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Summary: This paper presents a computational fluid dynamics (CFD)‐based modeling strategy for the prediction of cable tray fire development. The methodology is applied to a set of five horizontal trays (each 2.4‐m long and 0.45‐m wide) that are positioned with a 0.3‐m vertical spacing and set up against an insulated wall. Each tray contains 49 power PVC cables. Ignition is performed with an 80‐kW propane burner centrally positioned at 0.2 m below the lowest tray. A collection of four groups of cables per tray (made of one homogeneous material) is considered. These groups are separated by longitudinal slots of air to "mimic" their relatively "loose arrangement." The thermal properties and surface ignition temperature are estimated from cone calorimetry (CC). When the ignition temperature is reached, the cables burn according to a prescribed heat release rate per unit area (HRRPUA) profile obtained from CC, as is or in a modified shape. A realistic flame pattern is predicted. Furthermore, using only data from CC, the peak HRR is underpredicted, and the time to reach the peak is overpredicted. The proposed "design" for the modified HRRPUA CC‐profile significantly improves the results. [ABSTRACT FROM AUTHOR]

Fire safety analyses in nuclear power plants need to assess the heat release rate (HRR) of potential cable fires. This study deals with the FLASH-CAT model which assesses the HRR of a fire spreading over horizontal ladder cable trays. As part of the OECD PRISME-2 project, fire tests which involved horizontal trays supported by a wall, highlighted fast fire growth and large HRR peak. This study investigated the ability of the FLASH-CAT model to predict the HRR for such configuration. The first assessments of the PRISME-2 tests with the FLASH-CAT model significantly delayed the ignition and under-estimated the fire growth rate and the HRR peak. A video fire analysis method was developed and contributed to propose updated input parameters, such as the ignition time and the horizontal spread rate, for cable tray configurations with a wall. In addition, modifications in the model which affect the burning cable tray area and the local fire duration are also discussed. The assessments of the PRISME-2 experiments with the modified FLASH-CAT model and the proposed input parameters are consistent with the measured HRR. In addition, the modified model also gives acceptable predictions of the HRR for numerous tests of the CHRISTIFIRE programme. [ABSTRACT FROM AUTHOR]

The paper presents an application of video fire analysis (VFA) to a cable tray fire scenario, a scenario of interest to nuclear power plants where cables constitute a substantial part of the combustible load. Five horizontal trays, each 2.4 m long and 0.45 m wide, are positioned with a 0.3 m spacing (in the vertical direction) and set-up against an insulated wall. Each tray contains 49 power PVC cables of 13 mm outer diameter. Ignition is performed with an 80 kW propane burner centrally positioned at 0.2 m below the first (i.e. lowest) tray. Thanks to a flame detection algorithm, the VFA technique allows a reconstruction of the heat release rate (HRR) profile based on the estimated temporal evolution of flame and extinction fronts at the level of each tray. The obtained profile is generally in good agreement with the HRR measurements (from oxygen depletion calorimetry). However, the time to reach the peak HRR is overestimated by approximately 100 s and the peak HRR of 3 MW is underestimated by 17%. These results are nevertheless encouraging because they provide confidence in the flame spread measurements (which are estimated for the case at hand between 2 mm/s and 5 mm/s). Therefore, a systematic application of VFA to real-scale experiments is believed to generate a valuable set of data (e.g. flame spread rates) for the development of simplified modelling. [ABSTRACT FROM AUTHOR]

The objective of this work is to provide a 'support tool' to assess the burning rate of a pool fire in a well-confined and mechanically-ventilated room using a single-zone model based on conservation equations for mass, energy and oxygen concentration. Such configurations are particularly relevant for nuclear facilities where compartments are generally sealed from one another and connected through a ventilation network. The burning rates are substantially affected by the dynamic interaction between the fuel mass loss rate and the rate of air supplied by mechanical ventilation. The fuel mass loss rate is controlled by (i) the amount of oxygen available in the room (i.e. vitiation oxygen effect) and (ii) the thermal enhancement via radiative feedback from the hot gas to the fuel surface. The steady-state burning rate is determined by the 'interplay' and balance between the limiting effect of oxygen vitiation and the enhancing effect of radiative feedback. An extensive sensitivity study over a wide range of fuel areas and mechanical ventilation rates shows that a maximum burning rate may be obtained. For the studied HTP (Hydrogenated Tetra-Propylene) pool fires, the maximum burning rate is up to 1.75 times the burning rate in open air conditions. [ABSTRACT FROM AUTHOR]

