Dissertations / Theses on the topic 'Network safety assessments'

<p>The objective of the research has been to investigate the possibility to transfer the requirements of a software safety standard into Bayesian belief networks (BBNs). The BBN methodology has mainly been developed and applied in the AI society, but more recently it has been proposed to apply it to the assessment of programmable systems. The relation to AI application is relevant in the sense that the method reflects the way of an assessor's thinking during the assessment process. Conceptually, software reliability is almost impossible to compute, since many of the aspects of the software which influence the reliability are of qualitative nature and not directly measurable, but have to be estimated e.g. by expert judgement.</p><p>The conclusion from the research presented in this thesis is that the use of Bayesian Belief Networks for combining disparate sources of information in the safety assessment of software based systems, combined with questionnaires, offers a systematic way to combine quantitative and qualitative evidences of relevance for the safety assessment of programmable systems, e.g. in a licensing process or in a PSA analysis.</p><p>The BBN is constructed in two levels. The higher level is based on the four qualities: quality of the producer, quality of the production, quality of the product, and quality of the analysis. The higher-level BBN is general, and independent of the standard, and is based on the research discussed in chapter 2. The lower-level BBNs reflect the recommendations of RTCA/DO-178B. Each top node of the lower-level BBNs is linked to intermediate nodes representing the 10 lifecycle stages identified in DO-178B. Each of these nodes are again linked to other intermediate nodes, representing the objectives of each lifecycle. The further proposed step is to identify a list of questions to each objective. In the described research these questions are based on the understanding of the text in the main part of DO-178B, and formulated so that the answer could be given by a "yes" or a "no".</p><p>For both the higher and lower level networks there is a need for further validation. This is demonstrated through the experimental investigation with the BBNs. However, a hypothesis is that a reallocation of objectives or questions only will give local (or partial) effects, and not changes in the overall assessment. A reason for this could be that there are a few "soft evidences" and dependencies connecting these evidences that are more sensitive than the other. So fare, there has, however, not been possible to find such evidences.</p><p>Although the BBNs and results are based upon a real application, this approach has not been applied to a real development or assessment. A first try could be to apply the approach for decision support in the approval of safety critical programmable systems. Another try could be to apply the approach as decision support early in the development of a system, in order to point on where to set in the effort and thus being able to reach specific objectives of the final product.</p><p>The establishment of the BBNs and prior probability distributions can be rather time consuming. However, the process of building up the network, e.g. by making questionnaires, and doing the elicitation of the prior distributions related to a standard (RTCA/DO-178B), and not to the actual system, implies that the network and questions are of a general nature, and can be reused in many applications. They can also be gradually improved based on experience. The experiences with modelling the requirements of the avionics standard RTCA/DO-178B as BBNs, point in the direction that this approach can be transferred to the modelling of other software standards built on the same basic framework, and which follow the same principles. This holds even though they may differ in the aspect they put special emphasis on.</p><p>Conceptually, estimation of the dependability of programmable systems is nearly impossible to compute, since many of the characteristics to be considered are of qualitative nature and not directly measurable, but have to be estimated. The most difficult activity in the experiment described was to perform the expert judgment, in particular in the assignment of values to the conditional probability distributions. Even if some of the project members can be considered as experts within their fields, it is highly recommendable to make use of some expert judgment tools or expert judgment expertise. Note also that knowledge within BBN and probabilistic theory is of great advantage in the construction of the networks and the assessment of the probability distributions, and also an advantage in the evaluation of the results from the computations.</p>

This dissertation thesis deals with application of probabilistic approach to assessment of earthing system safety in distribution networks, especially for cases with common earthing of high and low voltage side of distribution transformers HV/LV. In these cases, the increased potential during fault might be transferred from high voltage to low voltage network and thus the individuals from public can be exposed to increased risk. Thus, for these cases were in this thesis defined expectable touch scenarios together with the resulting risk imposed on individuals from the public. Based on the results it seems that adoption of probabilistic approach for these cases of earthing systems might be more suitable compared to the conventional deterministic worst case approach. In accordance to the aims of the thesis, a thorough analysis of currently adopted probabilistic approaches was carried out as well and it was pointed out to some new possible simplifications in the adopted probabilistic based methodologies. For example, it seems that appropriate modelling of human body resistance by the full lognormal distribution is not completely necessary and similar results can be obtained when only the resistance for 50 % of population together with c3 and c4 fibrillation curves are used. Much of the work was also devoted to the determination of possible uncertainty of calculated risk of evaluated earthing system, especially due to inappropriate modelling of earthing system. The appropriateness of different earthing system modelling methods together with other parameters on the value of calculated risk was investigated through conducting sensitivity analysis. Based on the analysis results it seems, that due to using more, or less simplified modelling method, a possible underrating in the resulting risk of about 40 % (about half an order/decade) is expectable. On the other hand, the change of parameters related directly to calculation of fibrillation probability seems to exhibit greater change in calculated risk by up to units of orders/decades.

