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Yes / Fault tree analysis is a widely used method of risk assessment in process industries. However, the classical fault tree approach has its own limitations such as the inability to deal with uncertain failure data and to consider statistical dependence among the failure events. In this paper, we propose a comprehensive framework for the risk assessment in process industries under the conditions of uncertainty and statistical dependency of events. The proposed approach makes the use of expert knowledge and fuzzy set theory for handling the uncertainty in the failure data and employs the Bayesian network modeling for capturing dependency among the events and for a robust probabilistic reasoning in the conditions of uncertainty. The effectiveness of the approach was demonstrated by performing risk assessment in an ethylene transportation line unit in an ethylene oxide (EO) production plant.

Pathogen contamination, typically quantified by elevated levels of fecal indicator bacteria (FIB), remains the leading cause of surface water-quality impairments in the United States. Continuous watershed-scale models are typically employed to facilitate Total Maximum Daily Load (TMDL) restoration efforts. Due to limited understanding of microbial fate and transport, predictions of FIB concentrations are associated with considerable uncertainty relative to other water-quality contaminants. By focusing on a data-rich instrumented urban watershed, this study aims to improve understanding of microbial fate and transport processes. Weekly FIB concentrations in both the water column and streambed sediments were monitored for one year, and statistical correlations with hydrometeorological and physicochemical variables were identified. An intensive six storm intra-sampling campaign quantified and contrasted loading trends of both traditional regulatory FIB and emerging Microbial Source Tracking (MST) markers. Together, these intensive monitoring efforts facilitated evaluation of the impacts of bacteria-sediment interactions on the predictions of daily FIB concentrations in Hydrological Simulation Program-Fortran (HSPF) over multiple years. While superior overall model performance was demonstrated as compared to earlier efforts, the inclusion of bacteria-sediment interactions did not improve performance. Large wet-weather microbial loading appears to have dwarfed the effects of FIB release and resuspension from sediment. Although wet-weather loading is generally considered as a primary source of waterbody microbial loads, dry-weather periods are more directly associated with public health concern, which may be a more suitable area for future model-refinement efforts. Site evaluation is critical to determine whether the added model complexity and effort associated with partitioning phases of FIB can be sufficiently offset by gains in predictive capacity. Finally, a stochastic framework to translate simulated daily FIB concentrations into estimates of human illness risks is presented that can be can be readily integrated into existing TMDLs. As even small concentrations of FIB from human sources are associated with great risk, and monitoring efforts indicated moderate/high levels of human-associated MST marker in this watershed, remediation efforts to protect public health would be best directed toward infrastructure improvements. Uncertainty analysis indicates more site-specific knowledge of pathogen presence and densities would best improve the estimation of illness risks. / Ph. D.

Risk analysis is a powerful science-based tool that can be used to control and mitigate microbial food safety hazards. Codex recommends conducting preliminary risk management activities (PRMAs) to initiate risk analysis and to plan the risk assessment process. The information learned from these PRMAs should be utilized to construct a quantitative microbial risk assessment (QMRA) model. Then, risk management activities can utilize the QMRA model to identify and select microbial risk management (MRM) options. In this project, Codex recommendations for conducting risk analysis were followed to analyze the risk of acquiring salmonellosis from whole broiler (meat chickens) consumption within the United States. At the first stage, the risk of Salmonella on whole broilers was quantitatively estimated by attributing reported annual salmonellosis to whole broilers. A quantitative microbial risk assessment (QMRA) model was constructed to build an informative risk analysis model based on performance criteria, while minimizing associated modeling complications. The QMRA model was constructed in Excel® (Microsoft Corporation, Redmond, WA, USA) with the @RISK® Add-ins software (Palisade Corp., Ithaca, NY, USA). @RISK® software was used to perform Monte Carlo simulations that account for attendant uncertainties. After the model was tested and calibrated, it estimated the annual salmonellosis cases from whole broilers as 216,408 case/year that corresponds to the number of salmonellosis reported by Center for Disease and Control Prevention (CDC). Furthermore, sensitivity analysis was performed where 16 sensitive inputs (potential places for food safety interventions) and 10 data gaps (inputs that significantly affect the overall uncertainty) were reported. Some QMRA model results were transformed to MRM metrics. These MRM metrics, including ALOPs (Appropriate Level of Protection), FSOs (Food Safety Objectives), POs (Performance Objectives), and PC (Performance Criteria), were calculated along with a sampling plan for a food safety control system. The MRM metrics were utilized to identify and plan food control interventions such as risk communication, auditing, inspection, and monitoring. Furthermore, the QMRA model was utilized to identify and to quantitatively evaluate food safety interventions that affect Salmonella prevalence and/or concentration. / Ph. D.

