A numerical study of atrium fires using deterministic models

The smoke filling process for the three types of atrium space containing a fire source are simulated using the two types of deterministic fire model; zone model and field model. The zone model used in this simulation is CFAST (Version 3.1) developed at the Building and Fire Research Laboratories, NIST in the USA. The field model is a self-developed CFD model based on full consideration of the compressibility and k–ε modeling for the turbulence. This article is focused on finding out the smoke movement and temperature distribution in atrium spaces. A computational procedure for predicting velocity and temperature distribution in fire-induced flow is based on the solution of three-dimensional Navier–Stokes conservation equations for mass, momentum, energy, species etc. using a finite volume method and non-staggered grid system. Since air is entrained from the bottom of the plume, total mass flow in the plume continuously increases. Also, the ceiling jet continuously decreases in temperature, smoke concentration and velocity; and increase in thickness with increasing radius. The fire models, i.e. zone models and field models, predicted similar results for the smoke layer temperature and the smoke layer interface heights. This is important in fire safety, and it can be considered that the required safe egress time in three types of atrium used, in this paper is about 5 min.     

Predicting Spill Plumes with the Fire Risk Zone Model B-RISK

Recent experimental research on spill plume entrainment has developed a range of empirically-based formulae for smoke management design. These formulae form the spill plume entrainment model in B-RISK, a new fire risk zone model. This article describes the performance of B-RISK in predicting spill plume entrainment. Selected experimental data from the series of reduced-scale experiments used to form the new design formulae have been used for model validation, along with other full-scale experimental data from ‘hot smoke tests’ conducted to assess the performance of installed smoke management systems. B-RISK provides predictions of the plume clear-layer height that generally agree with experimental results within the range of experimental error. This gives confidence in its use to predict spill plume entrainment for smoke management design purposes.     

CFAST软件在高层学生公寓火灾区域模拟中的应用

介绍高层学生公寓火灾特点及其危害性,以某大学高层学生公寓楼5斋作为研究对象,采用CFAST区域模拟软件,模拟着火时,不同区域中烟气层下降高度、上部烟气层温度、下部烟气层温度、一氧化碳浓度、氧气质量分数和上部烟气层体积随时间的变化,模拟结果分析发现:其中烟气层高度、可能对封堵在区域1和11(楼梯)疏散人员产生危害,对其他区域的疏散人员均不会有危害。并在实际工作中可以通过在楼梯中安装消防排烟设备解决区域1和11烟气对人员产生的危害。     

A simple two-layer zone model on mechanical exhaust in an atrium

Provision of make-up air is essential in designing mechanical exhaust system in a compartment. There are always problems in determining the inlet positions for supplying make-up air. In this paper, a zone model for studying the effect of different positions of make-up air supply on the performance of a mechanical exhaust system in an atrium will be developed. Traditional two-layer approach with an upper smoke layer and a lower air layer will be assumed.Three scenarios of extraction with different relative positions of the air inlet are studied. These are scenarios with the smoke layer interface lying above, within, and below the air inlet. Conservation of mass and energy are considered for each scenario to study the smoke filling process. Transient variations of smoke layer temperature and interface height will be predicted under different fire sizes, exhaust rates and make-up air conditions.Full-scale burning tests in an atrium were conducted to justify the predicted results. In addition, results predicted by this zone model will also be compared with those predicted by Computational Fluid Dynamics (CFD) with the software Fire Dynamics Simulator FDS version 3.1; and another zone model CFAST version 5.0.1. It is observed that the predicted results from this new zone model agreed well with experiments and CFD results. However, results predicted by CFAST deviated from experiments for the scenario with the smoke layer interface lying below the air inlet.     

Scale Tests of Smoke Filling in Large Atria

The large Atriums of airports and railway stations facilitate the access to transport vehicles including shopping malls, cultural spaces, etc. For this reason, they are used by an elevated number of passengers and visitors. Numerous malls contain a large atrium too, as a principal access or as a food court, and they usually have high occupant loads. In case of fire, the smoke can affect human health seriously, and people may be unable to reach a safe place before being overcome by the conditions created by the fire. The traditional approach to fire protection by compartmentation is not applicable to these large volume spaces and the ability of sprinklers to suppress fire in spaces with high ceilings is limited. This work evaluated—using scale tests, fire computer modeling and analytical methods—a comparative analysis of the different results obtained for the smoke control in large atria when the smoke filling approach is applied. Smoke layer and plume temperatures have been registered during the scale test—based on the Froude Modeling—and they have been compared opposite to the FDS scale simulation and the FDS large scale simulation. Smoke layer descend has been studied and compared for the scale test, the computer simulations developed and the empirical equations used. The results demonstrated that the evacuation time calculation is conservative when the zone computer model CFAST, the field computer model FDS or the empirical equations are used, although it turns out to be difficult to define the interface height based on the temperatures registered during the scale tests. The zone computer models generate results faster than field computer models or smoke tests, so it would be necessary to develop better calculation algorithms to define the smoke layer interface.

