**5. Conclusion**

The chapter entitled "Failures in a Critical Infrastructure System" presents a comprehensive overview of a critical infrastructure system, which may be regarded as the basis for ensuring the functional continuity of society from both the economic and social perspectives. The introductory part of the chapter is designed as a historical framework, defining critical infrastructures in relation to legislative, normative, and institutional processes involved in addressing the issues concerned. The described framework formulates the basis, approaches, and logic of a hierarchical system arrangement in connection to interdependencies and linkages between elementary elements. Infrastructure failures have been classified in terms of their sources and causes because the potential impacts of failures in selected dependent systems can have profound effects on the functioning of society as a whole. It was argued that the impacts of failures in dependent systems increase the occurrence of cascading and synergistic effects, which fundamentally affect the resilience of individual elements and the general function of the system. This led to establishing the relationship between system resilience and failures with respect to critical infrastructure network elements.

Based on these facts, the impacts of failures and their propagation were described in the context of the necessity to model such impacts. In this regard, the significance and applicability of top-down and bottom-up approaches in relation to the exploration of mutual linkages was further compared as one of the identifiers describing the critical infrastructure status. The significance of identifying and labeling critical infrastructure elements is, therefore, also viewed from the perspective of the need for a more objective setting of cross-cutting criteria values, equally applicable at the regional level. As already mentioned, element resilience exerts a substantial effect on the overall impacts of potential failures. That is why a resilience framework for critical infrastructure subsystems was established with a view to defining resilience, formulating a resilience concept, and setting up a resilience evaluation process in a critical infrastructure system. The presented facts are based on the Ministry of the Interior of the Czech Republic Security Research project—RESILIENCE 2015: Dynamic Resilience Evaluation of Interrelated Critical Infrastructure Subsystems and form a resilience knowledge base as the ability of a system, community, or society exposed to adverse events to resist, absorb, accommodate, adapt to, transform, and recover from the effects of a hazard in a timely and efficient manner, including through the preservation and recovery of its essential basic structures and functions through risk management.
