Use of bifurcation analysis for identification of a safe CSTR operability

Exothermic reactions are the most interesting systems for safety analysis because of their potential safety problems and the possibility of exotic behavior like multiple steady states. An operability and safety analysis of an exothermic reaction (hydrolysis of propylene oxide to tri-propylene glycol with consecutive reactions in a CSTR) with cooling is reported in this work. The information obtained from the bifurcation diagram is used to identify a set of unsafe operation points, which have been chosen on the base of requirement of maximal production of the process. An important information of safe reactor operation is the time in which the operator must handle a critical situation. For this reason, dynamics simulation of a failure in the cooling medium flow rate has been done and discussed for each of the selected operation points.     

Model-based hazard identification in multiphase chemical reactors

Chemical productions operated in extreme conditions (high pressure, high temperature) require a detailed analysis of all potentially dangerous situations that can lead to a major industrial accident and thus cause a loss of life and property. Many accidents in the near or distant history underline the need of a detailed safety analysis in process industries, not only in the phase of plant design but also during the operation of the plant. It would be shown that simulation of a chemical unit using an appropriate mathematical model and the nonlinear analysis theory can be a suitable tool for safety analysis. This approach is based on mathematical modeling of a process unit where both the steady-state analysis, including the analysis of the steady states multiplicity and stability, and the dynamic simulation are used. Principal objective of this paper is to summarize problems regarding the model-based hazard identification in processes. A case study, focused on phenomena of multiple steady states in ammonia synthesis reactor will be presented. The influence of the model complexity and model parameters uncertainly on the quality of safety analysis would be underline.     

Influence of parameter uncertainty on modeling of industrial ammonia reactor for safety and operability analysis

Chemical reactors represent probably the most hazardous units of chemical industry. Safety analysis of a chemical reactor requires basic knowledge of all particular processes which can be described by mathematical models. Most of the model parameters involved in the prediction of reactor behavior are uncertain. These uncertainties can cause discrepancies mainly in the prediction by models with nonlinear behavior and they can be the source of confusion in the design of chemical reactors and consequently also in the safety and operability analysis.The main aim of this work was to analyze the influence of uncertainties in the model parameters on the prediction of operating quantities by mathematical models with nonlinear behavior. Such analysis can be used for safety and operability analysis of an industrial catalytic ammonia reactor. The industrial fixed-bed reactor was used by a mathematical model with nine parameters. Analyses of the influence of uncertainty in a single model parameter and their combination were carried out by the Monte Carlo approach. It is shown that even a small uncertainty in one of the key parameters or in a combination of these key parameters can result in several steady states results of the operating quantities and can be the source of confusion in the design and consequently also in the safety and operability analysis.     

内-外因事故致因理论与实现安全生产的途径

采用辩证的方法对事故发生的机理进行研究,提出了内-外因事故致因理论,阐明危险源是导致事故的内因,人—物—环—管中的不安全因素是导致事故的外因。根据危险源的存在形式,指出了有效控制危险源的基本手段和措施。通过深入分析人—物—环—管中的不安全因素的产生及导致的后果,从技术和管理方面论述了防止事故发生应采取的措施。最后提出将本质安全化与风险预控管理相结合,是实现安全生产的根本途径。内-外因事故致因理论为企业安全管理提供了理论,具有实用价值和参考意义。     

环氧丙烷在不同条件下的反应稳定性研究

环氧丙烷具有较强化学活性,分析了环氧丙烷生产过程中可能出现的安全问题;测试了不同温度、pH值和铁离子存在条件下环氧丙烷的反应稳定性。结果表明,环氧丙烷在低pH值和铁离子存在的环境中容易发生强烈放热反应。根据环氧丙烷工业化生产的特点,提出了相应的控制条件。     

Safety-centered process control design based on dynamic safe set

The objective of this research is to develop an approach for the process control design problem with safety as the primary target. The work proposes the concept of dynamic safe set (DSS) to characterize and evaluate the safeness of a closed-loop system.The DSS is defined as a set of initial states of the process that guarantees safe operation, which is represented by a set of safety-critical constraints that is to be satisfied at all times. The DSS calculation accounts for potential safety threatening disturbances that may significantly affect the dynamics of the system. An addon control scheme based on the DSS concept is proposed to guide the system when it is under sudden and large set point changes that may be needed during abnormal situations. Existing system theoretic concepts of maximal output admissible sets is used to mathematically formulate and determine the DSS. The concept of dynamic safety margin (DSM) is proposed as a quantitative measure of the size of DSS. An approach based on the DSS and DSM concepts for process control design with the objective to maximize safety, subject to other performance constraints, is proposed.The approach is tested on an exothermic CSTR case study. The results showed the strong effect of steady state operating conditions, control parameters and actuator design parameters on DSM. A grid of design parameters that includes the reactor set point, the controller parameters, and the heat exchanger design parameter was analyzed. The analysis led to identifying a maximally safe control system design. The proposed approach allowed to formulate the process control design problem by bringing safety upfront, without compromising performance metrics.     

