The LWF Blog

Fire Safety Engineering for Design – Pressurisation Systems – Part 203

September 30, 2024 10:53 am

LWF’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 202, LWF looked at the temperature of extraction fans and the use of the HVAC system. In part 203, we will discuss the use of pressurisation systems.

A pressurisation system is the opposite of depressurising the area of fire origin (by extraction), i.e. the areas surrounding the fire area are pressurised in order to prevent smoke leaking from the fire area into the surrounding areas.

Depending on where the project is taking place, the codes and regulations will require a certain level of pressure differential and so local codes should be checked prior to design completion.

European systems currently typically require a 50 Pa pressure difference, whereas in the US, a differential of 12.5 Pa in sprinklered areas and 25 Pa in unsprinklered and 2.7 metre ceiling height is required, as per the requirements for a depressurisation system.

Pressurisation is normally reserved only for areas which are essential for the escape route and/or Fire Service access routes. It’s commonly used for staircases and lift lobbies.

Supply air should be provided and the requirements must be calculated appropriately, as well as ensuring that adjoining spaces do not pressurise by providing an air release path. It is also important to establish that the pressurised area will not over-pressurise where such systems are provided as ‘compensated’ systems.

Compensated Systems

A compensated system is a pressurisation system that adjusts and compensates when doors are opened and closed. It adjusts for changing conditions by either modulating air flow supply, or by relieving excess pressure.

The area of the building in which the compensated system operates may be subject to two or more different scenarios requiring assessment and having different air flow requirements, subject to the leakage experienced when doors are opened.

In a closed-door scenario with minimal leakage and an open final exit with substantial air flow to the outside via the open door. The air flow should be calculated as a leakage, or calculated as that required to maintain a given air speed in m^.s^-1 through the opening.

In part 204 of LWF’s series on fire engineering we will continue to discuss planning for the use of compensated 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.