Fault Tree Analysis

NEBOSH National Diploma - Unit A | Managing Health and Safety Fault Tree Analysis (FTA) and Event Tree Analysis (ETA) It is easy to get confused between these two techniques. Indeed, the two are in fact complimentary (and are often used together) but focus on opposite sides of an undesired event. The diagram below shows how they fit together:

83 trees. However, the approach is theoretically sound for application to other types of fault trees. Further studies should be conducted in the future to ensure that the approach can successfully integrate with more complicated versions of fault tree analysis. In the future, the calculation of overall negative consequence probabilities across levels of severity could be augmented by applying weighting factors to the individual levels of severity as part of the calculation. This method would allow for easier tradeoff evaluations. The need for this compilation of negative consequence probability was further supported by the recommendation of a Safety expert, who participated in the evaluation study. Aside from the expansion of the new CSP application, the current software prototype needs to be developed into a fully functional software application with reference to the list of design features recommended by Human Factor experts (Fig. 3-1) and continuous interface improvements as recommended by the Safety experts, who participated in the evaluation study.

Fault tree analysis (FTA) is a method that describes all possible causes of a specified system state in terms of the state of the components within the system. A system model is used to identify the states that the system should be in at any point in time. This paper presents a method for diagnosing faults in systems using FTA to explain the deviations from normal operation observed in sensor outputs. The causes of a system’s failure modes will be described in terms of the component states. This will be achieved with the use of coherent and non-coherent fault trees. A coherent fault tree is constructed from AND and OR logic and therefore considers only component-failed states. The non-coherent method expands this, allowing the use of NOT logic, which implies that the existence of component-failed states and component-working states are both taken into account. This paper illustrates the concepts of this method by applying the technique to a simplified water tank level control system.

As mentioned in section 3, DFT extend fault trees by in- troducing dynamic gates such as the spare, PAND and FDEP gates. In this paper, however, only the spare-gate has been modelled with PTA and CTMC. This paper does not provide enough material to fully determine the usabil- ity of PTA as an approach to fault tree analysis. A pos- sible direction for future research could be to investigate the usability of PTA regarding the other dynamic gates in- troduced by DFT. Furthermore, this paper analyses PTA for two synthetic DFTs. To fully determine the usabil- ity of PTA, they should also be analysed when used to model more complex, real systems. Other research direc- tions include the investigation of the effects of changing the widths of the uniform intervals for the PTA models and an investigation of the reason behind the difference in reliability of the PTA and CTMC models. For now, it can be stated that a system whose upper and lower bounds for its failure and repair rates are known, can be modelled easily with the non-Markovian PTA with an uniform dis- tribution, whereas CTMC can be used when only mean times of the failure and repair rates are available.

National University of Sciences and Technology, Islamabad drafzal@ciitsahiwal>edu.pk , 03452325972 ABSTRACT The failure of engineering equipment causes loss of capital as well as human loss, injuries, and stoppage of production line. The hazards can be classified as safe, minor, major, critical and catastrophic Risk analysis or hazard analysis pin points the potential failures of engineering systems and or components when being used.. Failure mode and effects analysis is used to identify hazard and to make system safer. A system is broken down up to level of components and using reliability data the safety or probability of failure of assemblies and the system can be calculated. The failure mode and effects analysis is used with fault tree analysis to point the areas of a complex system where failure mode effect analysis is required. Fault tree analysis (FTA) is a technique which pinpoints any failure or severe accidents. It tells how things fail rather than emphasize on the design performance. It is a logic diagram connecting inputs an outputs using Boolean algebra. This paper shows how FTA can be applied to car carburetor failure and car brake failure.

Received April 17, 2011; revised July 12, 2011; accepted July 19, 2011 Abstract Being one of the most expensive components of an electrical power plant, the failures of a power transformer can result in serious power system issues. So fault diagnosis for power transformer is highly important to ensure an uninterrupted power supply. Due to information transmission mistakes as well as arisen errors while processing data in surveying and monitoring state information of transformer, uncertain and incom- plete information may be produced. Based on these points, this paper presents an intelligent fault diagnosis method of power transformer using fuzzy fault tree analysis (FTA) and beta distribution for failure possibil- ity estimation. By using the technique we proposed herein, the continuous attribute values are transformed into the fuzzy numbers to give a realistic estimate of failure possibility of a basic event in FTA. Further, it explains a new approach based on Euclidean distance between fuzzy numbers, to rank the basic events in accordance with their Fuzzy Importance Index.

7. Conclusion This paper has presented FFORT, a compilation of diverse fault trees for benchmark purposes. We have collected FTs from the scientific literature, described them in a uniform input language, and we make them publicly available together with metadata about the FTs. We provide the metadata both on a user-friendly website and in machine- readable form. We further hope to expand the FFORT both by collecting further FTs ourselves and by soliciting contributions from other re- searchers on fault tree analysis.