A APS (Análise Probabilística de Segurança) de instalações industriais é assunto que evoluiu com a complexidade dos sistemas. A princípio, foram desenvolvidas ferramentas e técnicas com o propósito de analisar plantas já instaladas, possibilitando a identificação de fenômenos e mecanismos de falha desconhecidos até então. Com a evolução dos estudos dos acidentes, foram desenvolvidas técnicas aplicáveis às fases pré-operacionais com o propósito de diminuir os riscos na operação. Observa-se, portanto, um bom número de técnicas ideais para analisar projetos prontos ou em fase de conclusão. O mesmo não é observado para a fase de concepção. Apesar disto, cada vez mais especialistas na área de risco propõem que as considerações de segurança são mais eficazes quando ponderadas ao longo de toda a vida dos sistemas críticos. O estudo das APS realizadas no mundo em várias indústrias ajuda a entender o consenso sobre a contribuição potencial destas análises no desenvolvimento de novos sistemas. Para explorar este potencial, é essencial a elaboração de processos e modelos prospectivos que sejam simples, quantitativos, realistas, capazes de alimentar análises no estágio de projeto e que tragam resultados que possam ser interpretados pelos profissionais envolvidos no processo decisório. Estas considerações são extensíveis à ACH (Análise de Confiabilidade Humana), i.e., poucas são as ferramentas que ponderam aspectos operacionais, em especial o desempenho humano, na fase de projeto. A reconhecida contribuição do fator humano em acidentes envolvendo sistemas complexos - por vezes atribuída à falta de ferramentas adequadas para sua consideração na fase de projeto - evidencia ainda mais esta lacuna. Neste contexto, esta tese apresenta o desenvolvimento de uma metodologia e de uma técnica para a consideração precoce da confiabilidade humana na concepção de sistemas complexos, sendo que: 1) o desenvolvimento desta metodologia primou pela facilidade de entendimento de suas etapas e resultados, i.e., procurou-se a inteligibilidade para as pessoas envolvidas no projeto, sendo especialistas em ACH ou não, e; 2) a TECHR (Technique for Early Consideration of Human Reliability) foi concebida com o propósito de desenvolver um modelo prospectivo para o desempenho humano que possa ser explorado na fase de concepção de sistemas, e se baseia no aproveitamento da opinião de especialistas em relação a sistemas que operam ou operaram nos últimos anos para obter estimativas das probabilidades dos diversos tipos de erro humano que podem ocorrer durante a execução de uma ação específica. A metodologia proposta e a TECHR resultam em um procedimento simples e capaz de produzir modelos extremamente úteis na fase de projeto, representando uma contribuição original para o estado da arte da concepção de sistemas baseada em dados incertos.<br>PSA (Probabilistic Safety Assessment) is an industrial plant issue that has evolved with the complexity of systems. Initially, tools and techniques have been developed with the main purpose of analyzing operational plants, enabling the identification of phenomena and fault mechanisms hitherto not highlighted. With the evolution of accidents studies, some techniques applicable to pre-operational phases were developed in order to reduce the risks in operation. Therefore, a number of techniques adequate to analyze ready or near completion designs can be found. The same is not observed for the early design phase. Despite this, more and more experts in the risk assessment field suggest that safety considerations are most effective when assessed over the whole life of critical systems. Probabilistic safety analyses performed worldwide in various industries help us understand the consensus on the potential contribution of these analyses for developing new systems. To exploit this potential, it is essential to develop processes and prospective models that are simple, quantitative, realistic, able to feed analyses at the design stage and to bring results that can be interpreted by the professionals involved in the decision making process. These considerations are extended to HRA (Human Reliability Analysis), i.e., there are few tools that consider operational aspects, especially human performance, during the design phase. The recognized contribution of the human factor in accidents involving complex systems - sometimes attributed to the lack of suitable tools for its consideration in the design phase - further highlights this gap. In this context, this thesis presents a methodology and a technique developed for the early consideration of human reliability in complex systems design, and: 1) the development of this methodology has prioritized the easy understanding of its steps and results, i.e., its intelligibility for people involved in the system design has been sought, with expertise in HRA or not, and; 2) the technique for early consideration of human reliability (TECHR) was designed for developing a prospective human performance model that can be exploited in the system design phase, and is based on the use of expert opinion in relation to systems that operate or have operated in recent years to obtain estimates of the probabilities of the various types of human error that may occur during the performance of a specific action. The proposed methodology and technique result in a simple procedure capable of producing useful models for the design phase, representing an original contribution to the state of the art of systems conception under uncertainty.

