Editorial

4 pages, 1519 KiB

Open AccessEditorial

Smoke Movement and Control in Tunnels under Construction: Recent Research Progress and Future Directions

by Yongzheng Yao, Ziyang Xia, Rui Wang, Fei Ren, Zihe Gao, Jinlong Zhao and Qiang Wang

Fire 2023, 6(5), 191; https://doi.org/10.3390/fire6050191 - 07 May 2023

Viewed by 1208

China is the country with the largest number of tunnels, the largest tunnel construction scale, and the fastest development of tunnels in the world [...] Full article

(This article belongs to the Special Issue Turbulent Combustion Modelling, Experiment and Simulation)

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Research

Jump to: Editorial, Review

11 pages, 3125 KiB

Open AccessArticle

Optimization of Ejection Characteristics for Twice-Detonating Device in Double-Event Fuel-Air Explosive with High Drop Velocity

by Binfeng Sun, Chunhua Bai, Caihui Zhao, Jianping Li and Xiaoliang Jia

Fire 2023, 6(7), 250; https://doi.org/10.3390/fire6070250 - 25 Jun 2023

Viewed by 970

Abstract

The key to ensure the reliability of the cloud detonation in high-drop-velocity double-event fuel-air explosives (DEFAEs) is to cause the twice-detonating device (TDD) to detonate in the dispersed fuel. Here, an ejection mechanism for a TDD is designed and the ejection process is [...] Read more.

The key to ensure the reliability of the cloud detonation in high-drop-velocity double-event fuel-air explosives (DEFAEs) is to cause the twice-detonating device (TDD) to detonate in the dispersed fuel. Here, an ejection mechanism for a TDD is designed and the ejection process is analyzed through an outfield ejection test. Accordingly, a simulation model for the description of the ejection process is established and verified to be reliable by comparing it with the experimental results. Based on the model, two extended ensamples for design optimization of the ejection mechanism are developed. The factors influencing the ejection characteristics of the TDD are further analyzed, including the ejection charge mass and screw (for baffle fixing) parameter. The research carried out here provides theoretical and experimental support for the optimal design of the ejection mechanism in high-drop-velocity DEFAEs. Full article

(This article belongs to the Special Issue Turbulent Combustion Modelling, Experiment and Simulation)

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15 pages, 2194 KiB

Open AccessArticle

Preliminary Study on Reconstruction of Building Thermal Field Based on Iterative Algorithm Acoustic CT

by Hengjie Qin, Jiangqi Wen, Zihe Gao, Lingling Chai and Haowei Yao

Fire 2023, 6(5), 199; https://doi.org/10.3390/fire6050199 - 12 May 2023

Cited by 1 | Viewed by 1167

Abstract

Real-time acquisition and visualization of temperature anomalies in building spaces and 3D temperature field data during fires are of vital importance for fire danger warnings, early rescue operations, evacuation commands, and subsequent fire accident investigations. Taking into account the non-contact, global (planar and [...] Read more.

Real-time acquisition and visualization of temperature anomalies in building spaces and 3D temperature field data during fires are of vital importance for fire danger warnings, early rescue operations, evacuation commands, and subsequent fire accident investigations. Taking into account the non-contact, global (planar and spatial), and high efficiency advantages of acoustic CT temperature measurement technology, this study involved the conducting of exploratory preliminary research in order to provide new ideas for the real-time global perception of information on building fires. The detailed research objective was as follows: obtain the temperature data at any time of a fire based on Fire Dynamics Simulator (FDS) and fit them to form the base temperature distribution diagram at that time. The large ill-conditioned matrix equation of acoustic flight under the scheme of multi-grid division was then constructed. The discrete temperature data of each grid in the building space was obtained by solving the matrix equation based on algebraic reconstruction algorithm (ART) and joint algebraic reconstruction algorithm (SART). The three-dimensional temperature field reconstruction of building space was realized by the interpolation of discrete temperature data. The reconstruction effect of each scheme was evaluated through the error analysis between the reconstruction data and the basic data. The results show that the real-time reconstruction of a 3D temperature field of a building thermal field can be realized based on acoustic CT temperature measurement technology, and the reconstruction algorithm and grid division scheme have a significant control effect on the reconstruction effect. Full article

