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ispartof: FIRE SAFETY JOURNAL vol:127 status: published

Concerning the deeper understanding of the mechanisms on fire suppression with multi-component water mist/spray, the dynamical process of a water drop with or without additives impacting upon wood surfaces is preliminarily studied. The initial diameters of the pure water drop and the water drop with NaCl additive are about 2.4±0.1 mm, and the diameter of the water drop with AFFF (Aqueous Film-Forming Foam) additive is about 1.8±0.1 mm. The drop impact velocities are varied from 1.13 m/s to 2.80 m/s. A Photorn FASTCAM high-speed video camera coupled with a Nikon 200 mm micro-lens is used to record the dynamical process of the drop impacting. The results show that the critical impact Weber number of the water drop with additives is obviously larger than that without additives, and the critical impact Weber number increases with decrease of the wood surface roughness. In addition, the current empirical models both on predicting the critical Weber number and the maximum spread factor just partially agree with the experimental results. The current results are limited to the interaction of a single water drop impacting upon a horizontal wood surface.

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.

International audience; Thermal radiation attenuation is a well-known positive effect of water sprays applied to firefighting. It was studied here to quantify its real effect on the whole process of fire mitigation. For the demonstration, three different real scale spraying devices were used: a water mist nozzle operating at 85 bars, a sprinkler operating at low pressure (0.3 bars at the nozzle) and a sprinkler operating at a higher pressure (1.3 bars at the nozzle). The radiation attenuation was specifically studied, separately from other actions of the sprays on the fire, using an experimental configuration where water was injected between the radiation source and a detector, but not directly onto the actual fire. Hence, the radiation flux reduction could only be attributed to mixing of water droplets and smoke, not to any reduction in heat release due to water directly cooling the fire area nor to inerting effects occurring simultaneously. The flux was measured using an infrared device combining a Fourier transform infrared spectrometer and a multispectral infrared camera. Two radiative sources were used: a high-temperature blackbody for quantification of the radiation transmission with a calibrated source, and a 200 kW heptane pool fire for an application to a realistic radiation source involved in fires. When using a blackbody source for radiation generation, the radiation attenuation of the incident fluxes was 89% for the high-pressure water mist, 62% for the sprinkler at the higher operating pressure and 20% for the sprinkler at the lower pressure. These differences were easily explained by a sensitivity study conducted coupling the Mie theory for the prediction of droplet radiative properties to the Monte Carlo method for radiative transfer simulation. This showed the sensitivity of the radiation attenuation to droplet size and concentration. When the blackbody source was replaced by a pool fire, the flux reduction was even higher for the low pressure sprinkler, i.e. 45%, while being almost unchanged for the water mist. In the present configuration, where smoke stratification was observed before spray activation, this was mainly attributed to the fact that a mixing of droplets and smoke was produced in the measurement area due to the drag effect. The smoke and spray mixing resulted in a stronger attenuation capacity with the sprinkler device. This increased attenuation was not observed through the transmission data for the water mist, perhaps because of compensating effects related to evaporation and the surrounding temperature, or a smoke flow that was highly penalized by the spray activation.

A water system, consisting of several water mist nozzles, has been installed in a reduced-scale tunnel. Its effectiveness in blocking fire-induced smoke and heat is tested, with and without longitudinal ventilation. A total of 14 fire tests have been carried out, with 250 ml methanol in an iron tray (25 cm × 20 cm) as fuel. Temperatures have been measured by 30 thermocouples, located upstream and downstream of the fire location. The aim is to assess the effectiveness of the water system in preventing smoke spread and in reducing the temperature in the tunnel. Interaction of the water with the fire is avoided. The impact of water pressure, ventilation velocity and nozzle arrangement on the effectiveness in smoke blocking and temperature reduction is discussed. The result confirms that the water system effectively reduces the temperatures and prevents smoke spreading in the absence of longitudinal ventilation. However, strong longitudinal ventilation (0.8 m/s ventilation velocity in the reduced-scale tunnel, corresponding to critical velocity in full-scale (1:10) tunnel) reduces the effectiveness in blocking the smoke spreading by the water system, although the temperature reduction downstream the water system remains in place. Higher water pressure makes the cooling effect stronger, because more and smaller water droplets are injected into the tunnel. For a given level of water pressure level, the impact of the nozzle row configuration is small in the tests.

