Safety, reliability and quick intervention are the characteristics behind the design of the new Mont Blanc Tunnel fire-fighting system, which is about to be completed. After roughly two years from the tragic event that led to the closure of the tunnel connecting Italy with France, it is scheduled to open this September. The difficulties that arose involved working and manoeuvring space, temperature ranges and the performance required of the system in relation to the size of the tunnel to be protected. The 12km long duct consists of pipes measuring 219.1 and 114.3 millimetres in diameter and 3 and 4 millimetres in thickness, with an overall weight of 220 tons, lined on the outside with an 80mm layer of polyurethane resin. The special EN 1.4404 (AISI 316L) stainless steel ducts were welded using both the TIG system and the LASER system. The non-destructive eddy current controls envisaged under the standards exclude the possibility of any loss during operations as they have to support pressure of up to 25 bars. The ducts are placed inside the tunnel’s service gallery. They can ensure a capacity of over 120,000 litres of water per hour, by connecting the four pump stations, the 84 intakes and the 37 shelters envisaged under the tunnel’s new safety system.
