Modern Building Services

16 MODERN BUILDING SERVICES FEBRUARY 2021 A lex Smith, Technical Director at flexible conduit manufacturer, Flexicon details the common myths around fire protection performance for critical data centre cabling. With an array of differing standards in place, he explains why operators should ensure that their cable protection meets all low fire hazard criteria requirements. Fire performance standards BS 7671, commonly referred to as the 18th edition wiring regulations refers to EN 61386 for flexible conduit performance requirements, including fire. However, this standard for conduit systems only addresses non-flame propagation (self-extinguishing) – and no other fire performance properties such as enhanced flame retardancy, smoke and toxic fume emission are included. This can lead to a potentially dangerous situation where cables can be laid in flexible conduit that, by its standard, only needs to clarify if it is self-extinguishing and does not offer a comprehensive level of fire performance. Assessing the risk Fire hazard assessment is essential in buildings where there is a significant risk to people, processes or property, such as in a data centre or server room. This assessment should include possible sources and likelihood of a fire starting and the consequences of such a fire including; evacuation and safety of people, loss of service and damage to equipment. For example, in a data centre environment, factors such as high temperatures in confined server rooms should be considered. Also, conduit systems containing halogens, such as PVC, will give off chlorine acid gas in a fire that can destroy electronic equipment in another part of the building. Almost all applications will require non-flame propagating (self-extinguishing) as called for within the UK wiring Regulations (BS 7671) and tested by means of the flame propagation test in EN 61386 as a bare minimum. Many customers will assume that this basic requirement will be met by any flexible conduit they specify, but this is not always the case. Meeting low fire hazard specification For a product to be classified as low fire hazard, it must display four clearly defined characteristics. It must be highly flame retardant, have low smoke emission, low toxic fumes and be halogen free. All metal conduit systems are inherently low fire hazard as there is no plastic to burn. However most composite conduit systems (for example, a metallic core with a plastic coating) or all-plastic conduit systems should be assessed for fire performance. Traditionally, Halogen Free conduits have been specified, often based on the commonmisconception that they offer comprehensive fire protection performance. Although such a conduit may prevent the generation of toxic gases in some settings, it does not mean necessarily that it is also flame retardant or have low smoke properties and may still be flammable if exposed to a heat source. Add to this the fact that there is no single European classification standard for low fire hazard cable management products that defines terms, test methods and results expected, and it is easy to see why there is confusion in the industry. Terms are commonly used which suggest that adequate fire protection is in place, when the product may only meet one of the four required facets. For example, products described as ‘low smoke and fume (LSF)’ may not address toxicity and product described as ‘low smoke zero halogen (LSOH)’ may not address flame retardancy. There are, however, numerous flexible conduit solutions available that meet all four requirements for low fire hazard specification, which we now examine in further detail. Flame Retardancy There are a number of established test methods to prove performance. Flammability – the measure of how difficult it is to ignite the conduit if it is exposed to a heat source - is often referred to. The minimum requirement is that the product is self-extinguishing, according to conduit system standard EN 61386. Here a vertical sample of conduit is exposed to a 1kW burner and must extinguish within 30 seconds of the removal of the flame with no flaming droplets. Ensuring adequate fire protection for data cabling. PROTECT or NEGLECT INSTALLER VIEW FEATURE INSTALLER VIEW