Learning from the application of nuclear probabilistic safety assessment to the chemical industry

This paper introduces the new approach of risk analysis established by the French Ministry of the Environment and develops the benefits of applying nuclear probabilistic safety assessment approaches to the chemical industry.In the aftermath of the AZF disaster in Toulouse on 21 September 2001, a new law was proposed by the French government asking for the investigation of all representative scenarios and the assessment of the probability of the resulting dangerous phenomena to demonstrate an acceptable level of safety. Therefore, any accident is investigated from a global point of view, according to its gravity and its probability.In 2000, the French Ministry of the Environment asked the Institute for Radiological Protection and Nuclear Safety (IRSN), and in particular its Systems and Risk Protection Assessment (SESPRI) and its Industrial Risks, Fire and Containment Assessment and Study (SERIC) departments, to conduct a Probabilistic Safety Assessment (PSA) study of an LPG distribution facility, specially for the BLEVE scenario. This study has showed the power of PSA for defining and prioritizing actions to be carried out to improve safety of facilities; however, it requires credible data for reliability and failure of the equipment, not available in generic failure databases.Since 2007, IRSN has taken several initiatives in collaboration with operators in order to provide more precise and representative failure rates for main safety equipment, ready to use in future PSA relative to LPG plants.     

Evaluation of risk and cost using an age-dependent unavailability modelling of test and maintenance for standby components

The improvement of safety in the process industries is related to assessment and reduction of risk in a cost-effective manner. This paper addresses the trade-off between risk and cost related to standby safety systems. An age-dependent unavailability model that integrates the effects of the test and maintenance (T&M) activities as well as component ageing is developed and represents the basis for calculating risk. The repair “same-as-new” process is considered regarding the T&M activities. Costs are expressed as a function of the selected risk measure. The time-averaged function of the selected risk measure is obtained from probabilistic safety assessment, i.e. the fault tree analysis. This function is further extended with inclusion of additional parameters related to T&M activities as well as ageing parameters related to component ageing. In that sense, a new model of system unavailability, incorporating component ageing and T&M costs, is presented. The testing strategy is also addressed. Sequential and staggered testings are compared. The developed approach is applied on a standard safety system in nuclear power plant although the method is applicable to standby safety systems that are tested and maintained in other industries as well. The results show that the risk-informed surveillance requirements differ from existing ones in technical specifications, which are deterministically based. Moreover, the presented approach achieves a significant reduction in system unavailability over a relatively small increase of total T&M costs.     

Decision analysis on fire safety design based on evaluating building fire risk to life

This study presents a framework of decision analysis on fire safety design alternatives based on evaluating building fire risk to life. A probabilistic risk assessment method for occupant life is presented with consideration of some uncertainties of evacuation process and fire development at first. For occupant evacuation time assessment, occupant pre-movement time is characterized by normal distribution. For onset time to untenable conditions assessment, its uncertainty is considered as probability distribution according to the range of design fires. Based on event tree technique, probable fire scenarios are analyzed with consideration of the effect of fire protection systems, employees extinguishing, etc. It is difficult to make a precise assessment on probability and consequence of every fire scenario, but their lower bound and upper bound can be achieved based on statistical data. Therefore, Supersoft Decision Theory [Malmnäs, P.E., 1995. Methods of Evaluation in Supersoft Decision Theory. Department of Philosophy, Stockholm University, 365 Stockholm; Johansson, H., Malmnäs, P.E., 2000. Application of supersoft decision theory in fire risk assessment. Journal of Fire Protection Engineering 14, 55–84] that allows decision maker to utilize vague statement is utilized to integrate with risk assessment to make decision on different fire safety design alternatives. To express how to make decision on different fire safety design alternatives based on evaluating building fire risk to life, two hypothetical fire safety design alternatives for a commercial building are presented.     

Uncertainty representation and propagation in quantified risk assessment using fuzzy sets

It is generally acknowledged that there are substantial uncertainties present in any analysis of risk. This paper provides a brief overview of the current techniques used for uncertainty analyses, and highlights their inappropriateness for practical use in the complete risk assessment process. The concept of fuzzy sets as a means for quantifying uncertainty is introduced and a case study demonstrates the application of this method to a simple consequence analysis where parameter uncertainty is considered. The results of this fuzzy analysis are compared with those of a more traditional probabilistic approach using a Monte Carlo simulation. This comparison demonstrates that the novel approach of fuzzy sets is a more appropriate technique due to its non-statistical nature and that the amount of computation required is substantially reduced compared to the traditional probabilistic approach. The versatility of fuzzy set theory suggests that this approach could also be used to quantify other types of uncertainty present in the risk assessment process, including model uncertainty and expert opinion.     

