The assessment of extinction mechanisms involving water mist applied to combustible liquids

Introduction. A number of problems accompany the development of new extinction methods applicable on the premises of buildings and structures and the use of advanced fire extinguishing agents. Subject-specific studies are needed to solve these problems. They include the identification of general principles of fire extinguishing efficiency and further development of the optimal mode of application of firefighting agents. The purpose of this work is the theoretical assessment of fire extinction mechanisms involving the water mist applied to combustible liquids. The objectives to be accomplished include the equations based on the mass/energy conservation laws and derived for flame zones with account taken of the water mist applied; the assessment of the water flow rate for different combustion mechanisms; comparison of assessment results with experimental data obtained in the process of extinguishing model fire seats that have burning combustible fluids. Methods of analysis. The calculations involve the equations based on the mass/energy conservation laws and derived for flame zones above the surface of combustibles. Research results. The author analyzes two fire extinguishing mechanisms that contribute to the suppression of burning in the flame zone: 1) the attainment of the value of mass concentration of water vapour that reaches the lower concentration limit of combustion of the combustible mixed gas (oxygen reduction); 2) cooling combustible mixed gas in the flame zone by evaporating water until the flash point temperature of combustible vapour is reached. Conclusions: Equations based on mass/energy conservation laws were derived for flame zones, formed in the course of combustion of flammable liquids, with account taken of a jet of water mist. Water flow rates needed for the implementation of various extinguishing mechanisms were analyzed using the proposed equations. Theoretical results were compared with the experimental data obtained in the process of using water mist to extinguish model fire seats that contain combustible fluids.