Pirelli Cable's FP Product Manager Gordon McKinnon looks at the FP sector, the progress made since the King's Cross fire and looks at what the future holds:
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| Pirelli Fire Performance cable - FP 200 Flex. |
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In the last twenty years, following such high profile disasters such as the King's Cross Underground fire, the electrical industry has made vast improvements in the safety of power cables, both in the quality of products and ease and safety of their installation. The King's Cross fatalities resulted from a lethal combination of flames, dense smoke and toxic fumes produced. Understanding the causes of disasters such as this accelerated the development of fire performance cables that limit smoke and other emissions. There have been continual refinements and developments by cable manufacturers in these areas and now there are comprehensive ranges of fire performance cables and accessories to meet every requirement.
Cables with improved performance in respect of fire, fire performance cables, fall into two types:
Fire resistant cables can be defined as 'a cable with the ability to continue operating in the designated manner while subjected to a fire test scenario for a specified period of time.' This means that, in case of a fire in a building or facility where fire resistant cabling is installed, they are designed to last longer than normal cable, keeping essential systems such as alarm systems, emergency lighting, sprinkler systems in operation, which can in many cases preserve lives. These types of cables are often referred to as 'FP' cables, the Pirelli-trademarked name for their range of fire resistant cables.
Applications:
Fire resistant cables and accessories are widely used to support essential systems in many countries, although the degree of standardisation around the globe, both in terms of the product specification and testing requirements, remain limited. With the growth of a fire safety engineering approach to building design, regulators in some countries are beginning to reconsider the performance requirements for the cables necessary to power life safety, fire fighting and property protection systems.
European Fire Regulations have recognised two distinct areas of application for fire resistant cables:
Circuits relating to alarm and evacuation might include fire detection, fire alarm sounders, central battery emergency lighting, safety signalling and voice alarm systems. This type of application is generally characterised by the need for many kilometres of small conductor size cable to be installed and many hundreds of terminations to be made. Ease of installation and reliable technical performance are therefore prime requirements of any fire performance cables and accessories.
Circuits relating to fire fighting systems might include smoke extraction, smoke venting fans, fire shutter control, water supply pumps, fire lifts and pressurisation fans. These are generally specific circuits using larger power conductor sizes and they're becoming increasingly important as such facilities are used as part of a fire safety engineering approach to building design. In some countries, armoured cables are preferred to give a combination of mechanical and fire protection to ensure the integrity of the circuit.
Cable types:
Pirelli Cables has always been at the forefront of fire performance cables and accessories. The Pirelli FP range, for example, offers solutions designed to meet every requirement, offering easy to use alternatives to standard cables for essential services. A full range of Pirelli FP cable accessories including fixing clips, saddles, glands and shrouds are also available.
The design of fire performance cable depends on the job that it will be required to do. As with any fire product, rigourous testing is carried out to make sure the cable meets the necessary standards. Using a combination of cable constructional design and the careful selection of the materials used in the cable's construction, manufacturers can maximise the fire performance of the cables, thus ensuring that it is as safe as possible and meets the safety standards required of it.
Cable insulation and sheathing:
Historically, various cable insulation and sheathing has been used to ensure fire resistant cables achieve their performance goals:
For example, mineral insulated copper sheathed design (MICC), in which an inert powder (usually magnesium oxide) is enclosed in a continuous copper sheath, is one of the options. Another is silicone insulated cable, where specially formulated filled silicone turns to a cohesive ash upon burning. A third type is mica tape insulated cable, in which the mica in a tape applied to the conductor fuses under heat to form an insulating layer. Finally, high performance extruded insulation, such as Pirelli 'Insudite', has been developed to perform in a similar manner to Silicone but exhibiting superior fire performance and mechanical robustness.
Whilst MICC designs can off a high degree of fire resistance, their need for special installation techniques means that the easier to install extruded insulation designs are more widely used. The use of silicone insulation is generally restricted to the smaller cables for fire alarm and emergency lighting use, but is often characterised by mechanical properties that make it prone to damage. These deficiencies are overcome by the newer high performance extruded insulation types.
Mica taped insulation is used for the larger power supply cables. Until recently, cable types subjected to a large-scale furnace test, required in some countries (particularly Belgium and Germany), have used mica tape constructions, but advances in performance given by new silicone based high performance insulations has resulted in these now being used in some designs.
The Construction Products Directive:
The Construction Products Directive (or CPD) is an EU directive (89/106/EEC) which has to be implemented into National requirements. The CPD is designed to remove technical barriers to trade in the area of construction materials and products. Its primary function is to ensure the safety of constructions in all countries of the European Economic Area. The Directive lays down certain essential performance criteria for buildings under six general headings:
The standards are set by the European Commission who issue mandates to the European Committee for Standardisation or the European Committee for Electrotechnical Standardisation or, if no European Standards exist, European Technical Approvals (ETA) are used instead.
Cables are influenced by the CPD both in terms of resistance to fire and reaction to fire. The only cable related Harmonised European Standard so far issued in support of the CPD is EN50200:2000 'Method of test for resistance to fire of unprotected small cables for use in emergency circuits'. Although issued as BS EN 50200, this test and the associated classification requirements have not yet been included in any UK regulatory requirements.
It has also been proposed that the reaction to fire performance of cables be subject to a Euroclass classification, as used for other building products. This proposed classification is still under discussion, but assuming a positive decision is reached, cables will have to be CE marked and their reaction to fire classification declared. In the UK cables are not subject to regulation in terms of reaction to fire and it is not expected that inclusion of cables under the CPD will change this principle.
Installation:
Installation features are also important in the selection of fire resistant cables. Consideration of the wide range of installation conditions suggests that a range of cables, each designed for specific installation conditions would be more appropriate than a single product type.
Each cable type should be compatible with the other components of the system in which it is to be used and should not require the use of accessories, such as glands, that will detract from the performance level achieved by the cable. Suitable fixings should also be available to ensure system performance.
Cables for such important circuits should also be selected according to their resistance to damage - during installation through the use of damage resistant insulation and appropriate handling features, and to external forces after installation through the use of armour or method or installation. Designs that offer easy and timely installation consistent with the skills available should be selected so as not to degrade the system performance through poor installation of a difficult to install or handle product.
The future:
Pirelli offers a wide range of products enabling customers to take a balanced view when considering product recommendations for a particular application. It guarantees the quality and long-term reliability of its products and technical performance is supported by third party assessments and approval from recognised bodies.
Pirelli is committed to providing new, cost effective and easy to use products to meet changing requirements as regulations, codes of practice and test methods are reviewed and revised. Material and product development has already lead to considerable improvements in performance of extruded insulation designs and it is to be expected that this will continue through further material improvements and innovative designs.
For more information information about Pirelli's range of Fire Performance cables and accessories, check out www.pirelli.co.uk
Gordon McKinnon is currently the FP Product Manager for Pirelli Cables Ltd. With nearly 10 years experience in the industry, both in the UK and mainland Europe, has been heavily involved with all aspects of fire performance products and their testing.
Pirelli Cables Ltd.,
PO Box 6, Leigh Road,
Eastleigh, Hants S050 9YE
Tel: +44 (0) 23 8029300 (0)
Web: www.pirelli.co.uk
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