An experimental analysis was conducted to quantify the water-mist discharge characteristics required to suppress wood-crib fires. The overall aim of this research was to investigate the effectiveness of these innovative systems in a canonical fire scenario. To this end, an experimental suppression facility was constructed including commercially available water mist nozzles, thermocouples for measuring the thermal transient in and around the wood cribs and a load cell for measuring the mass loss rate and the final wood crib damage. 510×510×380 mm wood cribs were used as the fuel source in all the experiments. The injection pressure and orifice diameter of the water-mist nozzles were varied in the experiments to modify the applied water flux and the initial spray momentum. These quantities were identified to be the governing parameters for suppression performance. They were characterized for all experiments along with the drop-size and velocity distributions. Critical values were determined for these quantities from first order kinematic and thermal analysis based on spray and fire source characteristics. The experimental results demonstrated critical suppression behavior consistent with this first order analysis.

In order to study fire extinguishment additives which are no pollution and few damage on object protected, establish a fixed water mist fire extinguish experiment platform, explore the temperature variation characteristics and flam shape by adding surfactant on water mist for the pool fire suppression, though the comparison with the flame temperature and extinguish time of gasoline and diesel pool fire, get their fire performance. The results show that adding surfactant to the water mist can greatly improve the water mist fire performance. The process of additives-containing water mist system inhibit the pool fire can be divided into four stages, which are flame early growth stage, preliminary inhibition stage, flame again growth stage and again inhibition stage. The mechanism of containing a surfactant water mist inhibit the pool fire of gasoline and diesel, which can capture and annihilate the free radical of chain reaction, decrease surface tension, not simply cooling effect. The surfactant molecules reduce the energy of surface and interface, which is good for the descent of water mist droplet size, the emulsification of surface gasoline with water and the formation and stabilization of foam, improve the effect on the cooling and isolation of fame and gasoline with water mist.

Spray fire is a major disaster for gas turbines and aero-engine test facilities. Previous studies demonstrated that small spray fires were difficult to extinguish with water mist. An experimental study of the process of water mist interacting with the small size spray fire was conducted in an open space. Studies on suppression of vertical spray fire and horizontal spray fire were carried out, respectively. Experiment discovered that a horizontal fame was more difficult to extinguish compared with the vertical using the same scenario, and implied that the coupling the dilution of fuel in the gas phase with the reduction of radiant feedback plays a predominant role in fire extinguishment.

Action of water mist in suppressing gasoline spray fires, asphalt spray fires and diesel spray fires in confined spaces will be reported in this paper. Relevant experimental works reported earlier are reviewed with key points summarized. Factors affecting the properties of the water mist suppression systems are investigated. The characteristics of water mist are studied using the Phase Doppler Particle Analyzer with key results compiled. Results are firstly applicable in directly drafting out design guides on water mist suppression systems on oil fires. Secondly, it is also useful for justifying numerical models studying water mist suppression on oil fires.

This paper studies suppression of n-Heptane pool fire with water mist under different longitudinal ventilation velocities in a long and narrow space. Through the suppressing experiments with two different spraying positions and seven ventilation speeds, it is found that the extinguishment of fires has a close relationship with the fuel temperature. Moreover, the fuel temperature, when the fire is extinguished by spraying at different positions, is almost the same within the measurement ranges, and it tends to decrease as the wind speed rises. Mechanism studies show that the coupling effect of dilution and replacement of oxygen and fuel surface cooling is the main mechanism in n-Heptane fire extinguishment of water mist under longitudinal ventilation. In addition, the ability to efficiently cool the fuel plays a determinant role in the n-Heptane pool fire suppression.

