(65az) Probit Models for the Determination of Damage Probability of Storage Tanks Due to Flooding Impact

Global climate changes may significantly influence temperatures and precipitation patterns, increasing the frequency of severe meteorological events which may lead to flooding.  Flooding may trigger severe accidents on population among urban as it may do on chemical process industries too, causing the damage of equipment and the loss of containment of hazardous materials which might transform into toxic dispersions, fires, explosions or severe environmental contamination. This type of events are known as Natech events (Natural-Technological). This type of events may lead to extremely severe consequences bringing up the need to develop approaches for the risk assessment of Natech scenarios. Recently important efforts have been dedicated to develop tools that include Natech events in the quantitative risk assessment framework. In order to allow a quantitative risk assessment of a Natech event, a key point is the definition of tools for the estimation of equipment damage probability on the basis of intensity parameters of flooding. Past accident data analysis evidenced that horizontal and vertical storage tanks were often damaged in Natech events triggered by floods. Because of this the present study presents specific probit models for the damage probability of horizontal and vertical storage tanks due to flooding intensity parameters (flooding water height and flooding water).

Probit models in this study were derived on the basis of a mechanical model used for the assessment of the vulnerability of storage tanks due to the impact of flooding. For the determination of damage probability Montecarlo simulations were applied over the mechanical model in order to obtain a more accurate value and a probabilistic distribution of this parameter in dependence of the flood impact vector. Once the damage probability distribution is determined the probit method was applied using a logarithm approach with the impact flood vector (water height and water velocity) as the dose variables and the probability of damage as the response variable. A logarithm regression using the minimum square method was utilized to determine the probit constants for the model. Since the mechanical model used as basis has a huge dependence on the geometry of the storage tank being studied, it was find the damage probability will be affected and its value will change. To make sure this affections will be taken into account in the probit modeling a relationship between the geometry of the tanks and the probit constants was established using a polynomic regression.  Once again the minimum square method was used and these two variables were related using a second order polynomic approach.  Probit constants were determined for two substances (gasoline and LPG) and two types of storages tanks (vertical and horizontal).

The results of this study are a useful tool for the development of the quantitative risk assessment of Natech events due to flood impacts in storage parks. Also contributes to the reduction of the uncertainty in the framework for the QRA of Natech events triggered by floods.