The damage of storage tanks in flood events may lead to severe "natural-technological" (NaTech) accident scenarios due to the release of hazardous substances causing damage to people and environment. In the present study, damage of atmospheric storage tanks in floods was analyzed in detail. A mechanical damage model was developed and validated by available literature data on past accidents. Simplified correlations were then obtained to calculate the probability of loss of containment on the basis of severity parameters of the flood event. The tank vulnerability model was integrated in a comprehensive approach for the quantitative risk assessment of NaTech scenarios triggered by floods. A case-study was discussed to test the potentialities of the method.