Fault Tree Analysis

1. Fault TreeAnalysis Pages 127 - 143 7.1 Fault Tree Symbols and Logic 7.2 Finding Cut Sets 7.3 Fault Tree Quantification 7.4 Example of a Fault Tree Construction of a Motor-pump Pressure System 7.5 Common Mistakes in Fault TreesPages 127 - 143 7.1 Fault Tree Symbols and Logic 7.2 Finding Cut Sets 7.3 Fault Tree Quantification 7.4 Example of a Fault Tree Construction of a Motor-pump Pressure System 7.5 Common Mistakes in Fault Trees

2. Fault Tree Analysis Used in both reliability engineering and system safety engineering Developed in 1961 for US ICBM program Guide published in 1981 Used in almost every engineering discipline Not a model of all system or component failures Page 127 1. Used in both reliability engineering and system safety engineering (More well known in reliability) 2. Developed in 1961 for US ICBM program 3. Guide published in 1981 Published by US Nuclear Regulatory Commission 4. Used in almost every engineering discipline From Mass Transit to commercial nuclear power plants Chemical process plants Oil drilling platforms NASA satellites Aircraft control centers Used to recreate events leading up to Challenger accident 5. Not a model of all system or component failures It is a model of particular system failure modes Can be events associated with any element that makes up the complete systemPage 127 1. Used in both reliability engineering and system safety engineering (More well known in reliability) 2. Developed in 1961 for US ICBM program 3. Guide published in 1981 Published by US Nuclear Regulatory Commission 4. Used in almost every engineering discipline From Mass Transit to commercial nuclear power plants Chemical process plants Oil drilling platforms NASA satellites Aircraft control centers Used to recreate events leading up to Challenger accident 5. Not a model of all system or component failures It is a model of particular system failure modes Can be events associated with any element that makes up the complete system

3. Applying Fault Tree Analysis Postulate top event (fault) Branch down listing faults in the system that must occur for the top event to occur Consider sequential and parallel or combinations of faults Use Boolean algebra to quantify fault tree with event probabilities Determine probability of top event Page 127 - 128 1. Postulate top event (fault) 2. Branch down listing faults in the system that must occur for the top event to occur 3. Consider sequential and parallel or combinations of faults 4. Use Boolean algebra to quantify fault tree with event probabilities 5. Determine probability of top eventPage 127 - 128 1. Postulate top event (fault) 2. Branch down listing faults in the system that must occur for the top event to occur 3. Consider sequential and parallel or combinations of faults 4. Use Boolean algebra to quantify fault tree with event probabilities 5. Determine probability of top event

4. Fault Tree Logic Use logic gates to show how top event occurs Higher gates are the outputs from lower gates in the tree Top event is output of all the input faults or events that occur Page 128 Use logic gates to show how top event occurs Higher gates are the outputs from lower gates in the tree Top event is output of all the input faults or events that occurPage 128 Use logic gates to show how top event occurs Higher gates are the outputs from lower gates in the tree Top event is output of all the input faults or events that occur

5. Terms Faults and failures System and subsystem faults Primary and secondary failure Command fault Page 128 1. Faults - something does not perform the action you desire, even though it operates as designed Failures - something has broken 2. System faults - the top event of the fault tree Subsystem faults - component faults below top event 3. Primary failures - failure that occurs under normal operating and environmental conditions Secondary failure - failure outside of normal conditions 4. Command fault - occurs when a component performs as designed but produces the output signal at the wrong timePage 128 1. Faults - something does not perform the action you desire, even though it operates as designed Failures - something has broken 2. System faults - the top event of the fault tree Subsystem faults - component faults below top event 3. Primary failures - failure that occurs under normal operating and environmental conditions Secondary failure - failure outside of normal conditions 4. Command fault - occurs when a component performs as designed but produces the output signal at the wrong time

6. Fault Tree Symbols