Pressurization is used to prevent smoke spread into a stairwell. The stairwell height is limited by the pressure to open doors, about 80 Pa, the pressure to prevent smoke spread, about 20 Pa and the outdoor–indoor temperature-induced pressure gradient, about 2 Pa/m. This limits the height to 30m ((80 20)/2). However, this limit can be increased by balancing the temperature-induced pressure gradient with an equal and opposite flow pressure gradient created by a flow passing through the whole stairwell.
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