An adaptive online safety assessment method for mechanical system with pre-warning function

The safety status of a dynamic mechanical system is determined by its historical, current and future states together. Therefore the safety assessment process of such system should have dynamic and diachronic characteristics, which helps to track the dynamic states of system and predict future probable danger in advance. In order to overcome the disadvantages of traditional static safety assessment approaches, the results from which are often delayed and prone to produce false alarms, an adaptive online safety assessment method is proposed in this paper, which consists of two steps. A dynamic adaptive weighting method is first introduced and an aggregation scheme based on “3-D” time perspective is further presented to integrate system’s historical, current and future safety performance in a unit framework, considering both of assessment and pre-warning functions. The proposed method is able to track and predict the safety status of system dynamically and discover the potential fault in time. Its feasibility and benefits are investigated with a field case study of gas turbine compressor system, which validates that the proposed method improves the accuracy of safety assessment in dynamic conditions, and finally helps to restrain the fault symptom by proactive maintenance successfully.     

某聚丙烯车间生产系统危险性评价

在分析某聚丙烯车间生产系统危险因素的基础上,应用道化学公司的火灾爆炸危险指数评价法(第7版)对某车问聚合闪蒸、原料精制、尾气回收及丙烯北罐区等主要危险工艺单元进行了火灾爆炸危险性评价,并提出了事故防范的安全对策。     

Safety Attitudes and Their Relationship to Safety Training and Generalised Self-Efficacy

This paper studies safety attitudes, their relationship with safety training behaviour, and generalised self-efficacy. From a sociotechnical perspective, training programs might be used as a mechanism for enhancing attitudes, especially to improve safety and occupational health. Also, self-efficacy allows to enhance training effectiveness. The aim of this paper is to validate a safety attitude scale and to examine its relationship to safety training behaviour and self-efficacy in organisational settings. With data from 140 employees, results show a conceptually meaningful 3-factor solution. Hier-archical multiple regression analysis shows a main effect of safety training behaviour and levels of self-efficacy on safety attitude. Study limitations and its implications on safety training design are also discussed.     

Impact of primary safety belt laws on alcohol-related front-seat occupant fatalities: five case studies

OBJECTIVE: Impaired drivers and other high-risk road users are less likely to use their safety belts, thus increasing the risk of fatal injury in the event of a crash. Although safety belt laws have been shown to increase wearing rates for daytime non-crash-involved drivers and their front-seat passengers, little evidence is available on the effect these laws have on belt usage by crash-involved drinking drivers and their passengers. METHODS: This study evaluated the influence of primary safety belt law upgrades from secondary laws on front-seat occupants of passenger cars driven by drinking drivers in fatal crashes in five states: California, Illinois, Maryland, Michigan, and Washington. The outcome measures used to evaluate these law upgrades were (1) the change in safety belt usage rates of front-seat occupants in passenger cars driven by drinking drivers in fatal crashes and (2) the change in alcohol-related front-seat occupant fatalities in passenger cars driven by drinking drivers. RESULTS: Four of the five states demonstrated increases in safety belt use by front-seat occupants of passenger cars of drinking drivers in fatal crashes following the upgrade to primary safety belt laws. Three states (California, Michigan, and Washington) experienced significant reductions in the number of front-seat occupant fatalities in vehicles driven by drinking drivers. CONCLUSIONS: The adoption of primary law upgrades was associated with significant increases in safety belt use (four of five states) and significant reductions in fatalities among high-risk occupants (i.e., front-seat occupants involved in fatal crashes in vehicles driven by drinking drivers) in three of the five states studied.     

关于高等院校安全工程专业的改革与探讨

阐述安全是人类社会稳定向前发展的主要目标之一 ,是国民经济的可持续发展的重要保证 ;在回顾安全工程专业建立和发展过程的基础上 ,分析了安全工程专业在学科建设过程中存在的问题以及产生的主要原因 ;就如何解决问题进行了全面的分析和探讨 ;提出了高校安全工程专业的教育 ,是培养高素质安全工程专业人才的主要途径 ;在安全工程专业学科建设过程中 ,必须明确安全科学技术体系的结构和内涵 ,合理设置安全工程专业的课程 ,加强安全工程专业的实践环节 ,加强安全文化知识的普及教育。     

Assessment of risks posed by chemical industries—application of a new computer automated tool maxcred-III

