A study of the probability distribution of pool fire extinguishing times using water mist

Water mist, a replacement for Halon gaseous agents in fire fighting, has been studied for decades. However, the fire-extinguishing reliability of water mist is debated. For example, there are significant differences in extinguishing times between tests conducted under the same conditions, and water mists have difficulty extinguishing small fires. To date, no study of the probability distribution of extinguishing times has been reported. In this study a statistical analysis of the extinguishing time distribution of pool fires extinguished using water mist is presented. The fire sources were circular/square stainless steel pans with gasoline, diesel, ethanol or daqing RP-3 as fuel. Two types of extinguishing scenarios were observed. In one situation, the fire was extinguished via a blow off process, when the flames had not yet been suppressed. Flame cooling is the primary fire extinguishing mechanism; the mass loss rate and combustion heat of the fuel are two key factors. In the other situation, the fire was initially suppressed and subsequently extinguished after a long suppression stage. Surface cooling is the primary fire extinguishing mechanism; the flash point of the fuel is the key factor.     

The inhibitory combustion reaction performance and tail gas analysis of composite ultra-fine dry powder extinguishing agent containing different additives

For lack of an extinguishing agent with high-efficiency, non-toxic and environmentally friendly, a new type of extinguishing agent was fabricated to solve such an urgent problem. In this study, the zinc borate (ZB) and ferrocene (Fe(Cp)₂) were utilized as two additives for extinguishants to suppress combustion reaction and the toxicity of the tail gas was detected. The mass fraction of ZB corresponding to the optimal inhibitory effect was determined to be 0.5–1.5%, by contrast, the optimum interval of Fe(Cp)₂ was detected as 0.5–1.0%. Similarly, with the increasing proportion of the two additives, the homologous inhibitory action was gradually weakened. From the perspective of thermogravimetric analysis (TGA), it was indicated that the ZB accelerated the pyrolysis process of the extinguishant, making its thermal decomposition process more thoroughly. Meanwhile, the differential scanning calorimetry (DSC) demonstrated that the decomposition efficiency was markedly improved when the amount of ZB was maintained at 0.5–1.5%. Besides, the tail gas tests were implemented to assess the extent of toxic and harmful properties. In terms of the carbon monoxide (CO) and carbon dioxide (CO₂) generated, once the mass fraction of ZB and Fe(Cp)₂ was less than 1.5% and 1.0% respectively, the concentration of CO and CO₂ was distinctly lower than that without additives. Moreover, the inhibitory ability on nitrogen oxides (NOx) was enhanced when the mass fraction of the two additives was kept below 1.0%. The results confirmed that a more practical extinguishant was proposed and it can provide guidance for the application and development of extinguishants.     

Extinguishing pool fires with aqueous ferrocene dispersions containing gemini surfactants

The objective of the present study was to explore the relationship between the dispersibility and fire-extinguishing capability of aqueous ferrocene dispersions containing gemini surfactants belonging to the same series, namely, olfin E1020, olfin PD 201, and surfynol 465. In this study, the dispersibility and ability to suppress pool fires were characterized by turbidity and extinguishing time, respectively. Ultrasonication enabled easy preparation of the aqueous dispersions of ferrocene powder containing the gemini surfactants. Visual observations and turbidity measurements clearly demonstrated that the order of dispersibility was as follows: ferrocene dispersion containing surfynol 465 ≥ ferrocene dispersion containing olfin E1020 > ferrocene dispersion containing olfin PD201. Fire suppression experiments indicated that the ferrocene diameter, in the ferrocene diameter range of 10.4–21.5 μm, negligibly influenced the extinguishing time. Furthermore, for the same ferrocene samples as were used for the turbidity measurements, the order of extinguishing ability was as follows: ferrocene dispersion containing surfynol 465 > ferrocene dispersion containing olfin E1020 > ferrocene dispersion containing olfin PD201; thus, the extinguishing ability was identical to the dispersibility order.     

