Contents
This detailed subject guide offers an explanation of the basic concepts in fault tree analysis (FTA) and some other key topics of the field.
What is a Fault Tree Analysis (FTA) - Definition
The fault tree analysis is a deductive process. Developers or engineers use it to find out the root cause or human errors for different types of software, engineering facilities or hardware. It usually starts at a single point (the undesired top-level event) and then goes downwards in the form of a tree (the top-down structure) with a number of blocks and symbols to show the relationship between events (mechanical components). More specifically, the definition of 'Fault' in fault tree analysis indicates the occurrence of an undesired state for a component or system. For example, the light is failed off due to the switch failure as shown below (click on it to see more details).
Furthermore, the term 'Fault' has the following three key types:
History of Fault Tree Analysis
The development of fault tree analysis has the following main stages:
Here is a fault tree analysis example for finding out the cause of aircraft crash. Feel free to click on it to see more information.
Why Use Fault Tree Analysis?
Overall, it offers a well-structured, highly visual and comprehensive picture of your system. It helps users or developers quickly understand the results based on the logical relationships in order to pinpoint drawbacks and errors in the design process. Some other important benefits are:
Fault Tree Analysis and other Analytical Models
Developers often compare the fault tree analysis, the Failure Mode Effects Analysis (FMEA) and the Reliability Block Diagram (RBD):
Relationship with FMEA
Relationship with RBD
Fault Tree Analysis Diagram Symbols
Fault tree analysis has three basic symbol types: events and gates symbols.
Events
This sub-category includes the following shapes:
Gates
These symbols mainly show the relationship between output and input events, and the two most popular ones in this sub-category are OR gate and AND gate.
More Fault Tree Analysis Diagram Symbols
Here you can see more fault tree analysis diagram standard symbols including the transfer type and the line type etc.
How to Undertake a Fault Tree Analysis?
Although the nature of the undesired event may be quite different, fault tree analysis has the same procedure for any types of undesired event. To do a comprehensive fault tree analysis, simply follow the process below:
1. Define and identify the fault condition (hazard) as precisely as possible based on the aspects such as the amount, duration, and related impacts etc.
2. Using technical skills and existing facility details to list and decide all the possible reasons for the failure occurrence.
3. Break down the tree from the top level according to the relationship between different components until you work down to the potential root cause. The structure of your fault tree analysis diagram should be based on the top, middle (subsystems), and the bottom (basic events, component failures) levels.
4. If your analysis involves the quantitative part, evaluate the probability of occurrence for each of the components and calculate the statistical probabilities for the whole tree.
5. Double-check your overall fault tree analysis diagram and implement modifications to the process if necessary.
6. Collect data, evaluate your results in full details by using risk management, qualitative and quantitative analysis to improve your system.
What else Should You Consider When Doing Fault Tree Analysis?
If you want to efficiently undertake or improve your fault tree analysis process or diagram, just have a try for the following tips:
More Free Fault Tree Analysis Templates
The best way to learn fault trees analysis model is to check out some easy fault tree templates. Free feel to click on any of these fault tree templates below to see more details or download them for free.
How to Create a Fault Tree Analysis Diagram?
Creating a fault tree analysis diagram is easier than you think. Just do the following steps:
Step 1: Open a Blank Page
Run the fault tree analysis diagram software, go to Business Diagram, then double-click the Fault Tree Analysis icon to open a blank drawing page. Alternatively, you can directly click a built-in template to start your work.
Step 2: Add Shapes
Drag and drop the fault tree analysis standard symbols on the drawing page, and edit them in suitable sizes to fit your tree structure. You can also explore the built-in library to switch to other kinds of fault tree analysis diagram shapes.
Step 3: Connect Shapes
Select proper connectors to connect shapes. Also feel free to add more connection points on your shapes.
Step 4: Add Text
Open a text block to add details or just double click shapes to add directly. You can also insert supportive materials such us hyperlinks or notes for your shapes.
