What we were asked to do
The A32 Turin-Bardonecchia Motorway is a major communication artery between Italy and France, on the Turin-Lyon route managed by SITAF SpA – Società Italiana Traforo Autostradale del Frejus.
To bring the section into compliance with Legislative Decree 264/2006, it was necessary to intervene in the following tunnels: Prapontin (4.4 km), Cels (5.2 km), Giaglione (2.5 km), Ramat (1.4 km), Serre La Voute (2 km) and La Perosa (1 km).
Greenpipe was requested to create a system capable of ensuring effective prevention of flame propagation in the event of spillage of flammable liquids.
Greenpipe could already boast significant experience with flame traps, gained in other areas with high tunnel density, including, to name a few, the A23 Udine-Tarvisio (click here to read the dedicated case history), various sections of Ligurian motorways, and the Abruzzo section of the A14.
The context
The A32 motorway is a 72.4 km stretch of asphalt connecting Italy and France via the Frejus Tunnel.
Its route develops in an Alpine natural context of extraordinary beauty, but at the same time rugged and complex, featuring numerous tunnels.
European Directive 2004/54, implemented in Italy through Legislative Decree 264/2006, established minimum safety requirements for road tunnels, requiring a risk analysis associated with a specific tunnel to identify hazard sources and define appropriate safety measures.
In particular, for tunnels longer than 500 m, works are required concerning the implementation of drainage systems for any hazardous liquids spilled. Where the transport of dangerous goods is authorized, “the drainage of flammable and toxic liquids must be carried out through specially designed drainage channels or other devices within the tunnel cross-sections.
Such drainage systems must be designed and maintained in operation to prevent fires and the spread of flammable and toxic liquids.” These requirements are so binding that if existing tunnels cannot meet these requirements, authorities must take this into account when deciding whether or not to authorize the transport of dangerous goods.
The project
Generally installed at a distance of approximately 30 meters from each other depending on the conditions of the various tunnels, the function and utility of flame traps are defined by their very name: preventing the spread of flames.
Connected, through transverse fittings, to the main drainage pipe—that is, the collector that, in most cases, runs beneath the roadway along the entire tunnel—flame traps fulfill their function thanks to the presence of an appropriate siphon system inside them.
Any spillage of flammable liquids on the asphalt requires rapid and efficient disposal, so the system includes a short section of grates for their absorption and, downstream of this, the flame trap that acts as a barrier against flame propagation.
The “siphoned” configuration of the manhole, at the bottom of which water must always be present, is capable of stopping oxygen access and consequent combustion due to lack of air exchange.
The initial project, developed by the design firm under SITAF, provided for the use of stainless steel flame traps with cast iron grates and/or covers secured with stainless steel screws.
These manholes differed from the standard ones produced by Greenpipe, namely the SMART PRO 150 FLAME TRAPS.
Therefore, starting from the initial drawings received, we set to work to develop a detailed project and present our version of the structure which, in collaboration with the technicians of the companies involved in executing the works, was repeatedly revised to adapt it to tunnel conditions and mechanical resistance specifications.
Thanks to on-site inspections and periodic technical meetings, we realized that the space available for installing the manholes was less than that provided in the initial project, which made it necessary to reduce the dimensions of the structure.
Not only that: the tunnel carriageways are narrower than those of a standard motorway section and the visible upper part of the various elements was very close to the white lane demarcation line. To minimize the risk of deformation or breakage of the manholes and grates due to traffic, it was necessary to add reinforcement rings inside the sheet metal structure.
At the same time, thanks to Greenpipe’s strong inclination toward the world of foundries and the design of cast iron grates and/or covers, specific D400 class closure elements were designed for these construction sites.
Greenpipe's solution: three different flame traps
We designed flame traps in three types: single-chamber, dual-chamber, inspection.
The single-chamber model, available in “right” and “left” versions, is complete with a D400 spheroidal cast iron grate and performs the “flame trap” function. The dual-chamber model, also available in “right” and “left” versions, has two non-communicating compartments, one equipped with a grate with “flame trap” function and one equipped with a cover with “inspection” function. The inspection model is equipped with a cover and has the “inspection” function, as is easy to understand.
The differentiation between “right” and “left” models is related to the installation location, i.e., whether the manhole is positioned in the “driving” lane or in the “passing” lane, as well as the direction of travel (“uphill” toward Bardonecchia, “downhill” toward Turin).
Project figures
Greenpipe was commissioned, for the six tunnels totaling 16.5 km (approximately 23% of the total A32), to supply 1,152 flame traps divided into the three versions: single-chamber, dual-chamber, and inspection.
The construction sites are still in progress.
Drawing on the experience gained in over 25 years of activity and thanks to the design capabilities that have enabled the development of a wide range of products suitable for every type of application, Greenpipe is increasingly positioning itself as a reference point for anyone in the industrial, business, and engineering fields interested in drainage and water treatment.
