Quantitative Assessment of Safety Barrier Performance in the Prevention of Cascading Events

PresentationThe prevention of high-impact low-probability (HILP) events in industrial clusters or complex industrial areas where critical infrastructures are present critically depends on the presence and the performance of safety barriers that may have the potential to prevent escalation. In recent years a set of tools and models were developed for the quantitative assessment of risk due to cascading events and domino scenarios. The aim of the present study is the integration of tools for risk assessment with a specific approach allowing a detailed assessment of safety barrier performance. A LOPA (layer of protection analysis) based methodology, aimed at the definition and quantification of safety barrier performance in the prevention of escalation was developed. The method allowed the quantitative characterization of alternative mitigated and unmitigated escalation scenarios. Data were collected on the more common types of safety barriers aimed at the prevention of fire escalation. An example of application was developed, allowing the quantitative assessment of risk mitigation of cascading events triggered by fire escalation based on the assessment of safety barrier performance

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

Quantitative evaluation of the safety barriers to prevent fired domino effect

A simplified methodology was developed for the assessment of fire protection barriers and to support the Quantitative Risk Assessment (QRA) of industrial facilities. Given a generic fire scenario, the aim of the methodology was to evaluate the probability of fire damages on industrial equipment both considering the availability and effectiveness of the protective barriers. Fire protections for industrial equipment were first classified, and then literature reliability data were used to build a dataset of Probability of Failure on Demand (PFD) for each protection type. Next, the effectiveness was determined from specific studies and surveys available in the literature. For passive protections, the effectiveness evaluation was based on the protective barrier response to fire. A case study was presented and discussed in order to exemplify the methodology implementation and to show the potential application in simplified QRA studies

Asset integrity in the case of Wildfires at Wildland-Industrial Interfaces

Wildfires are uncontrolled fires involving the combustion of wild vegetation. When a wildfire front approaches the Wildland-Industrial Interface there can be a serious threat for process and storage equipment items located at the plant boundary. Ensuring the integrity of such equipment prevents the fire from spreading inside the plant site and causing major accidents such as fire, explosion, and toxic gas dispersion. The provision of adequate clearance areas is paramount since the early stages of the plant design. Once the facility is built, the implementation of safety measures can protect industrial items and ensure tank integrity. A tailored methodology for the calculation of safety distances between wild vegetation and tanks accounting for the safety system was developed and applied to a case study. The outcomes provide useful information on the effectiveness of safety measures for the protection of industrial items exposed to wildfire

Asset integrity in the case of wildfires at wildland-industrial interfaces

Wildfires are uncontrolled fires involving the combustion of wild vegetation. When a wildfire front approaches the Wildland-Industrial Interface there can be a serious threat for process and storage equipment items located at the plant boundary. Ensuring the integrity of such equipment prevents the fire from spreading inside the plant site and causing major accidents such as fire, explosion, and toxic gas dispersion. The provision of adequate clearance areas is paramount since the early stages of the plant design. Once the facility is built, the implementation of safety measures can protect industrial items and ensure tank integrity. A tailored methodology for the calculation of safety distances between wild vegetation and tanks accounting for the safety system was developed and applied to a case study. The outcomes provide useful information on the effectiveness of safety measures for the protection of industrial items exposed to wildfire.Peer ReviewedPostprint (published version

Extension of Quantitative Risk Assessment to the Analysis of External Hazard Factors in the Chemical and Process Industry

The PhD research project is aimed at developing and applying an innovative framework toward Risk Assessment of cascading events within the chemical and process industry, addressing both domino and security-based events. Cascading events are catastrophic accidents, triggered by external hazard factors, including safety-based (i.e., domino) and security-based events. In the chemical industry domain, barriers provide a crucial role for the prevention, control and mitigation of cascading events. Therefore, it is necessary to apply innovative techniques, aimed at the evaluation of barriers technical performance and at their optimal economic allocation, to be inserted within Quantitative Risk Assessment (i.e., QRA). Concerning barriers technical performance, the research activity is aimed at applying Bayesian Networks to safety barriers performance assessment, regarding domino events. Starting from a conventional approach, preliminary applications have been aimed at implementing a Bayesian approach to barriers performance assessment concerning major accidents. Therefore, the approach has been extended to domino accident analysis, in purpose to evaluate the effect of barriers introduction within modelling. The case studies demonstrated that the application of a Bayesian approach provides a very accurate barriers performance assessment within QRA, with reference to external hazard factors driven accidents (i.e., domino events), offering a realistic risk picture. Concerning barriers optimal economic allocation, the research activity is aimed at developing and applying an original economic model for the prevention of security-based cascading events. The model includes security upgrades performance and costs assessment, evaluation of benefits and definition of threat and vulnerability probabilities. The application of economic techniques, by means of cost-benefit and cost-effectiveness analyses, enables barriers optimal allocation within budgets constraints. Validation of the model is provided by application to relevant case studies. Therefore, the model enables defining rational criteria for barriers optimal selection and allocation and its outputs support the inclusion of security hazards within QRA, and related decision-making

Analyzing Domino Effects Occurring on Gasoline Storage Tanks at the Bulk Oil Storage and Transportation (BOST) Depot

