An analysis of compartment fire doorway flows

A mathematical study is made to compute the doorway flow behavior due to fire in a room. Two approaches were taken, first a model attempting to include the effect of fire entrainment and vent mixing; second was a model based on an ideal point source plume fire—both in the zone model concept. Limiting analytic results were found for the latter to give insight into the physics. The results were compared to available flow data, and an approximate formula was developed to predict the doorway mass flow rate to within 20% for a wide range of fire conditions. CFD computations were also explored using FDS. Results are compared from FDS and the zone model with experimental data for a wide range of variables.     

The Response Time of Different Sprinkler Glass Bulbs in a Residential Room Fire Scenario

The response time of fire sprinklers is essential for their performance, especially in applications where life safety protection is desired. The earlier the sprinkler activates, the smaller the size of the fire. Most commercial residential sprinklers are fitted with 3 mm, 68°C glass bulbs. However, thinner sprinkler glass bulbs with lower operating temperatures are available. The aim of this study was to determine the response time—and the corresponding heat release rate—of different glass bulbs in a residential room fire scenario. A series of tests were conducted inside a compartment measuring 3.66 m by 3.66 m having a ceiling height of 2.5 m. The compartment was either enclosed or had two walls removed to provide a more ventilated scenario. A propane gas burner was positioned at one of the corners. The mass flow rate of the gas was controlled such that either ‘slow’, ‘medium’ or ‘fast’ fire growth rate scenarios were simulated. In each test, nine Response Time Index (RTI) and operating temperature combinations were tested. Each test was replicated three times. In addition, two commercial fire detectors were tested. The results show that the fire is considerably smaller upon activation with a combination of a low RTI and a low operating temperature, as compared to the 3 mm, 68°C glass bulb typically used for residential sprinklers. The operating temperature proved to have a larger impact on the results than the RTI. The heat from the fire was typically detected by the fire detectors prior to the activation of the sprinkler glass bulbs, especially for the ‘slow’ and ‘medium’ fire growth rate scenarios.     

Numerical simulation of the penetration capability of sprinkler sprays

Computational models have been utilized to investigate the penetration capability of sprinkler sprays directly above a fire source with respect to water flow rate, spray drop size, and spray momentum. The spray models are generated by assigning a representative drop size, mass flow rate, discharge speed, and discharge angle for each of 275 trajectories in such a way that they produce computed results which match the measured water flux distribution and spray momentum in the absence of a fire. The spray/fire plume interaction models are created by combining the spray models using a Lagrangian particle tracking scheme with free-burn fire plume models. Actual delivered densities and penetration ratios are computed through the interaction simulations at six flow rates, three fire sizes, and two ceiling heights. Drop sizes and spray momentum at two flow rates are increased by 25 and 50% from the original values without changing the other spray characteristics in order to investigate the effects of each parameter on penetration capability independently. The study indicates that there is an optimal flow rate for a given sprinkler that gives the highest penetration ratio within a practical flow range. It is also shown that increasing drop size is a much more effective way for obtaining a higher penetration ratio compared to increasing spray momentum.     

Development of a computational model simulating the interaction between a fire plume and a sprinkler spray

Numerical simulations to predict actual delivered densities (ADDs) of early suppression fast response (ESFR) sprinklers in heptane spray fire scenarios were sought. First, in order to supply input data for the development of numerical models and experimental data for validation of the models, four sets of measurements were carried out: the momentum and water flux distribution of two ESFR sprinkler sprays without fire; the temperature and axial velocities along the axis of free-burn fires; and the actual delivered densities. Then, a numerical model for a sprinkler spray was completed by assigning the representative drop size, mass flow rate, discharge speed and discharge angle of 275 trajectories in such a way that they produced reasonable agreement with the measured water flux distribution and spray momentum in the absence of fire. A numerical model for the free-burn fire was created by assigning a heat flux distribution on a horizontal surface and simulating a central, vertical air jet used in the experiment, varying parameters until a reasonable match was established with the measured temperatures and the axial velocities along the axis. Numerical computations of actual delivered densities were carried out by combining the water spray model and the free-burn fire model for different water flow rates of the sprinklers. The ADDs obtained from the simulations compared reasonably well with those from the measurements.     

