Fault-tree analysis for system design, development, modification, and verification

A methodology that uses fault-tree analysis (FTA) techniques to assess the weaknesses of a new chemical/process design at any time during system development is presented. FTA provides a cost-effective means of improving or verifying the reliability and efficiency of chemical/process design. It evaluates the consequences of conceivable failure to indicate where improvements are justified. FTA techniques were used to model the failure modes of an existing control-room heating, ventilation, and air-conditioning (HVAC) system of a large production facility. The fault-tree reduction revealed 129 single-, 434 double-, and 442 triple-failure combinations, any of which could cause system failure. Single failures and double failures consisting of an equipment malfunction and an operator failure error were targeted for design and/or procedural modifications. These modifications were then incorporated into the operating system design to enhance system availability. In an iterative fashion, FTA techniques were reapplied to the modified design and used to verify the adequacy of the proposed revisions prior to implementation. This resulted in a thorough review of system vulnerabilities and a clear understanding of how to correct them