1,720,979 research outputs found
An innovative framework for chemical and process facilities to support a comprehensive Natech risk assessment
Get PDFThe interaction between natural hazards and technological installations handling hazardous materials can produce complex cascading accidents termed as Natech events. Climate change and increasing vulnerability of industrial facilities caused a growing concern towards Natech hazards in recent years. Current methodologies addressing the identification and quantification of Natech scenarios mostly consider only the possibility of direct damage of process and storage equipment caused by natural hazards as earthquakes and floods. Nevertheless, recent severe Natech events as the Arkema accident (2017) demonstrated that the direct failure of equipment is not the sole possible accident trigger. Indeed, in these events the accident sequence was initiated by the impairment of auxiliary systems and utilities induced by the natural event. The present contribution proposes an innovative comprehensive framework to the identification of Natech scenarios and to the quantitative assessment of Natech risk. The new framework presented addresses the identification of both direct and indirect Natech scenarios and considers the possible failure of utilities in the evolution of the accident chain and in the escalation of accident consequences. Specific strategies for the identification of alternative routes leading to Natech events are suggested, considering loss of containment events caused either by the direct damage of equipment or by the failure of utilities or safety barriers. A test-case was defined to show the application of the framework. The results demonstrated the importance of the indirect route in determining the overall hazard due to Natech events when specific categories of hazardous substances are present on the site
Quantitative risk assessment of Natech scenarios triggered by earthquakes involving pipelines
Get PDFEarthquakes may cause severe damage to the technological infrastructure and to transport systems handling hazardous substances as oil, natural gas and flammable/toxic chemicals. Earthquake damage may trigger Natech scenarios involving the release of hazardous substances, resulting in major accidents including fires, explosions, and toxic releases. Most of the methodologies developed for the quantitative assessment of risk related to Natech scenarios only focus on stationary installations handling hazardous substances, as chemical and process plants. However, pipelines are widely used for the long-range bulk transport of hazardous materials. In the present study an innovative methodology was developed to address the Quantitative Risk Assessment (QRA) of Natech scenarios triggered by earthquakes involving pipelines handling hazardous substances. Specific vulnerability models are used to assess pipeline failure probability. A new specific procedure was developed to carry out the calculation of consequences and risk along the main dimension of the pipeline. The innovative methodology developed allows for the first time the calculation of local specific individual risk and societal risk due to Natech events along the route of the pipeline. Two different case studies are discussed to provide a notional application of the proposed methodology and to demonstrate the applicability of the approach to a real-scale pipeline risk assessment problem. The results obtained from the case studies show the relevance of risk due to Natech scenarios involving pipelines with respect to that deriving from possible conventional failures, as well as the potentialities of the proposed approach in considering different intensities of seismic hazard along the route of the pipeline. Thus, the methodology developed provides an important support to risk-informed decision making in the management and mitigation of major accidents involving pipelines
Tackling uncertainty in security assessment of critical infrastructures: Dempster-Shafer Theory vs. Credal Sets Theory
No full textSecuring critical infrastructures is a complex task. Required information is usually scarce or inexistent, and experts’ judgments may be inaccurate and biased. In this paper, two methodologies dealing with data scarcity, imprecision, and uncertainty are presented: Evidential network and Credal network. Evidential network is a graphical technique based on Dempster-Shafer Theory to explicitly model the propagation of epistemic uncertainty among variables while Credal network is an extension of Bayesian network to deal with sets of probabilities, known as Credal sets, based on experts’ judgments. Both methodologies constitute robust frameworks to account for high degree of imprecision on data, producing informative results despite the low-informative input. In the present study, the power in expressing uncertainty of these two methodologies have been showed, and their differences have been described through their application to a case study of security vulnerability assessment. Results demonstrate the substantial equivalence of the two methodologies in prognostic analysis, thus, an approximate updating procedure of Evidential network through equivalent Credal network has been proposed, to overcome the lack of possibility to compute updating in the context of Dempster-Shafer Theory
The Effect of Safety Barrier Degradation on the Severity of Primary Natech Scenarios
Get PDFThe impact of natural events on technological infrastructures may lead to severe accident scenarios involving hazardous materials, generating the so-called Natech events. This typology of accidents is particularly critical since, besides damaging process or storage equipment items, natural hazards might concurrently impair safety barriers implemented to prevent and mitigate technological scenarios, reducing the overall safety of the system and increasing the likelihood of unmitigated outcomes and domino effects. In this study, a novel methodology to perform the quantitative risk assessment of the primary Natech scenarios directly caused by the impact of natural hazards considering the presence of safety barriers with depleted performance is proposed. A multi-level approach is tailored to assess the performance modification of safety systems designed to mitigate the primary technological scenarios. An innovative procedure for the quantitative assessment of these scenarios is proposed to enable the characterization of the final outcomes considered in the quantitative risk assessment accounting for depleted barrier performance. A case study is developed to demonstrate the application of the methodology, evidencing a relevant increase in risk compared to that assessed considering the baseline performance of safety systems. The proposed methodology thus enables a more comprehensive assessment of the final outcomes of primary Natech events, fostering the development of a holistic framework for Natech quantitative risk assessment
