Smoke Layer Height Research Articles

Full-scale experimental and numerical study of smoke spread and temperature distribution in a room-corridor structure building

This paper aims to study the smoke spread and temperature distribution inside a full-scale room-corridor structure building. A series of experiments and simulations with different fuel properties and fuel configurations (crib and pool fires) were carried out. There was a barrier at the top of the left end of the corridor, and the end wall was on the right side. The fire source was located in the room. The evolution of the smoke spread process, pressure distribution, and temperature distribution in rooms and corridors were obtained and analyzed. The results indicate that the barrier and the end wall hinder the smoke spread and make it to accumulate below the corridor ceiling. This causes the smoke layer height of the corridor to be lower than the top of the door, which changes the pressure distribution inside and outside the room and also affects the temperature distribution. Based on the changes of pressure distribution, some correction formulas for the gas flow rate and mass flux at the opening are proposed. Under the effect of the barrier and the end wall, the smoke temperature in the room and the corridor increases. A smoke temperature decaying model along the corridor direction is proposed. Some methods are used and compared to calculate the smoke layer height based on the vertical temperature distribution. The smoke layer height determined by the buoyancy frequency method is most consistent with the experimental observation values.

Performance assessment of stairwell smoke prevention techniques in a model high-rise building

The complexities of construction and increased fuel loading in high-rise buildings implied engineers to shift towards performance-based design (PBD) instead of prescription design to ensure a higher level of fire safety. Since PBD is an iterative process, so engineering models and tools based on numerical techniques are generally used to evaluate the trial designs. In the present study, various methods of stairwell smoke prevention have been analysed and compared using Fire Dynamics Simulator (FDS) in a model high-rise building. Optimization is done by defining critical values of smoke layer height and maximum pressure differential as 2 m and 55 Pa, respectively. Results demonstrated that natural and cross ventilation in the stairwell are not fully effective for smoke prevention due to the enhanced stack effect observed in them. Further, the pressurization of stairwell at a minimum differential pressure of 25–30 Pa seems to be effective only when all windows in the stairwell are closed. Effectiveness of single and multiple injection pressurization techniques are also assessed. The single injection system fails to maintain the required pressure differential when multiple doors are opened and causes high-pressure differentials at the top stories. Open windows in the stairwell reduce the effectiveness of the pressurization method. Placing an exhaust duct near windows enhances the effectiveness of the PPV method, even at lower capacities of supply vents, and proves effective when stairwell windows are open by creating a higher stack effect in the exhaust duct. The current research involved a comparative analysis of various stairwell smoke prevention methods, as outlined in NFPA 92 and in accordance with the National Building Code of India. The findings may have broader applicability beyond the studied context.

Modelling the Smoke Flow Characteristics of a Comprehensive Pipe Gallery Fire with Rectangular Section

In this study, a numerical model of the cable cabin of a comprehensive pipe gallery was established to study the smoke flow diffusion behaviour of a comprehensive pipe gallery fire under a rectangular cross-section. The effects of fire source power (Q = 0.5, 1.0, 1.5, 2.0, 2.5, 3.0 MW) and fire source location (D = 10, 20, 40, 50, 60, 80, 100 m) on the smoke flow characteristics—such as smoke layer height and thickness, longitudinal airflow velocity, and ceiling temperature distribution—were analysed, and the corresponding prediction model was fitted. The results show the following: (1) The height of the smoke layer decreases with increasing fire power, and the predictive model of the smoke layer thickness obtained from the fitting is proportional to the smoke mass flow rate and inversely proportional to the aspect ratio of the pipe gallery. (2) Longitudinal air velocity prediction models of D < 50 m and D ≥ 50 m are fitted, and the average error between them and the numerical simulation values is 9.611%. (3) The temperature decay gradient of the smoke decreases gradually with increasing distance from the fire source, while there is a significant temperature difference between the two sides of the fire source. The average relative errors of the dimensionless temperature rise models fitted upstream and downstream of the fire source in the form of ΔTT0=AeBD−XH+C exponentials with respect to the numerical simulations were 11.688% and 7.296%, respectively. The results of the study can provide a reference for smoke flow and fire prevention and control in comprehensive pipe galleries.

