Until recently a pressurised means to control fire smoke in high rise residential buildings was considered too expensive, now thanks to a breakthrough in technology, a new fan design has been produced expressly to save lives in the event of fire.
Two recent fires in high rise flats have focussed attention on the dangers of such blazes and their inherent difficulties for the fire service. The fires, at Lakanal Flats in Camberwell and the 15-storey Shirley Towers in Southampton, caused fatalities and in both cases the flames and smoke rapidly spread out of control.
The problem is that no matter how structurally resilient a building is made, if a fire breaks out and renders the primary means of escape, stairways and elevators, unusable, the building quickly becomes unsafe. The dilemma of how to evacuate a building, if exits are jeopardised, remains the foremost safety issues for occupants working and living in high rises, and even low rises today.
A pressure differential system – commonly known as ‘pressurisation’ – is the only system where the objective of the design is to keep smoke out of the escape routes altogether, by producing pressure and/or air velocities across doors on the fire effected floor, using a supply air fan.
The design of the air system, based on European standards, is pure fan application engineering, hence the importance that designers understand the principles of fan engineering. The stairwell must be pressurised at the earliest stages of a fire.
It has become the system of choice for high rise buildings in countries outside the UK, and indeed for many prestigious building in the UK. Fläkt Woods in collaboration with fire systems design specialists Fire Engineering Associates and Interactive Special Projects has just launched Smoke Angel a new cost effective pressurisation system.
The appliance is automatically activated to clear hot smoke from within the stairways, with operation initiated by smoke detectors located within the common corridors or lobbies. Pressurisation is started within approximately 20 seconds of the start of a smoke detector. As it takes an average of 4–10 minutes, in urban areas, for the fire department to arrive, the new fan is HT rated, and reversible, so attending fire fighters can then use the control panel to choose the pressurisation/smoke exhaust option that is most appropriate to the situation.
The fan is temperature rated to F300, for operation at 300oC for 2hours and CE Marked. It includes an integrated fan module with an automatically opening ventilator, a differential pressure switch, and when required, a smoke detector.
Paul Wenden, Engineering Director of Fläkt Woods states "Traditionally in the UK, smoke control in residential high rise buildings has been provided for by natural ventilation, fitting vents, 1.5m2 free area, to allow the smoke to exhaust the building either directly, or via a vertical smoke shaft of the same area. These systems are very prone to external wind induced positive pressures and as such are unreliable as a live saving system. In addition, in any form of ventilation system the smoke will have to enter and pass along the escape routes to reach the vents contaminating the escape route in the process. Pressurisation is the only system that avoids this weakness.”
The ventilator opens and the fan starts automatically once the smoke detector is triggered, raising the pressure in the stairwell and preventing fire smoke from entering the vertical part of the escape route. When necessary, additional automatically operated air relief is provided.
Thanks to its compact external dimensions, it is suitable for use in new build as well as many refurbishment projects. For ease of design, it is only available in one size with constant air volumes that works for stairwells of many different heights.
Paul Wenden concludes, “Not only is the product concept already proven and preferred overseas, but we are able to provided site surveys before proposing the complete solution – right through to system commissioning – all endorsed by Fläkt Woods.”
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