How is a stair pressurisation fan sized?

The fan must hold the design pressure against door and wall leakage with all doors closed, and push air through the open doors at the required velocity. The larger flow, plus duct leakage, sets the fan.

What door opening force is allowed?

100 N at the handle in BS EN 12101-6 and 133 N in NFPA 92 and NFPA 101. The lab works out the force and the highest pressure your doors allow.

How much smoke exhaust does an atrium need?

The NFPA 92 plume equation gives the smoke mass rising past your target layer height. Exhausting that mass at the layer temperature holds the smoke above people, as long as no inlet plugholes.

FF-204 · FIRE FIGHTING · SMOKE CONTROL

Smoke Extract & Stair Pressurisation Lab

Three smoke control tools in one: size a stair pressurisation fan with door leakage, open door velocity, door force and relief damper; size atrium smoke exhaust with the NFPA 92 plume equations and plugholing check; and set car park smoke ventilation rates.

BS EN 12101-6NFPA 92UAE Fire & Life Safety CodeBS 7346-7EN 12101-3 F300AS 1668.1

How to use: pick a tool below. Defaults are set for a typical Gulf project, and every field has an i with a plain explanation.

1. Stair and doors

Pressure differential system for an escape or fire fighting stair.

Criteria

Standard and class

Pressure, doors closed (Pa)

Velocity, open door (m/s)

Doors open together

Max door force (N)

Building

Floors served

Stair doors per floor

Leakage per door (m²)

Wall leakage per floor (m²)

Door width (m)

Door height (m)

Door closer force (N)

Unidentified leakage (%)

Duct leakage (%)

Pressure across other closed doors when one is open (Pa)

2. View

3. Checks

4. Calculation

5. How the methods work

Stair pressurisation

Air leaks out through door gaps and wall cracks at Q = 0.83 × A × √ΔP (m³/s, m², Pa). With all doors shut the fan must hold the design pressure against that leakage. With doors open it must push air through them fast enough to keep smoke out. The bigger of the two sets the fan, plus duct leakage. When the doors shut again the surplus must escape through a relief damper so the doors can still be opened: F = closer force + W × A × ΔP / (2 (W − d)).

Atrium plume

NFPA 92 gives the smoke mass flow rising past height z in an axisymmetric plume: m = 0.071 Q_c^1/3 z^5/3 + 0.0018 Q_c, with Q_c = 0.7 Q. Exhausting that mass at the layer temperature holds the smoke at height z. Each inlet can only take so much before it pulls clear air through the layer (plugholing), so the lab works out how many inlets you need.

Smoke filling time

Without extract, the layer falls as the plume fills the space. The NFPA 92 filling equation gives the layer height against time, which the 4D view plays back.

Car parks

Conventional systems use about 10 air changes per hour in fire mode and 6 for normal pollution control, with fans rated for 300 °C for 2 hours. Impulse fan layouts are confirmed by CFD.

Learning and checking tool. Smoke control designs need the project fire strategy, the authority's approval and, for atria and car parks, usually CFD.

Standards and regions covered

Built around BS EN 12101-6, NFPA 92 and NFPA 101 as used under the UAE Fire and Life Safety Code, BS 7346-7, EN 12101-3 and AS 1668.1. Engineers use it on projects in Dubai, Abu Dhabi, Sharjah and the Northern Emirates, Saudi Arabia and Qatar, and in Auckland, the rest of New Zealand and Australia. Always confirm the edition your authority or client has adopted before relying on a result.

Smoke Extract & Stair Pressurisation Lab

1. Stair and doors

1. Atrium and design fire

1. Car park

2. View

3. Checks

4. Calculation

5. How the methods work

Stair pressurisation

Atrium plume

Smoke filling time

Car parks

Smoke Extract & Stair Pressurisation Lab

Topics you can explore

Practical engineering example

Standards and regions covered

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