Events and Causal Factors Analysis (ECFA) is an important component in the accident investigation repertoire of methods. It is designed as a stand alone

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® Events and Causal Factors Analysis Prepared by: J.R. Buys, INEL J.L. Clark, INEL Revised by: J. Kingston-Howlett, Aston University, Great Britian H.K. Nelson, SCIENTECH, Inc. Technical Research and Analysis Center SCIENTECH, Inc. 1690 International Way Idaho Falls, Idaho 83402 August 1995

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SCIE-DOE-01-TRAC-14-95 August 1995Events and Causal Factors Analysis iEvents and Causal Factors Analysis Executive Summary Events and Causal Factors Analysis (ECFA) is an important component in the accident investigation repertoire of methods. It is designed as a stand alone technique but is most powerful when applied with other techniques found in the Management Oversight and Risk Tree (MORT) programme. ECFA serves three main purposes in investigations: (1) assists the verification of causal chains and event sequences; (2) provides a structure for integrating investigation findings; (3) assists communication both during and on completion of the investigation. This document discusses the benefits of EFCA and provides a primer in the application of the technique.

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SCIE-DOE-01-TRAC-14-95 August 1995Events and Causal Factors Analysis 11 Introduction Accidents are investigated to identify the causes of their occurrence and to determine the actions that must be taken to prevent recurrence. It is essential that the accident investigators probe deeply into both the events and the conditions that create accident situations, and also the managerial control systems that let them develop so that the root accident causes can be identified. Identification of these root causes necessitates understanding the interaction of events and causal factors through a chronological chain of activity starting with an initiating event through to the final loss producing occurrence. Vital factors in accident causation emerge as sequentially or simultaneously occurring events that interact with existing conditions. This pattern of events and conditions are traced out to reconstruct the multifactorial path to unacceptable loss or loss-potential. A meticulous trace of unwanted energy transfers and their relationships to each other and to the people, plant, procedures, and controls implicated in accident occurrence, further defines the sequence of accident development. The Events and Causal Factors (ECF) chart depicts the necessary and sufficient events and causal factors for accident occurrence in a logical sequence. It can be used not only to analyse the accident and evaluate the evidence during investigation, but also can help validate the accuracy of pre-accident systems analyses. Events & Causal Factors Analysis (ECFA) is an integral and important part of the MORT-based accident investigation process. It is often used in conjunction with other key MORT tools, such as MORT tree analysis, change analysis, and energy trace and barrier analysis, to achieve optimum results in accident investigation. The fundamentals of this valuable MORT tool are discussed in this paper. 2Nature of Accident Investigation Experience has shown that accidents are rarely simple and almost never result from a single cause. Rather, they are usually multifactorial and develop from clearly defined sequences of events which involve performance errors, changes, oversights, and omissions. Accident investigators need to identify and document not only the events themselves, but also the relevant conditions affecting each event in the accident sequence. To accomplish this, a simple straight forward approach can be utilised that breaks down the entire sequence into a logical flow of events from the beginning of accident development . It is important to realise that the end point may be defined either as the loss event itself or as the end of the amelioration and rehabilitation phase. This flow of events need not lie in a single event chain but may involve confluent and branching chains. In fact, the analyst/investigator often has the choice of expressing the accident sequence as a group of confluent event chains which merge at a common key event, or as a primary chain of sequential events into which causative factors feed as conditions that contribute to event occurrence, or as a combination of the two.

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Events Condition sSCIE-DOE-01-TRAC-14-95 2 Events and Causal Factors AnalysisAugust 1995 Construction of the ECF chart should begin as soon as the accident investigator begins to gather factual evidence pertinent to the accident sequence and subsequent amelioration. The events and causal factors will usually not be discovered in the sequential order in which they occurred, so the initial ECF chart will be only a skeleton of the final product and will need to be supplemented and upgraded as additional facts are gathered. Although the initial ECF chart will be very incomplete and contain many information deficiencies, it should be started very early in the accident investigation because of its innate value in helping to: Corganise the accident data; Cguide the investigation; Cvalidate and confirm the true accident sequence; Cidentify and validate factual findings, probable causes, and contributing factors; Csimplify organisation of the investigation report; Cillustrate the accident sequence in the investigation report. With all its virtues as an independent analytical technique, ECFA is most effective when used with the other MORT tools (such as Fault Tree Analysis, MORT Chart Analysis, Change Analysis) that provide supportive correlation. Furthermore, ECFA can perform as the framework into which the results from other forms of analysis are integrated. An appropriate combination of the major MORT analytic tools, including ECFA, provides the core for a good investigation. 3Description of Technique A simple example of an ECF Chart is provided in Appendix 1. Sections 3.1 and 3.2 provide a set of conventions and criteria to be used in ECFA. These conventions are intended to improve comparability and consistency in accident reporting and to assist the communication of investigation findings. In section 3.3, more general guidelines are given for the administration of the ECFA method. These conventions are intended to be as simple as possible whilst preserving the effectiveness of ECFA. It is further intended that investigators be provided with helpful guidelines without inhibiting their use of this tool by imposing an overly complex set of rules. 3.1 Conventions for Events and Causal Factors Charts 3.1.1 Events should be enclosed in rectangles, and conditions in ovals.

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SCIE-DOE-01-TRAC-14-95 It may be found helpful to draw up an evidence matrix to correlate the analysis with the 1evidence collected. August 1995Events and Causal Factors Analysis 33.1.2 Events should be connected by solid arrows. 3.1.3 Conditions should be connected to each other and to events by dashed arrows. 3.1.4 Each event and condition should either be based upon valid factual evidence or 1be clearly indicated as presumptive by dashed line rectangles and ovals. 3.1.5 The primary sequence of events should be depicted in a straight horizontal line (or lines in confluent or branching primary chains) with events joined by bold printed connecting arrows. 3.1.6 Secondary event sequences, contributing factors, and systemic factors should be depicted on horizontal lines at different levels above or below the primary sequence (see Figure 1 and Appendix 1).

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