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Fire Resistant Fixings

It is not often that a coroner’s report makes specific recommendations on how a particular technical standard should be altered, so when this happens there is a very strong imperative on industry to react. The changes to the 17th edition of Wiring Regulations that were published in January 2015 and will come into effect on 1st July 2015 represent one such incident.

The revised regulations are also known as BS 7671: 2011+A3:2015 – Requirements for Electrical Installations and now include a specific requirement for fire resistant cable fixings to be used in escape routes and critical areas within public buildings.

The need for such a revision was highlighted in a tragedy that occurred in April 2010 when two fire-fighters, called to attend a fire in a block of flats, died from sudden exposure to intense heat after becoming ensnared in electrical cabling. The coroner’s report reviewed a series of possible actions that could address a number of contributory factors in this tragedy, but was unequivocal in his observations on the issue of cable fixing.

The recommendations reinforce the need for fire resistant fixings for fire detection and fire alarm systems (now covered by the new BS5839-1) but went further in highlighting the need to ensure that all cable used in escape routes (BS 7671: 521.11.201) should be fixed in such a way that the cable does not cause a hazard.

The report highlighted serious failings in the electrical cable support system. It explained that as the trunking softened or melted in the heat it allowed the contained cable to fall free. “Surface mounted electrical cabling was encased in plastic trunking which failed when exposed to heat so releasing cables. These cables then became a hazard to fire-fighters.”

The suggested resolution to this issue was spelled out in the coroner’s recommendations:

“It is recommended that Building Regulations are amended to ensure that all cables, not just fire alarm cables, are supported by fire-resistant cable supports. This could be achieved by an amendment to BS 7671: 2008 Requirements for Electrical Installations.”

This standard (otherwise known as the Wiring Regulations 17th Edition) is regularly reviewed by a committee made up of representatives from both the Institute of Engineering and Technology and the British Standards Institute. Prysmian’s view on the subject has always been to support the introduction of fire resistant fixings and the latest revision to the 17th edition – Amendment 3 – includes this change.

Image courtesy of the Prysmian Group

Image courtesy of the Prysmian Group

Amendment 3 provides a degree of enhanced fire risk protection which will see the phasing out of plastic cable clips, non-metallic cable ties or plastic trunking as the sole means of support for wiring systems. It now requires that all cable in risk areas must now be installed with a suitable fire-resistant means of support/retention.

A recent guidance document from the IET (Wiring Matters 54) has also added the recommendation that any Fire-resistant supports be fixed at regular intervals to a non-combustible substrate of the building.

Following the publication of the amendment on January 1st this year, industry has had a six month transition period to get up to speed with the changes and has been able to design, install and certify to either the new or previous standard. Any electrical installation designed after 1st July 2015 must comply with the updated regulations.

Prysmian cables fully supports the introduction of fire resistant fixings for all cables installed in escape routes and the company’s own range of products includes fixings developed for use with specific cable types. The technical team has developed a range of fire-resistant fixings which are manufactured using non-combustible materials including stainless steel copper and cast iron.

Prysmian has worked in conjunction with ITW Construction Products, manufacturers of gas nailing technology, to produce the FP Firefix System. This enables gas-nailing technology to be used to install fire performance cable supports directly to a wide range of substrates including concrete, steel, composite steel decking, masonry and block-work.

As a general rule, fire resistant cables can also be fixed with copper, stainless steel or galvanised cast iron fixings, such as Prysmian’s Bicon range. These are suitable for most electrical cable installations and will be the most appropriate fixings for cables in the public spaces included under the changes to the Wiring Regulations. Note: aluminium is not recommended because of its relatively low melting point.

Prysmian has been ready for the change for some time and the Prysmian FP website has a series of guidance documents that include suitable fixing advice for fire performance cables. These same guides can be referenced for suitable fixings to meet the changes for non-fire resistant cables installed in escape routes in the Wiring Regulations. These documents including;

Guidance documents to these British standards are available for download from: http://www.fpcables.co.uk/supporting_documents.html.

For more information, go to uk.prysmiangroup.com

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Jonathan Rawlinson is Technical Manager at the Prysmian Group.

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