The paper describes the application of a new computer automated tool, developed by us, in the risk analysis of a typical chemical industry engaged in the manufacture of linear alkyl benzene. Using the tool—a comprehensive software package maxcred-III (MAXimum CREDible accident analysis)—nine different scenarios, one for each storage unit, have been studied. It is observed that the accident scenario for chlorine (instantaneous release followed by dispersion) leads to the largest area-under-lethal-impact, while the accident scenario for propylene (CVCE followed by fireball) forecasts the most intense damage per unit area. The accidents involving propylene, benzene, and fuel oil have a high possibility of causing domino/secondary accidents as their destructive impacts (shock waves, heat load) would envelope other storage and process units.Besides demonstrating the utilizability of maxcred-III, this study also focuses attention on the need to bestow greater effort towards risk assessment/crisis management. The authors hope that the study will highlight the severity of the risk posed by the industry and thus generate safety consciousness among plant managers. The study may also help in developing accident-prevention strategies and the installation of damage control devices.     

铁路沿线可燃重气储罐最小隔离区域划分探讨*

为保护铁路线,以某化工厂距离高铁路线最近的丙烯球罐为例,提出丙烯球罐泄漏最小隔离区域划分方法以及2种保护高铁线路方案,利用重气扩散模型和定量风险评价（QRA）软件分别进行丙烯扩散模拟、爆炸模拟,并进行危险与可操作性分析（HAZOP）和保护层分析（LOPA）。结果表明:球罐发生泄漏及火灾爆炸等事故,会给附近铁路线带来严重破坏;丙烯泄漏或球罐因周围其他设备设施或可燃物质着火而温度升高时,保护措施不足;隧道的安全可靠性要高于仅设1道防爆墙,隧道长度需覆盖最小隔离区域的可及范围,在扩散区域内也需设立普通挡墙,在极度危险情况下,需要实施高铁停开等保护措施。     

安全管理力学分析方法(SMMA)及其应用研究

把自然科学中力的概念引入安全管理中,对其中的各种有形和无形联系进行研究,建立了一种安全管理系统的力学分析方法和实施程序。基于该方法把力学与轨迹交叉理论进行映射关联,建立"球体碰撞"模型。通过对比找出模型中存在的各种力,对模型进行受力分析并建立函数方程式。再据方程式及其参数对模型的各种状态进行分析,把分析结果反馈到安全管理系统中用以指导安全管理工作。最后,把安全管理力学分析法概括为定量分析法和定性分析法,并为研究安全管理提供了理论基础。由于力学具有准确、严谨、逻辑性强的特点,因此,引入力学后可以发挥力学与数学的优势。建立的安全管理力学分析方法是一种新方法,该方法对安全管理系统的定量化研究和实施有一定的促进作用。     

On the use of probabilistic and deterministic methods in risk analysis

Risks to human beings arise from an inherent characteristic to make plans and try to make them happen, while external forces resist and tend to move our endeavours away from the plan. Any such “endeavour” is a complex ensemble of a bewildering variety of interacting elements which together form something “whole”, usually called a “system” (e.g. a chemical process plant, a nuclear power plant, the stock market, air traffic control). A system has a certain state in the present and subsequent states in the future. There are deterministic and probabilistic systems and corresponding approaches to analyse them, that is to make their current states apparent and predict their future behaviour. In this paper, it is shown in which ways both analyses appear in risk analysis and it is hypothesised that both approaches are modelling the same process, though probabilistic analysis may reveal more information since it explicitly incorporates uncertainty in the form of numbers (and “there is safety in numbers”). The overall objective of this paper is to make clear what the differences between the two approaches really are. Their respective main strengths and weaknesses are discussed. A more refined objective is to discuss the specific role of probabilities in risk analysis. Examples of both approaches are given from applications in the nuclear power and chemical process industries, and some of the main problems encountered thereby are identified. Further, the challenge to system analysis posed by “chaos theory” is discussed. Due to its non-linear dynamic character, the future behaviour of a “chaotic system” is difficult to predict over a long period of time because it depends on arbitrarily small and thus not observable variations in the current state. Such behaviour might have serious consequences for human operators involved in the control of such systems. The paper concludes that, although both approaches to risk analysis can provide adequate safety levels to systems if applied in a correct and non-biased way, probabilistic methods seem to be more cost-effective and the results easier to communicate to decision- and policy-makers.     

