The LWF Blog
Fire Engineering Design and Risk Assessment – Fire and Smoke Ventilation – Part 12 – Firefighting ShaftsApril 6, 2017 10:55 am
In this Fire Engineering Design and Risk Assessment blog series for Architects and others in the building design industry, we have been looking at fire and smoke ventilation. In Part 12, we’re going to talk about firefighting shafts and the requirements.
In the UK, firefighting shafts are required by fire regulations in buildings more than 18m in height, or in those constructions with a basement deeper than 10m.
The building purpose is relevant too, with some groups requiring a firefighting shafts without a firefighting lift in building heights of greater than 7.5m and where the floor area is more than 900m2, and where there are two basement levels of 900m2 or deeper.
The construction of the shafts themselves are also subject to certain requirements. The shafts must be enclosed within 120 minute fire rated construction and should have a dedicated stairway and lift for the Fire Service, which is linked by a protected lobby. Each shaft should have a dry riser, or a wet riser where the shaft is over 50m high. The firefighting lobby and stairway leading to the shaft should be provided with ventilation.
BS 9999:2017 – Fire safety in the design, management and use of buildings. Code of practice lays out the requirements for firefighting shafts and outlines the area of vents required in the stairway and lobbies, which can be opened manually by the Fire Service. The smoke will then pass through the vents in the fire lobby, where it will be vented into a large vertical shaft, as long as the door between the lobby and stair is closed.
The vents to the firefighting shaft should have the following:
For lobby vents – Each opening window should measure 1m2 to outside air at each level, or where this is not possible, 1.5m2 vents to 3m2 smoke shaft, opening to the outside at the top and bottom of the shaft.
For stair vents – 1.5m2 vent at the head of the stairway, or a 1m2 vent at each level.
All vent operations in the firefighting shaft, stairways and lobbies are to be controlled manually by the Fire Service.
An alternative ventilation option is laid out fully in BRE 79204. This method channels ventilation from the lobby into a smoke shaft which is closed at the base. The vents in the smoke shaft and at the head of the stairs automatically operate when the smoke detectors are activated within the firefighting lobbies.
This method has the following requirements for vents:
For lobby vents – 1.5m2 vent to a 3m2 smoke shaft closed at the base. Vents at the fire floor and the top of the shaft operate automatically when smoke detectors in the firefighting lobby are activated.
For stair vents – 1m2 vent at the head of the stair, which opens automatically when smoke detectors are activated in the firefighting lobby.
In Part 13 of this series, we will look at Fan-assisted Ventilation. 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.