IMC 512 gives you three smoke control approaches: pressurize a barrier, push air across an opening, or exhaust a smoke layer. The method must hit targets without making doors impossible to open.
Plain English:
512.6 pressurization method
Smoke control uses pressure differences across smoke barriers to protect adjacent zones/egress.
A tenable environment is not required in the fire-origin zone.
512.6.1 minimum pressure difference
Fully sprinklered: ΔP >= 0.05 in. w.g.
Not fully sprinklered: ΔP >= 2x the max calculated design-fire ΔP.
512.6.2 maximum pressure difference (door forces)
Max ΔP is limited by door opening/closing forces. Exit doors must meet IBC opening force limits.
512.6.3 stairs + elevator hoistways
Pressurized stairs/hoistways must comply with IMC 512 plus the applicable IBC/IFC smoke control provisions.
512.7 airflow design method (openings fixed open)
With AHJ approval, airflow can limit smoke migration through fixed-open openings. Design per NFPA 92 and consider opening geometry to prevent flow reversal.
512.7.1 airflow method limit
Airflow toward the fire must be <= 200 fpm. If calculations exceed 200 fpm, airflow method is not allowed.
512.8 exhaust method (atriums/malls)
With building official approval, large-volume smoke control can use exhaust method per NFPA 92.
512.8.1 exhaust performance target
Keep the smoke layer at least 6 ft above any walking surface that is part of egress within the smoke zone.
On Plans: Why it matters
Common failures: meeting minimum ΔP but failing door forces, airflow methods that exceed 200 fpm toward the fire, and exhaust designs that don't protect the egress layer height.
Code Path: Where to show it
Smoke control report: method by zone and targets (ΔP, fpm, smoke layer height).
Controls diagram: smoke mode sequences and fan/damper commands.
Check: Calculations and Controls Diagram
Smoke control report must document the method per zone (pressurization, airflow, or exhaust) and the design target: ΔP in in.w.g., velocity in fpm, or smoke layer height in ft above walking surface.
For the exhaust method, show the smoke filling calculation, design fire size, exhaust rate, and makeup air rate on the drawings or engineering report.
Controls diagram must show smoke mode fan/damper commands and sequences per zone for each smoke control scenario.
Review Risk:
Atrium smoke control calculations using the wrong design fire size are the most common technical error - confirm the fire size is consistent with NFPA 92 and the AHJ's requirements before issuing.
Meeting minimum ΔP (0.05 in.w.g.) but failing door opening force limits is a commissioning failure - calculate max ΔP and verify door forces at the design stage.
Smoke exhaust outlets positioned at or below the design smoke layer height defeat the system - confirm outlet locations are above the 6 ft minimum egress-level smoke layer.
Field Tip:
Add a "SMOKE CONTROL TARGETS" box per zone: METHOD (ΔP / AIRFLOW / EXHAUST), MIN TARGET, LIMIT (door force or 200 fpm), and report reference.
Masterbuild QA Lens
Smoke control airflow design per 512.6 must show that air velocities through doorways prevent smoke migration during worst-case stack and wind conditions. Confirm the design velocity (100 fpm or 200 fpm for specific occupancies) is achieved at each controlled opening, that door widths match the drawings, and that the calculation accounts for all simultaneously open doors in the worst-case scenario.
Drawing / Submittal Check
For 512.6-512.8.1 (smoke control methods and atrium smoke control): the drawings must show the smoke layer height, the smoke filling calculation, the smoke exhaust rate, and the makeup air rate. For atrium smoke control, show the atrium geometry on the calculations and confirm the exhaust outlets are positioned above the design smoke layer.
Common Review Risk
Atrium smoke control calculations based on the wrong fire size are the most common technical error. IMC 512 and NFPA 92 require a specific design fire size - if the designer used a conservative small fire, the smoke filling time may be overstated and the exhaust system undersized for the actual fire scenario. Confirm the design fire size is consistent with the applicable standard and the AHJ's requirements.
When To Escalate
Escalate when the atrium smoke control design fire size is disputed between the design team and the AHJ. The design fire size is the most consequential assumption in a smoke control calculation - a disagreement on this value changes the required exhaust rate and the system capacity. Confirm the design fire size with the AHJ before the calculation is completed.