Fault Tree Analysis

10 Key excerpts on "Fault Tree Analysis"

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  eBook - ePub

  Hazard Analysis Techniques for System Safety

  • Clifton A. Ericson, II(Authors)
  • 2015(Publication Date)
  • Wiley

    (Publisher)

  Chapter 15 Fault Tree Analysis

  15.1 FTA Introduction

  Fault Tree Analysis (FTA) is a systems analysis technique used to determine the root causes and probability of occurrence of a specified undesired event. FTA is employed to evaluate large complex dynamic systems, in order to understand and prevent potential problems. Using a rigorous and structured methodology, FTA allows the systems analyst to model the unique combinations of fault events that can cause an undesired event to occur. The undesired event may be a system hazard of concern or a mishap that is under accident investigation.

  A Fault tree (FT) is a model that logically and graphically represents the various combinations of possible events, faulty and normal, occurring in a system that can lead to an undesired event or state. The analysis is deductive, in that it transverses from the general problem to the specific causes. The FT develops the logical fault paths from a single undesired event at the top to all of the possible root causes at the bottom. The strength of FTA is that it is easy to perform, easy to understand, provides useful system insight, and shows all the possible causes for a problem under investigation.

  FTs are graphical models using logic gates and fault events to model the cause–effect relationships involved in causing the undesired event. The graphical model can be translated into a mathematical model to compute failure probabilities and system importance measures. FT development is an iterative process, where the initial structure is continually updated to coincide with design development.

  In the analysis of systems, there are two applications of FTA. The most commonly used application is the proactive FTA, performed during system development to influence design by predicting and preventing future problems. The other application is the reactive FTA

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  eBook - ePub

  Aircraft System Safety

  Assessments for Initial Airworthiness Certification

  • Duane Kritzinger(Author)
  • 2016(Publication Date)
  • Woodhead Publishing

    (Publisher)

  4

  Fault Tree Analysis

  Abstract

  Any sufficiently complex system is subject to failure as a result of one or more subsystems failing. The aim of the Fault Tree Analysis (FTA) is to use deductive logic to understand all the underlying causes of a particular failure so that the likelihood of failure can be reduced through improved system design.

  Keywords

  Basic events; Common cause factors; Cut set; Deductive logic; Development assurance; Failure probability; Fault Tree Analysis; Functional independence; Gates; Human hazard; Item development independence; Model; MTBF; Reliability; Safety targets; Single point failure; System architecture; Validating; Verification

  The greatest of faults, I should say, is to be conscious of none. Thomas Carlyle (1795–1881)

  4.1. Introduction

  A system is a collection of components in a defined architecture with the sole purpose of accomplishing that system’s function (refer to Fig. 3.1 ). The functional failure probability of that function is determined by the integrity of the constituent components as well as the logic of the systems’ architecture. The more complex the system, the more there is a need for an in-depth analysis technique to identify all possible combinations of failure that could result in loss of the system’s integrity. The Fault Tree Analysis (FTA) is such a technique. A fault tree1 shows graphically, by means of a specified notation, the logical relationship between a particular system failure and all its contributing causes.

  This chapter considers the manner in which an FTA is used to show how an undesirable top-level failure (or event) may occur via the combination(s) of individual contributing failures, events and/or errors. In doing so, this chapter provides a simple process (in Fig. 4.1 ) on how to approach and manage the FTA process. The reader is encouraged to review the reference material for more specialist details on the intricacies of drawing an actual fault tree.

  4.1.1. Background

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  eBook - PDF

  System Safety Engineering and Risk Assessment

  A Practical Approach, Second Edition

  • Nicholas J. Bahr(Author)
  • 2018(Publication Date)
  • CRC Press

    (Publisher)

  205 7 Fault Tree Analysis Don’t meet troubles halfway. Sixteenth-century proverb Dig a well before you are thirsty. Chinese proverb Nothing is so easy as to deceive one’s self; for what we wish, that we readily believe. Orations, Vol. 1 , 349 BCE Demosthenes Fault Tree Analysis (FTA) is a graphical method commonly used in both reliability engineering and system safety engineering (though it is more well known in reliabil-ity circles). It is a deductive approach that is very powerful as a qualitative analysis tool that can be quantified. You postulate a top event—or fault—such as train derail-ment, then branch down from the top event, listing the faults in the system that must occur for the top event to occur. This top-down method forces you to go through systematically, listing the various sequential and parallel events or combinations of faults that must occur for the undesired top event. Logic gates and standard Boolean algebra allow you to quantify the fault tree with event probabilities and thus deter-mine the probability of the top event. It is important to understand that this is not a model of all possible system failures or all possible causes, but rather, a model of particular system failure modes and their constituent faults that lead to the top event. Not all system or component fail-ures are listed, only the ones leading to the top event. Like the other safety analysis techniques discussed previously, only credible faults are assessed. The faults can be events associated with component hardware failures, software glitches, human errors, and environmental conditions—in short, any of the elements that make up the complete system. The fault tree was first developed in 1961 for the U.S.

