A Comprehensive Guide to Fault Tree Analysis for Maintenance

In the world of maintenance and reliability, fault tree analysis (FTA) is a leading tool for identifying and mitigating risks associated with complex systems. Maintenance managers across various industries use this powerful technique to improve the overall reliability and safety of their assets.

In this guide, we will delve into the fundamentals of fault tree analysis, its key benefits, and how it can be effectively integrated into your maintenance strategy with the help of CMMS software.

Fault tree analysis is a systematic, top-down approach to identifying and assessing potential causes of various system failures. It involves the use of a graphic, known as a fault tree, to visually map out the relationships that lead to failure. It works backwards from an initial failure event placed at the top of the tree. The branches are then built by unraveling the potential causes and contributing factors that lead to the failure event.

Its purpose is to identify all potential root causes of equipment failure before they can occur. By breaking down complex systems into their components and analyzing the interactions between them, fault tree analysis helps maintenance managers pinpoint potential failures before they happen and implement targeted preventive measures.

Fault Tree Analysis can seem daunting, but at its core, it is simply about assembling ideas piece by piece. Following these steps will allow you to complete a basic Fault Tree Analysis.

1.  Define Failure
The first, and arguably most important step in the process is to identify the failure event you will analyze. The event at the top of the tree will be what dictates all following steps — as such, it needs to be well-defined to keep the rest of the process neat. Failure does not explicitly mean a catastrophic breakdown of machinery either. Failure can be defined as any occurrence that does not meet expectations. Unplanned downtime, employee turnover, or even maintenance delays can be analyzed using the failure tree analysis process.

2. Identify the Causes
Once the failure event has been defined, potential causes can be hypothesized. Start with the most straightforward causes and work outward. This step will require a solid understanding of the system experiencing the failure and how it should function when no issues are present. Pinpoint whether the failure event is strictly mechanical, software-related, or potentially a combination of both. Remember that human error can result in unforeseen issues as well. After all causes have been identified, they should be ranked by their probability of occurring.

3. Determine Contributing Factors
The last step before creating the diagram is to figure out any contributing factors at play. Determining if anything else affected the system and contributed to the failure guarantees that important details are not overlooked.

4. Create a Fault Tree Diagram
Now it’s time to lay out all the information that has been gathered. Create the Fault Tree with the failure event at the top and the causes mapped out below. Evaluate the relationships between the potential causes and contributing factors linking them as needed until the root cause is reached. If the failure and cause identification phases are thorough, this step should be fairly simple, like completing a puzzle where you’ve already laid out all the pieces in order.

5. Assess and Manage Risk
One of the most crucial steps in the process is to produce a risk assessment for the identified root causes. This requires you to gather all the available failure data so that you can determine the probability of each of the events and causes in your FTA diagram. Historical data can be helpful here, as well as future projections to determine where the highest risk is located.

Once that has been accomplished, steps are necessary to minimize the chance of failure. However, it’s also important to remember that fault tree analysis is an iterative process. Your risk assessment may change as you collect more data, or as you make changes to your systems.

6. Monitor Performance and Review Progress

After your initial fault tree analysis, it’s important to take steps to minimize risk in your operation. Continue to monitor performance and regularly assess your progress, so that you can determine whether you’ve successfully reduced risk. FTA is an ongoing process, and it’s a best practice to continually update your fault tree to reflect the latest data.

Which Industries Use Fault Tree Analysis?

Because of its deductive, methodical approach, FTA is widely used to analyze complex systems with multiple potential failure points.

Fault tree analysis is frequently used in manufacturing, chemical processing, nuclear power, oil and gas, transportation, healthcare, aerospace, and automotive, to name just a few industries.

The FTA methodology is invaluable for checking safety measure functionality, tracking efficiency, and improving the budgeting process.

Here are some examples where FTA is especially useful.

Designing and Installing New Equipment

FTA can be helpful whenever designing a new piece of equipment. The approach allows for potential failure points to be identified and corrected during the drafting process. A thorough FTA should also be done before installation to avoid any unforeseen issues and costly repairs.

Keeping a Factory Safe

Knowing if any potential accidents are waiting to happen in your facility can go a long way to keep workers safe.

Optimizing Maintenance

Identifying issues before equipment breaks down allows for a preventative maintenance plan that can save costs and avoid downtime.

Minimizing Aviation Failure

FTA is extremely important in the aviation industry, where a single failure can have catastrophic consequences. It can lead to improved safety guidelines and reduce mechanical delays.

Maintaining Regulatory Compliance

Identifying situations where equipment or systems may fall outside regulations is crucial; it enables prioritization before compliance becomes a real issue.

