SCAP: a new methodology for safety management based on feedback from credible accident-probabilistic fault tree analysis system

As it is conventionally done, strategies for incorporating accident--prevention measures in any hazardous chemical process industry are developed on the basis of input from risk assessment. However, the two steps-- risk assessment and hazard reduction (or safety) measures--are not linked interactively in the existing methodologies. This prevents a quantitative assessment of the impacts of safety measures on risk control.We have made an attempt to develop a methodology in which risk assessment steps are interactively linked with implementation of safety measures. The resultant system tells us the extent of reduction of risk by each successive safety measure. It also tells based on sophisticated maximum credible accident analysis (MCAA) and probabilistic fault tree analysis (PFTA) whether a given unit can ever be made 'safe'. The application of the methodology has been illustrated with a case study.     

A global view on ARAMIS, a risk assessment methodology for industries in the framework of the SEVESO II directive

The ARAMIS methodology was developed in an European project co-funded in the fifth Framework Programme of the European Commission with the objective to answer the specific requirements of the SEVESO II directive. It offers an alternative to purely deterministic and probabilistic approaches to risk assessment of process plants. It also answers the needs of the various stakeholders interested by the results of the risk assessment for land use or emergency planning, enforcement or, more generally, public decision-making. The methodology is divided into the following major steps: identification of major accident hazards (MIMAH), identification of the safety barriers and assessment of their performances, evaluation of safety management efficiency to barrier reliability, identification of reference accident scenarios (MIRAS), assessment and mapping of the risk severity of reference scenarios and of the vulnerability of the plant surroundings. The methodology was tested during five case studies, which provided useful information about the applicability of the method and, by identifying the most sensitive parts of it opened way to new research activity for an improved industrial safety.     

Precautions against industrial accidents: experience in applying the Seveso II Directive in central and eastern European countries.

Adopted approaches to safety reports and internal emergency plans are described. Based on the provisions of the Seveso II Directive and on the achieved state of hazard prevention management of the respective enterprises in central and eastern European states, reports and plans were prepared. Although these states are no members of the European Union, the parties recognised the requirements of the Seveso II Directive as a working basis. In detail: Methodical experience in preparing safety reports and emergency plans include a methodology in the three main steps: Analysis of information on hazardous substances, hazard analysis including all plants, more specific hazard analysis for representative plants. Basic ways of forming scenarios are given. According to a procedure, various types of scenarios were usually taken into account. Based on the assessment of effects of a substance release, important conclusions can be drawn regarding the extent of danger prevention. In most cases, the structure of the described internal accident emergency plan turned out to be helpful. The programmed system DISMA (Disaster Management) which is widely used in Germany turned out to be a suitable tool for the internal as well as external emergency planning. An example of information to the population is described.     

Application of Bayesian network to the probabilistic risk assessment of nuclear waste disposal

The scenario in a risk analysis can be defined as the propagating feature of specific initiating event which can go to a wide range of undesirable consequences. If we take various scenarios into consideration, the risk analysis becomes more complex than do without them. A lot of risk analyses have been performed to actually estimate a risk profile under both uncertain future states of hazard sources and undesirable scenarios. Unfortunately, in case of considering specific systems such as a radioactive waste disposal facility, since the behaviour of future scenarios is hardly predicted without special reasoning process, we cannot estimate their risk only with a traditional risk analysis methodology. Moreover, we believe that the sources of uncertainty at future states can be reduced pertinently by setting up dependency relationships interrelating geological, hydrological, and ecological aspects of the site with all the scenarios. It is then required current methodology of uncertainty analysis of the waste disposal facility be revisited under this belief.In order to consider the effects predicting from an evolution of environmental conditions of waste disposal facilities, this paper proposes a quantitative assessment framework integrating the inference process of Bayesian network to the traditional probabilistic risk analysis. We developed and verified an approximate probabilistic inference program for the specific Bayesian network using a bounded-variance likelihood weighting algorithm. Ultimately, specific models, including a model for uncertainty propagation of relevant parameters were developed with a comparison of variable-specific effects due to the occurrence of diverse altered evolution scenarios (AESs). After providing supporting information to get a variety of quantitative expectations about the dependency relationship between domain variables and AESs, we could connect the results of probabilistic inference from the Bayesian network with the consequence evaluation model addressed. We got a number of practical results to improve current knowledge base for the prioritization of future risk-dominant variables in an actual site.     