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  eBook - ePub

  Design for Safety

  • Louis J. Gullo, Jack Dixon(Authors)
  • 2017(Publication Date)
  • Wiley

    (Publisher)

  While FTA is included here as a hazard analysis tool, it really is a root cause analysis tool since it is used to determine the cause of a hazard, or undesirable event, that has been identified by some other hazard analysis technique. It is an important and much used technique. FTA can be used to evaluate an identified hazard or to analyze an accident. It is also used in reliability analysis.

  9.2 What Is a Fault Tree?

  A fault tree is a representation in tree form of the combination of causes (failures, faults, errors, etc.) contributing to a particular undesirable event. It uses symbolic logic to create a graphical representation of the combination of failures, faults, and errors that can lead to the undesirable event being analyzed. The purpose of FTA is to identify the combinations of failures and errors that can result in the undesirable event. The fault tree allows the analyst to focus resources on the most likely and most important basic causes of the top event.

  Paradigm 4: Prevent Accidents from Single and Multiple Causes

  FTA is a deductive (top‐down) analysis technique that focuses a particular undesirable event and is used to determine the root causes contributing to the occurrence of the undesirable event. The process starts with identifying an undesirable event (top event) and working backward through the system to determine the combinations of component failures that will cause the top event.

  Using Boolean algebra, the fault tree can be “solved” for all the combinations of basic events that can cause the top event. This results in a qualitative analysis of the fault tree. The fault tree can also be used as a quantitative analysis tool. In this case, failure rates or probability of occurrence values are assigned to the basic events, and the probability of the occurrence of the top level, undesirable event can be calculated.

  9.2.1 Gates and Events

  Logical gates are used, along with basic events, to create the fault tree. The standard symbols used in the construction of fault trees and the descriptions of these symbols are shown in Figure 9.1

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  Available until 16 May |Learn more

  The Certified Reliability Engineer Handbook

  • Mark Allen Durivage(Author)
  • 2017(Publication Date)
  • ASQ Quality Press

    (Publisher)

  44 Risk analysis techniques such as Fault Tree Analysis (FTA), success tree analysis (STA), risk matrix, hazard analysis, failure modes and effects analysis (FMEA), failure modes, effects, and criticality analysis (FMECA), common mode failure analysis, and system safety are used to quantify and manage risk. These tech- niques can be used to estimate the risk associated with various events. It then becomes possible to establish a prioritized list that will provide guidance as the root causes are addressed and mitigated or eliminated. Risk analysis and risk management are becoming increasingly emphasized as product and processes become more complex. For example, ISO 9001:2015 Quality Management Systems includes the integration of risk-based thinking as part of the quality management system and decision-making processes. 1. Fault Tree Analysis (FTA) Use Fault Tree Analysis (FTA) techniques to evaluate product or process failure. (Analyze) Body of Knowledge II.B.1 Fault Tree Analysis is a “top down” approach that is used to identify the cause, causes, or combinations of causes of failures. FTA utilizes symbols from the elec- tronic and logic fields. FTA can be performed without regard to the likelihood of occurrence of the event or cause, known as a qualitative Fault Tree Analysis. FTA can be combined with probability techniques, failure rate analyses, and other relevant quantitative reli- ability data to better estimate the probability of failure and to prioritize actions, known as a quantitative Fault Tree Analysis. FTA can be used to analyze complex systems including electronic, mechanical, and software elements and the interaction and interface of subsystems. Chapter 4 B. Analysis Part II.B.1 Chapter 4 B. Analysis 45 Part II.B.1 AND and OR Gates The primary symbols used in FTA are the AND gate and the OR gate. Each of these has at least two inputs and a single output (see Figure 4.1). The output for the AND gate occurs if and only if all inputs occur.

