The LWF Blog
Fire Engineers, who we are and what we do?August 5, 2011 3:52 pm
Whilst Fire Engineering has been around for many years now, it is still considered to be a relatively new discipline. In fact, even now, it is not uncommon for us, as Fire Engineers’ to work with project teams for the first time.
With some design teams using Fire Engineers for the first time, our level of involvement and our input into the design is not always clearly understood at the outset of a project. Occasionally this lack of previous involvement means that fire engineers are not always engaged at the most appropriate time. Examples of this come from projects where problems have been encountered, often with submissions being rejected from the approving authorities which has then led to fire engineers being engaged to try and resolve the problem; this should be avoided where possible. Whilst we can assist in these circumstances, due to the stage of the design the level of flexibility is lessened and often our resolution may require a level of compromise in the design from other areas.
This blog will give designers an improved overview of what fire engineers do, where we come from and how we can benefit a variety of projects.
Who we are
It is fair to say that fire engineering crosses a range of disciplines and on this basis it is not surprising that many people working in the industry have a background from other, more traditional design roles and have converted to fire engineering, often specialising using their previous skills and knowledge. Fire engineers have come from a multitude of disciplines, including structural engineering, mechanical, electrical, civil, chemical and enforcing authorities to name but a few. In more recent times, many of us working in the industry have trained specifically and qualified as fire engineers.
The reason fire engineers come from a range of backgrounds is understandable due to the range of activities we undertake. Fire engineering requires an understanding of structures, particularly when considering structural fire protection, material reaction to fire and relevant timescales, similarly, solutions can involve measures such as smoke control, in order to achieve this, an understanding of mechanical engineering is required. Equivalent examples can be made with most construction and engineering disciplines which means it is unsurprising that the industry is made up of a mixture of backgrounds. It is our belief that a full spectrum of engineers should be embraced as fire engineering impacts on all aspects of design.
What is fire engineering?
To start, let’s first define engineering. Collins English Dictionary defines engineering as:
“the profession of applying scientific principles to the design and construction of engines, cars, buildings, bridges, roads and electrical machines”.
This definition encompasses the principles of fire engineering, with the most common form taking the role of engineered design to buildings as this is typically where fire concerns us most.
Historically, before the advent of ‘fire engineering’ a very prescriptive approach to fire safety was adopted. A wide range of documents applied ‘rules’ to buildings that in turned governed what fire precautions were necessary. The main problems associated with these rules are that they could not encompass all of the variables that have an impact on fire. Even very simple features such as ceiling heights were not explicitly taken into account. For example, a storage facility for highly combustible material, with a floor to ceiling height of 3m would not necessarily require different precautions to a similar facility storing low risk goods with a ceiling height of 15m. However, common sense would indicate that due to the difference in risk of goods and the open space above occupants, the latter example will inherently be safer. Whilst it is acknowledged that this is a fairly crude example, the relevant points can be made. Buildings should be looked at on their own merits, taking into account all relevant features, including; building geometry, occupancy, construction (materials etc), design flexibility, building management, client objectives and so on. A key term in this, as with much current thinking, is that fire engineering should adopt a ‘risk based approach’, with the fire precautions measures commensurate to the risk.
It is important to understand that fire engineering is not a method used to reduce fire precautions in buildings, but is required to get the right precautions in place. On the example above, the higher risk facility, once subject to fire engineering review, may be deemed to require precautions in excess of traditional codes in order to ensure life safety, whilst the lower risk example is found to achieve acceptability with less onerous precautions than those given in a prescriptive document.
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 over fire. Large buildings, especially high rise, can not follow the principles of old, i.e. all occupants evacuating simultaneously, if this was necessary, the stair cores required would make the project unfeasible, fire engineering allows assessment of such buildings, using scientific principles and an understanding of fire to ensure the buildings can be constructed and occupied without compromise for 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 has also seen commercial benefits for end clients. By providing the correct fire precautions it can be ensured that the design is not over engineered, likewise, as the solution is not prescribed, it is often the case that a combination of fire precautions can be selected based on given criteria. For some clients, ongoing, or maintenance costs may not be as important as capital costs or vice versa and this, if required can be considered. Similarly, clients may also desire a flexibility in their design, for example, a speculative build, with the end use unknown until the latter stages of the construction. The fire engineer is capable of evaluating all of this information and making recommendations / providing options for consideration.
To enable us produce a fire engineering strategy, we rely on a variety of tools to assist our work and also to give validation to our design. Fire engineering, whilst moving away from prescription, will often follow a prescriptive analysis and reporting technique, commonly known as a Qualitative Design Review. This method allows the engineer to state the assessment methods and more importantly, the acceptance criteria; this should be agreed with all parties, including the approval authorities prior to assessment. Agreement at this stage should ensure approvals are made if the assessment criteria are met. Additionally, this analysis and reporting procedure gives credible and objective measurements prior to detailed assessment. Fire engineering, carries with it an element of subjectivity, therefore where analysis can be given objective and tangible results, these 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 an ability to calculate factors such as smoke movement, temperatures as well as human behaviour. The analysis can vary from simple ‘hand calculations’ to complex Computational Fluid Dynamics (CFD), and Evacuation modelling, this will be dependant on the complexity of the problem.
Additional tools will 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). ASET Vs RSET often forms the basis of any life safety assessment, which in real terms is most important consideration in any fire scenario, time. 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 / 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. It is our belief that bespoke buildings should have bespoke fire solutions, using the skills, knowledge and expertise of a fire engineer, along with the rest of the design team ensures you achieve life safety through the right fire precautions.