Introduction. It is known that the calculation of the parameters of uncontrolled combustion is very difficult because of its spontaneity and disordered forms. Therefore, they resort to the modeling of combustion on the basis of known geometric shapes. For example, for a strait fire the burning area is modeled in the form of a rectangle, when burning a torch - in the form of a circle, when igniting a tank with LVZh, GZh or LNG - in the form of a “fireball”, etc. Methodology. Models of the fire to the main gas pipeline (MG) in accordance with the recommendations of STO Gazprom 2-2.3-351-2009 is a vertical solid cylinder to fire column type (scenario C1) and two against solid-opalone directed truncated cones for jet-type combustion (scenario C2). However, there are no systematic methods of quantitative assessment of the intensity of thermal effects and geometric construction of heat affected zones in case of fires at MG in the existing regulations. This gap explains the relevance of this article, which presents methods for determining the emissivity of heat fluxes at ground level for fires scenarios C1 and C2 and justified methods of geometric construction of zones of thermal danger in the vicinity of the burning flame column or two oppositely directed burning jets. A numerical example of the calculation of thermal parameters for the construction of geometric shapes of heat affected zones is given and the illustrations of their graphical execution are presented. Conclusion. The method of construction of models of heat affected zones is put in the subsequent basis for the development of the software product “Expert system “Fire Analyst”, which provides operational monitoring of the level of potential fire risk operated by MG in the “online” mode.