Cooling characteristics of hot oil pool by water mist during fire suppression

Generally water is not favored for use in suppressing hot liquid fuel fires due to concerns of vapor explosion and boil-over, which could present potential danger to nearby personnel or firefighters. This paper reports on a series of full-scale fire experiments in which water mist was used in extinguishing large hot cooking oil fires. It was shown that water mist not only extinguished large fires effectively but also cooled hot oil from its ignition point (up to 360 °C) to below its flash point (200 °C) in a short period of time and prevented the fire from re-igniting. No vapor explosion was observed in the experiments when water droplets touched the hot oil whose temperature was higher than the superheat-limited temperature of water. A boiling layer of mixed bubbles, water droplets and oil was formed in the hot oil after all flames were extinguished, as water droplets boiled, bubbled and expanded in the hot oil. No boil-over or spillage of the oil over the container was observed in the experiments when water mist was discharged into the oil at high temperature (>300 °C) but boil-over did occur in experiments when the water mist was discharged into oil at a relatively moderate temperature (∼200 °C). In this paper, the mechanisms of cooling of hot oil by water mist are investigated, and the formation and development of the boiling layer during cooling are analyzed both experimentally and theoretically.     

A study of portable water mist fire extinguishers used for extinguishment of multiple fire types

This paper describes both theoretical and experimental studies on the application of a portable water mist extinguisher in suppressing multiple fire types. Two prototype portable water mist fire extinguishers were developed and their feasibility in extinguishing flammable liquid, cooking oil and wood crib fires, and for use in fires associated with an energized target was investigated. The interaction between water mist and the fire plume was studied by analyzing the instantaneous process of fire extinction, and fire and fuel temperature profiles. Both theoretical analysis and experimental results showed that the extinguishing mechanisms and process as well as water mist characteristics required (such as water flux density, droplet size and spray coverage) change with the types of fires encountered. The portable water mist extinguisher with appropriate mist characteristics was able to extinguish multiple fire types.     

Experimental study of water mist fire suppression in tunnels under longitudinal ventilation

This paper studies water mist fire suppression under different longitudinal ventilation velocities in tunnels by small-scale experiments. After a scaling study, two mist nozzles are used for suppressing crib fires under 5 ventilation speeds. The result comes out that fire suppression process can be divided into three stages including flame unitary restraining stage, surface flame extinguishing stage and inside flame suppression stage. Several factors influencing efficiency are investigated. When the interval between mist nozzle and fire source enlarges, the relationship curve between fire suppression time and ventilation velocity shows a ‘V’ figure. The best ventilation speed exists. Following the rules summarized, a coupling system of water mist and ventilation may increase fire suppression efficiency remarkably.     

含添加剂细水雾灭火技术探讨

细水雾灭火系统的添加剂仅限于水溶性的物质，而不能使用非水溶性的液态添加剂，使灭火添加剂的选择有一定局限性，迫切需要研制新型的含添加剂细水雾灭火系统，从真正意义上实现固、气、液三态的物理化学灭火方法的综合应用。从含添加剂细水雾灭火技术原理、灭火系统构成，以及添加剂添加方式出发，探讨了新型细水雾灭火系统以非水溶性液态物质作为添加剂，实现复合灭火的可能性及应用前景。     

高压细水雾灭火系统在档案库的灭火试验研究

细水雾灭火系统已被建议用于保护对水敏感的区域,如档案库房。通过试验研究了细水雾灭火系统控制与扑灭档案库房火灾的可能性,并比较不同喷头形式的细水雾灭火系统在扑救档案库房火灾中的局限性,为细水雾灭火系统在档案库房内的推广应用提供建议。     

两相流细水雾灭B类火实验研究

采用气液同管雾状流输送方式,在两相流系统中设置雾化混合器,使结构简化.实验研究不同热释放率时两相流细水雾的灭火特性及规律.采用热电偶树和气体分析仪测量火焰温度及火场氧浓度,通过灭火时间评价细水雾的灭火效率,将两相流细水雾的灭火效果同单相流进行对比.实验结果显示,热释放率对细水雾的灭火效果影响显著;两相流在较低压力下就可达到单相流较高压力的灭火效果.     

