Numerical analysis of smoke layer stability

International audienceThe EGSISTES project is a global reflection about risk and dangerous phenomena relative to underground infrastructures. One category of risk identified for such an infrastructure is the fire and its consequences in terms of temperature and smoke propagation. In some situations, smoke stratification is used to ensure safety of people located inside the tunnel. In such a case, it must be ensure that smoke stay stratified even in the case of an aerodynamic perturbation such as a jet fan or vehicles presence. Two ways enable the improvement of the understanding of smoke behaviour in underground infrastructure: experiments and numerical approach. Both strategies are used complementary during the project. Experiments are achieved in the INERIS fire gallery while two CFD codes, FDS and Phoenics, based on two different approaches for turbulence modelling, are used. The first step consists in a comparison between experimental and numerical results on a configuration given as a reference. This reference case was chosen as the backlayering smoke layer establishment and stability. The numerical objective was to reproduce the length and thickness of this layer. After having shown that both codes should predict with a quite good accuracy the backlayering length, those two codes are used to study the influence of perturbation on the stratification stability. This study shows firstly that a jet located upstream the backlayering smoke layer tends to modify the smoke layer front but influences slightly the smoke layer near the fire. Secondly, in case of the presence of vehicles downstream the fire in a congested tunnel, the stratification is not altered just above vehicles but can be altered downstream these obstacles

PORTFOLIO MANAGEMENT OF INNOVATION FIELDS : APPLYING CK DESIGN THEORY IN CROSS INDUSTRY EXPLORATORY PARTNERSHIP

Our paper refers to an industrial practice based on an integrated theoretical framework of design, CK design theory (Hatchuel and Weil, 2002, Hatchuel and Weil, 2003, Hatchuel and Weil, 2008), to support people in management of innovation fields. This study is based on an empirical case in a new form of R&D partnerships, the Cross Industry Exploratory Partnerships. MINATEC IDEAs Laboratory® is composed of a broad scope of partners 2 which aims to co-explore opportunities of micronanotechnologies. The paper deals with a strategic design tool, OPERA, which has been experimented since 2007 and involved participation of design team work and powerholders. During two years, creative insights and projects of the two laboratory's major innovation fields have been collected and structured within CK theory. This tool permits power-holders to drive innovation projects by giving an overview of explored concepts (and still not explored), activation and production of competencies and knowledge.CK theory; innovative design; innovation partnership; OPERA; design theory; management of innovation

Dispersion in confined building : a coupled approach

International audienceModelling gas dispersion in mechanically ventilated building is a challenge for safety engineers. A leak in such an infrastructure can generate two different consequences: toxic effect or blast effect after a flammable vapour cloud ignition. In both case, it is important to be able to predict the gas behaviour using numerical tools in order to be able to design adapted ventilation systems. Gaseous products are generally stored under pressure that induces high velocity in case of release from the tank or following a line rupture. Considering this important pressure, the jet zone is a highly complex zone with a Mach number higher than 1 that induces shock waves. These waves correspond to discontinuity of the flow. After this jet zone, a transition region (air entrainment) is observed and can be characterised by the beginning mixture of the gas with air. This also corresponds to an expansion of the jet diameter inducing a velocity decrease. Finally, after this zone, the flow becomes governed by the ventilation system where the Mach number is lower than 1. To model gas dispersion in closed enclosure, CFD models can be used. Such codes enable to predict the different physical quantities in the whole domain along time. However, most of these codes are not able to model complex phenomena such as ones that characterised the jet region. CFD codes are able to capture such a complex physic require mesh in the jet zone that is not in accordance with the objective to model the whole infrastructure considering current computing limitations. To overcome this and making achievable such modelling, a coupled approach between a 1D jet model and a CFD code is proposed. The 1D model predicts gas behaviour in the jet zone while the CFD code describes the concentration and velocity in the whole domain. The FDS CFD code was used. This code is based on the LES approach for turbulence modelling. Such an approach is highly interesting for safety because it enables not to predict an average configuration but a realistic one. Because of the well known capability of this code for predicting smoke behaviour considering ventilation, it is useful to wonder about its capability to model gas dispersion in buildings. A comparison between FDS, coupled with the 1D model, results and experimental ones are given. The experimental results were obtained in an 80 m3 room equipped with a ventilation system in which ammoniac was injected. Two different ventilation regimes were used and concentrations were measured in several locations inside the room at different heights. Comparisons between experimental and numerical values shows a great agreement and leads to the conclusion that the FDS code is a pertinent tool for gas dispersion modelling in confined building when coupling this code with a 1D jet model

