Traditional Rating of Noise Versus Physiological Costs of Sound Exposures to the Hearing
In occupational safety and health acts, ordinances, regulations, directives, standards and guidelines, A-weighted sound exposures, varying in level and duration, are traditionally converted to an 8-hour-average sound level by applying the 3-dB exchange rate. Under the prerequisite that the energy equivalent rating level does not exceed 85 dB(A)/8 h, even impulse noise exposures of up to 140 dB are declared harmless. Indeed, the mutual settlement of level and duration based on the concept of energy equivalence is correct as far as sound energy or physical dose is concerned. However, between this principle and work physiological and work psychological, i.e. ergonomics paradigms, some decisive discrepancies do exist. People react to exposures according to human characteristics rather than 'function' according to the laws of physics as they apply to inert matter. This has been demonstrated by a series of new experimental approaches, in which temporary threshold shifts and their restitution associated with various energy equivalent noise exposures have been measured. Also the impact of various types of loud music has been investigated. In addition to the conventionally determined maximum threshold shift, TTS2, and the time it takes to reach the resting hearing level again, the area under the restitution curve, indicate the total physiological costs the hearing has to pay for a preceding sound exposure. This book is an attempt to increase the transparency in existing evaluation methods and – in the interest of pertinent disclosure of risks associated with common procedures – to work towards the elimination of unacceptable simplifications and dangerously erroneous assessments.