Engineered approach
sufficient compartmentation or refuge areas (for a case study on this subject, see page 26).
Fire service access
One further factor that needs to be considered for large or complex buildings is access by the fire services. Effective smoke control is vital to ensure that firefighters can easily progress through the building. For this reason, mechanical smoke ventilation systems will be recommended to provide a higher level of smoke clearance. Another issue when fighting a fire in a large building is access to water. Running the charged hoses through the building or across multiple storeys is often impractical. An effective solution to this issue is dry or wet risers – a system of pipework within the building to provide access to water. These are either filled with water (wet risers), or left dry for the fire service to connect the water supply. These are mandatory in buildings over 18m, with wet risers mandatory for buildings over 50m.
Testing a solution
Finally, an important part of any fire engineered solution is demonstrating how the proposed systems will work in practice. Techniques such as computational fluid dynamics (CFD) modelling allow the systems to be tested virtually to ensure they achieve the required level of safety.
Using CFD modelling, it is possible to
simulate the fluid dynamics (movement) of the smoke and fire within a digital model of the building over a set time period. This allows the physical behaviours, such as smoke rising, to be observed as it unfolds. It shows how the proposed layout and features of the building will affect the spread of the smoke, enabling the creation of an informed fire safety strategy and then evaluation of how it will work in practice. The computer model also highlights any
areas of concern, such as where smoke is hotter or denser, or where fire may spread more quickly. In addition to this, evacuation modelling and time equivalence modelling allow the simulation of an evacuation to demonstrate that the proposed layout allows the occupants to leave in a timely and safe manner.
A code compliant approach to fire strategy
is often restrictive or impractical, especially for buildings that are complex either by their design, intended use or inherent characteristics. However, engaging with experienced fire design consultants early in the process will allow a bespoke, engineered solution to be formulated and tested to meet both the required level of fire safety and the needs of the occupants
Steven Morgan is associate director of FDS Consult. For more information, view page 5
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www.frmjournal.com OCTOBER 2018
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