Code raised the bar on cable fire safety
The publishing last year of BS 8519:2010 Code of Practice has led to a number of misleading claims being made for some cables, with the confusion appearing to have arisen from a misinterpretation of the different test methods required for power and control cables. Draka’s Mark Froggatt explains.
BS 8519:2010 [Selection and installation of fire-resistant power and control cable systems for life safety and fire-fighting applications. Code of Practice] replaces BS 7346-6:2005 [Components for smoke and heat control systems. Specifications for cable systems]. Among other changes it calls for power cables – cables connecting a device to the power supply – to be tested in accordance with BS 8491:2008 [Method for assessment of fire integrity of large diameter power cables for use as components for smoke and heat control systems and certain other active fire safety systems] that itself replaced BS 7346-6: 2005.
This new Standard aims to ensure that the level of circuit integrity is not compromised by other components of the whole electrical distribution system, including cable glands, terminations, joints and cable support systems. It covers: the source of supply; the high and low distribution voltage; the appropriate location of the main intake enclosure, high-voltage and low-voltage switchrooms, transformer rooms, generator rooms, risers, fire life-safety plant rooms and firefighting / evacuation lift motor rooms and shafts.
But what inspired the creation of a new Code of Practice?
The main drivers were the increased size and height of many high-rise and complex buildings, the sophistication of the active fire protection installed in many buildings, and the adoption of fire engineered solutions; solutions that demand a high level of reliable performance from building services, including the electrical supplies. In the UK, this change was set in motion by the Regulatory Reform (Fire Safety) Order 2005 that heralded in an entirely new approach to fire safety. In place of being told what they must do in terms of fire safety in a building, designers were told what must be achieved.
This Order was followed in 2007 by Approved Document B of the Building Regulations of England and Wales, where certain “large or complex” building structures were singled out: “Where it is critical for electrical circuits to be able to continue to function during a fire, protected circuits are needed. The potential for damage to cables forming protected circuits should be limited by the use of sufficiently robust cables ….” These cables have to achieve a 120 minute rating when subjected to integrated fire performance testing.
The main changes, when comparing BS 8519 with the now withdrawn BS 7346-6 were an expansion of content to include all life safety and firefighting systems – not only smoke venting and firefighting cores, and the inclusion of new and revised technical guidance relating to the selection and installation of fire-resistant cables and systems for life safety and firefighting applications.
BS 8519 also makes reference to the recommendations identified in BS 9999 [Code of practice for fire safety in the design, management and use of buildings] with regard to the design and installation of the electrical distribution systems and the design, management and use of buildings to achieve acceptable levels of fire life-safety for anyone in and around buildings.
Significantly, in terms of cable selection, BS 8519 identifies three categories of circuit that are required to maintain their integrity under defined fire conditions for fire survival times of 30 minutes, 60 minutes and 120 minutes. Appropriate cable tests are identified for each category, giving the relevant British Standard for the assessment of cable performance under fire conditions that might be expected in an actual incident.
Traditionally, the solution would have been to use mineral insulated cables [MICC] that incorporate insulation of highly-compressed MgO [Magnesium Oxide]. These cables are undeniably a robust and long lasting solution, but they are costly, difficult and expensive to terminate, and the quality of some imported mineral insulated cables has become suspect. Supply problems are also often cited as an additional reason for their not being used.
Currently though there are believed to be at least two cables available on the market that can justly claim to be viable alternatives to mineral insulated cables that meet the power cable requirements of BS 8519:2010. One of these is Draka’s 600/1000V Enhanced grade FTP120 cable – until recently called Firetuf Powerplus. This is an LPCB [Loss Prevention Certification Board] third-party approved SWA [Steel Wire Armoured] power cable that achieves BS 8491’s highest integrated-testing 120-minute rating.
This demanding integrated testing regime involves flame irradiation exposure, direct impact and high-pressure water spray testing for cables that are destined to provide a secure power supply that will retain its integrity in the event of fire for a whole raft of fire safety systems. These include: automatic fire suppression installations; fire detection and alarm systems; fire compartmentation; smoke control and ventilation; sprinklers and wet risers; ventilation and shutters; and firefighting lifts. The test incorporates 115 minutes of direct mechanical impact followed by five minutes of the application of water – in five-second bursts – at a pressure that equates to that of a fireman’s hose.
Somewhat alarmingly, cables are being promoted as complying with the new Standard and hence suitable for power applications that have been not ratified in accordance with BS 8491. These cables have been tested in accordance with BS EN 50200:2006 [Method of test for resistance to fire of unprotected small cables for use in emergency circuits] and are suitable only as control cables – cables that carry information as inputs and outputs. So, great care should be taken to ensure that claims of compliance are not misleading.
Like any Code of Practice, the aim of BS 8519:2010 is to encourage best practice and takes the form of guidance and recommendations. So, any company claiming compliance with a Code is expected to be able to justify any actions that deviate from the Code’s recommendations. Installing a cable that has not been tested to the required power cable regime is a high-risk decision that could have dire and expensive consequences.
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