Fault Tree Approach Research Articles

Improved Z-number based fuzzy fault tree approach to analyze health and safety risks in surface mines by I. M., Jiskani, F., Yasli, S., Hosseini, A. U., Rehman, S., Uddin [Resources Policy 76 (2022) 102591]: Suggested modification

Jiskani et al. (Resources Policy 76 (2022) 102591) claimed that to the best of their knowledge, there is no study for investigating undesired events and their specified primary causes in the surface mines and quarries. To fill this gap, they proposed a Z-number based fuzzy fault tree approach (ZNBFFTA). Jiskani et al. applied their proposed approach to the surface quarries to analyze the mine health and safety (MHS) risk in the surface mines and quarries in Pakistan. Mine managers of other developing countries may be attracted towards ZNBFFTA to analyze MHS risk in the surface mines and quarries. ZNBFFTA can be used in a variety of sectors and is highly effective. It is pertinent to mention that although ZNBFFTA towards the problem of MHS is valid. However, in Step 4 of ZNBFFTA, Kang et al.’s method (Journal of Information & Computational Science 9(3) (2012) 703–709) is used to transform Z-number (ZN) into fuzzy number (FN) as no other method was available at that time. While, an improved version of Kang et al.’s method is proposed in 2021 by Cheng et al. (33rd Chinese Control and Decision Conference (CCDC), Kunming, China, (2021) 3823–3828). So, the aim of this paper is to make the researchers aware that ZNBFFTA will be more efficient if in its Step 4, Cheng et al.’s method is used instead of Kang et al.’s method.

Failure probability estimation of natural gas pipelines due to hydrogen embrittlement using an improved fuzzy fault tree approach

The estimation of failure probability is challenging in hydrogen embrittlement in steel pipelines due to the complexity of the synergistic effect of multiple factors. The present study proposed a hybrid methodology to estimate the failure probability of steel pipelines due to hydrogen embrittlement. The methodology integrates the fault tree analysis with a fuzzy comprehensive evaluation. Fault tree analysis captures the logical relationships between influencing indicators to develop a new assessment model of hydrogen embrittlement in steel pipelines. An improved fuzzy fault tree analysis method was proposed to process aleatoric and epistemic uncertainties to estimate the probability of each basic event due to the difficulty in obtaining the actual probabilities. The failure probability of blended hydrogen natural gas pipelines was estimated by considering the correlation of events. A case study demonstrated the applicability of the proposed method. Maintenance measures can be implemented according to the evaluation results to ensure pipeline safety.

Fire accident risk assessment of high rise building based on fuzzy bow tie approach

Despite the numerous risks that high-rise buildings face, fire accidents happen most frequently. Studying fire accidents in high-rise buildings is crucial because they can result in harm to people’s health, fatalities, property damage, and pollution. The number of accidental fires in buildings is very large since it is difficult to isolate a single cause and all processes and control measures are not appropriately implemented. This paper proposes a fuzzy-bow tie approach to evaluating the risk of fire accidents by taking into account the various fire sources and effects. The fourteen-floor high-rise residential building is used as a case study for the proposed fuzzy bow tie approach. The fuzzy fault tree approach estimates that there is a 0.0968% risk of a fire accident occurring in that high-rise building, with a possibility for 9 out of 100 accidental fires annually. The fuzzy event tree model predicts that loss of life and loss of property are the most likely consequences of an accidental fire. Accordingly, mitigation strategies can be developed by building officials and fire safety practitioners.

