Over the past three decades there are worked out the general principles of flexible standardization fire protection facilities, taking into account material losses in fires. However, practical implementation of this approach is hampered by the absence of reliable data on the effectiveness of fire prevention measures and estimated effects of fire material. Often this is done expertly, at best - for statistical data on fires. The reasons for this state of affairs were the following factors: 1) the random nature of the process of real fires and fighting them, spreads of building structures parameters and characteristics of fire protection engineering; 2) lack of engineering tools to evaluate and compare the performance of individual fire protection measures, allowing to set the sound application of the relevant measures. In this connection, the article seeks to develop theoretical foundations of engineering method of choice of rational variants of objects of protection with economic responsibility. This will be used probabilistic approach (analysis), allowing not only to more adequately take into account the physics of the processes, but slightly lower requirements for accuracy of data than the deterministic analysis. The theoretical foundation of engineering method of calculation of rational fire protection options premises of buildings, including fire barriers and automatic fire suppression system is worked. It’s proposed an analytical approach to assessing the reliability of building structures, taking into account both the stochastic parameters of designs and parameters of the premises in which they are used, as well as the characteristics of the fire load in the premises. The proposed engineering method implements the criterion of reduced costs, economic feasibility criteria, which in conjunction with the criterion of individual fire possible to obtain a rational way to protect the object. If necessary, the content of the criterion of reduced costs can easily be expanded by taking into account indirect losses from fires, detailing the damage on buildings, equipment via loss ratios, etc. Analytical approach to the evaluation of stochastic parameters of the equivalent length of a fire on an example of local fires can be extended to constructions in terms of volume fires, fires developing freely, by using the results of numerical experiments. In principle, the introduction of simulated fire simulation systems using random input parameters and field model of fires, yield more valid results for the rational choice of protection options. However, due to the complexity of such an approach for the engineering protection of the parameter estimates in the practice of scientific research and design organizations can currently be used in these analytical assessments.