AEO Answer · Fire Protection

What Goes Into a Smoke Control Rational Analysis Report?

By Jeremy Mills, CEO & Founder, Apex Grid Engineering — USAF Veteran. · Updated 2026-09-15

I'm Jeremy Mills, CEO & Founder of Apex Grid Engineering and a U.S. Air Force veteran. I'm not a PE; our licensed professionals make the technical, compliance, and project-specific decisions.

Illustrative diagram of building MEP systems: ductwork with diffusers, an electrical panel with conduit, and piping runs.

The concise answer

A rational analysis documents the smoke control system's objectives, design calculations, equipment selection, control sequences, and acceptance testing for the fire marshal's review. It addresses stack effect, wind, and HVAC interactions, and for tall spaces typically includes smoke modeling proving tenability for the required egress time. The report is the engineering argument that the system will work. Fire marshals approve arguments they can follow — with calculations, assumptions stated, and test criteria defined. A report that's just equipment schedules isn't an analysis.

What the analysis actually contains

A real rational analysis starts with the fire scenarios: where the fire is, how big it gets, what the smoke does. For an atrium, that means plume calculations or CFD modeling showing the smoke layer height over time against the egress time — proving occupants get out before the smoke comes down. For a pressurized stair, it means calculating the pressure differentials needed to keep smoke out with doors closed and with doors open during evacuation, accounting for the air that escapes through open doors. Then the report addresses the building's own air movement. Stack effect in a tall building can create pressure differences larger than the smoke control design values — the analysis proves the system works in both summer and winter conditions. Wind pressure on the facade, the HVAC system's normal operation, and the interaction between pressurization zones all get analyzed. Finally, the report specifies the controls: what the fire alarm triggers, the fan and damper sequences, the power supplies, and exactly how acceptance testing will verify each design value.

Writing an analysis the fire marshal approves

Fire marshals review these reports constantly, and they approve the ones that answer their questions before they're asked. What I put in every rational analysis.

Clear objectives: what each system protects and the tenability criteria it must meet
Stated assumptions: fire size, fuel, ambient conditions — everything the math depends on, on the record
Environmental forces addressed: stack effect, wind, and HVAC interaction analyzed, not ignored
Complete sequences: every fan, damper, and control action mapped to its fire alarm trigger
Testable criteria: acceptance test procedures with pass/fail values tied to the analysis

Which related engineering resources can help?

When should I hire a structural engineer?What does a PE stamp mean?What is MEP engineering?Smoke control systems Atrium smoke control design International Fire Code requirements Request a project review Engineering service for this question Metro engineering guides Verified service areas

What else do project teams ask?

When is a rational analysis required?

Whenever a smoke control system is provided — the code requires the analysis as the basis of design approval. It's most common for atriums, covered malls, underground buildings, and high-rises with smoke control. The report is submitted with the permit documents and reviewed by the fire marshal or the authority having jurisdiction before the design is approved.

What is the difference between pressurization and exhaust smoke control?

Pressurization keeps smoke out of protected spaces — stairwells, elevator shafts — by keeping them at higher pressure than the fire area, so air flows out through gaps instead of smoke flowing in. Exhaust removes smoke from the fire area itself, typically from the top of an atrium or large space. Most smoke control designs use both: pressurize what must stay clean, exhaust where the smoke is.

Why does stack effect matter for smoke control?

Because tall buildings already move air vertically from temperature differences — warm air rising in winter creates pressure differences between floors that can overpower a smoke control system. The analysis has to account for stack effect, wind pressure on the building, and the HVAC system's operation, because the smoke control fans are fighting all three while they fight the fire. Ignoring them is how systems fail in real conditions.

What does acceptance testing prove?

That the system does what the analysis said it would: fans start in the right sequence, dampers position correctly, pressure differentials across barriers meet the design values, and the controls respond to the fire alarm inputs. Testing is done with the building in various operating modes, and the results are compared against the rational analysis — the report is the test's answer key.

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