A methodology to clarify logical relationship among failure modes and determine system probabilities

In the vulnerability analysis, correlations among failure modes have significant effects on the estimation of failure probabilities. However, the failure modes were assumed to be independent with each other or only parts of dependencies of failure modes were considered, which might lead to inaccurate results. In the present study, a novel methodology to clarify the entire logical relationship among failure modes and determine system probabilities is developed. Firstly, based on the form-changed limit state equations (LSEs) of failure modes, the LSE surfaces or curves are plotted. Subsequently, the logical relationship among failure modes can be identified with the LSE surfaces or curves. The system consequences are further developed by the logical relationship. Bayesian network (BN) is constructed with the input of logical relationship into arcs. With BN considering logical relationship, the occurrence probabilities of failure modes are calculated and system probabilities are estimated more accurately, which are verified well with Monte Carlo simulation and analytical solution. Furthermore, the detailed compositions of occurrence probabilities of failure modes are specified by the system probabilities. The methodology is illustrated by a case study. This study can be applied to the vulnerability analysis of various hazards or disasters as long as LSEs for corresponding failure modes can be developed.     

Fragility assessment of bottom plates in above ground storage tanks during flood events

This study aims to improve the fundamental understanding on the performance of bottom plates in above ground storage tanks (ASTs) during flood events. To this end, fragility models that estimate the probability of material yielding and rupture in the bottom plates were derived. A significant number of ASTs are located in coastal areas and are susceptible to hurricane hazards. Consequently, ASTs have suffered severe damage during past hurricanes resulting in spills with catastrophic environmental and social impacts. Therefore, several failure modes such as flotation, buckling, and sliding have been studied in past research. However, the literature lacks studies that consider the failure of bottom plate due to uplift pressure generated during floods and there are no design guidelines to address this issue. To address this gap, fragility functions that provide the probability of failure as a function of tank geometry, material properties, design parameters, and hazard conditions were developed herein. For this purpose, Latin Hypercube Sampling was performed to span the space of these parameters uniformly. For each parameter combination, maximum stresses in bottom plates were determined using analytical formulations for simply supported and clamped boundary conditions and were compared against two different failure thresholds. The results were used to develop a closed form fragility model using step wise logistic regression. Fragility functions were applied to four case study tanks. Sensitivity analysis were performed to understand the impacts of different probability density functions for various variables on the bottom plates’ fragility. The results provided several insights such as ASTs with larger diameter were vulnerable to bottom plate failure. Comparison with other failure modes revealed that the probability of bottom plate failure was higher than flotation failure for anchored ASTs with clamped boundary condition.     

基于Probit-Bayes方法的储罐地震易损性研究

为了研究地震对储罐造成的影响,结合历史上储罐的震害资料,将储罐的损伤程度进行分级,通过采用Bayes方法估计Probit模型参数,再转化成储罐的损伤概率,给出了各个损伤状态下的模型参数及给定地震加速度下储罐的损伤概率,提出了1种基于Probit -Bayes方法估计储罐易损性的计算方法。结果表明:所提出的地震损伤计算方法,能够有效的评估储罐在不同地震加速度下的损伤程度,可为震后储罐的安全评估提供理论依据。     

