Maximum Smoke Temperature Research Articles

The Effect of Slope on Smoke Characteristics of Natural Ventilation Tunnel with Shafts

Tunnels with natural ventilation and extraction have become the focus of ventilation research in recent years. It is significant to study the characteristics of smoke in tunnel fires to ensure the safety of people and the tunnel structure. Previous research has mainly focused on natural ventilation in horizontal tunnels, and there are few studies on sloped tunnels. In this paper, we studied the smoke characteristics of natural ventilation extraction in slope tunnel fires both experimentally and theoretically. The small-scale experimental results showed that the position of the fire source, heat release rate (HRR), and the size of the shaft had little effect on the deflection angle of the fire plume. The deflection angle of fire plume was only related to the tunnel slope and increased with the tunnel slope. The slope had no effect on the smoke temperature distribution on the downside of the tunnel, while the smoke temperature on the upside decreased with the increase in the slope. The calculation models of the maximum smoke temperature rise and the smoke temperature distribution were obtained based on the experimental results and theoretical analysis. Compared with the experimental data, the developed semi-empirical models could provide a reliable prediction of smoke temperature.

Numerical study on the smoke temperature distribution beneath the ceiling of a single-ended sealing tunnel under the condition of double fire sources

As a special tunnel structure, the single-ended sealing tunnel has only one evacuation port, which increases greatly the risk of fire. Numerical modeling of a double source fire in a single-ended sealed tunnel was developed based on FDS 6.7. The effects of double-source spacing and end walls on ceiling smoke temperature were analyzed and discussed. The results show that when the double fire sources are considered as a whole, there are varying degrees of smoke backflow throughout the tunnel, with the upstream smoke backflow phenomenon being more pronounced under the influence of the end wall. In this study, the dimensionless separation distance φ is introduced and divided into two regions to quantify the effect of the spacing of the double fires. When 0 ≤ φ < 0.625, the maximum smoke temperature beneath the ceiling falls exponentially with increasing separation distance. On the other hand, when 0.625 < φ ≤ 1, the maximum smoke temperature under the ceiling rises exponentially. Furthermore, we suggest empirical formulas for forecasting the longitudinal distribution of downstream temperatures as well as the maximum smoke temperature of the ceiling. The predictive equations’ dependability was further confirmed by contrasting the predicted equations with simulated and historical experimental data. The study results serve as a reference for fire prevention and rescue in similar special tunnel structures, such as single-end sealing.

Novel selective adsorption cooling materials for heating cigarettes

Heated cigarettes are becoming trendy due to their advantage of not burning the tobacco material and thus reducing the amount of harmful ingredients released, while being able to leave the nicotine and tar content of the smoke untouched. However, the high temperature of the smoke as it enters the human mouth can affect the user experience. Therefore, the development of adsorption cooling materials for use in heated cigarettes is gradually becoming a hot topic. In this work, an adsorption cooling material based on embossed rod powder was prepared. It was found that compared with the commercial Yoga cooling material, the embossed rod powder based adsorption cooling material was able to reduce the maximum smoke temperature to 45.16 °C. In addition, it reduced the adsorption of nicotine by the cooling material, and increased the glycerol and nicotine content in the cooled smoke, which effectively promoted the taste of the smoke. Furthermore, the molecular simulation results found that the higher specific surface area and rich microscopic pore structure could increase the heat conduction area of the high-temperature flue gas, which enhanced the heat transfer effect of the flue gas. Finally, the periodic characteristic velocity pulsation destroyed the boundary layer formed by the fluid in the wall region, which increased the convective heat transfer effect between the fluid and the particles. The optimum sample 03 had the largest specific surface area and the lowest crystallinity, and thus had the best cooling effect. This work could provide some reference significance for the development of cooling materials for heating cigarettes.

