Understanding UL 2079 for Firestop Systems
UL 2079 - Tests for Fire Resistance of Building Joint Systems defines how linear firestop systems are evaluated for their ability to prevent the passage of fire and hot gases through joints in building constructions. It is commonly referred to in building codes around firestopping, such as the International Building Code (IBC) in the USA and is referenced within IS 18190: 2023 - Fire Resistance of Perimeter Fire Barrier Joint System as the path to compliance for perimeter fire barriers in India.
In this Insights piece, we explore the test’s origins, what it covers, and how it works alongside other key fire resistance test standards to provide a holistic assessment of these systems.
What is UL 2079?
UL 2079 outlines how to test and evaluate the fire resistance performance of building linear joint systems, including those between floors, walls and ceilings, to determine the system’s ability to withstand fire exposure whilst accommodating structural movement resulting from wind, or seismic activity
It is important to note that, as it assesses full system performance, the results of a UL 2079 test only applies to the exact specification and assembly of products and materials as was tested, and components cannot be substituted or changed unless specifically permitted in the individual system.
Why do you often see ‘UL 2079/ ASTM E1966’ on perimeter firestop product listings?
There is a common misconception that ‘tested in accordance with ASTM E1966 / UL 2079’ means that these two tests are either the same or interchangeable. However, they are actually two different standards, with the UL standard building on the performance results of ASTM E1966 to provide a holistic understanding of linear joint performance.
ASTM E1966 = the foundation
ASTM E1966 – Standard Test Method for Fire-Resistive Joint Systems was developed by ASTM International to define how to test firestop joint systems. Specifically, it looks at:
Joint movement cycling– before fire testing, the joint system is subjected to a minimum of 500 movement cycles, during which it is extended and compressed at a prescribed rate to simulate in-service stresses such as thermal expansion, wind loading, and seismic activity. This preconditioning is intended to introduce a realistic level of fatigue to ensure that the system is evaluated in a realistic condition and can maintain the required fire resistance throughout the building’s design life.
Fire exposure- the joint is then exposed to standardised fire conditions to determine its:
F-Rating (Flame or Fire Rating): Measures how long a system prevents flames and hot smoke from passing through.
T-Rating (Temperature Rating): Measures how long a system resists heat transfer to the non-fire side of the joint within a specified limit.
Hose stream testing – for wall-to-wall assemblies, immediately after the fire test, the system is sprayed with a stream of high-pressure water to simulate the impact of firefighting activities. To pass, the sample must withstand the stream without degrading or dislodging.
UL 2079 = holistic performance and certification
UL 2079 takes the results of ASTM E1966 and builds on it with UL-specific elements to provide a more holistic look at the system’s performance.
This includes additional performance tests to assess:
W-Rating: evaluates resistance to water exposure prior to fire conditions.
L-Rating: measures air and smoke leakage performance, increasingly required to comply with legislation in various jurisdictions.
When third party certified, it also looks beyond just testing to look at the quality control measures around its production, including a manufacturing certification of the materials to be tested and ongoing annual, unannounced on-site manufacturing audits.
Once successfully evaluated, alongside the UL Mark, UL will issue a UL Listing and publish this to the UL Listing Database and the ULC Listing Database (for Canada.)
How does UL 2079 relate to other key standards such as ASTM E2307 and EN 1364-4 for perimeter firestops?
UL 2079 / ASTM E1966 looks at the linear joint firestop system in pure isolation. Meanwhile, fire resistance standards such as EN 1364-4 and ASTM E2307 evaluate the performance of perimeter fire barrier systems within a curtain wall assembly, that can incorporate elements such as mullions, transoms, and infill and spandrel panels. Perimeter fire barrier systems are sometimes tested to UL 2079 to prove their performance at a product level and then used as part of larger ‘system’ tests to prove their performance in a specific assembly.
What is UL certification?
Originally known as Underwriters Laboratories, and now operating as UL Solutions, UL develops testing methods and certifies products and systems to verify that they meet recognised fire safety and performance requirements. It operates across construction and life-safety applications, including building materials, firestop systems, electrical components, cables, and passive fire protection products. When a solution has been tested by UL and meets applicable safety standards, it may be granted a UL Listing and authorisation to display the UL Listed Mark on the product and associated materials as evidence of compliance.
(Note: As UL explains in its Firestop and Joint Application Guide: ‘“Certified” is another term used by UL Solutions to identify that the product has been evaluated by a third-party certification organization in accordance with the appropriate required standard. The terms “listed”, “certified” and “classified” as used by UL Solutions all meet the definition of “listed” and “labeled” as described in the model codes.”’)
A key piece of the comprehensive performance data jigsaw
UL fire protection standards, like all test standards, act as a bridge between laboratory testing and real-world building performance. They ensure that firestop systems and fire-rated products are not only designed for fire resistance, but are proven under defined, reputable conditions that reflect their intended use. Selecting systems that are tested, listed, and installed in accordance with the correct ASTM and UL standards, ensures verified performance in the conditions where it matters most.
How does Siderise uphold UL standards?
We champion the wider UL standards and their focus on life safety via:
In-house fire testing at our Global Innovation Centre, including a specialist furnace capable of testing to UL-related fire curves and standardised fire exposure conditions.
Engagement with UL Product iQ to ensure relevant solutions not only bear the UL Mark but are listed on UL’s official online database, making it easier for customers to verify their validity and access detailed technical data.
Siderise CW-FS Firestop has been tested and third-party certified to UL 2079, alongside various other key curtain wall perimeter firestop tests which enable compliance in countries around the world, including ASTM E2307-20 (25), ASTM E2874-19, BS EN 1364-4: 2014 and IS 18190: 2023. Together, this combination gives customers confidence that our firestop range has been independently evaluated to internationally recognised standards, providing verified, repeatable test data that supports safer specification, approval, and installation, and which should ultimately help to improve occupant safety and building fire performance in real fire conditions.
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