Human reliability analysis: A critique and review for managers

In running our increasingly complex business systems, formal risk analyses and risk management techniques are becoming more important part to managers: all managers, not just those charged with risk management. It is also becoming apparent that human behaviour is often a root or significant contributing cause of system failure. This latter observation is not novel; for more than 30 years it has been recognised that the role of human operations in safety critical systems is so important that they should be explicitly modelled as part of the risk assessment of plant operations. This has led to the development of a range of methods under the general heading of human reliability analysis (HRA) to account for the effects of human error in risk and reliability analysis. The modelling approaches used in HRA, however, tend to be focussed on easily describable sequential, generally low-level tasks, which are not the main source of systemic errors. Moreover, they focus on errors rather than the effects of all forms of human behaviour. In this paper we review and discuss HRA methodologies, arguing that there is a need for considerable further research and development before they meet the needs of modern risk and reliability analyses and are able to provide managers with the guidance they need to manage complex systems safely. We provide some suggestions for how work in this area should develop. But above all we seek to make the management community fully aware of assumptions implicit in human reliability analysis and its limitations.     

Root cause analysis of an old accident in an explosives production plant

Twenty-six years ago, a massive accident occurred in the Semtin explosives plant in Czechoslovakia. The results of investigations which were carried out (but kept confidential at the time) were made available after 1989, but have not been published in a summarized form to date. Reopening of the results of old investigations and application of root cause analysis deepens our understanding of accident causes and leads to the conclusion that, according to today’s standards, the analysis was not completed at the time of the accident and therefore neither some of the practical aspects of the event nor the social, professional, and political climate it should have exposed have ever been fully understood. New analysis shows that plant safety management had decayed. The results demonstrate as well how substantial a shift has occurred in the understanding of causes and in performing and organizing their analyses during the elapsed quarter-century. The new examination employs a few innovations of root cause analysis. A tight connection between the analysis and the assumptions about the structure of safety management of investigated processes will be underlined. Suitable illustration will be proposed. Detail requirements on the form and content of a root cause map will be specified. Finally it is shown that even the root cause analysis has its limitations and that it may not be sufficient to finish the investigation of causes satisfactorily. This motivates for the identification of levels of causes which underlie the root causes.     

公路建设项目对景观影响综合评价

针对高速公路建设项目的特点,从选取影响因子入手,采取定量分析的手段,研究了高速公路建设对景观的影响程度.结果表明,用景观功能与稳定性、景观冲突度和景观质量预测等3个指标,能够满足影响评价的要求.采用这些定量方法评价生态和景观受影响的程度,效果较好.     

Integration of Recursive Operability Analysis,FMECA and FTA for the Quantitative Risk Assessment in biogas plants: Role of procedural errors and components failures

With more than 350 GWh per year and thousands of installations around the world, biogas is an appealing strategy in the field of energy production and industrial waste optimization. In this sense, it is of paramount importance to address the risk associated with such plants, as an increasing trend of accidents have been recorded in the last 20 years. In this work, a representative biogas production plant was considered, and a risk assessment was carried out through the combination of Recursive Operability Analysis and Failure Mode and Effects Criticality Analysis. The methodology is rigorous and allows for both the identification and the quantification of accidental scenarios due to procedural errors and equipment failures, which miss in the literature for the case of biogas. The analysis allows the automatic generation of the Fault Trees for the identified Top Events, which can be numerically solved. Results show that the most critical accidental scenario in the biogas plant here considered is the formation of an explosive air-biogas mixture, which can occur in both anaerobic digester and condensate trap. The calculated probabilities agree with the results available in literature on similar plants. Pumps and Distributed Control System were found to be the most critical components.     

Process safety data management program based on HAZOP analysis and its application to an ethylene oxide/ethylene glycol plant

HAZOP analysis is a process hazard analysis method that has been widely applied both within and outside the chemical processing industries. This paper presents a design method for a process safety data management program for petrochemical plants based on HAZOP analysis and demonstrates the steps of application involved in building a process safety data management system for an ethylene oxide/ethylene glycol production plant. Firstly, the production data files and relevant documents of the plants should be classified and stored in the program database as reference documents and treatment schemes for coping with abnormal situations should be collected and summarized as guidance documents. Secondly, the HAZOP analysis method is employed to identify all the dangerous deviations possibly existing in the production process of the ethylene oxide/ethylene glycol plant. Then, the relationships among the deviations, the reference documents and the guidance documents should be considered and evaluated. Finally, each dangerous deviation will be given a corresponding reference document and guidance document. The reference documents and guidance documents stored in the expert system can be utilized to help operators solve the corresponding technical problems and cope with abnormal situations. The process safety data management program will contribute to the identification, analysis and resolution of operation problems. When an abnormal situation occurs, according to the deviations exhibited in the system, the necessary reference documents and guidance documents will be quickly consulted by the operators, and an appropriate decision will be made to address the abnormal situation. Therefore, by using the process safety data management program, plant security and human safety in the petrochemical industries will be improved.     