Step 5: Further Customize Your Shapes
Now you can do a series of formatting for your fault tree analysis diagram, for example, choose a new theme from the built-in themes, change the diagram background, customize the text color and align shapes by clicking the relevant menus.
Step 6: Save, Print and Export Your Work
Click Save on File tab to save as the default format. Choose Saveas on File tab to save as other formats. You can also choose to save in local files or save in the Edraw personal or team Cloud. Hit Export & Send to export your work to many different formats including PowerPoint, JPG, PDF and so on.
FTA Diagram Software Recommendation
Don't know where to start? Simply try the intelligent Edraw Max for drawing your fault tree analysis diagrams on Windows, Mac and Linux. Feel free to use the pre-made fault tree diagram standard symbols and templates based on the drag-and-drop editor and the straightforward user interface. You can also personalize your fault tree analysis diagram by changing the sizes and colors, replace the text with yours to gain a visually appealing diagram. Have a try right now by clicking on the free download button at the end of this page!
Read More:
This detailed subject guide offers an explanation of the basic concepts in fault tree analysis (FTA) and some other key topics of the field.
What is a Fault Tree Analysis (FTA) - Definition
The fault tree analysis is a deductive process. Developers or engineers use it to find out the root cause or human errors for different types of software, engineering facilities or hardware. It usually starts at a single point (the undesired top-level event) and then goes downwards in the form of a tree (the top-down structure) with a number of blocks and symbols to show the relationship between events (mechanical components). More specifically, the definition of 'Fault' in fault tree analysis indicates the occurrence of an undesired state for a component or system. For example, the light is failed off due to the switch failure as shown below (click on it to see more details).
Furthermore, the term 'Fault' has the following three key types:
History of Fault Tree Analysis
The development of fault tree analysis has the following main stages:
Here is a fault tree analysis example for finding out the cause of aircraft crash. Feel free to click on it to see more information.
Why Use Fault Tree Analysis?
Overall, it offers a well-structured, highly visual and comprehensive picture of your system. It helps users or developers quickly understand the results based on the logical relationships in order to pinpoint drawbacks and errors in the design process. Firefox background color. Some other important benefits are:
Fault Tree Analysis and other Analytical Models
Developers often compare the fault tree analysis, the Failure Mode Effects Analysis (FMEA) and the Reliability Block Diagram (RBD):
Relationship with FMEA
Relationship with RBD
Fault Tree Analysis Diagram Symbols
Fault tree analysis has three basic symbol types: events and gates symbols.
Events
This sub-category includes the following shapes:
Gates
These symbols mainly show the relationship between output and input events, and the two most popular ones in this sub-category are OR gate and AND gate.
More Fault Tree Analysis Diagram Symbols
Here you can see more fault tree analysis diagram standard symbols including the transfer type and the line type etc.
How to Undertake a Fault Tree Analysis?
Although the nature of the undesired event may be quite different, fault tree analysis has the same procedure for any types of undesired event. To do a comprehensive fault tree analysis, simply follow the process below:
1. Define and identify the fault condition (hazard) as precisely as possible based on the aspects such as the amount, duration, and related impacts etc.
2. Using technical skills and existing facility details to list and decide all the possible reasons for the failure occurrence.
3. Break down the tree from the top level according to the relationship between different components until you work down to the potential root cause. The structure of your fault tree analysis diagram should be based on the top, middle (subsystems), and the bottom (basic events, component failures) levels.
4. If your analysis involves the quantitative part, evaluate the probability of occurrence for each of the components and calculate the statistical probabilities for the whole tree.
5. Double-check your overall fault tree analysis diagram and implement modifications to the process if necessary.
6. Collect data, evaluate your results in full details by using risk management, qualitative and quantitative analysis to improve your system.
What else Should You Consider When Doing Fault Tree Analysis?
If you want to efficiently undertake or improve your fault tree analysis process or diagram, just have a try for the following tips:
More Free Fault Tree Analysis Templates
The best way to learn fault trees analysis model is to check out some easy fault tree templates. Free feel to click on any of these fault tree templates below to see more details or download them for free.