Correlation equations on fire-induced air flow rates through doorway derived by large eddy simulation

Air flow rates through a doorway are important in modelling compartment fires. The ventilation factor is regarded as a key parameter and numerous efforts have been made on deriving the correlation of air flow rates with it. Most of the correlation expressions reported in the literature were derived empirically from experiments. The results might be different if the fire geometry, fuel type and ambient conditions are changed. Further, the heat release rates measured in most of the experiments were based on the mass loss rate of fuel, not by the oxygen consumption method. There might be some deviations from the actual heat release rates.Computational fluid dynamics (CFD) is now a practical tool in fire engineering. Aerodynamics through a doorway induced by a compartment fire can be simulated accurately. Factors which are difficult to control in experiments but affecting the doorway flow can be studied.The Fire Dynamics Simulator (FDS) developed by the National Institute of Standards and Technology, USA, is one of such CFD software. This is a product achieved from long-term research on developing a CFD model capable of carrying out fire simulations. This model is different from the others based on the Reynolds Averaging Navier–Stokes equations method. Physical processes occuring at small length and time scales were modelled by large eddy simulation (LES). Larger length scale on buoyancy-induced turbulence flow structure was computed directly from the set of equations with acoustic waves filtered out. The new version of this CFD package, FDS version 3.01, is now applied to derive equations on doorway flow rates induced by a fire. Results will be compared with those reported in the literature.     

A general formula for the prediction of vent flows

A new formula for fire-induced wall vent flow rate is developed based upon a theoretical derivation and mathematical fit to data. Previous research had developed a formula of mass flow rate for fire-induced doorway flows only. Here it is extended to include window flows. A theoretical model based on an ideal point source fire plume is used to guide the form of the empirical correlation. A thorough examination concerning the difference between the window and doorway flow modes is conducted. Both sill height and width of the windows pose key influence on the formula. The two vent configurations are merged into one equation. The results were compared to available flow data and shown to be within 15% accuracy for a wide range of fire conditions.     

Energy balance in a large compartment fire

The National Institute of Standards and Technology (NIST) and the Nuclear Regulatory Commission (NRC) are collaborating to assess and validate fire computer codes for nuclear power plant applications. This evaluation is being conducted through a series of benchmarking and validation exercises. The goal of the present study was to provide data from a large-scale fire test of a simulated nuclear power plant cable room. The experiments consisted of a hydrocarbon spray fire with a 1 MW heat release rate, burning in a single compartment 7 m wide, 22 m long, and 4 m high. Measurements included the vertical temperature profiles, heat flux to the compartment surfaces, the velocity and temperature at the compartment doorway, and the total heat release rate. From these measurements, an energy balance was considered, in which it was determined that nearly 74% of the fire's energy went to heat compartment surfaces, 22% escaped through the doorway, and 4% heated gases in the compartment.     

Toward predictive simulations of pool fires in mechanically ventilated compartments

