The LWF Blog
Fire Safety Engineering for Design – Smoke Ventilation – Part 184
May 20, 2024 10:53 amLWF’s Fire Safety Engineering blog series is written for Architects, building designers and others in the construction industry to highlight and promote discussion on all topics around fire engineering. In part 183, LWF discussed smoke ventilation, beginning with the principles of smoke ventilation systems. In part 184, we discuss the objectives of a smoke control system, beginning with ‘Maintaining a smoke-free layer’.
Maintaining a smoke-free layer
Some smoke control systems are designed with the aim of maintaining a smoke-free layer and where this is the case, the layer height is of prime importance.
Where a building or parts, such as corridors, have low ceilings, a clear smoke-free layer is difficult to achieve. In such cases, it is often preferable to work on smoke dilution or smoke clearance, which may be more effective.
In determining the required clear layer height, either for escape or for property protection, the temperature of the smoke and depth of the smoke layer are important to limit radiation beneath the smoke layer.
BS 7346-4 contains recommendations for the clear layer height of 3 metres for public buildings (e.g. shopping centres, exhibition halls) and 2.5 metres for non-public buildings (e.g. office buildings). These minimums will help to ensure that the smoke is kept a safe distance above head height and that the downward heat radiation from the smoke layer is not excessive. This assumes a maximum smoke layer temperature of 200 °C.
BS 7346-4 also suggests that where the predicted layer temperature is less than 50 °C above ambient temperature, 0.5 metres should be added to a recommended minimum value to take into account smoke cooling. Should the smoke cool sufficiently, the smoke layer could drop into the clear layer height, hence the need to increase it.
In cases where smoke control is employed for property protection purposes, BS 7346-4 recommends that 0.5 metres be applied above the height of any stacked goods.
In part 185 of LWF’s series on fire engineering we will begin to look at the area of reservoir for smoke control systems, as well as discussing reservoir screens and curtains. 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 since 1986 to produce innovative and exciting building projects. If you would like further information on how LWF and fire strategies could assist you, please contact the LWF office on 0800 410 1130.
While care has been taken to ensure that information contained in LWF’s publications is true and correct at the time of publication, changes in circumstances after the time of publication may impact on the accuracy of this information.