Enhancing fire safety in underground mines: Experimental and large eddy simulation of temperature attenuation, gas evolution, and bifurcation influence for improved emergency response

The occurrence of underground mine fires remains a significant and persistent safety challenge in the mining industry, posing imminent risks to both miners' lives and the operational integrity of mining facilities. Current underground mine fire studies lack scale accuracy due to lab experiments and fail to consider bifurcation effects on smoke gas temperature. This study performed full-scale experiments and built validated CFD models to explore the interactive impact of ventilation and fire size on temperature attenuation, gas behavior, and CO generation in underground mines. A new empirical correlation for temperature decay in the mine drift was developed and its accuracy was compared with established models in the literature. In addition, the influence of bifurcation on maximum smoke temperature was analyzed. This research combines full-scale experiments and validated CFD modeling to address major gaps in underground mine fire studies. Unlike previous methods, this study explores the interactive effects of ventilation, fire size, temperature attenuation, and toxic gas spread, offering unprecedented insights. This innovation enables the development of tailored fire safety standards for mines, ensuring safer designs, rapid fire suppression, and improved evacuation strategies. By bridging theory and practice, this work transforms fundamental knowledge, empowering the mining industry to enhance safety measures, protect lives, and mitigate the impact of underground mine fires.

Study on the smoke evolution mechanism of a subway tunnel with a multi‐door carriage fire under longitudinal ventilation

AbstractThis paper has analyzed the longitudinal ventilation on the effect of the efficiency of the smoke evolution mechanism in a metro tunnel of multi‐window carriage fires. These were simulated by Large Eddy Simulation (LES) with Fire Dynamics Simulator (FDS). In the past, analyses of smoke temperature under the tunnel ceiling and smoke overflow characteristics have been conducted. However, longitudinal ventilation has a different impact on temperature than natural ventilation, especially in a subway tunnel with a multi‐door carriage fire. Consequently, several simulations were run in a subway tunnel (360‐m long, 6.0‐m wide, and 4.8‐m high). The longitudinal ventilation velocity is set by 0–10 m/s with the heat release rate of 1–10 MW. The results show that there is a linear relationship between the maximum temperature and the longitudinal ventilation velocity. An empirical model considering various longitudinal ventilation velocities was developed to predict the maximum smoke temperature underneath the subway tunnel ceiling. The effects of the longitudinal ventilation velocity, the heat release rate, and the distance of the fire source on the characteristics of longitudinal temperature distribution were analyzed. What's more, smoke overflow characteristics under different longitudinal ventilation velocities have been described. The findings and results can also provide a reference for the fire risk assessment of a metro tunnel of multi‐window carriage fires.

Estimating longitudinal maximum smoke temperature attenuation due to large-angle bifurcation in UTLT-like tunnels under longitudinal ventilation condition

Extensive studies have focused on single-straight tunnels or subway bifurcation tunnel fire. However, the effect of large angle bifurcation on longitudinal maximum temperature rise attenuation in Urban Traffic Link Tunnel（UTLT）needs to be further studied. In this study, based on the theoretical analysis, a double exponential prediction model for longitudinal temperature rise attenuation in bifurcation tunnels is established. To obtain the correlation coefficients, a series of full-scale numerical fire simulation experiments were carried out in an UTLT-like tunnels using Fire Dynamics Simulator. The results revealed that the bifurcation structure of the large-angle bifurcation angle tunnels impeded the longitudinal movement of the fire smoke and hot smoke diversion. Without longitudinal ventilation conditions, the longitudinal decay of the temperature rise in each region can be expressed as the sum of double exponential expressions with different coefficients. The law governing the effect of the bifurcation angle on the longitudinal decay of the temperature rise is the quadratic equation of the angle sin α. A prediction model for the longitudinal decay of the temperature rise in the tunnel downstream of the fire source under longitudinal ventilation is proposed. The findings of the numerical simulation corresponded to those of the model prediction.

Studying the Synergetic Effect of Point-Extraction and Longitudinal Ventilation on the Maximum Smoke Temperature and Back-Layering Length in Tunnel Fires

This study investigates the impact of combining longitudinal and point-extraction ventilated systems on temperature distribution and back-layering length in tunnel fires. Numerical simulations are conducted using a fire dynamic simulator (FDS), and reduced-scale tunnel fire experiments with a scale of 1/10 are introduced to provide supplementary data. Results indicate that the longitudinal velocity is more critical than other factors in reducing the highest temperature and casualties. Lowering the temperature below the tunnel ceiling is not caused by increasing the ceiling extraction velocity. Additionally, the study reveals that the fire source-ceiling distance and their relative positions play a crucial role in temperature distribution and plug-holing phenomenon in the tunnel. By using the Taguchi method, it is determined that a fire at a height of 0.125 m has a maximum ceiling temperature of 1.8, 1.3, and 1.1 times when the fire source happens on the floor with longitudinal velocities of 0.133, 0.265, and 0.53 m/s, respectively. The extraction point has diverse effects provided that the longitudinal ventilation velocity is set by critical velocity. The study’s objective is to provide tunnel engineering managers with a correlation to predict the highest temperature, which is a vital parameter for emergency evacuation. In conclusion, this study highlights the importance of considering longitudinal and point-extraction ventilated systems and their relative speeds in reducing the severity of tunnel fires.

