Natural hazards pose critical threats to chemical and process installations handling hazardous materials. In particular, severe technological accidents involving the release of chemicals can be triggered by natural events, namely Natech accidents. Moreover, natural hazards can impact and weaken safety measures for accident prevention and mitigation implemented in the impacted plant, increasing the credibility of severe domino effect escalation and, thus, affecting the risk induced by Natech scenarios. The present study is aimed at developing a structured approach aimed at supporting the probabilistic evaluation of Natech events in presence of safety barriers. Barrier performance are described with a specific metric, able to quantitatively assess the degradation due to natural hazards. The methodology is applied to the analysis of an industrial case study, showing the influence of the natural event impact on the performance of safety barriers and, thus, on the probability and frequency of escalation scenarios triggered by Natech events.