La sicurezza dei sistemi infrastrutturali è di fondamentale importanza per la società. Malfunzionamenti, danni o crolli possono avere notevoli impatti socioeconomici e ripercussioni sulla sicurezza pubblica. Secondo l’approccio classico, l'analisi della vulnerabilità dei ponti viene condotta attraverso l'adozione di curve di fragilità, che esprimono la probabilità di superamento di un certo livello di prestazione condizionata ad un determinato livello di intensità della fonte di pericolo. Tuttavia, è pratica comune utilizzare le curve di fragilità per fornire solo una panoramica globale della vulnerabilità del ponte, con scarsa attenzione all'estensione del danno o all'evoluzione dei diversi meccanismi che possono verificarsi all'interno della struttura. Infatti, vale la pena notare che i ponti possono mostrare diversi meccanismi di danno; in base a quali e quanti componenti strutturali sono coinvolti, essi contribuiscono in modo diverso alla fragilità complessiva del sistema e potenzialmente portano a diversi scenari post-disastro. Considerando quindi che ad oggi non è ancora disponibile un framework probabilistico completo e robusto per la valutazione del rischio, la presente Tesi fornisce alcuni contributi originali per un arricchimento dello stato dell’arte nel campo della sicurezza dei sistemi infrastrutturali. I principali obiettivi perseguiti nella Tesi sono i seguenti: sviluppo di un approccio innovativo per la descrizione e quantificazione probabilistica del danno sismico atteso sui ponti esistenti; analisi degli effetti dell’interazione terreno-struttura attraverso la proposta di formulazioni semplificate per la stima del comportamento di fondazioni su pali (comuni per le strutture da ponte) e di facile implementazione per un’ analisi affidabile della fragilità e del rischio; proposta di un framework omnicomprensivo per la valutazione del rischio e la quantificazione delle conseguenze di eventi sismici in termini economici, tenendo conto di aspetti quali l’interazione terreno-struttura, il degrado e gli interventi manutentivi; analisi degli effetti delle incertezze che interessano il sistema pali-terreno per la caratterizzazione probabilistica delle funzioni di impedenza e dei fattori di risposta cinematica di fondazioni profonde in sottosuoli omogenei. Il sistema trasportistico italiano è stato scelto per le applicazioni della presente Tesi, in quanto emblematico per l'elevata vulnerabilità e le importanti criticità presentate dalle reti stradali esistenti. Si considerano due diverse tipologie di ponti: catena cinematica in calcestruzzo armato e sezione composta acciaio-calcestruzzo. Tali tipologie risultano rappresentative della maggior parte dei ponti e viadotti presenti sul territorio italiano, ed esempi si possono trovare anche nel panorama internazionale. La scelta di casi studio significativi consente di mostrare le potenzialità delle metodologie proposte e la rilevanza del problema di interazione terreno-struttura nella valutazione della vulnerabilità, nonché di caratterizzare la vulnerabilità delle infrastrutture italiane con un livello di dettaglio più elevato, includendo fenomeni di degrado e interazione, il tutto all’interno di un approccio probabilistico. Inoltre, la scelta delle configurazioni strutturali risulta adatta per la caratterizzazione di uno scenario regionale, come quello marchigiano. I risultati dello studio di fragilità vengono quindi applicati a livello di rete stradale per la quantificazione dell'impatto degli scenari post-terremoto in termini economici. Sebbene presentate per il problema sismico e nel contesto italiano, le metodologie proposte sono abbastanza flessibili da essere facilmente applicate ad ulteriori scenari infrastrutturali (ed altre tipologie di ponti) e a diverse fonti di pericolo (frane, alluvioni, ecc.).<br>The safety of infrastructural systems is of paramount importance since high socio-economic impacts on the society would be expected in case of disruptions or people life could be seriously endangered in case of severe damages or collapses. The analysis of the vulnerability of bridges is classically carried out through the adoption of fragility curves, which express the probability of exceedance of a certain performance level conditional to a certain level of hazard intensity. However, it is common practice to use fragility curves to only provide a global overview of the bridge vulnerability, with scarce attention to the damage extension or the evolution of different failure mechanisms that may potentially verify within the structure. Indeed, it is worth noting that bridges may show different damage mechanisms, occurring in one or multiple structural components, that differently contribute to the overall fragility of the system and potentially lead to different post-disaster scenarios. In light of this drawback and considering also that an optimal, comprehensive and robust probabilistic framework for the risk assessment is not yet available, the present Thesis aims to provide some insights and original contributions for a state-of-the-art enrichment in the field of the safety of infrastructural systems. Advancements are indeed made on the following main subjects: fragility curves, with an innovative approach for a proper estimation of the bridge vulnerability, based on both a quantitative and qualitative assessment of failure mechanisms that may occur during a seismic event; analysis of Soil-Structure Interaction (SSI) effects through simple formulas estimating the behaviour of pile foundations (a common choice in case of bridge structures) and easy to be implemented for a reliable fragility and risk analysis; proposal of a holistic framework for the risk assessment and the quantification of consequences of a hazardous event in monetary terms, taking into account aspects such as SSI, degradation and maintenance; analysis of the effects of uncertainties affecting the combined pile-soil system for the probabilistic characterization of impedance functions and kinematic response factors of deep foundations in homogeneous soils. The Italian transport system is chosen as scenario for the applications of the present Thesis, since it is particularly emblematic due to the high vulnerability and the important critical issues presented by the existing road networks. Two different bridge typologies are considered: Reinforced Concrete Link Slab bridges and Steel-Concrete Composite bridges. Being very widespread, such typologies result representative of most of the bridges and viaducts present over the Italian territory, and examples can also be found in the international panorama. The choice of significative case studies allows to prove the potentialities of the proposed fragility estimation methodology and the relevance of the SSI problem in the bridge vulnerability assessment as well as to characterise the vulnerability of the Italian infrastructures with a higher level of detail, including degradation and SSI phenomena. Moreover, the choice of structural configurations is suitable for the characterization of a regional scenario, such as the one of Marche region. Then, fragility results are applied at road network level for the quantification of the impact of post-earthquake scenarios in economic terms throughout the proposed probabilistic framework. Finally, as part of the framework, a novel probabilistic characterization of the response of deep foundations in homogeneous soil is provided to evaluate effects of uncertainties in the embedded system. Although presented for the seismic problem and within the Italian context, the proposed methodologies are flexible enough to be easily extended to further applications involving other road network scenarios (and bridge typologies) and different natural hazards.

