December 21, 2017
As we continue to explore UL’s 120+ years of work towards fire safety we look back on a fire that occurred two years during the celebration of the New Year in 2016. The world watched as fire rapidly progressed on the exterior of The Address Downtown Dubai hotel. This hotel is located in the area of the Burj Khalifa, which is the world’s tallest skyscraper where thousands came to enjoy the New Year’s fireworks display.
Those in attendance, and countless others around the world watching on TV, were shocked to see the hotel building engulfed in flames. This fire event, along with several others before it, raised great concern over the issue of rapid fire progression on exterior wall construction materials. Since that time, there was staggering loss of life in the Grenfell Tower Fire. These and, other building fire events, along with plans for new tall wood building construction, have continued to drive discussion and debate over the issue of rapid fire progression on exterior wall construction materials.
To better understand the exterior wall flammability issue, and move towards solutions, this article will: 1) Discuss the factors that influence building construction related to these types of fires, 2) Provide an understanding of certain fire tests that are sometimes misconstrued as suitable for the evaluation of exterior walls, and 3) Examine the importance of selecting tests for specific regions, codes, and regulations. We will also discuss a third party certification approach used by UL, and some upcoming research activities in this area.
Building construction factors
There are several factors that are influencing building construction today as it relates to these types of exterior wall fires. First of all, new materials are constantly being introduced into the marketplace. The combination of new and existing products creates an expansive list of exterior wall components options for the designers and builders. Most exterior wall fire test methods involve testing of a complete wall assembly. So, we must consider the compounding effect of combining product types, such as drywall, various types of insulation, weather barriers, and veneers and cladding, as we address exterior wall fire performance. These material combinations and their means of installation must be evaluated appropriately to determine whether they are suitable for use as a complete assembly. However, the sheer volume of combinations of building components that might comprise an exterior wall proves to be a real challenge for the fire evaluation of these assemblies.
Another challenge is the growing attention to building envelope performance, such as thermal performance, air leakage, permeability, water infiltration, etc. In some areas, this is even driven by adopted local Codes and regulation. This has led to insulation products with higher thermal properties, and the increased use of air barriers and vapor barriers. Consequently, these new wall constructions also need to be evaluated and tested for their conformance to the appropriate exterior wall fire requirements as a complete unit.
Another building construction factor is the increased use of exterior veneer materials that are aesthetically pleasing, but lack evidence of compliance with Codes or regulations. In some areas, such as the UAE, there has been a focus on the challenges associated with non-fire retardant metal composite panel constructions that possess good versatility and aesthetics, but do not always perform well when subjected to certain exterior wall fire tests.
Lastly, some countries are considering changes in Code and regulation that would permit taller wood building construction. There is concern and discussions over the performance of these new building types if they were to be involved in an exterior wall fire scenario.
Other factors that led to a renewed focus on updating the safety testing and certifications available for these materials are the recent significant International Building Code changes pertaining to exterior walls (2012, 2015) which clarify the required testing of these walls. Another influence requiring fire testing of exterior walls is the growing focus on energy efficient (green) construction that requires the increased use of insulation materials within exterior walls, which in many cases requires reevaluation of the exterior wall assemblies.
Not all fire tests are suitable
Many building professionals, fire protection experts, design professionals, etc. are aware that there should be a holistic approach to fire protection within buildings. This encompasses the selection of materials that have been assessed for their reaction-to-fire properties (to slow the spread of fire), detection and alarm, fire suppression, and compartmentalization. However, there is not always a clear understanding of which fire tests or protection approaches should be used for exterior wall fires.
For example, there have been discussions in some areas about relaxing requirements for exterior wall testing if the interior of the building is protected by sprinklers. For an exterior wall fire originating external to the building, it should be understood that the interior sprinkler system is not designed to protect the building’s exterior surface, so significant fire and smoke damage could still occur to the structure. In some cases, the sprinkler may not activate at all. If sprinklers are activated, there are a finite number of sprinklers that are assumed to operate in a sprinkler system design. So there is the potential for more sprinklers to operate than included in the hydraulic calculation for the sprinkler system if the fire burns uncontrollably on or through the wall assembly. If this occurs, the ability of the sprinkler system to provide the desired level of protection to the interior of the building could be adversely impacted.
