**5. Case Study**

The pilot verification of the proposed process was performed by analyzing the results of case studies that were prepared for the electricity sector (transmission and distribution system), transport (road and railway network) and emergency services (fire stations). The results were then discussed with the operators of the evaluated elements and used to calibrate the method. The anonymized result of one of the evaluations (i.e., fire rescue service station) is presented in the following text to help explain how the proposed process works. This assessment was carried out by the security manager of the Fire and Rescue Service of the territorially relevant region in cooperation with the crisis manager of the same fire and rescue service. The crisis manager then developed recommended solutions, the implementation of which in the final phase of the process was decided by the director of the Fire and Rescue Service of the territorially relevant region.

An anonymized fire rescue service (FRS) station was selected for the process of indicating a disruption of the critical infrastructure element's resilience (Step 1). The station belongs to the emergency service sector and is located in an unnamed region of the Czech Republic. Subsequently, a description of this station was made, which consisted in determining its position in the critical infrastructure structure and the definition of its structural and performance parameters. The structural parameters of this station are specified by its topological structure and in the case of planar elements, by a list of key technologies. The fire station's performance parameter is the number of protected inhabitants (Vichova et al. 2017). These data are presented in Table 5.


**Table 5.** Description of the assessed element of emergency services of critical infrastructure.

The indication of resilience disruption of the selected element was carried out as part of the risk managemen<sup>t</sup> (ISO 2018) against three threat categories (Step 2). However, due to the extent of the results, this article will only present the result of one of the assessed categories of impacts, cascading threats. Cascading threats are threats that cause a disruption of the critical infrastructure element, the effects of which further spread across the critical infrastructure and cause the failure of dependent elements (Rehak et al. 2018b).

Next, the selected critical infrastructure element resilience level was determined (Step 3). The assessment of the fire station's resilience was carried out using the CIERA method (Rehak et al. 2019) and it consisted of the measurement of its levels of robustness, recoverability and adaptability in terms of the selected threat. The assessment of the resilience of this station was done in cooperation with the commander and the security manager of the FRS of the given region. The results of the assessment are presented in Figure 6.

**Figure 6.** The fire station's level of resilience to the impacts of cascading threats.

The resulting resilience of the fire station to the impact of cascade threats reached the level of 85%, which represents the lower end of high-level resilience.

The next step in indicating a disruption of the resilience of the selected element was the identification of resilience disruption indicators (Step 4). The identification of indicators was carried out using the Fault Tree Analysis method (IEC 2006a) and the results of the identification are presented in Figure 7.

**Figure 7.** Identification of indicators of disruption of resilience.

The threat of the disruption of the electric energy supply was selected for further analysis based on the results of the identification of the indicators in Figure 7. The reason for this selection is that it was proven that the fire station depends heavily on a supply of electricity. The description of this threat is present in Table 6.



Next, it is possible to proceed to the identification of indication parameters of the selected threat (Step 5). The identification of indication parameters is based on the National Energy Resistance Program of the Czech Republic (MIT 2019) and was performed using graphical–analytical methods, e.g., the Tree Diagram (Salkind 2007). An overview of the indication parameters of the threat of interest is presented in Table 7.


**Table 7.** Classification of indication parameters for the threat of "disruption of electricity supply".

The next step in the process of indicating a disruption of the resilience of critical infrastructure elements is the determination of the limit of disruption of the element's resilience (Step 6). This limit is based on a comparison of the already-calculated level of resilience (Step 3) and the indication parameters of threats (Step 5). In this case, the resilience level of the fire station was set at 85%, which is the lower limit of high-level resilience. In this case, the fire station would be able to operate in a limited mode even in the event of a power failure lasting over 36 h. The reason is mainly its high recoverability level, especially due to redundant capacities. Specifically, the station is equipped with a spare stationary electricity source (i.e., diesel generator) and has spare mobile sources of electricity available and a high area coverage of the Fire and Rescue Service units in the region.

The next step is to define, compare and evaluate alternatives to security measures (Step 7). Weak points in the fire station's resilience were identified using the CIERA method (Rehak et al. 2019). These are the (1) low level of indication of power failure, (2) low physical resilience of technical equipment to the effects of power failure, and (3) lack of funds for security measure innovation. Within the context of these results, it is possible to define adequate security measures and evaluate the suitability of their implementation based on comparison. A Multi-Criteria Analysis (Figueira et al. 2005) was used for this purpose where provided with a set of decision criteria and the linkages between them, it is possible to find the option which scores the highest in each criterion (see Figure 4). Security measures and individual criteria were consulted with the commander of the fire station and the security manager of the FRS of the region. The results of the evaluation of safety measures to increase the physical resistance of technical devices to the effects of power failure (i.e., weakness of resilience No. 2) are presented in Table 8.

**Table 8.** Evaluation of the suitability of the implementation of security measures to increase the physical resistance of technical means on the impact of power outages.


Based on the results of the evaluation, the second option was selected (i.e., the creation of a connection point for a mobile source of electricity), for which the process of implementation and feedback had subsequently been started (Step 8). The implementation process was carried out in accordance with the implementation plan (see Figure 5), which includes a set of activities aimed at the effective and systematic implementation of measures at a pre-determined time. Feedback was provided at the end of the process of indicating the disruption of the resilience of critical infrastructure elements, which allowed us to review the effectiveness of the implemented security measures. For this purpose, the level of resilience of the critical infrastructure element was reassessed (Step 3), reaching the level of 93% after the implementation of the selected security measure. This step finalizes the entire process of indication of the critical infrastructure element's resilience.