Time considerations in recovery analysis

Recovery analysis is the mechanism in risk assessment to account for a complex matrix of situational and engineered aspects of a plant's preparedness for incident response and accident management. This analysis needs to be as accurate and credible as possible in order that the utility optimally allocates necessarily limited risk management resources. A credible recovery analysis must appropriately identify the engineering context of incident response and correctly specify this response in probabilistic terms so as to meld into the overall assessment. Each of these recovery aspects involves complicated timing considerations, that apparently heretofore have not received much attention. The adequate accounting of timing is the focus of this technical note.     

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。     

A framework for evaluating hydrogen control and management

The present paper presents a new framework for assessing accident management strategies using decision trees. The containment event tree (CET) model considers characteristics associated with the implementation of each strategy. It is constructed and quantified using data obtained from NUREG-1150, other probabilistic risk assessments, and the MAAP4 calculations. The proposed framework for evaluating hydrogen control strategies is based on the concept of a measure using a risk triplet. Ulchin units of nuclear power plants 3 and 4 are used as the reference plant. On the basis of best-estimate assessment, it is shown that it is beneficial to execute hydrogen igniters rather than to do nothing with respect to expected value of hydrogen concentration in the containment during an accident. The proposed approach is shown to be flexible in that it can be applied to various accident management strategies based on the timing of mitigation. The advantage of using the CET for assessing an accident management strategy lies with its capability for modeling both the positive and negative aspects associated with progression of the accident, which may in turn affect the containment failure mode.     

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.     

Multi-attribute risk assessment for risk ranking of natural gas pipelines

The paper presents a decision model for risk assessment and for risk ranking of sections of natural gas pipelines based on multi-attribute utility theory. Pipeline hazard scenarios are surveyed and the reasons for a risk assessment model based on a multi-attribute approach are presented. Three dimensions of impact and the need to translate decision-makers’ preferences into risk management decisions are highlighted. The model approaches these factors by using a multi-attribute utility function, in order to produce multi-dimensional risk measurements. By using decision analysis concepts, this model quantitatively incorporates the decision-maker's preferences and behavior regarding risk within clear and consistent risk measurements. In order to support the prioritizing of critical sections of pipeline in natural gas companies, this multi-attribute model also allows sections of pipeline to be ranked into a risk hierarchy. A numerical application based on a real case study was undertaken so that the effectiveness of the decision model could be verified.     

A practical approach to fire hazard analysis for offshore structures

Offshore quantitative risk assessments (QRA) have historically been complex and costly. For large offshore design projects, the level of detail required for a QRA is often not available until well into the detailed design phase of the project. In these cases, the QRA may be unable to provide timely hazard understanding. As a result, the risk reduction measures identified often come too late to allow for cost effective changes to be implemented. This forces project management to make a number of difficult or costly decisions. This paper demonstrates how a scenario-based approached to fire risk assessment can be effectively applied early in a project's development. The scenario or design basis fire approach calculates the consequence of a select number of credible fire scenarios, determines the potential impact on the platform process equipment, structural members, egress routes, safety systems, and determines the effectiveness of potential options for mitigation. The early provision of hazard data allows the project team to select an optimum design that is safe and will meet corporate or regulatory risk criteria later in the project cycle. The focus of this paper is on the application of the scenario-based approach to gas jet fires. This paper draws on recent experience in the Gulf of Mexico (GOM) and other areas to outline an approach to fire hazard analysis and fire hazard management for deep-water structures. The methods presented will include discussions from the recent June 2002 International Workshop for Fire Loading and Response.     

Current practices for risk zoning around nuclear power plants in comparison to other industry sectors