How to Create a Fault Tree Analysis Diagram?
Creating a fault tree analysis diagram is easier than you think. Just do the following steps:
Step 1: Open a Blank Page
Run the fault tree analysis diagram software, go to Business Diagram, then double-click the Fault Tree Analysis icon to open a blank drawing page. Alternatively, you can directly click a built-in template to start your work.
Step 2: Add Shapes
Drag and drop the fault tree analysis standard symbols on the drawing page, and edit them in suitable sizes to fit your tree structure. You can also explore the built-in library to switch to other kinds of fault tree analysis diagram shapes.
Step 3: Connect Shapes
Select proper connectors to connect shapes. Also feel free to add more connection points on your shapes.
Step 4: Add Text
Open a text block to add details or just double click shapes to add directly. You can also insert supportive materials such us hyperlinks or notes for your shapes.
Step 5: Further Customize Your Shapes
Now you can do a series of formatting for your fault tree analysis diagram, for example, choose a new theme from the built-in themes, change the diagram background, customize the text color and align shapes by clicking the relevant menus.
Step 6: Save, Print and Export Your Work
Click Save on File tab to save as the default format. Choose Saveas on File tab to save as other formats. You can also choose to save in local files or save in the Edraw personal or team Cloud. Hit Export & Send to export your work to many different formats including PowerPoint, JPG, PDF and so on.
FTA Diagram Software Recommendation
Don't know where to start? Simply try the intelligent Edraw Max for drawing your fault tree analysis diagrams on Windows, Mac and Linux. Feel free to use the pre-made fault tree diagram standard symbols and templates based on the drag-and-drop editor and the straightforward user interface. You can also personalize your fault tree analysis diagram by changing the sizes and colors, replace the text with yours to gain a visually appealing diagram. Have a try right now by clicking on the free download button at the end of this page!
Read More:
When it comes to analysis of different systems, at the present times, there are a number of ways through which the developers can be able to assess their performance. One of the most effective and proven ways is through the use of fault tree analysis or FTA in short. To be able to enjoy the use of this system of system analysis, there is a need to download a fault tree analysis software.
Related:Open FTA
Open FTA is a fault tree analysis software which is open source application that is free to use. Also, other software developers can develop better versions of the software using its source code using the GNU license. The software is pretty advanced and offers great features that ensure an easier time. How to select multiple files on windows 7 1.
Fault Tree Analyser
Fault Tree Analyser is a fault tree analysis software which is a free download that will allow you to generate your fault tree with ease. The software is free and with cutting edge features making it suitable for a wide variety of applications. The application is web based and thus does not require to be installed.
Fault Tree Analysis
Fault Tree Analysis by Isograph is a powerful application that is premium based though it offers the ability for having a free trial. The software comes with complex algorithms that enable it to perform complex tasks and in an accurate manner. The software can also handle event tree analysis.
FTA
FTA offers an intuitive interface that makes the process of establishing faults on a system rather easy as well as effective. The software is easy to use and at the same time regularly updated to match up the recent trends. At the same time, the software integrates a safety analysis module.
Other Platform
The software in this category does not need to be installed in a computer system, there is still a substantial number that is dependent. This makes it essential to look at the platforms that they support to avoid downloading of unsupported applications.
Fault Tree for Windows
Fault Tree is a Windows based application that is designed to make it possible for the users of this platform to access a system analysis software. With this software, you will be able to deduct several time phases to a single event. In addition, there is the ability to create new projects from existing data.
ConceptDraw for Mac
ConceptDraw is a great failure analysis software for both simple and complex projects. The software is powerful and at the same time quite resourceful. It comes with samples from which the user can be able to get inspiration on the project that they have beforehand and thus making it easy to use.
Most Popular Software for 2016 â Fault Tree Software
Fault Tree Software is a leading application in this category both on the number of users as well as the features presents. With this, you will be able to create FTA diagrams in a very short time from the available templates. The software makes diagrams that are easy to read. You can also see Mind Mapping Software
What is Fault Tree Analysis Software?