Numerical Simulation of Fire in Library Atrium Based on FDS

In order to prevent the fire accident in the comprehensive library, using the fire dynamic simulation software (FDS), taking a comprehensive library of a university as the research object, and taking the atrium self-study area on the second floor with the fastest smoke diffusion as the fire point, the temperature, smoke flow, visibility The distribution characteristics of CO and CO2 volume fraction are analyzed by numerical simulation, and the variation characteristics of each parameter are obtained. The simulation results show that the temperature, visibility and smoke layer height near the fire source have a great impact on the safe evacuation in the process of fire development. Among them, temperature has a decisive impact on personnel safety in the range of about 1m from the fire source. In the range of 5-10 m, visibility has the greatest impact on safe evacuation. The closer to the fire source, the faster the height of smoke layer decreases.

Experimental study on the descent distance of fire smoke at the corridor corner

In this paper, a series of experimental studies were conducted in a L-shape scaled corridor to investigate the fire induced smoke descent behavior at the corridor corner. The effects of fire source location and fuel pool size on the smoke descent distance were studied. The variation of the thickness of smoke layer in the L-shaped corridor and the temperature attenuation under the ceiling were elucidated. Results showed that the smoke layer height decreased significantly at the corner. The descent distance increased with the increase of fuel pool size. The temperature of the incoming smoke decreased as the distance between the fire source and the corner increased, the Ri number of smoke layer also decreased. The effects of gas temperature, velocity and thickness on smoke settling distance were analyzed by experiments. A prediction model for the smoke descent distance at the corridor corner was proposed.

Numerical study on plug-holing of double fires in tunnel with centralized smoke exhaust

In tunnel fires, smoke is the main fatal factor causing casualties. The technical parameters of tunnel smoke extraction are particularly critical. However, the parameters related to smoke control have rarely been experimentally and quantitatively studied in a tunnel caused by two adjacent fire sources. Numerical simulations were performed to study the plug-holing phenomenon in the centralized smoke exhaust tunnel with multi-fire sources. A 1:10 small-scale tunnel (length 25 m; width 1.2 m; height 0.8 m) was built using FDS. The effects of different fire heat release rates Q̇, fire source separation distances, and smoke exhaust velocities (v) on the plug-holing were considered. Firstly, the smoke layer height beneath the exhaust vent gradually increases as the exhaust velocity becomes higher and then remains almost unchanged until the plug-holing phenomenon occurs. Additionally, the smoke layer height becomes lower as the fire source separation distance increases for the fires with constant heat release rate. For all Q̇ values, the critical plug-holing velocity increases with the increasing separation distance S and Q̇. In addition, by modifying the critical Froude number (Frc), a predictive model of the critical plug-holing velocity considering the dimensionless fire source heat release rate and separation distance is obtained. Furthermore, the modified critical Froude number model, accounting for two adjacent fires with different separation distances, is established. The correlation between the new model and the simulation results shows quite good agreement, indicating that the proposed model can provide a satisfactory prediction for the critical smoke exhaust velocity in plug-holing conditions of double fire sources. This work can provide valuable guidance for tunnel design concerning fire safety.

Experimental study on fire characteristics of sidewall fires in a long-narrow compartment with multiple lateral openings

This experimental study delves into the fire characteristics within a long and narrow compartment equipped with multiple lateral openings. The investigation encompasses aspects such as radiant heat flow, temperature distribution, and smoke layer height. The presence of lateral openings introduces asymmetry in suction, resulting in augmented radiative heat flow on the rear side of the fire source compared to the front and left sides. Smoke stratification remains stable, with minimal temperature influence from the fire source power at one opening and negligible impact at the other. Employing a customized two-dimensional method for thermal estimation, our experimental data display lower results than previous predictions due to structural disparities. The utilization of the N-percentage rule unveils two discernible regions in smoke layer height behavior: stable and decreasing, a pattern consistent across varying heat release rates. These insights offer valuable predictive tools for discerning fire characteristics in elongated, restricted compartments with multiple lateral openings. Consequently, this study enhances comprehension and informs safety measures within such configurations, contributing to the broader field of fire safety engineering.

