Smoke Layer Temperature Research Articles

Application of Nonlinear Dynamics in Studying Flashover Fire in a Small Open Kitchen

Open kitchen designs are found in small units in tall residential buildings of Asian-Oceania regions for better space utilization. As many combustibles are stored in small residential units, fire originated in the open kitchen can grow and spread fast. Consequently, flashover can occur to give a big fire and result in severe casualties and property damage. Nonlinear dynamics can be applied to predict critical heat release rate to flashover in the unit with an open kitchen and will be illustrated in this paper. Based on a two-zone model, temperature of the hot smoke layer was taken as the system state variable. An evolution equation was developed with selective control parameters. Onsetting of flashover using a nonlinear dynamical system was demonstrated in the example residential units. Effects of the floor dimensions, the radiation feedback coefficient and thermal properties of wall material on the onset of flashover were then examined and analyzed. The developed nonlinear dynamical model for studying the onset of flashover gives a better understanding of the various control parameters.

Effect of Smoke Barrier in Narrow Space on Smoke Flow Utilizing CFD

In this paper, we build the relational models between the height of smoke barrier and the flow of gas, the depth and mean temperature of smoke layer in critical value, respectively. These models are based on the analysis of gas flow in narrow space of smoke barrier which is combined with the classic Hydraulic Jump model in the field of mechanics. For different initial conditions of gas, we simulate the effect of smoke barrier height on flue gas flow via the fire dynamics simulation software FDS. The results show that: the air entrainment and the depth of smoke layer in critical value are decreasing constantly while the critical mean temperature of smoke layer is raising during the increasing of the height of smoke barrier. Thus, when it gets the zero value, the air entrainment and the depth of smoke layer in critical value will get the maximum and the critical mean temperature of smoke layer will get the minimum. And when the height of smoke barrier greater than or equal the value of z_0, the value of air entrainment will be zero.

A Multi-observable Approach to Address the Ill-Posed Nature of Inverse Fire Modeling Problems

This study considers the development and evaluation of a prototype inverse fire model (IFM) aimed at predicting the heat release rate of a compartment fire using smoke layer information gained from building environmental sensors. The proposed methodology consists in: performing a search for the unknown heat release rate (HRR) by performing hundreds of different zone model simulations; comparing model predictions to observation data and thereby formulating an error function; using an optimization technique to minimize the error function and thereby producing a best estimate of HRR. The prototype IFM algorithm uses a zone fire model called BRI2002 (developed by the Building Research Institute in Japan) in conjunction with a genetic algorithm for optimization. The IFM algorithm is here applied to a reduced-scale laboratory experiment consisting of steady, over-ventilated, fire conditions in a simple multi-compartment (three rooms) configuration. The IFM algorithm is applied using a multiple-variable formulation in which both the fire size and the fire compartment venting conditions are assumed unknown, and using a one-observable or a two-observable scheme providing information on either the smoke layer temperature or on both the smoke layer temperature and depth. This framework is of particular interest because in the case of a one-observable scheme, the inverse fire problem is ill-posed, i.e. the optimization problem features multiple solutions and may converge to incorrect predictions of the fire size. This study shows that the two-observable scheme provides a way to regularize the inverse fire modeling problem, i.e. a way to provide a unique fire size solution. Our tests indicate that IFM-based estimates of HRR have an accuracy of better than 40%.

Fire Hazards of Façade Materials for Energy Conservation under Flashover

Several fires had occurred in air-conditioned double-deck buses with energy-conserving façade foam materials in the past few years. Citizens in Hong Kong are now worrying whether they are safe while staying inside enclosures with energy-conserving foam materials. There are very few studies on evaluating the fire performance of façade materials. Solar heat gain control by using Overall Thermal Transfer Value in buildings would give shorter time to flashover. Flashover is hazardous in a room for fires with a sharp increase in burning rate and gas temperature. In this paper, nonlinear dynamics was used to study flashover in an example room using a two-layer zone model. A differential equation was set up to describe the rate of change of the layer temperature based on simple heat balance of the smoke layer. Evolution of the smoke layer temperature, equilibrium states of the system and their corresponding stabilities were then investigated.

