An innovative framework for chemical and process facilities to support a comprehensive Natech risk assessment

The 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

Assessment and Mitigation of Natech events caused by floods

PresentationRecent events pointed out the relevance of threats deriving from natural events impacting on chemical and process facilities where relevant quantities of hazardous substances are present. The framework of climate change is also causing the increase in the frequency of floods and intense storms resulting in the damage of facilities and in the release of hazardous substances, causing concerns for the safety of population, the protection of the environment and asset integrity. The specific features of technological accidents triggered by natural events are recognized since several years and the term Natech (Natural events causing a technological accident) is now used to identify such accident scenarios. The present contribution presents and further develops the framework for the analysis of Natech scenarios, also with reference to recent events that took place in Europe and in the US. Beside the conventional approach based on scenarios caused by the damage of equipment, a new framework is introduced to identify and assess specific accident scenarios caused by the loss of critical utilities (nitrogen, instrument air, cooling water, steam, etc.). Natech events caused by floods and the related cascading events were addressed, in the light of the methods and tools available for quantitative risk assessment

The role of safety barrier performance depletion in the escalation of Natech scenarios

Natural 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

Multi-risk Approach to the Qra of Natech Scenarios in the Chemical and Process Industry

A 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

Development of a Comprehensive Framework for the Assessment of Technological Scenarios Triggered by Natural Events (Natech) in the Chemical and Process Industries

The interaction between natural hazards and chemical and process installations might lead to severe technological scenarios involving hazardous materials. These events are termed as Natech accidents and have several peculiarities that fall beyond the features of industrial accidents caused by internal factors. Indeed, natural events can simultaneously trigger multiple technological scenarios, leading to complex situations hard to be managed by emergency teams. Moreover, natural hazards can affect utilities and lifelines required to guarantee the correct operation of processes and of the implemented safety measures. This impairment can produce peculiar scenarios if specific classes of substances are handled, and can influence the possibility of accident escalation and domino effect, eventually leading to complex cascading events. This thesis is aimed at developing the tools for a more comprehensive quantification of the Natech risk, with a specific focus on the possibility that utilities and safety barriers might be impacted during the accident. A novel paradigm is presented for the description of the dynamics of Natech events, to highlight the central role of utilities and safety barriers in accident chain progression. Subsequently, a complete approach to assess the modification of barrier performance during natural hazards is described and embedded in an approach to assess the modification of Natech escalation likelihood. Then, a set of quantitative risk assessment methodologies is presented, enabling the evaluation of Natech risk including the possibility of barrier depletion and accident escalation also via domino effects. The tools presented in this thesis will hopefully enhance the comprehension of complex Natech events and foster the development of effective strategies for risk reduction and management, pivotal issues to be addressed to improve the resilience of chemical and process sites to natural hazards also in the light of the possibility that their severity will be inflated by the effects of climate change

A generalized equipment vulnerability model for the quantitative risk assessment of horizontal vessels involved in Natech scenarios triggered by floods

Severe NaTech scenarios may be triggered by the impact of floods on chemical and process installations. The currently available equipment vulnerability models addressing the potential failure of equipment caused by floods suitable for use in a quantitative risk assessment framework are mostly limited to the specific case of storage tanks, not addressing other types of process equipment. The present study aims at filling this gap, proposing a generalized vulnerability model applicable also to other types of horizontal cylindrical vessels widely used in the chemical and process industry and in oil and gas installations (e.g., shell and tube heat exchangers, separators, etc.). The generalized vulnerability model developed allows a simplified assessment of the possible structural damage due to floating or displacement caused by floodwater, based on floodwater height and velocity, and on detailed geometrical data of the vessel. Shortcut correlations were also developed to provide a preliminary screening, allowing the identification of the more vulnerable equipment. The models were applied to the analysis of an extended case study, in order to assess their suitability and the interest of the results provided in the framework of quantitative risk assessment of NaTech events triggered by floods

Tackling uncertainty in security assessment of critical infrastructures: Dempster-Shafer Theory vs. Credal Sets Theory

Securing 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

Flood triggered oil spills: Lessons from the Natech accident in Saga prefecture in August 2019.

2020年9月1日(火), 於 : Zoomによるオンライン開催With the aim of extracting lessons learned, this study investigated a large oil spill at an ironworks factory in Saga prefecture, during the severe flooding that hit southwestern Japan in late August 2019. The oil spill dispersed by the flood waters contaminated adjacent crops, irrigation canals and citizens homes in a large area of Omachi town. Many citizens had practiced vertical evacuation. Due to the oil spill, the pumping of flood waters had to be stopped to prevent further contamination, resulting in oil stagnating in the area for several days. This meant that residents had to be rescued from their homes in the middle of strong oil vapours. The oil spil s possible long-lasting impact in terms of health and environmental pollution requires monitoring and further investigation. The study found that oil spills caused by floods had already occurred at the same site, highlighting the need to improve risk management of chemical hazards, develop flood risk maps that consider the potential for these types of secondary events and other compound disasters, and propose more effective strategies for emergency planning and response