Getting to grips with cabling and labelling

Published:  09 September, 2013

Prysmian’s Product Manager Simon Hopkins reviews cable standards which promote high standards of cable and fixings throughout public buildings. He advises that low smoke zero halogen cable should be designed and installed into electrical power and control circuits as the responsible choice as opposed to PVC.

UK Building Regulations have expanded to accommodate modern building technologies. More stringent measures are now required for the selection and installation of cable to continue the upkeep of public safety in the unfortunate event of fire.

It’s a common misconception that the principle danger to death in the case of a fire is the flames themselves when in fact it’s the noxious gases that some materials release when burning that can result in harm or even death.

Part B of the UK Building Regulations reiterates these threats when stating: “The primary dangers associated with fire in its early stages are not the flame but smoke and noxious gases”. It goes on to say: “Measures designed to provide safe means of escape must therefore provide the appropriate arrangements to limit rapid spread to smoke and fumes.”

Professionals advise using low smoke cables (LSOH) and indeed LSOH cable glands and fixings in our public buildings to ensure the utmost standards of safety. In terms of building regulations, they are yet to make full provision for the use of fire resistant fixings as legislation, but this may well be considered in the future. It is well documented that cable can fall when fixings fail and significantly increase the risks during escape from a fire.

Rigorously defined test methods and performance requirements validate the use of the phrases “low smoke” and “zero halogen”. “Low smoke” refers to the test method in accordance with BS EN 61034-2.  This smoke density test (the 3 metre cube test) measures the amount of light that breaks through the smoke produced by burning 1 metre samples of cable. 0% means the light is totally concealed and 100% means full transmission and at least 60% residual light transmission must be achieved by a compliant cable.

“Zero halogen” describes a product tested according to BS EN 50267-2-1. This requires less than 0.5 % emission of halogen acid gases when burnt.

Thermoplastic and thermoset compounds are used to manufacture LSOH cables. Their sheathing, insulation and bedding fillers emit extremely low amounts of smoke, gas and reduce the escalation of flames.

In strict comparison, standard cable is insulated with PVC, polythene or thermoplastic urethane. In the event of a fire, a standard cable’s reaction actually characterises many of the dangers associated with fire safety laid out in Part B. They release thick black smoke which can obscure fire exits and escape signs and emit hydrogen chloride also. Hydrogen chloride is a poisonous gas which creates hydrochloric acid when in contact with water. This causes extreme irritation if it comes in contact with skin or eyes and if inhaled it causes vomiting, choking and in some cases death. Low Smoke Zero Halogen cable conversely, has a flame retardant outer sheath which significantly reduces the level of toxic and corrosive gasses emitted when burnt.

With a range of LS0H cables on the market all possessing various acronyms and numbers it can be confusing knowing which to pick. People are commonly choosing improper cables disguised as the genuine article which can have calamitous consequences in the unfortunate event of a fire. For example, the use of modified PVC cables which are labelled as RP Reduced Propagation or Low Smoke and Fume do actually produce less hydrogen chloride gas than standard PVC cables, but only up to 6% less which is unacceptable. In worst case scenarios some cables are not marked with any numbers or letters at all. Firefighters can help with the extradition of counterfeit cable by alerting us to circumstances of unmarked cable.

Also, you must be conscious of some low-cost cables that have PVC insulated inner conductors and LS0H outer sheath which essentially offset the purpose of LS0H once the outer sheath has burned. Choose cables marked LSOH orOHLS as these are certain to emit no more than 0.5% hydrogen chloride gas.

Another option is to specify Prysmian Afumex cables. They are British manufactured and meet or exceed the cable construction standard, the low smoke standard, the zero halogen standard, the flame retardant standard and all have third party approval.

  • Operation Florian

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