Dynamic failure assessment of an ammonia storage unit: A case study

Chemical Process Industries usually contain a diverse inventory of hazardous chemicals and complex systems required to perform process operations such as storage, separation, reaction, compression etc. The complex interactions between the equipment make them vulnerable to catastrophic accidents. Risk and failure assessment provide engineers with an intuitive tool for decision making in the operation of such plants. Abnormal events and near-miss situations occur regularly during the operation of a system. Accident Sequence Precursors (ASP) can be used to demonstrate the real-time operating condition of a plant. Dynamic Failure Assessment (DFA) methodology is based on Bayesian statistical methods incorporates ASP data to revise the generic failure probabilities of the systems during its operational lifetime.In this paper, DFA methodology is applied on an ammonia storage unit in a specialized chemical industry. Ammonia is stored in cold storage tanks as liquefied gas at atmospheric pressure. These tanks are susceptible to failures due to various abnormal conditions arising due process failures.Tank failures due to three such abnormal conditions are considered. Variation of the failure probability of the safety systems is demonstrated. The authors use ASP data collected from plant specific sources and safety expert judgement. The failure probabilities of some safety systems concerned show considerable deviation from the generic values. The method helps to locate the components which have undergone more degradation over the period and hence must be paid attention to. In addition, a Bayesian predictive model has been used to predict the number of abnormal events in the next time interval. The user-friendly and intuitive nature of the tool makes it appropriate for application in safety assessment reports in process industries.     

Seismic risk of atmospheric storage tanks in the framework of quantitative risk analysis

The quantitative risk assessment of industrial facilities is based on integrated procedures to quantify human, environmental and economical losses related to relevant accidents. Accordingly, seismic risk analysis has to be integrated in order to obtain reliable results.In this work, some considerations regarding the intensity and probability of occurrence of earthquakes and the vulnerability of atmospheric storage tanks subjected to seismic actions are given.Structural vulnerability based on observational data has been processed in the form of “probit analysis”, a simple and useful statistic tool. Suggestions concerning industrial seismic-related accidental scenarios are also given.     

Safety study of an LNG regasification plant using an FMECA and HAZOP integrated methodology

A safety analysis was performed to determine possible accidental events in the storage system used in the liquefied natural gas regasification plant using the integrated application of failure modes, effects and criticality analysis (FMECA) and hazard and operability analysis (HAZOP) methodologies. The goal of the FMECA technique is the estimation of component failure modes and their major effects, whereas HAZOP is a structured and systematic technique that provides an identification of the hazards and the operability problems using logical sequences of cause-deviation-consequence of process parameters. The proposed FMECA and HAZOP integrated analysis (FHIA) has been designed as a tool for the development of specific criteria for reliability and risk data organisation and to gain more recommendations than those typically provided by the application of a single methodology. This approach has been applied to the risk analysis of the LNG storage systems under construction in Porto Empedocle, Italy. The results showed that FHIA is a useful technique to better and more consistently identify the potential sources of human errors, causal factors in faults, multiple or common cause failures and correlation of cause-consequence of hazards during the various steps of the process.     

基于贝叶斯网络的汽车起重机液压系统的可靠性评估

为评估汽车起重机液压系统的可靠性,首先结合故障树分析法(FTA)、贝叶斯网络(BN)构建液压系统故障树,然后映射成BN,再利用其在多态性和不确定性方面的优势,应用桶排除法,对系统进行可靠性评估。在给出底事件的发生概率后,通过正向推理,得到顶事件发生的概率为0.191 016。针对模型进行多态性和不确定性修正后,得到的顶事件概率为0.228 073,相对提高19.4%。最后利用反向推理,找出系统的薄弱环节并给出改正措施,为更全面高效的可靠性评估提出一种新方法。     

Fire risk management system for safe operation of large atmospheric storage tanks

This paper has been prepared by its authors to show the benefits coming from the application of the fire risk assessment methodology prepared by the “LastFire^© Project” group of experts. Now a days this methodology seems to be very effective to face the fire risk connected with large atmospheric storage tanks. It has been developed during the period 1997–2005 the HSE & operations experts from experts 16 worldwide operating oil companies. The authors, by “ad hoc” created software package, show the benefit coming from the applications of the LastFire^© methodology and how, from this, using the methodology and the supporting tad, realize a coherent fire strategy in the form of a Fire Risk Management System. Same workflow could also be extended to the issues connected with other problems related with large atmospheric tanks storing hydrocarbons, such as environmental impact by soil pollution, to create a common frame walk of assessment not can be shared with authorities as well. The proposed methodology, moving from the original project, sets as an effective “Fire Hazard Management Approach” in line with the most recent trends (even enforced by the regulations) shared at international levels, that propose the integration of risk assessment with prevention and protection measures selection based on achieved risk reduction, costs, time needed, etc.     

