Applicability of the L(eq) as a damage-risk criterion: an animal experiment

Within the European communities, the L(eq8h) is used as a damage-risk criterion (DRC) for hearing protection. The use of such a DRC supposes that sound exposures with equal energy imply equal risk for noise-induced hearing loss (NIHL). The aim of the present study, carried out with guinea pigs, was to test the applicability of the L(eq8h) for estimating the hazard of different noises having the same spectrum and acoustic energy. Therefore, only the temporal structure of noises was a variable (continuous, intermittent, or impulsive) and each noise had a L(eq8h) of 92 dB. The results indicate the L(eq8h) is not an accurate DRC. It overestimates the NIHL for intermittent and short-continuous noises, whereas it seems to be useful for moderate-intensity noises (95 dB) and for the impulse noise (101 dB). Furthermore, the data point out the notion of ¿critical intensity¿ which seems to play a determining role in the transition between metabolic and mechanical mechanisms involved in the acoustic trauma. Since the critical intensity and the existence of two mechanisms are parameters that the L(eq8h) cannot take into consideration, recommendations on the safety program of hearing loss prevention are discussed.