Home Environment Reflections on the Fukushima Daiichi Nuclear Accident
Resilience Engineering A New Horizon of Systems Safety
Abstract Having experienced natural disasters, accidents, and economic crises, people are getting skeptical about technological approaches to risk management. The conventional approaches have not considered sufficiently how to manage residual risks that spill out of the design basis of a complex socio-technical system. Resilience, which means the ability of a system to absorb changes and disturbances in the environment and to maintain system functionality, is a key concept for resolving the above situation, and resilience engineering is an area where technical methodologies to implement resilience into socio-technical systems are studied. In this chapter, the prehistory of resilience engineering will be described first where the focal point of systems safety has gradually shifted from hardware component failures to the resilience of complex socio-technical systems. Then some relevant topics in resilience engineering will be discussed: how systems resilience can be evaluated and implemented, and the key issues to be resolved in the future.
Keywords Resilience engineering • Socio-technical system • Safety management •
Crisis management • Human reliability
We are surrounded by various kinds of dangers including natural disasters, accidents, medical diseases, economic crises, and crime. Prevention of damage and protection of people's safe living are great missions for engineering. Remarkable efforts have been made in conventional safety, reliability, and disaster prevention engineering to assess risks qualitatively or quantitatively, prevent manifestation of damage, and suppress damage to the minimum extent. Such efforts contributed greatly to making our lives far safer. Risk is a measure for representing the degree of danger as a combination of the scale and the probability that damage will occur. When there is a possibility that disasters or accidents may cause damage to human lives, health, or assets, risk is a very useful measure for achieving safety.
Having experienced unanticipated disasters in this century, however, we have recognized that we need a new framework of systems safety that can cover unanticipated situations that spill out of the scope of conventional risk management.
Shift in the Focal Point of Systems Safety
Era of Technology
Figure 24.1 shows how the focal point of systems safety has changed in the past decades. Some events that characterize the changes are also indicated in the figure. When socio-technical systems were not very complex, specialists thought that problems occur for technical reasons, such as failures or malfunctions of hardware components, and that they can prevent accidents and disasters by further advances in technologies. Efforts were made, therefore, to carry out safety design and quality assurance based on understanding of failure mechanisms, and most problems
with hardware components were successfully resolved.
The world's fi commercial jetliner launched in 1951, de Havilland Comet, crashed repeatedly due to metal fatigue, which is a phenomenon in which a material breaks when great loads are repeatedly applied. The phenomenon itself had been known, but the validation testing method was immature at the time. Following the accidents, many technical improvements and redesigns were made, including improvement of the test method and the structural design method to stop fatigue crack propagation.
Fig. 24.1 Shift in the focal point of systems safety
Similar problems occurred in the early introduction stage of nuclear power. Stress Corrosion Cracking (SCC) in the recirculation loop piping of Boiling Water Reactors (BWRs) and wall thinning in the steam generator tubes of Pressurized Water Reactors (PWRs) were serious problems for the industry from the 1950s to 1980s. As technical studies revealed the mechanisms of cracking and degradation, which had not been understood at the beginning, the problems were resolved by substituting the materials with newly designed alloys, improving the management of water chemistry, and improving the method of fabrication.
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