Inherent safety tool for explosion consequences study

The lack of formal integration between process design stages with risk and consequence estimation is a hurdle to designing inherently safe process plants. Conventional risk assessment methodologies are often not carried out concurrently with process design. Therefore, process designers lack the information about risk levels and consequence that may result from the process conditions being considered in a particular process route until the design is completed. Hence, effects of changes in process conditions on risk levels and consequence cannot be studied in a time effective manner during the design stages. Few studies have been identified on the possibility and viability of integrating risk estimation with process design. But viable framework and methodology for doing so has not yet been reported. This paper presents a feasible framework in which risk and consequences estimation can be part of design stages. A demonstrative tool named as integrated risk estimation tool (iRET) was developed by using process simulation software, HYSYS and spreadsheet, MS Excel as the platforms. iRET estimates risk due to explosions by using TNT equivalence method and the TNO correlation method. iRET has a potential to be extended to include all forms of risk such as fire, explosion, toxic gas releases and boiling liquid expanding vapour explosion (BLEVE). The paper also presents case studies to demonstrate the functionality and viability of using iRET in conjunction with process design. The results of these case studies have successfully shown that the risk due to explosion can be assessed during the initial design stage ensuring a safer plant. The framework and iRET there by presented here provide systematic methodology and technology to design inherently safer plants.     

Risk-based shutdown management of LNG units

Global demand for natural gas may double by 2030, with Liquefied Natural Gas (LNG) growing perhaps fivefold - driven by continued cost reduction. Propane Pre-cooled Mixed Refrigerant (PPMR) of Air Products and Chemicals Inc. (APCI) currently holds 78% of the liquefaction plants on the market. Since the PPMR process has the largest production capacity, its operational reliability needs to be high as any failure may result in catastrophic consequences. Therefore, operational reliability has a key importance in LNG plants. To achieve an acceptable reliability, usually, a constant interval of a preventive maintenance method is used. The limitation of such a method is that the shutdown strategy is not optimum. This study focuses on determining a risk-based shutdown management strategy for APCI plants with capacity of 4.5 million tons per annum. To achieve the minimum risk for the expected life of an LNG plant, a combination of preventive maintenance, active redundancy and standby redundancy is considered. Results of this study reveal that such a combination can significantly reduce the operational risk. This combination improves the plant reliability and maintains it above a minimum operational reliability.     

Process plant safety information repository and support for safety applications

The consideration of safety of processing plants from design to operation involves many tasks. Different techniques and tools have been developed to assist in carry out those tasks. With the advances in computing technologies, both in hardware and software, there is the opportunity to bring together the vast amount of engineering, hazard and risk data and handle them in an efficient way to manage and improve safety throughout the life time of a plant. This paper proposes keeping such data in a process plant safety information repository which can be easily accessed by different safety-related tools to enhance the efficiency of safety identification and analysis tasks.     

质子交换膜燃料电池电站多米诺事故概率和风险研究

为探究氢能电站火灾爆炸事故发展规律,采用多米诺效应对电站进行事故概率和风险研究,建立氢能电站多米诺效应定量风险分析模型。基于设备受损概率模型与多米诺理论基础,提出氢能电站多米诺效应概率计算方法,并将方法运用到实际案例,结合SAFETI软件对具体多米诺事故场景进行定量计算。研究结果表明：氢能电站易发生多米诺事故,考虑一级多米诺效应后人员潜在死亡概率增加56%。研究结果可为制定氢能电站安全防控措施以及降低火灾爆炸事故对人员和设备的危害提供依据。     

Dynamic risk analysis of offloading process in floating liquefied natural gas (FLNG) platform using Bayesian Network