A fault tree analysis software is a computer based application that helps developers and designers of systems in deducting faults on their systems. The software in this category makes use of Boolean equations to check for the challenges available in a system. They deploy a top-down approach so that errors in a system can be able to establish at their root and thus offering a holistic approach. You can also see Graph Editor Software
The solutions presented by the software in this category is quite diverse though their principle of operations ease and convenience of use may differ considerably.For any category of software, there is usually a large collection of applications that are at the disposal of the users and in this category the case is no different. The above software are some of the best in this category that can be recommended for download based on their features.
Related Posts
A fault tree diagram
Fault tree analysis (FTA) is a top-down, deductive failure analysis in which an undesired state of a system is analyzed using Boolean logic to combine a series of lower-level events. This analysis method is mainly used in the fields of safety engineering and reliability engineering to understand how systems can fail, to identify the best ways to reduce risk or to determine (or get a feeling for) event rates of a safety accident or a particular system level (functional) failure. FTA is used in the aerospace,[1]nuclear power, chemical and process,[2][3][4]pharmaceutical,[5]petrochemical and other high-hazard industries; but is also used in fields as diverse as risk factor identification relating to social service system failure.[6] FTA is also used in software engineering for debugging purposes and is closely related to cause-elimination technique used to detect bugs.
In aerospace, the more general term 'system failure condition' is used for the 'undesired state' / top event of the fault tree. These conditions are classified by the severity of their effects. The most severe conditions require the most extensive fault tree analysis. These system failure conditions and their classification are often previously determined in the functional hazard analysis.
Fault Tree Analysis Template Online
Usage[edit]
Fault tree analysis can be used to:
History[edit]
Fault tree analysis (FTA) was originally developed in 1962 at Bell Laboratories by H.A. Watson, under a U.S. Air ForceBallistics Systems Division contract to evaluate the Minuteman IIntercontinental Ballistic Missile (ICBM) Launch Control System.[7][8][9][10] The use of fault trees has since gained widespread support and is often used as a failure analysis tool by reliability experts.[11] Following the first published use of FTA in the 1962 Minuteman I Launch Control Safety Study, Boeing and AVCO expanded use of FTA to the entire Minuteman II system in 1963-1964. FTA received extensive coverage at a 1965 System Safety Symposium in Seattle sponsored by Boeing and the University of Washington.[12] Boeing began using FTA for civil aircraft design around 1966.[13][14]
Subsequently, within the U.S. military, application of FTA for use with fuzes was explored by Picatinny Arsenal in the 1960s and 1970s.[15] In 1976 the U.S. Army Materiel Command incorporated FTA into an Engineering Design Handbook on Design for Reliability.[16] The Reliability Analysis Center at Rome Laboratory and its successor organizations now with the Defense Technical Information Center (Reliability Information Analysis Center, and now Defense Systems Information Analysis Center[17]) has published documents on FTA and reliability block diagrams since the 1960s.[18][19][20] MIL-HDBK-338B provides a more recent reference.[21]
In 1970, the U.S. Federal Aviation Administration (FAA) published a change to 14 CFR 25.1309 airworthiness regulations for transport categoryaircraft in the Federal Register at 35 FR 5665 (1970-04-08). This change adopted failure probability criteria for aircraft systems and equipment and led to widespread use of FTA in civil aviation. In 1998, the FAA published Order 8040.4,[22] establishing risk management policy including hazard analysis in a range of critical activities beyond aircraft certification, including air traffic control and modernization of the U.S. National Airspace System. This led to the publication of the FAA System Safety Handbook, which describes the use of FTA in various types of formal hazard analysis.[23]
Early in the Apollo program the question was asked about the probability of successfully sending astronauts to the moon and returning them safely to Earth. A risk, or reliability, calculation of some sort was performed and the result was a mission success probability that was unacceptably low. This result discouraged NASA from further quantitative risk or reliability analysis until after the Challenger accident in 1986. Instead, NASA decided to rely on the use of failure modes and effects analysis (FMEA) and other qualitative methods for system safety assessments. After the Challenger accident, the importance of probabilistic risk assessment (PRA) and FTA in systems risk and reliability analysis was realized and its use at NASA has begun to grow and now FTA is considered as one of the most important system reliability and safety analysis techniques.[24]
Within the nuclear power industry, the U.S. Nuclear Regulatory Commission began using PRA methods including FTA in 1975, and significantly expanded PRA research following the 1979 incident at Three Mile Island.[25] This eventually led to the 1981 publication of the NRC Fault Tree Handbook NUREGâ0492,[26] and mandatory use of PRA under the NRC's regulatory authority.