Sistemas de transporte marítimo são essenciais para o Comércio Global, em especial, navios-tanques e seus centros de carga e descarga de produtos líquidos ou gasosos inflamáveis; portanto, é crucial entender como estes sistemas podem falhar, para que seus operadores sejam capazes de manter a sua capacidade de operação. É preciso que cada e toda análise quantitativa de risco compreenda algumas das atividades básicas que devem ser desenvolvidas, para permitir a quantificação dos riscos envolvidos e associados, na operação do sistema ou do processo. Basicamente, devem ser calculadas as probabilidades de ocorrência dos eventos indesejados identificados, bem como a magnitude de suas consequências. O objetivo deste trabalho é aferir se a técnica denominada Rede Bayesiana RB é a mais adequada, comparando-a com as técnicas de árvores de falhas e de eventos, para realizar uma Análise de Risco da operação ou processo de descarga de líquidos inflamáveis, como etanol anidro e/ou produtos petrolíferos, de um naviotanque para um terminal portuário específico Terminal de Granéis Líquidos TGL com foco na interface entre dois sistemas: o navio e o porto, observado o elemento humano, ou seja, o erro humano (Análise da Confiabilidade Humana). Além disso, será realizado um estudo das consequências do vazamento de um líquido inflamável transportado pelo navio, olhando para o pior cenário, a partir da ruptura da tubulação ou do compartimento do navio-tanque. A análise tem por base as recomendações da Organização Internacional Marítima OIM (em inglês, IMO). A OIM tem adotado a Avaliação Formal da Segurança AFS (em inglês, Formal Safety Assessment FSA), como seu modo oficial de receber as sugestões de seus membros para criar ou modificar qualquer regulamentação correlacionada. Este processo é composto de cinco passos que a OIM descreve na guia AFS (IMO, 2002). Este trabalho irá mostrar todas as etapas, mas irá focar, com especial atenção, a segunda etapa Risk Assessment, porque será aplicada ao caso sob análise, envolvendo o comportamento humano. Existem muitas técnicas e muito trabalho envolvido na estimação das probabilidades dos eventos. O mesmo ocorre para a avaliação de suas consequências. Uma vez definida a quantidade total de vazamento, um software poderá ser usado para calcular as consequências. O mesmo será feito para na Análise de Risco, utilizando RB, e, neste ponto, o trabalho apresenta uma nova contribuição.<br>Maritime transportation systems are essential for World Trade, in special, Tankers ships and yours loading and unloading facilities; therefore, it is crucial to understand how these systems may fail, to be able to maintain their capacity. It need that each and every quantitative risk assessment comprises some basic activities that have to be developed to allow the quantification of the risks involved in the operation of a system or process. Basically, it must be estimated the likelihood of the identified undesired events as well as the magnitude of their consequences. The objective of this study is to assess if the technique called Bayesian Networks BN is the best suited, with respect to the Fault Tree Analysis FTA and the Event Tree Analysis ETA, to perform an Risk Analysis of the operation or process of unloading of flammable bulk liquids, such as anhydrous ethanol and/or oil products, from a Tanker to a port terminal specified the Bulk Liquid Terminal BLT, focusing on the interface between the two systems: ship and port with the inclusion of the human factor, i.e., human error: Human Reliability Analysis HRA. Furthermore, a consequence analysis of a specific liquid bulk leakage will be performed, looking at the worst scenario case, from the rupture of a pipeline or tank from a Tanker. The analysis came from based on the recommendations of the International Maritime Organization IMO. The IMO has adopted the FSA (Formal Safety Assessment) as its official way of receiving suggestions of its members to create or modify any regulation correlated. It is a process composed by five steps that IMO has described in its Guidelines for FSA (IMO, 2002). This thesis will to show all steps, but will look carefully to step two (Risk Assessment) because it will be applied in the example situation, involving human behavior (HRA). There are many techniques and much work involved in the estimation of the likelihood of the events. The same occurs for the evaluation of their consequences. Once defined the total leaked quantity, software will be used to calculate the consequences. The same will be done to Risk Analysis, using BN, and at this point, the work is a new contribution.

De nos jours, nous attendons des systèmes de systèmes d'être plus que simplement fonctionnel, mais aussi fiable, de préserver leurs performances, de mener les actions requises et, surtout, d'anticiper d'éventuelles défaillances. La résilience fait partie des nombreuses approches d'évaluation de la fiabilité. Elle est directement liée aux conséquences de perturbations et incertitudes. Il s'agit des conséquences en cas de perturbations et des incertitudes associées. La résilience est définie comme la capacité des systèmes à résister à une perturbation majeure selon paramètres de dégradation et à récupérer dans un délai, des coûts et des risques acceptables. Dans cette thèse, deux approches complémentaires sont proposées pour tenter d'analyser la résilience structurelle des systèmes de systèmes. La première est liée à l'extensibilité qui est une caractéristique des systèmes de systèmes puisqu'ils sont en continuelle évolution. L'un des principaux objectifs est d'évaluer la résilience structurelle en tenant compte de l'aspect dynamique et moyennant une évaluation de l'interopérabilité. D'autre part, un examen de la structure d'un système de systèmes et des flux internes représente la deuxième approche. Cela conduit à une évaluation de la résilience structurelle grâce à un ensemble d'indicateurs. Les deux approches proposées sont déterministes et peuvent être utilisées pour évaluer l'état courant de la structure du système de systèmes ou pour anticiper sa résilience dans des scénarios futurs. Un démonstrateur a été développé pour l'évaluation de la résilience structurelle. Dans la considération de territoires, il a servi à l'évaluation d'infrastructures industrielles réelles selon une approche systèmes de systèmes<br>Nowadays, we expect of SoS (systems-of-systems) more than just to be functional, but also to be reliable, to preserve their performance, to complete the required fonctions and rnost importantly to anticipate potential defects. The relationship with resilience is among the numerous perspectives tackling reliability in the context of SoS. It is about the consequences in case of disturbances and associated uncertainties. Resilience is defined as the ability of systems to withstand a major disruption within acceptable degradation parameters and to recover within an acceptable time, composite costs and risks. In this thesis, two complementary approaches are proposed in an attempt to analyze SoS structural resilience. First is related to extensibility which is a specific characteristic of SoS as they are in continuous evolvement and change. A major focus is to evaluate SoS structural resilience with regards to its dynamic aspect and through interoperability assessment. On the other hand, a consideration of the SoS structure and inner workflow pathways represents the second approach. This perspective leads to structural resilience assessment through a set of indicators. Both proposed approaches are deterministic and can be used to evaluate the current state of SoS structure or to anticipate its resilience in future scenarios. Futhermore, a prototype is designed in order to process the structural resilience assessment. Considering spatial objects, it has been used to conduct experiments on real-based industrial infrastructures approached as SoS

