SUBSTANTIATION OF TECHNOLOGY FOR EXTINGUISHING COMBINED FIRES IN THE PRESENCE OF LIGHT METALS OR PHOSPHORUS COMPOUNDS

Abstract

Formulation of the problem. During Russia's armed aggression on the territory of Ukraine, cases of combined fires in the presence of light metals or phosphorus compounds, accompanied by high combustion temperatures and the release of toxic combustion products, have been repeatedly recorded. Given the danger of these fires, it is important to quickly localise and eliminate them. The analysis of scientific papers on effective extinguishing agents and methods of their supply has revealed the absence of a single approach and algorithm for extinguishing these fires. Accordingly, the substantiation of the technology for extinguishing combined fires in the presence of light metals or phosphorus compounds and the study of the effect of the thickness of the extinguishing powder layer on the combustion and cooling temperature of magnesium is an urgent scientific and technical task. 
The aim of the work is to improve the technology for extinguishing combined fires in the presence of light metals or phosphorus compounds and to study the effect of the thickness of the extinguishing powder layer on the combustion and cooling temperature of magnesium. 
Research methods. A comprehensive method was used to conduct the study, which includes: the analysis and application of statistical data processing methods and a comprehensive method of fire research. To study the effectiveness of cooling during the process of extinguishing magnesium alloy cinders, a methodology was used to determine the required amount of fire extinguishing powder to achieve an insulating effect.
The main results of the study. For effective extinguishing of class D fires, it is necessary to study the thermal characteristics of fire extinguishing powders in the conditions of extinguishing magnesium alloy fires. The thermal insulation ability of fire extinguishing powders based on sodium chloride, ground slag, ammophos, aerosil, and zinc stearate was experimentally investigated. The effect of the thickness of the fire extinguishing powder layer on the combustion and cooling temperature of magnesium was determined. The dependence of the temperature at the metal/powder interface and the temperature at the air/powder interface on the thickness of the layer applied by the fire extinguishing powder was determined. Based on the experimental temperature values obtained, the coefficient of thermal conductivity and heat capacity of the fire extinguishing powder was determined and the required thickness of the powder layer was calculated to ensure thermal insulation of the burning centre of magnesium alloy shavings. The required thickness of the fire extinguishing powder layer, which will ensure a safe temperature for humans at the border with an air of 80 ⁰C, is 24 mm.
For effective extinguishing of combined fires at the initial stage of development, it is necessary to use a powder-foam extinguishing unit with a nozzle-soothing agent.
Conclusions. The influence of the thickness of the extinguishing powder layer on the temperature of magnesium combustion and cooling was experimentally investigated. The required thickness of the layer of extinguishing powder based on sodium chloride, ground slag, ammophos, aerosil, and zinc stearate (d = 24 mm) to achieve a safe temperature for humans at the border with an air of (80 °C) was determined.
Recommendations for extinguishing light metals or phosphorus compounds have been developed and the basic requirements for occupational safety when working with extinguishing powders and foams/extended life foams have been formulated.