Fault Tree Analysis (FTA)

As you know, production is a group of multiple processes. It is natural that there will be defects in a process, or during the design and development of a product, dangerous incidents arising out of the product will be encountered that need to be avoided. It is imperative that managers evaluate such processes or events. And yes, care must also be taken to ensure that the defective product does not reach the customer. Therefore, it is necessary to detect, evaluate and prevent such faulty products, processes, equipment, or incidents. Hence, fault tree analysis (FTA) is a useful tool.


Fault Tree Analysis (FTA)


 what is Fault tree analysis

What is Fault tree analysis (FTA)?

The Fault tree analysis (FTA) is actually a method that makes it easy to analyze the failures of complex systems, especially those using algebraic methods. Which can be called Boolean logic method. In this method, top-down processes solve knots and find the events, processes, or other causes that lead to failure.

"Fault Tree Analysis [FTA] is a graphical / tree formation chart that helps to identify potential failure in processes / system. This systematic tool usually also helpful to determine preventions during design phase and production development."

To effectively use the fault tree analysis feature in the system to eliminate faults and improve processes, take the following steps:

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Provides graphics to analyze a failed system or part of a process in any process. Visual content that identifies unreliable locations and processes that contain faults. which makes it possible to qualitatively or quantitatively analyze the reliability of processes and systems. Specialties are helpful in understanding, analyzing and debugging complex systems.

The Fault Tree Analysis is problem identifier tools using logical method, that helps to bring at mode at event which is responsible for potential failure in system / Processes.

Key Goal: Identifying failure event
Method: Representing Graphic Tree View format to visualize relationship between main system and sub-system.
Usual Symbols: Top Event symbol, OR Gate, And Gate, Basic Event System.

Instant Example:

Imaging if your "Bike does not start" and you wish to identify problem. What you will do next? Using FTA, you can identify failure event.

(A) Use OR Gate: There may be two reasons behind this issue: (1) Electrical Issue (2) Fuel Issue
(B) Use AND Gate, With Electrical fault - there will be two reasons - either cold weather or battery low (or failed) or both
(C) Use OR Gate, With Fuel fault - There will be also two reasons - either empty tank or fuel supply issues or both

Now, you can easily identify where the problem is? This may be helpful.

A simplified method

  1. Step 1. Define an undesirable event.
  2. Step 2. Search for causes
  3. Step 3. Quantitatively analyze and resolve fault trees
  4. Step 4. Consider steps and make improvements.

Whenever a subsystem fails, the main system or other connected systems are adversely affected, resulting in the failure of the main system as well. A particularly complex process group or system has one or more sub-systems that can be understood and corrected through fault tree analysis. So, the question is how to implement this process. Here we will see the general steps of fault tree.

 fault tree analysis method

Step 1. Define an undesirable event.

These steps are particularly focused on the topic. Here, we need to define all failures by placing the failures occurring in the processes at the "top of the tree". If these are fully and accurately determined, the cause of unwanted events and failures can be easily traced.

Look at the picture above there "Figure 1.1" shows - Top undesired event.

Step 2. Search for causes

When you complete the first step does it mean that you have displayed the main subject object, which indicates what is the failure? and where is So that all the immediate causes connected with the incident are easily resolved. Within these steps you can understand how far the analysis boundary is to be displayed. And it becomes easy to define it clearly.

Look in the picture above there it shows "Figure 1.2" - Intermediate event.

Step 3. Quantitatively analyze and resolve fault trees

This step is a type of resolution, where key actions, procedures, methods and basic occurrence probability of the event are analyzed. In fact, this step continues until the underlying causes are identified. Here we can give different levels like "very high", "high", and "low" for analysis of probabilities. Which presents possible sub-events responsible for the higher event.

Look in the picture above there shows "Figure 1.3" - Basic event.

Step 4. Consider steps and make improvements.

A fault tree diagram is actually a logical analysis, which displays the relationships between the events that occurred. But just finding the cause should not be the ultimate goal. Here we have to solve the problem and remove the obstacles. All critical failures that occur must address the root cause and consider actions and solutions to correct failures and deficiencies.

FTA Graphic Symbols

When you create a fault tree analysis, you can use your own graphical symbol that you standardize for your business. But mostly businesses use internationally recognized symbols which are as follows. These graphical symbols are used to understand main, sub-events and causal relationships. Here graphical symbols are of three types, which are event symbols, gate symbols, and transfer symbols. Especially useful are gate symbols, which are considered logical symbols.

  1. Event symbols
  2. Gate symbols
  3. Transfer symbols

fault tree analysis graphic symbols

Event symbols

These types of symbols are used to represent primary and intermediate events. which leads to basic events as a logical gateway to intermediate events. Event symbols represent failures in a key component or element, thus forming the foundation of your tree analysis. These symbols are basically of three types, which are basic event symbols, external event symbols, and conditioning events.

Gate symbols

Actually, gate symbols play an important role in fault tree analysis. These symbols are Boolean logic symbols that describe the relationship between input and output. There are six gate symbols in total here. They are the OR, AND, exclusive OR, priority and gate, and inhibit gate symbols used in FTA. Commonly used symbols are OR gate and AND gate.

Transfer symbols

Symbols of this type are especially used to indicate that inputs and outputs related to fault tree analysis are connected together. You can understand how a sub-system is connected to its main system to represent it.

Example for simple explanation

FTA is really useful when you use it for complex systems and analyze fault events. You can take a straightforward approach to creating this and display a summary of each step.

fault tree analysis example

As seen in the above picture, if a person misses a permanent bus, then doing a fault tree analysis for that, one can find out which root causes are actually responsible for all the incidents.

And yes, one thing to keep in mind is that the FTA model is meant to analyze only one undesirable event, it later leads to some other fundamental event or undesirable event.

First Published On Date: Sunday, March 04, 2018 04:10 AM

Author: ARUN RAVAL | Business & Systems Analyst