Effects of control zone, exhaust rate and station extent on smoke dispersal during emergency concourse fires in underground stations

Effective mass rapid transit plays an essential role in public transportation for sustainable urban development. This study investigates the temporary spreading behavior of smoke in the concourses of underground stations. The computational approach implements the software package FDS® 6.7.4 along with a post-processing visualization module (Smokeview) to simulate the smoke dispersal processes for determining the unsteady distributions of temperature and visibility during emergency concourse fires. The interfacial temperature between the lower air layer and upper smoke layer is employed to estimate the smoke layer height, as guided by NFPA-92B. The FDS predictions agree reasonably well with the measured fire plume temperatures at the heights of 7.0 m and 13.0 m above the fire source from the available literature in the time duration of 600 s for model verification. FDS calculations are then extended utilizing the validated computational model to explore the effects of the control area, exhaust rate and station size on the smoke spreading progressions. The simulated results reveal the effectiveness of installing static barriers to restrict smoke dispersal within a specific control space; however, the implementation of suitable mechanical exhaust system is required to extract the dense smoke out of the concourse. For the scenario of a high volume MRT underground station, the design adopting the smoke control area of 20 m × 15 m in conjunction with the exhaust rate of 15 m3/s can attain clear visibilities for emergency evacuation. However, the simulations show the inappropriateness of arranging the same design layout of control area and exhaust rate as safety measures of underground fires for a medium volume station.

Experimental study on vertical temperature distribution of the two-layer smoke flow in tunnel during construction

For a tunnel fire during construction, the formation of two-layer smoke flow underneath the ceiling accelerates the smoke descent threatening the personnel evacuation. As an important indicator of smoke diffusion, the gas temperature distribution inside tunnel is worthy of analysis in depth. However, the vertical temperature profiles within this kind of two-layer smoke flow inside tunnel have not been experimentally studied. To fill the gap, this paper conducts a series of fire experiments in a 1/20 reduced-scale tunnel model. Multi-variables including fire heat release rate, fire position, lifting-up height of fire source, inclined shaft slope, are considered. The visible flame shape, O2 volume fraction and gas temperature are recorded and measured. The burning of the propane gas persists steadily for 20 mins without the occurrence of self-extinction. The structural evolutions of the smoke layer are predicted by FDS simulation and traced by the laser sheet. The smoke descent process in the main tunnel is divided into three stages. The effects of fire source position, inclined shaft slope, fire heat release rate and lifting-up height on the gas temperature distributions inside tunnel are analyzed. The measured temperature rise and the perpendicular distance from the ceiling are normalized by ΔTmax and LT, respectively. At various longitudinal positions (1.82 ≤ │X-dm│/Hef ≤ 10.68), the normalized temperature distributions follow the same curve, independent of the values of Qm, dm and hm. The self-similarity of the vertical temperature distribution within the two-layer smoke flow are sufficiently proved. It is found that ΔT/ΔTmax with z/LT shows a two-regional variation. Based on over 1,740 temperature data from 36 experimental cases, an experimental equation is proposed to describe the gas temperature rise in the region between the fire source and the closed end. The proposed model shows good agreement with the measured data, which can help the researchers to better assess the smoke layer height inside tunnel.

Experimental study on the impact of asymmetric heavy rainfall on the smoke spread and stratification dynamics in tunnel fires