대공간의 기계배연 시스템에 대한 설계 및 수치해석적 분석

대공간은 높은 층고로 인해서 화재시 연기 발생량이 수십만 CMH에 달할 수 있으며, 연기의 국한화가 일반 건물에 비해 어렵기 때문에 대공간에 효과적인 연기제어 시스템의 설계와 운영이 요구된다. 본 연구에서는 실제 대공간 규모의 해석모델에 대해서 현재 제시되어 있는 설계기준을 근거로 대공간의 기계배연 시스템에 대한 설계를 수행하고, 3차원 수치해석 기법을 활용하여 설계안에 대한 수치적 분석을 수행하였다. 그리고 설계안의 배연량을 변경해 가며 수치해석을 수행하고 결과를 분석하였다. 연기층 두께, 발열량, 플럼의 질량유량, 공급공기의 속도, 배기구 1개당 최대유량 및 배기구간 최소거리 등의 주요 설계인자를 반영하여 설계를 수행한 결과 대공간의 건물높이가 25 m이고 정상성상의 발열량이 5,275 kW인 경우 전체 배연량은 527,459 CMH로 계산된다. 그리고 기계배연 시스템에서 배연량이 감소하면 연기층 높이가 낮아지고 연기층의 온도가 상승한다. Because of extended floor height in large space, smoke generated in fire would possibly reach to hundreds of thousands CMH and more difficulty in limiting the smoke than normal building requires effective smoke control system design and operation for a large space. In this study, design of mechanical smoke control for a large space was carried out based on existing design standard with regard to large space model and numerical analysis was also carried out using 3D numerical analysis method. Numerical analysis was carried out while changing flow rate of mechanical exhaust, which was followed by analysis of the result. As a result of implementing the design by incorporating major design factors including thickness of smoke layer, heat release rate, mass flow rate of plume, air supply velocity, maximum flow rate per exhaust outlet and minimum distance between exhaust outlets, total exhaust flow rate was calculated as 527,459 CMH when building height was 25 m and heat release rate of steady state was 5,275 kW. And the less the exhaust flow rate, the lower the smoke layer height and higher the smoke layer temperature.

Applied Research on Different Plume Models of Pool Fire in Hermetically Closed Room

The pool fire mathematical model of hermetically closed room is built by different plume models, the time of smoke filling and smoke layer temperature are calculated combined with experimental heat release rate. Theoretical calculations are compared with the experimental results to verify the usefulness of different plume models. The results indicate that: in initial period of fire, the smoke filling speeds of four plume models are similar, and McCaffrey plume model is most close to physical processes; in later period of fire, Zukoski plume model is most close to physical processes of smoke filling; during the fire, the results of Thomas plume model and Zukoski plume model are almost identical, and Thomas model is more suitable for engineering application; the smoke layer temperature discrepancy between theoretical calculation and experimental data is huge, and the theoretical calculation method of temperature is not recommended for predicting temperature in engineering.

Numerical Study on Temperature Distribution of Structural Components Exposed to Travelling Fire

In order to investigate the structure behavior under travelling fire, the numerical simulation of a full-scale travelling fire test with wooden fuels was completed by using FDS. The fire development and the heat release rate (HRR) were obtained. The temperature information, including gas temperature in the smoke layer, column surface temperatures at different heights, steel beam temperature and concrete ceiling temperature, were calculated from the FDS simulation. Although the compartment was rather small, obvious differences in temperature of the upper smoke layer and the steel beam, caused by the travelling fire, were observed. The maximum gas temperature under the ceiling was close to 1000°C.

水平天井面を軸対称に拡大する火災初期の煙先端部位置の近似解析解

The approximate analytical solution of the location of smoke front below horizontal ceiling at early time in fire is derived by the handling as the axi-symmetric problem. At first the approximate analytical solution of the average temperature of smoke layer is derived in assuming that the progress velocity of smoke front is proportional to 1/2 power of time based on the mass preservation. Then the integral equation to predict the location of smoke front is derived in this smoke average temperature. As this equation is not able to solve analytically, an approximate analytical equation is derived by approximation of integrand and being subject to temperature less exceeding initial inflow temperature. Particularly, in case of the treatment of center sprang out, the location of smoke front is proportional to 1/2 power at early time then to 3/4 power at time. The prediction is compared to the experimental data. It is shown that the location of smoke front is predicted by the approximate analytical solution.

