stair shaft

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The vertical shaft which contains a staircase.
McGraw-Hill Dictionary of Architecture and Construction. Copyright © 2003 by McGraw-Hill Companies, Inc.
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The stair shaft wall was also provided with a leakage opening on each floor with a size that was calculated based on the average building leakage rate.
For Tests 6-10, the base pressure difference produced by the stairwell pressurization system was reduced below the required design values to determine the conditions in the stairwell that would result in smoke migration into the stair shaft. In Tests 6 and 9, the base pressure difference between the stairwell and the floor area with all the doors closed was reduced to a minimum of 15 Pa (0.06 in.
This is consistent with results of an earlier study by Tamura that indicated that venting of the fire floor through smoke shafts or openings in the wall substantially reduced smoke migration into the stair shaft (Tamura 1994).
In RP-1203, it was assumed that air was supplied to the stair shaft at each floor level, and the base pressurization system used in RP-1203 appears to be in the upper limit of the required design values.
Further research would be required to determine if a pressure compensating system would be effective in keeping a stairwell tenable with the stair shaft door on the fire floor open.
Pressure drop characteristics of typical stair shafts in high-rise buildings.
The tightness of the stair shaft plays an important role in regulating the amount of combustion products that invade the stairwells on the first floor and limiting the volume of smoke that is ultimately distributed to the upper floors in the high-rise.
Even when there is no gap around the stairwell doors, smoke can still invade the stair shaft due to small unavoidable openings in the shaft's construction.
There is no universal consensus on the requirements to prevent smoke from entering the stair shaft. Some codes require a minimum amount of airflow from the pressurization equipment.
In an attempt to keep smoke from invading the stairwells, there is a practical upper limit on the amount of air that should be added to the stair shaft. Any amount of air that increases the stairwell pressure to such an extent that it becomes difficult to open the fire escape doors will certainly violate the objective of providing a safe exit route for building occupants.
The values in the figure assume the stairwell doors are tightly fitting (zero gap around the entire door perimeter), and the stair shaft consists of the relatively tight cast concrete construction.
In addition, smoke proof enclosures can provide a reasonable alternative to mitigate smoke from entering stair shafts. Thus, it is unclear if refuge floors are necessary.