One of the promising methods of fire safety processes of preparation and repair work on tanks for petroleum and petroleum products is desensitization with nitrogen of air separation membrane. The study of this process may be complicated by the need to conduct field experiments in the tanks of large capacity, whichis directlyproportional to the impactonthe costofthe membrane airseparation plant. Amodern numerical simulation using the software packages is a possible alternative. The paper presents the main results of numerical modeling of desensitization using the application package "Flow Vision" and fulfilled their comparison with the results of laboratory experiments. It's get high reproducibility and evaluated the relative error. The accuracy of the adopted criteria approximate simulation is confirmed. The specific places maximum concentrations of oxygen in the amount of horizontal tank are identified by using the visualization process. Despite the high reproducibility, numerical (CFD) modeling preferable to use in step research, due to the high required computational power and duration calculations. To obtain data on the basic parameters of the pre-repair training with the help of the air separation membrane unit on-site work must be more operational. It will implement a software product based on an integrated mathematical model obtained by solving a system of differential equations, which is the practical result of the study of desensitization.