CAFTA training

PRA and CAFTA Training : PRA and CAFTA Training Objectives Review basic PRA concepts Review CAFTA components and functionality Create a complete fault tree


What is PRA? : What is PRA? Probabilistic Risk Assessment (PRA) is an organized method of determining the likelihood that combinations of events lead to an unacceptable situation. Risk is defined as the product of expected frequency of occurrence and anticipated consequence for an accident or activity. PRA can be used to ensure cost effective, safe operation/use of facilities. PRA is also used to allocate limited resources among competing needs.


What is a Fault Tree : What is a Fault Tree Fault Tree model Models component / support system interdependencies. Used to generate minimal cutsets. Provides for a logical display of intra-system interactions and component interrelationships Describes ways system can fail Uses AND, OR and other gate types Can be linked together to explicitly model design dependencies Includes Common cause failures and operator errors


Developing Fault Trees : Developing Fault Trees Development of System Fault Trees Basic Logic of Fault Tree Models Component Failure Characteristics Testing and Maintenance Human Errors Dependent Failures


PRA Terms : PRA Terms Top Event Frequency is the estimated likelihood of the top event, per year. Top Event Frequency is expressed in units of: “expected events per year” A basic event is the lowest level in a fault tree Cutsets are the minimum combination of basic events required to occur in order to cause the top event. When sorted by probability, cutsets reveal most likely sequences of events, leading to a better understanding of vulnerabilities.


CAFTA : CAFTA CAFTA is: Database Editor Fault Tree Editor Cutset Editor


CAFTA Topics : Software Overview Reliability Database Editor Fault Tree Editor Model Quantification Cutset Editor General Information Case Study CAFTA Topics


CAFTA For Windows : CAFTA For Windows Software Overview


CAFTA For Windows : CAFTA For Windows Four Steps to Construct System Model Define Fault Tree Logic Build Reliability Database Evaluate Fault Tree to Obtain Cutsets Review and Analyze Cutset Results


CAFTA For Windows : CAFTA For Windows Fault Tree Model and Databases


Database Editor-- RDED : CAFTA Database Structures Basic Event database Failure Rate (Type Code) database Gate database Three databases work together to define the attributes of all events Database Editor-- RDED


BE Naming Conventions : Basic Event Naming Conventions: (Example) BE Naming Conventions


Calculation Formulas : Calculation Formulas Calculation Formulas


Fault Tree Editor-- FTED : Movement Commands Fault Tree Editor-- FTED


Navigating Through a Fault Tree : Navigation by Dragging Gates by searching Parents of a event/gate by viewing Top events Find Gate/Event by FIND menu function Jump to the Gate/Event if found View and Select Fault Tree Tops Navigating Through a Fault Tree


Gate Types : Gate and Basic Event Types ---Text Form Gate Types


Fault Tree Editor-- FTED : Gate and Basic Event Types ---Graphic Form Fault Tree Editor-- FTED


Fault Tree Editor-- FTED : Examples: Combination gate: G COM3 A B C D Indicates a 3-out-4 combination gate, while F COM3 A B C D E Indicates a 3-out-5 combination gate Fault Tree Editor-- FTED


Example : Example System B Failure is the top event in the fault tree. Valve failure and Operator failure are basic events. A cutset can consist of a single basic event. Pump failure occurs if Test & Maintenance make it unavailable OR if it fails to start OR if it fails to run. There are five possible combinations of these failures, or cutsets, that can lead to system B failing. Failure of System B results in the accident sequences TAB SAFE or TAB FAIL. Example


Fault Tree Editor-- FTED : FTED Editing Features Loading Existing Fault Tree File Connect to Different Databases Editing Database Records Text and Graphical Input Extract Subtree Delete event locally and/or globally Changing Gate Type Prune Gate: Gate -> Event Merging Files Drag-Drop Editing “Undo” to reverse the previous editing Fault Tree Editor-- FTED


Fault Tree Editor-- FTED : FTED Logic Modeling Features Circular Logic Checking A AND B C D B OR E F G G OR X A Z Compressing Equivalence and True/False Values: to make fault tree size smaller Prune Modules: Change all Modules to basic events; Module = Independent Subtree Fault Tree Editor-- FTED


Fault Tree Editor-- FTED : FTED Logic Modeling Features Check Gate Independence To produce list of events which prevent the gate from being independent Check Module Independence To produce list of events which prevent the module from being independent Define physical and logical links Fault Tree Editor-- FTED


Model Evaluation : Model Evaluation: Quantification Process Model Evaluation


Quantification : Quantification Setup: Quantification


Quantification : Four Parameters need to be set for Quantification: Quantification Method: Cutset generation or gate probability calculation; or other user-defined quantification Truncation Probability: decide how many cutsets are generated and how long it takes to generate Truncation order: remove any cutsets which has higher order than specified Module Operation: this is additional processing option, if any module exists. Quantification


