Key Issues in Resilience Engineering
Implementation Process of Resilience
The common characteristics of HROs give us a hint as to how we can incorporate resilience into socio-technical systems. In order to prevent resonance of function variability, the organizations have to repeat the process of four activities: anticipation, monitoring, response, and adaptation. In anticipation, the organization anticipates short-term and long-term threats and changes and gets ready for these threats and changes. In monitoring, the organization monitors operation conditions of the system to detect precursors of unfavorable performance variability that may cause resonance. The organization then takes actions to suppress performance variability so that the system will not go beyond its safety boundaries. Finally, the organization learns from past experience and restructures itself to adapt so that the system can absorb long-term changes.
Most of the base technologies for each step of the above process have already been developed in conventional domains, while more advanced technologies are also expected in the future. Based on these fundamental technologies, the methodologies for synthesizing them, assessing systems resilience, and social installation of the outcomes of research should be pursued. The key issues to be resolved in resilience engineering are as follows.
Assessment of Resilience
Though the resilience triangle shown in Fig. 24.5 is a simple but promising measure for quantitatively assessing systems resilience, the measure for representing system functionality has some arbitrariness. It is also argued that the cost of system recovery should be considered in the resilience measure [23]. The more cost is required, the less resilient the system becomes even if the area of resilience triangle is the same. In addition, the essential characteristics of resilience discussed in Sect. 24.5 should be reflected in the resilience measure. Among these characteristics, safety margin can be represented with risk measures that have been used in the conventional risk management, but the metrics for the other three characteristics have to be established in the future study.
Consideration of different stakeholders as discussed in the previous section is another issue in assessment of resilience. Which function of socio-technical systems is important depends on the situation where a particular stakeholder is placed. As shown in the case of the previous section, the needs for medical services are different between elderly people suffering some health problems and healthy young people. Socially vulnerable groups sometimes have to be taken into account in assessment of resilience rather than considering the average image of the public.
Interdependencies Between Systems
Our society is a complex system of systems that is composed of many systems linked together; it is impossible to understand the behavior of the total system if we look at systems separately. Critical infrastructures, for instance, including the electric power system, the water supply system, the transportation system, and the telecommunication system, are interrelated to each other, and one system depends on the others. The telecommunication system, for instance, does not work without electric power supply, and the electric power system is controlled using the telecommunication system. The breakdown of one system, therefore, sometimes leads to the breakdown of other systems.
A complex system spreads in a physical space and disturbance in one location sometimes propagates to another. It may cause the breakdown of the system over a wide area. The disturbance may propagate further to another system through the interdependencies among different systems. There is a fear that such cascading failures of critical infrastructures might result in serious damage to society.
In order to prevent such cascading failures in case of a devastating natural disaster, terrorist attack, or a crisis of the world market, it is necessary to understand system behavior including the interdependencies and take remedial actions to eliminate vulnerabilities in the system. In order to enhance the resilience of a system of systems, recovery plans must consider the interdependencies among different systems. Technologies allowing for a large-scale simulation are expected to be developed to consider the interdependencies of a system of systems.