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  eBook - ePub

  Risk Assessment

  Tools, Techniques, and Their Applications

  • Lee T. Ostrom, Cheryl A. Wilhelmsen(Authors)
  • 2019(Publication Date)
  • Wiley

    (Publisher)

  Chapter 14 Basic Fault Tree Analysis Technique

  The Fault Tree Analysis (FTA) technique is proven to be an effective tool for analyzing and identifying areas for hazard mitigation and prevention while in the planning phase or anytime a systematic approach to risk assessment is needed. FTA is used as an integral part of a probabilistic risk assessment. In this chapter we will cover the very basics of FTA. The NASA Fault Tree Handbook with Aerospace Applications (1 ) is a complete guide to FTA.

  14.1 History

  Knowledge of the history of the need for FTA is useful for understanding the simple yet powerful potential of the tool. This history begins with the inception of mechanical vehicles. One common problem that plagued vehicles was malfunction and failures caused by “little things.”

  Steam engines blew up when pressure relief valves stuck closed. Early autos scattered parts across the countryside as nuts and bolts separated. Airplanes fell to earth because poorly designed fittings tore apart. Always it was the little things that failed and set up potentially deadly chain reactions.

  Despite major advances in design and manufacturing techniques, significant numbers of accidents and failures continued to occur. Airplane accidents, attributable to training, accounted for over one‐third of the losses during the WWII years 1941–1945. Over 14 000 major accidents were recorded in the United States alone.

  Often, the airplane accidents were attributed to “pilot error.” However, the majority of crashes should have been linked to a malfunction of little things…a failed hydraulic pump…a broken feathering stop…a missing lock nut.

  As technology became more exotic, technological advances exceeded the average skill level for operation and maintenance of advanced air vehicles. Because of the complexity of systems, nuts and bolts errors became even more frequent. An improvement in safety analysis was needed.

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  eBook - PDF

  Reliability and Physics-of-Healthy in Mechatronics

  • Abdelkhalak El Hami, David Delaux, Henri Grzeskowiak(Authors)
  • 2022(Publication Date)
  • Wiley-ISTE

    (Publisher)

  A review of some of the important aspects and related improvements that have been made to the FTA methodology since its introduction is considered next before looking at the detail of the model-based approach, followed by a brief review of the relationship between the approach and other engineering tools such as FMEA. Chapter written by Felician CAMPEAN and Ed HENSHALL. 142 Reliability and Physics-of-Healthy in Mechatronics 3.1.1. Background to Fault Tree Analysis Fault Tree Analysis (FTA) was first developed by Bell Laboratories in 1962 as a graphically based technique for safety analysis on the Minuteman weapon system (Lee et al. 1985). Since its inception, the methodology has gained widespread use across many industries. The methodology links a particular system failure top-down through Boolean gates to multiple potential failure events. It is used to improve the reliability, maintainability and safety of complex systems through top-down root cause analysis where the potential or actual causes of failure that occur, either in isolation or inclusively, are not all immediately obvious. The identification of such causes enables system design improvement. FTA is also widely used to predict the reliability of system design where the probability of the failure events that can lead to system failure is known or can be estimated. Significant effort has been directed at improving the FTA methodology since its inception with a major focus of such work being directed towards improving the integrity of system reliability prediction using fuzzy logic (i.e. fuzzy set theory) when quantifying component failure rates (Nadjafi 2021; Yazdi and Zarei 2018). In recognition that most systems are dynamic, that is, exhibit time-dependent behavior, the original static FTA methodology has been extended to cope with dynamic systems, for example, through the introduction of additional logic gates featuring time dependency (Dugan 1992).

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  eBook - PDF

  Reliability Analysis and Prediction

  A Methodology Oriented Treatment

  • K.B. Misra(Author)
  • 2012(Publication Date)
  • Elsevier Science

    (Publisher)