多米诺效应下化工储罐区的脆弱性分析

为有效地减少和控制事故的多米诺效应,对影响事故扩展的关键装置,即脆弱单元的辨识及其有效控制措施进行了研究。根据具体的设计方案,依次选定不同储罐作为初始事故单元,借助ALOHA软件计算各储罐之间热辐射及冲击波相互作用强度的大小,与损伤阈值进行比较,并考虑设备间的协同作用,从而确定可能发生的多米诺事故;运用Probit模型计算事故扩展概率,根据计算结果通过Bayes Server软件建立贝叶斯网络,利用先验概率来进行整体脆弱性分析,从而确定各个方案的安全性;对优选的方案通过后验概率进行单元脆弱性分析,从而确定脆弱单元;在此基础上提出相应的控制措施。通过实例计算验证了该方法的可行性,结果表明,该方法能够在多米诺效应的预防和控制方面有效发挥作用。     

Strategies for assessing and reducing inherent occupational health hazard and risk based on process information

Over the last few decades, the concept of inherent occupational health has gained increasing attention to reduce occupational hazards that may adversely impact workers’ health. In order to assess occupational hazards in the chemical process, different inherent occupational health assessment methods have been developed at the early stages of process development and design. The methods in the order of process information availability – ranging from the detailed piping and instrumentation diagrams to a simple sketch of process concepts are the: occupational health index (OHI), health quotient index (HQI) and inherent occupational health index (IOHI). This paper proposes systematic heuristic frameworks to assist process designers and engineers in assessing and reducing inherent occupational health hazards or risks based on process information availability. Strategies for reducing health hazards or risks in the OHI, HQI and IOHI methods based on inherently safer design (ISD) keywords of minimization, substitution, moderation and simplification are included in this study. It is worth mentioning that the proposed frameworks act as guidelines for design engineers in systematically selecting the appropriate index and methodology to assess and reduce health hazards/risks based on the availability of the process information. A case study is solved to illustrate the proposed framework.     

Quantitative risk assessment of domino effect in Natech scenarios triggered by lightning

Lightning strike is the natural event more frequency causing Natech accidents involving atmospheric storage tanks. Despite the resulting fires have usually limited severity and only local effects, domino effect may cause the escalation of these primary events, possibly affecting nearby pressurized storages and process equipment, thus resulting in relevant increase in the potential area impacted. A methodology was developed for the quantitative assessment of risk due to domino effects caused by Natech accidents triggered by lightning. A comprehensive procedure was obtained, tailoring lightning risk assessment to include probabilistic models for domino escalation based on probit approach and combinatorial analysis. The methodology was applied to a case-study to evidence the shift in risk figures due to domino effect and the credibility of the secondary domino scenarios. The results of the case-study show that an increase up to two orders of magnitude with respect to risk calculated for conventional scenarios is possible when considering lightning-induced Natech primary scenarios and their escalation.     

Designing a developed model for assessing the disaster induced vulnerability value in educational centers

To date, the models developed for assessing the vulnerability of societies have only taken account of the economic problems in the societies. Offering a model based on analytical hierarchy process and failure mode and effect analysis logic, the current study aims to determine the factors influencing the vulnerability of a higher education center and finally defines a vulnerability index. This model divides the factors influencing vulnerability into three categories: (1) the structure and layout of the buildings, (2) the occupants’ characteristics, (3) the controlling and warning systems. The academy community center of Science and Research Branch was assessed in terms of vulnerability. The findings indicated that the vulnerability value relating to various sections and university buildings was higher than the acceptable level which entailed the due attention of educational managers. The findings showed that if some parts of the educational and administrative buildings were used for laboratory as well as for the storage of hazardous and flammable materials, then the vulnerability value will be increased to 200. This highlights the impact that the type of buildings application has on the level of vulnerability. The study has been performed in the Science and Research Branch as an educational center in Tehran during 2009–2010.     