近年我国家装材料变化对住宅火灾的影响研究

住宅火灾危险性和家装材料有着紧密联系。为研究近年我国家装材料变化对住宅火灾的影响,调研了近30年我国家装材料的变化趋势,分析了常见家装材料的火灾特性变化,并完成了对不同年代常见家装材料组合的火灾危险性综合评价,结果表明:随着近30年家装材料的变化,软体家具、木质家具、地板和壁纸的燃烧性能均有所改善,但软体家具产烟能力恶化;2000年~2010年合成材料的应用使得家装材料组合的综合火灾危险性有所提升,引起大型亡人火灾的可能性更大;2010年后阻燃材料的普及使得家装材料组合的综合火灾危险性有所降低,对消防安全的作用已经凸显,但同时我国住宅火灾中“小火亡人”事故可能更为频发,未来研究应该更加关注于降低阻燃材料的烟气危害性。     

Experimental investigation on extinguishing performance of a novel nanocomposite for gaseous fires

A novel nanocomposite was synthesized by incorporating three different types of flame-retardants and its extinguishing performance was tested for gaseous fires. The nanocomposite consists of the inorganic magnesium hydroxide (MH) nanoparticles as the dominant component, the nitrogen-based melamine cyanurate (MCA), and the phosphorus-based ODOPB. The wet mixing, dry mixing, and ultrasonic agitation were employed in the preparation process to enhance the homogeneity of the nanocomposite. The prepared powders were characterized using a series of analytical instruments including X-ray diffraction (XRD), scanning electron microscopy (SEM), thermal gravity analyzer (TGA), and differential scanning calorimeter (DSC). The efficiency of various samples in extinguishing gaseous fires was investigated in a lab-scale extinguishing system. The fire extinguishing tests indicated that the nanocomposite is considerably more effective in fire extinguishing than other powders in terms of extinction time and agent mass consumed. The fire extinction time of nanocomposite was 45.2% shorter than that of commercial ABC-MAP powder. Furthermore, the consumed amount of nanocomposite was 63.2% less than that of commercial powder. In addition, the order of extinguishing mass concentrations was as follows: the novel nanocomposite (103.7 g/m³) < MH/MCA (148.1 g/m³) < MH/ODOPB (155.6 g/m³) < MH (170.4 g/m³) < commercial ABC powder (281.5 g/m³) < MCA/ODOPB (384.1 g/m³). The fire suppression mechanisms of the nanocomposite were also discussed. It was inferred that the extinguishing mechanism of nanocomposite comprised of simultaneous chemical and physical inhibition actions involving chemical inhibition action, cooling action, and asphyxiation action. This study provides a promising attempt to gain benefits from the striking features of nanotechnology and flame-retardants in extinguishing gaseous fires.     

Development of a 3D risk analysis technique for fire disaster and its application on accident simulation of a public site

In this research, we constructed a three-dimensional fire risk analysis technique (3D-FRAT) for common building fires. To demonstrate its effect, the 3D-FRAT employed a self-developed 3D risk-calculating module in combination with the Fire Dynamics Simulator (FDS) software to simulate the Welcome Restaurant accident that happened on February 15, 1995 in Taichung City, Taiwan. This study only focuses on thermal radiation and provide a preliminary method to quantify a fire risk. Different firefighting equipment that comply with the related building and fire-preventive regulations have been used in the simulations to test their mitigating effectiveness on the accident. The results were shown by animation, 3D pictures, and sliced pictures to facilitate the researchers’ understanding of human hazards caused by thermal radiation or smoke in a specific fire accident. The minimal personnel escaping times for different hazardous factors were estimated; various firefighting designs that can reduce loss of human life and property were also perused. According to the simulation results, the individual risk values in Welcome Restaurant were between 3.108 × 10⁻⁹ to 2.719 × 10⁻⁵ (deaths/year). It is foreseeable that the 3D-FRAT can become a useful tool for related organizations to choose better fire-resistant buildings or fire-fighting equipment in the future.     