16. R. Manian, J. Bechta Dugan, D. Coppit, and K. Sullivan. Combining various solution techniques for dynamic fault tree analysis of computer systems. In Proc. IEEE Int. High-Assurance Systems Engineering Symposium, pages 21–28, 1998. 17. S. Montani, L. Portinale, A. Bobbio, M. Varesio, and D. Codetta-Raiteri. A tool for automatically translating dynamic fault trees into dynamic Bayesian networks.

Our goal is to develop a set of methods that address these weaknesses. In this paper, we propose a novel method to guide software reliability allocation by using software fault tree analysis (SFTA). With respect to the multi-user oriented software, we introduce a new algorithm to figure out each component’s importance, and establish a new reliability allocation model based on software utility and total development cost.

Abstract- Wireless communications became one of the most widespread means for transferring information. Speed and reliability in transferring the piece of information are considered one of the most important requirements in communication systems in general. Moreover, Quality and reliability in any system are considered the most important criterion of the efficiency of this system in doing the task it is designed to do and its ability for satisfactory performance for a certain period of time, Therefore, we need fault tree analysis in these systems in order to determine how to detect an error or defect when happening in communication system and what are the possibilities that make this error happens. This research deals with studying TETRA system components, studying the physical layer in theory and practice, as well as studying fault tree analysis in this system, and later benefit from this study in proposing improvements to the structure of the system, which led to improve gain in Link Budget. A simulation and test have been done using MATLAB, where simulation results have shown that the built fault tree is able to detect the system’s work by 82.4%.

D-86135 Augsburg Abstract Safety is an important requirement for many modern systems. To ensure safety of complex critical systems, well-known safety analysis methods have been formalized. This holds in particular for automation sytsems and transportation systems. In this paper we present the formalization of one of the most wide spread safety analysis methods: fault tree analysis (FTA). Formal FTA allows to rigorously reason about completeness of a faulty tree. This means it is possible to prove whether a certain combination of component failures is critical for system failure or not. This is a big step forward as informal reasoning on cause-consequence relations is very error-prone.

Figure 3.2 – Fault Tree Analysis model 3.1.4 Phase 4 – Implementation The FTA will be constructed from the data gathered from inspection reports and results of meetings of appropriate personnel. This data will be traced from final fault through to the construction of the bridge (no failures). A deterioration path will follow the typical design of FTA with specific information being formed from data collected. This FTA will then be subjected to the excel model which will then generate the probability of movement.

Currently, several software tools are required to conduct failure data analysis, parameter estimation, tie-set/cut-set identification, reliability block diagram analysis, analysis of state independent systems, analysis of state dependent systems, and fault tree analysis. Some of the tools are commercially available, while others are described in the literature by Semanderes (1971) – ReliaSoft (2009). This paper presents a revised Software Tool for Reliability Estimation (STORE) which was initially developed by Parekh (1999) and later revised by Li (2009). The revised tool, described here, not only integrates all of the above tasks, but is based on an efficient approach for representation and simplification of complex networks. The details of which were described by Ahluwalia (2011). The revised tool also utilizes a database to store and retrieve system, sub-system, and component data. The database enables users to build a library of sub-systems and components, which can be used to build new systems. The software was implemented in Microsoft Visual Basic 2008 with Microsoft SQL server as the database. It is not a commercial package, but can be obtained from the authors free of charge. A brief comparison of this software with the four (Isograph, Relex, Item, and ReliaSoft) commercial reliability software packages is provided in Table 12.

Keywords: Reliability Analysis, Fault Tree Analysis, Dynamic Fault Trees, Temporal Fault Trees, Uncertainty Analysis, Fuzzy Set Theory 1. Introduction Safety critical systems are widely used in many industries, e.g., aerospace, automotive, and energy sectors, and the failure of such systems has the potential to cause catastrophic effects on human life as well as the environment. An increasing amount of effort is now often devoted to ensuring that such failures cannot occur, and this can be achieved through dependability engineering techniques. One of the key goals in designing safety critical systems is to identify potential risks posed by such systems so that these risks can then be minimised. System safety and reliability are two key aspects of system dependability. Their estimation at design stage typically involves calculation of probabilities of system failures. In the case of safety, the focus is on failures that are potentially severe in their effects and therefore a low probability of occurrence must be demonstrated to keep risk at acceptable level. A wide variety of methods have been developed to perform safety analysis and reliability evaluation of systems. Fault tree analysis (FTA) is a well-established and widely used method for evaluating system safety and reliability. This is a graphical method to show the logical connection between different faults and their causes. Fault trees use Boolean logic and usually use AND and OR gates to show the combinations of component failures that are necessary and sufficient to cause the system failure.