This paper analyses the background and current status of the information basis leading to the definition of risk and emergency zones around nuclear power plants (NPPs) in different countries in Europe and beyond. Although dependable plant-specific probabilistic safety assessment (PSA) of level 2 and/or level 3 could in principle provide sufficiently detailed input to define the geographical dimension of a NPP's risk and emergency zones, the analysis of the status in some European and other countries shows that other, "deterministic" approaches using a reference accident are actually used in practice. Regarding use of level 2 PSA for emergency planning, the approach so far has been to use the level 2 PSA information retrospectively to provide the justification for the choice of reference accident(s) used to define the emergency plans and emergency planning zones (EPZs). There are significant differences in the EPZs that are defined in different countries, ranging from a few up to 80km. There is a striking contrast in the extent of using probabilistic information to define emergency zones between the nuclear and other high risk industry sectors, such as the chemical process industry, and the reasons for these differences are not entirely clear, since the risk of chemical industry is similar as that of the nuclear sector. The differences seem to be more related to risk perception than to the actual risk potential. Therefore, there is a strong need to be able to communicate risk information to the Public both before and following an accident. In addition, there is a need to educate the Public so that they can understand risk information in a comparative sense. Finally, based on the consensus discussions at a recent JRC/OECD International Seminar on Risk and Emergency Zoning around NPPs, a set of recommendations is given in the areas of: -a more comprehensive use of the available risk information for risk zoning purposes, -risk communication; -comparative (energy) risk assessment.     

An approach for assessing human decision reliability

This paper presents a method to study human reliability in decision situations related to nuclear power plant disturbances. Decisions often play a significant role in handling of emergency situations. The method may be applied to probabilistic safety assessments (PSAs) in cases where decision making is an important dimension of an accident sequence. Such situations are frequent e.g. in accident management. In this paper, a modelling approach for decision reliability studies is first proposed. Then, a case study with two decision situations with relatively different characteristics is presented. Qualitative and quantitative findings of the study are discussed. In very simple decision cases with time pressure, time reliability correlation proved out to be a feasible reliability modelling method. In all other decision situations, more advanced probabilistic decision models have to be used. Finally, decision probability assessment by using simulator run results and expert judgement is presented.     

ARAMIS project: a comprehensive methodology for the identification of reference accident scenarios in process industries

In the frame of the Accidental Risk Assessment Methodology for Industries (ARAMIS) project, this paper aims at presenting the work carried out in the part of the project devoted to the definition of accident scenarios. This topic is a key-point in risk assessment and serves as basis for the whole risk quantification.

The first result of the work is the building of a methodology for the identification of major accident hazards (MIMAH), which is carried out with the development of generic fault and event trees based on a typology of equipment and substances. The term “major accidents” must be understood as the worst accidents likely to occur on the equipment, assuming that no safety systems are installed.

A second methodology, called methodology for the identification of reference accident scenarios (MIRAS) takes into account the influence of safety systems on both the frequencies and possible consequences of accidents. This methodology leads to identify more realistic accident scenarios. The reference accident scenarios are chosen with the help of a tool called “risk matrix”, crossing the frequency and the consequences of accidents.

This paper presents both methodologies and an application on an ethylene oxide storage.     

Dynamic modeling of the tradeoff between productivity and safety in critical engineering systems

Short-term tradeoffs between productivity and safety often exist in the operation of critical facilities such as nuclear power plants, offshore oil platforms, or simply individual cars. For example, interruption of operations for maintenance on demand can decrease short-term productivity but may be needed to ensure safety. Operations are interrupted for several reasons: scheduled maintenance, maintenance on demand, response to warnings, subsystem failure, or a catastrophic accident. The choice of operational procedures (e.g. timing and extent of scheduled maintenance) generally affects the probabilities of both production interruptions and catastrophic failures. In this paper, we present and illustrate a dynamic probabilistic model designed to describe the long-term evolution of such a system through the different phases of operation, shutdown, and possibly accident. The model's parameters represent explicitly the effects of different components' performance on the system's safety and reliability through an engineering probabilistic risk assessment (PRA). In addition to PRA, a Markov model is used to track the evolution of the system and its components through different performance phases. The model parameters are then linked to different operations strategies, to allow computation of the effects of each management strategy on the system's long-term productivity and safety. Decision analysis is then used to support the management of the short-term trade-offs between productivity and safety in order to maximize long-term performance. The value function is that of plant managers, within the constraints set by local utility commissions and national (e.g. energy) agencies. This model is illustrated by the case of outages (planned and unplanned) in nuclear power plants to show how it can be used to guide policy decisions regarding outage frequency and plant lifetime, and more specifically, the choice of a reactor tripping policy as a function of the state of the emergency core cooling subsystem.     