Safety analysis of fire and explosion (F&E) accidents risk in bulk carrier ships under fuzzy fault tree approach

Minimizing fire and explosion (F&E) accident risk in bulk carrier ships are of paramount to enhance safety in maritime transportation. Due to nature of cargo carried by bulk carrier ships, the fire and explosion risk is relatively high. Therefore, a detailed risk analysis is required to understand potential root causes of F&E accidents. This paper aims at performing risk analysis under fuzzy logic, fault tree analysis (FTA) and Cut Set Importance Measurement (CS-I) technique for F&E accidents in bulk carrier ships. Since the fault tree presents a robust graphical tool to explore the causes of system level failures, the fuzzy sets deal with vagueness and ambiguity in decision-making process. In addition, the CS-I technique is used in the study to reveal the most effective accident combinations in the formation of such accidents. The result of the paper shows that probability of the F&E risk on bulk carriers is 9.27E-02. The findings of the paper provide valuable insights to the ship owners, safety inspectors, Health, Safety, Environment and Quality (HSEQ) managers of bulk carrier ships based on the proposed control actions to reduce risk and improve operational safety.

Automatic Generation of Event Trees and Fault Trees: A Model-Based Approach

In the past few decades, the increasing complexity of modern engineering systems has been driven by the integration of a large number of components whose operations may involve many disciplines (e.g., thermal hydraulics, plant operations, cybersecurity). Most computational tools used by industry and regulators for system safety and reliability assessments are still based on the traditional fault tree (FT) and event tree (ET) approach, which may not be able to capture complex interactions among system constituents. The use of simulation tools has widely increased in the past few decades to improve the fidelity of the reliability and safety analyses. However, the direct use of simulation tools as part of dynamic probabilistic risk assessment (DPRA) methods is not getting traction since (1) modeling the whole system under consideration with DPRA methods may be computationally expensive and unnecessary, and (2) the manual integration of DPRA models into existing state-of-practice probabilistic risk assessment models (i.e., based on FTs and ETs) can be time consuming and prone to errors. In this paper we propose a procedure to overcome this limitation by presenting several algorithms designed to automatically construct subsystem ETs and FTs from DPRA methods for integration into an existing ET/FT system model.

Safety Integrity Evaluation of crude oil heater According to IEC 61508 Standard

the main object of this paper is to evaluate safety barriers intervening against overpressure implemented on a crude oil heater using layers of protection analysis approach suggested in IEC 61508 (International Electrotechnical Commission) Standard for the determination of safety requirements are illustrated. Accident scenarios are pre-identified using Hazard an Operability approach, Fault tree approach is required for an effective risk assessment process. In order to better appreciate accident scenarios, PHAST (Process Hazard Analysis Software Tool) is utilized to simulate them.

Improved Z-number based fuzzy fault tree approach to analyze health and safety risks in surface mines

Surface mining is vulnerable and subject to a wide range of risks, requiring extensive risk analysis to ensure mine health and safety (MHS). Fault tree analysis (FTA) is a graphic representation tool for conducting safety and reliability analyses by modeling causal chains that lead to failures. However, conventional FTA cannot deal with uncertain and imprecise information. Therefore, in order to handle the uncertainty arising from lack of complete information and to enhance the reliability of qualitative judgment of experts, the concepts of Z-numbers and fuzzy theory are combined with FTA. The proposed approach used expert elicitation to comprehensively analyze MHS risks related to machine/equipment, environment, and workplace. Through causal inquiries of the FTA, 8 undesired events and 65 underlying basic events are explored and analyzed, taking into account the probability of occurrence of all basic events. Further, a sensitivity analysis is performed using Fussell-Vesely Importance and Risk Reduction Worth Methods to verify the model and examine how each of the basic events contributes to the occurrence of any undesirable incident. Results reveal that issues associated with blasting, dust, and explosive fumes are the most probable incidents to occur among the undesired events. The main basic events causing MHS risks result from non-implementation of regulations, staff incompetence, improper safety perimeter setting, and explosive calculations. This study assists practitioners in making risk management decisions and implementing corrective measures. The proposed approach can also be applied to investigate similar risk factors in different industries.