Effects of ambient pressure on smoke propagation in inclined tunnel fires under natural ventilation

This paper systematically studied the coupling effect of ambient pressure and tunnel slope on temperature distribution and smoke propagation in full-scale tunnel fires under natural ventilation by FDS. The downstream length (longitudinal length from fire source center to tunnel downstream exit) was also considered. The concept of "height difference of stack effect" was put forward when analyzing the mutual effect of tunnel slope and downstream length on smoke movement. The results show that the maximum smoke temperature beneath the ceiling decreases with the increasing ambient pressure or tunnel slope. The longitudinal smoke temperature decays faster with the decreasing ambient pressure or slope in inclined tunnel. The induced inlet airflow velocity increases with the increasing height difference of stack effect, while decreases with the increasing ambient pressure. And the smoke backlayering length decreases with the increasing height difference of stack effect. Taking heat release rate (HRR), ambient pressure, tunnel slope and downstream length into account, the prediction models of dimensionless induced inlet airflow velocity and smoke backlayering length in inclined tunnel fires at high altitude were developed, which agree well with our and others' results. The outcomes of current study are great meaningful to fire detection and smoke control in inclined tunnel fires at high altitude.

A comparative study on smoke temperature profile and corresponding different-exponential form correlation in single-line and bifurcated tunnel fires

A series of model-scaled tunnel fire tests were performed to investigate the temperature attenuation characteristics of thermal smoke. The internal temperature profiles of single-line tunnel and T-shaped tunnel were measured and compared. Results indicate that within the current measurement range, for the fire scenario with same fire power, the maximum smoke temperature of T-shaped bifurcated tunnel is slightly lower than that of the single-line tunnel under natural ventilation, which can be attributed to the reduction of smoke accumulation and the increase of air entrainment induced by bifurcation region. The longitudinal temperature decay of fire smoke in entire spread region shows an obvious region-variation feature. The temperature attenuation rate in the region near fire source is larger significantly than that of one-dimensional spreading region. Compared with the representation in the form of single exponential correlation, the double-exponential correlation can better characterize the temperature decay process in entire spreading region of fire smoke. While, if the single-exponential representation is adopted, the correlation formula is piecewise. Based on the analysis and physical observations of the longitudinal decay rate of smoke temperature in different spreading regions, a modified double-exponential correlation for longitudinal temperature attenuation is obtained. By comparing with the model-scaled measurement results in current work and the full-scaled experimental data of previous scholars, the proposed correlation is reasonably verified to be within an acceptable error range. This work is anticipated to serve as a resource for firefighters to evaluate the temperature profile and decay characteristics of fire smoke in tunnel-like space.

Study on the Air Inlet Velocity and Temperature Distribution in an Inclined Tunnel with Single Shaft under Natural Ventilation

The emergence of inclined tunnels under natural ventilation has brought many new fire safety issues. The smoke movement in the tunnel is affected by the chimney effect induced by the shaft and the downstream tunnel. The characteristics of temperature distribution in inclined tunnels are different from horizontal tunnels, which is worthy of further study. A series of conditions were carried out in an inclined model tunnel with a single shaft to investigate the temperature distribution characteristics. In this study, the longitudinal air inlet velocity is used to replace the longitudinal ventilation wind velocity. Results showed that the variation of fire source location Lf,, shaft height Ls, and the tunnel slope φ have obvious effect on the air inlet velocity. Based on the previous theories and the non-dimension analysis, the formulas of the dimensionless longitudinal inlet air velocity and the distribution of the maximum smoke temperature under the ceiling are proposed, which show good consistency with the simulation results. The reduced-scale experiments were conducted to validate the results of numerical simulation. The error range between the theoretical results and the simulation results is less than 20%.

