On the need for system-theoretic hazard analysis in the process industries

Most process hazard analysis (PHA) studies today are conducted using traditional methods such as the hazard and operability study (HAZOP). Traditional methods are based on a chain-of-events model of accident causality. Current models of accident causality are based on systems theory and provide a more complete representation of the causal factors involved in accidents. Consequently, it is logical to expect that PHA methods should reflect these models, that is, system-theoretic hazard analysis (STHA) should be used. Indeed, system-theoretic process analysis (STPA) has been developed as such a method. STPA has been used in a variety of industries but, at this time, it has not gained acceptance by the process industries. This article explores the reasons for this situation. Expectations for PHA in the process industries are examined and issues for the application of STPA in the process industries are discussed. It is concluded that a variety of matters must be addressed before STPA can be considered as a viable PHA method for the process industries and the case for the use of STHA in the process industries is not yet proven.     

基于SDG模型的HAZOP分析方法在钻井作业中的应用

HAZOP分析方法是目前危险性分析领域最盛行的分析方法之一,广泛地应用于石油化工行业。但是其分析过程仅依靠专家积累的知识与经验,不仅评价的内容不严格,而且分析的可信程度有限,对实际工作的指导意义不高,不能适应工业现场的要求。鉴于HAZOP分析方法中的不足,提出了基于SDG模型的HAZOP分析方法,并利用该方法对钻井作业过程进行了危险性分析。基于SDG模型的HAZOP分析方法从复杂系统的内部逻辑入手,进行深层次的推理,不仅提高了分析效率,而且分析所得结果的完备性较好。     

State of research on the automation of HAZOP studies

For more than 30 years, multiple research groups have worked on the automation of hazard and operability (HAZOP) studies, or more specifically on the hazard identification process. So far, very few of these approaches have been used in the chemical process industry. Automatic hazard identification is a knowledge-intensive process that demands high standards with regard to the way in which knowledge is stored and made available. There are various suitable approaches to the qualitative modeling of processes and plants, which are the foundation for reasoning systems that are used for the identification of hazards. Additionally, there are quantitative methods that are based on process simulations and can be used to identify potential hazards. The investigation of the state of research demonstrates that there are sophisticated technologies for automated systems that include powerful reasoning techniques. The benefits and shortcomings of existing technologies are discussed with regard to their industrial applicability. Often, the quality of the necessary specific and generic knowledge is not sufficient to detect potential hazardous events and operational malfunctions. Computer-aided HAZOP systems should be integrated with computer-aided design- or process simulation software using common data models based on the digital representation of the process plant. In order to be used by HAZOP practitioners automated systems need to be comprehensive, serve as specialized decision support systems, and be tested and evaluated using round robin tests.     

Reasonableness of a proposed System Theoretic Process Analysis (STPA) validation framework: An interview study

Since its inception, the STPA technique has gained increasing popularity among researchers and industry practitioners. Nevertheless, the validity of its application has not yet received much scientific attention. Although some informal validation approaches have been used by STPA users, no formalized validation framework has been elaborated for practical use. This paper investigates the reasonableness of the recently proposed STPA validation framework, which includes 15 validation tests, each focusing on a specific step of an STPA analysis. To do so, STPA experts in both academia and industry were interviewed. First, it is investigated what approaches they have been using for validating an STPA analysis, the findings of which were categorized and mapped with the proposed validation framework. This aims to investigate the similarities and dissimilarities between the theory-based validation framework and the informal methods applied by experts in current practice. Then, the proposed framework was presented to the interviewees to seek their judgments about its reasonableness. Feedback from practitioners indicated that the proposed STPA validation framework has certain strengths, while several opportunities exist for further improvement. In particular, the findings indicate that most of the proposed theory-based tests have been already used by STPA experts in an unstructured manner. The experts appreciated the framework in that it provides clear guidance on how to validate each step of an STPA analysis systematically, and found some additional theory-based tests interesting for consideration in practice. The results also suggest that further research is needed to develop systematic techniques for performing each test to facilitate its application by STPA experts.     

