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Lobby pressurisation (lift / stair)

Sample project — Tower A · Fire

Generated 15 Oct 2026 18:24
Pressurised lift / stair / fire-fighting lobbies: leakage to the floor, the stair and the …
Project code SAMPLE

Fan duty

46665 m³/h

Fan pressure

244 Pa

Motor

7.5 kW

Design ΔP

30 Pa

Governing case

doors open

Relief damper

0.2 m²

1. Inputs

Group	Input	Value	Unit
Code & criteria	Code basis	India — NBC 2016 Part 4 targets + BS EN 12101-6 method
Code & criteria	Purpose (sets the open-door air speed)	Means of escape — 0.75 m/s
Code & criteria	Lobby pressure difference, doors closed (0 = code: NBC 30 Pa · EN class · NFPA min)	0	Pa
Code & criteria	Air speed through the open door (0 = by purpose / class)	0	m/s
Code & criteria	Maximum door-opening force (0 = code: India 110 N · EN 100 N · NFPA 133 N)	0	N
Code & criteria	Door-closer force at the handle	40	N
Building	Floors with a pressurised lobby	15
Building	Floor-to-floor height	3.3	m
Lobby	Lobby	Lift + stair (fire-fighting) lobby
Lobby	Doors lobby → floor (accommodation)	1
Lobby	Lobby → floor door	Single leaf — opens into the pressurised space (0.01 m²)
Lobby	Lobby → floor door width	1.0	m
Lobby	Lobby → floor door height	2.1	m
Lobby	Door leakage from	BS EN 12101-6 Table A.2 values
Lobby	Lobby → stair door	Single leaf — opens out of it (0.02 m²)
Lobby	Lobby → stair door width	1.0	m
Lobby	Stair pressurised too	True
Lobby	Stair ΔP (to the floor)	50	Pa
Lobby	Lift landing doors into the lobby	2
Lobby	Lift well pressurised too	False
Lobby	Include lobby wall leakage (ASHRAE ratios — BS practice leaves it to the unidentified allowance)	False
Fire-floor door open	Lobby → floor doors open at the fire floor	1
Fire-floor door open	ΔP across the lobby's other doors, door open	10	Pa
Fan, ducts & air distribution	Allowance for unidentified leakage	25	%
Fan, ducts & air distribution	Duct leakage allowance on the fan	15	%
Fan, ducts & air distribution	Over-pressure control	Barometric pressure-relief damper(s)
Fan, ducts & air distribution	Standby fan (duty + standby)	True
Fan, ducts & air distribution	Duct run fan → farthest outlet (0 = shaft height + 10 m)	0	m
Fan, ducts & air distribution	Duct friction	1.0	Pa/m
Fan, ducts & air distribution	Fittings allowance on duct friction	50	%
Fan, ducts & air distribution	Intake louvre + dampers + grille losses	125	Pa
Fan, ducts & air distribution	Fan total efficiency	60	%
Fan, ducts & air distribution	Supply grille face velocity	3.0	m/s
Fan, ducts & air distribution	Riser duct velocity	8.0	m/s

2. Results

Criteria

Item	Value	Unit	Note / basis
Basis	NBC 2016 Part 4 — 25–30 Pa in lobbies / lift wells; open-door air speed by BS EN 12101-6
Design pressure difference, doors closed	30.0	Pa
Air speed through the open door	0.75	m/s
Maximum door-opening force	110.0	N
Pressure across the other closed doors with the door open	10.0	Pa	BS EN 12101-6
Lobbies	15	nos	one per floor, 3.3 m floor to floor
Air per lobby, doors closed	2392.21	m³/h	net of inflow from a pressurised stair / shaft
Air to the fire-floor lobby, door open	7087.33	m³/h
Inflow from the stair / lift shaft per lobby	267.25	m³/h

Air quantities

Item	Value	Unit	Note / basis
Doors closed (with unidentified leakage)	9.97	m³/s	35,883 m³/h
Doors open — 1 lobby door(s) 1 × 2.1 m at the fire floor	1.58	m³/s	0.75 m/s × 2.10 m²
Doors open — total	11.27	m³/s	40,578 m³/h
Design (larger)	11.27	m³/s	doors open
Fan duty (with duct leakage)	12.96	m³/s	46,665 m³/h · 27,466 cfm

Fan, relief & distribution

Item	Value	Unit	Note / basis
Duct run	59.5	m
Duct friction incl. fittings	89.25	Pa
Fan total pressure	244.25	Pa
Shaft power	5.28	kW
Motor	7.5	kW
Fresh-air intake louvre (free area at 2.5 m/s)	5.19	m²
Pressure-relief damper free area	0.1962	m²
Air release from the fire floor (vent / shaft / façade)	0.6001	m²	at 10 Pa for the open-door air
Injection points	15	nos	L0, L1, L2, L3, L4, L5, L6, L7, L8, L9, L10, L11, L12, L13, L14
Air per injection point	7087.33	m³/h
Supply grille (gross, ≤ face velocity, 75 % free)	1250 × 700	mm
Riser duct	1550 × 1050	mm	≤ 8 m/s

Leakage paths (doors closed)

Path	Basis	Each m²	Total m²
Lobby → floor door(s) × 1	single leaf, opening INTO the pressurised space	0.0100	0.0100
Lobby ↔ stair door (air IN from the pressurised stair)	ΔP 20 Pa	0.0200	−0.0200
Lift landing doors × 2 (shaft not pressurised)	lift landing door	0.0600	0.1200