Development of an analytical model to quantify downward smoke displacement caused by a water spray for zone model simulations

A stand-alone analytical model for downward smoke layer displacement caused by a water spray is developed. The model can be implemented into two-zone model calculations. Smoke flow into and out of the water spray envelope is incorporated, as well as a model for the heat exchange between the smoke and the water droplets. The model input quantities are water flow rate, orifice diameter, droplet diameter, spray angle, initial smoke layer thickness and temperature, and ambient air temperature. The quality of the model predictions is illustrated for a range of experimental conditions. Results are shown to be sensitive to the mean droplet diameter and the spray angle. Then, the combinations of values of these parameters are suggested for the sprinkler considered. A practically important phenomenon of abrupt strong downward smoke layer displacement is explained in that the upward buoyancy flow diminishes due to the entrainment of cool air into the water spray envelope. This only occurs for high enough water flow rates and as long as the smoke layer thickness is below a critical value. Therefore, this is particularly dangerous during the smoke layer build-up phase. Finally, the accuracy of the model for the heat transfer rate from the hot smoke layer to the droplets and the smoke temperature inside the spray region are evaluated by comparison to experimental data.

Determinations of the fire smoke layer height in a naturally ventilated room

According to the case-based reasoning of natural ventilation designs in recommended Green Buildings, an investigated model space was proposed in this study. FDS simulations and full-scale experiments were carried out to measure the impact of natural ventilation conditions and the installation of a natural ventilation shaft on smoke layer descent during different fire scenarios. The feasibility of using the N-percentage rule to determine the fire smoke layer height in a naturally ventilated space was also investigated.In a non-fire room, the smoke descent curve determined from the FDS simulated temperatures is consistent with the experimentally measured temperatures and visual observation of the smoke layer. However, the thermocouples in the fire room are affected by direct burning and fire radiation, and the experimentally measured temperatures cannot be used to determine the smoke height. Under these conditions, FDS simulations can be used to compensate for the lack of experimental measurements. In fire scenarios without outdoor winds blowing into the building's interior, FDS simulations can reliably model the fire smoke layer height. When outdoor air blows into the interior, it causes the smoke layer temperature to become unstable. Thus, the temperature will not be thermally stratified, and the use of the N-percentage rule is not recommended.

Analysis of Influencing Factors on Flashover in the Long-narrow Confined Space

The traditional theory of flashover is not available for the application of flashover in a long-narrow confined space, especially about the critical condition of flashover occurrence. In this paper, according to the measurement of reduced-scale fire tests, the smoke layer's temperature, thickness, gas concentration and heat release rate of fire source were studied. Furthermore, the effects of fire source, opening and ventilation to the occurrence of flashover were further discussed. It is shown that the critical line of flashover for the different fuels is between 600°C and 700°C, and critical condition is different for different fuels and different openings; for the different transverse ventilation, the smoke evacuation has the best effect only when the exhaust port neat the fire is opened.

Study on Flashover in an Open Kitchen Fire by Nonlinear Dynamics

There are concerns on open kitchen fires in small flats of tall residential buildings. Flashover should be avoided in providing fire safety. It is believed that flashover of a compartment fire is a nonlinear physical process. In this article, nonlinear dynamics was used to study flashover in an example open kitchen fire. The mathematical model developed earlier by taking the fire compartment as a thermal system with a hot and layer and a cool air layer was taken as the simulation tool. The two-layer zone model was simplified by taking the smoke layer thickness at a constant value. The compartment fire was then studied with only one variable on the hot smoke layer temperature. The model was programmed in symbolic mathematics software. The single variable on smoke or hot air temperature is then analyzed for system stability. An example open kitchen was selected to illustrate the concept. Control parameters for flashover to occur have been identified for providing fire safety to open kitchens.

A correlation for predicting smoke layer temperature in a room adjacent to a room involved in a pre‐flashover fire

SUMMARYAdvanced fire modelling software have been developed and improved during the last couple of decays and these kinds of software have been shown to be valuable tools for fire safety engineers. However, the advances made have not replaced the need for simple hand‐calculation methods. Simple hand‐calculations methods can be used to obtain a first estimate of, for example, smoke layer temperatures in a performance‐based design or to help an engineer determine if it is necessary to perform a detailed computational fluid dynamics calculation, but the current hand‐calculations methods are limited. The current methods can for example only predict smoke gas temperatures in the fire room. A correlation that could predict temperatures in an adjacent space would be useful in performance‐based design when, for example, evaluating the conditions for evacuees or sensitive equipment in an adjacent space to the room of fire origin. In this paper, a correlation for predicting gas temperatures in a room adjacent to a room involved in a pre‐flashover fire is developed. The correlation is derived from results from computer simulations and the external validity is studied by comparing results from the correlation with full‐scale test data. Copyright © 2012 John Wiley & Sons, Ltd.

