Assessment of attack likelihood to support security risk assessment studies for chemical facilities

Chemical and process facilities may be the target of external acts of interference, aimed at causing cascading events, which may escalate into severe fires, explosions or toxic dispersions. Recent accidents that occurred in European chemical facilities presented these features, showing that industry must address with the greatest urgency the need of increasing the attention to security issues. Objective, performance-based methods to verify the adequateness of the resources dedicated to the protection of assets against external attacks are needed. In the present study, a probabilistic risk analysis approach supported by a model based on Bayesian Networks is adopted to address the quantitative assessment of the attack likelihood and to incorporate the functional analysis of physical protection systems (PPS) applied the security of process and storage installations. A case study of industrial interest is analysed to exemplify the methodology, which may be adopted to evaluate the PPS in place in a given facility. The methodology also allows for a quantitative evaluation of attack success credibility and for the identification of the more critical escalation scenarios, thus supporting safety and security reviews of chemical and process facilities.