Design as a contributor to chemical process accidents

The paper discusses the design errors in chemical process industry (CPI) by analyzing major equipment related accident cases from Failure Knowledge Database (FKD). The aim is to recognize the contribution of design to chemical process accidents and to evaluate the time of occurrence of the errors in a plant design project. The analysis of accident cases found out that the contribution of design to accidents is very significant: 79% of accident cases analyzed were contributed by design errors. The most critical design errors were poor layout (17%), insufficient consideration of chemical reactivity and incompatibility (16%) and incorrectly chosen process conditions (16%). The design errors were initiated at basic (32%), detailed (32%) and preliminary (22%) design phases of the project. Errors in fundamental aspects of chemical processes e.g. route selections are more severe (as compared to others errors class) and might creates many similar errors in later phases of design project. Based on the accident information gathered, a straightforward point-to-look list for error detection and elimination was suggested for process lifecycle stages.     

Accident prevention approach throughout process design life cycle

The accident rate in the chemical process industry (CPI) has not been decreasing although majority of accident causes have been identified and could have been prevented by using existing knowledge. These recurring accidents show that the existing knowledge has not been used effectively. In this paper, accident knowledge learned from earlier accident analyses are utilized to predict the common design errors during chemical plant design. An accident prevention approach throughout process design life cycle is proposed for a safer design consideration where designers are guided to identify common design errors, accident contributors and critical points to look for. The accident prevention approach has been applied to analyze the BP Texas City Refinery Explosion and Fire tragedy.     

Method for identifying contributors to chemical process accidents

The paper presents a new method for identifying contributors to chemical process accidents by exploiting knowledge on causes of past accident cases. Accident reports from the Failure Knowledge Database were analyzed and utilized for hazard identification. The accident information gathered was used as a basis to develop an accidents ranking and points-to-look-for approach for the safe design and operation of chemical process equipment. In the method, accident contributors including technical, design and operation errors of major process equipment types and piping are identified. The method is applicable throughout the process lifecycle, even for process changes in the early design stages. The Bhopal tragedy is used as a case study to demonstrate and test the method. The proposed method can predict on average up to 85% of accident causes and design and operation errors.     

Origin of equipment design and operation errors

The paper discusses the origin of chemical process equipment accidents by analyzing past accident cases available in the Failure Knowledge Database (FKD). The design and operation errors of the process equipment that caused the accidents were analyzed together with their time of occurrence. It was found that design errors contributed to 79% of accidents while the rest were only due to human and organizational errors in the operation stage and external factors. The most common types of errors were related to layout, organizational errors in the operation stage, considerations of reactivity and incompatibility, and wrongly selected process conditions (each approx. 13% of total accident contributors). On average there were about 2 design errors per accident. The timing of the errors was quite evenly distributed between various lifecycle stages. Nearly half (47%) of the errors were made in process design-oriented stages, one fourth (26%) in detailed engineering, and one fifth (20%) in operation. In addition, the most frequent design and operation errors for each equipment type were identified. A points-to-look-for list was created for each equipment type, showing also the typical time of occurrence of the error. The knowledge of type and timing of design errors can be utilized in design to focus the hazard analysis in each stage on the most error-prone features of design.     

Inherently safer design review and their timing during chemical process development and design

This paper discusses the enhancement of inherent safety review and its implementation in the chemical process development and design. The aim is to update and improve the existing inherently safer design review (ISDR) practices during design of chemical process plant by exploiting major accident cases from the U.S. Chemical Safety Board (CSB) and Failure Knowledge Database (FKD). Although the basic guidelines to conduct ISDR during design phase are available, however they are too general and incomplete. The review criteria and their best timing for application are still missing. This paper attempts to develop the accident-based ISDR for chemical process plant design. The proposed accident-based ISDR is supported with detail review criteria for each phase of process design. The timing of ISDR application is corresponding to the common design tasks and decisions made in the design project. Therefore, timely design review could be done at the specific design task and the findings help designer to make a correct decision making.     

