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French super tunnel installs high-tech water mist system
Published:  01 January, 2007

The first section of the A86 West tunnel, the missing link in the Paris ‘super-ringroad’ is to be opened in October 2007. Built, financed and operated by Cofiroute, this 10km tunnel linking Rueil-Malmaison and Versailles will revolutionise traffic flow in the West Paris region.

The first section of the A86 West tunnel, the missing link in the Paris ‘super-ringroad’ is to be opened in October 2007. Built, financed and operated by Cofiroute, this 10km tunnel linking Rueil-Malmaison and Versailles will revolutionise traffic flow in the West Paris region.
With a particularly innovative design, made up of two superimposed road levels - one in each direction - and reserved for light vehicles, this tunnel will be equipped with the latest safety devices, exceeding the requirements of the new regulations concerning safety in tunnels.
This is the context in which an active firefighting system is being installed in the tunnel. Under the terms of the examination of the safety concept, the administrative monitoring commission requested trials and assessment of the effectiveness of a fixed water spraying system. The contractors deemed it useful, in the context of completing the A86 West as validated by the government, to install a fixed water fog system to limit and contain the spread of a fire. The system will reduce ambient temperature, facilitate the evacuation of motorists to the emergency exits located at 200-metre intervals, and improve the conditions for the emergency services arriving on scene.
The contract was awarded to the Marioff Corporation, world leader in water mist firefighting systems, by Socatop (Société de Construction de l’Autoroute de Traversée de l’Ouest Parisien), acting as designer/builder for Cofiroute (franchise holder for the A86 motorway).
This decision could result in significant modifications to the safety equipment and procedures used in European tunnels. In-depth studies have already been conducted with the aim of complementing passive safety equipment in tunnels, such as escape routes, with active firefighting systems but, until now, these have only been used in trials and small-scale applications.
The final section of the A86 West of Paris is the first major installation of a fixed firefighting system in Europe. As it will also be the largest water mist fire protection system ever built, it will be an interesting example for the transport ministries in the various European Union member states.
Petteri Saarinen, President of Marioff, explained: “The decision by Cofiroute and Socatop to invest in an active firefighting system for the A86 could, in the future, set a new standard in terms of safety in road tunnels. We are very proud to be associated with this major project. This firefighting system, combined with the innovative design and operation of the tunnel, will ensure an optimum level of safety, for the clients and the emergency services as well as for the tunnel infrastructure.”
The contract is for the design, manufacture, installation and maintenance of a fixed water mist firefighting system. This is sub-divided into sectors, throughout the length of the tunnel (10 km long on two levels, each level with two traffic lanes and a hard shoulder). The fire protection technology developed by Marioff was selected after two intensive trials. The company’s references in this sector of activity influenced the choice of the solution selected.
The HI-FOG safety system to be installed uses patented high pressure nozzles, which spray very fine droplets of water over uniformly-sized tunnel sections 33 metres long. Three sections will be triggered simultaneously in order to cover a zone about 100metres long around the seat of a fire. The water droplets rapidly absorb the heat, particularly by evaporation, giving very effective cooling.
They greatly reduce the amount of smoke a fire gives off, by limiting the development of its heat intensity. This contributes to safer evacuation of persons present and saves lives during the first critical phases of a fire, and also gains time to allow the arrival of the emergency services to contain and totally control the fire and extinguish it.
Water mist, composed of millions of fine droplets, is a very effective way of using water to extinguish a fire. This technology was originally developed to combat emergency situations on board ships.
In more than 5,000 fire trials under operational conditions, conducted over more than a decade, water mist generated by HI-FOG technology has proved extremely effective for extinguishing fires. Compared, for example, to a conventional spraying system, HI-FOG technology uses ten times less water, thus increasing the capability of the system to combat big fires, while minimising the risks of spreading fuel around.