How can mechanical smoke ventilation systems positively impact building design?
Added on April 5th, 2019
Category Building Design
By Bijan Fard
When fire strikes in a residential building it can take hold fast. At the design stage the incorporation of smoke control features, such as mechanical smoke ventilation systems, not only save occupants but ultimately protect the very fabric of the building too. Here’s a reminder of what smoke ventilation systems do, how they impact building design and at what stage it is best to get a specialist involved.
Smoke extraction plays a vital role
The primary role of a Mechanical Smoke Ventilation Systems (MSVS) is to control smoke, aiding the safe escape of a building’s occupants, improving visibility and allowing adequate access for firefighters.
This type of smoke extraction system comprises a mechanical extract shaft that serves the common corridor and/ or lobby.
When smoke is detected within a protected lobby, only the fire damper to the smoke shaft on the fire floor will open – all other dampers remain locked shut.
At the same time, the vent at the head of the staircase will open, providing make up air for the smoke extraction system. The fan at the top of the mechanical smoke shaft extracts the smoke and prevents migration of smoke into the adjacent compartments.
Why it’s important to consider smoke ventilation
early on in the design process
From a building design perspective, architects are often looking beyond industry standards to introduce more innovative fire safety solutions.
However, achieving the right level of smoke control using the correct systems whilst accommodating spatial, aesthetic and budget requirements can be a complex and challenging task.
Avoids ‘over specification’ without risking non compliance
The involvement of experienced fire engineers from a project’s early stages can ensure the most suitable smoke venting system, or combination of systems, is selected. This can form a bespoke solution to outperform standard code-based systems.
Whilst facilitating architectural design, engineering and input at this stage ensures project build and fire safety system costs could potentially be reduced too, preventing ‘over specification’ without risking noncompliance.
Depending on the design and construction objectives, it may not just be about looking at the systems to put into a building’s design. Careful consideration of location, minimising ongoing maintenance costs and maximising the saleable floor area all go some way to increasing the value of the scheme.
The specification should be supported with computational fluid dynamics (CFD) modelling analysis being submitted to building control with a report to describe and justify the mechanical smoke ventilation system design.
Aids the tender process
Smoke venting contractors may choose to achieve requirements in different ways, resulting in quantity surveyors receiving quotes that are not only for different systems but that are also difficult to compare.
Carrying out the detailed design and specification of the smoke ventilation system during the consultancy stage ensures it is specifically tailored to the building and its end use. Going forward therefore, this assists all sub-contractors in pricing for the same system specification at tender phase.
Reduces unnecessary design modifications on-site, saving time and cost
There are further benefits too. Getting it right early on will also save money on unnecessary design modifications as well as the build schedule.
Risk during construction is significantly reduced as the detailed design of the system goes through the approvals process at an early stage. The smoke venting contractor is only demonstrating to the Approving Authorities that the installed system achieves the performance and operation requirements of the design.
How can MSVS impact building design?
With cities becoming more densely populated than ever and developers having to build upwards, the requirements for highly efficient smoke ventilation systems have never been so strict. However, the benefits of incorporating MSVS into a building’s design, for a more engineered approach, are multiple:
Offers greater performance for means of escape
Depending on the building design, MSVS can provide significant advantages over a natural system in terms of smoke clearance.
Improved efficiency makes them the most appropriate system for buildings featuring large open areas where travel distances need to be extended beyond The Building Regulations Approved Document B (ADB) requirements.
Enables the use of smaller smoke shafts
As a further result of their greater efficiency, using MSVS in place of their natural counterparts allows the use of shafts as small as 0.5m2 or 0.6m2, in comparison with 1.5m2 for a natural shaft.
Greater design flexibility
This improved efficiency can also justify the inclusion of larger compartments, allowing extended travel distances in the common corridor.
Substantial space saving benefits
Engineering at an early stage may also allow for the removal of staircases for example. For common corridors in residential flats above 11m tall, ADB requires a maximum travel distance of 7.5m where a resident can only escape in one direction, whilst the maximum travel distance in a corridor where a resident can escape in more than one direction is 30m to a corridor exit or cross-corridor door.
By taking an engineered approach, where MSVS are included in the fire design, it’s possible to justify the inclusion of only one escape route – removing the second staircase.
MSVS offers multiple uses
Although the initial cost of a MSVS is much greater than a natural system, its components can be used with other systems – such as corridor environmental systems, which exploit the MSVS’, smoke shaft and dampers. This reduces costs by removing the need to install costly air conditioning units, which can be particularly beneficial in built-up urban areas where temperatures are commonly higher.
More saleable space within a property scheme
As an example of the benefits of value engineering, FDS Consult UK’s involvement in the Dalston Lane South project, headed by Barratt East London, provided total savings of £3.5 million for the developer.
This was achieved through the intelligent specification of MSVS, enabling a reduction in the number of stair cores included in the design, as well as a reduction in the number of smoke shafts required in each core, also saving space within the building.
In summary, when it comes to smoke control design it pays to involve a specialist company at the earliest stage of building design. It’s also worth looking for one that is able to provide a complete smoke extraction system including design, supply, installation, commissioning and maintenance to ensure a more rounded approach.
To ensure you get the right smoke ventilation solution for your next project call FDS Consult UK on +44 (0) 1322 387411 or email [email protected]