Experimental data and numerical modelling of 1.3 and 2.3 MW fires in a 20 m cubic atrium

Atria and large spaces are common architectonical features in modern buildings such as high rises, auditoria, warehouses, airports and mass transport stations among others. There is currently an international trend towards the performance-based design for fire safety of these building elements. This design process relies heavily on fire modelling but the knowledge in fire dynamics and the movement of smoke in atria and large spaces still presents some gaps. This paper aims at contributing to close these gaps and reports the three Murcia Atrium Fire Tests conducted in a 20 m cubic enclosure using pools of 1.3 and 2.3 MW. Detailed transient measurements of gas and wall temperatures, as well as pressure drop through the exhaust fans and airflow at the inlets were recorded. The study also includes the effect of the mechanical exhaust ventilation. Results have been compared with those predicted by the computational fluid dynamics (CFD) model Fire Dynamics Simulator FDSv4. In general terms, the comparisons between experiments and simulations show good agreement, especially in the far field of the plume, but the accuracy is poor at the lower plume region and near the flame.     

大空间烟气控制性能化设计影响因素模拟

利用FDS数值模拟大空间烟气流动情况,探讨大空间火灾烟气控制系统性能化设计中的影响因素.针对设计火灾荷栽、火源位僵、大空间的形状系数和大空间体积对烟气层高度和烟气温度的影响进行模拟分析,对大空间火灾烟气控制系统的性能化设计具有重要意义.     

Experimental measurements,integral modeling and smoke detection of early fire in thermally stratified environments

Building fires go through a series of stages. They start with a fire plume period during which buoyant fire smoke rises to the ceiling. A second stage is the following enclosure smoke-filling period. In this paper, the first stage is the subject, especially for the fire plume behavior in thermally stratified environments in large volume spaces. In NFPA 92B, Morton's integral equation was introduced for calculating the maximum plume rise, and beam smoke detectors were recommended for smoke detection design. In this work, experiments and CFD simulations were conducted in a small-scale enclosure and a large space to investigate early fire movements in temperature-stratified ambients. The results show that in a thermally stratified environment, the axial temperature and velocity of a fire plume decrease more quickly along the vertical axis than in uniform environment, and in some cases the fire plume ceases to rise. The previous integral equation was shown to underestimate the actual maximum height of a fire smoke plume, and also was unable to explain the differences of the maximum heights of low-density and high-density smoke plumes with the same stratification and outlet conditions. The integral equation was improved by introducing two correction factors, and extended for non-linear temperature stratified environments. A light section smoke detection method with three space-protected area was suggested and discussed.     

Application of FDS to Adhered Spill Plumes in Atria

In a recently published article (Poreh et al., Fire Saf J 43(5):344–350, 2008), Poreh et al. carried out a number of experiments in a small-scale atrium. They investigated the mass flow of the spill plume in case of fire emerging from an adjacent room or corridor. Based on these experiments, the equation for the mass flow rates of adhered spill plumes in atria was adjusted. In our article, we repeat the experiments in a computational fluid dynamics (CFD) program. The results agree well, both with the experiments and the suggested formula. After this first validation, large-scale CFD-simulations are carried out. It appears that the equation suggested by Poreh et al. is only valid in the case of a uniform smoke layer depth. If the smoke layer has a more complex configuration, the formula is no longer reliable for the design of the smoke and heat exhaust ventilation system.     

Model Considerations for Fire Scene Reconstruction Using a Bayesian Framework

Towards the development of a more rigorous approach for coupling collected fire scene data to computational tools, a Bayesian computational strategy is presented in this work. The Bayesian inversion technique is exercised on synthetic, time-integrated data to invert for the location, size, and time-to-peak of an unknown fire using two well-known forward models; Consolidated Model of Fire and Smoke Transport (CFAST) and Fire Dynamics Simulator (FDS). A Gaussian process surrogate model was fit to coarse FDS simulations to facilitate Markov Chain Monte Carlo sampling. The inversion framework was able to predict the total energy release by all fire cases except for one CFAST forward model, a 1000 kW steady fire. It was found that insufficient information was available in the time-integrated data to distinguish the temporal variations in peak times. FDS performed better than CFAST in predicting the maximum energy release rate with the posterior mean of the best configurations being 0.05% and 2.77% of the true values respectively. Both models performed equally well on locating the fire in a compartment.     

