Abstract of Meeting Paper

Society for Risk Analysis 1994 Annual Meeting

Dependency Matrix Generation Using Rule-Tester.* F. R. Hubbard, FRH, Inc., P. O. Box 65359, Baltimore, MD 21210; and J.-Y. VanHalle, VanHalle Consulting, 9224 Edwards Way, No. 3341, Adelphi, MD 20783

A new computer code has been produced and tested which develops a detailed dependency matrix for a large engineered system assemblage or plant from information about the dependencies for each individual system. This dependency matrix is of the type which can be used in a probabilistic risk assessment (PRA) to develop a detailed model for the plant or for qualitatively tracing the impact of the failure of each system in the plant on the other systems. RULE_TESTER can be used for "What if' analysis, by allowing the user to graphically specify failure of one or a combination of systems and then displaying onscreen or on paper the affect on the "downstream" systems. Previously all of this had to be done manually, both the generation of the matrix and the tracing of the cascaded impacts. Input to RULE_TESTER is in the form tables for each system showing the system failure/status change resulting from the change in systems on which it is dependent. Another form of input can be RISKMAN "split fraction rules files." RULE_TEST is a Microsoft Windows application programmed and compiled in Visual Basic. All tasks form file opening to scenario simulations are initiated with a pointing device either by clicking on drop

down menus or on buttons. In addition to the inherent simplicity of working in the Windows' environment, RULE_TESTER utilizes Windows' built-in security features. The essence of every plant model structure is that it represents dependencies between systems. RULE_TESTER helps in understanding the logical rules which represent these dependencies. These logical rules may take many forms including fault tree cutsets and event trees. RULE_TESTER illustrates these logical rules by generating the following:

• several different types of dependency matrices which show the logical "chains" between systems, including one in which the macros are replaced by the top events and initiating events that they contain
• a ranked list of all of the variables in the rules including top events, split fractions, macros, and initiating events
• indication of whether each variable fails (is lethal) another top event or if it just influences the choice of split fraction to be used
• simulations of the impact of the failure of top events on others by allowing the user to actually try the change and see how it propagates through the model
• a list of the split fractions chosen under each simulated combination of top event failures.

Windows and Visual Basic are the registered trademarks of the Microsoft Corporation. RISKMAN is the registered trademark of PLG, Inc.

Work supported by FRH, Inc. and VanHalle Consulting.