Study on the Effect of Blockage Ratio on Maximum Smoke Temperature Rise in the Underground Interconnected Tunnel

The model-scale tunnel is used in this investigation to analyze the maximum smoke temperature rise of the interconnected tunnel for various longitudinal ventilation velocities, blockage ratios, and heat release rates where the fire is at the confluence of the underground interconnected tunnel. The results showed that the longitudinal ventilation velocities of both the ramp upstream of the fire source and the adjacent ramp influenced the maximum temperature rise under the underground interconnected tunnel, and the ventilation of both ramps jointly affected the maximum temperature rise. The change in the maximum temperature rise depends on who is more affected by the longitudinal ventilation velocity or the vehicle blockage ratio. As the longitudinal ventilation velocity in the interconnected tunnel increases, the convective heat transfer near the fire source increases, resulting in a decrease in the maximum temperature rise, and the effect of the blockage ratio on the maximum temperature rise is reduced. In this paper, a maximum temperature rise prediction model suitable for the case of blockage in the interconnected tunnel is proposed.

Superheated steam similarity simulation on longitudinal distribution of maximum smoke temperature rise in tunnel fires

• The superheated steam is used to simulate the migration and heat transfer process of fire smoke. • The similarity between fire smoke and superheated steam motions is demonstrated. • The maximum steam temperature rise is related to buoyant flux and tunnel height. • A calculation model for predicting the longitudinal distribution of maximum smoke temperature is developed. Physical simulation of smoke migration and temperature evolution is an important measure for studying tunnel fires. In this work, based on the similarity theory of fluid dynamics, the motion of superheated steam in the air is used to simulate the migration and heat transfer process of high-temperature smoke generated by tunnel fires. The similarity criteria and similarity scales between the motion of superheated steam and fire smoke are derived by the similarity transformation method. The migration pattern and temperature evolution of superheated steam under natural ventilation are investigated by using a self-built superheated steam experimental system. Then, fire tests are conducted on a combustion wind tunnel to verify the feasibility of this method. The results show that the similarity between fire smoke and superheated steam motions is demonstrated by considering geometric conditions, kinematic conditions and dynamic conditions. The maximum steam temperature rise increases as a power function of the buoyant flux and depends on the 5/3 power of the tunnel height. Moreover, the maximum ceiling steam temperature rise attenuates exponentially with the increasing distance from the steam source. Finally, the calculation model for predicting the longitudinal distribution pattern of the maximum smoke temperature rise beneath the tunnel ceiling is developed, which agrees well with the experimental results.

Numerical study on the impact of wall thermal inertia on maximum smoke temperature and longitudinal attenuation in long channel fires

In order to better understand the law of smoke propagation in long channel fires and enhance the fire protection of channel structure with different lining materials, a series of fire simulations were carried out by Fire Dynamics Simulator (FDS) to investigate the impact of wall thermal inertia on the maximum smoke temperature and longitudinal attenuation under the channel ceiling. Five wall materials corresponding from the foam concrete to the steel with thermal inertia ranging from 0.1 to 165 kW2•s/(m4·K2) and four heat release rates (5 MW, 7.5 MW, 10 MW and 12.5 MW) were employed. The maximum smoke temperature above the fire source and the temperature distribution under the ceiling along the channel longitudinal centerline were attained and analyzed. The results show that the maximum smoke temperature is significantly affected by the channel wall thermal property and increases with the decrease of wall thermal inertia. Based on the simulative data, a modified model taking the influence of wall thermal inertia into consideration is put forward to predict the maximum gas temperature below the ceiling. Further, the effect of channel wall thermal inertia on the longitudinal smoke temperature decay can be negligible when the thermal inertia is greater than or equal to 1.21 kW2•s/(m4·K2), however, the foam concrete wall with the thermal inertia of 0.1 kW2•s/(m4·K2) results in a smaller attenuation rate due to less heat conducted into the channel wall. Meanwhile, the smoke temperature distribution along the channel longitudinal centerline is also related to the heat release rate (HRR), and the larger the HRR, the slower the temperature decay. The investigation indicates that the temperature distribution along the longitudinal direction follows an exponential attenuation in the near fire field but presents a form of the sum of two exponential functions in the one-dimensional smoke propagation stage. Then taking the effect of wall thermal inertia and heat release rate into account, two novel models characterizing the law of longitudinal temperature attenuation were developed near fire source and in the one-dimensional smoke spread stage respectively.