This work examines the impact of heavy rainfall on the smoke spread and stratification dynamics in tunnel fires with a reduced-scale (1:15) experimental platform. Scaled tests vary the rainfall intensity (up to 60 mm/h, equivalent to 232 mm/h in nature), raindrop size (1.0–1.5 mm, equivalent to 4–6 mm in nature), and fire heat release rate (2.1–6.7 kW, equivalent to 2–6 MW in real scale). We found that the asymmetric rainfall on one exit can induce the longitudinal airflow inside the tunnel due to the dissipation of the raindrop momentum and the rain-induced air entrainment. The velocity of such a longitudinal airflow increases with increasing rainfall intensity, and smaller raindrops tend to induce faster longitudinal airflow. The spread and stratification of hot smoke are sensitive to the induced airflow. In the absence of rainfall, there was a symmetrical temperature distribution from the fire source due to the symmetrical air entrainment. Under rainfall, the temperature distribution of tunnel fires gradually becomes less symmetrical, and the smoke stratification interface becomes unclear. With the increase in rainfall intensity, the phenomenon of smoke back-layering appears, and the smoke layer height decreases. Under a small rainfall intensity, raindrop size has a higher impact on the smoke stratification near the fire source. This study aims to attract more attention to tunnel safety under the dual disaster of fire and extreme weather and support the emergency response.

Experimental and Theoretical Analysis of the Smoke Layer Height in the Engine Room under the Forced Air Condition

The smoke layer height in the ship engine room under forced ventilation has been experimental and theoretical investigated in this work. A series of test were carried out in a scaled engine cabin experimental platform to obtain the influence of air supply volume and air inlet height on the burning parameters, including the mass loss rate, smoke temperature, etc. The research results show that under the experimental conditions, the fire source mass loss rate increases exponentially, and smoke layer height also increases gradually with the increase in the air supply volume. The empirical formula of smoke layer height under different air supply conditions was given. Then, a prediction model of smoke layer height under different forced ventilation conditions was constructed through theoretical analysis based on conservation equations. Within the range of experimental air volume and air inlet height, the relative error between theoretical prediction results and experimental results was less than 11%, which could effectively predict the smoke layer height in the ship cabin fire.

Experimental study on temperature characteristics in a subway train carriage with lateral openings in a longitudinally ventilated tunnel

Under the rapid development of subway systems, a fundamental understanding of subway fire safety is critically needed to benefit its designs and assessment. Previous studies on train carriage fires are limited to single-carriage fires under natural ventilation. However, it is still unclear how longitudinal ventilation affects the smoke movement in the train carriage with lateral openings. Therefore, a series of 1:3 reduced-scale experimental tests were conducted to investigate the smoke temperature characteristics in a train carriage located in a longitudinally ventilated tunnel. Under various fire sizes and ventilation rates, the ceiling gas temperature and smoke layer height were measured. Compared to the traditional fire scenario with end openings, the maximum ceiling gas temperature and the downstream temperature distribution decay factor are relatively smaller because of the lateral flame tilt and less heat loss during smoke propagation. The effects of ventilation velocity on the maximum ceiling gas temperature are significantly weakened under the blockage effect of the train carriage. The downstream temperature distribution followed a single exponential attenuation function, independent of the fire size and ventilation rate. However, the upstream temperature distribution is much more complex under the restriction of the end wall. A four-segment model was proposed to predict the upstream temperature distribution based on the relationship between the back-layering length and half the carriage length. The fire size and ventilation rate also show limited influence on the smoke stratification, with a layer height of 0.316 m in the stable region. The research outcomes offer adeeper understanding of the smoke propagation of the subway train carriage fire and a theoretical guide on the designs of future tunnels.

Numerical study on the smoke movement in office rooms with various exhaust vents settings

The ventilation system is essential to maintain a high level of the smoke layer to improve visibility during a building fire. The high level of the smoke layer allows the nearby exits can be easily located, and the fire sources can be identified during the building fire and rescue. Hence, the study of smoke movement in building fires with exhaust vent settings is essential to improve fire safety in the building. In this study, the smoke movement in real-scale offices is numerically investigated by utilising the Large Eddy Simulation (LES) computational model. Six scenarios with various exhaust vents settings are considered. The temperature distribution and the smoke layer height in the four office rooms and lobby area are analysed for all the cases. Results confirmed that the temperature distribution and the layer height have no significant difference by increasing exhaust vent size. However, the upper wall-mounted exhaust vents provide an effective smoke exhaust system, significantly increasing the smoke layer height in all office rooms.

