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Modern buildings, modern cables

Today’s modern, public access buildings require the highest standard of cabling for all power and control purposes.

Today’s modern, public access buildings require the highest standard of cabling for all power and control purposes

New buildings in the UK must adhere to rigorous Building Regulations and internal wiring is an important part of these obligations. Consider lighting and power in public sector buildings, shops, offices, sports stadia and transport hubs such as airport terminals or train stations.

All have high numbers of visitors passing through, some of which may be unfamiliar with the building but all need to be as safe as possible should a fire break out. To reflect this, Building Regulations have become more onerous over time. This means the need to install low fire hazard cables to power building services is increasing.

In fact, Part B (fire safety) of the Building Regulations, states: ‘The primary danger associated with fire in its early stages is not flame but smoke and noxious gases produced by the fire.’ It’s this that causes the majority of casualties and also obscures escape routes and exits. Part B goes on to explain: ‘Measures designed to provide safe means of escape must therefore provide appropriate arrangements to limit rapid spread to smoke and fumes.’

Good quality PVC cables will of course do the job of carrying electrical power and control signals around a building, but should fire break out they can react badly. In the event of fire, PVC cables produce hydrogen chloride acid gas. If this is inhaled or if it comes into contact with eyes or skin it will cause choking, vomiting and extreme irritation. By way of an example, a low smoke zero halogen cable should emit less than 0.5% hydrogen chloride gas when burnt. This is in stark contrast to PVC cables which can emit in excess of 20%. PVC cables will also release dense black smoke which can obscure emergency exit routes and signage restricting evacuation; the exact situation that Part B states must be avoided. Furthermore, PVC cables can ignite and spread flames easily, making the fire worse.

When this happens, unprotected cables can enable fire to follow their route throughout a building, acting as a pathway for the flames. This in turn can reduce available evacuation routes causing panic and ultimately accelerating a buildings’ destruction. On the other hand, low smoke zero halogen cables should self extinguish when the source of flame is removed. They will not set light easily due to good resistance to ignition, release small quantities of white smoke, no halogen acid gasses and reduce the spread of flame.

In the low smoke zero halogen cabling market, installing an unsuitable cable for the job could have disastrous consequences. Confusing the matter is the number of words, phrases and acronyms in the market place all related to these types of cables that pertain to produce low amounts of toxic smoke and gas in the event of a fire.

These cables can often be called ‘low smoke’, LSF or LSOH, as well as many others phrases. It is easy to see how this situation leads to widespread confusion, as there is no single agreed phrase or term. Purchasers must beware, as acronyms such as LSOH are increasingly used as generic descriptions despite actually being a trademark. A problem arises because not all manufacturers use LSOH with the same meaning as the actual trade mark owner. This means that buyers can be misled into believing they are purchasing a low smoke halogen free cable as defined by the appropriate tests, when actually they are getting a cable product that may not perform to the required level. Worse still would be to install a PVC cable masquerading as LSOH. The Approved Cables Initiative (ACI) has uncovered instances of this.

Used correctly, the phrases ‘low smoke’ and ‘zero halogen’ relate to clearly defined test methods and performance requirements. ‘Low smoke’ describes a product tested in accordance with BS EN 61034-2. This smoke density test measures how much light is transmitted through the smoke produced by burning one metre samples of cable, where 0% means the light is totally obscured and 100% is full light transmission. A minimum requirement of at least 60% residual light transmission must be achieved.

‘Zero halogen’ describes a product tested in accordance with BS EN 50267-2-1. Under fire conditions these products must emit less than 0.5 % halogen acid.

Relying on an acronym alone to specify a cable is extremely risky. Instead, it’s compliance with the relevant prescriptive and industry defined British Standards should be checked.

Following these simple pointers will help:
• Never place an over reliance on acronyms alone as this opens up the possibility of buying a product without the performance you expect and one that could place lives in danger
• Always be certain that the cable bought complies with the relevant British Standard
• If you are unsure of the manufacturer’s reputation check for approval by third party assessors such as LPCB or BASEC
• If no BS product standard exists, look for compliance with the low smoke, halogen free and flame retardant BS test standards and requirements as a minimum
• Only purchase products from a reputable manufacturer and brand

Simon Hopkins is Product Manager for Prysmian

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