Experimental Study On Flashover Restraining By Water Mist In Confined Space

With the development of society,fire breaks out more frequently with the enlarged use of fire.Confined space is in common in bedrooms,libraries,underground garages,marine power cabins,closed containers,underground engineering in daily lives.Because of the complexity structure of confined space,the diversity of fuel,the large fire load and the special nature of the fire scene,once fire breaks out,it is proned to flashover,resulting in difficult evacuation and fire rescue.Flashover is a fire stage,which is the fire comes into the fully developed stage in the confined space.If water mist is applied before flashover occurs,it could effectively reduce the temperature of flame,gas phase and thermal radiation in confined space and reduce probability of the occurrence of flashover,which could effectively reduce death and property damage.Therefore,experimental studies on water mist restraining flashover in confined space is essential and meaningfulAn experimental model was set up with 3.6m length,1.5m width and 0.6m height Industrial alcohol is assigned as the main fire source,and rubber as the secondary fuel,which is in common in the highway tunnels and underground garages.The velocity,particle size,mist flux rate,mist momentum and other water mist characteristics were adjusted by changing water mist activated pressure and nozzle flow coefficient.The thermal interaction instability between water mist,smoke and flame were measured and analyzed by monitoring water mist velocity field and particle size,the fire plume,hot smoke temperature,radiant heat flux and smoke constituents.The water mist suppression effectiveness and mechanisms on flashover by the water mist in the confined space were explored.Firstly,cone angle,particle size and velocity of water mist were measured by PIV systems.Contrasting with the velocity and droplet size of water mist by the interaction of fire or not,it studies the rules of mist droplet interaction with the flame.The horizontal droplet velocity decreases,particle size and the vertical upward velocity increased with fire.Secondly,by changing water mist activated pressure and nozzle flow coefficient,experimental studies have found that the water mist pressure can be divided into four zones:flashover intensification zone,transition zone,flashover inhibition zone and smoke spread area.Finally,combining with the theory analysis,the fire flashover mechanisms are analyzed by water mist activated in the confined space.Water mist can restrain flashover in confined space effectively,the process of interaction between water mist and the flame and smoke is strongly related to heat transfer,mass transfer and other complex physical and chemical changes.In this paper,the effectiveness of flashover suppression and its mechanisms by water mist are explored by analyzing water mist fog field features,which can provided some basic experimental data for the application of water mist on the project so that the water mist can be better applied to daily life.