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Event tree

Event tree

Owned by Patryk Pluskota (Unlicensed)


What is Event Tree Analysis? 

Event tree analysis (ETA) is a forward, bottom up, logical modeling technique for both success and failure that explores responses through a single initiating event and lays a path for assessing probabilities of the outcomes and overall system analysis. This analysis technique is used to analyze the effects of functioning or failed systems given that an event has occurred. ETA is a powerful tool that will identify all consequences of a system that have a probability of occurring after an initiating event that can be applied to a wide range of systems including: nuclear power plants, spacecraft, and chemical plants. This Technique may 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.  With this forward logic process use of ETA as a tool in risk assessment can help to prevent negative outcomes from occurring by providing a risk assessor with the probability of occurrence. ETA uses a type of modeling technique called event tree, which branches events from one single event using Boolean logic.

Methodology

The overall goal of event tree analysis is to determine the probability of possible negative outcomes that can cause harm and result from the chosen initiating event. It is necessary to use detailed information about a system to understand intermediate events, accident scenarios, and initiating events to construct the event tree diagram. The event tree begins with the initiating event where consequences of this event follow in a binary (success/failure) manner. Each event creates a path in which a series of successes or failures will occur where the overall probability of occurrence for that path can be calculated. The probabilities of failures for intermediate events can be calculated using fault tree analysis and the probability of success can be calculated from 1 = probability of success(ps) + probability of failure (pf).

Steps to perform an event tree analysis:

  1. Define the system
  2. Identify the accident scenarios
  3. Identify the initiating events
  4. Identify intermediate events
  5. Build the event tree diagram
  6. Obtain event failure probabilities
  7. Identify the outcome risk
  8. Evaluate the outcome risk
  9. Recommend corrective action
  10. Document the ETA


What is Event Tree?


Event tree is an inductive analytical diagram in which an event is analyzed using Boolean logic to examine a chronological series of subsequent events or consequences. For example, event tree analysis is a major component of nuclear reactor safety engineering.

An event tree displays sequence progression, sequence end states and sequence-specific dependencies across time.

Event Tree XML Format


Event Tree Initial Branch

Event Tree Initial Branch
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
 <eventTree xmlns:ns2="pl.wroc.pw.sa.et.EventTree">
    <id>1</id>
    <InitialBranch>
            <branch>true</branch>
            <child>
                ...
            </child>
            <child>
            	...
        	</child>
            <event>
            	...
            </event>
        	<id>7</id>
            <type>true</type>
    </InitialBranch>
</eventTree>

<id> - identifer of Event Tree

<type> - If the event happen (true or false)

<child> - occurs only when branch has a child (child has identical structure as Initial Branch)

<event> - stores information event like : scale, parametrs


Event Tree with Child

Event Tree with Child
 <event>
 	<trapezoid>
 		<name>nn</name>
 		<parameters>
 			<scale>LINEAR</scale>
            <a>0.5</a>
            <b>0.5</b>
            <c>0.5</c>
            <d>0.5</d>
        </parameters>
     </trapezoid>
     <child>
        <trapezoid>
            <name>nn</name>
            <parameters>
                <scale>LINEAR</scale>
                <a>0.5</a>
                <b>0.5</b>
                <c>0.5</c>
                <d>0.5</d>
            </parameters>
        </trapezoid>
        <id>5</id>
        <name>e6</name>
     </child>
     <id>4</id>
	 <name>e5</name>
 </event>

Event Tree without Child

Event Tree without child
<event>
 	<trapezoid>
    	<name>nn</name>
        	<parameters>
            	<scale>LINEAR</scale>
                <a>0.5</a>
                <b>0.5</b>
                <c>0.5</c>
                <d>0.5</d>
        	</parameters>
    </trapezoid>
	<id>5</id>
    <name>e3</name>
 </event>

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