  8 SYSTEM ANALYSIS THROUGH FAULT TREES 8.0 Introduction Reliability and safety analyses, particularly, of complex and high-risk systems like nuclear plants, large chemical plants, space vehicles, etc. have assumed ever-increasing importance in recent years, particularly after two major accidents in the history of nuclear power generation, viz., TMI-2, in the U.S.A on March 28, 1979 and more recently Chernobyl-4 in the U.S.S.R. on April 26, 1986. A single large catastrophe in the annals of safety of chemical plants, i.e., release of large amount of toxic gas in Union Carbide factory at Bhopal, India on December 3, 1984 resulting in the death of several thousand people and failure of Challenger causing loss of millions of dollars and loss of precious lives of astronauts have both shaken the confidence of reliability and safety analyst and the people at large. Although for these systems, the techniques presented in earlier chapters can also be used adequately, Fault Tree Analysis (FTA) offers a comparatively simple, new and very powerful approach for reliability and safety analyses under the most general frame of assumptions for such high risk and high tech systems which have far-reaching consequences. The FTA is an event-oriented analysis in contrast to the reliability models discussed in earlier chapters, which were structure-oriented and allowed only hardware failure considerations. The advantage of event-oriented methods is that we can consider not only hardware failures (as in earlier chapters) but also any undesirable events that may occur on account of software failure, human errors, operation and maintenance errors and environmental influences on the system. Another basic difference between the techniques used in earlier chapters and the fault tree methodology is : while the former use success frame of consideration, the latter works on the failure frame of consideration.

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  eBook - ePub

  Safety Risk Management for Medical Devices

  • Bijan Elahi(Author)
  • 2018(Publication Date)
  • Academic Press

    (Publisher)

  Chapter 12

  Risk Analysis Techniques

  Abstract

  Identification of hazards for risk analysis can be done using various tools. Two of the most common tools are Fault Tree Analysis (FTA) and Failure Modes and Effects Analysis (FMEA). In this chapter three types of FMEA are discussed: DFMEA, PFMEA, and UMFMEA. Additionally, two other tools are presented: Mind Map Analysis and P-Diagram. Ultimately it is the analyst's choice on how many tools to use. While extra analyses consume more resources, they also reduce the likelihood of missing some Hazards and their causal chains.

  Keywords

  Fault Tree Analysis; FTA; Failure Modes and Effects Analysis; FMEA; DFMEA; PFMEA; UMFMEA; Mind Map Analysis; P-Diagram

  12.1 Fault Tree Analysis

  12.1.1 Introduction

  The Fault Tree Analysis (FTA) technique was developed by Bell Labs in 1962 for use on the Minuteman missile system. Later it gained wide use in civil aviation, space, and military applications. MIL-HDBK-338B published in 1998 provides a reference for this technique. After the 1979 incident at Three Mile Island, the Nuclear Regulatory Commission expanded the use of FTA and published NUREG-0492—Fault Tree Handbook in 1981. This handbook was later updated by NASA in 2002 with the title Fault Tree Handbook with Aerospace Applications [24] .

  FTA is a deductive top-down reasoning process that starts from the undesired system outcomes and attempts to find out all the credible sequences of events that could result in the undesired system outcomes. The fault tree is a graphical model that depicts the logical relationships among the parallel and sequential combination of events that could lead into the event at the top of the tree.

  FTA can model both normal and fault conditions, under various environmental and operational scenarios. FTA can also identify and model fault dependencies, and common cause failures (CCFs).

  Fault Trees (FTs) are constructed using logic gates, such as AND and OR gates. As such, FTs lend themselves to logical simplification and reduction. Therefore there is not just one correct FT to describe a system, but potentially multiple logically equivalent FTs.

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  eBook - PDF

  System Reliability Theory

  Models, Statistical Methods, and Applications

  • Marvin Rausand, Anne Barros, Arnljot Hoyland(Authors)
  • 2020(Publication Date)
  • Wiley

    (Publisher)

  The assumptions should be recorded in a separate file and integrated in the report from the analysis. The lowest level of resolution in the fault tree in Figure 4.12 is a failure mode of a technical item. Some of these items are rather complicated, and it might be of interest to break them down into subitems and attribute failures to these. The valves may, for example be broken down into valve body and actuator. These subitems may again be broken down to sub-subitems, and so on. The failure of the pressure switches to give signal may be split into two parts, individual failures and common cause failures that cause both pressure switches to fail at the same time. A pressure switch may fail due to an inherent component failure, or due to miscalibration by the maintenance crew. How far we should proceed depends on the objective of the analysis. Anyway, the assumptions made should be recorded. ◻ 4.3.7 Dynamic Fault Trees A dynamic fault tree (DFT) extends the traditional fault tree by taking certain dynamic effects into account. A typical dynamic effect occurs when the output event of a gate depends not only on the logical combination of its input events but also on the order in which all the input events occur. To cater for relevant dynamic effects, several new gates have to be introduced in addition to the AND and OR gates. An example of such an effect occurs when a specific event (called a trigger) occurs and causes otherwise independent events to occur at (almost) the same time. The trigger event may, for example be a control system failure or a power failure.

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