In case of fire in a high-rise building the emergency stairways need to be kept free of smoke to allow safe egress for the occupants. Often building codes require a stair pressurization system to ensure the exit stairs stay free of smoke. One control unit per floor measures and controls the pressure in the staircase in reference to the main building. If the fire alarm system is turned on stair pressurization fans supply clean outside air into the staircase. The higher air pressure prevents smoke from entering the staircase when the emergency doors are opened, smoke is basically pushed back, clearing the escape route. SMI's sensors assist in smoke management by measuring the pressure in the staircase and the building.