Siderise’s Chris Hall asks whether an approach of merely complying with regulations in specifying passive firestopping in curtain wall systems is good enough, or if specifiers should be looking to other standards
Curtain wall systems are typically constructed with a gap between the facade and the floor slab to allow for building movement, with the addition of a fire seal solution to ensure passive fire safety. However, with two ‘test paths’ to compliance available, it is vital for specifiers to understand the accuracy of standards on the real-life performance of products.
The two ‘test paths’
Approved Document B (England and Wales), Technical Handbooks Section 2 (Scotland) and Technical Booklet E (Northern Ireland) all offer two test paths to compliance for the fire resistance of perimeter firestops. These are, firstly, BS 476-20 – ‘fire tests on building materials and structures – method for determination of the fire resistance of elements of construction (general principles)’. The second is EN 1364-4: 2014 – fire resistance tests for non-load bearing elements via classification standard EN 13501-2.
The significant differences in scope, methodology and evaluation mean that these two paths are not equivalent, and choosing which test method is the most appropriate will depend on the real-world demands of the application.
Product vs system
Published in 1987, BS 476-20 is a small-scale, static test that requires an insulation product to be installed between two concrete lintels within a furnace and subjected to defined heating and pressure conditions to establish its fire resistance (integrity and insulation) rating. While it offers a basic understanding of a product’s standalone performance, the test is designed to be generalised and therefore cannot give a clear indication of a product’s ability to resist fire in its intended application.
By contrast, EN 1364-4 is a ‘part configuration’ test that applies to ‘Type A’ non-fire-rated, and the less commonly used ‘Type B’ fire-rated, curtain walls. It examines the resistance to internal and external fire exposure of the complete spandrel system for the test duration; (including the spandrel panel, perimeter fire seal, fixing of the framing system used to attach the curtain walling to the floor, or combinations thereof.) The test’s wide scope means it can be used for different kinds of curtain walling constructions.
This systemised approach is much more reflective of a true spandrel construction, especially where the test assembly is also subjected to movement cycling (in accordance with EAD – European Assessment Document – 350141-00-1106) before fire testing.
The EAD requires that the perimeter fire seal is subjected to a minimum of 500 cycles between the minimum and maximum joint width, to simulate wind sway, seismic activity and thermal loads, at a rate designated by the test applicant. It is not compulsory, but it is required for CE marking when claiming a >7.5% movement capability, and there are only a select number of perimeter firestops on the market which have been tested and certified to this EAD.
Such testing is crucial to demonstrate that the perimeter firestop is capable of withstanding in-application deflection and dynamic movement without degrading, and thereby able to maintain its ability to achieve the required fire resistance over the building’s life. The results offer a clearer understanding of the fire resistance in terms of not only how the perimeter fire seal will perform as a product, but also how it will interact dynamically with other components of the spandrel under fire conditions.
Third party assurances
Whatever the route and standard used, it is advisable to validate fire test data with third-party certification from an accredited body, to provide confidence in the performance and consistency of the products. Gaining certification requires rigour, and usually involves reviewing product test data against appropriate standards and requirements, and submitting samples for analysis and comparison. Ad hoc factory visits and audits may also be carried out, and certification withdrawn, and re-testing required if any significant changes are observed.
Systematic thinking
The holistic approach to spandrel zone protection encouraged by standards such as EN 1364-4 also helps to better support fire and structural safety. While the UK regulations do not ask for passive fire protection beyond installing perimeter firestops and linear gap seals, in other jurisdictions such as the UAE, it is common practice to also protect the spandrel panel.
Although perimeter firestops are effective at inhibiting fire and smoke spread, compartmentation relies on them being able to maintain their fit between the floor slab and facade. A part of this is being able to withstand movement, however, they also need to abut to a stable structure that can withstand elevated fire temperatures for a satisfactory period.
Aluminium mullions and transoms that are often used in non-fire rated curtain wall systems can deform in the high-intensity heat of a fire, jeopardising the structural integrity of the spandrel and the system. This can lead to gaps forming between the facade and slab edge, opening paths for fire, smoke, heat and gases to spread.
To reduce this risk in aluminium systems, a fire-resistant board made of dense, non-combustible insulation that shields both the spandrel panel and the mullion can be used, alongside a perimeter firestop. This helps to preserve the integrity of the assembly and the stability of the curtain walling framing system, therefore allowing the firestop to perform its compartmentation function.
Guidance & future developments
The Association for Specialist Fire Protection (ASFP) has been recommending that linear gap seals used in curtain walls are “only tested to EN 1364-4” since 2014, and the Centre for Window and Cladding Technology (CWCT) announced in 2022 that it plans to update its guidance in Technical Note 98 to recommend that curtain wall fire stops should be tested in accordance with the standard. The proposed approaches are to use the firestop within the field of application of the test or within an extended field of application using EN 15254-6 to further widen the scope for approval.
Additionally, in a recent consultation which closed on 17 March this year, the Government sought industry views on removing national classes from Approved Document B. The responses are still being analysed, but if this goes ahead, EN 1364-4 would become the only test path to compliance.
Going beyond
Curtain wall facades are complex, with their overall performance reliant on the interaction of many different components. Selecting complete spandrel protection systems, which have been developed and third-party tested as full-system solutions, can help projects go beyond regulation compliance, and thereby adequately safeguard the lives and livelihoods of people using the buildings for lifetime.
Chris Hall is external affairs director at Siderise