Why are Model important What is a model? What do we use models for? "All models are wrong,some models are useful. George Box CLGO System Engineering by J.J.Gao 11
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Accident Causality Model Causality models influences the directions of our investigation,and the solutions that we find. Linear Chain of Events -System Theoretic Accident Modeling and Process (STAMP) CLGO System Engineering by J.J.Gao 12
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Chain-of Events Model Explains accidents in terms of multiple events, sequenced as a forward chain over time. Simple,direct relationship between events in chain Ignores non-linear relationships,feedback,etc. Events almost always involve component failure, human error,or energy-related event Therefore,preventing the lowest level event became the focus of system engineering,which is dominated by reliability engineering. System Engineering by J.J.Gao CLGO 13
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Chain-of-Events Model How would you prevent the undesired outcome? Equipment Operating damaged pressure Locate tank away from equipment Reduce pressure susceptible to damage. as tank ages AND OR Moisture Corrosion Weakened Tank Fragments Personnel metal rupture projected injured Use desiccant Use stainless Overdesign metal Use burst diaphragm Provide mesh Keep personnel from to keep moisture steel or coat of thickness so to rupture before tank screen to contain vicinity of tank while out of tank. plate carbon corrosion will not does,preventing more possible fragments. it is pressurized. steel to prevent reduce strength to extensive damage contact with failure point during and fragmentation. moisture. foreseeable lifetime. CLGO System Engineering by J.J.Gao 14
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Reason's Swiss Cheese Model Dofonoee Accident UnsafeActs Window of Opportunity Preconditions Line Management Decision Makers Unsafe Acts and L建ent Unsafe Conditions Latent Unsafe Conditions Assumes accidents are random events coming together accidentally-"High- consequence,low probability events." Ignores common cause failures of defenses(systemic accident factors). Does not include migration to states of high risk. Assumes some(linear)causality or precedence in the cheese slices. CLGO System Engineering by J.J.Gao 15
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