(This article belongs to the Special Issue Turbulent Combustion Modelling, Experiment and Simulation)

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12 pages, 5910 KiB

Open AccessArticle

Effects of Nano-Nickel Oxide on Thermokinetics, Thermal Safety, and Gas-Generating Characteristics of 5-Aminotetrazole Thermal Degradation

by Dan Zhang, Lifeng Xie and Bin Li

Fire 2023, 6(4), 172; https://doi.org/10.3390/fire6040172 - 21 Apr 2023

Cited by 1 | Viewed by 1286

Abstract

5-aminotetrazole (5AT) has been widely used as a fuel in SPGGs for its high nitrogen content, heat resistance, and environmentally friendly product. However, 5AT-based propellants still have disadvantages, such as a high exhaust temperature and unstable combustion rate, which somewhat limit their application. [...] Read more.

5-aminotetrazole (5AT) has been widely used as a fuel in SPGGs for its high nitrogen content, heat resistance, and environmentally friendly product. However, 5AT-based propellants still have disadvantages, such as a high exhaust temperature and unstable combustion rate, which somewhat limit their application. Given that transition metal oxides are typically employed in small quantities to enhance the performance of solid propellants, this study selected nickel oxide (NiO) nanoparticles as a catalyst and employed them in conjunction with 5AT via mechanical ball milling to investigate their impact on the pyrolysis behavior of 5AT. It was found that the nanoscale NiO particles can significantly reduce the thermal degradation temperature of 5AT according to TG-DSC tests. The calculation of the energy required to initiate the pyrolysis of 5AT using three kinetic methods, namely Friedman (FR), Flynn–Wall–Ozawa (FWO), and Kissinger–Akahira–Sunose (KAS), indicated that the use of NiO nanoparticles can reduce the energy required by more than 46 kJ mol⁻¹, thereby increasing the likelihood of 5AT pyrolysis. Meanwhile, the reduced thermal safety parameters indicated that NiO makes 5AT more susceptible to thermal decomposition due to thermal explosion transition, so more care is needed for the storage of 5AT. Moreover, the TG-FTIR test was conducted to study the pyrolysis mechanism with or without NiO; the results showed that NiO exerts different catalytic effects on the gas products. The results from this study can offer direction and recommendations for future research on solid propellants. Full article

(This article belongs to the Special Issue Turbulent Combustion Modelling, Experiment and Simulation)

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18 pages, 4604 KiB

Open AccessArticle

Flaming Ignition of PMMA, Pine Wood and Pine Needle by External Radiation: Autoignition and Radiant Distance Effect

by Jiayun Song

Fire 2023, 6(4), 163; https://doi.org/10.3390/fire6040163 - 18 Apr 2023

Viewed by 1520

Abstract

Flame radiation is one of the important causes of wildland–urban interface (WUI) fires. PMMA, pine needle and pine wood are the most common fuels in WUI fires, but the radiant distance effect on the flaming ignitions as well as the subsequent burning behavior [...] Read more.

Flame radiation is one of the important causes of wildland–urban interface (WUI) fires. PMMA, pine needle and pine wood are the most common fuels in WUI fires, but the radiant distance effect on the flaming ignitions as well as the subsequent burning behavior is still poorly understood. This work represents an experiment to investigate the flaming autoignition of PMMA, pine-needle and pine-wood fuel beds with different radiant distances (25 mm–100 mm) under a uniform incident radiant heat flux, 25 kW/m² The experiment results show that for PMMA and pine wood, they all transition from gas-phase ignition near the cone heater to solid-phase ignition. For pine needle, it has smoldering ignition and smoldering-to-flaming ignition. The relationship between radiant distance and ignition delay time is an approximately inverted u-shape curve, and there exists a critical radiant distance (D = 60 mm) for the minimum ignition delay time. For pine wood and PMMA, when D < 60 mm, there exists a linear relationship between radiant distance, D, and

t_{i g}^{- 1 / 2}

. Full article

(This article belongs to the Special Issue Turbulent Combustion Modelling, Experiment and Simulation)

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15 pages, 4592 KiB

Open AccessArticle

Simulation Research on Effects of Ambient Pressure on Plug-Holing Phenomenon in Tunnel Fires with a Shaft

by Yongzheng Yao, Yintong Wang, Yue Zhang and Jinlong Zhao

Fire 2023, 6(4), 143; https://doi.org/10.3390/fire6040143 - 03 Apr 2023

Cited by 2 | Viewed by 1449

Abstract

This paper studied the effects of ambient pressure on the plug-holing phenomenon in tunnel fires with a shaft by a Fire Dynamics Simulator. The influence of ambient pressures on the smoke movement, temperature distribution, critical Richard number (Ri_c) and critical [...] Read more.