The potential of the concept of combining video data analysis and numerical simulations for numerical fire forecasting is illustrated for the case of a burning sofa in an ISO room. The fire is monitored by means of a video camera. The temporal evolution of smoke layer height, flame height and flame width are obtained from the real-time video data analysis. The fire heat release rate, estimated from the flame height and width, serves as input for the numerical simulations. The two-zone model approach is adopted, because the calculations are very fast. This is necessary for forecasting: time scales in fire development are in the order of seconds (minutes), not hours (which are typical calculation times in CFD simulations). Data assimilation with real-time adjustments according to sudden changes in the fire development as observed, improves the predictions by the two-zone model and allows to make a forecast of the fire development and possible subsequent hazards, in terms of evolution of smoke layer height and temperature. [ABSTRACT FROM AUTHOR]

The present paper studies the fire-induced pressure evolution in an air-tight compartment. Two cases with different sizes (i.e., 0.3 m × 0.3 m and 0.5 m × 0.5 m) of square methanol pool fire are considered. Repeated tests were performed for each case, leading to a total of four fire experiments. The leakage of the compartment is measured under different pressure conditions in order to obtain the relationship between the leakage and the pressure increase. The pressure inside the compartment reaches peak values of 133 Pa and 697 Pa for the small and the large pool fire, respectively. Simulation results using the Fire Dynamics Simulator (FDS) 6.5.3 match well with experiments. The simulated leakage flow rates, which reach values up to 65 m3/h and 200 m3/h, respectively, depend on the pressure variation and leakage settings. The pressure rises strongly in the growth phase of the fire, in line with a rapid increase in fire heat release rate. The gradually increasing heat losses subsequently lead to a decrease in pressure. [ABSTRACT FROM AUTHOR]

Computational Fluid Dynamics (CFD) simulations of fire-induced pressure and ventilation flow in a mechanically-ventilated air-tight compartment, representative of a passive house, are presented. Experiments conducted by University of Mons are used to assess the results. The simulation heat release rate is prescribed based on experimental measurements. The experimental duct flow rate is about 80 m3/h. Two methods are used to meet the aforementioned value in simulations: 1) by modeling the actual fan curve and dampers, and 2) by modifying the fan curve to avoid simulations of dampers. The combination of real fan curve and dampers provides better results. The simulations reproduce well the pressure profile (maximum 433 Pa) and the duct flows. The simulated reverse inlet flow and increased outlet flow rates reach values of 157 m3/h and 165 m3/h, respectively. Besides, the fire-induced pressure is high enough to hinder evacuation and fire rescue operations due to the impossibility of opening inward-open doors. Moreover, the adjacent room pressure also reaches a high level. Reducing the gap area between rooms significantly reduces the adjacent room pressure, but leads to an increase of the fire room pressure. Temperature deviations are observed and are improved by modeling a more realistic fire source. [ABSTRACT FROM AUTHOR]

The paper presents a numerical study on an 18 cm-diameter liquid pool fire in a reduced-scale and mechanically-ventilated enclosure. The enclosure walls are made of a calcium silicate layer and a steel layer on five sides, the remaining sidewall is made of heat-tempered glass. The ventilation system is extracted mechanically with free air inlet. Three air renewal rates (ARR) and open atmosphere conditions are considered in the numerical study. Computational Fluid Dynamics (CFD) simulations are carried out with Fire Dynamics Simulator (FDS 6.7.5). The default evaporation model in FDS (i.e., forced convection approach) is compared to a natural convection approach implemented in the source code. The results show that the oscillatory combustion, occurring at ARR = 15 h−1, is best captured by the natural convection approach. It is also found that prescribing the fuel Auto-Ignition Temperature (AIT) is important to capture the fire oscillations and (local) flame quenching. At ARR = 8 h−1, extinction occurs. It is found that prescribing the fuel AIT allows to prevent spurious oscillatory combustion. At ARR = 22.5 h−1, there is a stable steady-state burning regime for which (as well as for open atmosphere conditions) prescribing the fuel AIT is not crucial. • Fire burning regimes are well predicted in a wide range of ventilation conditions. • Oscillatory combustion is captured by natural convection for evaporation modeling. • Prescribing Auto-Ignition Temperature is important in capturing fire oscillations. • Prescribing AIT prevents spurious fuel re-ignition in under-ventilated conditions. [ABSTRACT FROM AUTHOR]

