[Temporary hearing loss due to vibration and noise]

Studies of combined effects of sinusoidal whole body vibrations and noise of varying bandwidths and intensities on TTS2 in men

This study analyses the data from three laboratory experiments concerning the separate and combined effects on temporary threshold shifts in hearing (TTS2) of sinusoidal low-frequency (5 Hz--2.12 m/s2 and 10 Hz--2.65 m/s2), whole body vibration (along the Z-axis), and continuous (white) noise with eight different bandwidths and intensity levels of 85 dB(A), 90 dB(A) and 98 dB(A). Altogether 370 separate personal experiments were performed using a one-man exposure chamber system. A single experiment consisted of a 30-min pre-exposure period, three 16-min exposure periods, and a 15-min post-exposure period. The data suggested that the TTS2 induced by noise was increased by vibration. Actually, vibration at a frequency of 5 Hz and noise with bandwidths of 1-4 kHz, 1-8 kHz or 0.2-16 kHz comprised the most significant exposure combinations. After such exposures, the increase in TTS2 values was defined most clearly for 4 kHz and 6 kHz test frequencies. The increase of thresholds was most marked during the first 16-min exposure period, even though most TTS2 values determined after the third consecutive exposure period were higher than after the first and second exposures. Figures obtained after the third exposure period proved that exposure to simultaneous vibration and broad band noise (i.e. noise with a bandwidth of 0.2-16 kHz) increased TTS2 values 1.2-1.5 times more in the 4 kHz audio range than such a broad band noise alone. No single vibration condition induced the same amount of TTS2.