Bill of quantities

Item	Qty	Unit
Pressurisation fan, 46,665 m³/h @ 244 Pa, 7.5 kW motor (duty + standby)	2	nos
Motorised / non-return damper at each fan outlet	2	nos
Fresh-air intake louvre with bird screen, ≥ 5.19 m² free area (2.5 m/s), away from smoke outlets	1	set
Riser duct 1550 × 1050 mm, GI sheet, 60 m (fire-rated where outside the protected shaft)	309.4	m²
Lobby supply grilles 1250 × 700 mm with motorised damper (fire floor fully open)	15	nos
Interface with the fire-alarm panel (start on alarm, status / fault to FACP), fire-survival cable to the fans	1	set
Barometric pressure-relief damper per lobby, 0.20 m² free area, set to 35 Pa (relieves to the floor / a relief shaft)	15	nos

3. Checks

Check	Result	Note
Pressure hierarchy: stair 50 Pa > lobby 30 Pa > floor 0 Pa	PASS	the stair must stay above the lobby so smoke cannot pass into the stair
Lobby → stair door force at 20 Pa: 63 N ≤ 110 N	PASS
Design ΔP 30 Pa ≤ door-opening force ≤ 110 N (62 Pa)	PASS	door force at the design ΔP 74 N

4. Worked example

Per lobby, doors closed: 0.83 × 0.0100 × 30^0.5 = 0.045 m³/s to the floor + 0.546 m³/s to the stair / lift shaft, × 1.25 unidentified − inflow 0.074 m³/s = 0.665 m³/s; × 15 lobbies = 9.968 m³/s

Fire floor, door open: v × A = 0.75 × 2.10 = 1.575 m³/s + the lobby's other doors at 10 Pa 0.394 m³/s = 1.969 m³/s; + 14 other lobbies × 0.665 = 11.272 m³/s

Design = max(9.968, 11.272) = 11.272 m³/s (doors open); fan = × 1.15 duct leakage = 12.963 m³/s = 46,665 m³/h

Fan pressure = 60 m × duct friction × (1 + fittings) = 89 + fixed losses + 30 Pa = 244 Pa; shaft power = Q·p/η = 12.963 × 244 / η = 5.28 kW → motor 7.5 kW

Door force: F = Fdc + W·A·ΔP / (2(W − d)) = 74 N at 30 Pa; limit 110 N → ΔP max = 2(W − d)(F − Fdc)/(W·A) = 62 Pa

Relief: leakage at 62 Pa = 0.985 m³/s; excess = 12.963 − 0.985 = 1.279 m³/s → A = Q / (0.83 √ΔP) = 0.196 m²

5. Notes

Each lobby is supplied from the riser; on alarm the fire-floor lobby gets the open-door air (motorised damper fully open) and the others their doors-closed air — the fan is sized for that case or for all lobbies doors-closed, whichever is larger.
Leakage areas: BS EN 12101-6 Table A.2 (doors), A.3 (windows); wall leakage ratios from the ASHRAE Handbook of Smoke Control Engineering (NFPA 92 Annex). Verify the door schedule and construction with the architect.
Open-door condition: the required air speed through the open door(s), the other doors closed at the reduced pressure — BS EN 12101-6 Annex A method; the fire floor needs an air-release path (vent, shaft or façade opening) sized above.
The fan starts on fire alarm; the intake is taken from a smoke-free location at least 5 m from any smoke outlet; fans, controls and cables are on the fire-protected supply (NBC 2016 Part 4 / BS EN 12101-6).
Commissioning: measure the pressure difference with all doors closed and the air speed with the design doors open (BS EN 12101-13 acceptance test).

6. Standards and references

NBC 2016 Part 4 — National Building Code — Fire and life safety: Occupant load (Table 5), exit width (Table 22), travel distance (Table 21), stair widths
NFPA 101:2021 — Life Safety Code: Means of egress (international option)
NFPA 92 (2021) — Smoke control systems: Pressurisation and smoke-exhaust design and acceptance
EN 81-72:2020 — Firefighters lifts: Fire-fighter lift features
BS EN 12101-6:2005 — Smoke and heat control systems — Specification for pressure differential systems — Kits: System classes A–F, design pressure differences and open-door air speeds, door-opening force, leakage areas of doors / windows (Annex A), calculation method
BS EN 12101-13:2022 — Smoke and heat control systems — Pressure differential systems (PDS) — Design and calculation methods, installation, acceptance testing, routine testing and maintenance: Design and calculation of pressurised stairs, lobbies and lift wells; commissioning (pressure difference doors closed, air speed doors open)
ASHRAE Handbook of Smoke Control Engineering (2012) — Klote, Milke, Turnbull, Kashef, Ferreira — Handbook of Smoke Control Engineering: Flow through leakage paths, wall / floor leakage ratios, stack effect in pressurised stairwells and lift shafts, door-opening force
BS 9999:2017 — Fire safety in the design, management and use of buildings — Code of practice: Protected stairs, fire-fighting shafts and lobbies, when pressurisation is used in place of natural ventilation

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Results are design aids computed by designlink calc (calc.designlink.in) and must be reviewed by a qualified engineer before issue. Ground levels marked "assumed" have no survey level within reach — verify.