Time dependent reliability analysis for a critical reactor safety system based on fault tree approach

Loss of coolant in the operation of any nuclear power plant will eventually become the primary source of hazard in the sequence of events leading to reactor core uncovery. Subsequent failure in removing the nuclear decay heat and preventing the core uncovery will further lead to loss of coolant accident (LOCA). In conjunction to this safety concern, it is crucial that the reliability of the plant emergency core cooling system is systematically and critically analysed. This article presents a case study on the time dependent reliability analysis for a safety injection system (SIS) of an advanced pressurized water reactor, based on the failure mode and effect analysis (FMEA) and fault tree (FT) analysis approach. The identified generic data for component reliability are carefully reviewed and used in this study. Based on the base case model, sensitivity and importance measure analysis for basic events are performed and the outcomes gained are presented and discussed. From the analysis, it is shown that the safety injection pumps of the SIS contribute significantly to the reliability of the system. In the short (at 0.5 hour) and long (7.0 hours and 72.0 hours) run, safety injection pumps are critical and influence the reliability of the SIS the most. The SIS’s FT logic model that has been developed and calculated shows the usability of the FMEA and FT approach that are implemented in analysing SIS time dependent reliability.

Benchmarking the failure assessment of perishable product supply chain using fault tree approach: insights from apple case study of India

PurposeThe purpose of this paper is to facilitate perishable product supply chain (PPSC) managers and practitioners to assess PPSC failure events. The paper proposed fault tree methodology for assessing failures associated with PPSC for evaluating the performance in terms of effective PPSC management adoption.Design/methodology/approachInitially, different failure events were identified from literature and semi-structured interviews from experts. Fault tree model was developed from the identified failure events. Probability of failure events was calculated using Poisson distribution based on the annual reports and interviews conducted from experts. Further, qualitative analysis – minimum cut sets (MCSs), structural importance coefficient (SIC) – and quantitative analysis – Birnbaum importance measure (BIM), criticality importance factor (CIF) and diagnosis importance factor (DIF) – were performed for ranking of failure events. In this study, fault tree development and analysis were conducted on apple supply chain to present the authenticity of this method for failure analysis.FindingsThe findings indicate that the failure events, given as failure at production and procurement (A2), that is, involvement of middleman (BE3), handling and packaging failure (BE4) and transportation failure (A3), hold the highest-ranking scores in analysis of PPSC using fault tree approach.Originality/valueThis research uses the modularization approach for evaluation of failure events of PPSC. This paper explores failures related to PPSC for efficient management initiatives in apple supply chain context. The paper also provides suggestion from managerial perspective with respect to each failure event.

A Noisy-OR gate based fuzzy fault tree approach for micro-leakage evaluation of bolt-gasket-flange connection (BGFC)

In the natural gas gathering and transportation station, bolt-gasket-flange connection (BGFC) is the main connection mode, but due to its large number, the micro-leakage may result in serious consequences. For this reason, early BGFC micro-leakage evaluation can effectively assist decision-making and prevent the occurrence of accidents. To solve the problem of insufficient field data collection, we proposed a Noisy-OR gate based fuzzy fault tree approach, and calculated the corresponding minimum cut sets and the highest risk factors. Moreover, sensitivity analysis (SA) was used to determine that material problems (wear and corrosion of the sealing surface), man-made operation problems (bolts and flanges) and working conditions (pipe vibration and temperature fluctuations) are the key factors that contributing to the BGFC micro-leakage. In brief, the combination of the fuzzy fault tree analysis and Noisy-OR gate is an effective approach for BGFC micro-leakage evaluation, which is of great significance to the micro-leakage analysis, safe operation, and risk assessment of the gas station.

