Francesca Argenti

Quantitative assessment of safety barrier performance in the prevention of domino scenarios triggered by fire

The evolution of domino scenarios triggered by fire critically depends on the presence and the performance of safety barriers that may have the potential to prevent escalation, delaying or avoiding the heat-up of secondary targets. The aim of the present study is the quantitative assessment of safety barrier performance in preventing the escalation of fired domino scenarios. 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. Data on the more common types of safety barriers were obtained in order to characterize the effectiveness and probability of failure on demand of relevant safety barriers. The methodology was exemplified with a case study. The results obtained define a procedure for the estimation of safety barrier performance in the prevention of fire escalation in domino scenarios.

Accident scenarios triggered by lightning strike on atmospheric storage tanks

Severe Natech accidents may be triggered by lightning strike affecting storage tanks containing relevant inventories of hazardous materials. The present study focused on the identification of event sequences and accident scenarios following lightning impact on atmospheric tanks. Reference event trees, validated using past accident analysis, are provided to describe the specific accident chains identified, accounting for reference protection and mitigation safety barriers usually adopted in current industrial practice. An overall methodology was outlined to allow the calculation of the expected frequencies of final scenarios following lightning impact on atmospheric storage tanks, taking into account the expected performance of available safety barriers. The methodology was applied to a case study in order to better understand the data that may be obtained and their importance in the framework of quantitative risk assessment (QRA) and of the risk management of industrial facilities with respect to external hazards due to natural events.

Vulnerability assessment of chemical facilities to intentional attacks based on Bayesian Network

Abstract Chemical facilities may be targets of deliberate acts of interference triggering major accidents (fires, explosion, toxic dispersions) in process and storage units. Standard methodologies for vulnerability assessment are based on qualitative or semi-quantitative tools, currently not tailored for this type of facilities and not accounting for the role of physical protection systems. In the present study, a quantitative approach to the probabilistic assessment of vulnerability to external attacks is presented, based on the application of a dedicated Bayesian Network (BN). BN allowed the representation of interactions among attack impact vectors and resistance of process units, which determine the final outcomes of an attack. A specific assessment of protection systems, based on experts’ elicitation of performance data, allowed providing a knowledge support to the evaluation of probabilities. The application to an industrial case study allowed the assessment of the potentialities of the approach, which may support both the evaluation of the vulnerability of a given facility, and the performance assessment of the security physical protection system in place.

The Performance of Inorganic Passive Fire Protections: an Experimental and Modelling Study

The installation of fireproofing materials on equipment and structures is a widely applied and effective solution for the protection of critical process elements against severe fires, in order to prevent possible damages escalation. The choice and design of fireproofing materials is crucial for granting adequate performances. As a matter of fact, properties such as, among others, thermal conductivity and density change substantially when the material is exposed to severe temperatures. In the present study, a methodological approach, integrating experimental and modelling activities, was proposed. Focus was set on a particular class of PFP: inorganic fireproofing materials. A reference set of commercial PFP materials (rock wool, glass wool, silica blanket, etc.) was selected. Small scale experiments allowed determining the variation of the most relevant thermal properties of the coatings and to obtain detailed correlation models for their description. A finite element model (FEM) was developed in order to reproduce the behaviour of real scale equipment exposed to fire and to provide a sound design of the fire protection system.

Risk assessment of mitigated domino scenarios in process facilities

The propagation of accidents among process units may lead to severe cascading events or domino effects with catastrophic consequences. Prevention, mitigation and management of domino scenarios is of utmost importance and may be achieved in industrial facilities through the adoption of multiple safety layers. The present study was aimed at developing an innovative methodology to address the quantitative risk assessment (QRA) of domino scenarios accounting for the presence and role of safety barriers. Based on the expected performance of safety barriers, a dedicated event tree analysis allowed the identification and the assessment of the frequencies of the different end-point events deriving from unmitigated and partially mitigated domino chains. Specific criteria were introduced in consequence analysis to consider the mitigation effects of end-point scenarios deriving from safety barriers. Individual and societal risk indexes were calculated accounting for safety barriers and the mitigated scenarios that may result from their actions. The application of the methodology to case-studies of industrial interest proved the importance of introducing a specific systematic and quantitative analysis of safety barrier performance when addressing escalation leading to domino effect.

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.

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.