Deducing the Cause of Employee Turnover

Every employee has a different reason for leaving, but identifying the common aspects driving workers away can help reduce excessive churn in the workforce.

Making Modifications to Any Existing System

Don’t make changes to integral internal systems before analyzing the risks. It’s better to be prepared for a problem than have to deduce one on the fly.

Computerized maintenance management system (CMMS) software is a powerful tool that can help maintenance managers streamline their operations and improve overall asset reliability. Augmenting fault tree analysis with your CMMS software can provide several additional benefits, including:

Data-Driven Insights

By leveraging the wealth of data stored within your CMMS, you can enhance your fault tree analysis with real-time information on asset performance, maintenance history, and failure trends. This will prove beneficial during the risk assessment process, allowing for smarter predictions and well-informed decisions.

The amount of data already available in a CMMS can be the difference between a rough estimate and a pinpoint analysis. It is crucial for a more effective fault tree analysis process.

Automated Workflows

CMMS software can be configured to automatically trigger preventive maintenance tasks based on the insights gleaned from your fault tree analysis. This immediately turns your analysis into real risk management without having to deal with manual implementation. It helps ensure timely interventions and reduces the likelihood of critical failures.

Performance Tracking

With the ability to monitor maintenance key performance indicators (KPIs) related to asset reliability, managers can assess the effectiveness of their fault tree analysis efforts. They can then make continuous improvements to their maintenance plan, guaranteeing an efficient and cost-effective strategy.

Documentation and Compliance

CMMS software provides a centralized platform for storing and managing documentation, including fault tree analysis, ensuring easy access. Whenever a system is updated or a new piece of equipment is added, the existing FTA can be consulted and adapted to guarantee compliance and avoid compatibility issues.

The concept of fault tree analysis can be traced back to the 1960s when it was first developed by Bell Telephone Laboratories for the US Air Force. The primary goal was to improve the reliability and safety of the Minuteman missile system. Since then, fault tree analysis has been widely adopted across various industries.

Today, fault tree analysis has evolved into a sophisticated risk management tool, incorporating advancements in computing technology and benefiting from ongoing research in the field of reliability engineering.

A typical fault tree consists of several key components that help maintenance managers visualize and analyze the possible failure scenarios within a system. They are displayed as event symbols, gate symbols, and transfer symbols. Some of these components include:

Top Event

This represents the primary undesirable outcome or failure that the analysis aims to prevent. It is typically placed at the top of the fault tree diagram.

Intermediate Events

These are events that contribute to the top event and can be further decomposed into lower-level events or root causes.

Basic Events

These are the lowest-level events in the fault tree, representing the root causes of the failure. Basic events cannot be broken down any further. They may be hardware failures, human error, or any type of system failure.

Gates

Logical operators, such as AND and OR gates, are used to illustrate the relationships between different events in the fault tree. These gates help determine the probability of the top event occurring based on the probabilities of the contributing events.

What Are Fault Tree Analysis Symbols?

Fault tree analysis diagrams use symbols across industries. Symbols and naming conventions are standardized, making it easier to read an FTA diagram.

The symbols used in FTA diagrams all fall into 3 basic categories: event symbols, gate symbols, and transfer symbols.

Event Symbols

Events indicate a total or partial failure somewhere within the system. Fault tree diagrams use different symbols for top-level events — the catastrophic failure of a system — and intermediate or basic events.

Both intermediate and basic events contribute to the top-level failure of the system. Using different symbols makes it immediately clear which elements in your maintenance workflow need to be addressed. The symbols also graphically illustrate the severity levels of each issue.

Gate Symbols

Gate symbols indicate the relationship between events. They illustrate the different ways that basic and intermediate events can contribute to top-level events.

The most commonly used gate symbols are AND and OR.

OR indicates that any of a series of events can produce a certain outcome.

AND indicates that both events must take place in order to produce the outcome.

Transfer Symbols

Transfer symbols are useful in larger FTA diagrams, where events repeat.

Transfer in symbols indicate that a particular event is developed somewhere else in the diagram.

Transfer out symbols indicate that an event is repeated at a different point later in the diagram.

Fault tree analysis delivers many advantages for maintenance managers working to increase the reliability and safety of their assets. Some of the key benefits include:

Improved Risk Identification

By systematically breaking down an existing system into its components, FTA enables maintenance managers to identify and prioritize potential failure modes more effectively. It provides users with a better understanding of the entire system and gives managers a holistic look at their processes.

Considers All Failure Methods

FTA doesn’t only focus on equipment breakdown or software malfunctions — it also considers the human element that might be ignored in other analyses. Mechanical errors alone cannot fully explain failures; if you don’t take human error into account, you won’t fully understand the issues facing your plant.

Fault tree analysis takes all types of causes into account, allowing for a comprehensive list of preventive measures, including an update to standard operating procedures.

Enhanced Decision-Making

With a clear understanding of potential failure root causes, maintenance managers can make more informed decisions regarding resource allocation, preventive maintenance, and risk mitigation strategies. This results in better preventive maintenance and more efficient maintenance efforts.

Better Communication

The visual nature of fault tree diagrams facilitates communication and collaboration among different stakeholders, including maintenance teams, engineers, and management. In being easy to understand, it brings out fruitful discussion, not just explanation.

Quantitative Risk Assessment

Fault tree analysis allows for the calculation of failure probabilities, which can be used to assess and compare the risks associated with different failure scenarios. These probabilities can then be ranked and used to prioritize maintenance tasks.

Fault tree analysis is a valuable tool for maintenance managers looking to improve the reliability and safety of their assets. By leveraging a CMMS and doing FTA, you can tap into the power of data-driven insights, automate workflows, and continuously optimize your maintenance strategy. Embrace the potential of fault tree analysis and elevate your maintenance operations to new levels of efficiency and effectiveness.

Drawbacks of Fault Tree Analysis

Fault tree analysis is generally beneficial, but it has some built-in limitations. It’s a good idea to think of FTA as one tool in your toolbox, instead of a one-size-fits-all maintenance solution.

Fault tree analysis can be overly complicated, especially when used to analyze a complex system. Constructing and studying an elaborate fault tree diagram can be a demanding process. If you’re already under pressure and deadlines are looming, FTA can be an excessively time-consuming project.

FTA also requires some expertise. It takes time and training to get truly comfortable with the symbols, naming conventions, and deductive approach required by FTA. If you’re operating with a lean maintenance crew or a lack of experienced technicians, you may not have the resources you need to develop effective fault tree analysis.

Fault tree analysis can deliver great insights, but those insights may also be limited. FTA focuses on a single “top event” and its root causes. That insight doesn’t help maintenance teams plan ahead for other possible problems.

Finally, for some organizations, a lack of good data can make it difficult to carry out a strong fault tree analysis. As with many metrics, fault tree analysis is only as good as the data that goes into it. Incomplete data sets or inaccurate recordkeeping can skew your results so that your FTA analysis is not accurate.

Fortunately, there’s an easy solution to this problem. A good CMMS, like eMaint, captures, stores, and organizes plant data so that you can easily carry out necessary analysis.

eMaint captures and stores all of your asset health data, like vibration levels, temperature, and oil quality. The software also tracks work order data and preventive maintenance tasks. Essentially, eMaint CMMS acts as a central repository for the data required to perform effective fault tree analysis, identifying the root causes of asset failures and figuring out exactly how to improve your maintenance management. The result is greater efficiency and a dramatic reduction in downtime across your organization.

When should fault tree analysis be used?

Fault tree analysis is often carried out during the design phase to check for weaknesses within the system. Maintenance teams, though, typically use fault tree analysis during a system’s operation. It’s a powerful troubleshooting technique which serves to pinpoint the components of a system that are causing failure.

What is the difference between fault tree analysis and failure mode and effects analysis (FMEA)?

While both FTA and FMEA are used to identify and mitigate risks in complex systems, they differ in their approaches. Fault tree analysis is a top-down method that starts with a specific undesirable outcome and works backwards to identify the contributing factors. On the other hand, FMEA is a bottom-up approach that begins by examining individual components and their potential failure modes, then assessing the impact of those failures on the overall system.

What is the difference between fault tree analysis and event tree analysis?

Fault tree analysis and event tree analysis are like two sides of the same coin. Fault tree analysis is a top-down approach, which identifies a failure (top event) and then analyzes the events that led to that failure.

In contrast, event tree analysis starts with an event and then analyzes the potential outcomes of that event.

Both approaches are useful for understanding a system’s failure modes and working to increase reliability.

Can fault tree analysis be used for proactive maintenance planning?

Yes, fault tree analysis can be an integral part of proactive maintenance planning. By identifying potential failure modes and their root causes, maintenance managers can develop targeted preventive maintenance strategies to minimize the likelihood of critical failures, reduce downtime, and extend the life of their assets. Baking FTA insights into actions in your CMMS software can further enhance proactive maintenance planning through automated workflows and data-driven decision-making.