AS IEC 62502 pdf download.Analysis techniques for dependability— Event tree analysis (ETA)
1 Scope
This International Standard specifies the consolidated basic principles of Event Tree Analysis (ETA) and provides guidance on modelling the consequences of an initiating event as well as analysing these consequences qualitatively and quantitatively in the context of dependability and risk related measures. More specifically, this standard deals with the following topics in relation to event trees: a) defining the essential terms and describing the usage of symbols and ways of graphical representation; b) specifying the procedural steps involved in the construction of the event tree; c) elaborating on the assumptions, limitations and benefits of performing the analysis; d) identifying relationships with other dependability and risk-related techniques and elucidating suitable fields of applications; e) giving guidelines for the qualitative and quantitative aspects of the evaluation; f) providing practical examples. This standard is applicable to all industries where the dependability and risk-related measures for the consequences of an initiating event have to be assessed.
3 Terms, definitions, abbreviations and symbols
For the purposes of this document, the following terms and definitions, as well as those given in IEC 60050-1 91 , apply. 3.1 Terms and definitions 3.1.1 node point in the graphical representation of the event tree depicting two or more possible outcomes for the mitigating factor NOTE The top event of the corresponding fault tree can directly be linked to a node. 3.1.2 common cause cause of occurrence of multiple events [IEC 61 025:2006, 3.1 5]NOTE Under particular circumstances the timeframe should be specified in which the multiple events occur, such as “occurrence of multiple events occurring simultaneously or within a very short time of each other”. EXAMPLES Particular natural dangers (e.g. fire, flood), failures of an engineered system, biological infections or human acts. 3.1.3 event occurrence of a condition or an action [IEC 61 025:2006, 3.8] 3.1.4 headings listed mitigating factors in a line above the depiction of the event tree 3.1.5 initiating event event which is the starting point of the event tree and the sequence of events that may lead to different possible outcomes 3.1.6 mitigating factor system, function or other circumstantial factor mitigating the consequences of the initiating event NOTE Many industries have specific equivalent terms, e.g. lines of defense, protection lines, protection systems, safety barriers, lines of assurance, risk reduction factor, etc. 3.1.7 outcome possible result of the sequence of events after all reactions of relevant mitigating factors have been considered and no further development of the event tree is required 3.1 .8 sequence chain of events, from the initiating event, through subsequent events, leading to a specific outcome 3.1 .9 top event predefined undesired event which is the starting point of the fault tree analysis, and is of primary interest in the analysis. It has the top position in the hierarchy of events in the fault tree NOTE It is the outcome of combinations of all input events. 3.1.1 0 branch graphical representation of one out of two or more possible outcomes originating from a node
4 General description
Event tree analysis (ETA) is an inductive procedure to model the possible outcomes that could ensue from a given initiating event and the status of the mitigating factors as well as to identify and assess the frequency or probability of the various possible outcomes of a given initiating event. The graphical representation of an event tree requires that symbols, identifiers and labels be used in a consistent manner. Since the representation of event trees varies with user preference, a collection of commonly used graphical representations is given in Annex A. Starting from an initiating event, the ETA deals with the question “What happens if…”. Based on this question, the analyst constructs a tree of the various possible outcomes. It is therefore crucial that a comprehensive list of initiating events is compiled to ensure that the event trees properly depict all the important event sequences for the system under consideration.
AS IEC 62502 pdf download
