The LWF Blog
Fire Safety Engineering for Design – Cross-ventilation Systems – Part 197
August 19, 2024 10:29 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 196, LWF looked at smoke clearance/purging systems. In part 197, we continue discussing natural cross-ventilation and begin to look at mechanical cross-ventilation systems.
The required areas for ventilation are prescriptive and therefore the designer should refer to the appropriate codes of practice and standards for the relevant jurisdiction.
In a car park in the UK, the recommendations state that sufficient smoke ventilation equal to an aggregate of 2.5% of the floor area should be provided at each level of the car park. It should be distributed such that a minimum aggregate area of 1.25% of the total floor area is provided equally between two opposing walls (a minimum of 0.625% per opposing wall).
Provided that the minimum ventilation area is 1.25% of the floor area between two opposing walls, the remaining vents can be provided in any location.
Requirements for the ventilation of car fumes may exceed those for smoke.
Smoke vents in a wall or ceiling can be used to form any part of the ventilation strategy, provided a through draft is created. Where openings have louvres, the effective free area, noting the restriction created by louvres, should take into account the restriction.
Mechanical cross-ventilation
A mechanical cross-ventilation system may be comprised of either entirely mechanical systems with mechanical extract and mechanically-powered inlet, or, natural inlet and mechanical extract to provide cross flow.
Mechanical cross-ventilation systems are often found in car parks in the UK, they are designed to operate at 10 air changes per hour.
An average UK car park with a ducted smoke ventilation system has an extract system designed to run in at least two parts. This means that the total exhaust capacity of each part does not fall below 50% of the total extract rate.
If 10 m3 · s–1 is required to make 10 air changes per hour, then it should be provided in at least two parts, with each part capable of ventilating 5 m3 · s–1.
For all other system types, it should be designed so the extract system takes into account fan or component failure, without reduction in performance.
In part 198 of LWF’s series on fire engineering we will continue to discuss mechanical cross-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 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.