Code Compliant vs. Engineered Fire Strategies
Added on February 15th, 2017
Category FDS News
By Helen Thomas
For any project, whether it’s a residential apartment block, retail unit, factory or commercial office, one of the first decisions that must be made from a fire-safety perspective is whether to take a ‘code-compliant’ or ‘fire engineered’ approach to the creation of a fire strategy.
Each approach carries with it certain advantages, as well as considerations that need to be made. In either case, any decisions relating to fire safety strategies should be made at the earliest stage possible, as elements such as room (or compartment) sizes, corridor widths/length and the number of staircases in a building are all intrinsic parts of the strategy.
Here we look at the differences between code-compliant and engineered strategies, including the benefits and potential pitfalls of each method.
Seen as the ‘standard’ method of creating a fire safety strategy, a code compliant approach adheres closely to the requirements laid out in Approved Document B (ADB) of the Building Regulations and other British Standards.
Though prescriptive, working to the letter of the regulations can simplify the creation of a fire strategy, and make the selection and specification of fire safety systems straightforward.
In turn, these strategies will also be more quickly approved by Building Control, as working within the guidelines removes any ambiguity regarding the performance of a strategy or the systems used.
Due to its prescriptive nature, a code compliant approach is relatively narrow in the range of fire safety/smoke ventilation systems that it recommends. ADB largely calls for the use of Natural Smoke Ventilation systems, which make use of a 1.5m2 external window, or where this isn’t available a 1.5m2/3m2 natural smoke shaft. The performance of the natural ventilation relies on the use of wind and the property of hot air rising and drawing in colder, denser air to remove smoke.
Though this is a low-cost option, the amount of space taken up by such large smoke shafts significantly reduces the amount of saleable space within a property, and Building Regulations still call for buildings using natural smoke ventilation systems to feature multiple staircases if they are over 11m in height.
Alternatively, pressurisation systems can be installed, which create a high-pressure area, for instance in a staircase, to prevent the ingress of smoke, providing a means of escape.
The inclusion of pressurisation systems allows the single staircase even for the buildings more than 11m in height. The requirements on the pressurisation systems are outlined in BS EN 12101 Part 6 and their use can be easily justified by submitting calculations which demonstrate their effectiveness without a need for CFD (Computational Fluid Dynamics) analysis. Unfortunately, pressurisations systems can also have relatively high costs as requires a pressurisation shaft with AOV windows from all floors, and are complicated to both install and commission.
Many developers can also find this approach to be restrictive, with little flexibility on offer when it comes to the creation of larger or open-plan spaces, which are currently demanded by the end client.
- Low system costs
- Quickly approved
- Reduced compartment/room sizes
- May require the inclusion of additional staircases
- More space taken up by larger smoke shafts
- ‘One size fits all’ approach
The alternative to a code-compliant solution is to take an engineered solution.
In this case, specialist fire engineers will look at a building’s proposed plans and identify the most appropriate fire strategy based on its individual characteristics, effectively creating a tailored plan which varies for each building.
Engineered solutions offer far greater flexibility, using more advanced systems to provide additional benefits to project beyond simply increasing fire safety, such as the creation of larger, open-plan spaces, extended travel distances and reduced costs.
Keeping in mind that the Approved Documents are intended to provide guidance, rather than strict rules, it is possible to justify these changes, with ADB itself effectively stating that, provided a requirement is met, the method by which this is done is unimportant.
One of the primary ways in which these benefits can be brought to a development is through the use of solutions such as mechanical smoke ventilation systems.
Consisting of powered fans attached to a mechanical shaft, these systems allow smoke to be extracted from an affected floor in the event of a fire, providing a safe escape route for occupants.
Due to the increased efficiency of these units over natural smoke ventilation systems, they can provide the greater level of smoke ventilation while using much smaller smoke shafts, providing space savings for developers. In addition, the use of these systems in combination with an intelligently designed fire strategy can also allow the creation of far larger ‘compartment’ sizes, effectively allowing larger rooms to be included in a design without the need for dividing walls.
For the same reasons, travel distances can also be extended, and in some cases the removal of entire staircase can be justified, providing significant cost and space savings.
Due to the large amounts of variation between engineered solutions for different projects, any proposed engineered fire safety strategies must be submitted to Building Control for approval, accompanied by evidence of their effectiveness. Due to this slightly more complex approval process, engineered solutions can take more time to be approved.
- Increased design flexibility
- Extension of travel distance
- Allows increased compartment sizes
- Tailored approach prevents over specification
- Unlocks additional saleable space
- Slightly longer approval process
- Requires the involvement of qualified fire engineers from an early stage