改进的HAZOP风险评价方法

HAZOP方法是一种使用简单却高度专业化、系统化,能够覆盖过程工业安全评价各个环节的危险辨识与评估方法。但是,HAZOP方法作为一种定性风险分析方法,仅仅是从定性方面分析装置中是否存在的潜在风险,对于存在的潜在风险,不能量化其严重度和可能性,HAZOP定量/半定量化分析成为本研究领域的发展趋势。本文从三个方面提出了改进HAZOP分析方法。首先,由于工艺参数和引导词构成偏差,根据工艺参数的分类,将偏差划分为数值型和逻辑型,进行了一步半定量化;其次,引入了毒性参数,对后果严重等级重新划分为五级;最后根据风险矩阵理论,运用风险矩阵C=X＋Y规则,计算出风险矩阵,按照风险评价的需要并且根据生产的实际安全管理状况,划分风险等级为四级,得到了新的风险矩阵,从而把HAZOP分析法从一种定性的方法改进为一种半定量的方法。     

欧盟城市饮用水供应链风险管理与评价及其借鉴

结合欧盟2006年起开展的TECHNEAU(Technology Enabled Universal Access to Safe Water)项目,介绍了欧盟城市"从水源到用户的饮用水供应链"风险管理机制,以及"风险识别、评估、减缓和控制"综合风险评价框架;并从水源地、水处理系统、配水系统、历史风险事件、风险评价方法、评价结果6方面比较了捷克、德国、荷兰、挪威、瑞典5个国家典型城市风险评价实践,着重分析了瑞典哥特堡市风险评价中采用的综合概率故障树法和客户损失时间指数方法及其应用价值。总结了欧盟饮用水供应链的风险管理在全过程管理策略、"关口前移"管理方针、多样性的风险评价方法与技术、参与主体多元化、评价结果公开透明5个方面的成功做法和经验,可供国内参考。     

A Dynamic Bayesian Network-based approach to Resilience Assessment of Engineered Systems

Traditional risk assessment approaches mainly focus on the pre-failure scenarios with certain information. For complex systems, the scope of risk assessment needs to be extended to include the post-failure phase; because the emerging hazards of these systems cannot be wholly identified and are usually highly uncertain. Thus, resilience assessment needs to be investigated. Most of the existing literature quantify resilience based on a system's performance loss caused by disruptions. These studies fail to assess the probability of a system to sustain or restore to a normal operational state after disruptions occur, how this probability changes with time, and how fast the system can be restored. The dynamic and probabilistic characteristics of resilience must be considered in systemic resilience assessment, in which the engineered system, human and organizational factors, and external disruptions are considered. This paper aims to develop a dynamic Bayesian network (DBN)-based approach to the probabilistic assessment of the system resilience by incorporating temporal processes of adaption and recovery into the analysis of system functionality. The proposed method also provides a new way to define resilience in terms of the probability of system functionality change during and after a disruption. A case study on the Chevron refinery accident is used to demonstrate the applicability of the proposed methodology.     

基于集对分析法的煤矿危险性评价

煤矿危险性评价包含因素较多导致评价是一个比较复杂的过程,评价方法已经成为一个关键问题。讨论了集对分析相关理论,并将集对分析引入煤矿危险性评价中,建立了煤矿危险性评价指标体系,针对不考虑煤矿评价指标权重与考虑指标权重两种情况,通过联系度与集对势综合判断煤矿危险性态势,并对某煤矿的危险性进行评价,在不考虑指标权重与考虑指标权重两种情况下均处于"一般安全"等级,但后者的安全等级程度更低,两种情况的态势均属于微同势,也说明了该煤矿存在安全隐患,需要采取相关的安全措施并加强安全管理,该方法为煤矿危险性评价提供了一条新的方法和手段。     

Effects of soil-structure interaction on fragility and seismic risk; a case study of power plant containment

Safety-related structures are designed to provide a safe environment for the occupants and equipment during and after earthquakes. This is due to the fact that any damage imposed to the systems might lead to catastrophic consequences. Seismic probabilistic risk assessment (SPRA) is a systematic approach for the quantification of the seismic risk. One of the crucial steps in this assessment is to determine the seismic capacity of the structures by fragility method. After a review of available methodologies, this article analyzes the seismic fragility for a typical power plant containment considering the effects of soil-structure interaction (SSI). The structure and underneath soil profile are analyzed as a unified model by the subtraction method. Two steps are considered for the assessment of seismic response: In the first step, a fixed-base hypothesis framework is implemented to the computational problem. The second step covers computations taking into account the SSI effects. Using the results of seismic response analysis and safety factor method, seismic fragility of the structure is computed and related fragility curves are developed. Finally, by comparing the fragility curves, the effects of SSI are quantified on the overall seismic risk.     

