The LWF Blog
Fire Safety Engineering for Design – Cross-ventilation Systems – Part 199
September 2, 2024 10:39 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 198, LWF discussed mechanical cross-ventilation systems used in car parks. In part 199, we will talk about impulse jet ventilation.
Impulse jet ventilation systems are designed with locally mounted impulse jet fans, designed to control the movement of air around the car park.
The use of impulse jet ventilation in car parks is subject to local codes and regulations, and these requirements may affect the design of the system. The typical air exchange rate within the car park is 10 air changes per hour, but these systems can also be designed to control smoke from a fire to ensure means of escape is kept clear and firefighters have access.
When designing the system, care should be taken to ensure the number of impulse fans activated does not induce the movement of a volume of air greater than the extract fans are capable of extracting.
The car park should be permitted no stagnant areas. Impulse fan location should be decided upon with careful consideration to ensure doors are not exposed to dynamic pressure effects, which could cause smoke to enter lobbies and staircases forming a part of the means of escape provision.
Although local code requirements must be taken into account, in their absence, it is recommended that all fans which may need to exhaust hot gases from a fire should be tested for suitability, operating at 300°C for not less than 60 minutes.
Opposed air flow systems
An opposed air flow system is one which is designed to stop smoke movement through a volume and induce an air flow to keep smoke in the area of the fire.
In cases where opposed air flow is used to prevent smoke spread from the area of fire origin, the room in question should be ventilated at a sufficient rate to cause the average air velocity at the opening to exceed the limiting average air velocity.
In part 200 of LWF’s series on fire engineering we will continue talking about opposed air flow systems. 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.