The LWF Blog

Fire Engineering Design and Risk Assessment – Achieving Fire Safety Standards – Part 21

June 8, 2017 10:17 am

In this fire engineering design and risk assessment blog series for Architects and others working in building design, we have been recently covering fire and smoke ventilation and the fire engineering design. In Part 20, we looked at the issues to be addressed by the design team and in Part 21, we will continue by looking at the areas to be considered when analysing and making judgements on the design of fire engineering systems to achieve a cost-effective and adequately safe solution.


Although it would be very difficult to establish exact figures for fire and smoke potential in case of a fire, it is important that best estimates are made which include all contingencies and no unknown areas of redundancy. This enables a judgement to be made on the margin of safety and to determine the requirement for system diversity and reliability.


In cases where the system design is non-sensitive and clear definitions are in place for failsafe modes, there will be little or no need for a margin of safety. Use of this strategy requires that even substantial changes to fire size or hazard result in only small changes to the system design.


One example of such a system would be where the aim is to keep smoke temperature below a certain level. A natural ventilation system would be much less sensitive to changes in fire size than a mechanical ventilation system. However, a mechanical system is a more reliable means of maintaining a clear layer in cases of non-buoyant smoke.


While examples can be seen as ‘typical’, it does not mean that they apply to every situation and the judgements made must be based only on that particular design and design criteria. It is therefore essential that the output sensitivity relative to changes in input must be understood and taken into account.


The smoke control activation method needs consideration and thought to ensure that it will operate without unusual delay – incorporating transport time, dilution and thermal lag – as the design indicates.


It is worth noting that various fire disasters have been ascribed to the failure of control, as well as building performance. While the persons designing the building’s fire engineering provision cannot be expected to have an impact upon how the building is controlled when in use, they can use an understanding of the management requirements and ensure that that the design and maintenance requirements are clearly and reliably reported to the client.


In Part 22 of this series, we will be looking at ‘hot smoke tests’ which are commonly used in Australia and, although there is no requirement to do so, on occasion in the UK. 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 for over 25 years to produce innovative and exciting building projects. If you would like further information on how LWF and fire strategies could assist you, please contact Peter Gyere on 020 8668 8663.


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