Following process industry disasters such as the 1984 Bhopal disaster and 1988 Piper Alpha explosion, in 1992 the United States Department of LaborOccupational Safety and Health Administration (OSHA) published in the Federal Register at 57 FR 6356 (1992-02-24) its Process Safety Management (PSM) standard in 19 CFR 1910.119.[27] OSHA PSM recognizes FTA as an acceptable method for process hazard analysis (PHA).
Today FTA is widely used in system safety and reliability engineering, and in all major fields of engineering.
Methodology[edit]
FTA methodology is described in several industry and government standards, including NRC NUREGâ0492 for the nuclear power industry, an aerospace-oriented revision to NUREGâ0492 for use by NASA,[24]SAEARP4761 for civil aerospace, MILâHDBKâ338 for military systems, IEC standard IEC 61025[28] is intended for cross-industry use and has been adopted as European Norm EN 61025.
Any sufficiently complex system is subject to failure as a result of one or more subsystems failing. The likelihood of failure, however, can often be reduced through improved system design. Fault tree analysis maps the relationship between faults, subsystems, and redundant safety design elements by creating a logic diagram of the overall system.
The undesired outcome is taken as the root ('top event') of a tree of logic. For instance the undesired outcome of a metal stamping press operation is a human appendage being stamped. Working backward from this top event we might determine there are two ways this could happen: during normal operation or during maintenance operation. This condition is a logical OR. Considering the branch of occurring during normal operation perhaps we determine there are two ways this could happen: the press cycles and harms the operator or the press cycles and harms another person. This is another logical OR. We can make a design improvement by requiring the operator to press two buttons to cycle the machineâthis is a safety feature in the form of a logical AND. The button may have an intrinsic failure rateâthis becomes a fault stimulus we can analyze. When fault trees are labeled with actual numbers for failure probabilities, computer programs can calculate failure probabilities from fault trees. When a specific event is found to have more than one effect event, i.e. it has impact on several subsystems, it is called a common cause or common mode. Graphically speaking, it means this event will appear at several locations in the tree. Common causes introduce dependency relations between events. The probability computations of a tree which contains some common causes are much more complicated than regular trees where all events are considered as independent. Not all software tools available on the market provide such capability.
The tree is usually written out using conventional logic gate symbols. A cut set is a combination of events, typically component failures, causing the top event. If no event can be removed from a cut set without causing the top event, then it is called a minimal cut set.
Some industries use both fault trees and event trees (see Probabilistic Risk Assessment). An event tree starts from an undesired initiator (loss of critical supply, component failure etc.) and follows possible further system events through to a series of final consequences. As each new event is considered, a new node on the tree is added with a split of probabilities of taking either branch. The probabilities of a range of 'top events' arising from the initial event can then be seen.
Classic programs include the Electric Power Research Institute's (EPRI) CAFTA software, which is used by many of the US nuclear power plants and by a majority of US and international aerospace manufacturers, and the Idaho National Laboratory's SAPHIRE, which is used by the U.S. Government to evaluate the safety and reliability of nuclear reactors, the Space Shuttle, and the International Space Station. Outside the US, the software RiskSpectrum is a popular tool for fault tree and event tree analysis, and is licensed for use at almost half of the world's nuclear power plants for probabilistic safety assessment. Professional-grade free software is also widely available; SCRAM[29] is an open-source tool that implements the Open-PSA Model Exchange Format[30] open standard for probabilistic safety assessment applications.
