Effect of ventilation procedures on the behaviour of a fire compartment scenario

This contribution presents a study on the consequences of applying ventilation procedures during a fire scenario involving a TPH/TBP pool fire in a ventilated enclosure. This research is addressed to fire safety in the nuclear industry in which ventilated enclosures remain a configuration frequently encountered. This work presents experiments comprising a 300 kW liquid pool fire in a 400 m3 vessel connected to an industrial ventilation system featuring one inlet and one exhaust branch. The investigated ventilation procedures consist in closing the inlet branch only or closing both inlet and exhaust branches. The analysis compares fire behaviour with and without the implementation of a ventilation procedure and points out the effects of said procedures on the combustion rate, fire duration and gas temperature within the vessel. It highlights pressure variations within the vessel when both the inlet and exhaust ventilation branches are closed. Conclusions provide practical answers that would be useful when designing appropriate ventilation strategies limiting fire hazards. © 2005 Elsevier B.V. All rights reserved

Relative effects of inertia and buoyancy on smoke propagation in confined and forced ventilated enclosure fire scenarios

In this study, we focus on smoke propagation in confined and forced ventilated enclosure fire scenarios as it is a source of possible hazardous situations. The objective of the present contribution is to investigate the effect of the three physical mechanisms (buoyancy, gas expansion and forced ventilation) on diverse examples of smoke flow through transfer elements. Three types of pool fire scenario have been considered with several transfer elements typical of nuclear industry. The first scenario is a fire in one ventilated compartment and the propagation means are the release of smoke through the ventilation ducts. The second scenario is a fire in one ventilated room connected by a doorway to another ventilated room. The smoke flow investigated is the flow at the doorway. The last scenario is a fire in a ventilated compartment connected to an adjacent room with leakages. The smoke flow considered is a smoke leakage. Each scenario and the smoke propagation are analysed on the basis of large scale representative fire tests performed during the PRISME project and numerical simulations with a zone-modelling code, SYLVIA of IRSN. The results show ventilation is the driving mechanism for smoke propagation in the one-room configuration whereas buoyancy plays the major role for the doorway flow. Finally, depending on the kind of leakages, mechanical ventilation can act on the buoyancy-induced smoke propagation. © 2013 Elsevier Ltd. All rights reserved

Pressure variations induced by a pool fire in a well-confined and force-ventilated compartment

International audienceThis paper investigates the pressure variations induced by a pool fire in a well-confined and force-ventilated enclosure. This study finds practical applications to fire safety in the nuclear industry in which some compartments are often highly confined and ventilated by means of a ventilation network. In this paper, the question is to study and understand whether the pressure effect could be high enough to cause fire barriers to fail (fire door, dampers, etc.) and/or to release radioactive material inside the nuclear facility in spite of the pressure drop cascade strategy usually considered. Relying on two sets of large-scale fire tests performed by IRSN, this work quantifies and discusses the impact of pressure effects caused by hydrocarbon pool fires on the fire compartment and on the ventilation network. Pressure histories are presented for experiments involving 0.3-3.1-MW liquid pool fires and a fire room connected to an industrial ventilation system that includes both inlet and exhaust branches. The analysis of experimental data is supported with a theoretical approach in order to describe in detail the physical mechanisms that contribute to pressure variations. Then, a parametric analysis allows us to determine the effects of the fire heat release rate and the air flow resistance inside the ventilation network on the pressure peaks. Finally, the last part of this paper focuses on a correlative approach to estimate the overpressure peak at fire ignition. © 2012 Elsevier Ltd. All rights reserved

Determination of the heat release rate of large scale hydrocarbon pool fires in ventilated compartments

This contribution deals with the experimental determination of the Heat Release Rate (HRR) of hydrocarbon pool fires based on Oxygen Consumption (OC) and Carbon Dioxide Generation (CDG) calorimetry. This methodology, initially developed for open atmosphere fires, is modified for fires in ventilated compartments. The fire tests considered are under-ventilated large scale hydrocarbon pool fires in one confined and mechanically ventilated room. The formulation of the HRR for compartment application is presented as well as the fire experiments, the facility and the measurement techniques. This study presents the methodology that leads to the determination of the HRR and discusses the results and features of this method. First, the results of the mass balances of all species and soot within the compartment are presented and discussed. These are key elements to validate the accuracy of the HRR determination. Then, the calculation of the heat release rate with the two methods, OC and CDG, are presented. The OC methods give higher amplitude than the CDG methods. The effects of CO and soot production on the HRR calculation are discussed. This analysis points out the different features of each method (OC and CDG) and thoroughly discusses their advantages and drawbacks. The overall analysis gives guidelines for fire HRR calculation for fires in ventilated compartments. © 2013 Elsevier Ltd. All rights reserved

