Stair Pressurization Fan & Fire Detection integration

Stair Pressurization Fan & Fire Detection integration

According to the National Fire Protection Association, the process of evacuating some of today’s largest high-rise buildings may take upwards of two hours.  This is by far the most compelling argument for effective smoke control in building stairwells. 

Pressurized staircases keep exit routes smoke free in the event of a fire, lending precious minutes to building occupants during an evacuation. The pressures specified to keep a stairwell pressure positive vary by code.  However, the universal goal is to restrain smoke but still allow the opening of doors in the stairwell shaft.

In case of fire in a high rise building, a Stair Pressurization Fan (SPF) uses clean outside air to pressurize the air in stairwells. The pressurized air helps people escape the fire and firefighters battle the fire. It should be work during fire condition through FACP.

When there's a fire, clean outside air is forced by a Stair Pressurization Fan into a stairwell. The pressurization is used to push back on smoke, keeping the smoke out of the escape route.

Stairways are Fire Escape Routes

Nowadays, stairwells have better fire ratings than the rest of the building. In other words, so people can get out when the rest of the building is on fire, stairways don't burn.

Stairways Full of Smoke

The stairways may not burn, but they can still fill up with smoke. The smoke can not only make it harder to see as one is getting away from a fire, but it can:

·        Make it harder to breathe - possibly causing injury or death

·      Close off the escape route - possibly causing people to seek another pathway of escape

Open Doors

The problem is, as people are escaping the fire, they have to open the door to the stairway. When the door is open, preventing the stairway from being used by later escapees, smoke follows and billows into the stairway.

Smoke Push Back

The idea behind the stair pressurization is that during a fire the stairway should have more pressure than the rest of the building. That way, when the doors open, the higher pressure in the stairwell pushes the smoke back onto the floor, keeping the escape route clear of smoke.

The smoke free escape route also doubles as a smoke free entrance route for the firefighters as they combat the fire.

Turning On the SPF

Except when there's smoke, the stair pressurization fans aren't needed, so normally they're turned off. When the fire alarm system detects smoke, they're automatically turned on.

As firefighters battle the fire, if the fire alarm system has not turned on the stair pressurization fans, they're turned on by the firefighters.

Escape

As people are escaping a fire, and open the doors to get into the stairways, smoke would naturally billow from a fire floor into the stairwell. Keeping the smoke out of the stairwell by pushing it back onto the floor, a Stair Pressurization Fan pressurizes the air in the stairwell.

Integration

In every Fire Detection system has one devices named Control Module / Relay Module. This Module operate through FACP loop line. Module has Loop IN /OUT & NO COM NC. Module can be programed as NO / NC condition. An External relay may require (Depend on Module relay capacity) for integration. If Stair Pressurization Fan starter panel has an auxiliary circuit for Fire Alarm then only no need to put any external relay. During external relay operation you required one adjust power supply to energized relay coil.

Here’s a practical case study applying NFPA 92 and ASHRAE methods 👇
🏗️ Project Overview
🏢 Total Levels: 32 (2B + G +28 +Roof)
🧱 Internal Stair Interface Wall Area: 66.38 m² per level
🚪 Door Size: 2.15 m (H) × 1.055 m (W) → 2.27 m² per door
➡️ Total Stair Doors: 32
🧮 Design Conditions
1️⃣ All doors closed: Maintain max. 50 Pa
2️⃣ Single door open: Maintain up to 50 Pa
3️⃣ Three doors open: Maintain min. 20 Pa (above 12.5 Pa)
🔸 Max door opening force: ≤ 133 N

⚙️ Step 1: Basic Data
• Total leakage area (A): to be derived below
• Each door opening area: 2.27 m² = 24.42 ft²
• Face velocity through open door: 1.0 m/s = 196.85 fpm
• Pressure conversion: 1 in.w.g. = 249.09 Pa

⚙️ Step 2: Formula (IP Method)
Q=2610×A×(ΔP)1/2
Where:
Q = airflow leakage (CFM)
A = total leakage area (ft²)
ΔP = pressure differential (in. H₂O)
🔍 Simplified Leakage Calculation (How A = 1.479 m²)
A = A_walls + A_doors_closed
1️⃣ Stairwell walls (A_walls):
Leakage ratio (LR) = 3.5×10⁻⁴ (loose construction)
Wall area per level = 66.38 m² × 32 levels = 2,124 m²
A_walls = 2,124 × 3.5×10⁻⁴ = 0.743 m²
2️⃣ Closed doors (A_doors_closed):
Single-leaf door leakage ≈ 0.023 m² per door × 32 = 0.736 m²
→ Total leakage area, A = 0.743 + 0.736 = 1.479 m² (15.92 ft²)
This area represents the total equivalent leakage the fan must overcome during pressurization.

⚙️ Step 3: Calculations
Case 1 – All doors closed (ΔP = 50 Pa = 0.2007 in.w.g.)
Q = 2610 × 15.92 × √0.2007 = 18,616 CFM (8.79 m³/s)
Case 2 – Single door open (ΔP = 50 Pa)
Door flow = 2.27 m² × 1 m/s = 4,807 CFM (2.27 m³/s)
Total airflow = 18,616 + 4,807 = 23,423 CFM (11.05 m³/s)
Case 3 – Three doors open (ΔP = 20 Pa = 0.0803 in.w.g.)
Q = 2610 × 15.92 × √0.0803 = 11,774 CFM (5.56 m³/s)
Total airflow = 11,774 + 3 × 4,807 = 26,195 CFM (12.36 m³/s)

✅ Governing Design Case
Three-door-open condition controls:
➡️ Q = 12.36 m³/s (≈ 26,200 CFM)
➡️ Maintain pressure between 20–50 Pa
💡 Engineering Insight
A well-engineered system isn’t just about airflow — it’s about balancing:
✔️ Leakage (walls + doors)
✔️ Pressure stability
✔️ Door opening forces
✔️ Fan & damper control logic
Proper VFD tuning, DP switch placement, and humidity control ensure that the system remains stable and compliant under all conditions .

🌍 Design Tip
In hot, humid GCC environments:
✅ Add humidity control at fan inlet
✅ Use normally closed motorized smoke damper for standby sealing
✅ Set pressure range Above 12.5 Pa–Below 50 Pa
✅ Ensure door opening ≤ 133 N per NFPA 92 / ASHRAE 62.1

🔧 Testing Procedure
System compliance is verified using calibrated instruments under different door conditions:
1️⃣Door Open Scenario – Check pressure differential & airflow.
2️⃣Doors Open Scenario – Ensure minimum pressure is maintained.
3️⃣Doors Open Scenario – Validate performance under maximum leakage condition.
🌬️ Air Velocity Requirement:
At any open door, minimum 1 m/s airflow is required to prevent smoke entry.

🔹 Pressurization Strategy (based on sprinkler protection, building height & occupancy)
Buildings Without Sprinklers
Staircase → Lobby: 5 Pa
Lobby → Corridor: 5 Pa
Corridor → Smoke Zone: 25 Pa
Staircase only: 25 Pa to smoke zone
Buildings With Sprinklers
Staircase → Lobby: 5 Pa
Lobby → Corridor: 5 Pa
Corridor → Smoke Zone: 12.5 Pa
Staircase only: 12.5 Pa to smoke zone

🔥 The choice between staircase-only pressurization or staircase + lobby/corridor pressurization depends on building height and occupancy type – ensuring compliance with NFPA 92 & ASHRAE while providing maximum life safety.