护层分析-LayersOfProtAnalysis.ppt

? ABB - Page * Functional safety ? ABB - Page * E x t e n d e d A u t o m a t i o n S y s t e m 8 0 0 x A Functional safety Engineering - Layers of Protection Layers of Protection Analysis Fault Propagation Context Event Tree Method Layers of Protection Definition LOPA Event Tree Initiating Evnents and Failure Rates Example of Layers of Protection Fault Propagation modelling Analyze the Chain of events that leads to an accident Control System Fails Operator does not respond properly Mechanical relief failed Overpressure Event Initiating event Layers of Protection Analysis - LOPA A variant of Event Tree Analysis More structures Like event tree analysis, the initiating event start the chain of events Branches are layers of protection Consider only two outcome Accident No Event LOPA Version of Event Tree PL2, fails PL1, fails PL3, fails Accident Quantify using multiplications; all logical ANDs Ex, Column Rupture LOPA Draw the LOPA diagram for following situations Consequence of the accident = fire due to distillation column rupture has a root cause of loss of cooling water Layers of protection Operator respond to alarms and stops the process Process generally designed to withstand loss of cooling water The column has a pressure relief valve Source of ignition are controlled in the process area Ex: Column rupture LOPA LOPA Calculations Proceed as with event tree, but only need to calculate the frequency of accident Resulting accident frequency is initiating event frequency multiplied by PFD of all protection layers Example Cooling water failure frequency is 0,5/year Protection layers Operator response failure PFD = 0,15 Relief valve failure – PFD = 0,07 Process design inadequate – PFD = 0,01 Ignition source contacted – PFD = 0,3 Ex: Column Rupture, LOPA F=0,5/y * 0,15 * 0,01* 0,07 * 0,3 = 1,58E-5 per year Failure Rate Quantification Historical reliability data specific to your installation is best, but often difficult to get Plant maintenance and SIS fun