The Euroclass method is based on the agreement of national regulating authorities. With the exception of flooring, all construction products will be grouped into seven classes – A1, A2, B, C, D, E and F – according to their performance in four tests (see table 1).
Two of these tests will be used to classify the least combustible materials in classes A1 and A2. These are a non-combustion furnace test to the pre-normative standard prEN ISO 1182, and a so-called oxygen bomb calorimeter test to prEN ISO 1716.
A simple ignitability test for vertical specimens based on an existing small burner test, prEN ISO 11 925-2, will be used for products in classes B to E. Within classes A2, B, C and D, products will also be evaluated using the 'single burning item' (sbi) test. This test evolved from the European fire regulators' requirement for a standard test to simulate a single item burning close to the corner of a room.
In the sbi test, the corner of a room is represented by non-combustible boards mounted at 90° to each other. The products to be tested are mounted and fixed into a specimen holder so they represent a realistic end-use.
The ignition source is a triangular sand and gravel burner, fuelled with propane, that produces a heat output of 30 kW. Combustion products are removed from the room through a fan-assisted extract duct.
The test rig incorporates a 180° bend in the ductwork – introduced at the request of some EU member states to reduce the rig's space requirement. During the test, measurements are made of the rate of heat release and smoke production, the extent of flame spread and the occurrence of flaming droplets and debris.
These measurements are used to derive indices for classifying the products within the Euroclasses system. A product achieves classification based upon its potential contribution to fire growth in the early, pre-flashover stage of a fire.
A fire at this stage will normally be fully ventilated – a vital factor affecting smoke production. The performance level related to smoke production and burning droplets and debris will also be declared. The test is set up so that if a material ignites, flames will spread quickly up the corner, assisted by the naturally induced wind flow.
Lateral flames typically spread horizontally across the surfaces of the material more slowly than the vertical spread. In this respect, the sbi test differs substantially from BS 476: Part 7. Where the current standard tries to measure lateral opposed flame spread over a lining surface under an external radiant heat profile, the sbi test does not. Instead, the thermal attack relies purely on the ignition source located in the sample corner.
The flames spread upwards in the corner and are wind-aided, with only limited lateral flame spread observed in many cases. Lateral flame spread is only included in the Euroclass limits as a failure criteria in classes A2, B and C, when flames reach the edges of the sample.
Comparison with British Standards
It would be a mistake to look for equivalence between the current UK classifications and the Euroclasses. This is only the case for the best performance classes "non-combustibility and limited combustibility" and A1 and A2, where common tests prevail.
Likewise, it would be unfair to expect equivalence between UK classifications and the sbi classes B, C, D and E. The current Building Regulations control the use of wall and ceiling linings by classification in BS 476: Part 7, which makes the comparison analogous to comparing an apple with a pear.
The ISO 9705 room-corner test has been used as the basis of the sbi test. That said, the role for the ISO test within future European harmonised test methods has still to be resolved. As a test method it can be criticised for the low correlation between its smoke data and that of the sbi test.
This is due largely to how the two standards treat flashover and the smoke production generated after flashover. There is closer correlation between the two tests during the early stages of smoke production.
Wall and ceiling linings
In future, the control of wall and ceiling linings will change from mainly limiting the surface spread of flame performance to limiting the contribution to fire growth – in terms of heat release rate as a function of time.
The emerging European harmonised test methods are inevitably leading to widespread debate between Member States. Open dialogue is needed between regulators, product manufacturers and standards bodies.
In time, sbi and other test methods will become CEN standards. When this happens all conflicting British Standards will have to be withdrawn.
The challenge to the industry is clear: new data is required from the harmonised test methods like the sbi. Only this can demonstrate whether the proposed classification system is robust beyond the 1000 products already tested. If problems do emerge, it is important to identify them and seek constructive solutions.
On this basis, the Fire Research Station is working with a number of key product manufacturers to foster an understanding of the Euroclass system.
Source
Building Sustainable Design
Postscript
Dr Debbie Smith is head of the Reaction to Fire Centre at the BRE's Fire Research Station. Manufacturers who wish to become involved with Euroclasses should contact Dr Smith at FRS, BRE, Garston, Watford WD2 7JR. Tel: 01923 664923, e-mail: smithda @bre.co.uk