Detailed description of the flow fields induced by a fire in a mechanically-ventilated compartment obtained using PIV

International audienceThis study analyses the performance of non-intrusive PIV (Particle Image Velocimetry) for the study of flows induced during a fire scenario in a mechanically-ventilated enclosure. PIV can be used to obtain detailed measurements for velocity fields in the enclosure and thus offer new experimental data for the understanding of the physical phenomena involved as well as to validate CFD simulation tools. The study is carried out on a reduced scale on an ethanol pool fire positioned in a ventilated enclosure. Several areas of interest are studied such as interaction between the fire plume and the ceiling, the flow under the ceiling and parietal flows. These zones can be analysed to obtain a picture of the global mean flow and associated velocity fields rarely reported in the literature. The influence of the fire heat release rate on the velocity fields is studied and highlights the design parameters

Experimental and numerical study on low-frequency oscillating behaviour ofliquid pool fires in a small-scale mechanically-ventilated compartment

International audienceThe unstable oscillatory behaviour, with frequency in the order of few mHz, that has been occasionally observedin mechanically-ventilated compartment fires, is studied experimentally and numerically. First, a series of experimentsusing a small-scale compartment have been conducted using heptane and dodecane as fuels. Resultsshow that unstable and stable combustion regimes can occur depending on fuel type, pool size, air renewal rateof the compartment (ARR), and ventilation conditions. For a certain range of these factors, unstable low-frequency(LF) oscillatory combustion, accompanied by thermodynamic pressure and ventilation flow rate variationsand displacement of the flame outside the pan, is observed. The occurrence and persistency of LF oscillationsresult from the competition between oxygen supply and fuel vapor supply due to the heat feedback fromthe flame and enclosure to the fuel tray. Whatever the fuel type, it is found that i) the range of ARR where LFoscillations appear and the oscillation amplitude increase with the pool size, and ii) the frequency increases,while amplitude decreases, with increasing ARR, independently of the pool size. It is also found that the moreflammable the fuel, i) the smaller pool size for which LF oscillations appear and the higher the frequency for thesame ventilation conditions, and ii) the wider the range of ARR where LF oscillations appear for a given poolsize. The effects of air inlet position and blowing direction on the oscillations properties is also investigated.Second, predictive CFD simulations have been performed using the in-house SAFIR software. Although SAFIRdoes not correctly describe the displacement of the flame outside the fuel pan, it satisfactorily reproduces the LFoscillatory fire behaviour, especially its dominant frequency. Information about inaccessible or difficult-tomeasurelocal quantities, such as the local evaporation rate, temperature and heat flux at the liquid surface, andspecies concentrations, are provided from the numerical simulation

OECD PRISME project: Fires in confined and ventilated nuclear-type multi-compartments - Overview and main experimental results

For more than five years (2006-2011), the OECD/NEA/CSNI PRISME fire research program were conducted in an international framework. It dealt mainly with smoke and heat propagation mechanisms in multi-compartment fire scenarios and with the consequences of fire on targets of interest (thermal stress on electrical cables and their potential malfunction). The PRISME project included several organizations from 12 OECD/NEA member countries: Belgium (TRACTEBEL-Suez, BEL-V), Canada (AECL), Finland (STUK, VTT), France (IRSN, EdF, DGA), Germany (GRS, iBMB, BfS), Japan (JNES), Korea (KINS), Spain (CSN), Sweden (Vattenfall Ringhals), UK (HSE), The Netherlands (VROM-KFD, NRG), and USA (NRC). As PRISME project leader, the French Institut de Radioprotection et de Sûreté Nucléaire (IRSN) carried out many fire experiments in confined and mechanically ventilated compartments representative of fire scenarios in the nuclear industry. These fire tests were performed in a large-scale facility, named DIVA, including five compartments connected to an industrial ventilation network. The design of this experimental facility can quite easily be fitted for various fire scenarios of interest in nuclear area and to comply with fire hazard expertise needs. During this PRISME project, five experimental campaigns (more than 35 large-scale fire tests) were performed from early 2006 up to mid-2011, named PRISME Source (one single room), PRISME Door (two or three rooms with doorways), PRISME Leak (two rooms linked with leakages) and PRISME Integral (three and four rooms with doorways). This paper presents a general summary of the PRISME project (description of the experimental facilities, matrix of experiments, experimental instrumentation used during the fire tests, main objectives of fire experiments) and focuses on some outstanding results. The experimental outcomes obtained during this PRISME project provides a better understanding and an increase of knowledge in fire development in confined and ventilated large-scale compartments representative of nuclear area. Moreover, they also contribute to the improvement of fire modelling and constitute a huge experimental database used to validate fire safety softwares (based on zone modelling, lumped parameter approach and CFD). © 2013 Elsevier Ltd. All rights reserved