Staircase & Lift Well Pressurization Fan Sizing Calculator

Sizes emergency smoke containment pressurization fans per National Building Code (NBC 2016 Part 4) and NFPA 92. Computes closed-door crack leakage, open-door egress velocity airflow, total fan volume (CFM/CMH), and verifies maximum door opening force.

✔ 1. Formula Verified → ⚡ 2. Engineering Screening → 📐 3. Standards Referenced (NBC 2016 / NFPA 92) → ⚖ 4. Engineer Review Required

⚙ Stairwell Geometry & Ingress Inputs

Number of Building Floors Floors

Total levels served by the pressurized fire escape staircase.

Total Staircase Fire Doors Doors

Total self-closing 2-hour fire-rated doors connected directly to the stairwell shaft.

Doors Open During Fire Egress (Nopen) Doors

Design simultaneous open doors during evacuation (typically 2 doors: fire floor + ground exit).

Design Differential Pressure (ΔP) Pascals (Pa)

Design stairwell overpressure relative to adjacent unpressurized floor (50 Pa per NBC 2016 Part 4 / NFPA 92).

Leakage Area per Closed Door m² / Door

Perimeter crack leakage: 0.03 m² for standard fire doors; 0.015 m² for rebated gasketed doors.

Egress Air Velocity Through Open Doors m/s

Minimum outward airflow velocity per NBC 2016 Part 4 / BS EN 12101-6 (standard 1.0 m/s through 2.0 m² doorway).

Duct & Shaft Air Leakage Factor Factor

Safety reserve for masonry shaft wall porosity and duct joint leakage (standard 1.15).

📊 Pressurization Fan Sizing Sheet

Preliminary Screening

Total Required Fan Capacity
13,167 CFM
Volumetric Flow: 22,370 CMH (with 15% duct leakage margin)

Closed Doors Leakage

2,973 CFM

Open Doors Egress Airflow

8,476 CFM

Door Opening Force at Handle

94.6 N

NBC / NFPA Force Limit

Pass (≤ 133 N)

Recommended Fan Specification

Vaneaxial / Inline Centrifugal, Class H Motor (250°C / 2 hrs)

💬 Consult Smoke Control Engineers on WhatsApp

Governing Engineering Standards & Calculation Model

Governing Standards & References

NBC 2016 Part 4: Fire and Life Safety (Clause 4.4.2.5 Pressurization of Staircases).
NFPA 92: Standard for Smoke Control Systems (Pressurization criteria and door forces).
BS EN 12101-6: Smoke and heat control systems — Differential pressure systems.

Engineering Equations & Derivations

Q_closed = 0.827 × A_leak_total × √(ΔP) [m³/s]
Q_open = N_open × A_door × v_egress [m³/s] (A_door = 2.0 m²)
Q_design = (Q_closed + Q_open) × Safety_Margin
CFM = Q_design × 2118.88; CMH = Q_design × 3600
F_door = (ΔP × A_door × W_door) / (2 × (W_door - d_knob)) + F_closer

Door force check: Assumes standard door ($2.0\text{m} \times 1.0\text{m}$), latch knob offset $d = 0.1\text{m}$, and mechanical closer tension $F_{\text{closer}} = 40\text{ N}$. The maximum opening force must not exceed 100 N (133 N under NFPA 101/92).

⚖ Statutory Notice & Engineering Disclaimer (Tier D Integration)

This calculator provides preliminary air volume estimates for smoke containment shafts under simplified orifice leakage models. Staircases exceeding 8–10 storeys require multi-point bottom/top/mid-height air injection or vertical barometric bypass dampers to prevent overpressurization at bottom levels when upper doors open. Pressure sensor modulated variable frequency drives (VFDs) or barometric pressure relief dampers must be incorporated. Final design must receive clearance from the local Chief Fire Officer (CFO).