The basic factors causing the movement of smoke in a building are:
– chimney effect,
– heat emitted during a fire,
– Atmospheric conditions, especially wind and temperature,
– operation of mechanical air transport systems.

Smoke rising to the ceiling is observed within the fire compartment, followed by its horizontal spread, with a simultaneous increase in volume due to the convection of the surrounding air to the flowing smoke cloud. The spreading smoke tends to contain all the available volume. Assuming a constant volume and airtightness of the room, the increase in temperature caused by the emission of heat by the flames causes an increase in pressure. The overpressure generated in the fire compartment combined with the incomplete tightness of the building partitions, with which we are dealing in practice, causes the smoke to escape to the outside. Consequently, two pressure zones are created in the room, separated by a neutral plane, with a pressure equal to the pressure outside the room. In place of the smoke in the upper zone, at the bottom, fresh air is sucked in, supplying oxygen to fuel the combustion process. The height of the neutral plane depends on the parameters of the fire and the size of the leak.
In tall buildings, there is an additional risk of vertical smoke spreading. It is caused by the chimney draft and depends on the temperature difference inside and outside the building. The main routes of vertical smoke migration are staircases, elevator shafts and various types of installation shafts. This phenomenon is very unfavorable due to the limitation of the possibility of evacuation through staircases and the possibility of spreading smoke over many floors.. The pressure gradient caused by the temperature difference is particularly important in winter periods. Atmospheric conditions, especially the wind, they can in the event of a leaky structure, trigger additional, horizontal air flow in the building. In the event of a fire on the windward side of the building, this can have a significant effect on the movement of smoke. The effect of the wind action can be additionally intensified, if due to high temperature, windows will be damaged in the room under fire.