Optimal Safety System Design Using Fault Tree Analysis

This paper describes a design optimization scheme for systems that require a high likelihood of functioning on demand. The final design specification is achieved by solving a sequence of optimization problems. Each of these problems is defined by assuming some form of the objective function and specifying a sub-region of the design space over which this function will be representative of the system unavailability. An example of a high-pressure protection system has been used to demonstrate the practicality of the technique. Design parameters for this system include redundancy levels, the number of elements required for a voting system to function, component selection options and maintenance inspection intervals. Both implicit and explicit constraint forms have been used in the example. The implicit constraints require a full system analysis to determine whether the current design is feasible or not. All system assessments have been carried out using fault tree analysis.