The LWF Blog
Fire Safety Engineering for Design – Cross-ventilation Systems – Part 198
August 27, 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 197, LWF discussed natural cross-ventilation and began to look at mechanical cross-ventilation systems. In part 198, we continue to discuss mechanical cross-ventilation.
When using mechanical cross-ventilation in car parks, the extract points should be arranged so that half of the exhaust capacity is at high level and half at low level, with the extract points evenly distributed.
In the case of other types of usage for mechanical cross-ventilation, the extract points should typically be at a high level, as they do not require high/low level extraction.
Systems should be designed such that if there is a failure of one part of the system, the failure will not jeopardise the other, including power supplies. The designer should check all appropriate codes and regulations and decide whether to provide a sprinkler system or other automatic fire suppression system to cool smoke temperatures, which would help reduce the risk of fan failure.
The placement of the extract points for the smoke exhaust system should be located so that there is no danger of smoke being reintroduced to the inside of the building, or to any adjoining or adjacent building. Equally, the means of escape must be protected from smoke.
The system design should ensure there are no stagnant areas.
Unless relevant guidance or local codes state otherwise, all fans intended to clear hot gases should be tested suitable to operate at 300 °C for not less than 60 minutes. All ductwork and fixings should be comprised of materials having a melting point above 800 °C.
Most mechanical smoke venting systems can operate to remove smoke and CO. Using CO detectors, the systems can automatically operate when CO levels rise above a pre-set limit. Once the levels reach the limit indicated, the extraction fans operate automatically to return air quality to normal levels. In a fire situation, full smoke exhaust mode involves an increase in fan extraction rate to compensate for the additional load. The clearing of the smoke means that persons inside the car park are able to evacuate safely and firefighters are able to enter and tackle the source of the fire.
In part 199 of LWF’s series on fire engineering we will discuss impulse jet 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.