The LWF Blog
Fire Safety Engineering for Design – Smoke Ventilation – Part 185
May 28, 2024 10:33 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 184, LWF discussed the objectives of a smoke control system, beginning with ‘Maintaining a smoke-free layer’. In part 185, we will look at the area of a reservoir for smoke control systems, as well as discussing reservoir screens and curtains.
The area of a reservoir has historically been limited to around 2000 to 3000 m2 to prevent excessive cooling and the downward mixing of smoke.
Where required, a larger reservoir may be acceptable, subject to certain conditions. The design team should give consideration to the potential for heat loss to the surrounding structure and so the fire engineering analysis necessary would be more numerically complex or involve the use of computational fluid dynamics modelling.
Reservoir Screens & Curtains
Smoke curtains are used as part of a smoke control system to control smoke from a fire. Smoke curtains are generally rated to 600°C. Smoke curtains do not reach all the way to the floor, but are intended to reach the bottom of the smoke layer.
The screens and curtains constructed to enclose the edges of a reservoir must comprise materials able to withstand the predicted smoke temperature for the necessary duration of time.
The screens should be impermeable, but there may be some leakage at the junction of screens, for example, which is not likely to be critical for most applications.
Where fixed screens are employed, the depth or drop of the screens or curtains should reach at least to the level of the smoke layer base. An increase to the depth to add a margin of safety could be advantageous and this is backed by BS 7346-4, which suggests an additional 0.1 m.
Retracting screens or curtains may deflect from the normal vertically hanging position due to the pressure of gases rising from the base. The horizontal deflection causes the bottom of the curtain to rise, which may lead to the leakage of smoke underneath the curtain if the rise takes the bottom above the base of the smoke layer. The potential for this to occur should be taken into account when calculating the depth of the curtains, to include an appropriate margin of safety. Further information can be gained from BR 368.
In part 186 of LWF’s series on fire engineering we will begin to discuss replacement air. 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.