The growing demand for natural gas has pushed oil and gas exploration to more isolated and previously untapped regions around the world where construction of LNG processing plants is not always a viable option. The development of FLNG will allow floating plants to be positioned in remote offshore areas and subsequently produce, liquefy, store and offload LNG in the one position. The offloading process from an FLNG platform to a gas tanker can be a high risk operation. It consists of LNG being transferred, in hostile environments, through loading arms or flexible cryogenic hoses into a carrier which then transports the LNG to onshore facilities. During the carrier's offloading process at onshore terminals, it again involves risk that may result in an accident such as collision, leakage and/or grounding. It is therefore critical to assess and monitor all risks associated with the offloading operation. This study is aimed at developing a novel methodology using Bayesian Network (BN) to conduct the dynamic safety analysis for the offloading process of an LNG carrier. It investigates different risk factors associated with LNG offloading procedures in order to predict the probability of undesirable accidents. Dynamic failure assessment using Bayesian theory can estimate the likelihood of the occurrence of an event. It can also estimate the failure probability of the safety system and thereby develop a dynamic failure assessment tool for the offloading process at a particular FLNG plant. The main objectives of this paper are: to understand the LNG offloading process, to identify hazardous events during offloading operation, and to perform failure analysis (modelling) of critical accidents and/or events. Most importantly, it is to evaluate and compare risks. A sensitivity analysis has been performed to validate the risk models and to study the behaviour of the most influential factors. The results have indicated that collision is the most probable accident to occur during the offloading process of an LNG carrier at berth, which may have catastrophic consequences.     

Influence of new generic frequencies on the QRA calculations for land use planning purposes in Walloon region (Belgium)

In Europe, the article 12 of the “Seveso” Directive focuses on land use planning (LUP) around major hazard plants and imposes to keep a sufficient distance between a major hazard plant and populated areas. In Belgium, the LUP is treated at the regional level. The regional authority defines the policy and manages the LUP according to the quantified risk. The quantified external risk, around each Seveso company in the Walloon Region, is assessed by a unique technical expert, the Faculté Polytechnique de Mons, by means of a full probabilistic approach (QRA). This QRA methodology uses accident generic frequencies published by the Flemish Region (Aminal, 2004). In 2009-2010, the quantification of the external risk of the 90 walloon Seveso plants will be completed, based on this set of generic frequencies. However, the Flemish Region recently published a new set of generic frequencies (LNE, 2009), which, in some cases, are quite different of the previous ones for some equipment. This paper discusses the influence of the new frequency data on the quantified risk. An overview of the changes induced by the new set of data will be presented, as well as their impact on the already defined "consultation zones" in which decisions are made concerning the compatibility of the land use and the intensity of risk.     

Inherent risk assessment—A new concept to evaluate risk in preliminary design stage

Quantitative Risk Assessment (QRA) has been a very popular and useful methodology which is widely accepted by the industry over the past few decades. QRA is typically carried out at a stage where complete plant has been designed and sited. At that time, the opportunity to include inherent safety design features is limited and may incur higher cost. This paper proposes a new concept to evaluate risk inherent to a process owing to the chemical it uses and the process conditions. The risk assessment tool is integrated with process design simulator (HYSYS) to provide necessary process data as early as the initial design stages, where modifications based on inherent safety principles can still be incorporated to enhance the process safety of the plant. The risk assessment tool consists of two components which calculate the probability and the consequences relating to possible risk due to major accidents. A case study on the potential explosion due to the release of flammable material demonstrates that the tool is capable to identify potential high risk of process streams. Further improvement of the process design is possible by applying inherent safety principles to make the process under consideration inherently safer. Since this tool is fully integrated with HYSYS, re-evaluation of the inherent risk takes very little time and effort. The new tool addresses the lack of systematic methodology and technology, which is one of the barriers to designing inherently safer plants.     

Cost-based fire risk assessment in natural gas industry by means of fuzzy FTA and ETA

Fire is the most prevalent accident in natural gas facilities. In order to assess the risk of fire in a gas processing plant, a fault tree analysis (FTA) and event tree analysis (ETA) has been developed in this paper. By utilizing FTA and ETA, the paths leading to an outcome event would be visually demonstrated. The framework was applied to a case study of processing plant in South Pars gas complex. All major underlying causes of fire accident in a gas processing facility determined through a process hazard analysis (PHA). Fuzzy logic has been employed to derive likelihood of basic events in FTA from uncertain opinion of experts. The outcome events in event tree has been simulated by computer model to evaluate their severity. In the proposed methodology the calculated risk has the unit of cost per year which allows the decision makers to discern the benefit of their investment in safety measures and risk mitigation.     

On the operator action analysis to reduce operational risk in research reactors

Human errors during operation and the resulting increase in operational risk are major concerns for nuclear reactors, just as they are for all industries. Additionally, human reliability analysis together with probabilistic risk analysis is a key element in reducing operational risk. The purpose of this paper is to analyze human reliability using appropriate methods for the probabilistic representation and calculation of human error to be used alongside probabilistic risk analysis in order to reduce the operational risk of the reactor operation. We present a technique for human error rate prediction and standardized plant analysis risk. Human reliability methods have been utilized to quantify different categories of human errors, which have been applied extensively to nuclear power plants. The Tehran research reactor is selected here as a case study, and after consultation with reactor operators and engineers human errors have been identified and adequate performance shaping factors assigned in order to calculate accurate probabilities of human failure.     

