The costs of components of the fire extinguishing system based on light loose materials for extinguishing a medium-sized class "B" model fire were experimentally determined. According to the results of preliminary studies on extinguishing a model fire of class "B" of small sizes, as components of such a system, granular foam glass with a granule size of 10–15 mm, expanded perlite with a granule size of 1,2±0,2 mm or vermiculite with a plate size of 1×2 mm and sprayed water. Styrofoam in such a system ensures its buoyancy and cooling of the surface layer of the burning liquid. The fine powder of expanded perlite improves the insulating properties of the fire extinguishing system. The water supplied to the upper layer of loose materials, in addition to increasing the insulating and cooling properties of the system, ensured the long-term absence of re-ignition. To increase the economic parameters of the fire extinguishing system, its composition was optimized according to the effect-cost parameter. It was established that the lowest economic costs for extinguishing gasoline are provided by the sequential supply of three components: crushed foam glass, dispersed expanded perlite and sprayed water with such specific surface costs – 6,7 kg/m2, 1,6 kg/m2 and 2,0 kg/m2 in accordance. For the optimized composition, a study was carried out on extinguishing a standard model fire 2"B", the results of which are close to the results obtained on model fires of small and medium sizes. It is shown that the proposed fire extinguishing system based on light loose materials has advantages in terms of economic and environmental parameters compared to existing and previously proposed means of extinguishing flammable liquids. Means of feeding light loose materials are proposed. The areas of work in the implementation of a fire extinguishing system based on light loose materials in the practice of fire extinguishing have been noted.