The main techniques that have previously been implemented for the solution to phased mission problems are that of Fault Tree Analysis, Markov Analysis and Simulation. The technique of fault tree analysis (FTA) is a commonly used tool to assess the probability of failure of industrial systems. This method may be adapted for analysis of systems comprising of more than one phase, where each phase depends on a different logic model. Hence the complexity of the modelling is significantly more difficult than for single phase systems. The fault tree approach represents the failure logic of the system in an inverted tree structure, and allows for both qualitative and quantitative system reliability analysis to take place. The earliest inspection of the analysis of phased missions was that carried out by Esary and Ziehms [1]. This research employed a fault tree method by which the mission is split into consecutive phases whereby each phase performs a specified task. The success of the mission depends on the performance of the non-repairable components used in each phase. The probability of this success is referred to as the Mission Reliability. Mission unreliability is defined as the probability that the system fails to function successfully during at least one phase of the mission. An important problem is to calculate, as efficiently as possible, either the exact value or bounds for the mission unreliability parameter. Methods to obtain estimates of such bounds are discussed by Burdick et al [2].

Department of Aeronautical and Automotive Engineering, Loughborough University, Leicestershire, UK Abstract: Many types of system operate for missions that are made up of several phases. For the complete mission to be a success, the system must operate successfully during each of the phases. Examples of such systems include an aircraft  ight, and also many military operations for both aircraft and ships. An aircraft mission could be considered as the following phases: taxiing to the runway, take-off, climbing to the correct altitude, cruising, descending, landing and taxiing back to the terminal. Component failures can occur at any point during the mission, but their condition may only be critical for one particular phase. As such, it may be that the transition from one phase to another is the critical event leading to mission failure, and the component failures resulting in the system failure may have occurred during some previous phase. This paper describes a means of analysing the reliability of non-repairable systems that undergo phased missions. Fault tree analysis (FTA) has been used as a method for assessing the system performance. The results of the analysis are the system failure modes in each phase (minimal cut sets), the failure probability in each phase and the total mission unreliability. To increase the efŽ ciency of the analysis, the fault trees constructed to represent the system failure logic are analysed using a modularization method. Binary decision diagrams (BDDs) are then employed to quantify the likelihood of failure in each phase.

Nowadays safety and security are becoming more and more important because of the fact that modern information systems are increasingly distributed over web-services, grids and clouds. Safety critical systems that were not utilizing usage over Internet are being re-engineered in order to be use over Internet. As a consequence of this situation there is need of new methods that cover both security and safety aspects of software systems, since these systems are used in transportation, health and process control systems that arises risk of physical injury or environmental damage. Additionally when safety and security aspects are not considered together they may violate each other while one situation is making a case safe it may violate security and this is a problem. Such as in the sample of lock doors at dormitories for security purpose to protect inhabitants against robbery and some other possible crimes, those inhabitants of dormitories use distance keys to unlock them but in case of a fire situation in the building for safety purposes these lock doors are unlocking themselves and by activating fire alarms attackers can get access to inhabitants properties. In current thesis we introduce integrated domain models of security and safety, extracting definitions from safety and security domains and finding possible pairs to integrate. Developing interplays between security and safety technique that is misuse cases and fault tree analysis. We demonstrate alignment of fault tree analysis to safety domain model and making interplay between techniques from fault tree analysis to misuse cases.

This overview lead to several observations and direc- tions for future research. First of all, as is often the case with modelling lan- guages, fault tree analysis suffers — mildly — from the tower-of-babel-effect: whereas the (static) fault tree for- malism was coined as a relatively simple and intuitive mod- eling language, a “wild jungle” of different formalisms and techniques nowadays exist: Therefore, it would be valu- able to know which of the SFT extensions are most useful in practice. Similarly, it would be useful to identify which FT measures are most useful in practice. Also, a compara- tive case study that compares FT analysis with other risk analysis methods such as reliable block diagrams, AADL, UML/Marte provides useful insight in the capabilities and limitations for fault tree analysis. Thus, we suggest exten- sive field studies here.

2 Assistant Professor, Dept. of Mechanical Engineering, M.A.N.I.T, Bhopal, India ---------------------------------------------------------------------***------------------------------------------------------------------- Abstract - Fault tree analysis is a top –down failure analyzing method which uses logic gates and Boolean algebra. By the use of this method it is easy to identify the critical part of the system, causes of its failure and potential countermeasures. It is used for reliability and safety analysis and risk evaluation in complicated system. FTA has various applications in critical areas such as aerospace, automotive industry and nuclear power plant. In thus paper fault tree analysis of single cylinder vertical diesel engine is done for finding out the main causes of engine failure and maintenance of engine is done and engine brought into the operating condition.

The industry is passionately looking for a systematic way which proposes all probable root causes of cargo contamination briefly and produces a solution way to reduce the probability of a contamination event. Such kind of needs are motivated us to make this novel study which produces all probable root causes of chemical cargo contamination event as brief as not previously. Furthermore the proposed approach by using fault tree analysis (FTA) is suitable for making an extensive cost-benefit analysis. By FTA it is possible to observe how much the probability of contamination event reduces, when any of root causes is eliminated. For instance, according to our case study, for our sample company we deduced a cargo contamination event as of occurance in 3, 77 years. When we eliminate a root cause of the contamination event, the probability of contamination decreases to 4, 02 years.