Another misconception is that compartmentalization methods, such as UL263 or ASTM E119 should be challenging enough to examine fire growth for an exterior wall assembly. (These are relatively large scale furnace tests based on a standardized time-temperature fire exposure to represent a flashover fire condition). While these methods are proven fire resistance tests, these traditional methods evaluate containing the fire and do not assess vertical or horizontal flame travel over or within the wall assembly. Therefore, these methods are not intended to predict nor measure the behaviour of the fire as it progresses along the exterior wall assembly and are not located within a compartment.
There are other reaction-to-fire methods that examine the surface burning characteristics of materials, such as UL723 and ASTM E84 (Steiner Tunnel), EN13501 (fire classification), and EN 13823 (single burning item). While these methods provide data on singular components that are used within walls, they do not give data on the fire growth performance of the complete wall assembly, as the combustion of individual wall components may influence one another in a complete assembly.
Which tests are suitable for your region?
In recognition of the importance of establishing the most representative test for this purpose, there are various Standards groups around the world focusing on exterior wall test methodologies. The good news is that countries appear to be addressing the issue of flammability of exterior walls seriously, and many areas are creating new, or updating existing, Codes and performance Standards. The challenge is that there are several different methods being implemented in different countries and regions that may not have the exact same scope or deliverable. Of course this means manufacturers who sell to different areas may have to demonstrate conformity to various test methods. It is important to understand what method(s) has been used to qualify a product or system to ensure it is fit for purpose.
Many of these prominent full scale exterior wall fire test methods are already embedded into Codes and regulations. Table 1 below shows some of the test methods and the countries that are typically associated with enforcing them. This is not intended to be a comprehensive list, as there are other methods under development.
|TABLE 1 – Exterior Wall
|Test Method||Country||Fire Source|
|BS 8414-11||UK||Wood crib; app. 75 kW/m2 @ 1 m height above the opening|
|NFPA 285||US||Gas burner; up to 40 kW/m2 @ 1 m height above the opening|
|LEPIR II||France||600 kg wood crib|
|SP Fire 105||Sweden / Denmark||60 liters of heptane|
|ISO 13875-2||International||Propane; 55 kW/m2 @ 0.6 m height above the opening|
|CAN/ULC S134||Canada||Gas burner; 45 kW/m2 @ 0.5 m height above the window|
|FM 4880||International||340 kg wood crib; no opening|
New certification approach in the US
Historically, the acceptance of wall systems involve a fairly complex review of building code interpretation, individual component manufacturer’s test reports, engineering analysis, and application of the manufacturer’s installation instructions. For compliance with NFPA 285, primarily in the US, UL has developed a certification approach to simplify the review process by providing a public database that shows complete wall system designs, and detailing how individual components are evaluated as part of the systems. This approach meets the dire needs of manufacturers, architects, specifiers, and code officials for an available, no cost, accessible, up-to-date method of determining compliance with code. The illustrated designs within the UL certification reflect the precise details of the assembly that has been found to comply with the requirements of the fire test. A UL certified wall system must be tested in the presence of a UL engineer and must be constructed to the reviewed specifications within the illustrated design and the details included in the associated text to achieve the desired performance. Critical components used in the system are named specifically and will also bear the UL Mark. All certified wall systems and components, like System No. EWS0001 shown to the left, are now published in UL’s Online Directory and in the Building Materials Directory under the categories Exterior Wall Systems (FWFO) and Exterior Wall System Components (FWFX). Examples of wall system components covered by this program include, but are not limited to, various types of insulation products (including foamed plastic), water resistive barriers, air resistive barriers, laminates, sheathing, and composite panels.
While building codes in some countries are prescriptive and detail exactly what material can be included in building facades, building codes in other countries lack this detail. UL has also engaged with the premier education center in India, IIT Gandhinagar, to create a test cell and test façade materials for flammability and resiliency. This research work and its findings will be available in 2018 and will hopefully provide the data required for improving building codes and standards for fire behavior of facades. Testing of designs continue to be reviewed and are scheduled throughout the year.
There’s clearly a continued global focus on the challenges associated with rapid fire spread on exterior walls. As we strive to better understand the impacting factors, and the appropriate tests and certification approaches that can be used to evaluate these assemblies, we can move towards better solutions. For more information please visit contact Dwayne Sloan, BLST PDE Director.