In der Arbeit wird eine Methodik einer zusammenhängenden Analyse und modellhaften Beschreibung der Verkehrssicherheit in städtischen Hauptstraßennetzen am Beispiel der Stadt Dresden entwickelt. Die dabei gewonnenen Modelle dienen der Abschätzung von Erwartungswerten von Unfallhäufigkeiten mit und ohne Personenschaden unter Berücksichtigung der Verkehrsbeteiligungsart. Die Grundlage bilden multivariate Regressionsmodelle auf Basis verallgemeinerter linearer Modelle (GLM). Die Verwendung verallgemeinerter Regressionsmodelle erlaubt eine Berücksichtigung von Verteilungen, die besser geeignet sind, den Unfallentstehungsprozess wiederzugeben, als die häufig verwendete Normalverteilung. Im konkreten Fall werden hierzu die Poisson-Verteilung sowie die negative Binomialverteilung verwendet. Um Effekte im Hauptverkehrsstraßennetz möglichst trennscharf abbilden zu können, werden vier grundsätzliche Netzelemente differenziert und das Netz entsprechend zerlegt. Unterschieden werden neben Streckenabschnitten und Hauptverkehrsknotenpunkten auch Annäherungsbereiche und Anschlussknotenpunkte. Die Kollektive der Knotenpunkte werden ferner in signalisierte und nicht-signalisierte unterteilt. Es werden zunächst Modelle unterschiedlicher Unfallkollektive getrennt für alle Kollektive der vier Netzelemente berechnet. Anschließend werden verschiedene Vorgehensweisen für eine Zusammenfassung zu Netzmodellen entwickelt. Neben der Verwendung verkehrstechnischer und infrastruktureller Größen als erklärende Variable werden in der Arbeit auch Kenngrößen zur Beschreibung der Umfeldnutzung ermittelt und im Rahmen der Regression einbezogen. Die Quantifizierung der Umfeldnutzung erfolgt mit Hilfe von Korrelations-, Kontingenz- und von Hauptkomponentenanalysen (PCA). Im Ergebnis werden Modelle präsentiert, die eine multivariate Quantifizierung erwarteter Unfallhäufigkeiten in Hauptverkehrsstraßennetzen erlauben. Die vorgestellte Methodik bildet eine mögliche Grundlage für eine differenzierte Sicherheitsbewertung verkehrsplanerischer Variantenabschätzungen<br>A methodology is developed in order to predict the number of accidents within an urban main road network. The analysis was carried out by surveying the road network of Dresden. The resulting models allow the calculation of individual expectancy values for accidents with and without injury involving different traffic modes. The statistical modelling process is based on generalized linear models (GLM). These were chosen due to their ability to take into account certain non-normal distributions. In the specific case of accident counts, both the Poisson distribution and the negative binomial distribution are more suitable for reproducing the origination process than the normal distribution. Thus they were chosen as underlying distributions for the subsequent regressions. In order to differentiate overlaying influences, the main road network is separated into four basic elements: major intersections, road sections, minor intersections and approaches. Furthermore the major and minor intersections are additionally subdivided into signalised and non-signalised intersections. Separate models are calculated for different accident collectives for the various types of elements. Afterwards several methodologies for calculating aggregated network models are developed and analysed. Apart from traffic-related and infrastructural attributes, environmental parameters are derived taking into account the adjacent building structure as well as the surrounding land-use, and incorporated as explanatory variables within the regression. The environmental variables are derived from statistical analyses including correlation matrices, contingency tables and principal components analyses (PCA). As a result, a set of models is introduced which allows a multivariate calculation of expected accident counts for urban main road networks. The methodology developed can serve as a basis for a differentiated safety assessment of varying scenarios within a traffic planning process