Study on smoke temperature profile in bifurcated tunnel fires with various bifurcation angles under natural ventilation

A 1:10 small-scale bifurcated tunnel including main tunnel and branch tunnel was built, and the bifurcation angle was set to 60°. 21 tests with 7 possible fire locations were carried out in the small-scale tunnel under natural ventilation. Furthermore, 32 numerical simulation cases with 8 bifurcation angles were simulated by CFD. The results indicated that: 1) the maximum ceiling temperature in the bifurcated tunnel was independent of the fire location and bifurcation angle. Only when the fire was in the bifurcation area, the maximum smoke temperature rise was slightly higher than that located in other areas of the main tunnel. 2) the longitudinal temperature attenuation of the upstream and downstream from fire source in the main tunnel was independent of the bifurcation angle. 3) If the bifurcation angle varied between 20° and 160°, when the bifurcation angle ≤ 90°, the variation of bifurcation angle had a significant effect on the longitudinal temperature distribution in the branch tunnel. However, when the bifurcation angle > 90°, the longitudinal temperature distribution in the branch tunnel almost did not vary with the change of the bifurcation angle. A prediction model for the longitudinal temperature in the branch tunnel was established by considered the effect of bifurcation angle.

An improved theoretical model for the maximum smoke temperature rise in a tunnel based on equivalent fire source

The maximum smoke temperature rise underneath tunnel ceiling is of great importance for the assessment of heat exposure, estimation of fire detection time and possibility analysis of fire spread. Previous studies mainly focused on the scenario with a single fire source, but the existence of two fire sources is common due to the increase traffic volume. The maximum smoke temperature rise induced by two fire sources is studied through theoretical analysis in this study. A virtual equivalent fire source is proposed, which is mainly affected by the total fire heat release rate (HRR) of two fires, longitudinal ventilation velocity, effective tunnel height and separating distance between two fires. The HRR of the equivalent fire source decreases with a longer separating distance, which indicates that the influences of the downstream fire on the maximum ceiling temperature weakens gradually as the separating distance increases. An improved model on the maximum ceiling smoke temperature rise caused by two fire sources was developed, and the predictions based on the revised model agree well with the experimental data.

Temperature characteristics in a double long-narrow space with different fire locations

Maximum smoke temperature beneath the tunnel ceiling is always one of determining factors of the safety assessment of a tunnel fire. Although many studies have been undertaken, the double long-narrow space fire, such as in a subway tunnel with a train on fire, has been rarely considered and investigated. To benefit the fire safety assessment, the smoke temperature characteristics beneath the tunnel ceiling under various fire sizes and locations were then investigated in this study both numerically and theoretically. A new parameter called dimensionless offset distance (d∗) was proposed to address the influences of fire locations on fire behaviors. It was then known, as the d∗ keeps increasing, the maximum temperature moves from above fire source to above the train end. The change of the maximum temperature along with d∗ can be divided into two regions, namely Region I (0≤d∗<0.46) and Region II (0.46≤d∗<1). A new empirical model was also developed to predict the maximum temperature rise considering fire size and fire location. The smoke temperature rise was found attributing to the increased level of smoke accumulation inside the train, which can be characterized by factor af. Critical af for the transition from Region I to II was found between 0.145 and 0.165. This study will provide a reference for the relevant detection, protection and fire rescue in tunnel fires.

Experimental investigation on the smoke back-layering length in a branched tunnel fire considering different longitudinal ventilations and fire locations

Most previous works concentrated on the smoke back-layering length in traditional single tunnel fires, whereas very few studies have been performed related to the smoke back-layering length(L) in a branched tunnel fire. In the present paper, a series of fire tests were performed in a 1/10 scale branched tunnel to investigate L under various longitudinal ventilation velocities (v), heat source locations(d) (the distance between the heat source centerline and junction) and heat release rate (HRR). The smoke back-layering length and smoke temperature for various conditions are obtained and analyzed. The results are summarized as follows: With longitudinal ventilation velocity increasing to large enough, the smoke back-layering phenomenon will be observed and the maximum smoke temperature tends to deflect downstream. The larger the v and the farther the heat source is to the intersection, the smaller the L is. The dimensionless smoke back-layering length L/H is proportional to gHQ˙/ρ0cpT0v3A, which is consistent with Thomas's work. Whereas, due to that the smoke will split in intersection of branched tunnel, the proportional coefficient increases from 0.467 to 0.754, which is less than that in traditional single tunnels in previous work. Moreover, a revised relation is proposed to describe the smoke back-layering length in branched tunnel fires considering the longitudinal ventilation and fire location.