Blast damage to storage tanks and steel clad buildings

The 2005 Buncefield vapour cloud explosion showed the huge cost associated with blast damage to commercial property surrounding a major explosion incident. In most cases there was serious disruption to business activity; in many cases the buildings had to be demolished or abandoned for long periods until extensive repairs were carried out.Another key feature of this and other recent vapour cloud explosions has been the damage done to storage tanks. The blasts almost invariably cause immediate top and bund fires in any tanks surrounded by the vapour – even if they contain relatively high flashpoint materials such as diesel.The first part of this paper describes the patterns of damage observed in buildings in the industrial estates around Buncefield. Methods for assessing the degree of external and internal damage are presented.The second part of the paper deals with failure modes and ignition of various types of liquid storage tank during vapour cloud explosions. Again, the Buncefield data provides excellent examples that illustrate the importance of tank design, fill level, location relative to the cloud, etc.     

Scenario deduction of Natech accident based on dynamic Bayesian network: A case study of landslide accident in a liquor storage tank area in Guizhou Province,China

Industrial technical accidents caused by natural disasters are defined as Natech accidents, such as earthquakes and landslides, which can cause tremendous damage to industrial storage tanks, and lead to accidental leakage and even serious fire and explosion accidents. In this study, a landslide-induced storage tank accident model under earthquake disasters was proposed, and the relationship between landslide mass impact and target impact resistance was taken into account. Also, tank failure and the formation of the pool fire were considered to be the consequences of the Natech accident. Through scenario deduction, the dynamic process of landslide Natech was transformed qualitatively into a disaster chain network diagram composed of a scenario state, a disaster-causing factor and emergency management. The Bayesian network was used to learn and deduce the parameters of the network diagram, and in this process, the prior probability and conditional probability of nodes were obtained primarily by Monte Carlo simulation, and by an improved expert scoring method based on the fuzzy set theory. Through visualization software, the sensitivity analysis of landslide Natech was achieved. Finally, a case study of a liquor storage tank area in Guizhou Province, China was carried out, and the results show that a large amount of hazardous material leakage caused by buckling is key to the formation of pool fire accidents, and several prevention measures for earthquake-induced landslide Natech was proposed according to the sensitivity analysis.     

Protecting atmospheric storage tanks against vacuum collapse

Vacuum collapse causes many accidents involving equipment with low pressure ratings such as atmospheric storage tanks and bins. This paper presents methods to establish the appropriate relief capacities and specify pressure relief devices to protect atmospheric storage tanks and other similar equipment against this hazard. Calculations are based on simple heat balance and fluid flow calculations.     

An emergency response plan for cascading post-earthquake fires in fuel storage facilities

Natural disasters such as large earthquakes may rapidly result in cascading events such as post-earthquake fires (PEFs) to trigger. This is particularly the case in industrial facilities which is well known as natural-hazard triggered technological accidents (NaTechs). This study provides a response framework for NaTechs caused by earthquake in fuel storage facilities. To do this, seismic vulnerability of fuel storage tanks and possible damage fashions are studied. Considering fuel leakages can result in PEFs, possible scenarios are simulated numerically using Process Hazard Analysis Software Tool (PHAST). A case study including 20 fuel tanks adjacent one to another is investigated to simulate a domino effect when different arbitrary tanks start to ignite; hence, the worst case scenario can be determined. Based on the results of the case studied, inability to extinguish the possible PEFs over less than 9 min can lead to spreading them to the adjacent tanks. The results indicate that it takes about 40 min the adjacent tanks involve in the fires. Therefore, it is of paramount importance to provide an emergency response plan in advance to properly respond to the fires. The study here also highlights the role of preventive strategies in reducing the associated risks of PEFs in industrial facilities.     