Since processed crude oil products are very vulnerable (susceptible) and highly flammable to cause massive catastrophes, such as fire and explosion, which are frequent and can create a chain reaction (Domino effects). This research was carried out at the Bulk Oil Storage and Transportation LTD depot on the Accra plain in Ghana where gasoline and Gasoil are stored. The research was conducted on a flammable gasoline area subjected to a vapor cloud explosion and the hazardous zone. Analyzing domino effects, propagation of a gasoline flammable vapor cloud caused by the explosion, ALOHA (Areal Location of Hazardous Atmospheres) software was used to find out how to apply effective safety measures to prevent future risks at any BOST facilities across the country. After the analysis, it was realized that 5.0 miles to the west-south-west the fuel concentration in the air was 2100 ppm lower than the explosive limit (LEL), and could not be as severe as that at 2.3 miles distance from the source point (12600 ppm LEL) with a greater fuel concentration in the atmosphere. The results made available would be useful in maximizing (improving) safety at the facility, residential area, and as well as minimizing future incidents

Facility Siting and Layout Optimization for Risk Reduction of Offshore Operations

An MINLP optimization model has been created that optimizes the layout of a set of sections with fixed footprint areas bound to an offshore platform of a given size based on safety considerations due to fire, explosion, and toxic scenarios. Process parameters are used to estimate the probability of an event as well as the magnitude of the possible impact on other sections, which can be weighted in importance in the objective. The magnitude of the impact is directly dependent on several factors: the spacing between the sections, the congestion in the general vicinity of the section, escape routes, and domino effects of fire and explosion. Explosion modeling is carried out both for vapor cloud explosions ignited within the area that they are created, and dispersed flammable clouds with footprints based on weather conditions, congestion, and process conditions. Modeling uses an approximation to the TNO multi-energy method which takes into account the amount of congestion and confinement in the area and the size of the flammable cloud. Fire modeling is used to ascertain the adequacy of layout of both sections and muster points that the sections are assigned to. Modeling is done using three different correlations for different fire scenarios: pool fire, fireball, and jet fire. Toxic effects of combustion products and escape-hindering effects of smoke production are also incorporated into the model, accounting for weather conditions and local congestion. Toxic modeling is based on the same dispersion modeling estimation as the explosion and fire scearios use and focuses on the effect of hydrogen sulfide leaks causing incapacitation, escape difficulties due to eye irritation and disorientation, and death. Dispersion modeling to determine effects of smoke, dispersed gas clouds, and toxic vapors is carried out in three-dimensions using the CFD software FLACS and the anticipated congestion model (ACM), a method that has not yet been applied to generalized dispersion. The results are correlated to an expression as a function of flow rate, congestion, windspeed, and their interactions that can be used in the optimization formulation. Mitigations are also considered; blast walls and fire walls, both ideal (non-failing) and with failure mechanisms, are incorporated into the model as a key component considered during the layout. It is shown that the model is a positive step into an area that has sparsely been considered, contributing a framework for the integrated consideration and minimization of several key risk factors in the offshore realm that, as yet, have been unexplored from the numerical optimization viewpoint

Анализ эффектов домино, возникающих в резервуарах для хранения бензина на складе хранения и транспортировки нефтепродуктов

Since processed crude oil products are very vulnerable (susceptible) and highly flammable to cause massive catastrophes, such as fire and explosion, which are frequent and can create a chain reaction (Domino effects). This research was carried out at the Bulk Oil Storage and Transportation LTD depot on the Accra plain in Ghana where gasoline and Gasoil are stored. The research was conducted on a flammable gasoline area subjected to a vapor cloud explosion and the hazardous zone. Analyzing domino effects, propagation of a gasoline flammable vapor cloud caused by the explosion, ALOHA (Areal Location of Hazardous Atmospheres) software was used to find out how to apply effective safety measures to prevent future risks at any BOST facilities across the country. After the analysis, it was realized that 5.0 miles to the west-south-west the fuel concentration in the air was 2100 ppm lower than the explosive limit (LEL), and could not be as severe as that at 2.3 miles distance from the source point (12600 ppm LEL) with a greater fuel concentration in the atmosphere. The results made available would be useful in maximizing (improving) safety at the facility, residential area, and as well as minimizing future incidents.Переработанные сырые нефтепродукты очень уязвимы (восприимчивы) и легко воспламеняются, что может вызвать массовые катастрофы, такие как пожары и взрывы, они случаются часто и могут вызвать цепную реакцию (эффект домино). Это исследование было проведено на складе компании Bulk Oil Storage and Transportation LTD на равнине Аккра в Гане, где хранятся бензин и дизельное топливо. Исследование проводилось на подвергшемся взрыву парового облака участке с легковоспламеняющимся бензином и на опасной зоне. Для анализа эффекта домино от распространения вызванного взрывом облака горючих паров бензина было использовано программное обеспечение ALOHA (Areal Location of Hazardous Atmospheres), чтобы выяснить, как применять эффективные меры безопасности для предотвращения будущих рисков на любых объектах BOST по всей стране. После анализа было установлено, что в 5,0 мили к западу-юго-западу концентрация топлива в воздухе была на 2100 ppm ниже предела взрываемости (LEL) и не могла быть такой сильной, как на расстоянии 2,3 мили от исходной точки (12600 ppm LEL) с большей концентрацией топлива в атмосфере. Полученные результаты будут полезны для максимизации (повышения) безопасности на объекте, в жилом районе, а также для минимизации будущих инцидентов