Operating status of public toilets in the Hutong neighborhoods of Beijing: An empirical study

The provision of sanitation services for fast-growing urban populations is one of the world's urgent challenges. Hutong neighborhoods in Beijing, capital of China, cannot be rebuilt due to the protection of historical heritage, while residents still need to keep the habit of defecating in public toilets. One hundred public toilets with non-sewered sanitation in the Hutong neighborhoods of Beijing were visited to investigate the actual operating status in response to the “toilet revolution” campaign. The fault tree approach was used to identify the barriers toward a decent and environment-friendly public toilet and evaluate potential risks from the malfunction of various components. Four subsystems are defined and elaborated to calculate the fault possibility. These subsystems are environment- and user-friendly, regarded as ancillary facilities, and used for fecal sludge (FS) management. Statistical analysis of targeted cases indicated that fault probabilities of environmental considerations, user-friendly considerations, ancillary facilities, FS management are calculated as 0.79, 0.96, 0.96, and 0, respectively. The subsystems were weighted using a Delphi method concept. Results showed that the well operation ratio of Beijing Hutong public toilets is only 32%, and the sanitation service value chain can be further optimized. This study also provides references for other countries, which are dedicated to promoting urban sanitation and public health.

Risk-informed approach for safety improvement of domestic research reactor

This paper describes the effort to improve the safety level of a domestic research reactor and optimize its operation with regard to safety by conducting a probabilistic safety assessment (PSA) under full-power operating conditions. The PSA was undertaken to assess the level of safety for an operating research reactor in Korea, evaluate whether it is probabilistically safe to operate and reliable to use, and obtain insights about the procedure and design improvements for achieving increased safe operation. The scope of the PSA reported here is a Level 1 PSA, which addresses the risks associated with core damage. The technical objectives of this study were to identify the accident sequences causing core damage and to derive insights, such as design and procedure improvements, from the dominant accident sequences by conducting sensitivity analyses.The event tree (ET)/fault tree (FT) linking approach was used as the basic method for accident sequence quantification for the PSA. The accident sequence models followed the small ET/large FT approach. The total core damage frequency (CDF) was estimated as the sum of the frequencies of the individual ET sequences causing core damage. A truncation value of 1.0E−15/yr was applied for all the FTs or accident sequences. The PSA results indicated a point estimate of 4.55E−06/yr for the overall CDF, attributable to the internal initiating events for the Korea research reactor.Based on the dominant accident sequences from the PSA, eight types of sensitivity analyses were performed, and relevant insights for improved safe operation were derived. When the insights from these sensitivity analyses were applied to the reactor design and the operating procedure, the risk was reduced by approximately ten times compared to that before, and its safety was significantly improved. The PSA methodology is very effective in improving reactor safety in the full-power operating phase, and, in particular, it is a highly suitable approach to determine the deficiencies of a reactor at full power and improve the reactor safety by overcoming them.

RAM analysis and availability optimization of thermal power plant water circulation system using PSO

This paper presents reliability, availability, and maintainability (RAM) analysis framework for evaluating the performance of a circulation system of water (WCS) used in a coal-fired power plant (CFPP). The performance of WCS is evaluated using a reliability block diagram (RBD), fault tree analysis (FTA), and Markov birth–death probabilistic approach. In this work, the system under study consists of five subsystems connected in series and parallel configuration namely condensate extraction pump (CEP), low-pressure feed water heater (LPH), deaerator (DR), boiler feed pump (BFP), high-pressure feed water heater (HPH). The reliability block diagram (RBD) and fault tree approach (FTA) have been employed for the performance evaluation of WCS. The Markov probabilistic approach based simulation model is developed. The transition diagram of the proposed model represented several states with full working capacity, reduced capacity, and failed state. The ranking of critical equipment is decided on the basis of criticality level of equipment. The study results revealed that the boiler feed pump affects the system availability at most, while the failure of deaerator affects it least. The availability of the system is optimized using the particle swarm optimization method. The optimized availability parameter (TBF, TTR) based modified maintenance strategy is recommended to enhance the availability of the plant system. The optimized failure rate and repair rate parameters of the subsystem are used to suggest a suitable maintenance strategy for the water circulation system of the thermal power plant. The proposed RAM framework helps the decision-makers to plan the maintenance activity as per the criticality level of subsystems and allocate the resources accordingly.