Case study of a nylon fibre explosion: An example of explosion risk in a textile plant

This paper offers an overview of an explosion that occurred in a textile industry, due to the deflagration of a particular nylon fibre called flock. The evidence, the methods and the results of the inquiry are reported. The explosion occurred in a plant that produced a characteristic kind of flocked thread which is entirely made of a synthetic material. The explosion took place inside a dryer and propagated to the connected suction plant. The explosion occurred when the plant was switched on after a long stop due to a process fault. Three workers were injured. The inquiry includes the measurement of the most important properties of the flock such as the minimum ignition energy (MIE) and the lower explosion concentration (LEL), together with an examination the exam of the damage and of the testimony of the witnesses. The dynamics of the event are reconstructed in the paper and the effects, on the accident, of the many mistakes that have been made in the risk analysis are highlighted and discussed.     

A mathematical approach for retrofit and optimization of total site steam distribution networks

This paper presents a generic mathematical model for retrofitting the steam power plants in an industrial site. The industrial sector under review consists of one steel mill, one oil refinery, and several petrochemical plants, where only small-scale steam integration has been implemented before this study. The relevant unit models in a typical steam power plant are established, and the steam plant retrofit problem is formulated as a mixed-integer nonlinear program (MINLP). Feasible retrofit alternatives suggested by experienced field engineers are investigated in sequence to examine the revenue of those possible modifications. The first scenario examines operational optimization of existent plants; the second option allows installation of one new turbine and replacement of several boilers and turbines with lower efficiency; the third scenario considers using a steam ejector to upgrade the disqualified import steam in the oil refinery. The significant merits from these three retrofit alternatives show that the proposed MINLP formulation has been a great help to enhance the inter-plant steam integration in an industrial sector.     

火电机组氢冷系统安全评价

国外已经对火电厂的安全评价工作进行了一定的研究,但是国内对此项工作的研究还是比较匮乏,尤其对火电厂危险化学品更缺乏相关的安全评价方法及研究。在火力发电厂实际生产中,需使用到大量易燃、易爆危险化学品,由于使用、存储不当,极易造成重大事故。根据某火电厂实际情况,结合安全评价的基本程序,运用道(DOW)化学火灾、爆炸危险指数评价法对火电机组氢冷系统(GRH)单元进行了评价。结果显示,GRH单元的本质危险性很大,经过安全措施补偿后危险性较轻,说明利用道氏法对火电厂危险化学品使用状况进行评价,能够比较准确地反映被评价单位的实际情况,根据评价结果和存在的问题提出有针对性的对策措施,进一步改善火电机组运行环境的安全。评价结果可为火电厂提高安全管理水平提供有价值的参考。     

Integrating major accidents hazard into occupational risk assessment: An index approach

Major Accident Hazard (MAH) and Occupational Safety and Health (OSH) are two separated topics in both industrial practice and legislation; recently, interest is increasing toward an integrated risk assessment mainly forced by the tendency to a more efficient safety management system. The present study proposes a semi-quantitative approach to integrate MAH in OSH risk assessment. The two risk types are characterized by opposite features: the OSH analysis is usually task-based and focused on job profiles, while the MAH analysis is space-based and focused on plant characteristics. The basic idea of the proposed approach is to merge spatial information and job profile features in order to improve OSH assessment; thus, a risk index derived by the recent standard ISO 12100 (2010) has been adapted. In detail, the proposed index combines exposure times of each worker at each plant unit – derived from the OSH analysis – with damage areas derived from MAH analysis allowing a quantitative assessment of the MAH risk level for each individual job profile. The model has been tested in a large petrochemical plant; several hypotheses have been developed in order to validate the model. Results have showed the potentiality of the proposed approach in providing a common and coherent representation of both MAH and OSH risks, according to job profiles and plant units.     

Application of a multi-plant QRA: A case study investigating the risk impact of the construction of a new plant on an existing chemical plant's risk levels

The construction of chemical clusters whereby a variety of chemical plants are located next to each other provides great economic benefits. However, in such clusters, due to the mere scale on which hazardous materials are processed, stored and handled, the potential of various accidents is much higher than in single companies. Furthermore, the close proximity of process installations and storage tanks in such areas gives rise to the risk of domino effects. Therefore, land use planning and layout design has always been a challenge within such clusters.In this paper, a Quantitative Risk Assessment (QRA) is carried out and used as a decision making tool to evaluate the acceptability of constructing a new chemical plant adjacent to an existing one. For this purpose, standard parameters such as individual risk and societal risk were quantified, before and after the new plant would come into operation. Given the experience of past accidents in the process industries, the likelihood of domino accidents in the two neighboring plants has also been analyzed.