[Hearing loss of workers in mining--a 6-year longitudinal study].

Hearing threshold level (HTL) in miners, was determined after six years interval characterized by the same noise exposure. An attempt was made to establish the prognosis regarding the hearing losses extent and the time interval involved in the occurrence of these modifications in the subjects applying the HTL values. 132 workers (miners and miner apprentices) underwent audiometrical examinations, after 6 years interval in the same testing conditions. To evaluate the vibrations possible effects on the HTL, the results registered in a group of workers exposed solely to noise (n = 33)-identical continuous equivalent level/week-were compared to those found in miners. According to age range and the duration of noise exposure, the yearly mean rate for both the low (500-2000 Hz) and high frequencies (2-8 kHz), were calculated based on the hearing threshold differences. The miners, simultaneously exposed to noise and vibration presented yearly decreased HTL values (up to 2000 Hz), as against the subjects exposed solely to noise. The prognosis indicates that in a miner with a duration of exposure above 21 years and/or a mean age of 38, one may expect a loss of the HTL exceeding 30 dB at 4 kHz.