Physiological cost of energy-equivalent noise exposures with a rating level of 85 dB(A): Hearing threshold shifts associated with energetically negligible continuous and impulse noise

Author(s): Hesse, J. M., Strasser, H.

Journal/Book: Int J Ind Ergonomic. 1998; 21: PO Box 211, 1000 AE Amsterdam, Netherlands. Elsevier Science BV. 451-463.

Abstract: In industry continuous or impulse noise does not occur exclusively; rather it is a combination of bath. If low-level continuous noise or impulse noise (below 120 dB) is added to an already existing high-level continuous noise this often numerically causes no essential increase in the rating level. Yet, it cannot be expected that also aural strain of these exposures is always negligible. Therefore, in a cross-over test series, ten male subjects (Ss) were exposed to white noise of 94 dB(A) for 1 h (TS I), energy-equivalent to an 8 h-rating level L-Ard Of 85 dB(A). In a second lest series (TS II) the same exposure was combined with 900 energetically negligible 5-ms impulses with a noise level of 113 dB(A) which increased the rating level by only 0.4 dB. The noise exposure of TS I and TS II was followed by an idealized resting phase in a soundproof cabin. In a third test series (TS III) the continuous noise of 94 dB(A)/1 h was followed by 3 h of white noise at 70 dB(A). Such an additional load increases the L-Ard by merely 0.1 dB to 85.1 dB(A). In all three test series, the noise-induced temporary threshold shift (TTS2) and its restitution were measured. The continuous noise exposure of 94 dB(A) for 1 h was associated with a TTS2 of around 20 dB which disappeared completely after about 2 h. The additional impulse noise caused a small increase in the TTS, and a prolongation of the restitution time. The maximum mean temporary threshold shift for the group increased only slightly (from 22.5 to 25.9 dB, which nevertheless can be statistically proven at a significance level of p greater than or equal to 0.99). Yet, more importantly, the restitution time increased from 126 to 175 min, i.e. 3 h, which can be statistically proven at a significance level of p greater than or equal to 0.95. The TTS2-values of TS III did nor differ significantly from those resulting from TS I. That was expected as the conditions up to that point in time were identical. But due to the additional subsequent exposure: the mean restitution time increased considerably from 126 min up to 240 min (4 h). The mean total physiological cost represented by the integrated restitution temporary threshold shift (IRTTS) increased in TS II by approximately 40% and in TS III even by 140%.

Note: Article Strasser H, Univ Gesamthsch Siegen, Inst Prod Engn, Ergon Div, Paul Bonatz Str 9-11, D-57068 Siegen, GERMANY

Keyword(s): energy-equivalence principle; noise rating level; temporary threshold shift (TTS) and restitution time (t(0 dB)); integrated restitution temporary threshold shift (IRTTS); hearing risk factor (HRF)

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