This is a general awareness overview, not a substitute for a licensed fire protection or mechanical engineer's smoke control system design. Real smoke control system design — including fan CFM sizing — must be based on the current NFPA 92 standard, and the completed system often requires commissioning and acceptance testing per NFPA 92 and the local Authority Having Jurisdiction (AHJ) before it can be placed in service. Never rely on this page to size, install, or accept a smoke control system.
These two figures are consistently published across many independent secondary sources describing NFPA 92 pressurization design, making them lower-risk general reference values than the standard's detailed algebraic fan-sizing equations (discussed below).
NFPA 92's actual algebraic equations for sizing pressurization fan airflow live in the standard's annexes. Hand-calculating fan CFM from those equations is only valid for a simplified case — buildings with uniform floor area and all doors assumed closed. Real buildings frequently violate that assumption (varying floor plate sizes, stack effect, open-door scenarios during evacuation, elevator lobby interactions), which is why many real projects use computer modeling — for example, NIST's CONTAM multizone airflow software — to size and verify the system under realistic conditions.
This page is a general educational overview of smoke control system concepts under NFPA 92 — stairwell/enclosure pressurization and zoned smoke control / atrium smoke management. It intentionally does not calculate a fan CFM airflow value for any system; that determination requires either NFPA 92's actual algebraic fan-sizing equations (valid only for simplified uniform-floor-area, closed-door cases) or computer modeling such as NIST's CONTAM, applied by a qualified fire protection or mechanical engineer.
NFPA 92's fan-sizing equations are published in the standard's annexes and require exact, current-edition verification — the standard is copyrighted, and available secondary sources do not reliably publish the full algebraic equations in a form safe to transcribe. Because an undersized or miscalculated smoke control fan is a life-safety failure, this site does not attempt to derive or guess at those equations, and does not offer a tool that outputs a specific CFM value from building inputs. Presenting an unverified fan-sizing formula as fact could contribute to an inadequately designed system.
The general design criteria of a minimum ≈0.05 in. w.g. (≈12.5 Pa) pressure differential across a closed door and a maximum ≈30 lbf door-opening force are consistently published across many independent, reputable secondary sources describing NFPA 92 pressurization design, making them lower-risk to present as general reference figures. This page also covers stable conceptual material — the two main system types (stairwell/enclosure pressurization and zoned/atrium smoke management), why hand calculation is limited to simplified cases, why computer modeling (e.g., NIST CONTAM) is used for real buildings, and the role of commissioning/acceptance testing and the AHJ — none of which depends on reproducing the standard's exact numeric fan-sizing equations.
For any real building, smoke control system design should be performed by a qualified fire protection or mechanical engineer working from the current official edition of NFPA 92, typically as part of a broader life-safety and fire protection design coordinated with the architect, fire alarm designer, and AHJ. Design normally involves either the standard's own algebraic equations (only where the building's geometry and door-status assumptions fit those simplified equations) or multizone airflow modeling software to handle realistic variation in floor sizes, stack effect, and door-open scenarios. The completed system then requires acceptance testing per NFPA 92 and approval from the local AHJ before occupancy.
Because NFPA 92's actual algebraic fan-sizing equations are published in the standard's annexes and must be verified against the current official edition — this project found that publicly available secondary sources do not reliably publish those exact equations. Given that an undersized smoke control fan is a life-safety failure, this page stays at the conceptual/awareness level rather than risk publishing an unverified formula.
Stairwell/enclosure pressurization, which supplies air to keep a protected enclosure (stairwell, elevator hoistway) at a higher pressure than the fire floor so smoke cannot infiltrate through a closed door; and zoned smoke control / atrium smoke management, which uses coordinated supply/exhaust airflow across zones or within a large-volume space to contain smoke to its zone of origin or manage a large open space.
Commonly cited general design criteria are a minimum pressure differential of approximately 0.05 in. w.g. (about 12.5 Pa) across a closed door, and a maximum door-opening force of approximately 30 lbf at the door handle so occupants can still physically open egress doors. These figures are widely and consistently published, unlike the standard's detailed algebraic fan-sizing equations.
NFPA 92's hand-calculable equations are only valid for a simplified case: uniform floor area throughout the building and all doors assumed closed. Real buildings often have varying floor plate sizes, stack effect, and scenarios where doors are opened during evacuation — situations the simplified hand equations do not capture. Multizone airflow modeling software, such as NIST's CONTAM, is commonly used to size and verify systems under these more realistic conditions.
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