Quantitative assessment of risk due to major accidents triggered by lightning

• A method to evaluate the risk associated to NaTech caused by lightning was developed.
• Simplified fragility models to estimate equipment failure probability were applied.
• Individual and societal risk due to lightning-triggered scenarios was calculated.
• Risk reduction due to different lightning protection strategies was assessed.
• Residual risk due to lightning-triggered scenarios high even in the presence of protections.

Lightning is one of the most frequent accident causes in storage tank parks, and accidents triggered by lightning are the most frequent Natech event reported in past-accident analysis. In the present study, a methodology for the inclusion of accidents triggered by lightning in Quantitative Risk Assessment (QRA) was developed. A model for the assessment of lightning impact probability on process equipment and specific equipment vulnerability models were coupled to dedicated event trees, allowing the quantification of risk indexes. The methodology developed also allows the assessment of risk reduction by the implementation of different lightning protection strategies. The results obtained represent a step forward towards the introduction of risk-based design of lightning protection systems.