Quick Guide to Lift Lobby Pressurization System
Lift Lobby Pressurisation is designed to create a positive pressure difference which prevents lobbies & staircases from filling up with smoke during fire.
Typically this is a statutory requirement for lift lobbies that do not have any side open to the outside environment; especially basements.
Lobby pressurization based ventilation systems are pervasively used to ventilate mid-rise to high-rise multi-unit buildings. This system uses a make-up air unit (MAU), usually located on the roof of the building, to draw fresh air in with a large fan either continuously or on a pre-set schedule. Once the air is drawn into the building, it is distributed to each floor through a large vertical duct usually located in the building core.
(+) Mandatory as per NFPA 92 and NBC
(+) Should be a part of Fire protection system for the multi-storeyed buildings [high rise buildings] & the buildings, which are of 15 m. & above in height
(+) If the lift shaft & lobby is in the core of the building a positive pressure between 25 & 30 [pa] shall be maintained in the lobby
(+) For Underground Complexes, Industrial Storage, Meeting | Banquet Halls, Hazardous Occupancies etc.
extract from NFPA
In commercial buildings pressurisation is normally carried through up to the final door to the accommodation, with air release provided from the accommodation.
In apartment buildings it is usually impractical to carry pressurisation up to each apartment door due to the difficulty of providing air release from each apartment. Therefore lobbies are usually pressurised with air release from the corridor.
extract from NBC
A pressurisation system consists of three main components:
Supply Air [where air is injected into the area that is to be protected]
Pressure Relief [to avoid overpressure when doors are closed]
Air Release [air & smoke is released from the adjoining fire area]
Inlet Fans for introducing air into the designated area. The run, standby fans and control equipment should be housed in a separate plant room or outdoors and the inlet should be protected from smoke.
Ductwork & Outlet Grilles, to provide distribution of air exactly where it is needed.
Pressure relief dampers, to release excess air in the closed door condition from the stair area. This should be ducted to discharge directly to the atmosphere independent of the wind direction.
Automatic air release to prevent unwanted pressure build up in the adjacent spaces. This may be automatic vents, natural shafts or mechanical extract systems.
The control system should operate automatically from the smoke detection system with a manual on/off switch also provided within either the pressurisation plant room, near the building entrance [to suit fire service], or within the central building services control room.
There are two requirements to maintain within a pressurisation system:
Maintaining a pressure difference for a closed door condition. Here the pressure difference is required to overcome buoyancy pressure generated by the hot smoke layer, expansion of the gases in the compartment due to heating, stack pressure & wind pressure
Maintaining a velocity for an open door condition. Here maintaining a velocity for an opened door is required to hold back the smoke on the fire floor when the door onto the fire floor is open.
Getting the right balance for a pressurisation system needs careful design in order for the system to work effectively. Insufficient pressure difference across a closed door will allow the passage of smoke into the protected space.