在役柴油加氢装置HAZOP分析技术

柴油加氢装置属甲类火灾危险生产装置,为了保障其安全生产,实现事故早期预防,对其进行风险分析和安全评价势在必行.HAZOP分析方法是流程工业广泛使用的一种危险辨识和分析方法,具有较好的系统性和完备性.首先介绍了HAZOP分析方法的由来及应用情况,其次分析了在役装置HAZOP分析的难点,并提出了相应的建议,然后详述了在役装置HAZOP方法的分析流程.最后以中石油某石化公司在役柴油加氢装置为例进行了HAZOP分析,辨识出可能存在的安全隐患和潜在危险,对较高风险提出了必要的安全保护措施和合理的改进建议.结果表明,HAZOP分析是提高在役装置安全性的一种有效手段,其结果为装置安全管理提供了可靠的依据.     

TOPHAZOP: a knowledge-based software tool for conducting HAZOP in a rapid, efficient yet inexpensive manner

Hazard and operability (HAZOP) studies constitute an essential step in the risk analysis of any chemical process industry and involve systematic identification of every conceivable abnormal process deviation, its causes and abnormal consequences. These authors have recently proposed optHAZOP as an alternative procedure for conducting HAZOP studies in a shorter span of time than taken by conventional HAZOP procedure, with greater accuracy and effectiveness [Khan, F. I. and Abassi, S. A., optHAZOP. An effective and efficient technique for hazard identification and assessment Journal of Loss Prevention in the Process Industries, 1997, 10, 191–204]. optHAZOP consists of several steps, the most crucial one requires use of a knowledge-based software tool which would significantly reduce the requirement of expert man-hours and speed up the work of the study team. TOPHAZOP (Tool for OPTmizing HAZOP) has been developed to fulfil this need.

The TOPHAZOP knowledge-base consists of two main branches: process-specific and general. The TOPHAZOP framework allows these two branches to interact during the analysis to address the process-specific aspects of HAZOP analysis while maintaining the generality of the system. The system is open-ended and modular in structure to make easy implementation and/or expansion of knowledge. The important features of TOPHAZOP and its performance on an industrial case study are described.     

The integration of HAZOP expert system and piping and instrumentation diagrams

The main purpose of hazard and operability (HAZOP) analysis is to identify the potential hazards in the process design which nowadays is generally developed through a computer aided design (CAD) package. Due to the time and effort consuming nature of HAZOP, it is not done in every engineering firm for every design project. To make HAZOP an integral part of process design, an integration framework is proposed in this paper to seamlessly integrate the commercial process design package Smart Plant P&ID (SPPID, Intergraph) with one of the HAZOP expert systems (named as LDGHAZOP) developed by authors. This integration makes it possible to perform HAZOP analysis easily at anytime of the whole lifecycle of a chemical plant as long as the process design is available, which might help the improvement of design quality. One industrial case study is used to illustrate the ability of the integrated system.     

合成氨装置系统安全仪表系统安全完整性等级分析

论文在介绍安全仪表系统、安全完整性等级的基本原理基础上,综合分析了危险与可操作性分析(HAZOP)、保护层分析(LOPA)等系统风险分析理论的应用方法。并结合上述理论,确定了安全仪表系统的安全完整性等级(SIL)定级。以合成氨装置为例,应用HAZOP及保护层分析方法,得出了合成塔压力过高及废热锅炉液位过低2个场景下的安全完整性SIL等级。结果表明:合成塔装置仪表的SIL等级为1,废热锅炉仪表的SIL等级为2。     

Safety study of an LNG regasification plant using an FMECA and HAZOP integrated methodology

A safety analysis was performed to determine possible accidental events in the storage system used in the liquefied natural gas regasification plant using the integrated application of failure modes, effects and criticality analysis (FMECA) and hazard and operability analysis (HAZOP) methodologies. The goal of the FMECA technique is the estimation of component failure modes and their major effects, whereas HAZOP is a structured and systematic technique that provides an identification of the hazards and the operability problems using logical sequences of cause-deviation-consequence of process parameters. The proposed FMECA and HAZOP integrated analysis (FHIA) has been designed as a tool for the development of specific criteria for reliability and risk data organisation and to gain more recommendations than those typically provided by the application of a single methodology. This approach has been applied to the risk analysis of the LNG storage systems under construction in Porto Empedocle, Italy. The results showed that FHIA is a useful technique to better and more consistently identify the potential sources of human errors, causal factors in faults, multiple or common cause failures and correlation of cause-consequence of hazards during the various steps of the process.     

