Protect or neglect - Ensuring adequate fire protection for data cabling

Fire

With an array of differing standards in place, 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 common misconception 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.

To assess how flame retardant a material is, the normal test method is to measure the Limiting Oxygen Index (LOI) according to BS EN ISO 4589-2. This determines the percentage of oxygen that needs to be present to support combustion. The higher the LOI percentage, the greater the flame retardancy of the material.

Another method is to use a glow wire test, BS EN IEC 60695-2, which applies a glow wire to a plaque of material at 7500C, 8500C or 9600C.

Low smoke emission

If the conduit is involved in a fire, the smoke generated may obscure the vision of people trying to escape, or the firefighters trying to extinguish the flames.  It is important that the flexible conduit specified provides superior protection if this scenario occurs, to ensure staff are afforded sufficient time to exit the building safely.

There are a number of fire tests, where a specified sample of material is burnt under controlled conditions in a given size smoke chamber and the smoke obscuration of a defined beam of light is measured.

Low toxicity

The generation of toxic gases may incapacitate people trying to escape from the fire, so appropriate protection must be provided at all times.

To test for toxicity, a specified sample of material is burnt under controlled conditions in a given size smoke chamber and the fumes are analysed for various gases. The concentration of each gas is then multiplied by its toxic potency to give a toxicity index.

If halogens, sulphur or phosphorus are present in a material, it is unlikely to pass the low toxicity tests.

Halogen free

One of the main misconceptions is that a halogen-free material is automatically a low fire hazard product.  A material cannot be considered as low fire hazard if it contains halogen, but as we have learnt, without the accompanying low toxicity, low smoke and flame-retardant properties, it will not meet the full criteria.

Typical halogens are fluorine, chlorine, bromine and iodine. Chlorine is the most common in PVC, fluorine is present in fluoro-polymers and bromine appears in flame retardants. All of them produce highly toxic fumes and thick smoke if exposed to a naked flame; another reason why operators may have tended to rate this area of performance above other fire hazard properties.

Specification first

It is also worth remembering that specifying cable protection based on one property alone can be a costly mistake and the full range of environmental factors should be considered. These can include exposure to extremes of temperature, UV radiation, harsh chemicals, compression strength, abrasion resistance and the likelihood of water or dust ingress.

While many products may look the same, performance properties can vary greatly so customers should always check suitability and compatibility for their application and consider the installation as a complete end-to-end system.

Reputable conduit suppliers will provide product and material fire test reports to support their fire performance claims. These test reports should come from accredited fire test laboratories and should be less than five years old.

In conclusion

According to the Uptime Institute, many operators admit that most downtime incidents could be avoided if they were to invest more in the resiliency of their facilities, making it vital to put robust measures in place to mitigate against the risk of fire.

This should not only include the physical hardware and infrastructure, but extend to all aspects of an installation, particularly the performance of essential data cabling.

By considering all aspects of fire performance, operators can ensure the ongoing security and longevity of the installation.

Alex Smith is Technical Director of Flexicon

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