Risk assessment methods event tree analysis

Methods for performing hazard analysis and risk assessment include safety review, checkhsts, Dow Fire and Explosion Index, what-if analysis, hazard and operabihty analysis (HAZOP), failure modes and effects analysis (FMEA), fault tree analysis, and event tree analysis. Other methods are also available, but those given are used most often. 

A methodical examination of a process, plant and procedure which identifies hazards, assesses risks and proposes measures which will reduce risks to an acceptable level. (May use inter alia Hazops. Fault Tree Analysis, Check-lists, Event Tree Analysis. FMECA, etc). 

In CRIOP, the team does not make any probability assessments. It is thus not possible to evaluate the effectiveness of remedial actions in terms of risk reduction. CRIOP may be combined with other risk analysis methods such as event tree analysis, which is suited for calculations of probabilities. A probability assessment requires access to human reliability data. 

The assembly process (Figure 10-1) brings together all of the assessment tasks to provide the risk, its significance, how it was found, its sensitivity to uncertainties, confidence limits, and how it may be reduced by system improvements. Not all PSAs use fault trees and event trees. This is especially true of chemical PSAs that may rely on HAZOP or FMEA/FMECAs. Nevertheless the objectives are the same accident identification, analysis and evaluation. Figure 10-1 assumes fault tree and event tree techniques which should be replaced by the equivalent methods that are used. 

Event trees or networks show how a sequence of events can lead from primary events to one or more outcomes. Human reliability analysis (HRA) event trees are a classic example of this approach (Figure 6). If probabilities are attached to the primary events, it becomes possible to calculate the probability of outcomes, as illustrated in Section 3.2.4. This approach has been used in the field of risk assessment to estimate the reliability of human operators and other elements of complex systems (Gertman and Blackman 1994). Chapter 32 provides additional information on human reliability analysis and other methods of risk assessment. 

Based on any unacceptable and unmitigated risk identified during hazard analysis, further risk assessment and risk mitigation techniques need to be applied. LORA and conceptual SIS designs based on Risk Matrix can be employed if a qualitative to semi-quantitative method is preferred. Fault tree and event tree analyses with a robust LOPA can be applied if a quantitative method is essential... 

ABSTRACT Retention levels of road safety barriers are specified on the basis of risk assessment taking into account accidental data and further information available in the Czech Republic and also selected recommendations of Road Safety Association PIARC. The method of Bayesian networks is applied in the analysis and compared with event tree method. Newly proposed classes of retention for several categories of road surroundings considering the intensity of heavy traffic and two levels of hazard situation are incorporated to the revision of national prescriptive document that is expected to enhance the road safety. 

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