This paper studied the effects of ambient pressure on the plug-holing phenomenon in tunnel fires with a shaft by a Fire Dynamics Simulator. The influence of ambient pressures on the smoke movement, temperature distribution, critical Richard number (Ri_c) and critical shaft height for plug-holing were analyzed in detail. A new prediction formula of smoke flow velocity considering different pressures was modified. A prediction formula of smoke temperature distribution beneath the ceiling under different pressures was developed. As a result, a prediction model of Richard numbers to determine whether the plug-holing occurs was proposed by combining smoke flow velocity and smoke temperature distribution. The critical Richard numbers (Ri_c) and critical shaft height (h_c) increases as the pressure decreases. Outcomes in this study can provide references for the design of a natural ventilation system in tunnel fires at a higher altitude. Full article

(This article belongs to the Special Issue Turbulent Combustion Modelling, Experiment and Simulation)

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13 pages, 3536 KiB

Open AccessArticle

Numerical Study on Coupled Smoke Control Using Longitudinal Ventilation and Naturally Ventilated Shafts during Fires in a Road Tunnel

by Yongzheng Yao, Yintong Wang, Liang Chen, Fei Ren and Congling Shi

Fire 2023, 6(3), 126; https://doi.org/10.3390/fire6030126 - 19 Mar 2023

Cited by 1 | Viewed by 1530

Abstract

Longitudinal ventilation and smoke extraction by shaft are common smoke control methods in road tunnel fires. Tunnels often adopt one of these methods in practical engineering. However, it may have a better effect to adopt the method of mixing the two smoke exhaust [...] Read more.

Longitudinal ventilation and smoke extraction by shaft are common smoke control methods in road tunnel fires. Tunnels often adopt one of these methods in practical engineering. However, it may have a better effect to adopt the method of mixing the two smoke exhaust methods together, which has not been revealed in the previous literature. Hence, the coupled effects of longitudinal ventilation and natural ventilation with shafts on the smoke control in tunnel fires were studied in this work. Numerical simulation was carried out considering different longitudinal ventilation velocities (0–4 m/s) and 4 kinds of typical shaft arrangements (shaft lengths range of 3–12 m, shaft intervals range of 27–60 m). The smoke spread length and smoke exhaust efficiency were analyzed systematically. Results show that (1) with the increase in longitudinal ventilation velocity, the total smoke spread length firstly decreases (V < 1 m/s) and then keeps almost constant (1 m/s < V < 2 m/s), finally increasing significantly (V > 2 m/s). (2) The length of the dangerous area (over 60 °C) at human height is basically 0 for all cases (except for Scenario 4 of shaft arrangement) when the longitudinal ventilation velocity is less than 2 m/s. (3) The CO smoke flow rate through the shaft is relatively high when the longitudinal ventilation velocity is within the range of 1–2 m/s for 4 kinds of shaft arrangement scenarios. Factors such as smoke spread and smoke exhausted through the shaft are comprehensively considered to judge smoke exhaust performance. The following conclusions can be drawn: when the ventilation velocity ranges from 1–2 m/s, it has a positive impact on the smoke control in tunnel fires with natural ventilation with shafts. When the ventilation velocity exceeds 2 m/s, the total smoke spread length and the length of the danger area increase, and the smoke stratification becomes worse, which brings inconvenience to rescue work. The results can provide reference for the design of fire protection in tunnels. Full article

(This article belongs to the Special Issue Turbulent Combustion Modelling, Experiment and Simulation)

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14 pages, 5767 KiB

Open AccessArticle

Research on the Combustion Characteristics of Coal Piles and the Fire Risks of Closed Coal Bunkers

by Lihong Zhao, Ping Fang, Zhenhua Wang, Jinlong Zhao and Niqi Xiao

Fire 2023, 6(3), 123; https://doi.org/10.3390/fire6030123 - 16 Mar 2023

Viewed by 1727

Abstract

Closed coal bunkers emerged as a novel form of coal storage for coal-fired power stations. Nevertheless, heat builds continually in the storage process because of the constant oxidation of coal and combined with the impact of a confined coal bunker environment, it is [...] Read more.