Assessment of four turbulence models in simulation of large-scale pool fires in the presence of wind using computational fluid dynamics (CFD)

Pool fires are the most common of all process industry accidents. Pool fires often trigger explosions which may result in more fires, causing huge losses of life and property. Since both the risk and the frequency of occurrence of pool fires are high, it is necessary to model the risks associated with pool fires so as to correctly predict the behavior of such fires.Among the parameters which determine the overall structure of a pool fire, the most important is turbulence. It determines the extent of interaction of various parameters, including combustion, wind velocity, and entrainment of the ambient air. Of the various approaches capable of modeling the turbulence associated with pool fires, computational fluid dynamics (CFD) has emerged as the most preferred due to its ability to enable closer approximation of the underlying physical phenomena.A review of the state of the art reveals that although various turbulence models exist for the simulation of pool fire no single study has compared the performance of various turbulence models in modeling pool fires. To cover this knowledge-gap an attempt has been made to employ CFD in the assessment of pool fires and find the turbulence model which is able to simulate pool fires most faithfully. The performance of the standard k–? model, renormalization group (RNG) k–? model, realizable k–? model and standard k–ω model were studied for simulating the experiments conducted earlier by Chatris et al. (2001) and Casal (2013). The results reveal that the standard k–? model enabled the closest CFD simulation of the experimental results.     

Wet bench reactive hazards of cleaning stages in semiconductor manufacturing processes

According to the research from FM Global (Factory Mutual Insurance Company), most of the incidents that have occurred in semiconductor plants in the past two decades were reported as “Fire Cases”. They claim that the fires in wet chemical cleaning processes were mainly caused by heater failure. However, depending on the process conditions, electrical heaters are designed to turn off automatically when the temperature reaches a set point. Therefore, a thorough study of the situations related to possible fires in wet chemical cleaning processes is necessary.

This study focused on the incompatible behaviors of cleaning materials used in the wet bench stage. These results can be applied to determine the causes of fires in the wet bench stage from using reactive chemicals for cleaning purposes.

Another purpose of this study was to investigate the potential hazards of widely used chemicals (hydrogen peroxide, concentrated sulfuric acid, hydrochloric acid and isopropyl alcohol) within similar processes in semiconductor plants. Experimental data were also verified in order to establish a concentration triangular diagram, which could be used to identify a combustion, deflagration or even detonation zone. Finally, this study can provide basic design data for an inherently safer process to avoid potential hazards caused by dangerous mixtures, which may result in large property loss in semiconductor plants.     

雷击火形成及预防扑救对策

雷击火作为天然火源是一种难以控制的自然现象,其形成机理极为复杂。雷击火与雷暴的活动密切相关。     

Improved models of failure time for atmospheric tanks under the coupling effect of multiple pool fires

Fire accidents of chemical installations may cause domino effects in atmospheric tank farms, where a large amount of hazardous substances are stored or processed. Pool fire is a major form of fire accidents, and the thermal radiation from pool fire is the primary hazard of domino accidents. The coupling of multiple pool fires is a realistic and important accident phenomenon that enhances the propagation of domino accidents. However, previous research has mostly focused on the escalation of domino accidents induced by a single pool fire. To overcome the drawback, in this study, the failure of a storage tank under the coupling effect of multiple pool fires was studied in view of spatial and temporal synergistic process. The historical accident statistics indicated that the accident scenario of two-pool fires accounted for 30.6% in pool fires. The domino accident scenario involving three tanks is analyzed, and the typical layout of tanks is isosceles right triangle based on Chinese standard “GB50341-2014”. The thermal response and damage of a target tank heated by pool fires were numerically investigated. The volume of 500 m³, 3000 m³, 5000 m³ and 10000 m³ were selected. Flame temperature was obtained by FDS, and then was input onto the finite element model. The temperature field and stress field of target tanks were simulated by ABAQUS. The results showed that the temperature rise rate of the target tanks under multiple pool fires was higher than that under a single pool fire. The failure time of the tank under the coupling effect of multiple fires was lower than that under the superposition of multiple fires without the first stage. The stress and yield strength were compared to judge the failure of the target tank. The model of failure time for the tank under the coupling effect of pool fires was established. Through the verification, the deviation of this model is 4.02%, which is better than the deviation of 15.76% with Cozzani's model.     

