Quantitative assessment of missile impact hazard

In off-shore installations, the generation of missiles usually follows the catastrophic rupture of process equipment, either due to internal pressure exceeding design values or to mechanical failure of rotating components. The projection of fragments is one of the more important causes of domino effects in industrial accidents. Fragments are capable of generating secondary accidents at relevant distances from the primary scenario. In this framework, quantitative risk analysis (QRA) may provide useful criteria for the assessment of damage and of domino scenarios caused by fragment projection, based on both expected frequency and expected consequence assessment. Nevertheless, the quantitative assessment of missile impact damage requires the availability of a model for the assessment of fragments impact probabilities on a given target. In the present study, an approach based on quantitative risk analysis was developed for missile impact studies in off-shore facilities. The different categories of missile sources were identified, and correlations were developed to assess the initial probability of missile generation. An approach to the determination of the shape, the initial velocity and the number of fragments generated in the event was also developed. The categories of critical targets were identified, considering both damage to personnel and damage of structures that may trigger escalation events. A probabilistic model was used to assess fragment impact probability on a target vessel, based on the analysis of possible fragment trajectories.