The LWF Blog
Fire Engineering Design and Risk Assessment – Smoke Management System Components – Part 23June 22, 2017 12:15 pm
In this Fire Engineering Design and Risk Assessment blog series for Architects and others involved in building design, we have been looking at fire and smoke ventilation. In the last blog, Part 22, we talked about the use of hot smoke tests in some parts of the world and how they can be carried out without damaging the premises in question. In Part 23, we are going to look at the components of smoke management systems and considerations for each part, beginning with ductwork.
Smoke extract ducts are expected to carry hot smoke from a potential fire out of the building and so must be designed with that level of heat in mind. The rating for the ductwork must be sufficient for the calculated smoke temperature.
Ductwork which will pass from one compartment within the building to the next must be fire resistant. When considering a smaller building, in most instances the fire resistance should be for one hour. However, in larger and more complex buildings, including high-rise or shopping centres, a higher resistance period is likely to be required.
In cases where the entire smoke extract system is contained within a single compartment, as is often the case in a car park, then it does not require a fire rating. It should, however, comply with the requirements of Building Regulations, Approved Document B and be comprised of materials with a melting point of above 800ºc. An appropriate specification example can be seen in DSP DW144.
While most smoke management systems transport smoke to an extract point, some systems don’t use ductwork and instead use jet fans, for instance, to blow smoke towards outside air and away from enclosed spaces. This sort of system can be seen commonly in car parks and malls.
The fans used for smoke extract must be fit for purpose and in this instance, that indicates that the fan must be able to withstand the design temperature for the duration of the period indicated by the fire engineering calculations.
While it is important that smoke extract systems be able to operate in case of fire, it is not often considered that a back-up power source needs to be supplied.
In most cases, it is considered that the chances of a power outage to the area striking at the same time as a fire is minimal, but this situation must be considered and assessed and the risk taken into account as a part of the fire protection plan. In many cases of modern buildings, it would not be safe to operate the building during a power outage in any case, and so it may be closed until normal power service is resumed.
In the next fire engineering and risk assessment blog series, we will be looking at Fire Suppression. 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.