Dynamic-risk-informed safety barrier management: An application to cost-effective barrier optimization based on data from multiple sources

An integrated approach for performance assessment and management of safety barriers in a systemic manner is needed concerning the prevention and mitigation of major accidents in chemical process industries. Particularly, the effects of safety barriers on system risk reduction should be assessed in a dynamic manner to support the decision-making on safety barrier establishments and improvements. A simulation approach, named Simulink-based Safety Barrier Modeling (SSBM), is proposed in this paper to conduct dynamic risk assessment of chemical facilities with the consideration of the degradation of safety barriers. The main functional features of the SSBM include i) the basic model structures of SSBM can be determined based on bow-tie diagrams, ii) multiple data (periodic proof test data, continuous condition-monitoring data, and accident precursor data) may be combined to update barrier failure probabilities and initiating event probabilities, iii) SSBM is able to handle uncertainty propagation in probabilistic risk assessment by using Monte Carlo simulations, and iv) cost-effectiveness analysis (CEA) and optimization algorithms are integrated to support the decision-making on safety barrier establishments and improvements. An illustrative case study is demonstrated to show the procedures of applying the SSBM on dynamic risk-informed safety barrier management and validate the feasibility of implementing the SSBM for cost-effective safety barrier optimization.     

一种安全分析新思路--安全薄弱环节评价

职业安全和公共安全有许多共同点,可以把公共安全技术用于职业安全,公共安全主要有3种工作方法：安全监察、风险评价（或叫设计隐患）和薄弱环节评价。后者常常最有效。公共安全的薄弱评价法可以用于职业安全分析,象“坏人”一样思考有利于辨识安全薄弱环节。安全薄弱环节评价可以为职业安全分析提供新的视角。     

概率火灾安全分析方法研究

为分析和评估火灾对设备、建筑物等敏感目标结构安全的影响,结合化工定量风险评估方法和气体爆炸概率安全分析方法,提出概率火灾安全分析策略和实施流程。该方法包括火灾危害辨识、泄漏速率计算、火灾后果模拟、频率分析、绘制频率超越热载荷曲线、结构响应分析等关键步骤。以某柴油罐区为例,通过频率分析和火灾模拟,绘制出频率超越热载荷曲线,假定火灾风险可接受准则为10-4/a,求得对应的可信热载荷为21 kW/m2,并以此值作为结构热响应分析的输入参数。火灾概率安全分析方法侧重于描述火灾热辐射强度及其对应的发生可能性,判定敏感目标遭遇的可信火灾热载荷强度和结构热响应行为,评估消防减灾措施效果,确保结构完整性和可用性,不评价工艺系统潜在火灾风险的高低。     

A fuzzy logic and probabilistic hybrid approach to quantify the uncertainty in layer of protection analysis

Layer of protection analysis (LOPA) is a widely used semi-quantitative risk assessment method. It provides a simplified and less precise method to assess the effectiveness of protection layers and the residual risk of an incident scenario. The outcome failure frequency and consequence of that residual risk are intended to be conservative by prudently selecting input data, given that design specification and component manufacturer's data are often overly optimistic. There are many influencing factors, including design deficiencies, lack of layer independence, availability, human factors, wear by testing and maintenance shortcomings, which are not quantified and are dependent on type of process and location. This makes the risk in LOPA usually overestimated. Therefore, to make decisions for a cost-effective system, different sources and types of uncertainty in the LOPA model need to be identified and quantified. In this study, a fuzzy logic and probabilistic hybrid approach was developed to determine the mean and to quantify the uncertainty of frequency of an initiating event and the probabilities of failure on demand (PFD) of independent protection layers (IPLs). It is based on the available data and expert judgment. The method was applied to a distillation system with a capacity to distill 40 tons of flammable n-hexane. The outcome risk of the new method has been proven to be more precise compared to results from the conventional LOPA approach.     

