Thermal Stability of Flexible Tanks When Affected by a Heat Flux from Upper Forest Fire

To extinguish large-scale and complex fires that are, for example, forest fires, a significant amount of fire-extinguishing agents and their long-distance feed using high-performance fire equipment, e.g. «Shkval», «Vodoley», and PANRC, are required. For these cases, flexible tanks are recommended for use as intermediate and storage tanks to prepare water solutions for fire-extinguishing agents. Multilayered composite polymer materials are used for their manufacture. When affected by a heat flux, thermal destruction occurs. According to the literary sources, the destruction of polymer materials of foreign manufacture starts at the temperature of 280–290 °С and reaches its maximum at the temperature of 410–420 °С. In the front of the upper forest fire, total heat fluxes (radiant and convective compounds) up to 120 kW/m2 are implemented, with a radiant heat flux reaching the value of 50 kW/m2. As the distance from the fire front increases, the heat flux decreases exponentially depending on the distance. An unsteady heat conductivity equation can describe the heating of materials used to manufacture a flexible tank for a multilayered structure in the form of a plate. Three schemes of multilayered structures have been considered; their relevant initial and boundary conditions have been set. A numerical solution for the heat conductivity equation using MathCad 2000 has been proposed. The obtained solution has been verified based on the text example from the US standard ASTMF 1930; the results of the calculation have been compared with the experimental data of laboratory tests in accordance with the GOST R 53264—19 methodology. The calculations comply with the experiment. Based on the heat flux data for an upper forest fire, the safe distance from the burn front to the flexible tank has been determined by calculations; it exceeds 20 m.