Event Tree Analysis ETA

T/ e effect of altering major assumptions on the downwind distance (radius) of the estimated vulnerable zone. Calculations made using (1) credible worst case assumptions for initial screening zone. (2) reevaluation and adjustment of quantity released and/or rate rf release cf chemical, (3) reevaluation and adjustment of wind speed (increase) and air stability (decrease), (4) selection of a higher level of concern. Note that adjustment oftwo or more variables can have an additive effect on reducing the size cf the estimated vulnerable zone. 

Note also that the relative sizes cf the altered zones are not to scale (e.g., choosing a higher value for the level of concern does not always result in a smaller zone than the use of greater wind speed and less atmospheric stability). 

The event tree model is started from the initial occurrence and built upon by sequencing tlie possible events and safety systems tliat come into play. Tlie model displays at a glance, branches of events tliat relate tlie proper functioning or failure of a safety device or s) Stem and tlte ultimate consequence. 

The model also allows quick identification of die various hazards diat result from die single initial event. 

The use of event trees is sometimes limiting for liazard analysis because it may lack die capability of quantifying die potendal of die event occurring. Tlie analysis may also be incomplete if all inidal occurrences are not identified. Its use is beneficial in examining, rather dian evaluating, die possibilities and consequences of a failure. For this reason, a fault tree analysis (FTA) should supplement diis, to establish die probabilities of die event tree branches. Tliis topic was introduced in a subsection of Cliapter 16. 

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Event Tree Analysis (ETA) A method for illustrating the intermediate and final outcomes that may arise after the occurrence of a selected initial event. 

Event Tree Analysis (ETA) is suggested by the DOE-STD-1027-92, but not included in the PSM Rule. However, the PSM Rule does allow the use of "an appropriate equivalent methodology." Hence, if ETA is to be used as the PrHA, the PrHA report must justify that the ETA method is appropriate and equivalent to the methods listed in the rule. 

Three hazard evaluation procedures using logic diagrams are (1) fault-tree analysis (FTA), (2) event-tree analysis (ETA), and (3) cause-consequence analysis (CCA). Appropriate references are [2,3,251,261]. 

Fault tree analysis (FTA) and event tree analysis (ETA) are the methods most commonly applied quantitatively. Since they only address the likelihood of undesired events, these methods are often combined with consequence severity calculations in a quantitative risk analysis, as described by CCPS (1999b). Layer of protection analysis (LOPA) uses a semiquantitative, order-of-magnitude approach. It is documented with worked examples in CCPS (2001b). 

Other examples of inductive tools that have limited application in incident investigation include failure mode and effects analysis (FMEA), hazard and operability study (HAZOP), and event tree analysis (ETA). These are detailed in the CCPS book, Guidelines for Hazard Evaluation Procedures... 

Another type of logic tree, the event tree, is an inductive technique. Event Tree Analysis (ETA) also provides a structured method to aid in understanding and determining the causes of an incident.(i) While the fault tree starts at the undesired event and works backward to identify root causes, the event tree looks forward to display the progression of various combinations of equipment failures and human errors that result in the incident graphically. 

An Event Tree Analysis (ETA), which explores aU possible outcomes of an undesired event (i.e. the specific crew error of concern), because it is only when there is a derived architecture that the exact role of humans in the system becomes clear. By using ETA the potential role of critical Human Error is evident, as are the combinations of Failures and errors necessary to create Hazardous or Catastrophic systems states. 

This task is only carried out if the semi-quantitative analysis does not provide sufficient information. In the quantitative analysis we may use FTA, network models of the infrastructure and capacities, and event tree analysis (ETA). As discussed by Kroger (2008), methods like FTA may have some shortcomings for analysis of complex interdependencies. However, to further investigate specific nodes of interest revealed in the cascade diagram (in Figure 4 and Figure 5), should not he more comphcated than in most other situations when FTA is useful. An example of use of FTA for assessment of power system rehahihty, can he found in Volkanovski et al. (2009). 

There exist different methods like Fault Tree Analysis (FTA), Event Tree Analysis (ETA) and Monte Carlo Simulation (MCS) that can be applied and combined for the purpose of evaluating the frequency and probability of initiating events. However, the MCS can be handled much easier in order to accoimt for bormdary conditions like stochastic dependence, time dependence and physical impact (Hauschild Meyna 2007). The MCS has been apphed successfully for PSA in order to assess the safety of nuclear power plants (Devooght Smidts 1996, Woltereck2001) and especially for taking into account uncertain input data (BfS 2005). 

A quantitative risk review technique. Cause-consequence analysis is a hlend of fault tree and event tree analysis. This technique combines cause analysis (described by fault trees) and consequence analysis (described by event trees), and hence deductive and inductive analysis is used. The purpose of CCA is to identify chains of events that can result in undesirable consequences. With the probabilities of the various events in the CCA diagram, the probabilities of the various consequences can be calculated, thus establishing the risk level of the system. See also Event Tree Analysis (ETA) Fault Tree Analysis (FTA). 

Event Tree Analysis (ETA) is used where appropriate to model all the possible outcomes of a hazard taking account of the mitigations (usually external to the system element in question) that could be used to break an accident sequence ould a hazard occur. Working from left to right, each branch of the Event Tree represents a mitigation to which probabilities can be applied in order to express the relative likelihood of success (S) or failure (F) of the mitigation. 

Fault Tree Analysis FTA and Event Tree Analysis (ETA) (Figure 2) are alternative methods of depiction of causes of top events and lends themselves better at both expansion and quantification. 

Event Tree Analysis (ETA) uses the same logical and mathematical techniques as Fault Tree Analysis. However, whereas a fault tree analyzes how an undesirable top event may occur, an event tree considers the impact of the failure of a particular component or item in the system, and works out the effect such a failure will have on the overall system-risk or -reliability. Event trees are inductive fault trees are deductive. 

Consequence spectmm, accidental event definition step-by-step procedure, probability frequency of outcomes for manual and automatic procedures for event tree analysis (ETA), fault tree analysis (FTA), and LOPA, QRA and HRA with focus on E/E/PE. Discussions on relevant standards like lEC 31010, 60812, 61025, 61508/61511, 61582, ISA 84. Life cycle (LC) analysis SIS standard. Also batch process ISA 88. 

Event tree analysis (ETA) An event tree is based on the binary logic of the happening or nonhappening of an event or failure or no failure of a component. 

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