Eurotunnel fire fighting system - TunnelTalk
Fire fighting system unveiled by Eurotunnel Feb 2011
Patrick Reynolds, Freelance Reporter
Costly fire events in the running tunnels of the Channel Tunnel could be a thing of the past. A new in-tunnel fire suppressing system is being installed to provide a substantially more effective operating strategy for active fire-fighting any future events in the sub-sea rail link between UK and France, owned and operated by Eurotunnel. After suffering two serious freight shuttle-train fires over its operating life, something had to be done to better address the fire risk and its severe and costly consequences to tunnel infrastructure. Patrick Reynolds reports from a live demonstration of the new system.

Damage caused by the 1996 freight shuttle train fire

Eurotunnel has unveiled a new, active fire safety system for the Channel Tunnel using fine water-sprays housed in four fixed 'stations' to help limit costly infrastructure damage from blazes on freight shuttle trains, such as happened in 2008 and resulted in five months of restricted operations, costly repairs and higher insurance premiums.
Construction and installation work on the four in-tunnel fire suppression stations is well advanced, including tunnel breakouts and new excavations, and Eurotunnel anticipates it should be fully operational by the fourth quarter, possibly earlier. The water-mist system is being commissioned in stages and on completion of each 870m long station. All four stations could be installed by mid-year.
The system – called SAFE Stations, and for which Eurotunnel has applied for a patent – has been developed and is being installed at a cost of slightly more than €20 million (US$27.25 million). Stations are located in each 7.6m i.d. running tunnel, opposite each other, and slightly farther offshore than the crossovers from the English and French coasts.
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The fixed link between UK and France is 53km long, and was opened in 1994. The single track running tunnels have a service tube between them, and all three are joined every 374m by cross passages. The running tunnels crossover in two locations, at about the third points along the route.
Each fire-fighting station has two water pipes with specially designed nozzles that run at high level along each side of a running tunnel so that spray can cover trains rapidly. The nozzles are installed at 3m centres and the supply system delivers water to those points at 115 bar pressure. The result, from tests, can be a reduction in temperature of about 650-1000°C within a few minutes.
Fire incident protocols in the Channel Tunnel require passenger shuttles and other passenger transit trains, such as Eurostar services, to be driven out of the tunnel should an event happen. But freight trains stop, and the experiences of fires in the north running tunnel in September 2008, and previously in 1996 in the South tunnel, had major capacity and financial impacts on services, operations and businesses.

High pressure water-spray at the heart of four Eurotunnel SAFE Stations

Eurotunnel said the new system is aimed at providing greater protection for the tunnel infrastructure – its concrete lining as well as its mechanical, electrical and signalling equipment. It was not initiated due to safety concerns. Procedures for addressing incidents on passenger vehicle shuttle-trains are approved by train operating authorities and the process for evacuating staff and truck drivers from their special carriage on freight shuttle-trains have proven their effectiveness. There were no fatalities or serious injuries as a result of the previous two fire incidences.
While design of the overall fire-suppressing concept and much detailed work has been undertaken in-house by Eurotunnel, the infrastructure owner and operator has worked with a consortium of specialist firms on the detail and the installation. German fire-safety firm Fogtec with its Hungarian partner that specialises in water systems, with French electrical installation contractor Spie, have contributed to the project and have drawn upon the consultancy services of Ifab.
The concept of the water-mist system is to provide two actions as the suction of a blaze draws in air and also fine droplets: first, to create a cloud effect that will help reduce heat radiation, which can enable emergency services crews to get closer to the seat of a fire; and, secondly, to absorb a lot of heat energy as the water evaporates and form steam as a consequence. The significant volume increase in the moist air caused by the formation of steam results in a blanket effect that rapidly chokes off the flow of air and suffocates the blaze.

Mock-up trials of the SAFE Station water-mist system in Spain

Tests of the new SAFE water-sprays were performed last year in Spain in April, and then in November in the Channel Tunnel, on a 120m long prototype station. The only actual fires used in tests were in existing, specialist test tunnels at San Pedro des Anes in the Asturias area of Spain. Beginning with a series of small tests, the programme progressed to benchmark fires of 100MW, 150MW and 200MW, representing different sizes of potential lorries fires on freight trains.

Excavation of a pump equipment room

In the Channel Tunnel, the SAFE stations are each formed of 29 sections, each 30m long. These sections are sized to match the lengths of train wagons. In operation, the water-mist system would be centred on the section nearest the blaze on a train that had been taken to the station and stopped for fire suppression and evacuation. The spaying sections immediately either side would also be activated.
About 1 to 2 minutes after the train stops, and the fire location has been automatically determined, the water-mist comes on automatically and is not turned off until decided by fire fighters.
Key aspects of Eurtunnel's patent application for the SAFE Station concept are the combination of fire detection and fire fighting.

Schematic of the Channel Tunnel layout

The fire-fighting system is based on intense water-mists to douse fires, and the detection section is based on using two separate methods in parallel - thermocouples and fibre optics – to provide a crosscheck and accuracy.
Freight trains are designed to resist fires for 30 minutes, and the SAFE Stations can be reached within 15 minutes, said Eurotunnel. In comparison, a scheduled crossing of the entire tunnel is 35 minutes.
New tunnelling works have been undertaken to make way for the SAFE stations, though nothing significant in the running tunnels. The works were undertaken from the service tunnel to bore the 160mm diameter drill-hole connections, at 60m intervals, to carry the water supply pipes from the service tunnel to feed the thin nozzle pipelines along the running tunnels. With competent chalk marl at the locations, it was clear that ground conditions were suitable also for excavation of pump equipment rooms.

Cross-section of the water-spray region in a running tunnel

The equipment rooms are located between the service and running tunnels, and excavated via service tunnel access. Before excavation, the stability of concrete rings at the locations was ensured with arrays of rock anchors up to 4.6m long. The room openings were created by diamond-cutting through the concrete segments and excavating the chalk marl with mini breakers and roadheaders. The rooms were then lined with reinforced concrete.
Tunnelling and installation work is being undertaken during planned maintenance periods overnight at weekends. All four SAFE Station sites are being worked on concurrently. The pair closest to France are the most advanced with equipment installation underway, while those nearer the UK are completing the civil works.
More than 300 trains per day run through the Channel Tunnel and more than 250 million passengers have travelled on the sub-sea link between Britain and France, almost half travelling by Eurostar. There have been no major accident or injury to passengers.
References
Eurotunnel back to full capacity - TunnelTalk, February 2009
Polypropylene fibres to resist fire-induced concrete spalling - TunnelTalk, November 2010
UK rail from the Channel Tunnel and beyond - TunnelTalk, December 2010
Channel Tunnel in hindsight - TunnelTalk, February 1993

           

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