Please advise what code I need to refer to define when stairwell pressurization system is required?
Check NFPA 101. Section 7.2.3 is about smokeproof enclosure requirements (including pressurization). I don't remember any particular place where NFPA 101 requires stairwell pressurization.
The term "smokeproof enclosure" is essentially synonymous with a pressurized stairwell. Everywhere you see this term in NFPA 101, the implied meaning is a stairwell. There are other options but they are much less common. The 2015 handbook gives guidance in section 7.2.3.
A smokeproof enclosure has traditionally taken the form of anexit stair enclosure provided with additional features that limitthe infiltration of heat, smoke, and fire gases from a fire in anypart of a building. A pressurized stair enclosure is an example ofthis form of smokeproof enclosure. Smokeproof enclosures,other than exit stair enclosures, include pressurized elevatorhoistway shafts. A smokeproof enclosure improves protectionagainst the products of combustion entering the enclosure. TheCode requires the use of smokeproof enclosures in 18.104.22.168 forexisting, nonsprinklered, high-rise apartment building stairs. Theprovisions for smokeproof enclosures also are mandated forhoistway shaft systems for elevators providing access from anarea of refuge to a public way in accordance with 22.214.171.124.4(3).
To get guidance on the design features of smokeproof enclosures, you'll need to consult NFPA 92, 92A, and 105. There's also alarm and detection requirements in NFPA 72 that tie into insuring the integrity of the smokeproof enclosures with detection of smoke in the vicinity of the enclosure.
nfpa 101 nfpa 72 nfpa 92 nfpa 92a nfpa 105
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