Hugues Pretrel

Experimental Study of the Fire Mass Loss Rate in Confined and Mechanically Ventilated Multi-Room Scenarios

This paper presents an experimental study of the behaviour of the mass loss rate (MLR) of pool fires in mechanically ventilated compartments within the framework of fire research activities conducted at the French Institute for Radiological Protection and Nuclear Safety (IRSN). Two typical scenarios are investigated: the 1-room configuration and the 2-rooms configuration with an open doorway between the two rooms. This study is based on full scale tests carried out as part of the international OECD PRISME project (OECD: Organisation for Economic Co-operation and Development; PRISME: French acronym for “Fire Propagation in Elementary Multi-room Scenarios”). First the behaviours of the MLR for the two scenarios are presented independently. A comparison is then proposed that highlights the effect of the air change rate on the MLR. The analysis shows that the MLR depends on two effects: the oxygen concentration and a blowing effect towards the pool. For most tests, the effect of oxygen concentration is predominant and the MLR varies linearly with the change of oxygen concentration. For one test with the 2rooms scenario, the air flow at the door seems to induce higher oxygen level adjacent to the pool and the MLR is identical to that in the open air, albeit with an oxygen concentration below 21%vol; In this configuration, the air flow at the door may induce not only a locally higher oxygen level, but also a blowing effect that stokes the fire. This large-scale test campaign shows that the air flow around the pool is also an important parameter to predict the MLR.

Periodic puffing instabilities of buoyant large-scale pool fires in a confined compartment

This article presents an experimental study of the pulsating period of pool fires in a confined and ventilated compartment. Based on large-scale pool fire experiments, two modes of flame pulsation are identified. The first one is the common mode of flame puffing observed in an open atmosphere, and the second one is a perturbed pulsation mode induced by a hot vitiated environment. A description of these modes and their spectral analysis based on image processing are described. The second new mode differs from the common mode by a lower puffing frequency of the reacting gas phase. The effect of the pool diameter is analysed for the two modes.

Effect of vertical density stratification on the buoyancy-induced flow at a doorway opening

This study deals with the process of smoke filling in a compartment and the exhaust of smoke through a doorway located in a side of the enclosure. This configuration is a typical scenario of smoke propagation during a fire event in a compartment. This study focuses on the vertical temperature stratification in the smoke layer and its consequences on buoyancy flow induced at the doorway. From two theoretical approaches, considering or not considering the vertical temperature stratification in the smoke layer, this study highlights how vertical temperature stratification may modify the doorway flow. The first approach is a well-mixed description considering constant temperature and thus no thermal stratification in the smoke layer. The second one describes the vertical density stratification with multilayer approach. The results show that the vertical stratification is the consequence of the process of air entrainment within the plume. The consideration of temperature stratification in the smoke layer changes the prediction of the flow through the doorway. A sensitivity analysis points out how two variables (the initial buoyancy flux and the dimension of the enclosure) modify this influence. The discussion improves the understanding of the stratification in an enclosure and gives new insight into the predictions of smoke propagation for fire safety applications.