Occupational risks and the value and modelling of a measurement of severity

In studies of occupational risks, severity, which is a component of the estimation of every risk, appears as a multifaceted entity assessable according to numerous criteria. A method of measuring the degree of severity of the consequences of potentially dangerous events would be of undeniable value to organisations seeking to improve their understanding of the complexity of such events. The need to control severity is highlighted by scientifically acquired improvements in the understanding of occupational risks, by certain new regulatory obligations in Europe, and by some requirements in the financial management of organisations. We put forward a statistical way of integrating several constituent elements of severity and hence of determining a relevant, synthetic, one-dimensional index. This is achieved by means of principal component analysis (PCA), which is used here to calculate a resultant severity, as in some physical measurements. We also investigate how severity may be statistically modelled, with the aim of contributing to the quantitative assessment of occupational risks. The choice of parametric models is detailed and illustrated by the search for a suitable model for workplace accidents in an organisational setting. The practical value of modelling severity is two-fold. First, one is able to study the distribution of the numerical values of severity over a continuum (a theoretically infinite numerical set) rather than through a limited number of arbitrarily defined categories. Second, with a generally applicable parametric model, one can estimate the law of probability of a measurement of severity in a particular situation, notably recent or new. Lastly, the statistical concept of risk curve is defined and discussed. The goal is to incorporate the severity component into the risk assessment in the form of a probability law, thus circumventing the difficulties associated with an analysis of scenarios.     

北京市危险化学品企业安全生产风险评估分级研究

为对北京市危化品企业基本情况的全面掌握,开展了危险化学品企业安全生产风险评估分级研究,借鉴国外经验和国内有关科研成果,提出了固有风险和动态风险相结合的危化品安全生产风险评估方法。固有风险为企业的基本风险水平,主要由危险化学品物质量、工艺水平、安全监控和周边环境决定,为共性指标;动态风险,反映企业安全生产管理绩效的水平,主要包括安全基础管理和现场管理,为个性指标,不同企业类型,评估动态风险指标有差异。从大量数据中抽取了最能反应企业安全生产状态的指标因素,通过专家组打分法和层次分析法确定评价因素的权重,该评估方法具有较强的实用性和可操作性,是本质安全和安全绩效的创新结合,为企业安全生产评估分级提供了新思路。通过分级,按照"风险优先"原则,政府部门实行差别监管,降低安全监管成本,促进危险化学品安全生产工作向规范化、科学化转变。同时,研制了危化品企业安全生产风险分级系统,为建立北京市危化品企业风险分级数据库奠定了基础。     

基于潜在生命损失的危险化学品仓储区规划选址和安全布局方法研究

在现有基于风险的土地使用安全规划方法的基础上,通过引入潜在生命损失这一综合风险评价指标,建立了基于移动危险源潜在生命损失的危险化学品仓储区规划选址模型和基于固定危险源潜在生命损失的仓储区安全布局优化模型。在此基础上,提出了危险化学品仓储区规划选址和安全布局优化方法,并通过案例分析验证了该方法的适用性和可行性。采用该规划选址和安全布局优化方法可提高区域土地使用安全规划的效率,为进行城市重大危险源的规划选址和安全布局提供了新的思路。     

Assessment of hazardous material risks for rail yard safety

This paper illustrates the application of quantitative risk assessment in a rail yard where tank cars of hazardous materials are received and stored. The assessment was conducted in response to community concerns about the safety of a proposed yard expansion. Six different chemicals are involved. For each one, the average monthly volume and the hazard of most concern are specified. We use an event tree populated with empirical data to compute the probability of a major spill in each case and we estimate the corresponding critical impact distances using available modeling tools. We find that for some of the chemicals, the relative increases in risk are appreciable, but that in all cases, the absolute levels of risk remain low. Then we identify some ways in which such an analysis can be extended and discuss the potential difficulties associated with these extensions.     

A framework for human error risk analysis of coal mine emergency evacuation in China

Evacuation from underground coal mine in emergency as soon as possible makes the difference between life and death. Human factors have an important impact on a successful evacuation, but literature review shows that there is a lack of consideration of human error risk during coal mine emergency evacuation in China. To address the above problems, in this paper, we established a framework for human error risk analysis of coal mine emergency evacuation, consisting of scenario and task analysis, risk assessment and risk reduction. A general evacuation procedure which is applicable for different causes is detailed through the scenario and task analysis. A new method based on expert judgment, named OGI-Model, is proposed to evaluate the reliability of human safety barrier. In this new approach, human safety barrier is divided into three sub-barriers, i.e., organization safety sub-barrier (OSSB), group safety sub-barrier (GSSB), and individual safety sub-barrier (ISSB). Each sub-barrier consists of a series of concrete measures against specific evacuation actions. An example is provided in this paper to demonstrate the use of this framework and its effectiveness.