Situational Awareness Index Assessment of Transmission Line Using Fault Tree Approach

— The wide-area situational awareness attempts to detect the imminent system instability quickly and alerts the operator to initiate appropriate control action. Faults on the transmission line may result in interruption of power and substantial economic losses. Thus, their situational awareness assessment is very much critical, especially when the power sector is targeting reliability of 99.9999%. Phasor measurement units were introduced to increase the operator's situational awareness of the power network. A schematic representation of situational awareness (SA) of transmission line having three hierarchical levels has been developed. Based on the schematic representation which reveals the relationship between the hierarchical levels and the modules, a fault tree has been developed. The situational awareness index (SAI) of individual modules has been allocated based on their relative significance to the preferences of various user classes. With the help of minimal cut set and fault tree approach, the SAI of transmission line has been developed. The proposed work provides a quantitative approach for assessing transmission line SA and, therefore, plays a vital role in the power sector.

A weakest t-norm based fuzzy fault tree approach for leakage risk assessment of submarine pipeline

The leakage of oil and gas due to submarine pipeline damage will result in serious consequences while the reasons are diverse and complicated. The fault tree analysis (FTA) method provides an effective tool to systematically identify various root events and perform probabilistic risk assessments. However, crisp probability values of the basic events are requested for quantitative analysis due to the characteristics of the method itself. In this paper, a weakest t-norm (Tω) based fuzzy fault tree approach is proposed to obtain a relative reliable probability value using domain experts’ evaluations. The main contributes of this method include: a set of fuzzy numbers are defined based on the DNV-RP-F107, meanwhile, a converting method is also proposed to defuzzify the integrated fuzzy numbers; the weakest t-norm operators for trapezoidal fuzzy number are employed for less uncertainty accumulation during the aggregation process. Furthermore, a case study is presented for a detailed description of the proposed approach. A probabilistic risk assessment for leakage failure of submarine pipeline is conducted using both the proposed approach and traditional method. The results show good validity and applicability of the proposed method. The critical events are recognized after quantitative analysis and some improvement measures are put forward for engineering references.

Modeling and efficient quantified risk assessment of haze causation system in China related to vehicle emissions with uncertainty consideration

Urban haze has become a severe pollution problem in China. Vehicle emission may be a key factor leading to haze pollution in China's megacities due to the rapid growth of vehicles and corresponding energy consumption. Until now, the haze formation mechanisms in China remain highly uncertain, which have not yet been understood quantitatively. In this work, an efficient modified haze causation system related to vehicle emissions is developed for reliable quantified risk assessment of urban haze in China's megacities. And fuzzy mathematical theory combining with fault tree approach is investigated and employed as the analysis tool/strategy. To provide objective basis for the reliability and practicability of the quantitative assessment results, an efficient data extraction strategy and relevant mathematical models are proposed and developed for the probability determination of basic risk events. Besides, the probability uncertainty of basic risk events during the data extraction is taken into account, where the occurrence probability of basic events is described as triangular fuzzy number, the quantitative analysis results will be more reliable and more tally with the actual situation. After the haze causation system related to vehicle emissions is established along with the identification of all critical risk factors related to vehicle emissions, Beijing and Tianjin are taken as illustrated case studies for the quantified risk assessment of haze causation system related to vehicle emissions in China. All the analysis results demonstrated that this work may provide a useful and effective tool/strategy for efficient quantified risk assessment and risk management of haze causation system relate to vehicle emission in China.

Review on formation mechanism analysis method and control strategy of urban haze in China

Abstract Due to the rapid urbanization and industrialization, and excessive consumption of fossil fuel, haze weather characterized by PM2.5 has become a severe pollution problem in major Chinese cities recently, which has harmful effect on the air quality, visibility, clime system and human health. To indicate suitable directions for the prevention and control of haze pollution, the pollutant source apportionment and formation mechanism of urban haze should be figured out firstly. In this work, we briefly review the frequently-used methods for PM2.5 source apportionment and formation mechanism analysis of urban haze based on normal perspective in recent years. Furthermore, based on the new perspective of systematic methodology, the utilization of fault tree approach for the causation mechanism analysis of urban haze is significantly introduced and discussed. Finally, the recent progress on controlling strategies of urban haze in China is also synoptically introduced and discussed. It is expected that more effective tool/method can be found, developed and employed for the causation mechanism analysis and risk management of urban haze in China.