The objective of this work is to propose an effective modeling to perform predictive simulations of pool fires in mechanically ventilated compartments, representative of a nuclear installation. These predictive simulations have been conducted using original boundary conditions (BCs) for the fuel mass loss rate and the ventilation mass flow rate, which depend on the surrounding environment. To validate the proposed modeling, the specific BCs were implemented in the ISIS computational fluid dynamics (CFD) tool, developed at IRSN, and three fire tests of the PRISME-Door experimental campaign were simulated. They involved a hydrogenated tetrapropylene (HTP) pool fire in a confined room linked to another one by a doorway; the two rooms being connected to a mechanical ventilation system. The three fire scenarios offer different pool fire areas (0.4 and 1 m²) and air change rates (1.5 and 4.7 h⁻¹). For the one square meter pool fire test, the study presents, in detail, the effects of the boundary conditions modeling. The influence of the ventilation and fuel BCs is analyzed using either fixed value, or variable, function of the surrounding environment, determined by a Bernoulli formulation for the ventilation mass flow rate and by the Peatross and Beyler correlation for the fuel mass loss rate. The results indicate that a full coupling between these two BCs is crucial to correctly predict the main parameters of a fire scenario as fire duration, temperature and oxygen fields, over- and under-pressure peaks in the fire compartment. Variable BCs for ventilation and fuel rates were afterward both used to predictively simulate the fire tests with a pool surface area of 0.4 m². The predicted results are in good agreement with measurements signifying that the model allows to catch the main patterns characteristic of an under-ventilated fire.     

Experimental study of natural roof ventilation in full-scale enclosure fire tests in a small compartment

An analysis of full-scale fire test experimental data is presented for a small compartment (3×3.6×2.3 m). A square steady fire source is placed in the center of the compartment. There is an open door and a horizontal opening in the roof, so that natural ventilation is established for the well-ventilated fire. A parameter study is performed, covering a range of total fire heat release rates (330, 440 and 550 kW), fire source areas (0.3×0.3 m and 0.6×0.6 m) and roof ventilation opening areas (1.45×1 m, 0.75×1 m and 0.5×1 m). The impact of the different parameters is examined on the smoke layer depth and the temperature variations in vertical direction in the compartment. Both mean temperatures and temperature fluctuations are reported. The total fire heat release rate value has the strongest influence on the hot smoke layer average temperature rise, while the influence of the fire source area and the roof opening is smaller. The hot smoke layer depth, determined from the measured temperature profiles, is primarily influenced by the fire source area, while the total fire heat release rate and the roof opening only have a small impact. Correlations are given for the hot smoke layer average temperature rise, the buoyancy reference velocity and the total smoke mass flow rate out of the compartment, as a function of the different parameters mentioned. Based on the experimental findings, it is discussed that different manual calculation methods, widely used for natural ventilation design of compartments in the case of fire, under-predict the hot layer thickness and total smoke mass flow rate, while the hot layer average temperature is over-estimated.     

Temperature and velocity correlations in room fires for estimating sprinkler actuation times

Automatic sprinklers are increasingly used in residential occupancies to provide active fire protection. These sprinklers, known as quick response and residential sprinklers, may be located either at the ceiling (pendent-style) or on a wall (sidewall-style). Though several fire models are available for estimating actuation times for sprinklers located under unobstructed ceilings, these use engineering correlations that do not apply to residential-sized rooms. Thus, data are needed for estimating sprinkler actuation times for residential occupancies.This paper reports on fire tests that were conducted in various sized rooms to obtain temperature and velocity data for 73 kW, 100 kW, and 147 kW fires. The data were then used to develop nondimensional correlations for temperature and velocity at the sprinkler locations. The temperature data revealed a significant temperature transient in the hot gas layer, and thus a nondimensional correlation describing the transient phenomenon was developed. These correlations compared reasonably well with experimental data, and they were used to estimate the sprinkler actuation times. The estimates were in reasonable agreement for the pendent sprinkler, except for the smallest fire in a 4.27 m by 4.27 m occupancy. The estimates for sidewall sprinkler acuation were significantly lower than experimental values. This may have been due to the sprinklers' heat losses, which were not accounted for in the calculation.     

Questioning the linear relationship between doorway width and achievable flow rate

This paper challenges the currently assumed linear relationship between doorway width and achievable flow. The current view is seen as a simplification that may lead to an overly optimistic view of the achievable flow rates. Analyzed data are presented in order to demonstrate the impact that the actual use of the doorway and its design can have upon the flow rate generated. These data are then supported by the use of numerical simulations to demonstrate the impact that this overestimation can have upon the design process. It is contended that the specific flow rate assumed for a doorway should take into consideration not only its width, but also the design of the doorway (i.e., the opening and closing mechanism) and how evacuees behave in response to it. The issues raised have implications for the governing codes/regulations, engineering guidance and on the development of future computational egress models.     