Experimental investigation of the fire extinguishing capability of ferrocene-containing water mist

This study focuses on the fire-suppression capabilities and corrosive properties of ferrocene dispersions. The motivation behind the present study was to develop a high-performance, phosphorus-free fire suppressant. Aqueous dispersions containing micron-sized ferrocene particles and surfactants were prepared using sonication techniques. In this study, Triton X-100 (TX), Noigen TDS-80 (NT), Tween 60 (T60), and Tween 80 (T80) were used as surfactants. Suppression experiments involving pool fires clearly indicated that aqueous ferrocene dispersions containing TX and micron-sized ferrocene with a d₅₀=16.9 μm exhibit shorter extinguishing times than a conventional wet chemical. Corrosion trials using steel plates immersed in ferrocene dispersions containing TX confirmed that there was no pitting corrosion, implying that ferrocene dispersions containing TX do not present a corrosion risk.     

细水雾灭火系统研究思想和方法探讨

为了推动利用环保的液体灭火剂-水灭火系统取代卤代烷的研究工作，从水灭火的历史和国外细水雾产品的发展趋势，对细水雾灭火系统的研究开发及方法，进行了总结，结合BH-40型超细气细水雾灭火系统的设计和实体灭火研制经验，提出了细水雾灭火系统研制的新思路和新方法。     

Inhibition of counterflow methane/air diffusion flame by water mist with varying mist diameter

In the present study, the effect of fine water mist on extinguishment of a methane–air counterflow diffusion flame was investigated to understand the underlying physics of fire extinguishment of highly stretched diffusion flame by water mist. Twin-fluid atomizers were used to generate polydisperse water mist of which Sauter mean diameters were 10, 20, 40, and 60 μm. When water mist is not added, the critical stretch rate at extinguishment is 439 s⁻¹ as compared to the theoretical value of 460 s⁻¹. For the case with water mist addition, when the stretch rate is small enough, almost all the water mist evaporates within the flame zone. On the other hand, for high stretch rate case, large mist droplets pass through the flame zone and can reach the stagnation plane. However, no oscillatory motion was found around the stagnation plane. Critical stretch rate at extinguishment decreases monotonously with the mass fraction of water mist independently of the mist diameter within the range of D₃₂ from 10 μm to 60 μm. On the other hand, with increase in the surface area parameter, the critical stretch rate at extinguishment decreases rapidly and becomes less sensitive at large surface area parameter, of which tendency is qualitatively in good agreement with theoretical predictions. For a constant surface area parameter, the critical stretch rate decreases with mist diameter because the mass fraction of water mist should increase in proportion to the mist diameter to keep the surface area parameter constant. When the water mist evaporates completely in the flame zone as in the present study, the mass fraction of the water mist is the dominant factor for fire extinguishment, rather than the surface area parameter. Therefore, an appropriate combination of stretch rate and water mist mass fraction should be provided to suppress effectively a given fire with a small amount of water mist.     

Experimental and numerical study on water mist suppression system on room fire

Full-scale experiment and numerical simulations are carried out on a room fire to study water mist suppression system with heat release rate of 6 MW. A computational fluid dynamics (CFD) model of fire-driven fluid flow, FDS (Fire Dynamics Simulator), is used to solve numerically a form of the Navier–Stokes equations for fire. A fire experiment without water mist is performed and the temperatures are measured to validate the predictions of FDS code against the experimental data. Then a fire experiment with water mist suppression system is performed and the temperatures and extinguishing time are measured. The validated numerical model is used to simulate the experiment; the temperatures, oxygen concentration and extinguishing time are compared and studied. In numerical simulations, the cell size sensitivity is analyzed. The experimental results of temperatures and extinguishing time are compared with the results of numerical simulations. It appears that the numerical results are in good agreement (qualitatively) with the experimental data in temperature fields. These useful data can be helpful in accomplishing the design of water mist suppression system and the design regulations for fire safety management.     

