Experimental and analytical investigation of pressurized vessels exposed to fire

The possible occurrence of accidental fires impacting vessels for transportation and storage of hazardous materials represents a key safety issue in the process industry. In these situations, the vessel heats up, pressurizes and can fail catastrophically, generating devastating consequences. Such scenarios have been extensively investigated in the past decades to improve vessel design and emergency response planning. Numerous field studies and laboratory scale tests were carried out and several models were developed to predict the thermal and mechanical response of vessels exposed to fire. However, previous modeling approaches suffer several limitations and need to be improved and experimental data is not sufficient to effectively support the development of advanced modelling tools such as CFD. With the aim of overcoming these limitations, a novel research program was proposed. This combines fire tests, carried out by means of an innovative experimental apparatus, and a CFD based modelling approach. The present work focuses mainly on the modelling part (the experimental setup is briefly described and preliminary analysis of the data from tests is presented). Starting from previous approaches presented in literature, an improved CFD modelling setup was developed. Conditions of several fire tests involving LPG and water tanks were simulated and the results are compared with experimental measurements highlighting strengths and limitations of the modelling. In the last part of the work, an alternative approach is presented, based on models developed for the study of subcooled boiling flows that showed promising results in other fields of application. The aim was to explore the possibility of extending this approach to the case of fired vessels. The work proves that CFD is a powerful tool for the development of models able to accurately describe and predict the response of a pressure vessel exposed to fire. However, further work is needed especially regarding submodels for boiling

Analysis of the impact of wildland-urban-interface fires on LPG domestic tanks

Managing Wildland-Urban-Interface (WUI) fires is a challenging task due to the inherent complexity of the WUI environment. To ensure the success of strategies for the protection of population and structures, safety measures have to be implemented at different scales (landscape, community and homeowner). The present study is focused on the homeowner scale and deals with the threat related to the presence of LPG domestic tanks in a WUI fire scenario. Recent accidents have demonstrated that the risk associated with this type of installation is real, but often disregarded by residents. A methodology was developed, providing a set of indicators that may easily be compared with risk acceptance criteria, assessing whether the integrity of an LPG tank exposed to WUI fire scenarios is compromised or not. The methodology is applicable to a vast range of situations and at a different level of detail according to available data. A number of case studies were carried out, showing that WUI fire scenarios impacting on domestic LPG tanks complying with regulations currently adopted in several Mediterranean countries cannot be deemed safe. The methodology proposed represents an advanced tool to assist on safety distances sizing to be prescribed by standards, driving regulators towards better-informed decision-making. Peer Reviewe

Report on LPG infrastructure impact at the WUI microscale

Preprin

Cryogenic Hydrogen Storage Tanks Exposed to Fires: a CFD study

Hydrogen is one of the most suitable candidates in replacing heavy hydrocarbons. Liquefaction of fuels is one of the most effective processes to increase their low density. This is critical especially in large-scale or mobile applications such as in the maritime or aeronautical fields. A potential loss of integrity of the cryogenic storage equipment might lead to severe consequences due to the properties of these substances (e.g. high flammability). For this reason, this critical event must be avoided. The aim of this study is to analyse the behaviour of the cryogenic vessel and its lading when it is exposed to a fire and understand how to prevent a catastrophic rupture of the tank during this accident scenario. A two-dimensional computational fluid dynamic (CFD) analysis is carried out on a cryogenic liquid hydrogen (LH2) vessel to investigate its thermal response when engulfed in a fire. The model accounts for the evaporation and condensation of the substance and can predict the tank pressurization rate and temperature distribution. It is assumed that the vessel is completely engulfed in the fire (worst-case scenario). The CFD model is validated with the outcomes of a small-scale fire test of an LH2 tank. Critical indications on the dynamic response of the cryogenic tank involved in a worst-case accident scenario are provided. Tank pressurisation and temperature distributions of the case study can be exploited to provide conservative estimations of the time to failure (TTF) of the vessel. These outcomes represent useful information to support the emergency response to this type of accident scenario and can aid the selection of appropriate and effective safety barriers to prevent the complete destruction of the tank

