How Useful Is Quantitative Risk Assessment?

Abstract

This article discusses the use of Quantitative Risk Assessment (QRA) in decision-making regarding the safety of complex technological systems. The insights gained by QRA are compared with those from traditional safety methods and it is argued that the two approaches complement each other. It is argued that peer review is an essential part of the QRA process. The importance of risk-informed rather than risk-based decisionmaking is emphasized. Engineering insights derived from QRAs are always used in combination with traditional safety requirements and it is in this context that they should be reviewed and critiqued. Examples from applications in nuclear power, space systems, and an incinerator of chemical agents are given to demonstrate the practical benefits of QRA. Finally, several common criticisms raised against QRA are addressed.3

Search of critically important objects of the gas industry with the method of determining critical elements in networks of technical infrastructures

“…The indicator by which the elements making the main contribution to the synergistic effect of a certain set of failures can be determined in [2] is calculated as follows…”

“…In the case of insufficient knowledge of the infrastructure, probabilistic methods of risk analysis are used to assess its vulnerability [1,2]. If historical data are stored, then the theory of statistics is used to analyze and predict the impact of natural disasters on the performance of infrastructure [3].…”

Introducing the STAMP method in road tunnel safety assessment

“…fault and event trees) of QRAs have been subject to strong criticism for their limitations to capture the overall risk picture of complex socio-technical systems (Rasmussen, 1997;Hollnagel, 2004;Leveson, 2004). Indeed, the chain-of-event conception of accidents typically used in QRAs cannot account for the indirect, non-linear, and feedback relationships that characterize many accidents in complex systems and such a type of analysis has limitations to handle safety critical factors such as human behavior, organizational aspects, software errors, design flaws, and risk migration over time (Apostolakis 2004;Leveson 2004). Since road tunnels have organizational, social and managerial dimensions that impact their safety, it is considered of outmost importance to examine whether the general limitations of QRAs, as have been highlighted in the literature, also exist in the road tunnels field.…”

“…fault and event trees), have been subject to strong criticism for their limitations to capture the overall risk picture of complex socio-technical systems (Rasmussen, 1997;Hollnagel, 2004;Leveson, 2004). In such systems, even proponents of QRAs argue that human and organizational factors, software errors, design flaws and the safety culture of the system are not efficiently handled by the currently existing QRA methods (Apostolakis, 2004;Bier, 1999). Taking into account that road tunnels are not merely technical, engineering systems but also have intrinsic organizational, social and managerial dimensions that impact or contribute to their safety (Piarc, 2007), it is open to question whether QRA, with the aforementioned limitations, is the appropriate tool to investigate potential risks and evaluate the overall safety level of these infrastructures.…”

Probative blindness and false assurance about safety

“…ÒAssessmentÓ improves knowledge about safety. Quantitative Risk Assessment is the stereotypical assessment technique Ð it does not directly make a system safer, but is supposed to inform ensurance effort (Apostolakis 2004) and thus indirectly improve safety. ÒAssuranceÓ is the demonstration of safety, often directed towards increasing the confidence of stakeholders not directly involved in ensurance and assessment.…”