Closed coal bunkers emerged as a novel form of coal storage for coal-fired power stations. Nevertheless, heat builds continually in the storage process because of the constant oxidation of coal and combined with the impact of a confined coal bunker environment, it is difficult for heat to dissipate, resulting in frequent coal bunker fires. Consequently, research on coal pile combustion characteristics is crucial to the design of coal bunker safety. The experimental platform was set up in this study to conduct combustion tests of various specifications, and the burning rate, flame height, flame temperature, and heat radiation flux were analyzed to identify the critical parameters impacting coal bunker safety. First, the maximum burning rate of coal heaps during steady burning was calculated, improving coal pile combustion theory and providing guidance for coal bunker design. Second, the maximum flame height was determined, which can provide an important design guide for coal bunker height designs. In addition, it was discovered that high temperatures in flames, smoke, and smoldering coal might cause coal bunker buildings to collapse, so future designs should strengthen coal bunker fire resistance and keep the coal pile away from the load-bearing structures to prevent collapse from excessive temperatures. Moreover, the diameter of coal piles has an influence on the heat flow. For this reason, a coal bunker’s design must consider the coal pile’s fire separation distance from the coal bunker and avoid large coal piles. Consequently, the study gives recommendations and support for planning coal bunker safety and enriches experimental data for coal pile fires. Full article

(This article belongs to the Special Issue Turbulent Combustion Modelling, Experiment and Simulation)

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14 pages, 4413 KiB

Open AccessArticle

Effects of Fire Location and Forced Air Volume on Fire Development for Single-Ended Tunnel Fire with Forced Ventilation

by Jinlong Zhao, Zhenhua Wang, Zhenqi Hu, Xinyuan Cui, Xiandu Peng and Jianping Zhang

Fire 2023, 6(3), 111; https://doi.org/10.3390/fire6030111 - 11 Mar 2023

Cited by 3 | Viewed by 1468

Abstract

Single-ended tunnels are a typical structure and an important part during tunnel construction. In the case of a fire in a single-ended tunnel, forced ventilation is commonly used to create a safe area near the excavation face. This work is aimed at examining [...] Read more.

Single-ended tunnels are a typical structure and an important part during tunnel construction. In the case of a fire in a single-ended tunnel, forced ventilation is commonly used to create a safe area near the excavation face. This work is aimed at examining the effects of fire location and air volume on fire development for single-ended tunnel fires with forced ventilation. A single-ended tunnel was built in Fire Dynamics Simulator (FDS), and twenty simulation tests were carried out. In the simulation, the distribution of flow field, temperature, and CO concentration in the tunnel were measured and analyzed. The results show that three regions can be identified based on airflow directions and velocity: (1) turbulent flow zone, (2) turbulent flow transition zone, and (3) steady flow zone. It was found that the maximum ceiling temperature rise decreases first with the distance between the fire source and the excavation face (X_L), and then increases with a further increase in X_L. The simulation results also showed that CO can easily accumulate on the ventilation duct side at the fire source position and the opposite side of the ventilation duct 5.0–15.0 m downstream of the fire source. Both the CO concentration and the maximum ceiling temperature rise decrease with increasing air volume, while the larger forced air volume will result in a higher risk for the downstream regions. The present results are of practical importance in firefighting and personnel evacuation in single-ended tunnels with a forced ventilation system. Full article

(This article belongs to the Special Issue Turbulent Combustion Modelling, Experiment and Simulation)

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19 pages, 2148 KiB

Open AccessArticle

Evacuation Time Estimation Model in Large Buildings Based on Individual Characteristics and Real-Time Congestion Situation of Evacuation Exit

by Qing Deng, Bo Zhang, Zheng Zhou, Hongyu Deng, Liang Zhou, Zhengqing Zhou and Huiling Jiang

Fire 2022, 5(6), 204; https://doi.org/10.3390/fire5060204 - 29 Nov 2022

Cited by 5 | Viewed by 5346

Abstract

Fire is one of the most common and harmful disasters in real life. In 2021, firefighting teams in China reported 748,000 fires, resulting in 1987 deaths, 2225 injuries and CNY 6.75 billion of direct property losses, which account for 0.05‰ of GDP. Scientific [...] Read more.