Using FDS to Simulate Smoke Layer Interface Height in a Simple Atrium

This study examines the possible effects of various make-up air supply arrangements and velocities in an atrium smoke management system. Variations include velocities ranging from 0.5 to 3.0 m/s. The arrangement of make-up air supply injection points include symmetrically located vents placed low in the spaced, an array of vents distributed from the floor to the ceiling, and asymmetrically located vents. Fire Dynamic Simulator version 4.06 is applied to simulate ten scenarios in a 30.5 m cubical domain with a fire source simulating a stack of pallets with an approximate peak heat release rate of 5 MW. Results show that make-up air supply velocities should be diffused such that little to no velocity effects reach the fire. Make-up air should be supplied to the fire symmetrically for the best chance of not disturbing the fire plume. Disturbing the fire and smoke plume results in a significant increase in the smoke production rate, as evidenced by a deeper smoke layer.     

Fire in a residential building: Comparisons between experimental data and a fire zone model

Fire hazards in residential buildings were investigated by conducting a range of fire experiments on a typical New Zealand dwelling built for this purpose. Hazards evaluated ranged from limited liquid-fuel fires to larger-scale burns using items of furniture. The effectiveness of detection and suppression devices was also tested.A series of experiments in a three-bedroom dwelling were conducted and included both a nonflashover and a flashover fire, and a selection of experimental results were analyzed to determine smoke and gas movement together with temperature rises in the various rooms. These results were compared to the predictions of the CFAST fire and smoke transport computer model.     

A comparison of the use of fire zone and field models for simulating atrium smoke-filling processes

The smoke filling process for the three types of atrium spaces commonly built in Hong Kong are simulated using the two types of deterministic fire model: zone models and field models. The zone models used are the FIRST, CFAST, and CCFM.VENTS models developed at the Building and Fire Research Laboratories, NIST, USA and the NBTC one-room model of FIRECALC developed at CSIRO, Australia. The field model is a self-developed fire field model based on computational fluid dynamics theories. The results predicted by the two approaches are very similar. Simulation using a field model requires much more computing time compared with the use of a zone model, but it can give more detailed information on the fire-induced flow and temperature fields.     

Early fire smoke movements and detection in high large volume spaces

The maximum rise equation was obtained by differential solution of the integral equations of a plume in linearly thermally stratified environment and its applicability in piecewise linearly stratified environment was discussed. To better understand early fire smoke movements in thermally stratified environments in large volume spaces, a detailed study of smoldering cotton wick and flaming diesel oil smoke plumes in thermally stratified environments in a small scale enclosure was investigated by experimental measurements and CFD simulations. The reasonably good agreements of the experimental results and the simulated results indicate that the thermally stratified environment intensifies the decreases of the axial temperature and velocity of a fire smoke plume until makes it stop at a maximum height. Comparisons of the maximum plume heights between the experimental measurements and the integral equation results show that the available equation underestimates the actual maximum heights of fire smoke plumes and is unable to predict the influence of smoke density upon the maximum heights. A new smoke detection method of light section image detection was suggested to overcome the shortcomings of conventional beam-type smoke sensors and detect the early fire effectively.     

Full-Scale Validation Tests of a Forensic Methodology to Determine Smoke Alarm Response

The potential utility of enhanced soot deposition patterns around the openings of smoke alarm horns during post-fire forensic analysis has been realized through the findings of several experimental studies (Phelan, An investigation of enhanced soot deposition on smoke alarm horns. Master of Science Thesis, Worcester Polytechnic Institute, Worcester, MA, 250 pp, 2005; Fire Technol 37(4):343–362, 2001; Fire Technol 39(4):309–346, 2003). The data and analytical discussions put forth in these studies have provided a strong technical basis for describing the development of these patterns as well as for outlining the analysis of patterns to determine the operability of an alarm during a fire event. The purpose of this paper is to expand upon the findings of the previous work and validate the inspection heuristics developed by Phelan et al. Validation of the inspection heuristics was performed using data obtained from alarms exposed to full-scale enclosure fire scenarios permitted to reach flashover conditions.     