### **6. Discussion and Conclusions**

This article offers a contribution to the debate on the need to address the predictive disruption of critical infrastructure elements' resilience. Throughout the work, the authors asked themselves the following question: is the current managerial decision making in the area of the researched problem, i.e., critical infrastructure protection, sufficient? A literature search has shown that in such a specific area as the disruption of critical infrastructure elements' resilience, common decision-making methods are used, lacking a systematic arrangement. For this purpose, a special procedure was created to indicate the violation of the resilience of critical infrastructure elements. The work and the proposed procedure was limited to the area of critical infrastructure in the electricity, transport and emergency services sectors. However, with the elaboration and light transformation, this approach can be used in other areas of critical infrastructure; however, this option is a matter for future research and detailed analysis of other areas.

Risk managemen<sup>t</sup> is currently being used in most cases of the preventive protection of critical infrastructure elements, making it possible to assess and manage risks (ISO 2018). The current risk assessment methods are an effective general preventive tool (Giannopoulos et al. 2012; Theocharidou and Giannopoulos 2015); however, they lack linkages to the specifics associated with the resilience of the critical infrastructure systems. By linking risk managemen<sup>t</sup> and strengthening resilience, the protection of critical infrastructure is extended by the repressive part, i.e., the reaction to already occurring adverse events (NIAC 2009). However, current approaches in various areas focus only on assessing and strengthening critical infrastructure resilience (Alizadeh and Sharifi 2020; Argyroudis et al. 2020; Quitana et al. 2020; Li et al. 2020; Shandiz et al. 2020) even though resilience goes beyond traditional risk managemen<sup>t</sup> (Petersen et al. 2020). Therefore, it can be stated that there is currently no appropriate managerial tool that would explicitly deal with preventive measures for the protection of critical infrastructure elements. For this reason, the authors of this article have designed an entirely new process of managerial decision making for indicating the disruption of the resilience of critical infrastructure elements, which allows for the early identification of a potential resilience disruption of these elements and subsequent setting of the framework for improving the elements' resilience (Labaka et al. 2015).

The indication process consists of eight interconnected steps, which provide the assessor with comprehensive instructions for the indication of a possible disruption of the resilience of critical infrastructure elements. This enables the assessment of the current level of the element's resilience to disruptive events evaluated according to available methods (ISO 2018; IEC 2019; Bernatik et al. 2013) and serves as a basis for the decision to implement security measures and mitigate the impacts of the disruptive events weakening the resilience of the element (Blumenthal and Stoddard 1999). The resilience disruption indication process, among other things, sets the limit of exhaustion of the resilience absorption capacity, i.e., the limit beyond which the function of the element fails or is disrupted.

This information is valuable to security managers of critical infrastructure entities, as it enables them to rapidly indicate disruptions of the resilience of critical infrastructure elements. With this information, managers can make adequate security measures to strengthen the resilience of these elements. The pilot verification of the proposed process was performed by analyzing the results of case studies, which were prepared for the electricity sector (transmission and distribution system), transport (road and railway network) and emergency services (fire stations). The results were then discussed with the operators of the evaluated elements and used to calibrate the method. Currently, the method can be used for the predictive indication of the resilience of elements of all technical sectors (i.e., energy, transport, information and communication systems and water management) and selected socio-economic sectors (i.e., emergency services and health) of the critical infrastructure.

The process of indicating the disruption of the critical infrastructure elements' resilience was designed from a managerial point of view, so its use in the top managemen<sup>t</sup> of state institutions is very likely. In particular, it is suitable as a support tool when deciding on investments in strategic public infrastructures and their development. It is also expected that the proposed process will be used in the modernization of public infrastructures to increase their resilience to predicted threats. The proposed process is a comprehensive procedure that supports decision making in the implementation of optimal security measures, and in the context of step seven (i.e., defining, comparing and evaluating alternatives to security measures), contribution to good governance and the economical drawing of institutional funds.

The process of indicating disruption of resilience was created as a support tool for managerial decision making in the critical infrastructure elements protection management. The theoretical benefit of this tool is the interdisciplinary integration of managerial decision making in the field of preventive protection of critical infrastructure elements. This expands the portfolio of the currently available literature dealing with the use of managerial decision making in the field of critical infrastructure protection. At a practical level, it is a matter of creating a new tool that will enable security managers to increase the preventive protection of critical infrastructure elements. This also answers the research question, as the created tool allows us to preventively indicate the potential disruption of the critical infrastructure elements' resilience before the actual occurrence of the adverse event. In the context of practical use, this tool was created primarily for managers of public critical infrastructure operators, with whom the authors have been cooperating for a long time. The tool can also be used in the private sector, but without the possibility of considering the market environment.

The future development of this instrument could therefore not only consider the needs of the private sector, but could also include economic factors to minimize costs. Furthermore, it is appropriate to pay attention to the research of the indicators themselves, which could be structured in more detail, based on functional parameters (i.e., indicators considering structural and performance parameters of critical infrastructure elements) and indication parameters (i.e., indicators of changes in internal but also external environment of critical infrastructure elements).

**Author Contributions:** Conceptualization, A.S. and D.P.; Methodology, A.S., D.P., N.K. and M.H.; Validation, A.S., D.P., N.K. and M.H.; Investigation, A.S. and D.P.; Writing—original draft preparation, A.S., D.P., N.K. and M.H.; Writing—review & editing, A.S., D.P., N.K. and M.H., Visualization, A.S.; Supervision, M.H.; Project administration, A.S.; Funding acquisition, M.H. All authors have read and agree to the published version of the manuscript.

**Funding:** This research was funded by the Ministry of the Interior of the Czech Republic under Project VI20192022151 'CIRFI 2019: Indication of critical infrastructure resilience failure' and by the VSB—Technical University of Ostrava under Project SP2020/40 'Research on approaches and methods of strengthening the resilience of critical infrastructure elements in the electricity sub-sector'.

**Conflicts of Interest:** The authors declare no conflict of interest.