丙烯腈装置安全预警及控制技术研究

丙烯腈生产装置危险性极高,其主要设备大部分为压力容器、压力管道;其原料、中间产物、产品、副产品理化性质复杂,具有易燃、易爆、剧毒的特点。为提高丙烯腈生产企业管理水平,实现丙烯腈生产的远程监控、实时预警、过程控制和应急控制,为装置处于非正常工况下快速有序地实施风险控制,降低事故危害,减少事故损失提供技术支持,达到丙烯腈装置安全平稳生产的目的。在对某炼化企业丙烯腈生产装置风险分析的基础上,确定需监控的重点设备和关键参数,通过OPC通讯技术实时采集DCS操作参数数据并进行多参数趋势预警分析,建立起丙烯腈装置非正常工况下安全预警系统。系统主要包括关键参数安全预警分析、偏差标准操作处置程序、突发事件的应急评估、相关辅助信息等技术内容,涵盖安全保障的预防、预警、应急和处置的各个环节,实现了多参数实时监控、自动预警和应急辅助决策。     

Improvement principles

Introduction: The improvement principles are a group of safety principles whose central message is that no risk level above zero is fully satisfactory, and that we should therefore always strive to improve safety. The major safety principles in this group are: as low as reasonably achievable (ALARA), best available technology (BAT), the substitution principle, vision zero, and continuous improvement. Method: This article investigates their similarities and differences, the ways in which they can incorporate compromises with objectives other than safety, and the difficulties that may arise in their application. A particular emphasis is put on comparisons with two major competing groups of principles, namely acceptance principles, which draw a sharp line between acceptable and unacceptable states of affairs, and weighing principles such as CBA that search for an optimized compromise between safety and other objectives. Results: In comparison to their main competitors, the improvement principles have the important advantage of consistently encouraging safety enhancements. However, some of the problems in their application can probably best be tackled by including them in a combined approach that also makes use of acceptance and/or weighing principles. Two such combined approaches are proposed. The choice between them should be based on the underlying value structure of the decision problem. Practical applications: Guidance is given for the choice of safety principles and for the combined use of more than one such principle.     

Measurement of traffic conflicts

Traditionally road accident statistics are used to assess the level of road safety and evaluate road safety programs. In some cases, the lack of good and reliable accident records have hampered proper analyses. A promising approach that overcomes this problem is the traffic conflict technique which relies on observations of critical traffic situations for safety analysis. However, despite the extent of work undertaken in traffic conflict research, there are still a number of issues on conflict measurement and application that have not been well understood by many safety analysts. This has resulted in a general lack of support for the wider application of the technique in safety analysis. This paper shows that one way of using the traffic conflict technique effectively is to ensure that conflicts are quantitatively defined, objectively measured and suitably applied. Before establishing the proposed framework for conflict analysis, the paper first discusses the problems and weaknesses often associated with conflict studies. Considerations for a conflict study based on the proposed approach are then presented and the case of an expressway merging is used to illustrate the method adopted.     

A framework for estimating the safety effects of roadway lighting at intersections

National- and state-level guidance documents conclusively state that fixed lighting improves intersection safety. The sentiment is consistent with other design and safety manuals and is supported by a series of consistent safety findings; however, most published lighting-safety research is focused on rural, stop-controlled intersections and is limited by several methodological issues. The relationship between safety and intersection lighting at rural, signalized and urban locations is not as well documented. Methodological advancements in highway safety analysis justify new estimations of the safety effects of intersection lighting. This paper describes a proposed framework to estimate the safety effects of fixed lighting at a variety of intersection types and locations. Several key issues are explored including availability of relevant crash, lighting, and roadway inventory data; relevant data element structures; proposed analysis taxonomies to assess lighting-safety effects within and across different intersection classifications; specification and estimation of models to estimate expected crash frequencies during day and night; techniques to interpret model parameters, including variable elasticity; and tests of model transferability across states. A sample framework execution using Minnesota intersection data is provided. Results indicate a much lower overall safety benefit from lighting than published studies, but are consistent with estimates included in Highway Safety Manual research.     

Failure rate evaluation with influencing factors

A new methodology for failure rate evaluation with influencing factors is proposed. A quantitative part allows integrating potential available data from feedback. Then, a qualitative analysis deals with influencing factors such as design, environment, and use to provide more coherent and argued results. The main idea is to use some criteria to fix the failure rate within a prior interval, according to the influencing factor states. To this end, the system is broken up into main component groups. When a component group is susceptible to an influencing factor, its baseline failure rate is multiplied by the relevant influencing coefficient. A seven-step methodology is presented to define the model, identify and rate the influencing factors, set indicator functions taking the uncertainties into account, and calculate the influencing coefficients. The proposed methodology is global enough to be usable for a large number of safety instrumented systems and influencing factors. For example, an application regarding safety pressure relief valves is given. The prospect is for more efficient risk management by acting both on systems and influencing factors.