Four Criteria for Fire Performance – Protecting Network Cabling Infrastructure

Four Criteria for Fire Performance - Protecting Network Cabling Infrastructure

https://www.flexicon.uk.com/

Alex Smith, Technical Director, Flexicon

In its recent whitepaper entitled Fire Protection Options in Data Centres, The European Data Centre Association (EUDCA) examines the correct approach to fire safety.  It acknowledges that as critical facilities become larger and more complex, with significant growth in power concentration, the risk of fires will increase.

The paper outlines features that should be taken into consideration in data centre design, such as the protection of critical infrastructures, including electrical rooms, UPS rooms, diesel engines and carrier rooms via a risk-based analysis.

Alex Smith, Technical Director at flexible conduit manufacturer, Flexicon examines why these considerations should extend to the appropriate protection of data and power cabling. He explains some of the common myths around fire protection performance and the variety of differing standards in place.

Assessing the risk

Fire hazard assessment is essential in buildings where there is an element of risk, such as in a data centre or server room. It should include possible sources, examine the likelihood of a fire starting and address the consequences, such as evacuation protocols, loss of service and damage to equipment. 

The UK Wiring Regulations (BS 7671) requires applications to be non-flame propagating (self-extinguishing) and tested by means of the flame propagation test in EN 61386.  Many customers will assume that this basic requirement will be met by any flexible conduit they specify, but this is not always the case.

The definition of low fire hazard

For a product to be classified as a 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 an inherently low fire hazard; however, most conduit systems are now plastic coated or all plastic, so their performance needs to be assessed.

For example, although a ‘halogen free’ 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.

Common terms suggest that adequate fire protection is in place, when the product may only meet one of the four required facets.  For example, ‘low smoke and fume (LSF)’ rated products may not address toxicity and ‘low smoke zero halogen (LSOH)’ specification may not address flame retardancy.

However, there are numerous flexible conduit solutions available that meet all four requirements for low fire hazard specification. 

Flame Retardancy

First, the product must demonstrate appropriate flame retardancy and there are several established test methods to prove performance.

Flammability is the measure of how difficult it is to ignite the conduit if it is exposed to a heat source. The minimum requirement is that the product is self-extinguishing, according to conduit system standard EN 61386. Here a vertical sample of the conduit is exposed to a 1kW burner and must extinguish within 30 seconds of the removal of the flame with no flaming droplets.

Low smoke emission

If the conduit is involved in a fire, the smoke generated may obscure vision and it is important to limit this as much as possible.

There are several 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

To test for toxicity, a specified sample of material is burnt under controlled conditions in a 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

A common misconception is that a halogen-free material is automatically a low fire hazard product. A material certainly cannot be considered a low fire hazard if it contains halogen, but in addition, it should meet the full criteria for low toxicity, low smoke and flame-retardant properties.

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 these 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.

Suitability and compatibility

While many products may look the same, performance properties can vary greatly so customers should always check suitability and compatibility for their application.

Polypropylene, NFR (Non-flame retardant) is a commonly used material for network cable protection as it is halogen, sulphur and phosphorous free, so will not aid acid formation, but is highly flammable, and flame propagating.

In contrast, PA6 (nylon) is self-extinguishing, and halogen, sulphur and phosphorous free. 

Bespoke-designed cable protection

For more complex application requirements, customers should speak to their supplier to discuss bespoke options. These could include conduit supplied in non-standard or pre-cut lengths, in larger or smaller diameters or with different thread termination or fitting options.  45º and 90º elbows can also be used to help maintain bend radius.

Additionally, more complex requirements, such as altering performance characteristics to meet a certain temperature requirement, compression strength or abrasion resistance or to achieve a greater fatigue life may also be considered.

In conclusion

Flame retardancy, low smoke emission, low toxicity and halogen-free manufacture. When prioritising the fire performance of electrical installations, ensure that all aspects of fire performance have been considered. This should include evidence of the material properties, the breadth of any testing undertaken and proof that all the four criteria identified have been met.

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