The LWF Blog

Fire Engineers | Why use them?

March 5, 2014 12:19 pm

Last week’s blog looked at who fire engineers are and talked a little about background knowledge. This week we will examine why you might consider using a fire engineer and what tools they can bring to your project. 

Why use fire engineering?

Building design has changed considerably in recent times for a number of reasons; we are consistently seeing larger, more complex buildings and these, by their very nature, bring new concerns about fire safety.  

Large buildings, especially high rise projects, cannot follow the old principles, e.g. all occupants evacuating simultaneously. If simultaneous evacuation was required, the stair cores needed would make the project unfeasible.  Fire engineering allows the assessment of such buildings using scientific principles and an understanding of fire to ensure buildings can be constructed and occupied, without compromise of life safety.  In some instances it is likely that an engineered solution is the only solution as it will not be possible to meet the requirement of prescriptive codes.

Fire engineering often results in commercial benefits for clients.  By providing the correct fire precautions, it can be ensured that the design is not over-engineered. 

For some clients, ongoing or maintenance costs may not be as important as capital costs or vice versa and this, if required, can be consideration.  Similarly, clients may also desire flexibility in their design, for example, a speculative build, with the end use unknown until the latter stages of the construction.  A fire engineer is capable of evaluating all of this information and making recommendations and providing options for consideration.

Fire Engineering Tools

To enable fire engineers produce a fire engineering strategy, a variety of tools are likely to be used to assist in the work and to give validation to the resulting design. Fire engineering, whilst moving away from prescriptive methods, will often follow a prescriptive analysis and reporting technique, commonly known as a Qualitative Design Review.  

The QDR method allows the engineer to state the assessment methods and more importantly, the acceptance criteria, which should be agreed with all parties, including the approval authorities prior to assessment.  Agreement at this stage should ensure the relevant approvals are made, if the assessment criteria are met.  

This analysis and reporting procedure gives credible and objective measurements prior to detailed assessment.  Fire engineering carries with it an element of subjectivity and therefore where analysis can be given objective and tangible results, they should be used as they will lessen design risks when approvals are required.

As well as a relatively stringent reporting process, fire engineering utilises mathematical analysis for a range of activities.  Mathematics has given the engineer the ability to calculate factors such as smoke movement and temperatures, as well as predicting human behaviour.  The analysis can vary from simple ‘hand calculations’ to complex Computational Fluid Dynamics (CFD), and Evacuation modelling, this will be dependent upon the complexity of the problem.

Additional tools may be used, dependant on individual cases.  Many of the tools are based around an assessment to predict two fundamental criteria, both of which can be controlled, within reason, by the fire engineer; the Available Safe Egress Time (ASET) and the Required Safe Egress Time (RSET).  The ASET vs RSET time calculation often forms the basis of any life-safety assessment, which in real terms is the most important consideration in any fire scenario.  This assessment identifies all of the critical stages from the fire ignition, recognition, reaction, movement etc., to indicate an escape time from a building or compartment. At the same time, the fire conditions in the same building or compartment can be evaluated, with key criteria observed – such as smoke layer heights and temperatures – which are then considered against set tenability limits.  In general terms, if the tenability limits are not reached within the escape time (allowing some design redundancy and safety factor) the design is considered acceptable.

Fire engineering is becoming more widely embraced for a range of scenarios.  As fire engineering is more widely understood, all parties are recognising the increasing benefits that the discipline brings. In this era of bespoke buildings, it would seem only sensible to have bespoke fire solutions. Utilising the skills, knowledge and expertise of a fire engineer, along with the rest of the design team, ensures you are able to achieve life safety through the right fire precautions.

If you are interested in knowing more about fire engineering or have any queries about this blog article, please contact Peter Gyere on 0208 668 8663.

Lawrence Webster Forrest is a fire engineering and fire risk management consultancy established in 1986, with experience in the development of fire engineered technology and the application of fire safety standards including fire engineered techniques.

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