A methodology for the quantitative risk assessment of major accidents triggered by seismic events

A procedure for the quantitative risk assessment of accidents triggered by seismic events in industrial facilities was developed. The starting point of the procedure was the use of available historical data to assess the expected frequencies and the severity of seismic events. Available equipment-dependant failure probability models (vulnerability or fragility curves) were used to assess the damage probability of equipment items due to a seismic event. An analytic procedure was subsequently developed to identify, evaluate the credibility and finally assess the expected consequences of all the possible scenarios that may follow the seismic events. The procedure was implemented in a GIS-based software tool in order to manage the high number of event sequences that are likely to be generated in large industrial facilities. The developed methodology requires a limited amount of additional data with respect to those used in a conventional QRA, and yields with a limited effort a preliminary quantitative assessment of the contribution of the scenarios triggered by earthquakes to the individual and societal risk indexes. The application of the methodology to several case-studies evidenced that the scenarios initiated by seismic events may have a relevant influence on industrial risk, both raising the overall expected frequency of single scenarios and causing specific severe scenarios simultaneously involving several plant units.     

Definition of a short-cut methodology for assessing earthquake-related Na-Tech risk

Na-Tech (Natural and Technological) refers to industrial accidents triggered by natural events such as storms, earthquakes, flooding, and lightning. Herein, a qualitative methodology for the initial assessment of earthquake Na-Tech risk has been developed as a screening tool to identify which situations require a much more expensive Quantitative Risk Analysis (QRA). The proposed methodology, through suitable Key Hazard Indicators (KHIs), identifies the Na-Tech risk level associated with a given situation (i.e., a process plant located in a given territory), using the Analytical Hierarchy Process as a multi-criteria decision tool for the evaluation of such KHIs. The developed methodology was validated by comparing its computational results with QRA results that involved Na-Tech events previously presented in literature.     

The assessment of risk caused by domino effect in quantitative area risk analysis

A systematic procedure for the quantitative assessment of the risk caused by domino effect was developed. Escalation vectors, defined as the physical effects responsible of possible accident propagation, were identified for the primary scenarios usually considered in the QRA procedure. Starting from the assessment of the escalation vectors, the methodology allows the identification of credible domino scenarios and the estimation of their expected severity. A simplified technique was introduced for consequence and vulnerability assessment of domino scenarios. The overall contribution of domino effect to individual risk, societal risk and to the potential life loss index was calculated by a specific procedure, taking into account all the credible combinations of secondary events that may be triggered by each primary scenario. The development of a software package allowed the application of the procedure to several case-studies. The results evidenced the relevant modifications of the risk indexes caused by domino effect and the importance of including the quantitative analysis of domino effect in QRA, in order to correctly assess and control the risk caused by escalation scenarios.     

Using quantitative risk assessment in the chemical process industry

Growing concern about the risk of major chemical accidents in the USA has led both government and industry to find new ways to identify and evaluate potential hazards. Among the most promising (and misunderstood) approaches is a collection of techniques called quantitative risk assessment (QRA). Adapted primarily from probabilistic risk assessment approaches developed in other industries, the use of QRA is spreading rapidly through the US chemical industry. Of equal importance, legislators and regulatory agencies at the state and federal level are embracing QRA as part of their proposals for mandatory accident prevention measures.The Chemical Manufactures Association (CMA) and its member companies recognized the need to provide management personnel with a guide to QRA. Chemical process industry (CPI) managers need criteria for determining when risk assessment will provide information that will aid their decision making. Executives need help in understanding and evaluating QRA results that are often inscrutable to nonexperts, and CPI managers need advice concerning how detailed an analysis must be if it is to provide adequate information for a specific decision.JBF Associates, Inc., assisted by the Process Safety Analysis Task Group of CMA, prepared A Manager's Guide to Quantitative Risk Assessment (Arendt, J.S. et al., CMA, 1989). This paper gives an overview of the Guide and discusses important implications concerning the increasing acceptance of QRA as a chemical regulatory tool.     

A semi-quantitative approach to risk analysis, as an alternative to QRAs

In quantitative risk analysis (QRA) risk is quantified using probabilities and expected values, for example expressed by PLL values, FAR values, IR values and F–N curves. The calculations are tedious and include a strong element of arbitrariness. The value added by the quantification can certainly be questioned. In this paper, we argue that such analyses often are better replaced by semi-quantitative analyses, highlighting assessments of hazards and barriers, risk influencing factors (RIFs) and safety improvement measures. The assessments will be based on supporting information produced by risk analysts, including hard data and analyses of failure causes and mechanisms, barrier performance, scenario development, etc. The approach acknowledges that risk cannot be adequately described and evaluated simply by reference to summarising probabilities and expected values. There is a need for seeing beyond the standard probabilistic risk results of a QRA. Key aspects to include are related to uncertainties in phenomena and processes, and manageability factors. Such aspects are often ignored in standard QRAs.     