HAZOP研究与故障树分析在合成氨装置危险辨识中的应用

合成氨装置的原料、产品危险性高,并且生产过程复杂,因此在运行过程中可能导致火灾、爆炸、中毒等事故,有些事故甚至给社会和环境造成严重破坏.对HAZOP研究与故障树分析进行组合,应用在合成氨装置的危险辨识中.通过HAZOP研究,合成氨主体装置共发现风险因素23项,其中合成氨装置的合成气压缩单元安全隐患较多,因此对其进行故障树分析,合成气压缩机单元火灾、爆炸故障树的最小割集为72个,最小径集为6个.从基本事件结构重要度结果来看,压缩机三级出口压力探测器( PIA3-2)故障,对压缩机发生火灾、爆炸的影响程度最大,应重点防范.     

基于三角模糊数的HAZOP分析在石油化工装置中的应用

工艺危害分析强调运用系统的方法对危害进行辨识、分析,并采取必要的措施消除和减少危害。HAZOP分析能对工艺过程非常系统、全面的进行分析,但传统的HAZOP分析在量化风险时,对于偏差原因发生的可能性评价存在较大的主观性。本文对于没有统计资料的HAZOP分析偏差原因发生可能性,采用专家打分法,利用三角模糊数来表示其模糊发生概率。对于有统计资料的偏差原因,直接表示成三角模糊数。这种方法能够很好的表示HAZOP分析偏差发生概率。介绍了基于三角模糊数的HAZOP分析步骤,并在石油化工装置中进行了应用。这对HAZOP分析技术在石油化工装置中的推广具有重要意义。     

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.     

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.     

Safety assessment of the film boiling chemical vapor infiltration (FB-CVI) process through a system-theoretic accident model and process (STAMP)

Film boiling chemical vapor infiltration (FB-CVI) is considered as one of the fastest process methodologies for manufacturing carbon-carbon (C–C) composite products and possesses various advantages compared to conventional methodologies. However, there are safety concerns associated with this process for large-scale manufacturing, mainly owing to the intrinsic nature of the precursor and the process conditions. Considering the multifunctional interactions of the various systems during the process, a system-theoretic process analysis (STPA)/system theoretic accident model and process (STAMP) model is used to perform a safety analysis of the hazardous states of the FB-CVI process at the system level. As a case study, the FB-CVI process equipment employed for the manufacturing of C–C composites is considered. The safety constraints present in the system are assessed for adequacy through a hazard analysis by STPA/STAMP. The analysis through STPA/STAMP demonstrated the capability to create proactive strategies for the design and realization of process equipment that can be employed to manufacture C–C composite products through the FB-CVI process.     

Inherent safety in offshore oil and gas activities: a review of the present status and future directions

Inherent safety is a proactive approach for hazard/risk management during process plant design and operation. It has been proven that, considering the lifetime costs of a process and its operation, an inherently safer approach is a cost-optimal option. Inherent safety can be incorporated at any stage of design and operation; however, its application at the earliest possible stages of process design (such as process selection and conceptual design) yields the best results.Although it is an attractive and cost-effective approach to hazard/risk management, inherent safety has not been used as widely as other techniques such as HAZOP and quantitative risk assessment. There are many reasons responsible for this; key among them are a lack of awareness and the non-availability of a systematic methodology and tools.The inherent safety approach is the best option for hazard/risk management in offshore oil and gas activities. In the past, it has been applied to several aspects of offshore process design and operation. However, its use is still limited. This article attempts to present a complete picture of inherent safety application in offshore oil and gas activities. It discuses the use of available technology for implementation of inherent safety principles in various offshore activities, both current and planned for the future.     

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.     

A novel knowledge database construction method for operation guidance expert system based on HAZOP analysis and accident analysis

An expert system for operation guidance will contribute to identifying the operatoration problems and indicating the resolutions thereof, because the information stored in the expert system can be utilized to resolve the corresponding technical problems. However, there are several problems that should be solved in the practical application of the expert system, such as lack of corresponding knowledge or resolutions utilized to cope with the problems, inapplicable resolutions, too many resolutions for the operators to choose from to obtain the best one in the first time, etc. Obtaining and storing as much as information in the database of the expert system are important issues in the construction process of the expert system. The accident analysis results contain a limited number of accident cases and the HAZOP analysis only refers to a single deviation analysis. This paper has presented a novel knowledge database construction method for an operation guidance expert system based on the HAZOP analysis and the accident analysis, which can be used to resolve the above problems. The HAZOP analysis results are combined with the accident analysis results and the combination information can be stored in the database of the expert system, and can be employed to forecast accidents or identify accident causes. The structures of the operation guidance table and the accident investigation table have been illustrated. The residuum hydrotreating process expert system is taken as an example to illustrate the knowledge database construction method. With the aid of this expert system, the operators will well understand the operations and adopt the best resolutions to deal with the abnormal situations. Also the operators can identify potential risks existing in the plant which will result in accidents according to the accident analysis results associated with the HAZOP analysis results.     