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

WUI state of the art and regulatory needs in Europe

The document summarizes the state of the art of the regulationsrelevant to WUI in Europe, providing an organized set of references to the specific regulatory documents. It is focused on three main relevant topics: i) fuel-reduced fringes; ii) Building codes and standards; iii)Wildland-Industrial Interface. Current regulations are analysed and compared, leading to the identification of important needs and limitations of the current European regulatory frameworkPreprin

Modelling pressure tanks under fire exposure: past experience, current challenges and future perspectives

CFD and lumped parameter models are available in the literature for the analysis of pressure tanks under fire exposure. The first type of models allows for a detailed representation of the phenomena occurring in the tank, providing accurate results in terms of pressurization rate and temperature distribution. However, they are computationally expensive and are currently unable to simulate PRV opening. Lumped parameter models run in very short time, but may lead to not conservative results. The present contribution provides an overview of the strengths and limitations of both approaches, highlighting the new challenges posed by the development of models for the analysis of cryogenic tanks exposed to fire

Main specifications of CFD codes for WUIVIEW activities

CFD simulations will be the core activity of the WUVIEW performance based fire safety analysis. The purpose of this document is to provide WUIVIEW partners with a general overview of the CFD codes to be used in the Action. The general simulation framework is described, particularly highlighting data inputs and scenario description requirements, to be developed in subsequent WUIVIEW WPs. This TN provides the technical foundations and main specifications of the databases to be designed within the WUIVIEW working program (ongoing action by UPC).Postprint (updated version

Investigation of lightweight geopolymer mortars as fireproofing coatings

Fireproofing coatings are passive fire protection (PFP) systems adopted to increase the fire safety of structural components in several civil and industrial applications. They are generally spray-applied systems that behave like thermal barrier for heat transfer to the substrate. Their use is aimed at slowing down the temperature rise of the substrate and maintaining the temperature of the component below its critical temperature (e.g. steel loses about one-half of the strength at 500 °C), thus providing time to control or extinguish the fire. When good resistance to high temperature is required, geopolymers are considered highly competitive materials thanks to the intrinsic thermal resistance of their structure. For this reason, this study investigates the possibility of using fly ash-based geopolymers, activated at room temperature, as fireproofing coatings for steel components. Lightweight geopolymer mortars (LWGs) were synthesized at room temperature using low-calcium coal fly ash as precursor and 8 M NaOH and sodium silicate solutions as activators. The weight ratio between the sum of the alkaline solutions and the fly ash was maintained constant, whereas the amounts of 8M NaOH and sodium silicate solutions in the mix were varied, thus obtaining two different geopolymer matrices with different compositional SiO2/Al2O3 and Na2O/SiO2 ratios. The mix design was completed using expanded perlite (EP) as aggregate and hydrogen peroxide solution as foaming agent to increase thermal insulation properties and to decrease products density, both essential features for fireproofing coatings. Physical, mechanical and thermal properties of the lightweight geopolymers were investigated as a function of the compositional parameters and of the amount of lightweight aggregate and foaming agent. Furthermore, considering that the performances of a fireproofing coating are temperature dependent, the variation of thermal conductivity and specific heat as a function of temperature were studied to provide data on the heat transfer to the substrate during heating. Thermogravimetric analysis confirmed the remarkable weight stability at high temperature of all the investigated geopolymers, which showed a total mass loss always lower than 8% at 900°C. Results showed that the use of expanded perlite as lightweight aggregate, combined with the foaming agent, allowed obtaining lightweight geopolymer mortars characterized by bulk density of 0.77 g/cm3 and thermal conductivity of 0.23 W/mK at T = 20°C. These features are comparable to the ones of commercially available cementitious-based fireproofing coatings. Results obtained from the experimental characterization were used to simulate the performance of the most promising LWG as fireproofing coating during a fire accident. A finite volume software set-up was used to simulate the temperature rise of steel components covered by different thickness (15, 20, and 25 mm) of the selected LWG, under cellulosic and hydrocarbon fire curve conditions. The performance of a commercial Portland cement-based fireproofing mortar (LWC) was also simulated for comparison. The simulations confirmed that the selected lightweight geopolymer mortar was effective in delaying the increase of the steel temperature, providing a protection for the steel substrate for at least 30 minutes in the case of cellulosic fire conditions. In addition, the thinnest layer (15 mm) of LWG coating considered in this study exhibited the same behavior of a 20 mm layer of cementitious-based product

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