Graphic symbols[edit]
The basic symbols used in FTA are grouped as events, gates, and transfer symbols. Minor variations may be used in FTA software.
Event symbols[edit]
Event symbols are used for primary events and intermediate events. Primary events are not further developed on the fault tree. Intermediate events are found at the output of a gate. The event symbols are shown below:
The primary event symbols are typically used as follows:
An intermediate event gate can be used immediately above a primary event to provide more room to type the event description.
FTA is a top-to-bottom approach.
Gate symbols[edit]
Gate symbols describe the relationship between input and output events. The symbols are derived from Boolean logic symbols:
The gates work as follows:
Transfer symbols[edit]
Transfer symbols are used to connect the inputs and outputs of related fault trees, such as the fault tree of a subsystem to its system. NASA prepared a complete document about FTA through practical incidents.[24]
Basic mathematical foundation[edit]
Events in a fault tree are associated with statisticalprobabilities. For example, component failures may typically occur at some constant failure rate λ (a constant hazard function). In this simplest case, failure probability depends on the rate λ and the exposure time t:
A fault tree is often normalized to a given time interval, such as a flight hour or an average mission time. Event probabilities depend on the relationship of the event hazard function to this interval.
Unlike conventional logic gate diagrams in which inputs and outputs hold the binary values of TRUE (1) or FALSE (0), the gates in a fault tree output probabilities related to the set operations of Boolean logic. The probability of a gate's output event depends on the input event probabilities.
An AND gate represents a combination of independent events. That is, the probability of any input event to an AND gate is unaffected by any other input event to the same gate. In set theoretic terms, this is equivalent to the intersection of the input event sets, and the probability of the AND gate output is given by:
An OR gate, on the other hand, corresponds to set union:
Since failure probabilities on fault trees tend to be small (less than .01), P (A â© B) usually becomes a very small error term, and the output of an OR gate may be conservatively approximated by using an assumption that the inputs are mutually exclusive events:
An exclusive OR gate with two inputs represents the probability that one or the other input, but not both, occurs:
Again, since P (A â© B) usually becomes a very small error term, the exclusive OR gate has limited value in a fault tree.
Analysis[edit]
Many different approaches can be used to model a FTA, but the most common and popular way can be summarized in a few steps. A single fault tree is used to analyze one and only one undesired event or top event, which may be subsequently fed into another fault tree as a basic event. Though the nature of the undesired event may vary dramatically, a FTA follows the same procedure for any undesired event; be it a delay of 0.25 ms for the generation of electrical power, an undetected cargo bay fire, or the random, unintended launch of an ICBM. Due to labor cost, FTA is normally only performed for more serious undesired events.
FTA analysis involves five steps:
Comparison with other analytical methods[edit]
FTA is a deductive, top-down method aimed at analyzing the effects of initiating faults and events on a complex system. This contrasts with failure mode and effects analysis (FMEA), which is an inductive, bottom-up analysis method aimed at analyzing the effects of single component or function failures on equipment or subsystems. FTA is very good at showing how resistant a system is to single or multiple initiating faults. It is not good at finding all possible initiating faults. FMEA is good at exhaustively cataloging initiating faults, and identifying their local effects. It is not good at examining multiple failures or their effects at a system level. FTA considers external events, FMEA does not.[32] In civil aerospace the usual practice is to perform both FTA and FMEA, with a failure mode effects summary (FMES) as the interface between FMEA and FTA.
Alternatives to FTA include dependence diagram (DD), also known as reliability block diagram (RBD) and Markov analysis. A dependence diagram is equivalent to a success tree analysis (STA), the logical inverse of an FTA, and depicts the system using paths instead of gates. DD and STA produce probability of success (i.e., avoiding a top event) rather than probability of a top event.
See also[edit]
References[edit]
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