State-based modelling in hazard identification

The signed directed graph (SDG) is the most commonly used type of model for automated hazard identification in chemical plants. Although SDG models are efficient in simulating the plant, they have some weaknesses, which are discussed here in relation to typical process industry examples. Ways to tackle these problems are suggested, and the view is taken that a state-based formalism is needed, to take account of the discrete components in the system, their connection together, and their behaviour over time. A strong representation for operations and actions is also needed, to make the models appropriate for modelling batch processes. A research prototype for HAZOP studies on batch plants (CHECKOP) is also presented, as an illustration of the suggested approach to modelling

Combining qualitative and quantitative reasoning to support hazard identification by computer

This thesis investigates the proposition that use must be made of quantitative information to control the reporting of hazard scenarios in automatically generated HAZOP reports. HAZOP is a successful and widely accepted technique for identification of process hazards. However, it requires an expensive commitment of time and personnel near the end of a project. Use of a HAZOP emulation tool before conventional HAZOP could speed up the examination of routine hazards, or identify deficiencies I in the design of a plant. Qualitative models of process equipment can efficiently model fault propagation in chemical plants. However, purely qualitative models lack the representational power to model many constraints in real plants, resulting in indiscriminate reporting of failure scenarios. In the AutoHAZID computer program, qualitative reasoning is used to emulate HAZOP. Signed-directed graph (SDG) models of equipment are used to build a graph model of the plant. This graph is searched to find links between faults and consequences, which are reported as hazardous scenarios associated with process variable deviations. However, factors not represented in the SDG, such as the fluids in the plant, often affect the feasibility of scenarios. Support for the qualitative model system, in the form of quantitative judgements to assess the feasibility of certain hazards, was investigated and is reported here. This thesis also describes the novel "Fluid Modelling System" (FMS) which now provides this quantitative support mechanism in AutoHAZID. The FMS allows the attachment of conditions to SDG arcs. Fault paths are validated by testing the conditions along their arcs. Infeasible scenarios are removed. In the FMS, numerical limits on process variable deviations have been used to assess the sufficiency of a given fault to cause any linked consequence. In a number of case studies, use of the FMS in AutoHAZID has improved the focus of the automatically generated HAZOP results. This thesis describes qualitative model-based methods for identifying process hazards by computer, in particular AutoHAZID. It identifies a range of problems where the purely qualitative approach is inadequate and demonstrates how such problems can be tackled by selective use of quantitative information about the plant or the fluids in it. The conclusion is that quantitative knowledge is' required to support the qualitative reasoning in hazard identification by computer

Computer-aided HAZOP of batch processes

The modern batch chemical processing plants have a tendency of increasing technological complexity and flexibility which make it difficult to control the occurrence of accidents. Social and legal pressures have increased the demands for verifying the safety of chemical plants during their design and operation. Complete identification and accurate assessment of the hazard potential in the early design stages is therefore very important so that preventative or protective measures can be integrated into future design without adversely affecting processing and control complexity or capital and operational costs. Hazard and Operability Study (HAZOP) is a method of systematically identifying every conceivable process deviation, its abnormal causes and adverse hazardous consequences in the chemical plants. [Continues.

Hazards in advising autonomy: incorporating hazard modelling with system dynamics into the aerospace safety assessment process for UAS

This paper describes the further continuation of an investigation to identify and develop tools for the identification and management of hazards likely to arise with the quality and behavioural aspects in and resulting from automatic advice - such as might arise with an automated system advisory function facilitating critical decision-making with an autonomous vehicle. An example of a representative critical advisory function is identified in that supporting a necessary “Sense & Avoid” capability, as embodied within a airborne autonomous system. In consideration then of how might a model driven approach, combining physical and dynamical models, statistical data and belief be combined to aid system evaluation, work has so far been undertaken to investigate the nature of suitable models to provide representations of the control structure and system dynamics. Whilst the system engineering methods are to be generic, the context of “Sense & Avoid” provides a relevant framework within which to pose a “toy-problem” with complex behaviour, against which to judge the methods and models

Computer-aided applications in process plant safety

Process plants that produce chemical products through pre-designed processes are fundamental in the Chemical Engineering industry. The safety of hazardous processing plants is of paramount importance as an accident could cause major damage to property and/or injury to people. HAZID is a computer system that helps designers and operators of process plants to identify potential design and operation problems given a process plant design. However, there are issues that need to be addressed before such a system will be accepted for common use. This research project considers how to improve the usability and acceptability of such a system by developing tools to test the developed models in order for the users to gain confidence in HAZID s output as HAZID is a model based system with a library of equipment models. The research also investigates the development of computer-aided safety applications and how they can be integrated together to extend HAZID to support different kinds of safety-related reasoning tasks. Three computer-aided tools and one reasoning system have been developed from this project. The first is called Model Test Bed, which is to test the correctness of models that have been built. The second is called Safe Isolation Tool, which is to define isolation boundary and identify potential hazards for isolation work. The third is an Instrument Checker, which lists all the instruments and their connections with process items in a process plant for the engineers to consider whether the instrument and its loop provide safeguards to the equipment during the hazard identification procedure. The fourth is a cause-effect analysis system that can automatically generate cause-effect tables for the control engineers to consider the safety design of the control of a plant as the table shows process events and corresponding process responses designed by the control engineer. The thesis provides a full description of the above four tools and how they are integrated into the HAZID system to perform control safety analysis and hazard identification in process plants

HAZOP: Our Primary Guide in the Land of Process Risks: How can we improve it and do more with its results?

