A risk perspective suitable for resilience engineering Riana Steen, Terje Aven ⇑ University of Stavanger, Centre of Risk Management and Societal Safety, Stavanger, Norway article info Article history: Received 14 January 2010 Received in revised form 29 July 2010 Accepted 3 September 2010 Keywords: Resilience Risk perspectives Uncertainties Vulnerability Extended risk assessment abstract In recent years, resilience engineering has been given considerable attention among safety researchers and analysts. The area represents a new way of thinking about safety. Whereas conventional risk man- agement approaches are based on hindsight knowledge, failure reporting and risk assessments calculat- ing historical data-based probabilities, resilience engineering looks for ways to enhance the ability of organisations to be resilient in the sense that they recognise, adapt to and absorb variations, changes, disturbances, disruptions and surprises. The implications of this shift in thinking are many. We focus in this paper on the understanding of the risk concept and how risk can be assessed and treated. The tra- ditional ways of looking at risk are not suitable for use in resilience engineering, but other risk perspec- tives exist. A main purpose of this paper is to draw attention to such perspectives, in particular one category of perspectives where probability is replaced by uncertainty in the definition of risk. We argue that the basic ideas of resilience engineering can be supported by such risk perspectives. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction Resilience engineering has become an important field for the understanding and management of safety in socio-technical sys- tems. Considerable effort has been made in the last years to clarify basic features of resilient systems and develop suitable concepts, principles and methods that can provide the basic building blocks of the field; see for example Nemeth et al. (2009), Dijkstra (2007), Saurin et al. (2008), Hollnagel et al. (2008,2006) and Woods (2000). In many respects, resilience engineering represents an alternative to conventional risk management approaches which are based on hindsight knowledge, failure reporting and risk assessments calcu- lating historical data-based probabilities. The proponents of resil- ience engineering consider conventional safety management and risk assessment methods to be inadequate for present-day systems (Hollnagel, 2007): ‘‘It is a simple fact that whereas technological and socio-technical systems have developed rapidly, and continue to do so, the repertoire of methods to address safety issues has not. There is therefore a clear need for new approaches to risk assess- ment and safety management, and resilience engineering has been proposed as a solution to satisfy that need.” Hollnagel (2007) pro- vides an excellent summary of the resilience engineering approach, and the basic premises and features of the field. For the purpose of the present paper, it is sufficient to draw attention to a few key points (Hollnagel, 2007):  Many adverse events cannot be attributed to a breakdown or malfunctioning of components and normal system functions (‘‘intractable events”). They are best understood as the result of unexpected combinations of normal performance variability.  Effective safety management cannot be based on hindsight, nor rely on error tabulation and the calculation of failure probabil- ities. Safety management must not only be reactive, but also proactive.  The conventional view on safety (risk) management considers performance variability, of any kind, as a threat and something that should be avoided. The result is often the use of constrain- ing means (in particular for human performance variability) such as barriers, interlocks, rules, procedures and the use of automation.  In resilience engineering, performance variability is considered both normal and necessary. It is the source of both positive and negative outcomes. Safety cannot be obtained by constraining performance variability, since that would also affect the ability to achieve desired outcomes. The solution is instead to dampen the variability that may lead to negative outcomes and at the same time to reinforce the variability that may lead to positive outcomes. There are many formal definitions of resilience in a resilience engineering context; see the above-cited references. They capture more or less the same ideas. Resilience is the intrinsic ability of a system to adjust its func- tioning prior to or following changes and disturbances, so that it can sustain operations even after a major mishap or in the 0925-7535/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.ssci.2010.09.003 ⇑ Corresponding author. E-mail address: terje.aven@uis.no (T. Aven). Safety Science 49 (2011) 292–297 Contents lists available at ScienceDirect Safety Science journal homepage: www.elsevier.com/locate/ssci