Comparison of the fire consequences of an electric vehicle and an internal combustion engine vehicle

International audienceSince energy storage systems represent key new technologies in the development of electric vehicles (EV), risks pertaining to them have to be examined closely. Lithium-ion (Li-ion) batteries powering EV contain highly energetic active materials and flammable organic electrolytes, which raise safety questions, different to conventional cars. In case of EV fire, concerns remain about batteries fire behavior, about their impact on the fire growth, about their fire-induced potential toxicity, especially in confined spaces and underground car parks and about their reaction with water in case of firemen intervention. Fire tests were therefore achieved for two French car manufacturers on two battery units, on a full battery pack, on an EV and on an analogous internal combustion engine (ICE) vehicle. Thermal and toxic threat parameters governing the fire risk were quantified. For this purpose, the heat release rate and the effective heat of combustion were determined to qualify the thermal impact whereas the main emitted gases governing the toxic potency of the fire effluents were measured. Fire consequences of an EV and the corresponding ICE vehicle were compared. This paper aims at presenting the main results of these fire tests

PORTFOLIO MANAGEMENT OF INNOVATION FIELDS : APPLYING CK DESIGN THEORY IN CROSS INDUSTRY EXPLORATORY PARTNERSHIP

International audienceOur paper refers to an industrial practice based on an integrated theoretical framework of design, CK design theory (Hatchuel and Weil, 2002, Hatchuel and Weil, 2003, Hatchuel and Weil, 2008), to support people in management of innovation fields. This study is based on an empirical case in a new form of R&D partnerships, the Cross Industry Exploratory Partnerships. MINATEC IDEAs Laboratory® is composed of a broad scope of partners 2 which aims to co-explore opportunities of micronanotechnologies. The paper deals with a strategic design tool, OPERA, which has been experimented since 2007 and involved participation of design team work and powerholders. During two years, creative insights and projects of the two laboratory's major innovation fields have been collected and structured within CK theory. This tool permits power-holders to drive innovation projects by giving an overview of explored concepts (and still not explored), activation and production of competencies and knowledge

Combustion rate of medium scale pool fire, an unsteady parameter

International audiencePool fire is a classical dangerous phenomenon that can occur in various infrastructures and generates different consequences. Several investigations were achieved to improve the understanding of this phenomenon from theoretical to experimental. Experimental studies have lead to a classification of fuel as a function of combustion rate. These tests are generally based on constant level fire with fuel feed at the bottom of the sample. Theoretical studies have detailed the fire heat release distribution and the impact on the liquid fuel. Based on these results, the expected evolution of the fire includes three main parts: the fire increase, a constant maximal heat release period and the fire decrease. If this evolution suits with external pool fire, behaviour of the liquid can be impacted by contextual configuration. In confined infrastructures, such as building or tunnels, the liquid fuel combustion velocity becomes an unsteady parameter and the heat release rate from the fire varies, and often a runaway phase of the reaction is observed. Because such fires could be used for demonstrating the efficiency of a ventilation system, the power release must be controlled. This may have an important impact on the design of a mechanical ventilation system or the fire resistance of the infrastructure. To control the released power of such a fire, it is important to have a good understanding of this diffusion flame influenced by the environment. Then, understanding the phenomena that occur in the fire region means characterizing: the radiative fraction, the thermal exchanges and the impact of the flow on the fire. Using the results obtain along several experimental campaigns, both confined and unconfined, that were achieved in INERIS concerning pool fire, the different physical parameters are discussed and confronted with theoretical one. This paper proposed a physical characterization that finally leads to a power control strategy for pool fir

Are the tunnel ventilation systems adapted for the different risk situations ?

