Oil Spills In Harbour Area: A ConservativeApproach To Risk Assessment And EmergencyPlanning

Abstract

The study of dispersion and transformations following an open sea oil spill has been faced by several authors, on the basis of mathematical models of different complexity, so as to quantify the different phenomena involved in the release evolution: convective transport by sea currents, possibly in connection with wind action; turbulent diffusion; buoyant action on dispersed particles; wave action; superficial spreading of the oil due to different density between sea water and hydrocarbon; evaporation and emulsification rates. Dealing with a release in a port area, besides the environmental consequences, the most severe hazards are linked to fires and explosions due to the formation of a flammable cloud by evaporated hydrocarbons and air and subsequent ignition. If a cloud of sufficient size is formed and ignition occurs instantly, a large fire, jet flame or fireball may occur, but significant blast-pressure damage is unlikely. Instead, the blast effect produced by vapour cloud explosion (i.e. cloud formation and ignition delayed typically by some minutes) can vary greatly depending on the speed of flame propagation and can result in extensive widespread damage. We considered such types of events, focusing our attention to individual intervention times and types more suitable to contain the risk into an acceptability level. Considering that intervention time and dispersion time are comparable, the basic variables considered in developing the mathematical model were oil spill spreading rate, hydrocarbon evaporation rate, cloud transport and dispersion into the atmosphere. The developed model allows the separation of the risk areas and intervention times in confined regions and ports of relative simple geometry. The same model can be applied, as well, to more complex geometry, typical of port areas, obtaining conservative results for a preliminary risk evaluation.