Assessment of Risk Zones in A Seveso Plant: A Case Study

Roberto Lauri, Mariano Ciucci, and Alessandra Marino

INAIL, Department of Technological Innovations and Safety of Plants, Products and Human Settlements, Via del Torraccio di

Torrenova 7, 00133 Rome, Italy

Abstract: The assessment of the consequences of industrial accidents takes on a significant interest in the risk analysis of a “Seveso” plant. In fact the estimate of risk zones extent represents a basic element for the characterization of accident scenarios and for the definition of the outcomes to include in the Safety Report, which is mandatory for Seveso plants. In this paper, a case study, referred to a release of a toxic gas liquefied under pressure (anhydrous ammonia), is illustrated. This choice depends on massive ammonia use in several industrial processes. In many cases, when a gas liquefied under pressure is released, aerosol formation is predominant and often causes that all spilled liquid flow forms the gaseous cloud without generating the puddle (two-phase release). Aerosol presence increases vapor mass in the cloud and its density. It follows that gases, which usually should be lighter than air, act as heavy gases. In the paper, effect of toxic release (top event) on human health has been determined by the risk zones extent calculation, which has been performed by a specific software (Effects).

Key words: liquefied ammonia, Seveso plant, atmospheric stability class, risk zones