Multicriteria reliability modeling and optimisation of a complex system with dual failure modes and high initial reliability

PurposeSystem reliability optimisation in today’s world is critical to ensuring customer satisfaction, businesses competitiveness, secure and uninterrupted delivery of services and safety of operations. Among many systems configurations, complex systems are the most difficult to model for reliability optimisation. The purpose of this paper is to assess the performance of a novel optimisation methodology of the authors, developed to address the difficulties in the context of a gas carrying system (GCS) exhibiting dual failure modes and high initial reliability.Design/methodology/approachThe minimum cut sets involving components of the system were obtained using the fault tree approach, and their reliability constituted into criteria which were maximised and the associated cost of improving their reliabilities minimised. Pareto optimal generic components and system reliabilities were subsequently obtained.FindingsThe results indicate that the optimisation methodology could improve the system’s reliability even from an initially high one, granted that the feasibility factor for improving a component’s reliability was very high. The results obtained, in spite of the size (41 objective functions and 18 decision variables), the complexity (dual failure modes) and the high initial reliability values provide confidence in the optimisation model and methodology and demonstrate their applicability to systems exhibiting multiple failure modes.Research limitations/implicationsThe GCS was assumed either failed or operational, its parameters precisely determined, and non-repairable. The components failure rates were exponentially distributed and failure modes independent. A single weight vector representing expression of preference in which components reliabilities were weighted higher than cost was used due to the stability of the optimisation model to weight variations.Practical implicationsThe high initial reliability values imply that reliability improvement interventions may not be a critical requirement for the GCS. The high levels could be sustained through planned and systematic inspection and maintenance activities. Even so, purely from an analytical stand point, the results nevertheless show that there was some room for reliability improvement however marginal that is. The improvement may be secured by: use of components with comparable levels of reliability to those achieved; use of redundancy techniques to achieve the desired levels of improvement in reliability; or redesigning of the components.Originality/valueThe novelty of this work is in the use of a reliability optimisation model and methodology that focuses on a system’s minimum cut sets as criteria to be optimised in order to optimise the system’s reliability, and the specific application to a complex system exhibiting dual failure modes and high component reliabilities.

Estimating BOP Kill-Line Failure Probability Combining High level and Experts Opinion Informations

Most deepwater oil prospection activities are carried out by dynamic positioning rigs. Due to the risks of such activities, these rigs are more often subject to emergency disconnections and, therefore, the blowout preventer (BOP), which is a safety equipment, must have high reliability level. Hence, BOP is used to ensure the safety of well drilling process and become one of the most important safety device available, and its reliability becomes even more critical, specifically its kill and choke line, which are especially important for well control. Considering the non-homogeneity of failure data available from BOP system, the main issue for reliability estimates is based on Bayesian inference. Due to the above-mentioned limitation, the present paper will present a simplified application considering a Bayesian fault tree approach for a typical BOP kill line failure probability. The results showed some advantages of considering such methodological approach that make possible to combine different information sources for reliability figures.

A fuzzy Bayesian network approach for risk analysis in process industries

Abstract Fault tree analysis is a widely used method of risk assessment in process industries. However, the classical fault tree approach has its own limitations such as the inability to deal with uncertain failure data and to consider statistical dependence among the failure events. In this paper, we propose a comprehensive framework for the risk assessment in process industries under the conditions of uncertainty and statistical dependency of events. The proposed approach makes the use of expert knowledge and fuzzy set theory for handling the uncertainty in the failure data and employs the Bayesian network modeling for capturing dependency among the events and for a robust probabilistic reasoning in the conditions of uncertainty. The effectiveness of the approach was demonstrated by performing risk assessment in an ethylene transportation line unit in an ethylene oxide (EO) production plant.