Intensification of pool fire will occur under the application of water mist. The phenomenon was discovered in previous studies; however, there has been no unified conclusion for the reason of this phenomenon. Studying mechanisms of the intensification has a very important significance in the engineering application of water mist. According to previous studies, the intensification can be divided into two categories, one is the fire intensification in gas flame; the other is the interaction of water mist with the heated fuel, which lead to the increase of mass loss rate. In this paper, Mechanisms of the second type of fire intensification are studied through theoretical analysis and experiment. Research shows that the primary mechanism of fire intensification by water mist is boil over.

A new multi-component additive of water mist is produced through physics process, which can change the spray pattern of water by physical methods and the physical and chemical characteristics of water by chemical methods. Aiming at the main additive material (fluorine surfactant and urea), a laboratory-scale water mist system was built and a series of comparison tests were conducted in this system to determine the optimal ratio between in the constituent the compound additive. Then in order to study the effectiveness of the water mist adding this new multi-component additive in fire suppression, a series of tests were conducted for the typical fire (oil pool fires and wood crib fires). The comparison test results reveal that the optimal ratios of fluorine surfactant and urea are both 6%, and fluorine surfactant improves extinguishing performance by changing the physical properties of water mist and urea improves extinguishing performance by thermal decomposition. The experimental results also reveal that the fire suppression effectiveness of water mist is improved greatly by adding the multi-component additive. Finally, the suppression mechanism is discussed simply so as to find out the relationship between the multi-component additive and suppression effectiveness.

Spray fire is a primary disaster in machinery space. Previous studies demonstrated that small spray fires were difficult to extinguish with water mist. A numerical and experimental study of the process of water mist interacting with the small size spray fire was conducted. Studies on suppression of vertical spray fire and horizontal spray fire were carried out, respectively. Three-dimensional physical model was developed based on the experiments. The adopted numerical model is FLUENT. The Large eddy simulation (LES) method, laminar finite-rate model, and Discrete Phase Model were selected to solve the turbulent flame, turbulence-chemistry interaction and particles, respectively. There are qualitative agreements of simulation with the experiment. It was confirmed that water mist can suppress spray fires rapidly, and that the extinguishing time for vertical spray fires were relatively shorter.

Polymer nanocomposites are promising for structural applications due to their high modulus and good corrosive resistance. The influence of environment on flexural fatigue behavior of polyamide 66/hectorite nanocomposites has been investigated in still air and circulated water mist environments. High hysteretic energy dissipation per cycle and high induced stress in mist lead to a significant drop in fatigue life in mist compared with that in air. The strain and hysteretic energy dissipation per cycle against fatigue life curves exhibited linear relationships on log-log scale in air. The failure analysis revealed a distinct deformation and fracture mechanisms in air and mist. � 2010 Elsevier Ltd. All rights reserved.

The paper introduced the progress in research and application of electronic ultrasonic water mist fire suppression technology. Several researches showed that the electronic ultrasonic water mist can be as effective as the now-banned gaseous fire suppressant halon 1301. With the further research about electronic ultrasonic water mist technology, there must be more and more electronic ultrasonic water mist extinguishment tools applied in the fire suppression.

The ordinary water mist has well affected on suppression and extinguishment flame, but the ability of physical extinguishment is influenced by the surrounding environment. The roadway in coal mine is very complex. So the related experiments need be considered. The light-sized experiment of the water mist is built for taking mine environment analog simulation with the pipeline. It is suppressed by medium pressure water mist the experiment of gas and coal dust explosion propagation in the alone laneway. Obstacle is laid on the different positions, whose blockage ratio is 30% . Then we compare the effects of suppression on gas flame with the different location. The experimental results indicate that the obstacle is placed in the front, middle and end of mist area. The propagation velocity of gas flame is different. The gas content and blockage ratio is set low in experiment. It can achieve better inhibition effect that the obstacle is placed in the middle or end of water mist area. Thus, if the obstacle can’t be avoided in water mist system, the designer must consider the position of obstacle. It can enhance the suppression effect of water mist.