Characteristics of Fire Scenarios in Which Sublethal Effects of Smoke are Important

A number of simulations were performed using the CFAST zone fire model to predict the relative times at which smoke inhalation and heat exposure would result in incapacitation. Fires in three building types were modeled: a ranch house, a hotel, and an office building. Gas species yields and rates of heat release for these design fires were derived from a review of real-scale fire test data. The incapacitation equations were taken from draft 14 of ISO document 13571. Sublethal effects of smoke were deemed important when incapacitation from smoke inhalation occurred before harm from thermal effects occurred. Real-scale HCl yield data were incorporated as available; the modeling indicated that the yield would need to be 5 to 10 times higher for incapacitation from HCl to precede incapacitation from narcotic gases, including CO CO₂, HCN and reduce O₂.The results suggest that occupancies in which sublethal effects from open fires could affect escape and survival include multi-room residences, medical facilities, schools, and correctional facilities. In addition, fires originating in concealed spaces in any occupancy pose such a threat. Sublethal effects of smoke are not likely to be of prime concern for open fires in single- or two-compartment occupancies (e.g., small apartments and transportation vehicles) themselves, although sublethal effects may be important in adjacent spaces; buildings with high ceilings and large rooms (e.g., warehouses, mercantile); and occupancies in which fires will be detected promptly and from which escape or rescue will occur within a few minutes.     

Enclosure smoke filling revisited

Building fires go through a series of stages. They start with a fire plume/ceiling jet period during which buoyant fire gases rise to the ceiling and spread radially beneath the ceiling. A second stage, the enclosure smoke-filling period, follows; this second stage is the subject of this paper. It has been more than 20 yr since Zukoski first addressed the smoke filling stage of enclosure fires in terms of thermodynamic control volume concepts and fire plume entrainment, yet his analysis remains pertinent. This paper reviews and extends fire modeling concepts related to enclosure smoke filling developed by Zukoski. The mass-based analysis of Zukoski is recast in terms of the volumetric flow rates typically used for ventilation system design; it is extended to consider global average temperature rise and the effects of oxygen consumption on the maximum global average temperature rise that can be achieved in a closed-room fire. A spreadsheet template is developed to compare hand calculations based on a global analysis with numerical smoke filling calculations. Results of this comparison suggest that there is little difference in conditions predicted with the global hand calculations and the numerical smoke filling calculations; consequently, the hand calculations are suitable for preliminary fire hazard analyses.     

Method of Determining Smoke Detector Spacing in High Ceiling Applications

Simple tools for the design application of smoke detectors in commercial spaces with high ceilings and/or complex geometries do not exist due to the complexity in accurately estimating smoke densities and smoke detector activation characteristics. The response of commercial smoke detectors to UL/ULC standard flaming acceptance test fires and non-standard test fires in large open spaces with ceiling heights varying from 3 m to 21 m with radial distances from the fires up to 11.4 m is measured. Two algebraic models intended for unconfined ceilings, the two-zone computer model CFAST and the computational fluid dynamics computer model FDS are compared against each other and the experimental results. The ability to predict obscuration levels and detection times for these fires is evaluated. Recommendations are made for using the various models in commercial applications.     

Application of field model and two-zone model to flashover fires in a full-scale multi-room single level building

This paper presents a comparison of the results from a computational fluid dynamics (CFD) model and a two-zone model against a comprehensive set of data obtained from one flashover fire experiment. The experimental results were obtained from a full-scale prototype apartment building under flashover conditions. Three polyurethane mattresses were used as fuel. The CFAST two-zone model (version 2.0) was also used to predict results for this flashover fire test. The mass release rate, gas temperature, radiation heat flux and gas compositions (O₂, CO₂ and CO) were measured. A CFD program, CESARE-CFD Fire Model, has been developed and was used also to predict results for polyurethane-slab fire. A simple flame spread model was incorporated into the CFD program to predict the mass release rate and heat release rate during the fire instead of providing it as an input as is required for most zone and CFD models. It was found that the CFD model provided reasonable predictions of the magnitude and the trends for the temperatures in the burn room and the species concentrations, but over-predicted the temperatures in the adjacent enclosures. From a life safety perspective, the CFD model conservatively predicted the concentrations of CO and CO₂. The predicted temperatures from the CFAST fire model agreed well with the experimental results in most areas. However, the CFAST model under predicted the temperature in the lower layer of the room of fire origin and the concentration of CO in most areas.