Fault Tree Analysis: A Comprehensive Guide to Identifying and Preventing System Failures

Every hour of unplanned downtime costs industrial facilities thousands of dollars in lost productivity, emergency repairs, and missed deadlines. You know that identifying potential failures before they occur isn't just good practice. It's essential for operational survival. Fault tree analysis (FTA) provides a systematic method to trace failures back to their root causes, enabling you to prevent equipment breakdowns rather than react to them.

Key takeaways

• Fault tree analysis is a top-down approach that maps system failures to root causes using visual diagrams and logic gates.
• FTA prevents costly downtime by identifying critical failure paths before breakdowns occur.
• Logic gates and standardized symbols create clear visual maps of how component failures combine to cause system breakdowns.
• CMMS integration amplifies FTA benefits through automated maintenance scheduling and real-time failure prediction.

What is fault tree analysis?

Fault tree analysis (FTA) is a systematic, graphical approach that starts with an undesired event such as a system failure or safety incident. It works backward to identify all possible causes. Using visual fault tree diagrams, your maintenance team can map complex failure scenarios and understand how individual component failures combine to create system-wide problems.

FTA serves as both a proactive and reactive tool. Teams primarily use it proactively to analyze potential failures before they occur, starting with hypothetical "what if" scenarios to prevent future breakdowns. However, FTA also proves valuable for post-incident analysis, helping you understand how actual failures happened to prevent recurrence. 

This approach prevents costly downtime and improves operational efficiency, transforming maintenance from an expense into a strategic advantage. It reduces emergency repairs, extends equipment life, and maximizes your production uptime.

Beyond qualitative analysis, FTA enables mathematical modeling of failure probabilities. By assigning probability values to basic events, your team can calculate the likelihood of system failures. This helps you prioritize maintenance resources and make data-driven decisions about backup systems and risk reduction.

Key benefits of fault tree analysis

FTA delivers measurable improvements through qualitative and quantitative analysis. With FTA, you can:

Prevent costly downtime: By identifying failure paths before breakdowns occur, you can schedule preventive maintenance during planned outages rather than scrambling during emergencies.

Improve system reliability: FTA reveals single points of failure and critical dependencies, enabling your team to add redundancy where one component failure could shut down an entire system, implement backup systems for critical processes, and eliminate weak links that cause cascading failures.

Optimize maintenance resources: Understanding failure probabilities helps you focus effort and budget on the most critical components.

Enhance safety: In high-risk industries, FTA identifies potentially dangerous failure combinations before they threaten personnel or equipment.

Consider an oil refinery using FTA to analyze pump system failures. The analysis might reveal that combining specific valve positions with certain pressure conditions creates a high failure risk. Armed with this knowledge, operators could implement procedural controls and monitoring systems to prevent these conditions from occurring simultaneously.

Components of fault tree analysis

1. Fault tree diagrams

The fault tree diagram provides the visual framework for analysis of your existing system. Starting with the top event (undesired outcome), the diagram branches downward through intermediate events to basic events (root causes). This hierarchical structure makes complex failure relationships easy to understand and communicate.

2. Event types and symbols

FTA uses standardized symbols to represent different event types:

• Rectangle: Top event or intermediate events requiring further analysis
• Circle: Basic events (root causes) needing no further breakdown
• Diamond: Undeveloped events lacking sufficient data for analysis
• Oval: Conditional events that must exist for failures to propagate
• House: External events outside system control

3. Logic gates

Logic gates show how events combine to cause failures:

• AND gate: All input events must occur for output event
• OR gate: Any single input event causes output event
• Inhibit gate: Input causes output event only under specific conditions

These gates mathematically model failure propagation, enabling both qualitative understanding and quantitative risk calculation.

How fault tree analysis works

Implementing FTA follows a systematic five-step process that transforms complex system failures into actionable maintenance strategies:

Step 1: Define the undesired event

Start by precisely defining the specific system failure you want to prevent. Clear definition is crucial because vague descriptions lead to unfocused analysis and wasted effort.

Example: A pharmaceutical manufacturer might define their top event as "Clean room loses positive pressure," which could lead to contamination. This specific definition is more actionable than a vague "HVAC problem."

