Abstract. This paper presents preliminary results of a study aimed at evaluating the impact on man and environment of major accident hazards related to transmission pipelines carrying toxic substances. In particular, it describes the assessment of the consequences of potential toxic release from pipelines, expressed in terms of hazard area, that is the zone in which the concentration of a toxic substance exceed a critical threshold level and induce harmful effects on people and the environment. Moreover, a sensitivity analysis has been undertaken, emphasizing the role of threshold values on the results obtained.Keywords: pipeline safety, major accident, toxic releases, consequence analysis, threshold level. Abstract.Il lavoro presenta i risultati preliminari di uno studio finalizzato alla valutazione dell'impatto sull'uomo e sull'ambiente degli incidenti rilevanti associati al trasporto in condotta di sostanze tossiche. In particolare, esso descrive la valutazione delle conseguenze di un potenziale rilascio di sostanza tossica da condotta in termini di area di danno, definita come l'area in cui la concentrazione di sostanza tossica supera un predeterminato valore di soglia ed induce effetti nocivi sulla popolazione e sull'ambiente. Viene altresì proposta una analisi di sensitività finalizzata alla valutazione dell'incidenza dei parametri di input richiesti per la simulazione dell'evento incidentale sui risultati ottenuti.Keywords: trasporto in condotta, incidente rilevante, rilasci di sostanze tossiche, analisi delle conseguenze, valore di soglia.

The consequence assessment of a major accident involving a release of toxic gas by a pipeline is usually performed through the evaluation of the associated hazard area, which is an area where the concentration of the toxic substance exceeds a fixed threshold level and induces harmful effects in people and the environment; its extension represents a significant source of information required for the development of both safety and security strategies associated with dangerous pipelines. Since the threshold level adopted in the calculation strongly affects the extent of this hazard area, the purpose of this paper is to analyse such influence and the potential implications on the decisional process concerning prevention, preparedness and response actions in the case of major accidents. The paper describes the methodological approach adopted for this purpose, as well as the main results obtained using the threshold levels most commonly applied in the industrialized countries. Although the estimate of the hazard areas involves a high level of uncertainty, this study aims at supporting the development of pipeline safety and security strategies, thus increasing the overall safety level in this vital sector.

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