Abstract Blast waves, fires and fragment projection are by far the most common causes of escalation leading to domino accidents. The present chapter deals with less-frequent and more controversial domino scenarios: domino events due to indirect escalation and external events. Indirect causes of escalation, even if not frequent, may be extremely important since they are likely to be overlooked, in particular in complex industrial clusters. External hazard factors can also cause severe domino accidents. Natural events or intentional malicious acts of interference can escalate to cause severe domino events. The present chapter focuses on these particular causes of escalations, aiming to provide an approach for the assessment of these specific domino scenarios.