PresentationAll risk management starts in determining what can happen. Reliable predictive analysis is key. So, we perform process hazard analysis, which should result in scenario identification and definition. Apart from material/substance properties, thereby, process conditions and possible deviations and mishaps form inputs. Over the years HAZOP has been the most important tool to identify potential process risks by systematically considering deviations in observables, by determining possible causes and consequences, and, if necessary, suggesting improvements. Drawbacks of HAZOP are known; it is effort-intensive while the results are used only once. The exercise must be repeated at several stages of process build-up, and when the process is operational, it must be re-conducted periodically. There have been many past attempts to semi- automate the HazOp procedure to ease the effort of conducting it, but lately new promising developments have been realized enabling also the use of the results for facilitating operational fault diagnosis. This paper will review the directions in which improved automation of HazOp is progressing and how the results, besides for risk analysis and design of preventive and protective measures, also can be used during operations for early warning of upcoming abnormal process situations

New trends for conducting hazard & operability (HAZOP) studies in continuous chemical processes

Identifying hazards is fundamental for ensuring the safe design and operation of a system in process plants and other facilities. Several techniques are available to identify hazardous situations, all of which require their rigorous, thorough, and systematic application by a multi-disciplinary team of experts. Success rests upon first identifying and subsequently analyzing possible scenarios that can cause accidents with different degrees of severity. While hazard identification may be the most important stage for risk management, it depends on subjectivity issues (e.g., human observation, good judgment and intuition, creativity, expertise, knowledge) which introduce bias. Without a structured identification system, hazards can be overlooked, thus entailing incomplete risk-evaluations and potential loss. The present Thesis is focused on developing both managerial and technical aspects intended to standardize one of the most used techniques for hazard identification; viz. HAZard & Operability (HAZOP) study. These criteria have been carefully implemented not only to ensure that most of the hazardous scenarios will be identified, but also that US OSHA PSM Rule, EPA RMP, and Seveso Directive requirements will be accomplished. Chapter I pioneers the main research topic; from introducing the process safety concept up to the evidence of more detailed information is required from related regulations. A review of regulations (i.e., US, Europe legislation) focused on Hazard Identification has been conducted, highlighting, there is an absence of specific criteria for performing techniques intended to identify what can go wrong. Chapter II introduces the risk management system required to analyze the risk from chemical process facilities, and justifies that hazard identification stage is the Process Safety foundation. Hereafter, an overview of the key Process Hazard Analyzes (PHA) has been conducted, and the specific HAZOP weaknesses and strengths have been highlighted to establish the first steps to focus on. Chapter III establishes the scope, the purpose and the specific objectives that the research covers. It answers the following questions on the spot: why the present research is performed, which elements are included, and what has been considered for acquiring the final conclusions of the manuscript. Chapter IV gathers HAZOP-related literature from books, guidelines, standards, major journals, and conference proceedings with the purpose of classifying the research conducted over the years and finally define the HAZOP state-of-the-art. Additionally, and according to the information collected, the current HAZOP limitations have been emphasized, and thus, the research needs that should be considered for the HAZOP improvement and advance. Chapter V analyzes the data collected while preparing, organizing, executing and writing HAZOPs in five petroleum-refining processes. A statistical analysis has been performed to extract guidance and conclusions to support the established criteria to conduct effectively HAZOP studies. Chapter VI establishes the whole set of actions that have to be taken into account for ensuring a wellplanned and executed HAZOP study. Both technical and management issues are addressed, criteria supported after considering the previous chapters of the manuscript. Chapter VI itself is the result of the present research, and could be used as a guideline not only for team leaders, but also for any related party interested on performing HAZOPs in continuous chemical processes. Chapter VII states the final conclusions of the research. The interested parties should be released about the hazard identification related-gaps present in current process safety regulations; which are the key limitations of the HAZOP study, and finally, which are the criteria to cover the research needs that have been found Annex I proposes the key tools (tables, figures and checklists "ready-to use'') to be used for conducting HAZOPs in continuous chemical processes. The information layout is structured according to the proposed HAZOP Management System. This information is intended to provide concise and structured documentation to be used as a reference book when conducting HAZOPs. Annex II is intended to overview the most relevant petroleum refining processes by highlighting key factors to take into account in the point of view of process safety and hazard identification, i.e. HAZOP. In this sense, key health and safety information of specific petroleum refining units is provided as a valuable guidance during