Fire is one of the most common and harmful disasters in real life. In 2021, firefighting teams in China reported 748,000 fires, resulting in 1987 deaths, 2225 injuries and CNY 6.75 billion of direct property losses, which account for 0.05‰ of GDP. Scientific and accurate estimation of evacuation time can provide decision support for intelligent fire evacuation. This paper aims to effectively improve the evacuation efficiency of people in large buildings, especially for a scenario with intricate evacuation passages. There are many factors that make a difference in evacuation time, such as individual behavior, occupant density, exit width, and so on. The people distribution density is introduced to effectively assess the impact of unstable pedestrian flow and unbalanced distribution in the process of evacuation. The verification results show that there is a strong positive correlation between people distribution density and evacuation time. Combining the people distribution density with many other factors, the training dataset is built by Pathfinder to learn the relationship between evacuation time and influencing factors. Finally, an evacuation time prediction model is established to estimate the consumption time that occupants spend on moving in the evacuation process based on stacking integration. The model can assist occupants in choosing different channels for evacuation in advance. After testing, the average error between the predicted evacuation consumption time and the reference time is 3.63 s. The result illustrates that the model can accurately predict the time consumed in the process of evacuation. Full article

(This article belongs to the Special Issue Turbulent Combustion Modelling, Experiment and Simulation)

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13 pages, 1217 KiB

Open AccessArticle

Theoretical Prediction Model of the Explosion Limits for Multi-Component Gases (Multiple Combustible Gases Mixed with Inert Gases) under Different Temperatures

by Qiuju Ma, Yuhao Guo, Mingyu Zhong, Jingfeng You, Ya He, Jianhua Chen and Zhaokun Zhang

Fire 2022, 5(5), 143; https://doi.org/10.3390/fire5050143 - 21 Sep 2022

Cited by 2 | Viewed by 1674

Abstract

Combustible gases often lead to fire and explosion accidents due to their unsafe characteristics. Furthermore, their explosion limits are influenced by various factors. In the industrial production process, the operating unit is often in a high-temperature environment, and the multi-component gas explosion limits [...] Read more.

Combustible gases often lead to fire and explosion accidents due to their unsafe characteristics. Furthermore, their explosion limits are influenced by various factors. In the industrial production process, the operating unit is often in a high-temperature environment, and the multi-component gas explosion limits under this condition are difficult to determine. Therefore, it is urgent to have a universal theoretical prediction model to rapidly predict the multi-component gas explosion limits at high temperatures. This paper proposes a theoretical prediction model for the lower explosion limit of multi-combustible gases containing inert gases at different temperatures based on the heat balance equation and radiation heat loss, which can be used to solve the lower explosion limit of the “multiple combustible gases + multiple inert gases” mixture at different temperatures. It solves the explosion limits of methane, ethylene, propane, and propylene mixed with nitrogen with relative errors of 2.66%, 5.98%, 6.82%, and 5.88%, respectively, compared with experimental data. It also obtained theoretically predicted gas explosion limits for methane, ethylene, propane, and propylene mixed with carbon dioxide, with relative errors of 3.24%, 5.13%, 6.19%, and 5.58%, respectively. Although the reference experimental data made the model validation somewhat limited, validation with data for multiple single gases and temperatures still gave the model considerable reliability. Full article

(This article belongs to the Special Issue Turbulent Combustion Modelling, Experiment and Simulation)

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16 pages, 7636 KiB

Open AccessArticle

Experimental Study of the Effect of Slope on the Spread and Burning Characteristics of a Continuous Oil Spill Fire

by Xiaoxiao Sun, Hong Huang, Jinlong Zhao and Guangheng Song

Fire 2022, 5(4), 112; https://doi.org/10.3390/fire5040112 - 03 Aug 2022

Cited by 6 | Viewed by 2299

Abstract

Elucidating the characteristics of continuous oil spill fires for different slope conditions can provide important theoretical support for the prevention of, and rescue strategies during, oil spill fire accidents. For this research, we conducted experiments to observe the spread and burning process of [...] Read more.

