Tianca McHenry, Senior fire engineer and Tom Lewis, Senior fire engineer
With more than half of the world’s population living in cities, land is at a premium and there has been a rapid increase in the number of high-rise and super high-rise buildings around the world, using lighter and stronger building construction elements.
Traditional norms over fire evacuation have had to be thrown away, with the increasing number of tall buildings, including supertall (over 300m) and megatall (over 600m) ones, meaning standard methods of fire evacuation have to be rethought.
Such tall buildings bring about a unique set of challenges for fire engineers which we work to integrate with architectural and client aspirations, to produce a safe yet efficient and functional building.
We aim to minimise disruption to the building occupants by initially evacuating those in immediate danger and progress in a phased regime to adjoining evacuation zones where necessary. In this way we minimise severe delays and revenue loss if total evacuation were to be deployed.
We design lifts so they can be used in an emergency for large scale evacuation, which is combined with fire compartmentation, refuge areas and air pressurisation to help ensure occupant life safety. This can also lead to reduced stair widths and more efficiently designed cores allowing lettable floor area to be maximised.
There are varying types of smoke control systems that can be adopted as part of the building’s smoke strategy system. The sandwich or zone pressurisation system is a common approach in New Zealand and Australia where non-fire floors are positively pressurised to minimise smoke spread along egress paths. Typically, all escape cores, lobbies and lift shafts are positively pressurised throughout the building to prevent smoke ingress. This helps maintain these areas clear of smoke during both the evacuation and firefighting phases and can be designed to increase or decrease relative pressures depending on the type of operation e.g. evacuation or fire fighter search and rescue operations.
As evacuation of tall buildings may not be immediate, redundancy is built into the design of fire safety systems, to include diverse cabling routes, fire rated cabling elements and an extended period of power supply from multiple sources. Systems are centralised into a main control centre from which the phasing and oversight of evacuation is conducted. It is essential to provide good communications from this control centre to all parts of the building.
The building structure also has a designed fire duration performance, to reflect the potential longer evacuation and firefighting periods, when compared to low rise buildings. The length of duration and type of protection is considered on a case by case basis and optimised internally to provide a cost beneficial solution whilst maintaining life safety.
To assist with challenges when fighting fires in tall buildings we ensure dedicated fire lifts are provided. This is combined with positive pressurisation systems, communication systems and pressurised water systems, fully charged at each level. This minimises the amount of equipment fire fighters may have to carry vertically and provides a rapid means of moving up through the building, within the safety of a protected core. This allows fire fighters to set up a forward bridgehead within the core which may be many storeys above ground floor level.
Consideration to vertical fire spread externally via the façade of the building is critical. We can help set the performance design criteria of products to minimise the potential for surface spread of flame along the façade, which will often be beyond the reach of ground-based firefighting equipment. The provision and correct installation of fire breaks and cavity barriers are essential to reflect the building’s internal compartmentation and phased evacuation.
We design tall buildings appropriate to their location in the world. Whether it be in New Zealand, Dubai or elsewhere, we ensure that all external and internal design variables are factored into the design to provide a safe and holistic approach for building occupants.