<p dir="ltr">Protecting workers, the public, and the environment from the potential hazards associated with radiation exposure relies on two disciplines: safety and security. Historically, these two disciplines operate in isolation, but new emerging threats have exploited weaknesses in the disciplines’ isolated practices. A method for overcoming weakness in isolation and strengthening protection is the integration of nuclear safety and security. Integration can provide increased protection for nuclear facilities and operations. This research identifies and fills gaps within integration research that promotes the active practice of integration. </p><p dir="ltr">Eight integration points were identified across the overlap of nuclear safety and security. Definitions for the points of overlap were determined using qualitative research methodologies. These definitions provided measurable aspects of practiced integration among the eight points. The eight integration points were also analyzed for importance using a quantitative methodology known as an analytical hierarchy process with an assisted Monte Carlo simulation. This study found that reactor staff placed access control and transportation of materials as the highest points of importance. However, a 10-year review of United States Nuclear Regulatory Commission violations and citations revealed culture as the most common issue for research reactors. This supports the need for a shift in perspective regarding nuclear safety and security practices.</p><p dir="ltr">An integration assessment tool was designed to measure the active practice of integrative techniques among research reactor staff. When applied to a research reactor, specific integration points were assessed, and an overall integration score for the facility was provided. The results of the integration assessment tool were applied to a newly developed integrated risk model that determined the facility’s vulnerability, consequences, and integrated risk score. </p><p dir="ltr">Through the efforts of this research, the eight points of integration have clearly and concisely identified how integration can be exercised at a facility level—this is something that has not yet been done. This research identified trends in safety and security practices that indicated strengths and weaknesses and how integration can improve those strengths and address the weaknesses. This research also provided a novel risk analysis model focused on actively applied integrative techniques instead of simulated hypothetical probabilities. Through this adjusted focus on integration, this research has found a new method for increasing the safety and security of nuclear operations.</p><p><br></p>

Yes / Quantitative risk assessment (QRA) approaches systematically evaluate the likelihood, impacts, and risk of adverse events. QRA using fault tree analysis (FTA) is based on the assumptions that failure events have crisp probabilities and they are statistically independent. The crisp probabilities of the events are often absent, which leads to data uncertainty. However, the independence assumption leads to model uncertainty. Experts’ knowledge can be utilized to obtain unknown failure data; however, this process itself is subject to different issues such as imprecision, incompleteness, and lack of consensus. For this reason, to minimize the overall uncertainty in QRA, in addition to addressing the uncertainties in the knowledge, it is equally important to combine the opinions of multiple experts and update prior beliefs based on new evidence. In this article, a novel methodology is proposed for QRA by combining fuzzy set theory and evidence theory with Bayesian networks to describe the uncertainties, aggregate experts’ opinions, and update prior probabilities when new evidences become available. Additionally, sensitivity analysis is performed to identify the most critical events in the FTA. The effectiveness of the proposed approach has been demonstrated via application to a practical system. / The research of Sohag Kabir was partly funded by the DEIS project (Grant Agreement 732242).

An extensive bibliographic search of domestic and foreign resources was elaborated within the diploma thesis. In the sphere of major accident prevention, risk analysis and assessment are necessary to fulfill the aims. The development of this sphere is mentioned in the thesis. It also discusses reasons why the exact and detailed instruction for those analyses cannot be provided and why the standard methods of risk analysis cannot be introduced (as well as the methods for particular risk recipients). The thesis also discusses available software tools for evaluating the emergency impacts. The study suggests the optimal software tool for simulation of emergency impacts in the conditions of the Czech Republic and also recommends the possible technical precautions for increasing safety of dangerous chemical substances. The conclusion contains discussion on the finding the author revealed and their relation to the information found in the literature and it also summarizes author’s opinion.