As a designer or specifier, you want to be sure that your smoke ventilation system will provide fire safety in all situations. If your design includes a pressurisation system, there are a few pitfalls to avoid. Here are seven good practices that will help you avoid them and design an effective pressurisation system:
1) Build quality. Check that the builder achieves the correct level of build quality. For example, penetrations need to be properly sealed, there should be no gaps in mortar joints and there should be continuous sealing around plasterboard – even when hidden above false ceilings! Excess structural leakage is the main cause of problems in commissioning systems (See point 6).
2) Air inlet ventilator siting. If the pressurisation air inlet becomes contaminated by smoke, the system will quickly fill the stairs with smoke. Therefore, the correct siting of the air inlet ventilators is important. If air inlet comes from the roof, two separate inlets are required so that, if one is contaminated, it can close and the other can continue to provide pressurisation air. In-duct smoke detection is needed for protection.
3) Quick response to change in conditions. Pressure controlled inverters may be used to ensure correct design conditions, but they need to be able to respond quickly to any change in conditions. EN 12101-6 stipulates a maximum of 50 Pa across closed doors and a minimum of either 0.75 or 2 m/s when doors are open. A quick response between the two conditions is essential to the proper working of a pressurisation system, as otherwise the fans can over-pressurise the internal space, slam doors or make them too difficult to open.
4) Adjustable door closers. Similarly pressurisation systems put additional demands on the performance of door closers. Consequently, these should be specified as adjustable. Most importantly, they should be correctly set up at the time of commissioning to avoid outward opening doors from being blown ajar, and inward opening doors from needing excessive opening force.
5) Check actual door size. Designers shouldn’t just assume a standard 2.0 x 0.8 m door size. Larger doors seem to be becoming more and more common, and door size can make a big difference to the system design.
6) Correct commissioning is critical and ample time should be allowed for it. Small changes to the finishes (such as carpets for instance) can affect the ability of the system to perform. Therefore final commissioning cannot be properly completed until all finishes are in place and the building is virtually ready for occupation. All the more reason for builders to get point 1 right, as resealing the construction at this stage can be difficult and time consuming – and no time is likely to be available.
7) Get specialist advice. The design, installation and commissioning of pressurisation systems is a specialised subject. It is not easy to comply with the Standard EN 12101-6 and therefore we would always advocate getting advice from a specialist such as Colt.
Paul Compton is Technical Director for Colt, experienced in smoke control, HVAC, solar shading and louvre systems.