La probabilité et la causalité sont deux outils indispensables à la prise en compte des situations de risque social. Lesrelations causales sont le fondement des représentations à partir desquelles on peut évaluer le risque et concevoirdes actions de prévention, de mitigation ou d'indemnisation. La probabilité permet de quantifier cette évaluation et de calibrer ces actions. Dès lors, il semble non seulement naturel, mais nécessaire d'expliciter la place de la causalité et de la probabilité dans la définition d'un problème de décision en situation de risque social. C'est l'objet de cette thèse.Un tour d'horizon de la terminologie du risque et des logiques d'intervention publique dans différentes catégories de risque social nous permettent de mieux comprendre la notion et les problèmes soulevés par sa représentation. Nous approfondissons notre analyse dans le cas de la sûreté nucléaire, en examinant en détail les méthodes et doctrinesdéveloppées dans ce domaine et leur évolution au cours du temps, ce qui nous conduit à formuler différentesobservations au sujet des évaluations de risque et de sûreté.En généralisant la notion d'intervention dans les réseaux bayésiens, nous développons une forme de réseau bayésien causal qui répond à nos besoins. Nous parvenons, par son biais, à une définition du risque qui semble pertinente pour un grand nombre de situations. Nous proposons ensuite des applications simples de ce modèle à certains aspects de l'accident de Fukushima et d'autres problèmes de sûreté nucléaire. Outre certains enseignements spécifiques, ceci nous amène à souligner la nécessité d'une démarche systématique d'identification des incertitudes dans ce domaine.Étendu en direction de la théorie de la décision, notre outil débouche naturellement sur un modèle de décision dynamique dans lequel les actes causent les conséquences et sont causalement liés entre eux. Il apporte en outre une interprétation causale au cadre conceptuel de Savage et permet d'en résoudre certains paradoxes et clarifier certains aspects. Il conduit enfin à envisager la question de l'ambigüité comme incertitude concernant la structure causale d'un problème de décision, ce qui correspond à une vision courante du principe de précaution.

The research area of this work is online threat awareness within an information security context. The research was carried out on secondary school learners at boarding schools in Grahamstown. The participating learners were in Grades 8 to 12. The goals of the research included determining the actual levels of awareness, the difference between these and self-perceived levels of the participants, the assessment of risk in terms of online behaviour, and the determination of any gender differences in the answers provided by the respondents. A review of relevant literature and similar studies was carried out, and data was collected from the participating schools via an online questionnaire. This data was analysed and discussed within the frameworks of awareness of threats, online privacy social media, sexting, cyberbullying and password habits. The concepts of information security and online privacy are present throughout these discussion chapters, providing the themes for linking the discussion points together. The results of this research show that the respondents have a high level of risk. This is due to the gaps identified in actual awareness and perception, as well as the exhibition of online behaviour patterns that are considered high risk. A strong need for the construction and adoption of threat awareness programmes by these and other schools is identified, as are areas of particular need for inclusion in such programmes. Some gender differences are present, but not to the extent that, there is as significant difference between male and female respondents in terms of overall awareness, knowledge and behaviour.

This work aimed at the definition of a Network-wide Road Safety Assessment procedure for two-lane two-way rural roads, namely Human Factors Evaluation procedure, which accounts for the influence of Human Factors in accidents triggering factors. The purpose of such a procedure is to provide an instrument to evaluate the risk of accidents occurrence because of wrong perceptions and expectations caused by the road. This often translates in operational errors, which may become driving errors that finally results in accidents, if uncorrected. The need of a Network-wide Road Safety Assessment procedure which accounts for Human Factors, together with an overview of considered methodologies, is discussed with a focus on Road Safety Inspection procedures. Indeed, visual site inspections and surveys allow to identify specific critical issue that may otherwise be missed while using big data analysis. Moreover, it has been decided that the Human Factors Evaluation procedure must follows the requirements of the updated 2008/96/EU directive (European Parliament and the Council, 2019). This will let it be a usable instrument for road agencies.

博士<br>國立臺灣科技大學<br>營建工程系<br>103<br>Fall or tremble is the most common accident on the steel construction (SC) sites. To reduce the fall risk, current site safety management relies mostly on checklist evaluation. Nevertheless, the classical approaches ineffectively address dependencies among safety factors at different levels, which fail to provide early warning to prevent the occupational accidents. To overcome the limitations of the traditional approaches, this paper discusses the development of a safety risk assessment model for the SC projects by establishing the Bayesian Networks (BN) based on Fault Tree (FT) transformation. Through the analysis and comparison, it is found that the results of BN analysis are consistent with actual safety records; and further, It can be observed that the ranks of posterior probabilities from the BN model are also consistent with the actual accident occurred at each project site. The model provides accurately site safety management ability by calculating the probabilities of the safety risks and further analyzing accident causes through their relationships in BN. In practice, based upon the analysis of the accident risks and significant safety factors, proper preventive safety management strategies can be established to reduce the occurrences of these accidents on the SC sites.

碩士<br>國立高雄第一科技大學<br>營建工程研究所<br>102<br>The construction industry is a sector with a high rate of occupational accidents. Although management systems and policies for maintaining labor safety have improved significantly, workplace accidents still happen from time to time. Hence, examination of safety management should be focused on assessment of on-site safety climate. Through a review of the literature, this research first proposed 16 factors influencing safety climate that are categorized into three aspects as well as the relations among the factors, which were used for developing an assessment model using the analytic network process method. Next, three experts representing the safety inspection office, project owners, and contractors separately were invited to assess the factors in a questionnaire survey. Their assessments were processed via the model for producing the importance weights of the factors. The results show that the three most important factors are: “supervisors can execute their safety management jobs well”, “supervisors communicate with workers and notify them to follow safety regulations”, and “workers demand their own safety”. The research can be used as a reference by construction practitioners in enhancing workplace safety climate in order to improve safety management.