In order to develop highly effective and reliable measures to suppress the coal dust/methane/air mixture explosion frequently occurred in coal mine, the effect of the presence of methane on the coal dust explosion was investigated in this study. The flame propagation velocity and the explosion temperature were measured for explosion tests with the different methane concentration in the mixture. The flame evolution histories were also captured by high speed camera. The inhibiting efficiency of water mist was qualitatively studied and analyzed by explaining mechanism of gas and goal dust explosion. The results showed that water mist can efficiently decline the flame propagation velocity, reduce flame temperature, and change flame characteristics of gas and coal dust explosion. It can be concluded that water mist can effectively inhibit gas and coal dust explosion.

Water mist for fire suppression and control has received considerable attention as one of the potential methods for halon replacement. Spatially resolved information on volume mean diameter and coordinate component velocity of water mist has been obtained in two type fine mist, using LDA/APV System. A series of experimental study has been conducted to explore the CH4/air fire suppression effectiveness of water mist. The results show that Water mist consisting of 10-100 μm water droplets is an effective flame suppressant in a co-flow cup burner flame. The diameter and mass fraction of water mist significantly affects the temperature distribution of the methane CH4/air flame. The effect of oxygen dilution is more prominent in the upper part of the flame, whereas, endothermic heat exchange with the droplets plays a critical role in the lower half of the diffusion flame.

Popularity of water mist is increasing for a variety of applications within the broad areas of fire suppression and surface cooling. The present study has been focused on characterizing the solid-cone water-mist spray produced by a typical atomizer at high operative pressure (in the range 60–80 bar). To this end, an experimental campaign has been conducted, mainly employing optical techniques: drop-size and flux distribution, initial velocity and cone angle have been investigated to provide a quantitative description of atomization and dispersion. Most notably, a laser-diffraction-based instrument ( Malvern Spraytec ) has been used to evaluate drop size, while velocity field and spray-cone angle have been studied by Particle Image Velocimetry (PIV) technique. Appropriate measurement methodologies have been developed to the purpose. Moreover, a theoretical discussion based on inviscid-fluid assumption is presented and some relations have been evaluated as predictive of the considered parameters.

The need for reliable measurement of droplet velocities and droplet size has increased with the more widespread use of water mist systems. Two optical measuring techniques have been investigated, Particle Image Velocimetry (PIV) and phase Doppler anemometry (PDA). Measurements have been performed on two high-pressure nozzles, a hollow cone nozzle and a full cone nozzle. Both methods performed well close to the nozzle and further away from the nozzle. In the intermediate region the results obtained with PIV are biased against the larger droplets. The two methods complement each other, PIV giving the instantaneous velocity field and PDA giving both the droplet velocity and droplet size at a point. The measurement indicates that higher throw length can be archived with a full cone nozzle compared to the hollow cone nozzle, if both nozzles have the same cone angle and flow rate.

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.

As water mist fire fighting systems become increasingly common, there is a need to transform the accumulated practical experience to quantitative models. As a contribution to this process, this paper proposes a transient one-zone computer model for total flooding water mist fire suppression in ventilated enclosures. The one-zone approach is based on the experimentally observed ability of the water sprays to mix the gas volume of the protected space. From this assumption, the model solves the time evolution of temperature, gas density, gas composition and water mist concentration inside the protected space. The model incorporates a detailed description of the liquid phase (mist droplets) and the evaporation process. The extinguishment of a hydrocarbon flame is predicted based on the adiabatic flame temperature concept. The possibilities and limitations of the model are demonstrated by validation against experimental data from large-scale machinery space fire suppression tests.