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Reaction and resistance

technical & practice

The amendment to Part B includes reference to, but no explanation of, European fire classes. We explain the detail

As a traditional Christmas goodwill gesture, the Office of the Deputy Prime Minister (ODPM) issued the Amendments 2002 to Approved Document B (Fire Safety) on Friday 20 December - a late stocking filler.

Instead of being a stand-alone document, it takes the form of an addendum which requires the reader to compare and contrast its clauses with the - still relevant - Part B (2000). It seems that the strangled comprehensibility of the deputy prime minister has found its match in the formatting of ODPM documents.

Although 'it is envisaged' that subsequent reprints of Part B will include these amendments, until then, you will have to cut and paste new clauses into your existing copy.

Annoyingly, many changes simply refer to minor reference alterations, but instead of saying, for example in clause 7.11, 'replace paragraph 16 and paragraph 19 with paragraph 17 and paragraph 20 respectively', you are led to believe that there are greater changes, by being asked to replace the whole paragraph. It is only when you have spent 10 minutes squinting to see what you are missing that you realise that only two numbers have changed.

The main purpose of the update is to introduce the new technical specifications of the Construction Products Directive (CPD) (see AJ 18.7.02), Euroclasses (see below) and, inter alia, improved standards and procedures for the reaction and resistance to fire.

On page 11 (referenced to page 109 of the 2000 Approved Document), there are new notes appended to several clauses which suggest that the BRE and BBA have been taken off the list 'of accredited bodies which have the necessary expertise for conducting the relevant tests in terms of European Technical Approvals'. The United Kingdom Accreditation Service (UKAS) is now the sole national accreditation body recognised by government to assess, against internationally agreed standards, organisations that provide certification, testing, inspection and calibration services. However, a spokesman from BRE said that this represented 'nothing sinister', but that given it has become a privately run business since Part B: 2000, it appears that UKAS (a government body which accredits BRE, BBA et al) has used its name as an umbrella contact, especially since there are now more private testing agencies than cited in Part B: 2000.

Resistance to collapse, fire penetration and transfer of excessive heat are denoted R, E and I respectively in the new guidance. No guidance is possible on the performance in terms ofthe resistance of roofs, or roof coverings to external fire exposure as determined by the methods specified in DD ENV 1187:2002 (Test methods for external fire exposure to roofs) as this is currently under review.

Appendix A: Clause 7: Reaction to fire is a new clause explained below, detailing the new fire classification system in accordance with BS EN 13501: 2002: Part 1 'Classification using data from reaction to fire tests' which replaces the existing Class 0 - 4 (and unclassified). The new coding system is more detailed to take account of smoke creation and the ability of a material to fragment and create particles or droplets which carry the fire.

The tables in Appendix A have simply been tidied up and columns added to include the European testing and classification provisions. At the bottom of Table 2, a new 'Note' has been added, indicating the 'deemed to satisfy 15 minutes' fire resistance of various steel elements.

As a bit of light relief, the document states that all fire doors should have the appropriate performance classification demarcating its integrity with suffix S as determined by BS 476: Part 22 or be 'classified in accordance with BS EN 13501: Part 2 xxxx (where 'xxxx' denotes the year of a Standard not yet published).

In addition to the current exemption on fire doors to lift entrances - fire doors to landings (in domestic and non-domestic environments) will no longer need to have signage complying with BS 5499 'Fire safety signs, notices and graphic symbols'.

This brief overview outlines the main changes to the text. Nothing too significant in terms of amended data; the main changes are the inclusion of European classification codes which phase out the current British classifications. Anna Cherry examines the implications of these European standards below.

Euroclasses

The new European classification for 'reaction to fire'performance - will replace the UK's outmoded Class O, Class 1 system that is unable to differentiate many contemporary fire hazards, writes Anna Cherry.

In the past, each country in the EU developed its own fire tests in support of its national building regulations and guidance.

Consequently, it has been extremely difficult to compare the data.

Now, for the first time, a common system of fire testing for construction products and classification of the resulting test data is being implemented across the EU member states. This Euroclass system is part of the CE Marking initiative to allow the free trade of goods throughout the EU (see AJ 18.7.02). About 80 per cent of all construction products will need to be classified for performance in fire.

From the architect's point of view, the new Euroclass system will provide a common basis for comparing the fire performance of products irrespective of the EU member country in which they were made or tested.

National regulations and guidance are now being amended so that the old 'traditional' parameters will be transposed into the new Euroclasses and agreed across the EU. Scotland has already changed the Technical Standards with effect from March 2002, while changes in England and Wales become effective from 1 March 2003.

