A number of high profile fires in the 1990s involving composite panels threw the spotlight on these products. Russell Harris says that not all panels are the same and runs through their many features.
It should go without saying that sandwich panels do not start fires on their own. Indeed, fire statistics confirm that fire spread via the external envelope is not common. A technical briefing by the Association of British Insurers (ABI) on the fire performance of sandwich panel systems states that where these systems have been implicated in fire spread, the fire has often started in high risk areas such as where cooking takes place, subsequently spreading as a result of poor fire risk management, as well as insufficient prevention and containment measures.
Prevention of ignition and containment of early fire spread are critical, and specific and detailed risk assessment is crucial. Where high levels of risk management are not achievable, due to the nature of the processes of the business and/or the quality of the management, and the risk of ignition is high, the use of panel systems with high fire performance characteristics should be considered. Systems meeting accreditation schemes such as LPS 1181 or LPS 1208 demonstrate such characteristics.
In the fire performance of construction materials, wall panels form a critical element of a building, so the composition of these panels is vitally important and should be considered no later than at design stage. There is an increasing number of composite panel products available in the UK, most of them claiming excellent fire performance. But to ensure they select a product that meets their requirements, specifiers also need to be aware that these products are not all the same.
The performance of a fire wall is time related, with 30 minutes 60 minutes or 120 minutes denoting the minimum time period the product must fulfil its fundamental requirement. During these times, the wall must not allow the passage of flame or hot gases from one side to another. The temperature of the face of the wall away from the fire must also be maintained within prescribed limits, since if the face of the wall reaches a temperature which could cause a flashover, then the construction has failed. Only when the fire performance of a wall panel is tested and proven for both internal and external fire exposure can it be suitable for compartment walls, or external walls situated less than a metre from a boundary.
In order to obtain LPCB certification (to LPS 1208 for elements of construction used to provide compartmentation), manufacturers have to put their composite wall panel products through an extensive series of tests, to demonstrate their ability to resist fire from both directions. A key distinction is between composite panels manufactured with PIR foam core and a mineral wool core. Despite the fact that many PIR panels are accredited to LPS 1181, these products are generally only suitable for fire exposure from the inside of the building, which limits their application to firewalls situated away from the boundary.
By contrast, composite panels with a mineral wool core are typically suitable for a much broader range of applications. Products such as these have been tested and proven for both internal and external fire exposure on the three key criteria for firewall construction – stability, integrity and insulation. As such, they can be used for compartment walls and external walls situated less than a metre from a boundary, as well as in more standard applications.
In the case of Promfire, for example, a range of different panel thicknesses and fixing regimes were tested, satisfying LPCB that the panels can provide fire resistance for up to 120 minutes (to LPS 1208 for elements of construction used to provide compartmentation). The tests were conducted in accordance with EN 1364-1 Fire Resistance Tests for Non-Loadbearing Elements (Walls).
The installation requirements for fire resistant insulated panels also vary depending on the type of product. For example, some PIR cored panel systems have to be installed in maximum two-metre lengths and require additional joint restraint fasteners and internal joint cover plates fixed at 250mm centres. Mineral wool panels, on the other hand, can typically be installed in lengths up to 13 metres with a maximum span of four metres, and require no additional fasteners or internal cover plates. These differences in installation requirement can become important in terms of construction times and access costs.
Much of the damage caused by fires is smoke damage rather than that caused by the flames, and an additional benefit of using composite panels with a mineral wool core is that these products give off less smoke than PIR cored panels in the event of a fire. For instance, Promfire achieved A2-s1,d0 to EN 13823 (single burning item test).
Here, the s1 suffix denotes a smoke growth rate index (SMOGRA) requirement of <=30 m2/s2 coupled with a total smoke production over the first 10 minutes (TSP600s) of <=50m2. The actual values achieved were 0m2/s2 and 32.4m2 respectively. Generally, a PIR cored product would generate more smoke and would therefore typically only achieve suffix s2 (representing a SMOGRA of up to 180 m2/s2 and a TSP600s of up to 200m2).
Wall panels that contain a non-combustible stone wool core and have a density of 100kg/m3 will achieve Euroclass A1 Classification to EN 13501-1 2002 when sandwiched by structural grade steel. The products are tested to determine the gross calorific value (prEN ISO 1716) and to determine whether they are non-combustible (prEN ISO 1182). Class A1 is the best possible.
With the introduction of the Regulatory Reform (Fire Safety) Order last year, there is no better time for specifiers and contractors to review their approach to building fire safety. And building owners and managers too need to take into account the fabric of their premises when conducting a fire risk assessment.
Russell Harris is technical and marketing officer at Arcelor Construction UK.