ExSys-LOPA for the chemical process industry

The chemical process industries are characterized by the use, processing, and storage of large amounts of dangerous chemical substances and/or energy. Among different missions of chemical plants there are two very important ones, which: 1. provide a safe work environment, 2. fully protect the environment. These important missions can be achieved only by design of adequate safeguards for identified process hazards. Layer of Protection Analysis (LOPA) can successfully answer this question. This technique is a simplified process of quantitative risk assessment, using the order of magnitude categories for initiating cause frequency, consequence severity, and the likelihood of failure of independent protection layers to analyze and assess the risk of particular accident scenarios. LOPA requires application of qualitative hazard evaluation methods to identify accident scenarios, including initiating causes and appropriate safeguards. This can be well fulfilled, e.g., by HAZOP Studies or What-If Analysis. However, those techniques require extensive experience, efforts by teams of experts as well as significant time commitments, especially for complex chemical process units. In order to simplify that process, this paper presents another strategy that is a combination of an expert system for accident scenario identification with subsequent application of LOPA. The concept is called ExSys-LOPA, which employs, prepared in advance, values from engineering databases for identification of loss events specific to the selected target process and subsequently a accident scenario barrier model developed as an input for LOPA. Such consistent rules for the identification of accident scenarios to be analyzed can facilitate and expedite the analysis and thereby incorporate many more scenarios and analyze those for adequacy of the safeguards. An associated computer program is under development. The proposed technique supports and extends the Layer of Protection Analysis application, especially for safety assurance assessment of risk-based determination for the process industries. A case study concerning HF alkylation plant illustrates the proposed method.     

基于HFACS的空中相撞事故分析及建议

空中相撞事故往往是由诸多人为差错相互叠加、耦合和作用而导致的,要找出事故的真正诱因,防止类似事故再次发生,难度非常大。为了有效地分析和定位人为差错,以更好地服务于防相撞的管理与决策,提出一种基于人为因素分析分类系统（HFACS）的空中相撞事故分析方法,它按照从显性差错到隐性差错的思路来分析事故的诱因,最终找出组织因素对事故的影响。并利用HFACS对巴西卡欣布上空发生的一起空中相撞事故进行了系统分析。案例分析结果表明,该方法不仅能够找出导致空中相撞事故的人为差错,解释事故发生的原因和过程,而且能够据此提供防止相撞事故发生的安全建议。     

性能化设计思想在化工设施布局安全设计中的应用

指令性规范是目前化工设施平面布局安全设计的主要依据,但其在应用中存在着条款僵化、安全理论基础不全面、可拓展性不明确等问题。本文将性能化设计思想引入到化工企业平面布局安全设计中,初步提出了一种包含危险辨识、性能化目标确定、后果评估及安全设施效用评估等主要组成部分的基于性能化设计思想的平面布局安全设计体系。对体系中最重要的部分—性能化目标确定进行了重点分析,将化工设施布局安全设计分为装置内设备之间的位置设计、厂区内装置区之间的位置设计以及厂区与外部单位之间的位置设计三个级别,从工艺关联性等角度对各级别布局设计中事故场景选择及设施可接受受损水平进行分析,并提出了通过匹配事故场景和设施可接受受损水平来确定性能化目标的方法。     

Why bad things happen to good people

Accidents in the process industries are extensively investigated to determine root causes, for lessons learned, and many times in search of the “guilty”. Accidents are seldom simple and most accidents have human elements that led to or facilitated the accident. Many times the people involved in these accidents, when considered individually on their merit, would be considered “good” people yet “bad things” (accidents) still occur.Human errors can be classified as individual, group, and organizational. Individual human errors have been addressed in a number of studies and papers. Many of these classify human errors and treat them probabilistically or cognitively. Less has been said regarding the individual psychological/sociological response/interaction mechanisms that might contribute to an industrial accident. These elements also contribute to a lack of situational awareness which often plays a large part in human error. Group and organizational interactions/dynamics can also contribute negatively to situational awareness and to the chain of events of an accident. Organization errors, which are typically latent, can also facilitate an accident and are many times people enabled for personal and business vested interests.This paper will discuss the effect of human error at the practical plant level in contributing to accidents in the process industries from individual, group, and organizational perspective. The discussion will include psychological/sociological response/interaction mechanisms that can contribute to situational awareness and human error. It will also discuss how complexity, veracity, and quantity of available information can affect the human decision-making process leading to mistakes.Accidents are seldom simple and most accidents have a number of elements that led to or facilitated the accident. When looking at individual elements probabilistically, multiplying probabilities together, it is hard to see how an accident could have occurred. A common refrain “That’s double jeopardy and we don’t have to consider that” is essentially a qualitative probabilistic analysis. Yet we have cases of triple, quadruple, n-jeopardy occurring to cause accidents. The paper will discuss the superimposition of causes and a similar concept of functional resonance in causing accidents.     