Yes<br>System safety, reliability and risk analysis are important tasks that are performed throughout the system lifecycle to ensure the dependability of safety-critical systems. Probabilistic risk assessment (PRA) approaches are comprehensive, structured and logical methods widely used for this purpose. PRA approaches include, but not limited to, Fault Tree Analysis (FTA), Failure Mode and Effects Analysis (FMEA), and Event Tree Analysis (ETA). Growing complexity of modern systems and their capability of behaving dynamically make it challenging for classical PRA techniques to analyse such systems accurately. For a comprehensive and accurate analysis of complex systems, different characteristics such as functional dependencies among components, temporal behaviour of systems, multiple failure modes/states for components/systems, and uncertainty in system behaviour and failure data are needed to be considered. Unfortunately, classical approaches are not capable of accounting for these aspects. Bayesian networks (BNs) have gained popularity in risk assessment applications due to their flexible structure and capability of incorporating most of the above mentioned aspects during analysis. Furthermore, BNs have the ability to perform diagnostic analysis. Petri Nets are another formal graphical and mathematical tool capable of modelling and analysing dynamic behaviour of systems. They are also increasingly used for system safety, reliability and risk evaluation. This paper presents a review of the applications of Bayesian networks and Petri nets in system safety, reliability and risk assessments. The review highlights the potential usefulness of the BN and PN based approaches over other classical approaches, and relative strengths and weaknesses in different practical application scenarios.<br>This work was funded by the DEIS H2020 project (Grant Agreement 732242).

Marine structures are widely used in the oil and gas industry, marine transportation and exploration areas and renewable energy applications. Understanding dynamic behaviour of these structures is necessary to allow their evaluation under the effects of environmental loads such as wave, wind and currents. However, the sea environment is very complex, and the response of these structures is affected by considerable uncertainties that should be predicted accurately. Due to the stochastic trend of the sea environment, different types of failure are expected to be observed during the life time of a structure. Consequently, failure of a marine structure may pose various major risks in terms of environmental pollution and loss of assets for companies. Therefore, a great deal of research on the improvement of marine safety is carried out to mitigate the associated risks. It is also necessary to take into account the process of risk escalation in a more realistic way than relying only on either precursor data or expert judgments. This requires a comprehensive approach when it comes to accident modelling and risk analysis of marine structures. This PhD research is focused on developing advanced probabilistic models for representing dynamic risk assessment of marine structures in a harsh environment. The developed frameworks will assist industries to model marine accidents and improve the reliability of marine structures to minimize the risk of failure. The main content of the thesis investigates a developing practical framework for incorporating the reliability of floating offshore structures while considering hydrodynamic performance of the structure as real monitoring data based on modelling the physics of the failure. In order to evaluate response of the marine structure in harsh environment, the storm condition was developed to help researchers to generate necessary data for conducting reliability assessment of the system. The outcome of this achievement led to analysis performance of either the marine structure or the human on board for future risk analysis and decision-making. As a result, the developed methodologies include time-dependent reliability strategies that can model long-term failure scenarios in marine environment which is able to consider marine accident and human failure in respect to the time of operations. Overall, this thesis provides a comprehensive probability model for evaluating the dynamic risk assessment of marine structures under different operational conditions. The outcome of this research will assist industries to improve the reliability of the structures in the design phase or in their operating conditions to mitigate the associated risks to assets, human life and the environment.

The research aims to build a behavioral models of electrical power systems through the use of Petri nets, covering both traditional reliability analysis (quantitative measurement) and behavior analysis (qualitative measurement) for the detection of topology defects. The development models has allowed to study the operating sequence of the electrical system, where the evolution of the system to be monitored is compared with its ideal evolution. The modelling criterion is then validated by the implementation in two case studies. In the first case, the whole approach is applied to the identification of a complex electrical plant supplying a critical structure such as a hospital. Petri nets are capable of modeling and simulating all the functional dependencies between the system elements and also the correct fault repair behavior for the tested power system. This allows the system to be analyzed for properties such as tolerance of failures and isolation of the safety hazards to determine which functions are most critical and moreover need to be enhanced in order to mitigate the accidental risks. In the second case study, a new approach for LOTO procedures using Petri nets is introduced. The suggested methodology supports mechanical development of the operational procedures that can assists the operator especially for not automatic operations. It proposes some simple rules, a graphical representation of electrical status and an algebraic model to allow an autocheck of the interlocking procedure.