Investigation of the performance of lateral ventilation in subway station fires

Lateral ventilation has been widely used in tunnel ventilation in recent years. But the effect of lateral ventilation in subway stations has received little attention and discussion. Based on numerical simulation, a real standard subway station is modelled in this paper to study the applicability of lateral ventilation in subway stations. Both the traditional ventilation system with vents located at the bottom of ventilation ducts and the proposed lateral ventilation system with vents located at the side of ventilation ducts are presented and compared. Parameters including temperature, CO concentration, and smoke layer height are adopted to qualitatively study the smoke control effect of different vent layouts. Parameters including ventilation efficiency and fractional effective dose are adopted to quantitatively model the ventilation performance of different vent layouts. The results indicate that: (1) The side vent layout is recommended in subway station emergency ventilation with slower horizontal smoke diffusion, slower vertical smoke settlement, and better smoke layer stability. (2) The advantage of side vent layout is quantitatively validated with higher ventilation efficiency in every vent and lower gas toxicity at eye-sight height. (3) Sensitivity analysis of fire location, heat release rate, vent amount, and vent size are conducted to verify the advantage of the side vent layout. In all scenario groups simulated, a better smoke control performance, higher ventilation efficiency, and lower fractional effective dose value is acquired in side vent layout. This research presents the application prospect and design method of lateral ventilation in subway stations.

Fire Safety Evaluation of Natural Smoke Ventilators Opening to outside due to Changing Outside Wind Speed

The reduction of the smoke exhaust performance of the natural smoke ventilator due to the influence of the external wind speed causes the problem of not being able to appropriately exhaust the heat and smoke generated by the fire compartment into the outflow air, which has a huge impact on the evacuation of the occupants, and at the same time can be a major problems to remaining life safety and fire suppression of the fire brigade. In this study, the type of projected window natural smoke ventilators opening to exterior which was selected from the preliminary smoke performance evaluation study and then the fire simulation was performed to quantitatively evaluate the smoke exhaust performance of the n atural smoke v entilator by the s iz e of the outside w ind speed. A s a result of the analysis, a s the wind speed increased, the smoke exhaust performance of the natural smoke ventilator was further reduced, and the amount of flue smoke due to the inlet flow was reduced, and it was predicted to negatively affect the main evacuation factors such as smoke layer height and fire room temperature.

A simplified analytical approach for the clear height in compartment fire based on a two‐layer zone model

AbstractCompartment fire is an important research area in fire science and fire safety. Owing to its simplicity, the zone model remains attractive in studying compartment fire. Although computer software packages for the two‐layer zone are in popular use, a basic understanding of the physical phenomena involved and the mathematical formulation thereon would benefit users of the zone model in terms of critical judgement of software outputs, which could be unreasonable, and insight of the general trends of important variables. In general, the differential equations based on a two‐layer zone model have no analytical solutions and numerical methods are required. However, stiffness is present in using numerical methods to solve these differential equations, and reliable results are obtained only when very small time steps are used in computation. Nevertheless, in some special cases, analytical solution for the clear height in the zone model exists, as demonstrated in the present study. Predicted values of smoke layer height in the present approach are shown to be in good agreement with experimental results reported in the literature. The present work would provide insight into the tenability condition of a compartment on fire and is an important issue in fire safety management.

Study on the smoke layer height in subway platform fire under natural ventilation

The smoke layer height under fire scenario is a vital parameter for emergency evacuation. Aiming at the effects of fire locations and heat release rate in a subway platform, series of numerical simulations were conducted under natural ventilation, and the temperature and visibility in the platform were measured. Results showed that the distinguishing characteristics of smoke layer height were presented in different regions (named Region Ⅰ ∼ Ⅳ) of the platform space, and the decreasing process could be divided into two stages: the first stage (0.6＜ Z1*≤1) and the second stage (Z2*≤0.6). For the first stage, the prediction model of smoke layer height in the four regions was uniformly proposed. Smoke layer height changed exponentially with time, and the attenuation factor at every position was basically the same but increased linearly with dimensionless heat release rate. For the second stage, the smoke layer height in the Region Ⅰ, Ⅱ, Ⅳ and Region Ⅲ decreased with time exponentially and linearly respectively, and the prediction models in different regions were developed separately. This work may provide guidance for personnel evacuation under fire emergency, and also provide reference for ventilation design in such a metro building engineering.