细水雾灭火影响因素研究进展

总结了细水雾灭火特性的影响因素研究进展,着重阐述了不同压力下雾滴粒径分布、不同添加剂对细水雾灭火性能的影响、通风条件对细水雾灭火效果的影响、障碍物是否存在及其位置对细水雾灭火的影响以及喷雾动量的内容、意义及其确定方法等,进一步提出了未来在对细水雾灭火特性影响因素的研究中应关注的问题。     

A comparative study of the effects of chemical additives on the suppression efficiency of water mist

This paper reports the results of a comparative study of the effects of various salt additives on the flame extinguishing efficiency of fine water sprays. The relative suppression efficiencies are gauged by comparing the extinguishment time of a heptane flame. Preliminary tests are performed in a reduced scale cup-burner; major results are obtained using the closed reduced compartment set-up.The addition of NaCl, KCl or KHCO₃ resulted in large improvements of the suppression efficiency of the water mist. Potassium compounds show the greatest effect as 10% solution of KHCO₃ reduces the average extinction time by up to 96% compared to pure water. The other additives tested have a less noticeable effects, with aqueous solutions of MnCl₂, ZnCl₂ and CuCl₂ showing minimal improvement over water, whereas (NH₄)₂HPO₄, (NH₂)₂CO and FeSO₄·7H₂O actually increasing the time taken to extinguish the flame.     

Major fire spread in a tunnel with water mist: A theoretical model

A model of the effect of water mist on major fire spread in a tunnel is described. It employs the concepts of non-linear dynamical systems theory and identifies the onset of instability with major fire spread in a tunnel. The purpose is to identify the thermo-physical and geometrical conditions which lead to instability and sudden fire spread. It uses as a starting point one of the non-linear models for major fire spread which have been developed by the author over many years and assumes that a water mist system operates.The case considered assumes the existence of a longitudinal forced ventilation and predicts the critical heat release rate needed for a fire to spread from an initial fire to an item with a given assumed shape; in the presence of water mist. There is assumed to be no flame impingement on the target object. The target object may be taken to approximate a vehicle. The illustrative case approximating fire spread from an initial fire to a heavy goods vehicle (HGV) is presented; it is not restricted to this case, however. The model is being identified with the name FIRE-SPRINT C1, which is an acronym of Fire Spread in Tunnels, Model C, Version 1. It has been developed from an earlier model, FIRE-SPRINT A3 and considers a case where, in the absence of a fire fighting system, there is the potential for a major fire.     

细水雾灭空间不同位置油池火的数值模拟

细水雾灭火以其高效、环保的特点，已成为最具潜力的哈龙灭火系统替代技术之一。本文采用计算流体力学（CFD）的方法，使用火灾场模拟软件FDS4．05模拟研究细水雾灭火系统对空间4个位置油池火的灭火效果。研究结果表明，细水雾对喷头正下方的火源灭火效果最好，且灭火效果随火源距离喷头横向距离的增加而减弱。     

对含添加剂细水雾灭火系统的分析

含添加剂细水雾灭火系统是当今火灾科学研究的热点之一。结合细水雾灭火系统的灭火机理对碱金属化舍物和泡沫添加剂的灭火效果进行了分析，指出了影响含添加剂细水雾灭火系统灭火性能的主要因素。讨论了目前含添加剂细水雾存在的问题，并展望了系统今后的研究方向和发展趋势。     

油盘形状对细水雾灭火效果影响的研究

采用正庚烷为燃料,在长4.6 m,宽3.2 m,高4 m的空间内,对圆形和方形油盘在不同预燃时间条件下进行灭火实验,在实验过程中采用热电偶树和气体分析仪对火焰温度及火场氧气体积分数进行测量,得到不同油盘形状对细水雾灭火的影响规律.     

Physical modelling of fire spread in Grasslands

The propagation of grassland fires is simulated using a fully physical based model, partially developed during the FIRESTAR European Union programme. This approach, based on a multiphase formulation, includes the calculation of the degradation of the vegetation (by dehydration and pyrolysis) and the turbulent/reactive flow resulting from the mixing between the ambient gas (wind flow) and the pyrolizate. The solid fuel is simulated as homogeneous distribution of solid particles forming a porous media, interacting with the gas flow using a continuous distribution of drag forces. Other source terms representing the interactions between the vegetation and the gas flow are also taken into account, such as the production of water vapour and gaseous fuel, the radiation of soot particles and ashes, and the convective exchange in the energy balance. The model was validated from preliminary calculations carried out at small scale, for a homogeneous fuel bed (pine needles, excelsior, sticks) and compared with experimental results obtained in a wind tunnel. Calculations are then extended to study the propagation of fires through a flat grassland, for various wind speed conditions. The numerical results are compared to empirical and semi-empirical predictions obtained in similar conditions.