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Colt shaft frees up valuable floor space

Colt UK has launched Colt Shaft, an active fan smoke extraction system for residential buildings, hospitals, schools/colleges, offices and hotels, that frees building designers from the constraints imposed by the need for ‘fire-fighting cores’ in these types of buildings and extracts smoke more quickly than passive natural ventilation systems.

Fire-fighting cores, which are required in buildings over 18m to an occupied top floor level, are voids containing stairs, lifts and lobbies to allow fire fighters access to any floor. These cores must be kept free from smoke and this is achieved by ventilation, either by openable windows or, if they are remote from outside walls, by a ‘BRE shaft’, which takes up a large amount of valuable floor space, or a pressurisation system which is often complex and expensive to design and install.

Colt Shaft, which is suitable for use in any fire-fighting core, requires a shaft of only 0.6m2 compared with 3m2 for the BRE shaft. This represents an 80 per cent reduction in the floor space required. It opens up the space on each floor, which allows architects to be more creative in their design, and improves the saleable or lettable space in commercial buildings for the client.

Colt Shaft also solves two common problems associated with mechanical extraction. Firstly, since the lobby is fire rated, the area of ventilation into it is usually small, so even a small amount of extract will cause a high negative pressure in the lobby, which could make doors difficult to open. Secondly, negative pressure could cause smoke to be drawn into the lobby from the fire compartment, with devastating effect.

However, Colt Shaft overcomes excessive negative pressures without compromising the integrity of the stairs and lobby by automatically reducing the ventilation rate when the lobby doors are closed. It does this via a pressure sensor linked into the control system that varies the fan speed. With all doors open, the fan runs at full speed to extract smoke discharging from the accommodation. With all doors closed, the fan runs at minimum speed to help mop up smoke leaking past the closed door. In intermediate conditions, the fan speed modulates to ensure adequate ventilation without excessive depressurisation.

Colt has conducted a comprehensive series of smoke tests, witnessed by the London Fire Brigade, which now has the confidence to accept that the Colt Shaft could perform to an equivalent standard as a standard 3m2 BRE Shaft, fitted in the same situation. The tests also showed that the system reacts quickly to pressure changes, smoke clears quickly from the lobby when the accommodation or stair doors are opened, and the lobby is kept clear of smoke once the accommodation door is closed.

With the door to accommodation closed, a typical 5m2 lobby will clear totally within 15 to 20 seconds of opening the stair door.

Email: simon.ohea@uk.coltgroup.com