brainstorming sessions. Annex III illustrates the complete set of data collected during the field work of the present research, and also analyzed in Chapter V of the manuscript. Additionally, it depicts a statistical summary of the key variables treated during the analysis. Finally, the Nomenclature, References, and Abbreviations & Acronyms used and cited during the manuscript have been listed. Additionally, a Glossary of key terms related to the Process Safety field has been illustrated.La present Tesis doctoral té com a objectiu estandarditzar l'aplicació d'una de les tècniques més utilitzades a la industria de procés per a la identificació de perills; l'anomenat HAZard & OPerability (HAZOP) study, específicament a processos complexes, com per exemple, unitat de refineria del petroli.El capítol I defineix el concepte de Seguretat de Processos, i progressivament analitza les diferents regulacions relacionades amb la temàtica, detallant específicament les mancances i buits d'informació que actualment hi ha presents a la primera etapa de la gestió del risc en industries de procés: la identificació de perills.El capítol II defineix el sistema de gestió del risc tecnològic que aplica a les industries de procés, i es justifica que l'etapa d'identificació de perills és el pilar de tot el sistema. Finalment, es mencionen algunes de les tècniques d'identificació més utilitzades, els anomenats Process Hazard Analysis (PHA), i es detallen les seves mancances i fortaleses, característiques que han acabat definint la temàtica específica de la Tesis. Concretament, es dóna èmfasis a la tècnica anomenada HAZard & OPerability (HAZOP) study, objecte principal de la recerca.El capítol III defineix l'abast, el propòsit i els objectius específics de la recerca. La intenció d'aquest capítol és donar resposta a les següents qüestions: el perquè de la recerca, quins elements han estat inclosos i què s'ha considerat per tal d'assolir les conclusions de la Tesis.El capítol IV descriu l'estat de l'art de la literatura relacionada amb el HAZOP. Aquesta revisió no només permet classificar les diferents línies de recerca relacionades amb el HAZOP, sinó que també permet assolir un coneixement profund de les diferents particularitats de la pròpia tècnica. El capítol finalitza amb un conjunt de mancances tant de gestió com tècniques, així com les necessitats de recerca que poden millorar l'organització i execució dels HAZOPs.El capítol V analitza la informació que ha estat recopilada durant la fase experimental de la tesis. Les dades procedeixen de la participació en cinc estudis HAZOP aplicats a la industria de refineria del petroli.En aquest sentit, el capítol V desenvolupa una anàlisi estadística d'aquestes dades per extreure'n conclusions quant a la preparació, organització i execució dels HAZOPs.El capítol VI estableix el conjunt d'accions que s'ha de tenir en compte per tal d'assegurar que un estudi HAZOP estigui ben organitzat i executat (la metodologia). Es defineix un Sistema de Gestió del HAZOP, i a partir de les seves fases, es desenvolupa una metodologia que pretén donar suport a tots aquells punts febles que han estat identificats en els capítols anteriors. Aquesta metodologia té la intenció de donar suport i guia no només als líders del HAZOP, sinó també a qualsevol part interessada en aquesta temàtica.El capítol VII descriu les conclusions de la recerca. En primera instància s'enumeren les mancances quant a la definició de criteris a seguir de diferents regulacions que apliquen a la Seguretat de Processos.Seguidament, es mencionen les limitacions de la pròpia tècnica HAZOP, i finalment, es descriuen quins són els criteris establerts per donar solució a totes aquestes febleses que han estat identificades.L'Annex I és una recopilació de diferents criteris que han estat desenvolupats al llarg de l'escrit en forma de taules i figures. Aquestes han estat ordenades cronològicament d'acord amb les diferents fases que defineixen el Sistema de Gestió HAZOP. L'annex I es pot utilitzar com a una referència concisa i pràctica, preparada i pensada per ésser utilitzada directament a camp, amb la intenció de donar suport a les parts interessades en liderar estudis HAZOP.L'annex II recopila informació relacionada amb aspectes clau de seguretat i medi ambient en diferents unitats de refineria. Aquest informació és un suport per tal de motivar el "brainstorming" dels diferents membres que conformen l'equip HAZOP.L'Annex III recopila les dades de les diferents variables que han estat considerades a la fase experimental de la recerca, juntament amb un conjunt de figures que mostren la seva estadística bàsica

Process hazard analysis, hazard identification and scenario definition: are the conventional tools sufficient, or should and can we do much better?

Hazard identification is the first and most crucial step in any risk assessment. Since the late 1960s it has been done in a systematic manner using hazard and operability studies (HAZOP) and failure mode and effect analysis (FMEA). In the area of process safety these methods have been successful in that they have gained global recognition. There still remain numerous and significant challenges when using these methodologies. These relate to the quality of human imagination in eliciting failure events and subsequent causal pathways, the breadth and depth of outcomes, application across operational modes, the repetitive nature of the methods and the substantial effort expended in performing this important step within risk management practice. The present article summarizes the attempts and actual successes that have been made over the last 30 years to deal with many of these challenges. It analyzes what should be done in the case of a full systems approach and describes promising developments in that direction. It shows two examples of how applying experience and historical data with Bayesian network, HAZOP and FMEA can help in addressing issues in operational risk management