Fault Tree Analysis (FTA)

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Fault Tree Analysis (FTA) is a diagnostic and troubleshooting tool used to identify the cause of a problem. FTA helps identify potential causes of an event, and determine how those potential causes might interact to produce the event. This information can then be used to develop solutions to prevent the event from occurring. FTA is commonly used in maintenance and engineering industries, where it can help identify issues before they become costly or hazardous problems. In this post, we will explore what FTA is and how it can be useful for business owners and maintenance technicians.

What is Fault Tree Analysis?

Fault tree analysis is a common tool for engineering, maintenance, and safety analysis. It helps determine the cause of an event by tracing the sequence of events that led to it. This can help with troubleshooting mechanical or electrical systems, as well as improving safety protocols. Also, you can use FTA to identify potential points of failure in a system and mitigate their impact. By understanding how different failures can interact with each other, you can design systems that are more reliable and less likely to experience a catastrophic failure.

Furthermore, a fault tree analysis is helpful by providing a visual representation of the event that led to a failure and the possible pathways that led there. In FTA, a fault tree diagram is used to identify the root cause of an event. Using this process, you can determine the precise root causes of an event by following a logical sequence. It can also provide a better overall picture for maintenance decisions when used in conjunction with FMEA (Failure Mode & Effects Analysis) or another analysis method.

When to Use Fault Tree Analysis

Safety and reliability engineers commonly use fault tree analysis because it is the most efficient way to find flaws. You can use fault tree analysis for a variety of purposes, such as:

  • Identifying the events leading to a machine or system failure
  • Ensuring compliance with safety rules and regulations
  • Optimizing and minimizing maintenance, downtime, and safety costs
  • Supporting system reviews, overhauls, or redesigns

The Components of Fault Tree Analysis

Fault Tree Diagram

In fault tree analysis, events are arranged in a diagram. The framework consists primarily of a flowchart. The diagram helps you trace back to the root cause through logical deductions that start with the failure event.


Fault tree analysis considers events as occurrences in the system. Generally, they can be classified as input events or output events. Input events cause other events, while output events are the results of input events. In a nutshell, events are all the things that have happened or might have happened. Your end result or failure event is the output event, and everything else would be input events.


You will begin building your diagram by using gates to link events. When two input events result in the same output event, an “and” gate is used to connect them. Alternatively, you will use an “or” gate if only one input event results in the output event. For example, you have a lightbulb that goes out. If you find that both the lightbulb was bad and the wiring was defective, you would connect these events using an “and” gate. But, if only the lightbulb was defective, you would connect these events with an “or” gate.

Steps to Perform Your Own FTA

Define Your Top Event

To begin the diagram, let’s ask what specifically went wrong. The clearer your starting point, the smoother the process will be. The following are examples of well-defined top events:

  • The entire building’s electrical system went down.
  • Heat or cold cannot be maintained in the required zones by the HVAC system.
  • A machine’s important part keeps failing.
  • Company regulations have changed and it must comply with them by a certain date.

The process will not work well if the top event is too broad. You will have the best results when you narrowly define your top event.

Get Clarity on the System

Get as much knowledge about the system as you can in this phase. Here are a few examples of questions you might ask:

  • What constitutes the system’s many components? How are these components supposed to work together? How are they actually working together?
  • What kind of malfunction is it? (Mechanical, electrical, hardware, software, etc.)
  • Do you have schematics and boundary diagrams to reference?
  • Do you have code requirements to meet?
  • How practical are the suggested changes?
  • What ideas and viewpoints do your system engineers have?
  • How do systems like these operate?

Finding out how the system operated prior to the top incident and before it became a significant or crippling issue is the goal of this step.

List Potential Causes

Next, you will list the likely causes of the top event. This can be done easily by:

  • Creating five possible causes.
  • Calculating the likelihood that each may have caused the occurrence.
  • Listing the causes in order of probability.

Estimating the failure probability of the system’s or event’s most vulnerable components is another method for doing this. You can get creative with this step and adjust it to your facility’s needs.

Draw Your Fault Tree Diagram

Your fault tree diagram is now ready to be created, whether visually or otherwise. Basically, you list your top event and diagram the several possible causes. When you reach potential root causes, connect each step with “and” or “or” gates. The final product will resemble a flow chart quite closely. It’s crucial to keep in mind that for this fourth step to succeed, the previous steps must be followed closely. Return to the first three steps and make sure you are building on a firm foundation if your diagram is becoming disorganized or clogged.

Risk Assessment

The following step is to give each basic event a level of risk and probability. Again, depending significantly on the first three phases, this can become quite difficult. You can take a few quick actions to more accurately determine the right risk, including:

  • Relying as much as possible on data
  • A future projection of your current data
  • Consult with those who are most knowledgeable about the systems

Risk Mitigation

Taking action to reduce the most likely and high-risk events is the final phase in the process. Again, if the other steps of the procedure have been carried out well, this final one should follow naturally. One of the greatest ways to tell how well your fault tree analysis turned out is whether or not this step organically follows the ones that came before it.

A Useful Tool in Your Root Cause Analysis

Powerful tools, including fault tree analysis, are used in maintenance management and other fields. It offers an adaptable, reproducible method of discovery that is simple to understand and use. Its potency can swiftly rise when combined with other analytical techniques like FMEA and event tree analysis. It does, however, depend on precise data and astute predictions. The entire procedure runs the risk of unraveling if the initial stages are hasty or rushed. While it takes an investment of time to develop a fault tree analysis procedure, you gain great insight into the underlying causes of your problems and preventive measures you can take.

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