The LWF Blog
Fire Engineering Design and Risk Assessment – Fire and Smoke Ventilation – Part 15 – Firefighting ShaftsApril 27, 2017 2:13 pm
In this Fire Engineering Design and Risk Assessment blog series for architects and others in the building design business, we have been looking at fire and smoke ventilation and how the various methods employed can sustain breathable conditions in an area for a duration of time. In Part 15, we will be talking about firefighting shafts, considerations of design and the effects.
A firefighting ventilation shaft is a vertical shaft which is the full height of a given building, usually a high rise building. The vent shaft is connected to each firefighting lobby via an automatically opening vent. In cases of fire, the vent on the floor of fire origin is opened to the shaft.
When designing a building with such a fire protection feature, it is important to take into account the potential for smoke in the lobby, the size of the lobby, any other fire protection measures which are to be provided within the building and the potential Fire Service response time from notification to arrival.
A fan-assisted system of this type is dependent upon passive fire protection measures in order to prevent smoke entering the stairway, for example, clean air must replace the extracted air in the lobby in order to avoid smoke being drawn from the floor of fire origin and the associated fans and ducting should be appropriately temperature rated in order to withstand the design fire temperatures.
One example of a commonly-seen firefighting shaft configuration in the UK is where the smoke shaft is 0.6m2 for the height of the building and an automatically opening vent (operated by smoke detector) is placed between the shaft and the lobby at each floor level. When the fire alarm system is triggered by a smoke detector, the vent on that floor only will open into the shaft. In addition, at the top of each stairway, an automatically opening vent is provided which too becomes operational upon activation of the smoke detector.
In this case, replacement air is not deliberately added to the area to replace the removed smoke/air, but the opening of the stair vent and natural leakage (for buildings are not usually air tight) is usually sufficient.
If there is a potential for negative pressures across the lobby door, pressure sensors are provided on each floor which reduce the fan speed until the pressure is within normal range.
While each fire engineered design must be undertaken on individual basis and so can be subject to performance criteria from regulatory authorities, the primary aim of this system is to ensure the stairs remain clear of smoke and safe evacuation can be progressed, as well as allowing the Fire Service access to the building.
In Part 16, we’re going to look at systems designed to aid firefighting specifically. In the meantime, if you have any questions about this blog, or wish to discuss your own project with one of our fire engineers, please contact us.
Lawrence Webster Forrest has been working with their clients for over 25 years to produce innovative and exciting building projects. If you would like further information on how LWF and fire strategies could assist you, please contact Peter Gyere on 020 8668 8663.