Configuration predictions of large liquefied petroleum gas (LPG) pool fires using CFD method

Liquefied petroleum gas (LPG) has potential pool fire risks due to its flammability. The configuration of pool fires plays a significant role when applying the solid flame model or point source model to assess the risks from heat radiation. However, no existing correlations can precisely predict the configuration of large LPG (100% propane) pool fires. To enhance the fundamental understanding on how pool diameter and wind velocity can influence the configuration of large LPG pool fires, an experimentally validated Computational Fluid Dynamics (CFD) model is employed to simulate fires using different burning rate models. Fire temperature profiles, flame heights, and flame tilts predicted by the CFD model were compared with empirical models and experimental data. Accordingly, new correlations for flame height and flame tilt as functions of pool diameter D and wind velocity u_w have been developed. The comparisons demonstrate that the new correlations have the best overall accuracy in the prediction of flame height and tilt for large LPG pool fires under different conditions (10 m ≤ D ≤ 20 m, 0 ≤ u_w ≤ 3 m·s⁻¹).     

受限空间脉冲细水雾灭火数值模拟

为研究脉冲细水雾灭火效果和灭火机理,采用FDS软件对连续和脉冲细水雾熄灭受限空间油盘火进行了数值模拟。通过模拟和理论分析确定了脉冲细水雾周期为8 s开启、8 s暂停,并设置了冷却和窒息两种灭火条件,对两种细水雾熄灭不同尺寸的柴油池火进行了研究。结果表明:连续细水雾无法熄灭直径15 cm和20 cm的小尺寸油盘火,对直径25 cm中尺寸油盘火的灭火机理为冷却,对直径为30cm和35 cm大尺寸油盘火的灭火机理为窒息;脉冲细水雾能够熄灭不同尺寸的油盘火,且灭火效率高,火焰熄灭均发生在喷头暂停喷水期间,灭火机理为水雾蒸发稀释氧气而窒息。     

Function of Basic Fire Research

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中国舰船消防现状及发展趋势

本文从体制、装备、消防教育等方面简略介绍了中国舰船消防体系，对目前舰船火灾及消防形势进行了分析，提出了舰船消防面临的任务和主要课题，并对中国舰船火灾及其防治前景进行了探讨．     

二氧化碳灭火系统扑灭汽车发动机舱内火灾试验研究

本文使用二氧化碳灭火系统进行了汽车发动机舱火灾灭火试验,试验表明:系统采用闭式洒水喷头自动启动时,在风的作用下,火羽向风的下游偏移,可能导致下游的喷头启动,不能有效灭火.系统手动启动时,在发动机舱内部安装4个或者8个开式喷头,均能迅速扑灭汽车发动机舱火灾,且具有灭火时间短,灭火剂用量少,灭火效果好的特点.     

火灾科学的发展前景

本文研究了火灾科学的发展前景，指出了火灾科学必然包括各种领域并列举了课题的分类，阐明了每一领域的研究都是防止火灾损失必不可少的。通过分析火灾科学近年来的工作，阐述了火灾研究的现状。大多数研究都是以最近的火灾为背景展开的，虽然其中许多侧重于基础研究，并未针对某一特定火灾。最后本文提出了火灾研究的将来需要。由于未来技术的发展和生活方式的改变有的难以预测，与之紧密相关的未来火灾也难以想象，因此，只能试从当前火灾研究去推测将来。本文认为将来的火灾研究课题大多数为基础研究，虽然它也或多或少与未来火灾有关系。并且预测随着新概念的引入，将来的火灾研究的数据和方法都活发生很大变化。     