Elucidating the characteristics of continuous oil spill fires for different slope conditions can provide important theoretical support for the prevention of, and rescue strategies during, oil spill fire accidents. For this research, we conducted experiments to observe the spread and burning process of continuous oil spill fires under different slope conditions. The changes in physical attributes, such as flame spread rate, burning rate, heat convection at the bottom surface, and flame feedback radiation, were analyzed for the different slope conditions. The results showed that the shrinking phase becomes difficult to see, and the steady phase disappears when the slope increases in the spread and burning process. When the slope increases, the spread speed and spread area increase, and burning rate decreases. Compared with a non-burning process, the resistance to spread decreases in the burning process. We show that the slope directly affects the spreading process, and indirectly affects the burning process. Full article

(This article belongs to the Special Issue Turbulent Combustion Modelling, Experiment and Simulation)

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Review

Jump to: Editorial, Research

16 pages, 4101 KiB

Open AccessReview

Fire-Safe Biobased Composites: Enhancing the Applicability of Biocomposites with Improved Fire Performance

by Dan Zhang

Fire 2023, 6(6), 229; https://doi.org/10.3390/fire6060229 - 08 Jun 2023

Cited by 1 | Viewed by 1794

Abstract

Research has recently transitioned from the study of fossil-based materials to bio-sourced ones, following the quest to achieve sustainability. However, fire presents a unique hazard to bio-composite materials, which limits their applicability in various sectors. This necessitates an in-depth assessment of the fire [...] Read more.

Research has recently transitioned from the study of fossil-based materials to bio-sourced ones, following the quest to achieve sustainability. However, fire presents a unique hazard to bio-composite materials, which limits their applicability in various sectors. This necessitates an in-depth assessment of the fire behaviour of biobased composites used for specific applications. Improving the fire properties of bio-composites with flame retardants tends to reduce mechanical strength. Therefore, this review focused on biobased composite materials for packaging, structural, automotive, and aeronautical applications that are both mechanically strong and fire safe. It was noticed that the interfacial bonding between the matrix and the reinforcement should be optimized. In addition, optimum amounts of flame retardants are required for better fire performance. This article covers flame retardants for biobased composites, the optimum amount required, and the extent of improvement to the thermal stability and flammability of the materials. This research will help material scientists and the like in their selection of biomass feedstock, flame retardants, and general materials for different types of applications. Full article

(This article belongs to the Special Issue Turbulent Combustion Modelling, Experiment and Simulation)

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15 pages, 1009 KiB

Open AccessReview

Review of Structural Fire Hazards, Challenges, and Prevention Strategies

by Chenting Zhang

Fire 2023, 6(4), 137; https://doi.org/10.3390/fire6040137 - 29 Mar 2023

Cited by 3 | Viewed by 3828

Abstract

Reducing the occurrence of structural fires is the common goal of all countries. However, the development level of different countries determines the degree of perfection of local fire management regulations. Developed countries have a more rational urban layout, sufficient firefighting resources, and the [...] Read more.

Reducing the occurrence of structural fires is the common goal of all countries. However, the development level of different countries determines the degree of perfection of local fire management regulations. Developed countries have a more rational urban layout, sufficient firefighting resources, and the ability to guarantee fire safety. In contrast, haphazardly built residential areas in developing and underdeveloped countries have more safety hazards, which increases the challenges of local fire management. This study provides an overview of the causes and impacts of fires in different countries and identifies gaps in fire safety between developed and developing countries, as well as corresponding strategies to deal with fires. It is worth mentioning that the development and evolution of artificial intelligence (AI) has made it possible to predict fires, thereby greatly reducing damage and losses caused by fires. In addition, the development of new fire-resistant building materials, etc., provides more means to reduce the possibility of fire. Full article

(This article belongs to the Special Issue Turbulent Combustion Modelling, Experiment and Simulation)

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