A dynamic approach to fire safety system design

Here Bijan Fard, group marketing manager at FDS Consult looks at the role of digital tools such Computational Fluid Dynamics (CFD) Modelling in the design of fire safety systems and the advantages it can provide.

During a fire, smoke can present an even greater threat to safety than the fire itself. Not only can smoke impede evacuation but can quickly cause breathing difficulties and asphyxiation. Therefore, understanding how heat and smoke will spread through a building is vital in planning the most effective fire safety solution. This is especially important if the intended use or layout of the building presents a challenge to the design. Specialist fire engineers and consultants not only rely on experience but also utilise a number of analysis tools to create the optimum solution.

Computational Fluid Dynamics (CFD) modelling is used for a wide range of applications to analyse how fluid or air will move over a surface or within a space. It is commonly used in the aerospace, automotive and engineering industries to test new designs or prototypes. When applied to the design of fire safety systems, CFD modelling software is used to map the spread of smoke and hot air though a building using a detailed virtual representation created from the building plans. In the simulation, the physical behaviours and dynamics (movement) of the smoke and fire are plotted over a given timeframe. It shows how the proposed layout and features of the building will affect the spread of the smoke, and highlights any areas of concern, such as where smoke is hotter or denser, or where fire may spread more quickly.

Establishing this information allows designers and fire engineers to make informed design decisions about the type, positioning and extent of safety measures, including smoke ventilation, pressurisation systems and sprinklers. Once these decisions have been made, the recommended solution is then factored into the virtual building and the simulation is rerun. This demonstrates how the systems will perform in their designated configuration and allows improvements to be made to optimise the proposed systems.

A further benefit of achieving a greater degree of accuracy and detail is that it can provide confidence in an architect’s plan even if the layout of the building does not follow the approach recommended in Approved Document B. Where room sizes and corridor lengths have been increased beyond what is suggested, CFD modelling can deliver a demonstration that occupant safety has been maintained or even improved. For example, travel distances may be extended through the use of Mechanical Smoke Ventilation Systems (MSVS), which, due to their high-powered motorised fans, are more efficient when compared with options that utilise natural air flow though the building. CFD Modelling will illustrate the increased smoke clearance capabilities and corresponding improvement in safety to offset the longer evacuation distance.

Furthermore, the results of the CFD modelling can be supported by other digital techniques such as Evacuation Modelling, Time Equivalence Modelling and Finite-Time Analysis. These methods help to prove the effectiveness of evacuation strategies. When taken together, the results of these simulations can also allow space within the building to be optimised. For example, the number of staircases may be reduced if it is shown that occupant safety will not be affected. This can create more usable or saleable space and therefore increase the value of the property for developers.

Finally, it is important to engage with consultants early in the project as these techniques are most valuable when employed during the initial stages. This is when changes to the design can be made far more easily and with fewer cost implications than after the build has begun.

The design of fire safety systems is a complex process due to the need to predict how the features of a building will affect the spread of smoke and fire. Engaging with expert fire consultants during the early stages of a project will allow the use of advanced digital techniques to ensure occupant safety and an optimised building design.