Chris Hall of Siderise highlights the critical importance of fire stops in tall buildings and the considerations that specifiers need to bear in mind.
As tall buildings are set to continue to play a significant role in meeting our housing and workspace needs, it’s more vital than ever that they benefit from adequate passive fire protection.
Smoke generated by fires in high-rise buildings can spread vertically throughout the building, even if the fire itself is contained within one unit.
When the linear gap at perimeter edge between the floor and curtain wall is not properly sealed, flames and smoke can spread vertically to higher floors and horizontally to adjacent spaces. To avoid that, it is essential to properly install fire stops to maintain the compartmentation the building.
Perimeter barrier firestops seal the gap between the edge of the compartment floor slab and the external curtain wall. Due to project designs and site tolerances, the size of this linear gap can vary, so the fire stop system needs to have a degree of dynamic movement capability – compression and recovery – in order to accommodate serviceability movement, and more significant movement under fire load. In addition, the fire stop system must match the period of fire resistance of the compartment floor.
Integrity & insulation
All firestop systems need to be tested to two performance criteria – integrity and insulation. Integrity refers to the ability of the system to prevent the passage of flame, smoke and combustible gases through and around the material or through joints in an assembly. Insulation refers to a measure of the increase in conducted heat transferred from exposed to unexposed surfaces of 180°C rises above ambient.
These two criteria are critical in the development of curtain wall perimeter firestop products. The most effective products combine a number of material features – density, thickness, resin
content, fibre structure and controlled compression – which together determine the resistance properties.
When looking at the ‘integrity’ criteria, the material chosen must be impervious to the transfer of flame and gases, easy to install with minimal site management and accommodate all real-world requirements at interfaces, joints and details.
In order to meet the fire and smoke stop requirements in all external facade applications, Certifier Approved perimeter barrier and fire stop systems offer a combination of performance, practical installation and service benefits. These systems offer fire rating options ranging from 30 minutes to five hours and accommodate void widths up to 1,200 mm. In addition to providing an effective seal against the passage of smoke and fire, the products can also form an acoustic barrier and plenum lining.
Key design considerations
Before specifying a fire stop, test evidence, demonstrating the product is capable of accommodating movement of a facade, needs to be examined. It is imperative
that the installed seal is able to function effectively with due regard to all designed movement serviceability limits – curtain walling and cladding facade systems will deflect due to positive and negative wind loads as well as occupational live loads. The criteria are covered by EN 13116:2001.
Typically, a project may stipulate that
the curtain walling system may have the following allowable deflection limits: under the declared wind loads the maximum frontal deflection of the curtain walling’s framing members shall not exceed L/200 or 15 mm when measured between the points of support or anchorage to the building’s structure – in compliance with EN 13116. These factors may inevitably combine to preclude the suitability and therefore use of certain systems, such as high-density material slab products.
Perimeter barriers must be installed to provide horizontal compartmentation
on each level, while vertical cavity barriers should be provided as a minimum to fall in line with any compartment wall and more frequently if dictated by the fire strategy of the building. Fire stops should be fitted tightly around all bracketry to restrict the passage of smoke.
Where there is potential for gaps, the product must be sealed with a sealant that carries the same fire insulation and integrity rating as the perimeter barrier. All installations should be carried out in accordance with manufacturers’ instructions; where fixing brackets are required, these should be fitted and spaced in accordance with a certified fire test report.
Products used for fire safety installation should carry a third-party certification in order to ensure that the product supplied
is the same as that tested. In addition, any products used to improve the acoustic performance must not contribute to the fire load or inhibit the performance of the perimeter barrier.
A high-profile project
The recently-completed Al Fattan Crystal Towers in Dubai, UAE, had to adhere to vertical and horizontal compartmentation requirements, the specification of Siderise CW-FS 120 firestops provided the contractor Cladtech with a comprehensive solution that could maintain a fire and smoke seal in one product and could successfully fill linear gaps at the podium levels in excess of 300 mm.
For the Crystal Towers project, Cladtech installed 12,000 linear metres of the fire stops, including horizontal (floor slab) and vertical compartmentation. With the timeline on the project being absolutely critical, the use of this dry fix system enabled the work to be completed quickly and efficiently, ready for handover to subcontractors.
While specifying the correct product is vital, the quality of installation is equally as important, as a well-designed and installed system can mean the difference between life and death.
Chris Hall is commercial development officer of Siderise