Economic assessment of human errors in manufacturing environment

Traditional human reliability assessment techniques and accounting system cannot directly provide loss information for assessing the impacts of human errors. This obstacles force industrial managers to justify the proper accident and injury prevention process through their experiences. The efficiency and effectiveness of the system safety barriers are in doubt and the smooth operation of manufacturing activities are insecure. In this study, a human error cost estimation model is introduced to facilitate line managers with a proper tool to collect and calculate the total losses of its impact. Experts’ judgments and pair wise comparison technique are incorporated to interrogate managers’ knowledge of human errors and correspondent costs. This approach can overcome the problem of insufficient cost information caused by current accounting system and compensate the influence of safety and health department due to the low organizational status in quo. Although the cost figures may not represent exact amount of losses, the percentage of each cost factor in terms of department operation budget gives the managers a practical way for justifying how the resources should be allocated.     

Bi-directional connectivity diagram for accident propagation analysis considering the interactions between multiple-process units

An incident may propagate to an accident with different severity dependent on its propagation scenarios. Since the accident propagation is a two-way process, the current research is focusing on the one-way analysis. This paper aims to analyze the combined effect of multi-units sources and their interactions during the accident propagation. The bi-directional connectivity diagram (BDCD) is applied to visualize the interactions between multiple process units as hazardous sources. The deployed safety barriers interrupt the connection between the hazardous sources and thus minimize the influence of one BDCD node on another. Through which, the accident propagation is reduced. The proposed method can be suitable to the general accidents, and it is applied to a case study of the LNG terminal station to assess the potential consequences of explosion caused by the leakage, in which the cost of the safety barrier is also considered. The BDCD approach is found more effective than traditional single-hazardous source methods for analyzing the accident propagation of multi-units sources in the chemical plant and achieving intrinsic safety.     

A new intelligent assistant system for HAZOP analysis of complex process plant

There are several problems that should be solved in the practical application of HAZOP analysis, such as the inheritance instrument of experience knowledge, the classification of accident reasons, the recurrence of analysis process and the verification of analysis results. This paper presents a new HAZOP assistant program named HELPHAZOP, which can be used to cope with these problems. With the aid of this program, a number of influence relationship models, which can be utilized to present the relationship structure of the whole system, can be established, and a variety of spread paths, which can be employed to describe the occurrence of the accidents, can be identified. These models and paths can help analyzers to understand the analysis process of different chemical processes and to verify the analysis results. Experience knowledge or information of process parameters stored in this program, including deviations, abnormal reasons, consequences and disaster-causing ways, can contribute to the analysis of some new plants. The program has been applied in the HAZOP analysis process of residuum hydrotreating process. The probability of the human errors which would be happened because of the misunderstanding or the deficiency of plant experience in the HAZOP analysis has been reduced and the accuracy, practicability and analysis efficiency of the accident forecast have been greatly improved.     

石化企业平面布局安全设计中事故场景的选择研究

基于安全性能思想的设计方法是石化行业平面布局安全设计的一个重要发展方向,文章对这种设计方法中目前存在的主要不确定因素——事故场景的选择问题进行了研究。对《石油化工企业设计防火规范》等指令性规范中各级别平面布局安全设计的依据进行了统计分析,给出了各级别布局设计中主要的安全考虑和大致的安全间距范围,并对目前安全考虑中存在的模糊性进行了分析,给出了导致其存在的原因主要为＂事故场景考虑不同＂和＂‘相互影响’的含义不同＂;由此,结合事故伤害理论,对石化行业常见的9种19类常见事故场景的后果分析估算,得到了各事故场景对目标设施造成不同程度＂影响＂的范围,并以之为依据,分析给出了各级别布局安全设计中适合考虑的事故场景及适当的安全设计目标。     

CREAM-based communication error analysis method (CEAM) for nuclear power plant operators’ communication

Communication error has been considered a primary cause of many incidents and accidents in the nuclear industry. In order to prevent these accidents, a method for the analysis of such communication errors is proposed here. This paper presents a qualitative and a quantitative method to analyze communication errors. The qualitative method focuses on finding a root cause of the communication error and predicting the type of communication error which could happen in nuclear power plants. We develop context conditions and antecedent-consequent links of influential factors related to communication errors. The quantitative analysis method focuses on estimating the probability of communication errors. To accomplish the quantification of communication errors, the Cognitive Speaking Process (CSP) is defined and a method to estimate the weighting factors and the probability is suggested. Finally, case studies conducted to validate the applicability of the proposed methods are detailed. From the results, we can foresee the effects of given plant conditions on communication errors and reduce the error occurrences.     