Until then, the old and new systems will coexist, as we familiarise ourselves with EU supplements to national regulatory guidance, and as product manufacturers complete the procedures for providing fire performance data on the product CE Marking labels.

Reaction, not resistance

Confusion may arise because there are, in fact, several new EU classification systems for fire performance. This article deals solely with the introduction of the seven-grade A1 to F Euroclass system for 'reaction to fire'- indicative of a product's fire performance in the growth stages of a fire. Another sub-system - dealing with 'resistance to fire'- classifies the fire performance of building elements, as opposed to individual products, in a fully developed fire.There will also be classification systems for roofing products subject to external fire exposure, building services, and smoke control equipment.

Each construction product will be categorised into one of seven Euroclasses for 'reaction to fire'. These are A1 - A2 - B - C - D - E - F, with A1 being the safest. The new system for 'reaction to fire' is based on the tendency of a product to promote the conditions for flashover in a room or enclosure (see table 1). Euroclass A1, A2 and B products do not promote flashover and are therefore much safer in fire than Euroclass C, D and E products.

Product selection

The data from a battery of small- and medium-scale fire tests is used for the classification process in correlation with a large-scale reference test.

Flashover is not measured in the small-scale 'reaction to fire' tests of construction products but is measured in the larger Room Corner Test ISO 9705 - the underlying reference test for Euroclasses in the EU 'reaction to fire'classification system (now drafted as EN 14390 Full-scale Room Test for Surface Products). The reference test is also used as the appeal system when there is uncertainty regarding the classification of some contemporary products, or when initial classifications are formally challenged.

Products that do not exhibit flashover in the reference test (Euroclass A1, A2 and B) are differentiated and classified on their proximity to non-combustibility, and according to their potential heat release rate under specified exposure conditions.

Architects will need to specify using the new Euroclasses to enable tenders to be submitted from all over the EU. Products will be defined by their Euroclass category, which will help to simplify the preparation of the Health and Safety Plan.

From the clients' perspective, the Euroclass system provides additional information to aid the 'risk assessment' requirements under the Fire Precautions (Workplace) Regulations 1997, as amended 1999 (a statutory duty on most employers). In particular, the Euroclass differentiation between products that contribute to flashover and those that do not is most helpful. Data will also be available to indicate the tendency of a product to generate smoke and flaming droplets/ particles. This is paramount for designs where the potential for smoke inhalation could be a major issue - since smoke is responsible for about two-thirds of deaths in fire incidents.

Smoke and flaming droplets/particles In the EU classification system for 'reaction to fire', a construction product will be classified as Euroclass A1, A2, B, C, D, E or F depending on its tendency for 'burning'. The product testing will provide data, which indicates the tendency to release smoke, represented by s1, s2 or s3.The measurement of smoke release has been put into these three broad bands that can be translated as s1 - 'little or no smoke'; s2 - 'quite a lot'; and s3 - 'substantial'.

Some construction products can melt and ignite to form flaming droplets. Wooden products, on the other hand, might char, which could fall away as flaming particles to expose more material. These flaming droplets/particles will tend to initiate new fires away from the original point of ignition, and must be considered when the products are used horizontally, in ceiling or roof applications. The classification system ranks the level of release of flaming droplets/particles as d0 (none), d1 (some) and d2 (quite a lot).

The 's' and 'd' ratings must be declared within the CE Marking label, even if some countries fail to regulate for the production of smoke or flaming droplets/particles in their national guidance. Bringing all this information together indicates the complete Euroclass for a construction product, as defined in BS EN 13501-1, paragraph 12.1 for 'reaction to fire' (see table 2). More information overleaf.

Common construction materials - likely Euroclasses

The following synopsis is extracted from the results of research conducted by Warrington Fire Research for the government. For full details see www. wfrc. co. uk Smoke is naturally assumed to be produced from Euroclass E products and is not measured. A similar assumption is made for flaming droplets/particles that are only measured in the categories in Table 2, overleaf.

See also www. rockwool. co. uk for detailed information on fire safe design and legislation, including EU classification systems and fire testing for construction products.The classification below is for 'reaction to fire'and does not indicate the long-term stability of installed products in fire - 'resistance to fire', which will need to be taken into account when selecting products.

For specifiers, it will be critical that the design, hazard and risk evaluations, assess the difference between, for example, a Class C - s1, d0 product and a B - s3, d2 product. Is the B or C burning data the dominant issue, or is the high smoke production a more vital characteristic?

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