Prediction of temperature and velocity profiles in a single compartment fire by an improved neural network analysis

A novel hybrid Artificial Neural Network (ANN) model, denoted GRNNFA, has been developed for fire studies. The major feature of the model is its ability to work in a noisy environment, which is usually the case with fire experiment data. The GRNNFA model is applicable in the determination of the location of the thermal interface in a single compartment fire. The performance of the GRNNFA has been proven to be comparable to that of the Computational Fluid Dynamics (CFD) model. In addition, the computational speed of the GRNNFA model is much faster than that of the CFD model. However, the original GRNNFA model is only capable of handling the training samples with scalar output. This shortcoming restricts the application area of the model. Hence, this paper presents a modification of the original GRNNFA model for multi-dimensional prediction problems. It also demonstrates the first application of ANN techniques to predicting the velocity and temperature profiles at the center of the doorway in a single compartment fire. These profiles are commonly used to benchmark the performances of CFD models. They are employed in this study to evaluate the performance of the modified GRNNFA model. The predicted profiles are compared with the experimental results and the results simulated by the CFD model. These results show that the prediction errors of the GRNNFA model are less than those of the CFD model in actual application.     

自动喷水灭火系统对地铁烟气特性的影响

以岛式地铁站台为研究对象,利用FDS 软件建立火灾数值模型,模拟计算有、无自动喷水灭火系统对地铁站台中部行李火灾烟气特性的影响。结果表明：有自动喷水灭火系统时,地铁站台烟气蔓延速度及烟气温度会得到抑制;自动喷水灭火系统对烟气中CO 质量浓度及烟气能见度影响不大;烟气中CO 质量浓度在火源附近区域变大,远离着火源区域变小;烟气能见度在火源附近区域会降低,远离火源区域会提高。     

水喷淋控制下小室火灾的数值模拟研究

研究了水喷淋控制下对小室火灾发展过程的影响，结合一安装有水喷淋的实体小室，采用数值模拟方法进行了初步分析，设计了没有喷淋、0．1MPa喷淋控制和0．2MPa喷淋控制等三种工况。结果表明，水喷淋的启动，虽然可以控制火灾的发展，降低小室内的烟气温度，但也会增加烟气的生成量，使溢出的烟气增加。同时，水喷淋的压力增加，小室内的烟气温度继续下降，CO、炭黑以及水蒸气的生成量也会随之增加。这些都对大空间的人员安全疏散以及大空间整体的消防安全带来很大的影响。     

Limited-water-supply sprinklers for manufactured (mobile) homes

A prototype limited-water-supply (LWS) sprinkler has been developed for manufactured (mobile) homes in a research program sponsored by the United States Fire Administration. The LWS sprinkler is designed to be installed at a 2.44 m (8-foot) spacing and to have a total water supply of 380 (100 gallons). The installation spacing was determined in a series of freeburn fire tests that indicated that the heat release rate at sprinkler actuation could be halved by reducing the sprinkler spacing from 3.66 m to 2.44 m (12 feet to 8 feet). A series of eight fullscale fire tests, including a corner living room scenario similar to that used in the Los Angeles Residential Test Program, was conducted to evaluate the performance of the prototype sprinkler. In five of the tests, room tenability was maintained during the 10-minute period following the actuation of a single sprinkler at a flow rate of 38 pm (10 gpm). In three tests, tenability was maintained with multiple sprinkler actuation (2 or 3 sprinklers) and a total system flow rate of 49 pm (13 gpm). The spray of the sprinkler was characterized in terms of its water flux distribution and drop size distribution. The thermal sensitivity requirements of the sprinkler are to be based upon RTI, C, and temperature rating, which would ensure that sprinkler actuation would occur at fire sizes comparable to those encountered using the prototype LWS sprinkler in this study.     