A probabilistic quantitative risk assessment model for the long-term work zone crashes

Work zones especially long-term work zones increase traffic conflicts and cause safety problems. Proper casualty risk assessment for a work zone is of importance for both traffic safety engineers and travelers. This paper develops a novel probabilistic quantitative risk assessment (QRA) model to evaluate the casualty risk combining frequency and consequence of all accident scenarios triggered by long-term work zone crashes. The casualty risk is measured by the individual risk and societal risk. The individual risk can be interpreted as the frequency of a driver/passenger being killed or injured, and the societal risk describes the relation between frequency and the number of casualties. The proposed probabilistic QRA model consists of the estimation of work zone crash frequency, an event tree and consequence estimation models. There are seven intermediate events – age (A), crash unit (CU), vehicle type (VT), alcohol (AL), light condition (LC), crash type (CT) and severity (S) – in the event tree. Since the estimated value of probability for some intermediate event may have large uncertainty, the uncertainty can thus be characterized by a random variable. The consequence estimation model takes into account the combination effects of speed and emergency medical service response time (ERT) on the consequence of work zone crash. Finally, a numerical example based on the Southeast Michigan work zone crash data is carried out. The numerical results show that there will be a 62% decrease of individual fatality risk and 44% reduction of individual injury risk if the mean travel speed is slowed down by 20%. In addition, there will be a 5% reduction of individual fatality risk and 0.05% reduction of individual injury risk if ERT is reduced by 20%. In other words, slowing down speed is more effective than reducing ERT in the casualty risk mitigation.     

Risk assessment and early warning systems for industrial facilities in seismic zones

Industrial equipments and systems can suffer structural damage when hit by earthquakes, so that accidental scenarios as fire, explosion and dispersion of toxic substances can take place. As a result, overall damage to people, environment and properties increases. The present paper deals with seismic risk analysis of industrial facilities where atmospheric storage tanks (anchored or unanchored to ground), horizontal pressurised tanks, reactors and pumps are installed. Simplified procedures and methodologies based on historical database and literature data on natural-technological (Na-Tech) accidents for seismic risk assessment are discussed.Equipment-specific fragility curves have been thus derived depending on a single earthquake measure, peak ground acceleration (PGA). Fragility parameters have been then transformed to linear probit coefficients in order to obtain reliable threshold values for earthquake intensity measure, both for structural damage and loss of containment. These threshold values are of great interest when development of active and passive mitigation actions and systems, safety management, and the implementation of early warning system are concerned.The approach is general and can be implemented in any available code or procedure for risk assessment. Some results of seismic analysis of atmospheric storage tanks are also presented for validation.     

A perceptual computing–based method to prioritize intervention actions in the probabilistic risk assessment techniques

Probabilistic risk assessment techniques as the systematic tools have been widely used on the different type of industrial sectors to reduce the estimated risk to an acceptable level. The fact is to design inherently safety; hazards have to be eliminated and reduced in risk as much as possible with the consideration of several interventions. In this regard, multicriteria decision making (MCDM) science is commonly integrated with the probabilistic risk assessment techniques to improve the safety performance of a system. Thus, it has been widely used to assist decision makers in controlling the identified process hazards in a different type of engineering applications. However, by increasing the complexity of industrial sectors as well as human being judgments, typical MCDM methods cannot highly guarantee their output results. According to this point, proposing MCDM methods based on mathematical programming have been interested in scholars due to high reliability and feasibility of the results. In this paper, we extended integration of MULTIMOORA approach with the Choquet integral under subjectivity circumstances to prioritize corrective actions in a typical probabilistic risk assessment technique. To illustrate the efficiency and feasibility of the proposed method, it has been applied in a real case study.     

Development of a framework for the risk assessment of Na-Tech accidental events

Natural events impacting on chemical and process plants may cause severe accidents, triggering the release of relevant quantities of hazardous substances. The present study focused on the development of the tools needed to build up a general framework allowing the extension of quantitative risk assessment procedure to include the analysis of the industrial accidents caused by natural events. Specific methods and models were developed to allow the quantitative assessment of risk caused by two categories of “Na-Tech” accidents: accidents triggered by earthquakes and accidents triggered by floods. The approach allows the identification of the different damage modes expected for process equipment and of the accidental scenarios that may be triggered. The damage models developed allow the calculation of the damage probability of equipment items due to the natural events. A specific methodology was issued to take into account the consequences of the possible contemporary failure of several process units due to the impact of the natural event. The procedure allows the calculation of the overall individual and societal risk indexes including the multiple-failure scenarios caused by the impact of natural events. The overall methodology was applied to the analysis of specific case studies.     

