Smoke control: stair pressurization, floor exhaust, and atrium baffles

One-line orientation

Smoke — not flame — is the leading killer in building fires, which is why codes devote whole mechanical systems to controlling it. Smoke control keeps escape routes usable and removes smoke from affected spaces. Exit stairs use positive pressure, while the fire floor uses exhaust; atrium baffles can guide smoke toward exhaust outlets.

Key points

• Stairwell pressurization: fresh air is pumped into the exit stair to hold it at higher pressure than adjacent areas, so smoke can’t enter. Purpose: keep the escape route usable. Often required in tall or underground buildings.
• Floor (fire-floor) exhaust: smoke is pulled out of the floor where the fire is to aid containment and protect escape routes. Activated by fire/smoke detection so it runs only where smoke is present.
• Atrium smoke control: smoke rises into the large open volume. Smoke baffles or draft curtains near the ceiling can guide it toward exhaust outlets.
• The unifying idea: the stair is kept at positive pressure (smoke excluded) while the fire floor is driven negative (smoke removed). Opposite pressures, same life-safety goal.

Confusions / comparison

System	Pressure intent	Airflow	What it protects	Trigger
Stair pressurization	Positive (higher than adjacent)	Air pushed in	The exit stair / egress route	Fire alarm; keeps stair clean
Fire-floor exhaust	Negative	Smoke pulled out	The floor of origin + escape routes	Smoke detection on that floor
Atrium baffle + exhaust	n/a (physical baffle)	Smoke redirected to exhaust	The open atrium volume	Smoke control sequence

Related

→ Egress (this module): the stairs and corridors this smoke control is protecting · Exterior wall ratings and parapets (this module): the other half of compartmentalizing fire and smoke · Code in the design process (this module): when life-safety systems get coordinated.