study was therefore carried out to check carefully the physical characteristics of the noise via statistical analysis and octave frequencies band analysis in real time. The measurements revealed higher noise levels at the high and medium high frequencies (3.15-6.3 Hz) both for impulsive and continuous noise. The results of the audiometric tests differed from those of a group of 50 workers employed in two different metal engineering factories, where the noise levels were similar but at medium-low frequencies, with no pure tones. In this group of subjects, hearing loss occurred at 6 kHz in 28% of the cases; the differences thus seemed to be related the particular physical characteristics of the noise levels measured in the first factory. The data are discussed against findings already reported in the literature, in relation to their prevention-related aspects and a more correct interpretation of the audiograms.