Multi-risk Approach to the Qra of Natech Scenarios in the Chemical and Process Industry
Get PDFA novel quantitative methodology to perform a multi-risk assessment of technological scenarios triggered by natural hazards (Natech events) is presented. The framework is based on a multi-hazard approach and is proposed to assess the risk associated to the different natural events to which an industrial site where relevant quantities of hazardous substances are present is exposed to. The quantitative methodology allows the calculation of failure frequencies, consequences of the scenarios and risk indexes which are compared and benchmarked. Finally, a case study is defined taking into account the impact of earthquakes, floods and lightning strikes. The application leads to the quantification of the contribution of each reference natural event considered to the overall risk figures. Moreover, the methodology proposed enables the evaluation of the relative weight of the risk related to each natural hazard for the selected facility
The role of safety barrier performance depletion in the escalation of Natech scenarios
Get PDFNatural hazards can cause severe damages to chemical and process facilities, triggering technological scenarios involving hazardous materials. The risk related to this type of cascading events, defined Natech accidents, is expected to grow in the foreseeable future due to the enhanced severity of some categories of natural phenomena brought by climate change. A critical feature of Natech events is that the safety systems implemented might undergo some extent of depletion and performance reduction due to the natural event, and this might heavily influence the likelihood and the features of accident escalation. While methodologies have been proposed to perform a quantitative assessment of Natech risk, the role of the concurrent depletion of the safety systems has been only recently investigated and has not been addressed systematically yet. Hence, a comprehensive framework to assess the risk related to the escalation of Natech scenarios and to possible domino effects due to concurrent safety barrier depletion is presented. A specific three-level approach was conceived to evaluate barrier performance according to system complexity and uncertainty in the impact of natural events. A straightforward analysis (L0) based on a Boolean approach is applied for simple barriers when their missing action can be assessed with a low uncertainty. A more detailed analysis (L1) leveraging specific performance modification factors to express the likelihood that similar reference barriers will fail is applied in case of relevant uncertainty. For the analysis of complex barriers and situations when system architecture differs from reference configurations, a further level (L2) based on fault tree analysis is introduced to consider barrier subsystem failure during natural events and to update the overall unavailability of the system. A dedicated event tree approach is then used to embed barrier performance into the quantitative risk assessment of Natech scenarios. The methodology was applied to a test case demonstrating that the quantification of the updated performance of the considered set of safety barriers during natural hazards leads to a relevant increase in overall Natech risk figures
Vulnerability Assessment of Industrial Sites to Interface Fires and Wildfires
Get PDFIn the framework of climate change, the hazard caused by wildfires approaching the anthropic settlements is raising an increasing concern. Fatalities and relevant damage to properties were recently caused by wildfires affecting the Wildland-Urban and Wildland-Industrial Interfaces. Industrial sites storing large quantities of hazardous materials are vulnerable to interface fires, which have the potential to trigger specific cascading events such as Natech scenarios followed by domino effects. The present study aims at providing a methodology for the quantitative assessment of the vulnerability of industrial sites exposed to wildfires. The approach provides a novel framework for the identification and quantification of all the chains of failures that may occur due to wildfires or interface fires approaching industrial sites. The methodology accounts for the thermal radiation from fires in both primary Natech scenarios and cascading scenarios triggered by domino effects. The dynamic features of interface fires and the synergistic effects of multiple fires are also taken into account. The results of a case study demonstrated the importance of considering the dynamic behavior of wildfire, which strongly affects the vulnerability of industrial structures. The results also evidence the importance of emergency management and first response on the overall vulnerability figures
Diagnostics for advanced laser acceleration experiments
Get PDFThe first proposal for plasma based accelerators was suggested by 1979 by Tajima and Dawson. Since then there has been a tremendous progress both theoretically and experimentally. The theoretical progress is particularly due to the growing interest in the subject and to the development of more accurate numerical codes for the plasma simulations (especially particle-in-cell codes). The experimental progress follows from the development of multi-terawatt laser systems based on the chirped-pulse amplification technique. These efforts have produced results in several experiments world-wide, with the detection of accelerated electrons of tens of MeV. The peculiarity of these advanced accelerators is their ability to sustain extremely large acceleration gradients. In the conventional radio frequency linear accelerators (RF linacs) the acceleration gradients are limited roughly to 100 MV/m; this is partially due to breakdown which occurs on the walls of the structure. The electrical breakdown is originated by the emission of the electrons from the walls of the cavity. The electrons cause an avalanche breakdown when they reach other metal parts of the RF linacs structure
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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