Dissertação de mestrado em Engenharia Urbana<br>De acordo com a Organização Mundial da Saúde (OMS), a forma mais eficaz de garantir uma água segura pode concretizar-se através da implementação de planos de segurança da água (PSA) que contemplam a descrição detalhada do sistema de abastecimento, a identificação de perigos, a avaliação dos riscos e o estabelecimento de medidas necessárias para os controlar, abarcando todas as etapas do sistema, desde a bacia de captação até à torneira do consumidor. Uma das grandes dificuldades na aplicação deste conceito situa-se nas redes prediais urbanas, uma vez que a propriedade privada limita a responsabilidade das entidades gestoras (EG) dos sistemas públicos em assegurar a qualidade da água nestas redes. O presente trabalho de investigação teve como objectivo avaliar a qualidade da água em reservatórios de serviço prediais e em torneiras de consumidores. Para tal, estabeleceu-se uma metodologia específica para contemplar este aspecto particular da rede de abastecimento de água, aplicando-a ao caso de estudo da cidade da Póvoa de Varzim, constituindo-se num contributo para a implantação de um PSA nesta cidade portuguesa. O estudo demonstrou que, apesar de se ter constatado não existir qualquer plano de inspecção, limpeza e higienização dos reservatórios, bem como de controlo da qualidade da água armazenada, os resultados obtidos se encontravam dentro dos parâmetros legais, apresentando valores muito próximos dos obtidos no âmbito do PCQA. Não se pode afirmar, no entanto, que a segurança da água esteja completamente garantida, configurando-se pertinente a análise a outros parâmetros, não contemplados no presente estudo, como trihalometanos e hidrocarbonetos, bem como a outros que possam demonstrar os efeitos dos usos indevidos dos espaços de acomodação dos reservatórios prediais bem como da sua manutenção. Espera-se que os resultados obtidos possam vir a constituir uma base para a melhoria dos processos de monitorização da qualidade da água, bem como para a apresentação de propostas de normas municipais que atendam a uma adequada gestão dos riscos no domínio particular das redes prediais de abastecimento.<br>According to the World Health Organization, the most effective way to ensure good safe drinking water can be achieved through the implementation of water safety plans which is a comprehensive risk assessment and risk management approach that encompasses all steps in a drinking-water supply chain, from catchment to consumer. Notwithstanding that the water supplied by the water utility is safe to drink, the water quality can be affected in the building plumbing systems due to various factors, such as not properly cleaned water tanks, or contaminated water due to stagnation or use of unappropriated plumbing materials. Considering these aspects, a research work was developed in order to evaluate the quality of water in building tanks and internal distribution systems. A case study was applied in the city of Póvoa de Varzim, constituting a contribution to the implementation of a water safety plan (WSP) in this Portuguese city. The study showed that, although there was any plan for inspection, cleaning and sanitation of the water in building tanks, as well as for the control of the quality of the stored water, the results obtained were within the legal parameters. It cannot be said, however, that water safety is fully guaranteed. It is relevant to analyze other parameters not considered in the present study, such as trihalomethanes and hydrocarbons, as well as others that can demonstrate the effects of improper use of the accommodation spaces of the water tanks, as well as their maintenance. The results obtained should provide a basis to improve water quality monitoring processes as well as for the presentation of municipal norms that provide adequate risk management in the particular domain of the water supply systems.

In der Arbeit wird eine Methodik einer zusammenhängenden Analyse und modellhaften Beschreibung der Verkehrssicherheit in städtischen Hauptstraßennetzen am Beispiel der Stadt Dresden entwickelt. Die dabei gewonnenen Modelle dienen der Abschätzung von Erwartungswerten von Unfallhäufigkeiten mit und ohne Personenschaden unter Berücksichtigung der Verkehrsbeteiligungsart. Die Grundlage bilden multivariate Regressionsmodelle auf Basis verallgemeinerter linearer Modelle (GLM). Die Verwendung verallgemeinerter Regressionsmodelle erlaubt eine Berücksichtigung von Verteilungen, die besser geeignet sind, den Unfallentstehungsprozess wiederzugeben, als die häufig verwendete Normalverteilung. Im konkreten Fall werden hierzu die Poisson-Verteilung sowie die negative Binomialverteilung verwendet. Um Effekte im Hauptverkehrsstraßennetz möglichst trennscharf abbilden zu können, werden vier grundsätzliche Netzelemente differenziert und das Netz entsprechend zerlegt. Unterschieden werden neben Streckenabschnitten und Hauptverkehrsknotenpunkten auch Annäherungsbereiche und Anschlussknotenpunkte. Die Kollektive der Knotenpunkte werden ferner in signalisierte und nicht-signalisierte unterteilt. Es werden zunächst Modelle unterschiedlicher Unfallkollektive getrennt für alle Kollektive der vier Netzelemente berechnet. Anschließend werden verschiedene Vorgehensweisen für eine Zusammenfassung zu Netzmodellen entwickelt. Neben der Verwendung verkehrstechnischer und infrastruktureller Größen als erklärende Variable werden in der Arbeit auch Kenngrößen zur Beschreibung der Umfeldnutzung ermittelt und im Rahmen der Regression einbezogen. Die Quantifizierung der Umfeldnutzung erfolgt mit Hilfe von Korrelations-, Kontingenz- und von Hauptkomponentenanalysen (PCA). Im Ergebnis werden Modelle präsentiert, die eine multivariate Quantifizierung erwarteter Unfallhäufigkeiten in Hauptverkehrsstraßennetzen erlauben. Die vorgestellte Methodik bildet eine mögliche Grundlage für eine differenzierte Sicherheitsbewertung verkehrsplanerischer Variantenabschätzungen.<br>A methodology is developed in order to predict the number of accidents within an urban main road network. The analysis was carried out by surveying the road network of Dresden. The resulting models allow the calculation of individual expectancy values for accidents with and without injury involving different traffic modes. The statistical modelling process is based on generalized linear models (GLM). These were chosen due to their ability to take into account certain non-normal distributions. In the specific case of accident counts, both the Poisson distribution and the negative binomial distribution are more suitable for reproducing the origination process than the normal distribution. Thus they were chosen as underlying distributions for the subsequent regressions. In order to differentiate overlaying influences, the main road network is separated into four basic elements: major intersections, road sections, minor intersections and approaches. Furthermore the major and minor intersections are additionally subdivided into signalised and non-signalised intersections. Separate models are calculated for different accident collectives for the various types of elements. Afterwards several methodologies for calculating aggregated network models are developed and analysed. Apart from traffic-related and infrastructural attributes, environmental parameters are derived taking into account the adjacent building structure as well as the surrounding land-use, and incorporated as explanatory variables within the regression. The environmental variables are derived from statistical analyses including correlation matrices, contingency tables and principal components analyses (PCA). As a result, a set of models is introduced which allows a multivariate calculation of expected accident counts for urban main road networks. The methodology developed can serve as a basis for a differentiated safety assessment of varying scenarios within a traffic planning process.