AEO Answer · Fire Protection & Life Safety

How Are Atrium Smoke Control Systems Designed?

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

Atrium smoke control keeps the smoke layer above occupied levels by exhausting smoke from the top at a calculated rate, with low-level makeup air and protected adjacent spaces, proven by full-system acceptance testing.

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.

Plume calculations and exhaust sizing

The plume calculation is the engineering core of the design. From the agreed design fire, I compute the plume mass flow at the design smoke layer height — the rate at which smoke and entrained air arrive at the ceiling — and size the exhaust to remove that flow with a margin. Taller atriums entrain more air and need more exhaust, which is why a dramatic 80-foot atrium needs a serious fan plant while a modest two-story atrium might get by with natural venting or smaller fans. I also check the smoke layer depth against the highest occupied walking surface with a safety margin, and I verify that the exhaust inlets are arranged to pull evenly across the ceiling rather than short-circuiting to the nearest opening.

Protecting the spaces around the atrium

The atrium is only half the problem — the floors and corridors that open onto it are the other half. I protect adjacent spaces with a combination of smoke barriers, draft curtains, and pressurization so that smoke leaving the atrium does not pour into the egress paths. Corridors connecting to the atrium get special attention: they are both egress routes and the boundary the smoke control is defending. Door opening forces are checked wherever pressurization is used, because a corridor held at high positive pressure with a door nobody can pull open is a failed design. The control sequence ties it all together — detection in the atrium triggers the exhaust, opens the makeup air, and pressurizes the protected adjacencies in the right order.

Atrium smoke control design checklist

An atrium smoke control design is ready when it clears this checklist. The fire marshal will ask about every one of these. • Design fire size proposed per NFPA 92 guidance and accepted by the AHJ in writing • Plume calculation setting the exhaust rate, with the smoke layer held above the highest walking surface • Makeup air introduced low and slow, sized to match exhaust without disrupting the layer • Adjacent corridors and tenant spaces protected with barriers and pressurization, door forces checked • Full-system acceptance test procedure written into the documents, including visualization of the smoke layer

Which related engineering resources can help?

When should I hire a structural engineer?What does a PE stamp mean?What is MEP engineering?How Is Smoke Control Designed for Apartments?How Does Atrium Smoke Exhaust Design Work?How Are Fire and Smoke Dampers Designed Into Ductwork?Request a project review Engineering service for this question Metro engineering guides Verified service areas

What else do project teams ask?

How do you decide between exhaust and pressurization for an atrium?

For the atrium volume itself, exhaust is the standard answer — you remove the smoke at the top and hold the layer up. Pressurization is the tool for the spaces around the atrium: corridors, lobbies, and tenant entries that connect to the atrium get pressurized or separated so smoke does not migrate into them. I use both in most designs, each doing the job it is good at. The choice also depends on the atrium geometry — a very tall, narrow atrium behaves differently from a wide, low one — which is why the plume calculation comes before the strategy is finalized.

What is a design fire and who picks it?

The design fire is the assumed fire size — heat release rate — that the smoke control system is engineered to handle. I propose it based on what the atrium actually contains (retail kiosks, seating, landscaping, event setups) and the guidance in NFPA 92, and the fire marshal or the AHJ's reviewer agrees to it. It is a negotiation grounded in reality: too small and the system is under-designed, too large and the fans and shafts become absurd. Getting the design fire accepted in writing early avoids redesigning the whole system at plan check.

Why does makeup air matter so much in atrium smoke control?

Because exhaust fans cannot move air that cannot get in. If the atrium is sealed tight, the fans will pull the building into negative pressure, doors will be hard to open, and the exhaust rate will collapse. Makeup air has to be introduced low — at the occupied levels, below the design smoke layer — and at low velocity, so it feeds the plume without stirring the smoke layer down. I coordinate the makeup air path with the building's HVAC and the architectural openings, because a beautiful glass atrium with no intentional makeup air path is a smoke control problem waiting for its first test.

How is an atrium smoke control system tested?

As a complete system under realistic conditions. Acceptance testing verifies the full sequence: detection initiates the system, exhaust fans start, makeup air paths open, adjacent spaces pressurize, and the smoke layer holds. Testing often uses theatrical smoke or tracer gas to visualize the layer, plus measurements of fan flows, pressure differentials, and door opening forces. I write the test procedure into the design documents so the commissioning agent, the fire marshal, and the installing contractor all know what passing looks like before test day.

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