Harry H. West

A new algorithm for computer-aided fault tree synthesis

Abstract Fault tree analysis (FTA) has been used in the chemical process industry (CPI) for systematic safety and reliability analysis during the past decades. Conventional manual construction of fault trees can be extremely time consuming and vulnerable to human error. A computer-aided fault tree synthesis methodology can be an initial step, or as an independent check to assist or supplement manual FTA. However, no entirely satisfactory algorithm has been published for fault tree synthesis, especially when control loops are encountered. A potential methodology to construct fault trees automatically is proposed in this paper. This algorithm works directly form the system block diagram, thus avoids the tedious work of generating digraphs, transition tables, decision tables, and knowledge-based rules. Mini cause-and-effect trees are used to model the cause and effect logics around each item of equipment. Control loops are treated by special cause-and-effect unit models — logical combinations of the unit models of their constituent components. Multiple or complex control loops can be easily taken into account by providing their corresponding cause-and-effect unit models. In particular, the fault tree construction algorithm presented here is based on a component-by-component basis instead of a loop-by-loop or node-by-node basis. The tree structure is much more concise and easier to read. An example is embedded in the description of the methodology for better understanding. Analysis shows that the fault tree generated here is equivalent to the published result.

Algorithmic fault tree synthesis for control loops

Abstract Efficient process control is an integral part of the design and operation of a safe and productive chemical plant. It is crucial for fault tree analysis since control systems are designed to prevent process deviations. How to handle control loops is a major concern in the research of computer-aided fault tree synthesis for the chemical process industry (CPI). This paper presents a systematic methodology to produce fault tree models for control loops and protective safe guards. Two examples are provided to illustrate the basic idea.