Fault Tree Editor-- FTED : Options of Module Operations: Expand Module: module cutsets are included in the final cutsets of the fault tree top Prune Modules: Module is declared as a basic event and its probability is used rather than module cutsets Only Module: cutset generation is for all modules, rather than for all tops of the fault tree. Fault Tree Editor-- FTED


Printing : Printing Fault Trees Use Properties -> Group Pages menu function to turn on/off of group of page Printing


Printing : Printing Fault Trees Use Properties->Auto Page Breaks menu function to decide appearance of each page Printing


Cutset Editor-- CSED : CSED Provides Cutset Review Functions Do the cutsets make any sense? Are there single and double, and higher order cutsets? What are the dominant cutsets? What do you think should be the dominant cutsets? What recovery actions should be added to some of cutsets? Cutset Editor-- CSED


Cutset Editor-- CSED : Cutset Editor Screen: Class Name: enabled by the display option Top Event and Probability Cutset Properties: (In different font and colors) Generated : original Deleted: not counted for module probability Added: added by user; not generated Recovery : added by user Cutset Editor-- CSED


Cutset Editor-- CSED : Cutset Editor Screen: Cutset Properties: (In different font and colors) True: prob. = 1 False: Prob. = 0 Subsumed: no longer contribute to top probability Truncated: cutset probability below the cutoff Delete-term: cutset not count to top probability Cutset Editor-- CSED


Cutset Editor-- CSED : Reporting Cutsets Results Cutset Editor-- CSED


CAFTA Files : CAFTA Files .CAF - Fault Tree Files .RR - Basic Event Database, Gate Description Data, Failure Rate (Type Code) Database .CUT - Cutset File .RAW - Temporary output from cutset generator .FTP - Temporary input to cutset generator CAFTA Files


CAFTA Data Flow : CAFTA Data Flow: CAFTA Data Flow


Advanced Features : Fault Tree Editor Drag a .caf file from explorer and drop it in FTED will open the file in the FTED window Copy and Paste a gate logic between different fault tree files Drag&Drop gate logic between different fault tree files Could open many windows to view different parts of one fault tree file Ctrl+DlbClick between events(gates) will automatically add new event to the gate logic Advanced Features


Advanced Features : Fault Tree Editor Can set some event as Flag and use the event string in sequence quantification Seven types of links to other PSA project files, and go to those file directly from FTED Can load different formats of fault tree files, as long as filters for those files are supplied and specified in the CAFTA configuration Advanced Features


Begin Using FTED : Begin Using FTED


Begin Using FTED : Begin Using FTED Choose a standard template and standard Access database. Name your database. The database will have an extension .rr It will contain a basic event table, a gate table, and type code table.FTED will display one basic event as shown below.


Input Fault Tree Logic : Input Fault Tree Logic Next, Click and hold the left mouse button on the basic event symbol (the circle). A palette of gate types will pop up, as shown below As you drag the cursor across each button in the pallette, the gate type label will appear in the lower left of your screen (on the status line). Choose the “OR” gate symbol


Input Fault Tree Logic : Input Fault Tree Logic This will put two basic events below the new “OR” gate.


Input Fault Tree Logic : Input Fault Tree Logic While the top gate is highlighted (surrounded by a dashed box), choose Edit and then Add Event to place the third event under this gate


Input Fault Tree Logic : Input Fault Tree Logic  Fault tree logic may also be entered using the following input methods: In the toolbar click on the yellow down arrow key (with plus sign) to convert an event to a gate Press the Ctrl key and double click between two existing gates (be careful not to click in a description box). A quick way to add a large number of gates is to use the Edit, Input option. After events are added, they can also be changed to gates by clicking on basic event circle to pull down the palette of gates and events.


Input Event Data : Input Event Data Double click on a basic event to enter event data


Input Event Data : Input Event Data Select the appropriate calculation method


Merging Two Fault Trees : Merging Two Fault Trees If two fault trees share the same database (*.rr), then merging the two fault trees will include all of the basic event, gate, and type code data. If you are merging two fault trees with separate databases, then you must open the database editor and import the basic event, gate and type code data for the second tree.


Merging two fault trees : Merging two fault trees Open tree1.rr Select File, Import In the file name box type “*.rr” this will show you all files with the extension .rr


Merging two fault trees : Merging two fault trees Find the database for the second tree and click ok. This will allow you to choose field within that database to import.


Merging two fault trees : Merging two fault trees Select the double arrows to import all fields. Click Ok To import Gate data, select Window, GATE DATA. Repeat the import process for the gate data To import Type Code data, select Window, TYPECODE DATA. Repeat the import process for the type code data


Failure Modes : Failure Modes Example of failure modes: Fail to Run Fail to Start Fail to Open Transfers Open Transfers Closed Common Cause Failure Operator Error Test & Maintenance