This document is intended to provide a guideline, not a standard, for using fault tree analysis (FTA) to improve the quality of the outputs of the project or product by providing a comprehensive and systematic way to identify, assess, and prioritize risks. FTA enhances a decision-maker’s understanding of the complex relationships regarding potential risks or failure points that should be addressed to improve or optimize project outcomes. This document further provides practitioners with the opportunity to improve the reliability of design and to improve the quality by reducing potential failures. Examining what would potentially cause the product to be less reliable is also related to decision analysis. For an organization that executes capital projects, the FTA is also applicable in providing insight into performing other analyses, such as:

• Functional analysis of highly complex systems
• Evaluation of safety requirements and specifications
• Evaluation of system reliability and the identification of potential design defects and safety hazards
• Simplification of design to support operations and maintenance requirements (for lifecycle cost analysis)
• Evaluation of human interfaces (project teams and systemic risks)

System failure analysis is an overarching process that includes different techniques, which include fault tree, logic tree, fishbone diagrams, failure mode and effects analysis, etc. Fault tree analysis is just one tool that can be used in system failure analysis. With that said, this RP is intended to introduce the purpose and basic methods of developing a fault tree, calculating the consequence for the failure of the overall system (called the top event) given the structure of the tree and the probability (P) that the building block elements (called gates and events) occur, and identifying the most important sources of potential failure for inspection and action.

FTA is a deductive, top-down method aimed at analyzing the effects of initiating faults and events on a complex system and is defined as “a risk analysis method used to evaluate risk threats employing a deductive logic tree linking a parent event to the combinations of sub-events that could cause it.” A fault tree is not the same as an event tree analysis. Fault trees assist project teams in examining undesired events, identifying the cause(s) leading to potential failures, and determining how to prevent them in the future.

Fault tree analysis necessitates a robust level of engineering that accurately represents events and their interactions. This requires an engineering framework that delineates basic events and their interactions, enabling the construction of the fault tree. Even in early partial designs, FTA can identify major causes of system failure, guiding engineering efforts to mitigate these issues, for example, by incorporating backup systems for failure-prone events.

Using the FTA methods described in this RP assists in asset planning. These planning efforts include the optimization, optioning, and value-engineering assessments of the equipment and systems. This further includes improving the quality of the design to ensure the operability, reliability, and maintainability of the asset(s). Asset planning, value engineering, and quality management all support risk management functions. These efforts ultimately determine the lifecycle cost of the equipment, systems, etc., which supports the decision to invest in the asset.

Contributors:

Dr. David T. Hulett, FAACE (Primary Contributor)
Lance Stephenson, CCP, FAACE Hon. Life (Primary Contributor)
James E. Arrow, DRMP
Tim Boatwright, EVP
Francisco Cruz, CCP
Larry R. Dysert, CCP CEP DRMP FAACE Hon. Life
Rafi Polak
John R. Schuyler, CCP DRMP
Pei Tang, PRMP PSP

About David: