Fault Tree Analysis: how to apply it in your industry

Fault Tree Analysis (FTA) seeks to identify hazards and risks based on a chosen event. In other words, the technique aims to establish combinations of faults and conditions that could cause this event to occur.

Therefore, it is defined as deductive and can be qualitative and/or quantitative in nature, with the aim of building a system. This way, the representation (or system) starts from the specific or top event and unfolds it sequentially to map the events that produced it.

What is Fault Tree Analysis for?

FTA is a tool for mapping out possible scenarios. In this way, it helps asset management by documenting possible failures and mapping the probability of occurrence. Thus, combined with the concept of criticality, the manager can make decisions about the choice of maintenance model, for example, among a series of other issues.

Thus, FTA contributes to:

• Understanding how the system can fail.
• Estimating the frequency of accidents.
• Identifying ways to reduce the risk.
• Determining the risks associated with the system.
• Diagnosing the root cause of the failure.

Therefore, mapping serves to increase compliance with safety regulations by providing means to avoid or reduce the risk of possible accidents. In addition, the technique makes it possible to see the relationship between faults and subsystems, as well as the likelihood of these problems occurring. This set of information makes it possible to establish priorities and, as a result, implement changes to the project.

FTA can use concepts of probability and statistics, making it quantitative. In other words, in addition to presenting the logical mapping of the fault, the diagram is also based on percentages and calculations of the probability of occurrence. For this reason, it is one of the most common ways to conduct a probabilistic risk or safety assessment, which is a systematic approach that makes it possible to estimate the risks, the probability of occurrence and the magnitude of the consequences.

How to apply the technique? Root cause analysis

The first step to set up an FTA is to select the event of interest. First, it’s interesting to map out what the common events are in industrial machinery, which could be a heating event, unbalance, and so on.

The next step is to build the subsequent levels or branches, identifying faults that could cause the occurrence in question. At this stage, it is important to map possible failures, whether they are random component failures, common failures, human failures or even equipment unavailability.

FTA makes it possible to calculate the probability of occurrence of basic events, the frequency of which is known and generally available in a database. Based on this information, the diagram can be constructed in a logical sequence.

This type of diagram applies Boolean logic, in which events are linked by logic gates (“and”, “or”). In addition, the structure is made up of symbols representing each of the events that can cause the fault. Here’s an example of the construction:

Fault tree model

In the diagram, failure or “non-function” occurs as a result of the presence of any of the intermediate events or cut sets. In this model, the FTA consists of only two hierarchical levels.

The first hierarchical level is made up of the cut sets, connected to the top event via an “OR” logic gate. In this part of the diagram, if any of the possibilities occur (C1 or C2, in the example) there is the possibility of the next scenario occurring.

The second hierarchical level is made up of the components of each cut set, connected to the first level via a set of “AND” logic gates. Thus, for the cut set to fail, all its components must fail.

For example, the pump can stop if there are any of the following basic undetected events: misalignment, bearing wear, inadequate lubrication, clogging, seal wear, electronic component failure or cavitation. And for any of these events to occur, a combination of factors is required. This is an example of fault tree analysis, which is useful for discovering the cause of an anomaly. The fault tree in the example illustrates how pump failure can result from various undetected conditions. This highlights the importance of predictive maintenance to monitor and identify these potential faults early before they lead to unplanned downtime.

When to use the fault tree in maintenance?

FTA is used to make a probabilistic risk assessment, which is why it is mainly applied in industries or for high-risk assets. As a curiosity, FTA is a method used by NASA in its processes and studies. In fact, it has even published a book on the application of the method in the aerospace sector.  

In the case of industry, and maintenance in particular, FTA has a number of extremely useful applications. For example, when there is an unexpected shutdown, or a fault that almost causes a shutdown, it is important to correct it, of course, but also to analyze what led to the problem. Otherwise, the error will persist.

Thus, fault tree analysis is useful for investigating the problem. This makes it possible to plan maintenance strategies more precisely and to calculate the risk associated with an asset. As a result, it is possible to increase plant availability and reliability.

FTA is a very effective method, but it also has its limitations. That’s why it’s important for asset managers to use complete systems that cover everything from monitoring to making diagnoses based on the data collected. 

In this sense, the Dynamox solution is the best choice for effective and agile management. After all, our sensors and our gateway (Ex-certified) are suitable for high-risk industries and highly critical assets, as they collect data in real time and allow this information to be analyzed on a practical, visual platform.

Learn about Dynamox’s platform and automated diagnosis module:

DynaPredict: Integrated predictive maintenance solution by Dynamox (2023) – YouTube