Actionable tips:

• Focus on failures with significant operational or safety impact.
• Use measurable criteria (e.g., "pump output drops below 100 GPM," not "pump performs poorly").
• Interview operators who witness failures firsthand, as they often provide the most accurate event descriptions.
• Define time boundaries (immediate failure vs. degradation over hours/days).

Step 2: Understand the system

Thoroughly document how the system operates under normal conditions. This includes understanding how your system and its components work, whether failures are mechanical, electrical, or software-related, requirements for changing the system, and input from system engineers and operators. This comprehensive understanding helps determine how the system functions normally, making it easier to identify abnormal conditions and failure paths.

Example: For a hydraulic press system, the team would document:

• All hydraulic components (pumps, valves, cylinders, filters)
• Operating pressures and cycle times
• Electrical control systems and sensors
• Past failures from maintenance logs showing pump seal failures every 6 months

Actionable tips:

• Walk the system with experienced operators—they know undocumented workarounds and quirks.
• Photograph equipment nameplates and configurations for reference during analysis.
• Review the last two years of maintenance records to identify recurring issues.
• Create a simple block diagram before starting the fault tree to visualize system relationships.

Step 3: Construct the fault tree

Build your fault tree from top to bottom, systematically breaking down the failure into increasingly specific causes. Start with major failure categories, then drill down to root causes.

Example: For a conveyor system that stops unexpectedly:

• Top event: "Conveyor stops during production"
• Level 1: Motor failure (OR) drive system failure (OR) control system failure
• Level 2 under motor failure: Overheating (OR) bearing failure (OR) electrical fault
• Level 3 under overheating: Blocked ventilation (AND) high ambient temperature

Actionable tips:

• Start with 3-5 main branches. You can always add details later.
• Use sticky notes on a whiteboard for initial drafts to easily rearrange logic.
• Stop drilling down when you reach a component you can inspect or test.
• If unsure between AND/OR gates, consider: "Can this failure alone cause the problem?" If yes, use OR.

Step 4: Analyze the fault tree

Evaluate your fault tree both qualitatively and quantitatively. Qualitative analysis identifies which event combinations lead to failure. Quantitative analysis calculates failure probabilities using data like manufacturer MTBF (mean time between failures), historical maintenance records, and industry failure databases.

Example: Analysis of a cooling tower failure might reveal:

• Path 1: Fan motor failure (probability: 0.02/year based on manufacturer MTBF data)
• Path 2: Pump failure AND backup pump failure (combined probability: 0.001/year from your maintenance history)
• Path 3: Control valve stuck closed (probability: 0.05/year from industry reliability databases)

This analysis shows the control valve represents the highest risk and should be prioritized for preventive maintenance.

Actionable tips:

• Start with qualitative analysis if you lack failure data. Identifying critical paths is valuable even without exact probabilities.
• Use manufacturer reliability data as a starting point, then adjust based on your actual operating conditions.
• Focus on "single point failures" first: components that alone can cause the top event.
• Color-code your fault tree: red for high-risk paths, yellow for moderate, green for low.

Step 5: Develop preventive measures

Transform your analysis into concrete actions that prevent failures. Target high-risk failure paths with specific interventions based on probability and impact.

Example: Based on the cooling tower analysis above, the maintenance team would:

• Install a position indicator with automated alerts on the control valve.
• Implement monthly valve cycling procedures to prevent sticking.
• Add valve maintenance to the PM schedule every 3 months.
• Install a manual bypass for emergency operation.

Actionable tips:

• Calculate ROI for each intervention: prevention cost vs. (failure cost × probability).
• Start with low-cost, high-impact fixes, which may include procedural changes or enhanced inspections.
• Consider "mistake-proofing" for human error events: physical changes that make errors impossible.
• Set up condition monitoring for parameters identified in your FTA to catch degradation early.
• Document which fault tree events each PM task addresses to justify maintenance schedules to management.

End Downtime, Boost Production

Try MaintainX for Free

Applications of fault tree analysis in industries

The following examples illustrate how different sectors apply FTA to prevent failures, enhance safety, and optimize maintenance strategies. These represent just a fraction of FTA's potential applications across all industries.

