Long distance propagation of shock waves in the open atmosphere

International audienceDespite significant progresses in the understanding of the formation and propagation of pressure waves in the open atmosphere in the past decades, experience form past accidents (AZF, Toulouse, 2001, Billy-Berclau, 2003 and even Buncefied 2005) reveals that overpressure levels may be greatly ill estimated. This is obviously a concern when the protection of citizens is concerned. There are some indications that both the topography and weather conditions may play a significant role but this remains rather qualitative and there is a need to clarify such points. In this paper, the results of a preliminary experimental campaign are presented in which up to 500 kg eq TNT was detonated in the open atmosphere and the pressure field measured up to 10 kms

Investigation on the diffraction of a medium scale gaseous deflagration pressure wave behind a protective wall

International audienceSEVESO industrial sites are suspected to produce major accidents, as for instance explosions, meaning that the disruptive effects of the blast wave may significantly impact the neighborhood. Despite effective mitigation measures may be taken, some residual risks exist which sometimes requires a protection of the buildings. In the specific case of blast, walls may be constructed to try and shelter important buildings. This kind of technique was developed decades ago in the pyrotechnical/ammunition industry for instance to avoid the transmission of an accidental explosion from a depot to the next one [1]. The protection is often a bund which characteristic sizes (thickness, height…) are much larger than that of the pressure wave. In the case of SEVESO industrial sites, the blast originates from a vapor cloud explosion, not from a detonation, so that not only the form of the pressure wave is different (“N” type rather than “triangular”) but also its duration, usually longer by orders of magnitude [2]. The duration of the wave might be hundreds of ms so that the wavelength of the wave amounts easily tens of m, larger than the characteristic dimensions of a bund. What kind of protection a blast wall would be able to offer in such circumstances? This specific aspect was investigated experimentally and a tentative interpretation is proposed using a CFD tool

Thermal history resulting in the failure of lightweight fully-wrapped composite pressure vessel for hydrogen in a fire experimental facility

We must improve our understanding of the thermal behaviour of composite gas storage in the event of fire in order to reduce the risk of bursting. In this research, results of pool fire tests were used to improve understanding of the failure mechanisms of epoxy carbon fibre composite pressure vessels with a polymeric liner (type IV vessel) designed for a working pressure of 70 MPa. The failure mode in a pool fire test depends on the storage design and on the initial pressure of the storage. For instance, for a 100 L type IV storage without any safety system, initial pressures of 70 MPa down to 52.5 MPa result in pressure vessels bursting, and initial pressures of 35 MPa down to 17.5 MPa lead pressure vessels to loss of liner tightness. The occurrence of one mechanism or the other is due to the predominance of either heat transfer through the wall, leading to a loss of tightness; or of the degradation of the materials, leading to bursting. Thermogravimetric analyses were carried out on the pressure vessel materials to determine the onset of degradation take during pool fire tests. The temperature measurements allowed for proper characterisation of the conditions leading to the loss of liner tightness. Temperature profiles were used to link the position of the composite degradation front to the loss of tensile strength leading to bursting

Resistance to explosion assessment of an electric transformer building

The ability of technical buildings to resist internal explosions produced by short circuits occurring in electrical transformers is an issue for the public authorities. Even if the probability of such an event is very low, the consequences can be significant and can easily put the surrounding public in danger due the blast, the projection of fragments and to the subsequent very toxic fire. The aim of this article is to investigate the consequences the blast on the structure of the technical building in which the transformer is located. The first part of this study deals with the estimation of the pressure load on the walls of the transformer’s building. A complete modelling of the phenomenology is proposed starting from the electrical energy delivered into the arc, its transformation into gases, the efforts applied through the liquid onto the casing of the container, the expansion of the gases inside the building, the blast wave produced and its interaction on the inner walls of the building. In particular, the characteristics (amplitude and duration) of the shock waves are evaluated using the modelling tool ‘DIFREX’, developed by INERIS. This tool considers the evolution of the shock waves intensity, during their propagation and their reflection on obstacles (like walls). The overpressure signals and their time evolution are calculated according to an optimized spatial discretization in order to get the worst case for the structure. The second part describes the modelling of the building structure using SAP2000 software in order to evaluate its dynamic behaviour and estimate the internal forces induced by the explosion. The structural behaviour depends mainly on the characteristic duration of the overpressure and the overall stiffness of the building. The calculation is performed according a dynamic transient analysis. The results in terms of displacement and the effect on the reinforcement are given

Fire risk on high-pressure full composite cylinders for automotive applications

International audienceIn the event of a fire, the TPRD (Thermally activated Pressure Relief Device) prevents the highpressure full composite cylinder from bursting by detecting high temperatures and releasing the pressurized gas. The current safety performance of both the vessel and the TPRD is demonstrated by an engulfing bonfire test. However, there is no requirement concerning the effect of the TPRD release, which may produce a hazardous hydrogen flame due to the high flow-rate of the TPRD. It is necessary to understand better the behavior of an unprotected composite cylinder exposed to fire in order to design appropriate protection for it and to be able to reduce the length of any potential hydrogen flame. For that purpose, a test campaign was performed on a 36 L cylinder with a design pressure of 70 MPa. The time from fire exposure to the bursting of this cylinder (the burst delay) was measured. The influence of the fire type (partial or global) and the influence of the pressure in the cylinder during the exposure were studied. It was found that the TPRD orifice diameter should be significantly reduced compared to current practice

Fire risk on high-pressure full composite cylinders for automotive applications

International audienceIn the event of a fire, the TPRD (Thermally activated Pressure Relief Device) prevents the high-pressure full composite cylinder from bursting by detecting high temperatures and releasing the pressurized gas. The current safety performance of both the vessel and the TPRD is demonstrated by an engulfing bonfire test. However, there is no requirement concerning the effect of the TPRD release, which may produce a hazardous hydrogen flame due to the high flow-rate of the TPRD. It is necessary to understand better the behavior of an unprotected composite cylinder exposed to fire in order to design appropriate protection for it and to be able to reduce the length of any potential hydrogen flame. For that purpose, a test campaign was performed on a 36 L cylinder with a design pressure of 70 MPa. The time from fire exposure to the bursting of this cylinder (the burst delay) was measured. The influence of the fire type (partial or global) and the influence of the pressure in the cylinder during the exposure were studied. It was found that the TPRD orifice diameter should be significantly reduced compared to current practice