Corner fires are known to spread more intensely in comparison with single wall fires. In view of the challenges associated with prediction of such fire behavior, the fire growth in a corner configuration of Medium Density Fiberboard (MDF) panels is investigated to provide a set of experimental data, performing Single Burning Item (SBI) tests. First, though, test results with inert calcium silicate panels are discussed for three values of HRR (10, 30 and 55 kW), allowing to address the main physics involved. The experimental data for 30 kW, the default SBI HRR, is used for detailed discussion of the observations. The SBI testing methodology, materials, and set-up are described. The results of total Heat Release Rates (HRR) and Smoke Production Rates (SPR), as well as the panel temperatures and total heat fluxes at several characteristic locations are analyzed. Moreover, the puffing frequency of the corner fire is characterized thanks to Video Fire Analysis (VFA) of the experimental footage. Additionally, flame heights are discussed, including the concept of mirroring. A new correlation for mean flame height is introduced, using the hypotenuse of the triangle as characteristic length for entrainment of air into the fire plume, and expressing that the flame height increases proportional to the square root of the fire heat release rate. The 30 kW propane burner of the standard SBI test is shown to feature a mean flame height of nearly 0.9 m and a puffing frequency of 2  ±  0.3 Hz, and an average total heat flux exceeding 44 kW/m 2 near the burner early on in the test. The completeness of the dataset is expected to be useful for testing and development of CFD codes for corner fire scenarios. [ABSTRACT FROM AUTHOR]

Having explained the characteristics of a corner fire in the configuration of Single Burning Item (SBI) test in Part I [1], the results of three flame spread experiments conducted with Medium Density Fiberboard (MDF) panels are discussed. The fire growth, in terms of flame heights and spread, is examined from two different angles visually and through Video Fire Analysis (VFA) with a flame detection algorithm. Total Heat Release Rates (HRR) and Smoke Production Rates (SPR), as well as total heat fluxes at several characteristic locations, are presented. Moreover, temperature evolutions are discussed for multiple locations and through the thickness of the panels. Also the backside temperatures, important as boundary condition for numerical simulations, are reported. The corner fire tests with MDF panels yield an average peak HRR of 151 kW and an average total heat flux exceeding 60 kW/m 2 close to the burner, with average flame heights surpassing 1.5 m in about 60 s. [ABSTRACT FROM AUTHOR]

The paper presents experimental results indicating the influence of the fire heat release rate (HRR) evolution on the fire-induced pressure variation in air-tight compartments, which increasingly appear in modern buildings. The fire evolution is stipulated according to a power law with variations in fire growth/decay rate coefficient, maximum steady state HRR, fire growth/decay exponent and fire duration. It is illustrated that the higher the fire growth/decay rate coefficient, the higher the over-pressure/under-pressure peaks become. The peak values approach a maximum level when the fire growth/decay rate coefficient exceeds a certain level (0.0926 kW/s2 in the present cases). Besides, the over-pressure and under-pressure peak values increase monotonously with the increase of the maximum steady state HRR. For cases with fire growth/decay exponent below 1, the pressure reaches peak values before the HRR reaches a steady state (maximum value or zero) because the net heat gained per unit time in the gas phase already reaches its peak values then. In cases with fire growth/decay exponent above 1, the pressure reaches peak values at the moment where the HRR reaches the steady state. Finally, in one test low-frequency oscillatory behavior is illustrated with gaseous fuel during the well-ventilated phase. • Comprehensive studies are conducted by parameterizing the heat release rate. • Increase in fire growth/decay rate causes the pressure to rise to a plateau level. • Higher maximum heat release rate leads to higher over-pressure and under-pressure. • The fire growth/decay exponent affects pressure variation and under-pressure peak. • Oscillatory behavior is reported with gaseous fuel in the well-ventilated phase. [ABSTRACT FROM AUTHOR]

