Parameter average temperature Tcp is necessary, for example, to estimate the mass of natural gas involved in the formation of a fiery torch in case of emergency destruction of the main pipeline. However, the methodology for a systematic calculation of this parameter in the current methodological and normative documents, the author has not found. Despite the apparent simplicity of the problem, the analysis showed that the parameter of Tcp depends primarily on the calculation of the parameter of the gas temperature TK at the end of the emergency section of the pipeline, which, in turn, depends on the mass performance of the Qc pipeline, specific heat of natural gas Cp, the relative density of natural gas A, the length of the section of the pipeline L, the outer diameter of the pipe dH, the heat transfer coefficient KT and more than two dozen parameters that characterize the state of a gas in terms of its transport and depressurization of the pipeline. Calculations of the number of parameters regulated in several regulatory documents, which introduces uncertainty in the choice of the calculation scheme and is accompanied by the production of different calculation results. Calculations of other parameters recommended by the standard methods are complex, three-dimensional routine, require access to specialized software products that are not available in the current engineering activities. To clarify these discrepancies, the rationale for the recommended design solutions and adapting them in a simple, systematic methodology for calculating the average temperature in different parts of the main pipeline the subject of this article.