The flame trap for tunnel safety
WHAT GREENPIPE WAS ASKED FOR
European Directive 2004/54, transposed in Italy in 2006 (with Legislative Decree no. 264/2006), established minimum safety requirements for road tunnels, so measures have been taken to adapt tunnels to these requirements.
For tunnels longer than 1,000 metres, jobs involve, inter alia, the construction of a drainage system for hazardous liquid spills.
To this end, Greenpipe was asked to design and implement a drainage solution for the A23 Motorway, having as its main feature that of preventing the spread of fires caused by flammable fluids.
Greenpipe designed and implemented a solution that proved to be applicable to many other cases.
To date, in fact
8 motorway sections
involved (A1, A14, A23, A26, A12, A16, A10, A7)
170 i km
of adapted motorway tunnels
THE GENERAL CONTEXT
Since a tunnel is a covered stretch of road not subject to direct rainfall, it normally features a different drainage system to that of an open road, which is designed to drain mainly rainwater conveyed by cars or caused by infiltration from surrounding areas.
Regulations required solutions which would also permit collecting up flammable liquids from accidental spills (e.g. spillage of fuel from vehicles in the event of an accident or from tankers) and able to effectively prevent the spreading of flames in the event of fire, as well as collect up water from the fire-fighting system.
THE PROJECT AND FINDING THE SOLUTION
A major construction company specialising in infrastructure and civil and industrial building works contacted Greenpipe and asked for a solution to upgrade 26 km of tunnels on the A23 motorway in the Udine South -Tarvisio section managed by Autostrade per l’Italia.
More specifically, the project involved 5 tunnels (Del Lago, Campiolo, Maggio Udinese, Zannier and Raccolana) that needed to be upgraded in accordance with regulations and for which Autostrade per l’Italia had designed a suitable drainage system chematically made up of:
- a gravity collection system for water infiltrating through the rock walls;
- flame traps that collect up the liquids spilled onto the road surface in order to reduce the size of the puddle of liquid and prevent flames spreading to other parts of the tunnel;
- an underground pipe that runs along the entire length of the tunnel, into which the fluids run;
- special traps outside the tunnels by means of which the underground pipe is intercepted. Inside these traps is a system of probes able to detect the presence of hazardous fluids and, if necessary, provide an alarm to the system for their correct management: this allows direct drainage into the final vessel or, in case of the actual presence of dangerous fluids, their conveyance to a storage and treatment tank.
In particular, Greenpipe supplied the flame traps to be installed, in accordance with the project of Autostrade per l’Italia, every 30 or 50 metres (depending on the conditions existing in each tunnel), along the entire shoulder, and to be connected via cross-pipes to the dorsal line, i.e. the underground pipe.
THE SMART PRO 150 SIPHON FLAME TRAP
For its project, Autostrade per l’Italia required a product with characteristics that we found to match those of our Smart Pro 150H210 drainage channel. From this product, with the appropriate modifications studied and perfected by the Greenpipe Technical Department, the flame trap was created, which combines all the main features of the channel and those of its accessories:
The trap body consists of the above-mentioned channel, i.e. the Smart Pro 150H210, made of vibro-compressed concrete and steel fibres, with high resistance to compression (Rck > 45N/mm2), to freeze/thaw cycles in the presence of stagnant water containing de-icing salts and to aggression due to atmospheric agents, to which the galvanised steel containment profiles for the gratings are firmly anchored;
P-SHAPED SIPHON and FILTER
The bottom of the channel is perforated and features an additional external pipe of suitable length and a diameter of 110 mm anchored to the channel body with a single- component polyurethane sealant with high elastic modulus for joints.
A P-shaped siphon Φ110 is connected to the additional pipe in the lower protruding part and, in the upper part (i.e. inside the channel), is an anti-debris and anti-rat filter. The connections to the additional pipe of both the siphon trap and the filter are made via a socket joint with NBR gasket. The additional pipe, the P-shaped siphon and the filter are made of AISI 316 stainless steel.
Two Smart 150 spheroidal cast-iron GJS 500/7 class D400 drainage grids are screwed to the channel.
At both ends, the channel is fitted with two galvanised steel plates inserted under pressure in order to close and compartmentalise the product.
The connection of the trap to the main underground pipeline, or dorsal line, is made by means of cross-pipes (not supplied by Greenpipe) which start from the P-shaped siphon and intersect it.
The 3D and 2D graphic design was screened by Autostrade per l’Italia’s engineers, who also validated it in the light of technical assurances which Greenpipe, after initial prototyping, was able to provide regarding the water flow rate that can be drained off, the type of gaskets used and the type and thickness of the stainless steel.
THE FLAME TRAP PRINCIPLE: THE P-SHAPED SIPHON
The purpose of the trap is to prevent flames spreading inside the underground drainage pipe. This is ensured by the P-shaped siphon and by the presence of water inside its “gooseneck”.
Each trap, normally installed at a distance of between 25 and 50 metres from the next one, is linked to the main drainage pipe that runs along the entire tunnel and the shape of its gooseneck siphon ensures the insulation of the flame trap from the rest of the drainage system, preventing the spreading of any flames.
THE MAIN FEATURES OF THE SIPHON TRAP
WATER RUNOFF RATE – 6.67 litres a second,, certified by Istituto Giordano laboratories.
NON-COMBUSTIBLE MATERIALS RESISTENT TO HYDROCARBONS
HIGHLY RESISTENT GASKETS
TOP-QUALITY RAW MATERIALS
Thanks to the combination of several factors and the design of a system based on a simple but complex principle, Greenpipe has been able to contribute to the long process of modernisation and safety of the Italian motorway network, in particular the tunnels, which have always been seen as “inhospitable” and dangerous places.