Critical velocity for preventing thermal backlayering flow in tunnel fire using longitudinal ventilation system: Effect of floor-fire separation distance

To design a reliable longitudinal ventilation system in a roadway tunnel, it is crucial to know the optimum value of the forced airflow velocity which must be applied to minimize hazards to users trapped in the building during a fire. This optimal value known as the critical longitudinal ventilation velocity, is a crucial criterion for tunnel safety when designing ventilation systems. Analysis of the influence of the fire development location from the tunnel floor on the critical velocity has rarely been studied, although this situation really exists due to the difference in vehicle sizes in practice. CFD simulations were performed in this paper to study this scenario and to estimate the critical velocity for a fire developing in different locations relative to the tunnel floor. The results indicate that as the elevation of the fire location increases from the tunnel floor, the critical velocity decreases. A new model involving the separation distance of the fire location on the tunnel floor and relating the critical velocity to the fire heat release rate is proposed. Furthermore, under critical conditions of ventilation velocity, the results show that the elevation of the fire source location from the floor has a significant effect on the maximum smoke temperature rise below the tunnel ceiling.

Numerical Simulation of Converter Station Fire: A Study focus on the Fire Hazard of Valve Tower

The fire hazard of a valve tower in converter station fires were investigated by using the Fire Dynamics Simulator (FDS). The 2 m2, 5 m2 and 10 m2 transformer oil pool fires with the calculated heat release rate (HRR) of 2.02, 6.23 and 13.78 MW were considered in the simulations, and the smoke propagation process, smoke temperature and visibility were mainly concerned. The results showed that the whole valve tower was immersed in the fire smoke at about 600 s in 2 m2 fire condition, and the maximum temperature rise inside the valve hall was about 20ºC. In the 5 m2 fire condition, the smoke layer height descended to the bottom of the valve tower at about 300 s, and the visibility around the valve modules was lower than 5 m at about 450 s. The maximum smoke temperature inside the valve hall was over 60ºC, and the temperature of smoke around the valve modules ranged from 43 to 52ºC. In the 10 m2 fire condition, the valve tower was immersed in the fire smoke at about 210 s, and the visibility around the valve modules was lower than 5 m at about 300 s. The smoke temperature beneath the ceiling of the valve hall was over 100ºC, and the temperature at the height of valve towers ranged from 65 to 80ºC. It was observed that the larger the fire size was, the higher the fire hazard of the valve tower would be found. In the 5 m2 and 10 m2 pool fire conditions, the thermal damage to the valve tower was non-negligible. The normal operation of the electrical components in the valve tower might be affected, and the failure of electrical components might be occurred.

Impacts of ambient pressure on the stability of smoke layers and maximum smoke temperature under ceiling in ventilated tunnels

In tunnel fire, smoke is a great threat to successful emergency escapes, and its spreading patterns at high altitude tunnel may differ. Therefore, the impact of ambient pressure on the stability of smoke layers and maximum smoke temperature under ceiling in ventilated tunnels were investigated in this study. Results show that the temperature of smoke layer is negatively correlated with the longitudinal velocity and ambient pressure. Besides, the influence of longitudinal velocity at different ambient pressures on the shear velocity between the smoke and air layers was further studied. Using Richardson number ( Ri) and Froude number ( Fr), smoke flow can be classified into three patterns, namely stable and obvious smoke stratification ( Ri&gt;3.2 or Fr &lt; 0.38), a stable smoke layer but with blurred interface (2.3 &lt; Ri &lt; 3.2 or 0.38 &lt; Fr &lt; 0.53) and a completely unstable smoke stratification ( Ri &lt; 2.3 or Fr &gt; 0.53). Furthermore, a model has been developed to predict maximum smoke temperature under the tunnel ceiling, which agrees well with previous studies at standard atmospheric pressure. The results of the present work provide information for tunnel structure protection and safe evacuation in fire accidents at different ambient pressures.