Stairwells equipped with a system that prevents stairwells in highrise buildings from becoming smoke-filled in case of fire. Stairwells are pressurized by using fans or otherwise forcing fresh outside air through air ducts in the building's exterior walls and down the stairwell shafts. As the system pumps increasingly more air into the stairwells, the air pressure rises until it is greater than the air pressure on the building's floors. Given that stairwell doors must open into stairwells in the direction of egress from the building interior, standards are typically in place to regulate the pressure so that it is not too great to prevent ease of opening.
