Cable standards in the firing line
Cabling has the potential to be the Achilles' heel of a fire detection system if the correct cable is not installed, or if it falls short of the performance it is expected to deliver. Draka’s Mark Froggatt raises the alarm on a number of issues that should concern us.
Concerns about the use of sub-standard fire-rated cable – usually originating outside of the EU – continue unabated, despite the widespread publicity on the issue.
The problem seems to have its origin in the fluctuating and often escalating price of copper, which prompted some unscrupulous manufacturers to cut corners and use less copper in the manufacturing process. From there the situation deteriorated, and there have been instances where materials other than pure copper, such as steel wire, copper-coated aluminium or badly recycled copper have been used. Cable is now turning up that is incorrectly constructed, resulting in a serious detrimental impact on the safety and reliability of fire detection and alarm systems, and emergency lighting installations.
The reality of the current situation is that, if the cable is not third-party approved, there is no guarantee that it is manufactured to the standard being claimed for it. It is the only way to be confident that the cable being supplied today is built exactly to the same standard and specification as the cable that was originally tested and approved. This is important even when buying cable from a well known manufacturer. Earlier cable from that supplier may have been up to standard, but re-sourcing materials and accepting a different specification, changing the formulation of the coating or sheathing, or modifying the design can affect the performance of a cable that still proudly – but now erroneously – bears a BS or EN compliance mark.
Document B compliant cable
The use of rogue cable is not the only issue that needs to be addressed. An important fire safety provision of Clause 5.38 of Volume Two (buildings other than dwelling houses) Protected Power Circuits of Approved Document B (Fire safety) to the Building Regulations does not appear to be universally understood, applied or enforced other than – inexplicably – in the London area.
According to Clause 5.38: ‘In large or complex buildings there may be fire protection systems that need to operate for an extended period during a fire. Further guidance on the selection of cable for such systems is given in BS 5839-1, BS 5266-1, and BS 7346-6.’ However, cables are still regularly being specified and installed for these safety-critical installations that do not comply with the stringent requirements of BS 7346-6.
Clearly, the aim of Clause 5.38 is to ensure that there is a robust power supply in any building where life safety is dependant upon the reliable operation of active fire precautions or electrically-operated passive measures. So why is the correct cable not being installed? Is it a failure to understand the importance of Clause 5.38, or confusion as to what a ‘large or complex building’ is? It cannot be a lack of BS 7346-6 compliant cable because cables are available (such as Draka’s Firetuf Powerplus) that satisfy the demanding requirements of Clause 5.38 and are third-party accredited.
BS 9999 and the Category F2 myth
The importance of specifying and installing the correct fire performance cable where safety regimes are entirely dependant upon the continued supply of electrical power should a fire break out is also enshrined in BS 9999:2008. [Code of practice for fire safety in the design, management and use of buildings]. In clause 38.2.3.2 [Protected circuits for the operation of equipment in the event of fire] it clearly states that, where the power supply to electrical equipment is required to operate in the event of fire, the wiring systems should conform to one of three specific recommendations.
One of these options is to use mineral-insulated, copper-sheathed cable conforming to BS EN 60702-1 [Mineral insulated cables and their terminations with a rated voltage not exceeding 750 V. Cables] and meet the fire safety performance objectives given in BS 7346-6 [Components for smoke and heat control systems. Specifications for cable systems]. However, while this type of cable is certainly robust and long lasting, both specifiers and installers have moved away from mineral insulated cables due to their high cost. They are also difficult and costly to terminate, and their declining use has meant that the skills required are fast disappearing. Mineral insulated cable manufacture has all but disappeared from the UK, and the quality of imported cables has become suspect and supply problems are often being cited as an additional reason for their not being used.
A second option given in BS 9999 is to adopt passive fire safety measures – such as walls, partitions or floors with a fire resistance of not less than that required for the building – to protect the cable against exposure to fire, which frequently is not a viable or practical solution.
This leaves the third option, which is to use cables that meet the relevant life safety and/or fire safety performance objectives in 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]. This means that, contrary to some assertions, Category F2 cable is not acceptable for these protected circuits in BS 9999 or Approved Document B, as it complies only with a less demanding requirement of BS 7846 [Electric cables. 600/1000 V armoured fire-resistant cables having thermosetting insulation and low emission of smoke and corrosive gases when affected by fire]. Indeed, its status is made clear in the Draft for Public Comment of the latest planned revision of BS 7846, namely that Category F2 is the ‘minimum fire resistance requirement’ for life safety, property protection, fire fighting and business continuity applications.
Category F2 cable separately measures resistance to fire, resistance to fire with water spray, and resistance to fire with mechanical shock, while cables complying with the new F30, F60 and F120 categories measure in combination the resistance to fire with direct mechanical impact and water jet. Its retention in the Standard is due solely to its use in non-UK-regulated export markets.
Indeed, there is no mention of Category F2 cable or a ‘less-onerous’ category in BS 8519 [Code of Practice for the selection and installation of fire resistant cables and systems for life safety and fire fighting applications] which is currently at the committee stage. This will include a detailed matrix where each fire safety equipment application is categorised as F30, F60 or F120, stipulating the need for Firetuf Powerplus type of cable for every application.
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