Analysing the risk of LNG carrier operations

This paper presents a generic, high-level risk assessment of the global operation of ocean-going liquefied natural gas (LNG) carriers. The analysis collects and combines information from several sources such as an initial hazid, a thorough review of historic LNG accidents, review of previous studies, published damage statistics and expert judgement, and develops modular risk models for critical accident scenarios. In accordance with these risk models, available information from different sources has been structured in the form of event trees for different generic accident categories. In this way, high-risk areas pertaining to LNG shipping operations have been identified. The major contributions to the risk associated with LNG shipping are found to stem from five generic accident categories, i.e. collision, grounding, contact, fire and explosion, and events occurring while loading or unloading LNG at the terminal. Of these, collision risk was found to be the highest. According to the risk analysis presented in this paper, both the individual and the societal risk level associated with LNG carrier operations lie within the As Low As Reasonable Practicable (ALARP) area, meaning that further risk reduction should be required only if available cost-effective risk control options could be identified. This paper also includes a critical review of the various components of the risk models and hence identifies areas of improvements and suggests topics for further research.     

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。     

基于本质安全的工业事故风险管理方法研究

从风险管理角度对生产过程中的安全防护方法进行了分类和论述,提出了基于本质安全思想的工业 事故综合风险管理方法与程序,其核心内容是在常规的危险辨识和风险评价基础上,优先应用本质安全原理来 减少、消除危险,综合采用无源安全措施、有源安全措施或多层安全防护措施与功能安全标准,将风险降低至 可接受水平;提出了本质安全应与清洁生产、绿色化学、循环经济同等纳入优先发展的技术和政策等建议。     

The development and application of the accident dynamic simulator for dynamic probabilistic risk assessment of nuclear power plants

This paper describes the principal modelling concepts, practical aspects, and an application of the Accident Dynamic Simulator (ADS) developed for full scale dynamic probabilistic risk assessment (DPRA) of nuclear power plants. Full scale refers not only to the size of the models, but also to the number of potential sequences which should be studied. Plant thermal-hydraulics behaviour, safety systems response, and operator interactions are explicitly accounted for as integrated active parts in the development of accident scenarios. ADS uses discrete dynamic event trees (D-DET) as the main accident scenario modelling approach, and introduces computational techniques to minimize the computer memory requirement and expedite the simulation. An operator model (including procedure-based behaviour and several types of omission and commission errors) and a thermal-hydraulic model with a PC run time more than 300 times faster than real accident time are among the main modules of ADS. To demonstrate the capabilities of ADS, a dynamic PRA of the Steam Generator Tube Rupture event of a US nuclear power plant is analyzed.     

Marked point process framework for living probabilistic safety assessment and risk follow-up

We construct a model for living probabilistic safety assessment (PSA) by applying the general framework of marked point processes. The framework provides a theoretically rigorous approach for considering risk follow-up of posterior hazards. In risk follow-up, the hazard of core damage is evaluated synthetically at time points in the past, by using some observed events as logged history and combining it with re-evaluated potential hazards. There are several alternatives for doing this, of which we consider three here, calling them initiating event approach, hazard rate approach, and safety system approach. In addition, for a comparison, we consider a core damage hazard arising in risk monitoring. Each of these four definitions draws attention to a particular aspect in risk assessment, and this is reflected in the behaviour of the consequent risk importance measures. Several alternative measures are again considered. The concepts and definitions are illustrated by a numerical example.     

The ARIPAR project: analysis of the major accident risks connected with industrial and transportation activities in the Ravenna area

The paper describes the ARIPAR project aimed at the assessment of the major accident risks connected with storage, process and transportation of dangerous substances in the densely populated Ravenna area in Italy, which includes a large complex of chemical and petrochemical plants and minor industries, essentially distributed around an important commercial port. Large quantities of dangerous goods are involved in various transportation forms connected with the industrial and commercial activity of the port. The project started by making a complete inventory of fixed installations and transportation activities capable of provoking major fire, explosion and toxic release events; then relevant accident scenarios were developed for the single hazard sources; probabilities were assigned to the events and consequences were evaluated; finally iso-risk contours and F-N diagrams were evaluated both for the single sources and for the overall area. This required the development of a particular methodology for analysis of area risk and of associated software packages which allowed examination of the relative importance of the different activities and typologies of materials involved. The methodological approach and the results have proved to be very useful for the priority-ranking of risk mitigating interventions and physical planning in a complex area.