Air cavities and gaps between material layers are common in construction systems, e.g. ventilated façades. Air cavity may provide a pathway for smoke and flame spread in case of fire. Performing physical testing to investigate different systems and fire scenarios is resource demanding. Fire Dynamics Simulator (FDS version 6.7.0) was used to simulate fire driven flow between two parallel vertical walls. Flame heights, thermal impact to the interior wall surface and upward flow velocities were predicted with FDS and compared with experimental results. The fire source was a propane burner with 8 × 391 mm2 gas outlet area. Heat release rates were 6.6 kW and 12.4 kW and the distance between the parallel walls was 40 mm. Two different convective heat transfer coefficient sub grid scale models available in FDS were investigated. In this study the cavity width to mesh cell size ratio was equal or above 10, resulting in good predictions of flame heights, upward flow velocities and wall temperatures. 2 mm grid resulted in 25% lower HRR in locations near the burner gas inlet, compared to 4 mm grid, indicating the importance of well resolved gas outlet boundary. • Cavity width divided by mesh cell size should be greater than 10 in FDS simulations. • Predicted flame heights and flow velocities corresponded well with experiments. • Refining the grid in FDS resulted in lower cumulative HRR in the flame region. • FDS models for heat transfer at surfaces must be revised for transitional flows. [ABSTRACT FROM AUTHOR]

Numerical simulations are performed to investigate the classical compartment fire problem involving a single door opening. Three different configurations were considered, namely a full-scale (ISO 9705), an intermediate and a small-scale enclosure with various opening heights and widths. A large number of numerical simulations was carried out using the CFD code Fire Dynamics Simulator (FDS)(version 6.7.0). Based on the variation of the average temperature inside the compartment, three combustion regimes were identified namely well-ventilated, transitional and under-ventilated regime. This variation also allowed us to identify the boundaries between regimes. Furthermore, by adopting a non-dimensional representation of the fire heat release rate inside the compartment as a function of the Global Equivalence Ratio (GER), a clear demarcation between these combustion regimes was obtained. A linear correlation has been established between the maximum heat release rate inside the compartment and the ventilation factor. The latter is expressed as Q ̇ i n max = 850 A H. A linear relation between the maximum air flow rate m ̇ i n and the ventilation factor A H was found, i.e. m ̇ i n max = 0.46 A H where A is the door surface area and H its height. [ABSTRACT FROM AUTHOR]

The corner fire characteristics with two inert walls are compared against those with one or two combustible corner walls through a set of standard Single Burning Item (SBI) tests. The study examines how the corner fire behavior is affected by flame spread over one or two walls. In the case of flame spread over one corner wall, the inert side is a Calcium Silicate (CS) panel. As for the combustible wall, two different materials have been tested, namely, plywood and Medium-Density Fiberboard (MDF) panels. The results indicate that the simultaneous burning of two panels in the corner geometry increases the Heat Release Rate (HRR) contribution of each panel by 45–50%. This is because the burning of one corner wall increases the temperatures on the adjacent wall significantly, occasionally by more than 200 °C, and increases the heat fluxes on both corner walls at the same time, sometimes by nearly 20%. The results of HRR, Smoke Production Rate (SPR), flame heights, pyrolysis front propagation, panel temperatures, and total heat fluxes at several characteristic locations are presented. [ABSTRACT FROM AUTHOR]

This paper presents a detailed experimental and numerical study on the interaction, at a reduced scale, between a turbulent buoyant propane flame of about 15.5 kW and a water mist spray with a flow rate of 0.43 L/min from a nozzle positioned at 1 m above the burner. The water spray has been characterized experimentally without a fire, by measuring the water mass flux and droplet size distributions at the level of the burner surface. The whole assembly was installed under a hood and the following three parameters were measured: (1) the chemical heat release rate (HRR) (using the oxygen consumption method), (2) the rise in gas temperature at the top, and (3) the radiative heat flux at 0.72 m from the axis of the burner and at a height of 0.05 m. Reductions of about 40% and 30% were recorded for, respectively, the gas temperature (in the hood) and the radiative heat flux, while the chemical HRR did not change. Computational Fluid Dynamics (CFD) simulations with the Fire Dynamics Simulator (FDS, version 6.7.0) predicted relatively well the gas temperature, without a reduction in the HRR, but, in contrast to the experiments, the radiative heat flux did not change. • A gas analysis system is used to accurately characterize the heat balance. • The cooling power of the spray is estimated using a single temperature measurement. • The water spray is well characterized experimentally and numerically. • The cooling power of the spray is underpredicted by about 34%. • The reduction in the radiative heat flux to the surroundings has not been predicted. [ABSTRACT FROM AUTHOR]