On the use of dynamic process simulators for the quantitative assessment of industrial accidents

The present work discusses the use of dynamic process simulators as supporting tools for the quantitative risk assessment of industrial facilities. In particular, a commercial process simulator was set up for the analysis of industrial accidents, obtaining on one side a detailed characterization of the source term in case of release events from process equipment or pipes. On the other, the possibility of implementing in the simulator control actions, interlocks, emergency shut-down, allowed monitoring the response of a given process unit, verifying the effectiveness and robustness of safety devices in emergency situations. The application to two case studies was used to demonstrate the potentialities of dynamic process simulators in the framework of industrial safety analyses. © Copyright 2014, AIDIC Servizi S.r.l

Advanced attractiveness assessment of process facilities with respect to malevolent external attacks

In the present contribution, a semi-quantitative methodology for the attractiveness assessment of industrial facilities as potential targets of malevolent external attacks is developed. The attractiveness is hereby proposed as a proxy to the likelihood of attack in order to support a security risk screening analysis. Technical and not technical factors are considered in order to adequately depict the motives and triggers which play a role in determining attractiveness. The plant hazard potential, determined through a simplified estimation of damages on population due to a major accident triggered by an attack, formed the objective basis of the evaluation. Then, the assessment was completed through the characterization of the "perceived" value of a potential target facility. To the purpose, a set of relevant factors that influence the targeting logic on the basis of strategic and geo-political considerations was identified; next, an analytic hierarchy process was adopted to prioritize the relevant factors and define a scoring system to evaluate overall plant attractiveness. The procedure for attractiveness assessment was exemplified through the analysis of case studies, which demonstrated the importance of not limiting plant attractiveness assessment to a consequence-based evaluation, stressing the importance of geo-political, ideological and strategic incentives

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

Dynamic evaluation of risk: From safety indicators to proactive techniques

This contribution presents a short review of dynamic risk evaluation techniques based on human and organizational factors, from the first approaches developing indicators to the aggregation methodologies integrating risk analysis. A methodology for the evaluation and update of expected release frequencies is taken as example of last generation techniques. The methodology aiming to support dynamic risk assessment studies is named TEC2O - Frequency modification methodology based on TEChnical Operational and Organizational factors. The potential of such methodology is described also in terms of support to risk based decision making for Oil&Gas integrated operations

Quantitative consequence assessment of industrial accidents supported by dynamic process simulators

In the present work, process simulators are adopted in the framework of consequence assessment support. A novel methodology is developed, with particular reference to consequence assessment specific for O&G offshore sector. A commercial, high-fidelity process simulator, Honeywell UniSim® Design R460, is applied for the analysis of accidental scenarios in order to perform a detailed evaluation of dynamic response of a given process unit and to support the consequence assessment of industrial accidents. A specific set-up of process simulator is developed to reproduce either source term, e.g. estimation of gas or liquid flow rate from process leaks, and physical effects dynamics. In particular, the physical effects evaluation through integral models of hydrocarbon fires is integrated in the dynamic process simulator, possibly accounting for the presence of safety barriers. Specific features of simulators are exploited to evaluate the consequences of possible failures in actuators and safety barriers. Some case studies of industrial interest are discussed to demonstrate the application of the methodology

An innovative and comprehensive approach for the consequence analysis of liquid hydrogen vessel explosions

Abstract Hydrogen is one of the most suitable solutions to replace hydrocarbons in the future. Hydrogen consumption is expected to grow in the next years. Hydrogen liquefaction is one of the processes that allows for increase of hydrogen density and it is suggested when a large amount of substance must be stored or transported. Despite being a clean fuel, its chemical and physical properties often arise concerns about the safety of the hydrogen technologies. A potentially critical scenario for the liquid hydrogen (LH2) tanks is the catastrophic rupture causing a consequent boiling liquid expanding vapour explosion (BLEVE), with consequent overpressure, fragments projection and eventually a fireball. In this work, all the BLEVE consequence typologies are evaluated through theoretical and analytical models. These models are validated with the experimental results provided by the BMW care manufacturer safety tests conducted during the 1990's. After the validation, the most suitable methods are selected to perform a blind prediction study of the forthcoming LH2 BLEVE experiments of the Safe Hydrogen fuel handling and Use for Efficient Implementation (SH2IFT) project. The models drawbacks together with the uncertainties and the knowledge gap in LH2 physical explosions are highlighted. Finally, future works on the modelling activity of the LH2 BLEVE are suggested

Innovative LOPA-based methodology for the safety assessment of chemical plants

The aim of the present work was the development and application of a methodology for the safety assessment of chemical plants based on LOPA (Layer of Protection Analysis) techniques. The approach integrates the use of consolidate hazard identification techniques (HazOp) and the adoption of quantitative literature models for consequence assessment (e.g., integral models) into the LOPA framework, allowing to limit the role played by expert judgment in the evaluation in order to reduce the causes of uncertainty in the results. Furthermore, a systematic and quantitative assessment of safety measures contribution to the reduction of plant residual risk was included in the analysis. In order to apply the methodology, a case study was defined taking into account an actual industrial facility. The results obtained allowed demonstrating the potentialities of the method

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

Damage models for storage and process equipment involved in flooding events

The present study focuses on the accidents caused by the impact of floods on storage and process equipment. This type of accident is classified as a NaTech (Natural-Technological) event and resulted in severe consequences in several past accidents. A methodology was developed for the determination of vulnerability models aimed at the estimation of equipment damage probability on the basis of severity or intensity parameters of the flooding. A mechanical model was developed, based on the comparison between the flooding intensity and the resistance of a vessel and/or its support. Simplified vulnerability functions were derived. Finally, a case-study was set up and analysed to show the potentialities of the methodology and the implementation of results in quantitative risk analysis. © 2013, AIDIC Servizi S.r.l

Domino effects related to explosions in the framework of land use planning

The present study analyses the possible escalation due to the damage of industrial equipment containing hazardous materials loaded by pressure waves produced either by an accidental source as a Vapour Cloud Explosion, or by a voluntary external attack such as the explosion of a TNT charge located nearby the industrial facility. The results obtained evidence the similarities and the differences for the two explosion sources in terms of structural damage, loss of containment and of expected impacts on the population. In particular, a specific vulnerability assessment was carried out defining a case-study in order to evidence the different potential impact of domino effect triggered by internal process causes respect to escalation scenarios caused by external acts of interference. © 2013, AIDIC Servizi S.r.l