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The impact of changes to approved Document B to accommodate the new Euroclass reaction to fire classification systems

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The adoption of a harmonised system of reaction to fire tests across the EUmeans that Approved Document B (2000 Edition) of the Building Regulations 1991 will require further revision. It is proposed to do this by publication of European supplements for use with Approved Document B. Currently, the classification of building products according to their reaction-to-fire performance is achieved by the BS 476 series of fire tests.

The CEN test methodology developed for Euroclassification of products (excluding floorings) is different from the BS 476 tests.

The field of application of the Euroclassification is identical to the field of application resulting from the CEN tests where the test conditions are determined in relation to the end-use application of the product. If different end-use applications are envisaged for a particular product (eg use of different substrates), this may result in different classifications. The Euroclassification of a product is based on its reaction to fire performance assessed as its contribution to the generation and spread of fire and smoke within and beyond a small room of origin. The ISO 9705 small room test18 was used as a reference scenario for validation of the small and intermediate scale EN tests specified for Euroclassification.

Research projects under the name RADAR were initiated to assist the DETR (now DTLR) to prepare the European supplement for Approved Document B and to bring together the wide experience of UK Official Fire Testing Laboratories with the experience of the building industry. The objective was to ensure that no significant change to the regulatory status quo would occur due to the introduction of the new reaction to fire tests and to the new Euroclass systems.

The essential objective of the experimental programmes was to test a representative range of building and roofing products to both the UK and European reaction to fire test methods. This back-to-back testing was necessary so that differences between the methods could be determined accurately.

Industry partners had to define carefully how their products were installed in buildings and the testing laboratories then performed the tests under similar end-use conditions. This requirement ensured that end-use variables such as type of substrate, presence or not of an air-gap, type and application of adhesive, type and position of joints, etc. were addressed by both the industry partner and the testing laboratory.

Analysis of the RADAR results obtained for cellular plastics shows that there is no overall correlation between the Euroclass system and the UK system. For plasterboard and steel faced products, there was a good correlation with Euroclass B corresponding with UK Class 0. This correlation between Euroclass B and Class 0 was confirmed also for a variety of non-insulation products. There were some significant discrepancies; e. g. aluminium foil faced PIR and PF foams give Class 0 in the UK system but they only gave Euroclasses D and C respectively due to early penetration of the Al foil by the 30kW flame in the SBI test and resulting high FIGRA values. Some thermoplastic products (such as XPS) are unclassifiable in the BS 476 Part 7 test due to their melting behaviour during the first minute of the test.

Moreover, the fire performance of some unfaced cellular plastics (especially thermoplastic types) can be dependent on the thickness of the product. Hence, the results shown in Tables 1 and 2 should not be assumed to apply across a wide thickness range for all insulation products. The fire performance of char-forming polymers is less dependent on thickness; for example, PIR block foam retained its Euroclass C-s2, d0 classification over a thickness range of 12.5mm to 60mm.

As a result, based on further research, the DTLR has now proposed a transposition table for reaction to fire performance. It should be noted that the Euroclasses in Table 3 only refer to fire growth. When the new Euroclass system is introduced, manufacturers will also have to declare the smoke and flaming drop classifications, even though there are no requirements for these parameters in the UK Building Regulations. But even this transposition process is not simple for all building products since the classifications depend on certain key factors; for example:

There is a fundamental difference in the UK and EC testing systems, especially the use of overall flame spread for UK classification compared to rate of heat release during the early stages of flame attack in the SBI test for Euroclassification.

Mounting and fixing arrangements, especially the presence or not of air-gaps, position and type of joints, substrate, etc.

Efficiency of protective facings and coatings to limit the thermal contribution of the core material.

Peter Briggs is at Warrington Fire Research Centre

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