What is Fault Tree Analysis?

Fault Tree Analysis (FTA) has a lot of benefits, it allows you to visually and mathematically represent the system in order to determine the possibility of system or machine failure. It’s a top-down process that reverse-engineers potential failures through the root-cause analysis process. Check out some fault tree analysis examples and history below.

Fault Tree Analysis benefits can help answer the question “How likely is it that this machine will fail to function?”

FTA shows how failures move through a system. This creates a graphic model that shows how system-wide failures can be caused by component failures. These models are used by reliability engineers to create systems that have the right redundancies and prevent component failures from becoming system-wide failures. In other words, it can create fault-tolerant systems.

FTA is a simple process, even though it sounds complicated.

FTA models are modeled using analytical graphs that look like trees. They are therefore called fault tree. A fault tree diagram can help you see how one or more failures can lead to catastrophic failure. This will allow you to choose the best preventive and corrective actions for the future.

Fault Tree Analysis: The History

The fault tree analysis history starts with Bell Telephone Laboratories creating safeguards in 1962 for the intercontinental missile (ICBM), a system that was used by the US air force, the Minuteman Systems. For such a dangerous and complex technology, safety was essential. Bell Laboratories developed the fault tree method to improve reliability analysis.

The new method added a graphic element to help visualize the concepts of Failure Mods and Effects Analysis, a very similar method of preventing failure. Boeing later adopted the Fault Tree Analysis history and it became a widely-used analysis method to evaluate failure potential in critical systems.

This thorough analysis ensures complex systems work safely and reliably. It keeps the planes and cars flying and the world running as efficiently and effectively as possible.

Fault Tree Analysis: When should it be used?

Fault Tree Analysis is done during design or operation to anticipate possible failures and take preventative actions. It is intended to increase the likelihood of subsystem failures or major incidents before they actually happen.

FTA: Who and why?

Fault tree analysis can help prevent future failures and pinpoint critical areas of concern in new products and workflows. FTA is used by many industries for safety analysis and risk mitigation.

• Aerospace, aviation, and defense operations
• Safety of the system and power generation
• Analysis of Cybersecurity System
• Manufacturing of specialty chemicals
• Healthcare and pharmaceuticals
• Disaster management and environmental study

Do you see a pattern? These industries could have a significant impact on the lives of people if something goes wrong. The risk of losing lives or other tragic events occurs when a plane crashes or a medical device malfunctions. FTA is the safety measure used by these industries to protect high-risk activities.

Fault Tree Analysis benefits

The Fault Tree Analysis benefits can be complex and require a lot of math and problem-solving. It is worth learning and applying it in your business. It:

• Assists with the analysis, understanding, and improvement of your systems
• Let’s address each fault one at a time, in a very systematic manner
• An assessment of multiple systems and their relationship to one another
• It is important to focus on the root cause and not the repair.
• Prioritize your repairs based upon failure rates and issues that can lead to catastrophic failures
• This tool helps to plan and design maintenance according to the failure probability for each system.
• Takes human error into account

FTA has all these benefits so it makes sense to add FTA to your analysis toolbox. FTA gives you the ability to predict the future and see the future.

How to Perform Fault Tree Analysis Process

Types of Analysis for Fault Trees

The Standard Fault Tree Analysis is not the only option. For specific industries and use cases, FTA has been extended. These extensions could visualize features that are difficult to express by standard fault trees. These are some of them:

• Dynamic FTA Dynamic Fault Trees: Dynamic fault trees (DFT), which extend existing fault trees, model complex system behaviors and interact with them.
• Repairable FTA – Repairable Fault Trees – Enhance the FTA model with the ability to describe complex dependent repairs to system components.
• Extended : Takes into account multi-state components as well as random probabilities.
• Fuzzy : This complex mathematical concept, called fuzzy set theory, takes into account unreliable variables that are hard to predict (like wind and weather).
• State-event FTA : The SEFT is used to analyze dynamic behavior that fault trees can’t model.

FTAs generally fall under two categories: qualitative or quantitative.

Qualitative analysis must be performed at all times. Quantitative analysis can only be used in cases where you have a good idea of the likelihood of certain events. Let’s look at each one in detail.

Qualitative Fault Tree Analysis

Qualitative fault tree analysis is used to understand the fault tree structure and analyze the system’s vulnerabilities. You can conduct qualitative fault tree analysis in many ways.

• Minimal cut (MCS) helps to identify vulnerabilities in a system. A system that has a low number of components, or a large number of elements with high failure probabilities, would be deemed unreliable. These elements are identified in MCS’s fault tree. You can improve reliability by reducing the likelihood of failure or adding redundancies.
• The Minimal Path Sets (MPS) will help you to determine the system’s strength. This is a method that identifies the minimum number of components necessary to keep the system functioning. Once you have identified the elements, you can work to reduce their failure rate. This improves the system’s reliability.
• Common causes errors (CCF) Determine if multiple elements can cause failures. CCF identifies critical components. Your team must ensure that these components are regularly inspected and replaced if necessary. Limble, a computer-aided maintenance management system (CMMS), can plan and schedule maintenance for these critical components.

Quantitative Fault Tree Analysis

The quantitative FTA method can be used for calculating the probability of failure in the analysis. This will allow you to better understand your risk and prioritize it.

Quantitative FTA may produce stochastic or important measures.

• You can use stochastic measures to determine the likelihood of the system failing.
• Importance Measures indicate the importance of a cut set, path or system to reliability.

Once you have a good idea of the probability of your basic events you can calculate the probabilities for your intermediate events using the gates connecting them. OR gates and AND gates are the most common gates. Here is an example.

Examples of Fault Tree Analysis Process

To help you understand the Fault Tree Analysis process better, here are examples of Fault Tree Analysis from Limble CMMS.

You get up in the morning and prepare for work. You get in your car and turn the key. It won’t start. The car won’t start.

You know a lot about cars so you get out and pop the hood to check the battery. You then check the gas gauge to be sure that you have enough gas. Finally, get back in the car and make sure the lights are on.

The failure of the car starting is called Top Event (TE) in this example. All three possible reasons the car won’t turn on are connected by an OR gate. This means that any combination of them could result in the vehicle not starting.

You can also check for other things that might be causing the battery to fail. Either the battery is worn out and should be replaced or it is flat and requires a jump. Next, you need to find out why the battery is so flat. The next step is to find a way to prevent the headlights from flickering in the future. Before you get out of your car, make sure they are checked.

Let’s say you want to calculate your probability of success. You will need to assign a probability of the event to each event and then use the qualitative FTA technique to calculate the highest chance of failure.

In conclusion

Fault Tree Analysis is not an easy process even though the examples might tell you otherwise. You will feel more able to see the future and predict failures if you have the right team. You will be the one who plans fault repair into scheduled maintenance downtime, and your team will work proactively rather than reactively.

• What is Root Cause Analysis (RCA)?
• Failure Effect
• Failure Modes and Effects Analysis (FMEA)
• Failure Mode
• Failure Modes and Effects Analysis Online Training (Complete with Certification)