A Simulation Study on the Smoke Control Effect with Different Smoke Exhaust Patterns and Longitudinal Air Supply for Ultra-Wide Tunnels

This study was motivated by the lack of understanding of the smoke control effect on an ultra-wide tunnel fire, with different smoke exhaust patterns (sidewall and top exhaust patterns) and longitudinal air supply volume (0, 30%, 50%, 70%, and 90%). A full-scale ultra-wide tunnel model was constructed based on the FDS and the fire parameters were analyzed, such as the longitudinal spread distance of smoke, the smoke layer height and the temperature at safe height. In addition, the smoke exhaust efficiency was calculated based on the mass flux of CO2, and the smoke control effect with different smoke exhaust patterns and air supply volumes was compared. Results show that the smoke exhaust patterns and air supply ratios have a great influence on smoke spread distance and exhaust efficiency. The smoke spread distance is shortened by increasing the longitudinal air supply volume, and when the ratio of air supply volume to smoke exhaust volume is less than 50%, the top exhaust pattern can control the spread of smoke better with a smaller smoke spread distance. In addition, the height of the smoke layer is controlled above the safe height of 2 m under the top smoke exhaust, and the temperature at both ends of the tunnel (25 °C) is lower than that under the sidewall exhaust pattern (35 °C). The smoke exhaust efficiency was calculated based on the mass flow rate of CO2, and the exhaust efficiency of the top exhaust pattern (~70%) is significantly higher than that of the sidewall exhaust pattern (~55%). However, as the air supply volume increases, there is a reduced increase in the exhaust efficiency. Therefore, taking the economic cost into account, the air supply ratios of 30% and 50% are the best for top and sidewall exhaust patterns, respectively. The results of this work provide important information about smoke distribution characteristics in an ultra-wide tunnel fire and may guide its design of smoke exhaust.

Effects of passenger blockage on smoke flow properties in subway station fires.

This study investigates the effects of the passenger blockage on the smoke flow properties in the subway station fires. A series of numerical simulations was conducted in a full-scale subway station model under different smoke exhaust volumes (24-96 m3/s) and passenger blockage scenarios. The parameter uncertainty and the model uncertainty were fully analyzed. Results demonstrate that the optimal smoke exhaust volume is 96 m3/s when there is no passenger blockage. When the passenger blockage exists, its effects on the smoke exhaust efficiency, the smoke layer height, and the temperature profile beneath the ceiling are significant. The optimal smoke exhaust volume can only guarantee the passenger's safe evacuation in the blockage scenarios with the low passenger blockage level. For the high passenger blockage level, some measures should be taken to reduce the harm to the passengers near the fire source.

Extended CFD models for numerical simulation of tunnel fire under natural ventilation: Comparative analysis and experimental verification

This paper proposed Air Entrainment Model (AEM) and Mass Transfer-Volumetric Heating Source model (MT-VHS). Then different physical models of tunnel, gas description models and combustion models were used. CFD results were compared with reduced scale experiments and previous theories. The results show that traditional numerical simulation on tunnel model may cause asymmetrical temperature profile, because the pressure of tunnel portal is always set to be constant. Expanded computational domain can avoid this unreasonable setting. Boussinesq approximation underestimates temperature profile under ceiling because it ignores the variation of air property with temperature. Fitting parameters of air properties are more reasonable. In terms of combustion model, Volumetric Heating Source (VHS) neglects the plume generation. Heat release rate by Eddy Dissipation (ED) is not stable because it is affected by turbulent mixing. The mass sink of AEM entrains not only fresh air but also hot smoke. So the temperature profile by AEM deviates from experimental data much. Maximum temperature, temperature profile under ceiling and smoke layer height predicted by MT-VHS is close to experimental data and theoretical predictions, especially when the heat convection between wall and hot smoke is considered.