SDG-based HAZOP analysis of operating mistakes for PVC process

As modern chemical plants are becoming more complex and bigger in scale, the associated chance of things going wrong is also increasing rapidly. Due to the flammable, explosive, toxic and corrosive nature of chemical process, any single accident may trigger a major catastrophe that brings tremendous environmental, social and economical loss. In order to prevent any accident from happening, hazard and operability (HAZOP) analysis has been brought in to monitor chemical process and provide early warning for signs of accident. However, most existing HAZOP is carried out manually, and there are always obstacles in terms of cost overrun and incompleteness of the analysis. To address the difficulties in current HAZOP method, this paper proposes a signed digraph (SDG)-based HAZOP analysis method. It is used to identify the most likely operating mistakes that may cause certain process variable deviating from its normal value, which is the main source of safety concern. A case study on polyvinyl chloride (PVC) plant is presented to demonstrate the effectiveness of SDG-based HAZOP analysis method in providing complete analysis result.     

基于事故逆向再现的车辆追尾事故仿真分析研究

为认定车辆碰撞事故的性质及责任,动态还原事故发生过程。提出1种逆向事故分析再现方法,经过坐标系旋转后构建确定方程组的车辆碰撞瞬间解析计算模型,并经过实车碰撞实验数据验证其计算精度与三维再现的准确性。利用Crashview软件对1起车辆追尾事故进行仿真分析,解析计算得出车辆碰撞瞬间车速和碰撞前行驶车速,实现事故二维过程重构和三维模拟再现。结果表明:计算分析车速与VDR记录车速误差在5%以内,模拟再现轨迹与事故现场实测痕迹基本吻合,所构建的方法可有效用于车辆追尾碰撞事故辅助分析鉴定,为事故过程分析提供理论依据。     

Study of chemical supply system of high-tech process using inherently safer design strategies in Taiwan

The photoelectric, semiconductor and other high-tech industries are Taiwan's most important economic activities. High-tech plant incidents are caused by hazardous energy, even when that energy is confined to the inside of the process machine. During daily maintenance procedures, overhauling or troubleshooting, engineers entering the interior of the machines are in direct contact with the source of the energy or hazardous substances, which can cause serious injury. The best method for preventing such incidents is to use inherently safer design strategies (ISDs); this approach can fully eliminate the dangers from the sources of hazardous energy at a facility.This study first conducts a lithography process hazard analysis and compiles a statistical analysis of the causes of the fires and losses at high-tech plants in Taiwan since 1996, the aim being to establish the necessary improvement measures by using the Fire Dynamics Simulation (FDS) to solve relevant problems. The researchers also investigate the lithography process machine in order to explore carriage improvement measures, and analyse the fires' causes and reactive materials hazardous properties, from 1996 to 2012. The effective improvement measures are established based on the accident statistics. The study site is a 300 mm wafer fabrication plant located in Hsinchu Science Park, Taiwan.After the completion of the annual maintenance jobs improvement from September 2011 to December 2012, the number of lithography process accidents was reduced from 6 to 1. The accident rate was significantly reduced and there were no staff time losses for a continuous 6882 h. It is confirmed that the plant safety level has been effectively enhanced. The researchers offer safety design recommendations regarding transport process appliances, chemical storage tanks, fume cupboard devices, chemical rooms, pumping equipment, transportation pipelines, valve manual box (VMB) process machines and liquid waste discharge lines. These recommendations can be applied in these industries to enhance the safety level of high-tech plants, facilities or process systems.     

库存弹药事故人误危险性分析与评估模型研究

针对库存弹药安全的特殊性,提出库存弹药事故人为失误的定义,并从个体角度分析人误事件发生的机理。根据人为失误的不同主体,从管理决策、组织和勤务处理、操作两个方面构建了29个人误危险性的评价指标及相应的评判标准;综合考虑生理、心理、知识与技能、设备、环境、监督与管理等6类危险性抵消因子对人误危险性的影响;进而建立了库存弹药事故人误危险性的理论评估模型。研究结果表明:人为失误属于弹药仓储安全管理中的一类特殊危险源,人误评估指标体系和评估模型的构建过程应充分考虑人自身条件以及内、外部环境等因素的综合影响;同时研讨了人为失误危险性分析和评估模型存在的问题,并从发展人误数据采集技术、完善人误事故报告制度以及建立人误数据库等方面,指出下一步的研究重点。     

基于MAIB事故报告的人为失误灰色关联分析

人为失误作为海上交通事故的主要原因,受到多种因素的影响。为了识别这些影响因素,避免或减少因人为失误导致的海上交通事故,基于96件英国海事调查委员会(MAIB)事故报告,应用熵加权灰色关联分析,分别按船旗国、船舶类型、事故类型计算人为失误与影响因素之间的关联度。结果表明,能力/技能/知识、团队协作、程序和现行规程、设备、交流(内部和外部)和管理/检验/检查是影响人为失误的主要因素。