M&E contractor Derry Building Services of Newark initially approached Colt for a pressurisation system. Simon Palmer, Mechanical Contracts Engineer, explained: “Colt proposed using its shaft system as an alternative. Not only is this option half the cost, it requires a shaft of only 0.6m2 compared with 3m2 for a conventional BRE shaft. This represented an 80% reduction in the floor space required. The additional floor space available for hotel rooms will significantly increase our client’s profits”.

The project involved Colt supplying, installing, wiring and commissioning its Colt Shaft for the 205-bedroom, seven storey Hoxton Hotel in the heart of the City of London. This is the first contract in which Colt Shaft has been specified.

In the event of a fire, the Colt Shaft – which runs vertically through the hotel – would use a fan system to draw smoke away from the fire fighting core to ensure access for the emergency services.

The Colt Shaft system has been approved by the London Fire Brigade for use in this application, following tests witnessed at Colt International’s facility in Havant, Hampshire.

The Colt Shaft solves two problems commonly associated with mechanical extraction. First, 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, the 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.

The £17 million Hoxton Hotel, which opened on 1 September, is the brainchild of Sinclair Beecham, the co-founder of the Prêt a Manger sandwich chain, who has invested more than £1m of his own money in the project.

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