A structural approach to the HAZOP – Hazard and operability technique in the biopharmaceutical industry

Recently, the use of analytical techniques to identify, assess and address risks within the pharmaceutical industry is increasing from the initial and operating phases until the final use of products aiming to eliminate or reduce the severity of deviations. The hazard and operability studies – HAZOP establish that accidents are the result of failure modes in process variables out of operational parameters. In this paper, the HAZOP methodology was used to assess risks in the system for recombinant protein production where a multidisciplinary group used the brainstorming strategy to identify the risk level and deviations in nodes defined by functionality in the system. Nineteen critical nodes were identified, deviations were established in based on knowledge, and experience by the group, thus precluded the need of deviation's records to estimate frequency and impacts of events. It was also shown that in the pharmaceutical industry the most-critical risks are those that have adverse impacts on production like partial and total losses and when noncompliance of regulations are involved. The HAZOP risk assessment tool can be easily followed by people who are interested in starting to use this technique to improve the security environment within the institution and when required by regulatory agencies.     

Qualitative Assessment for Inherently Safer Design (QAISD) at preliminary design stage

Conventional hazard evaluation techniques such as what-if checklist and hazard and operability (HAZOP) studies are often used to recognise potential hazards and recommend possible solutions. They are used to reduce any potential incidents in the process plant to as low as reasonably practicable (ALARP) level. Nevertheless, the suggested risk reduction alternatives merely focus on added passive and active safety systems rather than preventing or minimising the inherent hazards at source through application of inherently safer design (ISD) concept. One of the attributed reasons could be the shortage of techniques or tools to support implementation of the concept. Thus, this paper proposes a qualitative methodology that integrates ISD concept with hazard review technique to identify inherent hazards and generate ISD options at early stage of design as proactive measures to produce inherently safer plant. A modified theory of inventive problem solving (TRIZ) hazard review method is used in this work to identify inherent hazards, whereby an extended inherent safety heuristics tool is developed based on established ISD principles to create potential ISD options. The developed method namely Qualitative Assessment for Inherently Safer Design (QAISD) could be applied during preliminary design stage and the information required to apply the method would be based on common process and safety database of the studied process. However, user experiences and understanding of inherent safety concept are crucial for effective utilisation of the QAISD. This qualitative methodology is applied to a typical batch reactor of toluene nitration as a case study. The results show several ISD strategies that could be considered at early stage of design in order to prevent and minimise the potential of thermal runaway in the nitration process.     

Process hazards review applied to the use of anhydrous ammonia in agriculture: an example of chemical process safety for small business

Process hazards review (PHR) techniques have generally been applied by large, sophisticated companies in the nuclear, aerospace, and chemical process industries. There remains, however, a large population of smaller distributors and consumers of hazardous materials which could benefit equally from the application of PHR. These consumers unfortunately are generally less sophisticated and individually lack the necessary resources required to apply such state-of-the-art safety techniques.

Where common processes can be identified, it is possible to conduct a more generic PHR that will provide a sound technical basis for recognizing and preventing the development of hazards wherever these processes are used. Some facility-specific issues will always need to be considered, but the existence of the generic PHR should make the conduct of a PHR by each facility considerably easier and less costly.

Researchers from the National Institute for Occupational Safety and Health (NIOSH) contracted with DNV Technica Inc. to lead a hazard and operability study (HAZOP) of agricultural handling of anhydrous ammonia, from the receipt of ammonia at the retail distribution centre to the application of the ammonia by farmers to the fields. The multidisciplinary HAZOP team consisted of representatives from NIOSH, an agricultural chemical trade association, an ammonia producer, state ammonia facility inspectors, a retail distributor, and an equipment manufacturer. Several participants were part-time farmers with ammonia application experience.

Some specific aspects of applying the HAZOP technique in the context of this study, the findings obtained, and the plans to disseminate the important safety information developed during the course of the PHR are discussed. Finally, it is suggested that this approach could prove to be a useful addition to the product stewardship activities of chemical producers.