International audienceThe ventilation design criteria for both road and rail tunnel is based on the design fire defined by the standards and the general knowledge about smoke propagation. The problem of such an approach is that it considers only the impact on the safety ventilation of the smoke propagation and dispersion inside the tunnel excluding other possible accident. However some other situations, such as toxic gas release, are possible and even if the aim is not to design the ventilation on other dangerous phenomena with a lower occurrence frequency, it must be ensure that the ventilation system does not increase the consequences of the accident. Mainly, the problem of toxic gas dispersion is pointed out in this paper. Because of the large variety of dangerous materials that can transit in tunnel, the probability of an accident that impacts a toxic transport cannot be neglected. In the worst case scenario, such as a massive release of high toxic gases, the ventilation is useless because of the toxic quantity that induces a large number of deaths inside the tunnel. However, when the toxic release is lower and ventilation can be used, having in mind that toxic gas is generally heavy gas or a cold gas, the behaviour will of course be different than the one of smoke and the ventilation system may not be adapted for such a situation. This case has scarcely been studied yet. In this study, both experimental approach and numerical tools were used to improve the global understanding of dense gas dispersion in underground infrastructure such as road tunnels. The experimental work was achieved in the INERIS fire gallery which represents a 50 m long 1/3rd scale tunnel using Argon. It was achieved for different leaks conditions in order to appreciate the dense gas natural behaviour. This work has also enabled the comparison between experimental work and CFD calculation with FDS code for the particular application of dense gas dispersion. . The work was extended to some other configurations and geometry in order to simulate real scale situation with different kind of gases : a highly toxic dense gas such as Chlorine, a light gas stored as a liquid at a very low temperature such as Ammonia, and a gas which remains liquid at ambient temperature and pressure and is drained into an evaporating pool such as Acrolein. This work will consider the natural behaviour of the gases and the influence of longitudinal ventilation both inside and outside of the tunne

An insight of combustibility induced safety issues pertaining to ionic liquids

International audienceThis study is a consolidated overview on explosion and fire safety issues pertaining to ionic liquids. Indeed safety performance of ionic liquids relating to physico-chemical hazards is very rarely investigated as it is often perceived as a non-existing issue due to the lack of traditional flashpoint for these liquids. It focuses on the experimental evaluation of the fire hazard of imidazolium, phosphonium and pyrrolidinium-based ionic liquids by use of the Fire Propagation Apparatus. It provides experimental data that can quantify the flammability of ionic liquids in all its aspects (ease of ignition, mass burning rate, heat release rate, fire-induced toxicity data...). A case study featuring a major failure in a process unit leading to a given fire scenario is also illustrated. This case study is examined in terms of fire induced toxicity by use of CFD modeling of fire product releases dispersion and using the concept of fractional effective concentration

New energy carriers in vehicles and their impact on confined infrastructures Overview of previous research and research needs

International audienceThe global warming debate forces the vehicle industry to come up with new environmentally friendly solutions. In 10 years time, or even faster depending on the pressure from different governments in particular in Europe, vehicles will not only use gasoline, diesel and LPG, but also CNG, Hydrogen, ethanol, DME and other bio-fuels, as well as batteries and fuel cells. This quick development and the diversity of new energy carriers can jeopardize the safety in underground infrastructures such as tunnels or car parks. This can cause a major drawback in the adoption of new energy carriers as regulators or operators may prohibit use of these vehicles in underground systems if no new relevant measures will be taken. Unclear situation will also affect the implementation of international policies aiming at reducing the environmental footprint and especially CO2 emission in road traffic. The problem became clear after a workshop with the vehicle industry, tunnel operators, authorities, and safety experts organised in November 2008 by L-surF Services with the support of ITA-COSUF, ECTP and HYSAFE. This workshop demonstrated that the construction sector lacks appropriate design data and tools as well as knowledge to build safe underground infrastructure compatible with a diversity of new and alternative energy carriers. Vehicle industry, infrastructure operators and regulators have not yet addressed this problem. In a first part, an overview of the regulatory situation regarding safety and security of the admission of new energy carriers for vehicles in underground infrastructures is presented. Then, a detailed review of previous relevant research projects performed makes it possible to formulate recommendations in terms of a strategic research & development agenda. The overview shows that it is necessary to develop an integrated risk assessment and management method specific for underground transport systems, metros and hubs in confined spaces taking into account the "emerging risk" aspects