Resilience in a critical infrastructure system can be viewed as a quality that reduces vulnerability, minimizes the consequences of threats, accelerates response and recovery, and facilitates adaptation to a disruptive event. In this context, comprehensive knowledge of the environment and of the main factors whereby resilience is determined, limited, and affected can be said to represent the fundamental precondition for strengthening the resilience of critical infrastructure elements. Based on this idea, the article defines the initial and functional conditions for building and strengthening the resilience of critical infrastructure elements, i.e., the resilience concept in a critical infrastructure system. Subsequently, factors determining the resilience of these elements are identified, both in terms of technical resilience (i.e., robustness and recoverability) and organizational resilience (i.e., adaptability). In the final part of the article, these factors are presented in greater detail in the context of case studies focused on the electricity, gas, information and communications technology, and road transport sectors. Determination of these factors is examined with regard to the intensity of a disruptive event and the performance of the respective critical infrastructure element.

A critical infrastructure is a complicated system whose failure (in whole or in part) has a significant impact on national interests, including security, the economy and basic human needs. The system consists of relevant sectors, elements and their mutual linkages. In order to study critical infrastructures, it is necessary to apply a systems approach based on cross-sectoral evaluation and research into the linkages between the individual critical infrastructure sectors. Specifically, it is necessary to describe the individual vertical and horizontal levels of each critical infrastructure and the associated linkages. From this point-of-view, a critical infrastructure is embedded within the broader context of emergencies and enterprises, representing a compact and mutually-interconnected system.This paper focuses on quantitatively assessing the impacts of critical infrastructure failures. It presents a theory of synergistic linkages, their levels and the synergistic effects due to the joint action of impacts, which increase the overall impact on the critical infrastructure and on society. The concepts are formalized in the SYNEFIA methodology, which is applied in a case study involving the critical infrastructure of the Czech Republic. In particular, the methodology is applied to determine the synergistic effects of disruptions to multiple sub-sectors of the Czech infrastructure