液化石油气泄漏的危险性分析及其事故后果评价方法

液化石油气（LPG）在其运输和存储过程中存在着各种与火灾和爆炸相关的危险性。由于LPG的泄漏可能导致包括闪火，不可控蒸气云爆炸，沸腾液体膨胀蒸汽爆炸等一系列灾害的发生，针对上述的各种灾害的具体发生条件及其危险性进行了分析；在事故后果评价中采用量化风险分析，提出了沸腾液体膨胀蒸汽爆炸和不可控蒸气云爆炸对周围人员可能造成伤害的评价方法。     

On the quantification of the effects of organizational and management factors in chemical installations

The quantitative effects of organizational and management factors in chemical installations are assessed through a linking of the results of a safety management audit with the basic events of a quantified risk assessment (QRA). A safety management audit establishes the relative position of the organizational and management aspects of a particular chemical installation with respect to an ideal management scheme, and for a number of failure causes and failure prevention combinations. A quantitative risk analysis including detailed system analysis offers a plant-specific decomposition of the plant-damage-state frequencies into events like hardware failures, maintenance-related failures, operation-related failures and so on. The basic events incorporated in the QRA are then categorized into classes similar to those explored by the management audit and are quantitatively linked to the audit results. Knowledge of these quantitative links would allow for the reflection of the deficiencies or strengths that might exist in the safety management system on the quantitative risk indices. A case study of an ammonia storage facility that has been audited demonstrates that the sensitivity of the risk indices to the value of the quantitative links is extremely high and that hence great care should be exercised in assessing these links.     

Appraising the flammability hazards of hydrocarbon refrigerants using quantitative risk assessment model. Part II. Model evaluation and analysis

Hydrocarbon refrigerants present are fire and explosion hazards due to their flammability. This paper describes a quantitative risk assessment (QRA) model to evaluate the potential for ignition when hydrocarbons are employed in stationary refrigeration and air-conditioning equipment. QRA enables examination of the effects that design, installation of equipment and external conditions on the frequency of ignition of the refrigerant and its consequences. Part I of this study presents the modelling approach for ignition frequencies, sub-models for refrigerant leakage and development of flammable concentration, and the associated consequences, being overpressures and thermal radiation. Part II provides recommended empirical input data and example results generated from the model.     

The accidental risk assessment methodology for industries (ARAMIS)/layer of protection analysis (LOPA) methodology: A step forward towards convergent practices in risk assessment?

In the last ten years, layer of protection analysis (LOPA) emerged as a simplified form of quantitative risk assessment (QRA). The European Commission funded project Accidental Risk Assessment Methodology for Industries in the context of the Seveso 2 Directive (ARAMIS) has recently been completed. ARAMIS has several modules which give a consistent simplified approach to risk assessment which does not approach the complexity or expense of full QRA. LOPA is potentially a means of carrying out the assessment of barriers required in ARAMIS. This paper attempts to explain the principles of LOPA and the means by which it can be used within ARAMIS.     

关于概率地震需求模型的讨论

概率地震需求分析作为地震易损性分析和地震风险分析的重要一环,已经成为新一代基于性能地震工程(PBEE)的主要研究内容。概率地震需求分析的核心内容是建立概率地震需求模型,它表征了地震动强度与地震需求之间的概率关系。在某一强度地震动作用下,通常假设地震需求服从对数正态分布,其中,地震需求的中位值和地震动强度之间假设服从对数线性关系,而地震需求的对数标准差则假设保持不变。该文以4个不同高度、不同设防水准的钢筋混凝土框架结构为例,挑选100条实际地震动为输入,针对上述概率地震需求模型基本假设的合理性进行了讨论。研究结果表明:综合考虑计算精度和效率,关于地震需求中位值和对数标准差的假设可以满足概率地震需求模型的要求,而传统的对数正态概率地震需求模型无法考虑倒塌的影响,应予以修正。     

Seismic PSA method for multiple nuclear power plants in a site

The maximum number of nuclear power plants in a site is eight and about 50% of power plants are built in sites with three or more plants in the world. Such nuclear sites have potential risks of simultaneous multiple plant damages especially at external events. Seismic probabilistic safety assessment method (Level-1 PSA) for multi-unit sites with up to 9 units has been developed. The models include Fault-tree linked Monte Carlo computation, taking into consideration multivariate correlations of components and systems from partial to complete, inside and across units. The models were programmed as a computer program CORAL reef. Sample analysis and sensitivity studies were performed to verify the models and algorithms and to understand some of risk insights and risk metrics, such as site core damage frequency (CDF per site-year) for multiple reactor plants. This study will contribute to realistic state of art seismic PSA, taking consideration of multiple reactor power plants, and to enhancement of seismic safety.     