Smoke production,radiation heat transfer and fire growth in a liquid-fuelled compartment fire

A detailed investigation is described of the interaction between fire development, smoke production and radiative exchange in a half-scale ASTM compartment in which the source is a heptane pool fire. Measurements of heat flux, fuel mass loss rate, ventilation flow rates, temperature and soot volume fraction are reported for the compartment for varying door widths. Data from the compartment are compared with open pool fire measurements using the same equipment. The confined geometry is shown to exert a strong influence on pool fire development and suggests that considerable caution is needed in employing open pool fire data as boundary conditions for CFD simulation. Numerical simulations based on the direct calculation of radiative exchange between the liquid fuel surface, the smoke-laden environment and bounding walls do reproduce the behaviour observed when combustion, soot production and radiation are modelled in detail and finely resolved spatially.     

Simplified Calculation Method for Determining Smoke Downdrag Due to a Sprinkler Spray

A simplified method has been developed to predict smoke behavior subject to a sprinkler spray. The method considers whether downdrag is likely to occur and the distance that smoke is then pulled down should downdrag be present. The method is validated using third party experimental data. Empirical equations are applied in the calculations to determine the heat loss from a smoke layer due to the sprinkler spray and therefore the smoke layer temperature. Comparative results show that the simplified method might expect the onset of smoke downdrag regardless the difference in temperature predictions. The empirical equation to predict the penetration depth of downdrag smoke is based on previous research and compared with third party experimental data. The predicted depths are acceptable for engineering use. For a 15 mm nominal sprinkler the water flow rate that leads to the onset of downdrag for typical smoke layers up to 2 m in depth is less than 100 L/min which leads to an operating pressure being less than 0.16 MPa. Experimentally data for sprinklers other than the 15 mm nominal sprinklers are unavailable and therefore the method should be used with care for any other sprinkler.     

Development and evaluation of two new droplet evaporation schemes for fire dynamics simulations

The evaporation of sprinkler droplets is an important phenomenon in fire simulations both for heat removal from the gas and for heat removal from surfaces. In this paper, we address the problems of potential numerical instability and super-saturation that may occur in explicit time integration of the droplet equations. Two novel numerical approaches are developed and evaluated. The first is based on an analytical solution that relaxes the cell composition and temperature toward the equilibrium values. The second method is an implicit solution to the droplet equations. The two approaches are implemented in the Fire Dynamics Simulator (FDS) and verified and validated using both single droplet and practical sprinkler calculations. Ultimately, the implicit approach is deemed the most cost effective for practical fire simulations.     

CFD and experimental studies of room fire growth on wall lining materials

CFD simulation and experimental tests have been carried out to study the room corner fire growth on combustible wall-lining materials. In the CFD simulation, the turbulent mass and heat transfer, and combustion were considered. The discrete transfer (DT) method was employed to calculate the radiation with an absorptivity and emissivity model employed to predict the radiation property of combustion products including soot, CO₂ and H₂O, which are usually the primary radiating species in the combustion of hydrocarbon fuels. The temperature of the solid boundary was determined by numerical solution of the heat conduction equation. A simple and practical pyrolysis model was developed to describe the response of the solid fuel. This pyrolysis model was first tested against the Cone Calorimeter data for both charring and non-charring materials under different irradiance levels and then coupled to CFD calculations. Both full and one-third scale room corner fire growths on particle board were modelled with CFD. The calculation was tested with various numbers of rays and grid sizes, showing that the present choice gives practically grid- and ray number-independent predictions. The heat release rate, wall surface temperature, char depth, gas temperature and radiation flux are compared with experimental measurements. The results are reasonable and the comparison between prediction and experiment is fairly good and promising.