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The HRA process
Published in Barry Kirwan, A Guide to Practical Human Reliability Assessment, 2017
The following recommendations are relevant for event-tree vs fault-tree assessments: If the scenario is time-dependent (i.e. sequential in nature, or ‘event-driven’), use an event tree. If the sequence of errors in relation to other (e.g. hardware) events does not matter, use a fault tree.Select the method which gives most meaning to the scenario.If the PSA is heavily biased towards fault or event trees, then the use of the PSA’s favoured format will help to ease the integration of the HRA into the PSA, and to facilitate a sensitivity analysis, etc.If there are many possible outcomes from an event sequence, an event-tree analysis may prove problematical: and in these such cases, although a fault-tree analysis may be less meaningful, it can be made mathematically equivalent, and may prove a more tractable form of analysis.
Risk Assessor's Toolbox
Published in Charles Yoe, Principles of Risk Analysis, 2019
An event tree is a qualitative or quantitative analytical technique for modeling a system, a pathway, or a sequence of events. It uses forward logic and begins with an initiating event and proceeds to the many different outcomes possible with that event. It is constructed of a sequence of nodes and branches that describe the unfolding possible outcomes of an initiating event. Each unique pathway through the tree describes a unique sequence of events that could result from the initiating event. It is believed to have been introduced during the WASH-1400 nuclear power plant safety study of the 1970s (Ericson 2005). A simple example of an event tree is shown in Figure 10.9.
Safety Risk Assessment and Management
Published in Debi Prasad Tripathy, Mine Safety Science and Engineering, 2019
Event tree analysis is a forward, bottom-up, logical modeling technique that uses decision trees and logically develops visual models of the possible outcomes of an initiating event (Diamantidis et al., 2000; Hong et al., 2009). ETA is a graphical representation of the logic model that identifies and quantifies the possible outcomes following the initiating event. This technique can be applied to a system early in the design process to identify potential issues that may arise rather than correcting the issues after they occur (Beim and Hobbs, 1997).
A mixed quantitative approach to evaluate rockfall risk and the maximum allowable traffic on road infrastructure
Published in Georisk: Assessment and Management of Risk for Engineered Systems and Geohazards, 2022
M. Marchelli, V. De Biagi, D. Bertolo, M. Paganone, D. Peila
The event tree analysis is a logical based procedure in which both success and failure are evaluated, starting from a single initiating event and defining all the possible alternative pathway options which can develop. The latter are mapped as branches and the nodes serve as transition from one position to another along the event tree, defining binary (Yes/No) mutually exhaustive possibilities, realising different scenarios. The end points identify a unique outcome, whose probability is given by the product of the conditional probabilities along their own pathway. The probability of more outcomes is given by the sum of the probabilities of each outcome. The value of each occurrence probability depends on different parameters, to which a certain degree of uncertainty is inevitably associated (Macciotta et al. 2017).
Digital project twin for quantitative cost, risk and schedule assessment of capital projects
Published in Australian Journal of Multi-Disciplinary Engineering, 2022
Philip Sander, Markus Spiegl, Taylor Burns, John Reilly
For complex risks, event tree analysis helps distinguish between, and analyse different, interdependent scenarios within the risk. Figure 10 shows how the risk of a tunnel boring machine (TBM) advancing through a fault zone was broken down into scenarios (also known as knots). The first knot depicts if the TBM is halted, in which case possible further events are TBM deadlock or, in the worst case, a bypass tunnel. Each knot has its own probability of occurrence and probabilistic cost and time impact, all of which are combined to represent the aggregated cost (yellow) and schedule (blue) risk profile on the right-hand side of Figure 10.
Offshore wind decommissioning: an assessment of the risk of operations
Published in International Journal of Sustainable Energy, 2022
Mahmood Shafiee, Tosin Adedipe
ETA is a bottom-up (inductive) diagrammatic technique that uses reasoning to show escalation/development of a potential unwanted initiating incident/event and different possible outcomes. It shows the safety/hazard promoting factors at each level of the event tree with each level developing into two branches (one for success and one for failure) for different potential outcomes. The consequences of operational (or system) failure depend on the safety gates at each stage of the tree development. In order to determine an event sequence, the ETA can be performed or a functional block diagram to be used (Aneziris et al. 2008).