The aggregate state of combustible substance is the basis for allocation of some classes of the fires and classification of indicators of fire danger. Besides solid, liquid and gaseous substances in fire and technical literature it is accepted to consider disperse systems, in particular dust. Feature of these systems is the fact that actually combustible material in the dust systems are small particles of solid substance, and among indicators of fire danger are available such which aren’t allocated for solid combustible substances and materials, but are applied to gases and liquids. Other fire-dangerous disperse system it is necessary to consider the porous soil structures impregnated with combustible liquids. Such systems are widespread on objects of an oil and gas complex and are a dangerous combustible material on many fires. Indicators of fire danger to these systems aren’t established. Fire-dangerous characteristics of the soil deposits containing oil products are obviously connected with concentration and a type of oil product, and also with soil type. Combustible substance in them are liquid oil products, but it is unacceptable to apply to them indicators of fire danger to liquids. As an indicator of fire danger to the disperse systems containing a combustible liquid phase it is offered to use the concentration of ignition defined experimentally. She is the smallest concentration of oil product in the soil at which ignition and steady burning of system is possible. In work experiments on establishment of concentration of oil products in soils of various type at their limiting saturation are made by oil products. In all studied types of soils ignition of system the soil - oil products perhaps at concentration by 4-8 times smaller, than concentration at which oil product is capable to be emitted in a separate phase and to form liquid congestions on a soil surface. Such conclusion significantly increases potential danger of emergence of the spillage fire at hit of oil products in soil deposits.