Anyone specifying, inspecting or regulating fire resistant cabling for large or complex buildings should now be aware of the new standard, BS 8519, introduced February 2010 and effective immediately. It gives advice and recommendations for the selection of fire resistant power and control cables in life safety and fire fighting systems such as smoke barriers, sprinkler systems, fire fighting and evacuation lift supplies. Building regulations Approved Document B refers to BS 7346-6, which is now withdrawn and replaced with BS 8519 for large or complex buildings. It does not cover the wiring of fire detection and fire alarm systems which are still covered by BS 5839.
Focussing on large and complex buildings recognises that life safety solutions developed for such buildings require a high level of performance from all components including the electrical supplies.
For the first time fire survival times are introduced. This means that in intense situations - where fire fighters and other emergency service workers need to enter or occupy a building after evacuation say 30, 60 or even 120 minutes after the fire or emergency began - under BS 8519 they can now be certain that the cables operating the fire fighting power and control systems will remain fully operational.
Cable selection
Three fire survival times are recognised under the new standard. Life safety systems must remain operational for 60 minutes in large and complex buildings and 30 minutes in other types of building. Fire fighting systems should be fully functioning 60 or 120 minutes depending on the application being used.
Prysmian’s FP 200 Gold, FP Plus, FP400 and FP 600S cables meet the full range of fire survival times required under the new standard and are BASEC and LPCB approved.
Installation
BS 8519 also impacts other components in the cable systems such as fixings, containment systems, glands and joints to ensure they do not compromise the circuit integrity in the event of fire. The code proposes that joints should be avoided unless absolutely essential and that cable fixings and fixing centres should always be fitted according to the cable manufacturer’s recommendations.
Robust armoured cables should be fixed either directly to the building structure or to a cable management system. If additional mechanical protection is needed for cables, a cable management or containment system is advisable. This must be able to maintain its full function in adverse conditions such as fire, direct mechanical impact and under pressure from water jets and for the same period of time as that set out for cables. Specific tests for cable management systems under BS 8519 are still in the process of development so manufacturers should be consulted before installation.
High voltage
For security of supply, BS 8519 also recommends that HV supply cables serving life safety and fire fighting systems should directly enter fire-rated switch rooms and not pass through buildings.
In situations where cables have to be routed through buildings they need to be fire protected. As suitable HV cables with intrinsic resistance to fire are not currently available, normal cables need to be used with the right protection. There are several ways of doing this. Installing the cable in a concrete trench with a concrete cover, routing it within a dedicated shaft or void with the appropriate fire rating, or enclosing it with passive fire protection material giving 120 minute fire resistance together with the capability of withstanding the effects of the direct impact and water jet specified. Certain high performance systems based on composite panels of fibre-reinforced cement, bonded to steel sheets are also suitable.
It is already clear that high-rise buildings, such as London’s tallest skyscraper, the Shard and other large and complex sites, will be inherently safer during an emergency now this new standard is in place.