Analytical Tools: FMEA, Fault Tree, Fishbone, and Change Analysis

Choose the analysis tool that fits the question

Safety professionals use structured tools to reduce guessing. The tool should match the decision. Some tools look forward to find potential failures before an event. Some work backward from an event. Some organize causes for discussion. Some compare a changed condition with the expected condition. The ASP exam may ask which tool is most appropriate for a scenario.

Failure modes and effects analysis, or FMEA, is a forward-looking method. A team reviews a process, component, or task step and asks how it can fail, what the effect would be, what causes the failure, what controls exist, and what actions are needed. FMEA is useful during design, procedure development, equipment selection, maintenance planning, and process changes.

Fault tree analysis starts with a top event such as explosion, fall from elevation, chemical release, or unexpected startup. The team then maps the combinations of failures that could produce that event. Fault trees help show how barriers interact. A serious event may require several things to fail together, such as isolation not performed, verification skipped, and startup initiated by another worker.

Fishbone diagrams, also called cause-and-effect or Ishikawa diagrams, organize possible causes into categories. Common categories include people, methods, machines, materials, environment, and management systems. Fishbones are useful for brainstorming and organizing investigation thinking, but they are not proof. Each possible cause still needs evidence.

Change analysis compares the incident or new condition with the normal or expected condition. It asks what changed in people, equipment, materials, methods, environment, timing, workload, supervision, software, layout, production rate, maintenance, or contractors. It is especially useful when a familiar process suddenly produces an unexpected result.

A common error is selecting a tool because it sounds sophisticated rather than because it answers the question. If the question asks how a new process step could fail before startup, FMEA is often a good fit. If it asks what combinations of failures could lead to a catastrophic event, fault tree logic fits. If a team needs to organize many possible causes during an investigation, a fishbone can help. If the key clue is that the task worked for years until something changed, change analysis is strong.

These tools should lead to controls. Analysis without action is not risk reduction. Results should identify higher-level controls, procedure changes, training needs, maintenance changes, purchasing changes, alarms, interlocks, inspections, or management system improvements. Actions should be assigned, tracked, verified, and reviewed for residual risk.

Use evidence to avoid bias. Interviews, records, photographs, monitoring data, maintenance history, training records, inspection reports, and field observations can confirm or reject suspected causes. Do not stop at the first explanation, especially if it blames the worker while ignoring design, scheduling, supervision, or system contributors.