When designing commercial or residential premises, there is always pressure to create the maximum lettable or saleable footprint to ensure a good return on investment.
One of the factors that limits the amount of lettable space is the requirement for a smoke shaft. BRE guidelines state that any structure over 18 m to its top occupied floor must have a smoke shaft to ensure smoke safety and fire fighter access in the event of a fire.
A compliant BRE-style natural ventilation shaft would require up to 3 sq m of building footprint to safely enable smoke ventilation away from safe areas.
However, with some clever engineering this can be reduced by up to 80 per cent, with a smoke shaft of just 0.6 sq m.
One building to enjoy this liberating freedom of space is the new American Express headquarters in Brighton, which is situated directly behind the existing 1960s structure.
As part of its development - and in keeping with RRO legislation and BRE guidance on smoke safety - two reduced fire shafts are to be installed with mechanical extraction.
The systems feature louvered smoke ventilators, AOV dampers and grilles and smoke extract fans, using sensors and intelligent control functions to identify the fire floor and provide clear access to rescuers.
With the aid of CFD (computational fluid dynamics) analysis, they are designed to adapt to conditions in order to avoid the hazards of negative pressurisation (doors becoming difficult to open or smoke being allowed to leak back into safe areas).
Control is handled by a combination of MCC/fan starter panel (with auto-changeover), pressure sensors and smoke detectors in each lobby, fireman’s override switch, local outstation panels and a touchscreeen HMI mimic panel.
This hi-tech combination of technologies is clearly the way forward in modern building design, offering a safe solution that is cost-efficient and minimises the impact on a structure’s architectural vision. The new system also has a car park ventilation system using slimline induction fans.
The site is one of a number of developments to feature this modern smoke shaft system, designed to replicate the performance of the BRE Natural Shaft, as detailed in BS9999, BS5588 Part 5, and BRE Technical Report number 79204. The system adopts depressurisation principles in accordance with BS EN 12101:6.
Ian Doncaster is fire engineering manager for Airvent