Description and application of an analytical model to quantify downward smoke displacement caused by a water spray

An analytical model is developed from basic principles to quantify the downward smoke displacement as caused by a water spray from e.g., a sprinkler head. The underlying assumptions are identified and the global balance is described between downward drag force, potentially downward buoyancy due to a cooling effect within the water spray envelope in the smoke layer, and the upward buoyant force in the ambient air below the smoke layer. From this balance, the downward smoke displacement is quantified. It is explained that the classical Bullen theory to define a criterion for smoke layer stability is in general not valid. There is always downward smoke displacement, although potentially small, depending on the circumstances. The tracking of individual water droplets leads to the evolution of the spray envelope radius and provides the total downward drag force on the smoke. An extensive sensitivity study is presented, varying the water spray angle at the nozzle, the water droplet diameter, the smoke layer temperature, and inclusion or not of the cooling effect by water and air entrainment in the downward smoke displacement. It is highlighted that the downward smoke displacement is more pronounced for smaller droplets (for fixed water mass flow rate), and for lower smoke layer temperatures. For larger water spray angle at the nozzle, the downward displacement also increases monotonically with initial smoke layer thickness. A smaller spray angle at the nozzle leads to stronger downward smoke displacement and the variation of downward smoke displacement with initial smoke layer thickness is non-monotonic: stronger descent of smoke for thinner smoke layer, but beyond a critical smoke layer thickness also again a stronger descent with increasing smoke layer thickness. The accuracy of the model as presented is illustrated by means of an experimental data set.

Experimental study of the downward displacement of fire-induced smoke by water sprays

A set of experiments is presented on the effect of a water spray on a fire-induced smoke layer. The downward smoke layer displacement as a result of the interaction with the water droplets is quantified for a wide range of settings, including variable fire conditions, smoke layer temperature, smoke layer thickness and water spray operation pressure. The experiments include temperature measurements. The importance of entrainment processes is highlighted. In addition to the merit of the phenomenological observations, the experimental data set can be useful for model testing purposes.

Numerical Simulation of Smoke Exhausts Function of Roof Vent in Compartment Fires

The influence of roof vent area and fire source area on smoke exhaust function of roof vent is provided in this paper. Numerical simulation results show that the temperature of hot smoke layer increases with the increases of heat release rate and decreases as the roof vent area increases. For the evaluation criterion with temperature difference, with the increase in roof vent area and fire source area, the smoke exhausts function of roof vent was enhanced. But for the evaluation criterion with efficiency of smoke exhaust, the smoke exhaust efficiency increases as the roof vent area increase and decreases with the increases of fire source area.

Numerical Simulation of Temperature Profile in a Compartment Fire with a Roof Opening

Fifteen numerical simulations are presented in this article to investigate the influence of roof opening size and fire source size on gas temperature profiles in a compartment. The fire source size has a significant impact on the temperature hot smoke layer. The temperature of hot smoke layer increases as the increase of fire source size. The roof opening has cooling function to gas temperature in the compartment especially for large roof opening. The temperatures of hot smoke layer decrease with the roof opening size increase in all cases.

Heat Lost of Smoke Layer at Quasi-Steady State of Mechanical Exhaust

Under mechanical extraction in a fire room, a quasi-steady state will be eventually formed based on a two-layer zone concept. Heat loss through solid boundaries is a key factor which determines the temperature of smoke layer at quasi-steady state and will be discussed in this paper. A simplified model on heat loss of smoke layer is proposed. Calculation is performed and results are plotted. It is indicated that the ratio of heat loss through solid boundaries to the convective part of fire power, χ, varies under different exhaust rates and heat release rates of the fire. Heat loss of smoke layer through solid boundaries should be considered and calculated using heat transfer theory, instead of taking as a constant part of convective heat release rates of the fire.

On the Use of Real-Time Video to Forecast Fire Growth in Enclosures

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.

Scale modeling and numerical simulation of smoke control for rescue stations in long railway tunnels

Rescue stations are usually provided in very long railway tunnels. Those stations already constructed or under construction worldwide are reviewed and the basic pattern of smoke control during a rescue station fire is identified. A total of 54 model scale tests were carried out to investigate smoke control issues in rescue station fires. The effects of heat release rate, train obstruction, fire source location and ventilation condition on smoke control in the cross-passages of a rescue station were tested and analyzed. A critical smoke layer temperature near the fireproof door protecting the rescue station was investigated theoretically and experimentally and a simple equation for this temperature is obtained. A height of 2.2 m is proposed for the fireproof doors in cross-passages of rescue stations. Language: en