Manufacturing

Manufacturers use FTA to maintain production continuity and quality standards across complex automated systems:

• Robot cell reliability analysis: FTA maps how sensor failures, programming errors, and mechanical wear combine to cause robot malfunctions. This helps teams prevent costly production stoppages.
• Conveyor system fault mapping: Analysis reveals how motor failures, belt issues, and control problems interact, enabling targeted maintenance that keeps materials flowing smoothly.
• Quality control failure prevention: FTA identifies how equipment variations, environmental factors, and procedural gaps lead to defects. This supports consistent product quality.

Retail

Retailers apply FTA to enhance supply chain reliability and ensure continuous product availability:

• Warehouse equipment failure analysis: FTA examines potential failures in systems like conveyors and palletizers. This allows retailers to schedule preventive maintenance and minimize downtime, especially during peak seasons.
• Inventory management optimization: Analysis helps retailers identify causes of stock-outs and mismanagement, enabling them to improve stock control and reduce inventory shortages.
• Shipping and distribution risk analysis: FTA reveals risks in shipping and distribution, helping optimize routes and minimize delays to maintain timely product deliveries.

Facility Management 

Facility managers leverage FTA to maintain building system reliability and avoid operational disruptions:

• HVAC system failure prevention: FTA can help identify failure risks in HVAC systems, such as motor or sensor malfunctions. With this information, facility managers can prioritize maintenance and ensure comfort.
• Power supply interruption analysis: Mapping risks like power surges and wiring issues allows managers to implement backup systems, ensuring operations continue smoothly.
• Plumbing and water system reliability: Assessing potential issues like pipe bursts enables timely maintenance scheduling and prevents water-related disruptions.

How to integrate fault tree analysis with CMMS and predictive maintenance

Fault tree analysis provides valuable insights, but these insights only create real value when integrated into daily maintenance operations. By connecting FTA findings with modern maintenance technologies, organizations transform static diagrams into dynamic tools that actively prevent failures.

CMMS integration

A computerized maintenance management system (CMMS) serves as the central hub for maintenance activities. When FTA insights feed directly into your CMMS, the platform becomes a powerful failure-prevention engine.

Automated scheduling: Link fault tree events to preventive maintenance triggers. If FTA identifies bearing failure risk at 2,000 operating hours, the CMMS automatically generates inspection work orders at 1,800 hours, preventing failures before they occur.

Failure tracking: Every breakdown provides data to improve fault tree accuracy. The CMMS captures root causes, repair times, and costs, helping validate or adjust FTA failure probabilities for increasingly accurate predictions.

Resource planning: FTA-based failure probabilities optimize spare parts inventory and technician scheduling, ensuring resources are available when needed without excess costs.

Example: A manufacturing plant integrates compressed air system FTA with its CMMS. When the fault tree shows bearing failure warnings appearing 200 hours before breakdown, the CMMS monitors runtime and schedules vibration testing accordingly, while maintaining appropriate bearing inventory.

Predictive maintenance

Predictive maintenance uses condition monitoring to identify developing failures early. FTA provides the roadmap for deploying these technologies effectively.

Sensor placement: Instead of sensors everywhere, FTA identifies critical monitoring points. If analysis shows pump cavitation leads to seal failure, vibration sensors at the pump provide targeted early warning.

Alert thresholds: FTA-mapped failure progression helps set meaningful alarm limits that are early enough for intervention but without excessive false alarms.

Real-time risk assessment: Advanced systems combine FTA logic with live sensor data to continuously calculate failure probability, dynamically adjusting maintenance priorities as conditions change.

Example: A wind farm uses FTA to identify gearbox bearing wear patterns. Vibration sensors feed data to analytics software using FTA-based algorithms. When degradation accelerates, the system automatically adjusts maintenance schedules and orders parts to prevent failures that could cost hundreds of thousands in repairs and downtime.

Catch Problems Before They Catch You

Try MaintainX for Free

Transform your maintenance strategy with FTA

Fault tree analysis transforms your maintenance from reactive firefighting to strategic failure prevention. By systematically mapping how failures occur, FTA empowers you to intervene before breakdowns impact operations.

MaintainX’s CMMS platform integrates automated maintenance scheduling, real-time monitoring, and robust failure tracking to help teams stay ahead of downtime. Transform your maintenance strategy from reactive to predictive. Explore how MaintainX can help you prevent failures before they happen.

‍