In risk analysis, what is a fault tree analysis and when is it used?

• A. A random inspection method used after a failure occurs.
• B. A top-down method to deduce possible failures leading to a hazard; used to identify root causes and mitigations.
• C. A test to measure operator reaction times.
• D. A checklist for maintenance tasks.

Answer: (B)

Fault tree analysis is a top-down, deductive method used in risk analysis to determine how a hazard can occur by breaking it down into contributing causes arranged with AND/OR logic. You start with the undesired top event and decompose it into immediate causes, then into lower-level events, until you reach basic events such as component failures or human errors. This structure lets you see the combinations of events that could lead to the hazard, identify root causes, assess how mitigations affect the likelihood, and prioritize risk reduction efforts. It can be qualitative—just mapping possible causes—or quantitative, where probabilities of basic events are combined to estimate the probability of the top event. It’s used during system design and safety analysis to reveal weaknesses and justify mitigations. It is not a random post‑failure inspection, not a test of operator reaction times, and not a maintenance checklist.