贫数据条件下海底电缆故障概率评估方法*

为解决贫数据引起海底电缆失效概率评估的不确定性影响,实施有效的海底电缆故障风险管理,提出1种耦合模糊集理论、层次贝叶斯分析（HBA）和贝叶斯网络的海底电缆失效概率评估方法,识别海底电缆失效致因因素,梳理各因素之间的关联关系,并采用贝叶斯网络(BN)构建海底电缆失效模型;根据数据源特点将电缆失效因素分为数据完全缺失和具有稀少的先兆数据,采用模糊集理论(FST)计算完全没有可用数据的失效致因发生概率,通过HBA估计有稀少数据失效致因的发生概率;以失效致因发生概率为输入,通过贝叶斯网络实现海底电缆失效概率的动态评估。研究结果表明:FST-HBA-BN方法可以解决基本风险因素的数据稀缺问题,量化评估海底电缆失效概率,研究结果可为贫数据条件下的电缆失效风险管理提供支撑。     

Study on the dynamic response of polyurea coated steel tank subjected to blast loadings

Steel tanks are widely used in the storage of various chemical liquids, and the blast resistance of the tanks is very important because of the explosiveness of these liquids. To explore a feasible method to improve the blast resistance of steel tanks, the effect of polyurea coating on the blast resistance of steel storage tank is investigated in this paper. The responses of monolithic steel tanks and polyurea coated tanks under blast loads are studied by field blast experiments using TNT explosive, and the results shows that the polyurea layers are effective in reducing the maximum and residual displacements of the tank. Numerical simulations are performed and validated, and the deformation process and stress and strain distribution of the tanks are analyzed accordingly. The increase on the bending moment of the plastic hinge lines of the tanks and the increase of the area density of the cylindrical shell induced by the polyurea layers are believed to be the two main factors contributing to the displacement reduction effect of polyurea in this paper. The validated numerical model is used to study the influence of polyurea layer's thickness on the deflection of the tank, and a nearly inversely proportional relationship between the thickness and the maximum displacement is found. Three deformation modes of the tanks are identified when subjected to blast load with varying intensity and it is found that the displacement reduction effect of polyurea varies in different deformation modes.     

Comparison of API650-2008 provisions with FEM analyses for seismic assessment of existing steel oil storage tanks

API650-2008 is one of the prominent codes consisting of seismic specifications to design steel storage tanks for earthquakes resistance. In spite of the code's broad application, there are some failure modes such as slide bottom, elephant-foot buckling, sloshing and uplift needing more evaluation. In this paper, 161 existing tanks in an oil refinery complex have been classified into 24 groups and investigated using both API650-2008 rules and numerical FEM models. Failure modes and dynamic characteristics of studied models have been calculated by numerical FEM analysis and compared with code requirements. The results demonstrate that, in some cases, there are some imperfections in the code requirements that require further investigation.     

化工储罐间距和体积对爆炸碎片多米诺效应概率的影响

化工储罐爆炸后将产生大量碎片,这些抛射碎片一旦击中相邻罐体容易引发多米诺效应。碎片的抛射方位和抛射距离具有很大的随机性,已有研究多采用概率模型来描述碎片抛射的各分过程。通过总结和发展已有的分过程模型,建立了求取多米诺效应的综合概率模型,并基于蒙特卡罗算法编制了模拟软件,可对化工储罐多米诺效应的发生概率进行预测计算。选取若干常用化工球罐为相邻目标储罐进行实例分析,计算结果表明储罐间距和体积是影响多米诺效应发生概率的两个重要影响因素：随着距离的增大,多米诺效应发生概率不断减小;目标储罐体积越大,多米诺效应发生概率将越大。其中,爆炸碎片对目标储罐的击中概率受上述因素的影响程度更大。该文工作对化工储罐区的安全评价具有一定的参考价值。