Analytical modelling of hydrocarbon pool fires: Conservative evaluation of flame temperature and thermal power

As well known, risk is a combination of probability and consequences of an accident. In analyzing the consequence of accidental hydrocarbon fires and the potential for domino effects, the evaluation of the flame extent and temperature are of the utmost importance. Since the primary effects of pool fires are connected to thermal radiation and issues of interplant/tank spacing employees’ safety zones, firewall specifications are to be addressed on the basis of a proper consequence analysis. By means of real scale experimental tests it was verified that both the thermal power and the flame temperature, T_f, increase as the pool area increases, up to reach maximum values in connection with a “critical pool dimension”. Dealing with pool areas higher than the critical one, experimental results, performed by different researchers at different scales, show a decrease of T_f. An in-depth analysis of the different concurring phenomena connected to a pool fire development allowed identifying the limiting step controlling the flame temperature. In fact, the trend of T_f is mainly determined by the increasing difficulty of oxygen diffusion within the internal bulk of gaseous hydrocarbons. In this article, we propose a novel pool fire modelling approach based on the simplified physical phenomena occurring in a circular turbulent diffusion fire and suitable to provide a theoretical insight into the above-mentioned experimental trends and to obtain the maximum values of the flame temperature and of the thermal power.The geometry of the pool is dictated by the surroundings (i.e., diking) and the analytical models here presented were successfully applied to the common situation of circular pools.However, it must be remarked that the developed model, matching fairly well experimental data for different hydrocarbons, can be applied in modelling similar scenarios characterized by different geometric or environmental conditions (e.g. road and rail tunnel fires).     

Do home fire and safety checks by on-duty firefighters decrease the number of fires? Quasi-experimental evidence from Southern Sweden

Introduction: Fire and rescue services Syd, in the south of Sweden, started to conduct home fire and safety checks on a large scale in 2010. The goal was to reduce the damages from residential fires. Method: We estimate the effects of the intervention on the incidence of residential fires and evaluate its economic effect. We use a difference-in-kinks design to analyze time-varying intervention effects and conduct a cost–benefit analysis for the economic evaluation. Results: The results demonstrate that fires and developed fires decrease by a maximum of approximately 6% and 8% per year (assuming 100% causality) and that the intervention has positive economic effects, with the benefits estimated to be maximum 8–11 times higher than the costs. Practical applications: The results should be valuable as input when deciding whether to implement home fire and safety checks elsewhere.     

Metal hydride fires and fire suppression agents

Most metal hydrides are pyrophoric and water-reactive. Summaries of metal hydride fire incidents are presented to illustrate ignition scenarios, threats to personnel and equipment, and fire suppression experiences. Met-L-X™, a sodium chloride-based, certified, Class D fire suppression agent, has successfully extinguished some metal hydride fires by coating the hydride and excluding air access. However, the still hot hydride is prone to re-ignition upon surface disturbance, such as may be necessary during disposal. Previously reported testing of various Class D agents and moist sand for sodium hydride fires is reviewed here along with certification and ad hoc testing of existing Class D agents and recent testing of a new candidate Class D agent. Hydride explosibility testing is also briefly summarized. Additional fire and explosibility tests, as well as suppression agent reactivity evaluations, are recommended.     

燃烧烟尘凝团形貌的分形辨别方法研究

对火灾现场常见聚合物材料和易燃液体燃烧烟尘凝团进行了分形研究,通过线性回归得到了描述其形貌特征的分形维数和分形前置因子。研究发现大多数材料烟尘凝团的分形维数在1.5~2.0之间,燃烧时发烟量较大的材料通常具有较高的分形维数值。利用分形分析结论,对烟尘进行判别分析,可以准确判别烟尘种类。