‘First class’ fire safety for Kings Cross’ Canal Tunnels

As part of the £6 billion Thameslink Programme, a new rail link is being created allowing passengers to travel for the first time from Peterborough and Cambridge, directly to Blackfriars and then on to Brighton.

In order to achieve this outcome, the programme is linking the East Coast main line north of Kings Cross station and the Thameslink route at St Pancras station via two new parallel rail tunnels in north London that are each over 650m in length. The tunnels pass about 15 metres under the Regents Canal and so have become known as the Canal Tunnels.

As a result, trains travelling through these Canal Tunnels will provide up to eight of the possible 24 services an hour which will travel through central London when the Thameslink Programme is completed in 2018.

These tunnels were bored at the same time as the redevelopment of St Pancras station to accommodate HS1 and Eurostar services between 2004 and 2006.  In 2012, Carillion was named as the principal contractor for fitting out the tunnels and connecting them to the main lines. Track, power, signalling and safety systems are now being installed to permit Thameslink trains to run through the tunnels.

Arup was appointed for the design work and specified a fire-resistant Connection Box system to provide lighting along both tunnels.  In turn, LPA Connection Systems was asked by Arup to use a proven product which had been installed for providing emergency lighting in the Service Tunnel of the Channel Tunnel.

AEI Cables’ products were utilised to provide the cabling of lighting for the tunnels.

Solution:

Firstly, high performance S1085 (Fire performance of materials) compliant cables were required to deliver power while meeting the Codes of Practice. AEI Firetec Power is a long-established armoured power cable with a long track history, so this was utilised for the fixed line cabling.

The tap-off cable needed to be flexible and fire resistant for the rail environment so AEI Firetec FRF2 was the ideal solution. Originally developed for London Underground for just these lighting applications, the cable is flexible and meets S1085 and the Codes of Practice requirements.

Secondly, the cost-effective solution comprised a sealed and robust stainless steel box for reliable service under the harsh conditions associated with tunnel applications such as damp, heat and rodent attack. The boxes, spaced every 4 metres, provide a tap-off from the armoured power supply cabling installed along the tunnel.

To provide the tap-off for the luminaires, a fire-resistant LPA metal socket was mounted on the connection box and an in-line fuse added to internal wiring between the socket and a ceramic terminal block connecting the main circuit.

The mating fire resistant LPA metal plug was also supplied so that it could be wired to the luminaire spur cable and so provide quick plug-and-play connections to the luminaires as they were installed along the tunnels.

AEI Cable’s armoured Firetec Power SWA was used between the junction boxes, with Firetec FRF2 flexible cabling installed between the connection boxes and the light fittings.

Outcomes:

With the connector and in-line fuse pre-wired under controlled conditions and 100% end-of-line tested in LPA’s factory prior to delivery, the box assembly provided quick and reliable on-site assembly without the need for special tools or skilled personnel.

Fire resistance of the Connection Box was provided to the same high levels as the cable specification (BS 6387 Categories C, W and Z), which requires that electrical continuity is maintained after three hours at 950°C as well as testing with water and impact.

The luminaire spur connection is provided via the proven Niphan metal clad connector which has long been a favourite in London Underground stations, of which the standard range carries its own LU APR listing under Registration number 158.

Benefits of the system include:

  • Compatible with earthing of armoured cabling
  • IP66 rating
  • Low smoke and toxicity
  • Fire resistant to +950°C, BS 6387 Categories C, W and Z
  • Quick connection of luminaire to the main lighting circuit.

Author: Cable Technology News Team

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