In case of accidents at the underground gas pipelines, there is a high probability of fire development in the pit (at calm conditions) as a specific case of the fire in the cluttered space. Thermal radiation of fire in most cases is the dominant affecting factor of accidents, therefore it is required to estimate as accurately as possible the parameters of the thermal effect of fire in the pit, in particular, the thermal radiation intensity, and the geometric dimensions of the flame.
The article describes in detail the methodological approach to the assessment of geometric dimensions of the cylindrical fire flame in the pit in case of accidents at the gas pipelines. It is based on impurity transport model with developed gas turbulence under the influence of buoyancy forces. Presence of the developed turbulence implies that regardless of the boundary conditions the self-similar gas flow is formed with constant profiles of material flows. Thus, when the floating jet is approaching from the point source, it is possible to describe the relative change in the attached mass of air with the growth of height and the distribution of the molar concentration of the carbon impurity depending on the gas flow rate. For natural gas, the approximating dependences of the diameter and length of the flame on its flow rate were obtained. It is shown that within the framework of these dependencies, with an increase in gas consumption, the ratio of the lateral flame size to the longitudinal one decreases, and does not remain constant, as it follows from the regulatory established methods.
Therefore, the obtained dependencies can be used at the assessment of fire consequences and at prediction of emergency situations.