基于概率的高层建筑地震需求模型与风险评估EI北大核心CSCD

提出了基于贝叶斯理论的地震风险评估方法,综合考虑了地震危险性模型、输入地震动记录、结构参数和需求模型的不确定性,并以云南大理地区1970年-2017年间的地震数据为研究基础进行了详细讨论。在传统基于概率地震危险性分析方法的基础上,提出了基于贝叶斯理论的地震危险性分析方法,通过贝叶斯更新准则,确定了地震概率模型中未知参数的后验概率分布;通过贝叶斯理论建立了基于概率的地震需求模型,并在易损性中考虑了需求模型认知不确定性的影响;以42层钢框架-RC核心筒建筑为例,开展了地震作用下的风险评估。研究表明:基于贝叶斯理论的地震危险性分析方法,能够获得更为合理的危险性模型;忽略需求模型中参数不确定性的影响,将错误估计结构的地震易损性;不同加载工况将对高层建筑的地震风险产生显著影响。提出的概率风险评估方法,提供了可以考虑固有不确定性和认知不确定性的有效途径,有助于推动高性能结构地震韧性评价和设计理论的发展。     

Fire safety assessment and optimal design of passive fire protection for offshore structures

The article presents a unified probabilistic approach to fire safety assessment and optimal design of passive fire protection on offshore topside structures. The methodology was developed by integrating quantitative risk analysis (QRA) techniques with the modem methods of structural system reliability analysis (SRA) and reliability based design optimisation (RBDO). Reliability analysis methodologies are presented for both plated (e.g. fire and blast walls) and skeletal structures (deck framing), which take into account uncertainties in fire and blast loading, thermal and mechanical properties of the steel and insulation. Probability of component and system failure are evaluated using first- and second-order reliability methods (FORM/SORM). The optimisation of passive fire protection is performed such that the total expected cost of the protection system is minimised while satisfying reliability constraints.     

第二代基于性能地震工程中的地震易损性模型及正逆概率风险分析

第二代基于性能地震工程理论中的地震易损性主要是指结构构件以及非结构构件的抗震能力,与传统地震风险理论中的地震易损性定义和内涵并不相同。为了澄清二者的不一致性,首先介绍传统地震风险理论中地震易损性的定义和概率模型,然后指出第二代基于性能地震工程理论存在五个层次的地震易损性模型:地震需求易损性模型、抗震能力易损性模型、地震损伤易损性模型、地震损失易损性模型和抗震决策易损性模型,指出了这五种模型的区别及其相互关系,推导得到了地震需求易损性模型和地震损伤易损性模型分布参数的解析表达式。在此基础上,根据不同的不确定性传递路径,提出了正向PBEE和逆向PBEE的概念,以通过不同方式求解第二代基于性能地震工程理论的风险积分公式。基于地震危险性函数的近似表达式以及地震易损性模型及其分布参数的解析表达式,通过正向PBEE和逆向PBEE方法,分别得到了具有相同表达形式的工程需求参数EDP、地震损伤DM和决策变量DV三个层次的概率地震风险表达式。通过该文的研究,将传统地震风险分析理论与第二代基于性能地震工程理论统一在一致的理论框架之中。     

Analytical simulation and PROFAT II: a new methodology and a computer automated tool for fault tree analysis in chemical process industries

Fault tree analysis (FTA) is based on constructing a hypothetical tree of base events (initiating events) branching into numerous other sub-events, propagating the fault and eventually leading to the top event (accident). It has been a powerful technique used traditionally in identifying hazards in nuclear installations and power industries. As the systematic articulation of the fault tree is associated with assigning probabilities to each fault, the exercise is also sometimes called probabilistic risk assessment. But powerful as this technique is, it is also very cumbersome and costly, limiting its area of application. We have developed a new algorithm based on analytical simulation (named as AS-II), which makes the application of FTA simpler, quicker, and cheaper; thus opening up the possibility of its wider use in risk assessment in chemical process industries. Based on the methodology we have developed a computer-automated tool. The details are presented in this paper.     

基于LHS-MC方法的矮塔斜拉桥地震风险概率分析

提出一种既能避免繁琐积分,又能综合考虑结构材料和地震波动随机性问题以及地震危险性的地震风险概率计算方法。基于结构材料参数的概率分布,采用拉丁超立方抽样(LHS)方法考虑结构构件材料参数的随机性,并结合选取的地震波,形成地震动-桥梁组合样本集。针对典型矮塔斜拉桥结构体系建立非线性有限元纤维模型,确定各主要构件的损伤指标,与增量动力分析方法相结合进行了地震易损性分析,选取合适的分布函数,拟合加速度峰值-结构损伤概率曲线。采用蒙特卡罗(MC)抽样方法离散地震危险性概率模型,避免了繁琐的积分,针对典型矮塔斜拉桥的地震风险概率进行了评估。