In the scientific article, the authors investigated the critical conditions of transition of the design mode of the smoke removal system in the non-calculation mode "boost" to create a design engineering method that allows to determine the parameters of the system. Also, the components of the phenomenon of passing through the smoke-removing hole of clean air, due to the action of lifting forces, from under the near-flood smoke layer are considered. An example of a room with a model combustible load under different conditions is considered: the height of the wall of the smoke-removing hole is zero and the neglect of the speed component of the smoke-gas mixture parallel to the roof.