Guaranteeing That Tunnels are Sealed Effectively for Carrying Hazardous Materials
Managing the risks associated with transporting hazardous goods through tunnels is high on many countries’ agendas. Disasters and near-accidents have ensured that many of these nations are imposing stricter requirements on the fire-resistance of tunnels used to transport hazardous goods. Among these are the transportation of oil, petrol, gas or chemical products.
The fire-resistance covers not just the tunnel itself, but also the systems used to seal the transit openings for cables and pipes. Constructional openings such as escape route doors and construction walls also need to be assessed. This might appear to be an impossible task when you consider that space must also remain for future expansions, improvements or to perform maintenance during the tunnel’s lifespan. That it is in fact possible has been proved by Beele Engineering from Aalten in the Netherlands.
A wide range of systems is available to seal the openings for cables and pipes. An example of this is the NOFIRNO system, which can be deployed for both cable and pipe transit openings. The system combines a high degree of fire resistance with sealing against gas, water and smoke. Things become trickier when the opening is not standard. That’s the case with the Victoria Park Tunnel in New Zealand for instance – a closed tunnel which was built using the cut-and-cover principle, and which is a vital part of New Zealand’s road and transportation network.
The tunnel walls are constructed of prefab concrete elements. There are openings between the separate elements and between the tunnel wall and roof, which could become a potential source for smoke or fire to spread in an incident. This has been prevented because these openings have also been sealed. Beele Engineering developed a special fire-resistant sandwich system for this: ACTIFOAM/ULTRA, with some 4,000 metres of it incorporated into the tunnel. The system guarantees that in the case of fire, the escape routes will stay clear of smoke, heat and flames.
ACTIFOAM/ULTRA consists of several layers of ACTIFOAM and RISE/ULTRA rubber which together guarantee the best possible fire resistance. The material is easy to process and can be pressed in so that it clamps securely into openings. Fire resistance can be improved still further by finishing the edges of the sandwich sheets with NOFIRNO sealant. In the case of fire, this sealant forms a ceramic, protective layer which ensures that the ACTIFOAM/ULTRA material remains intact and can do its work.
If an inferno breaks out, everyone needs to be able to reach the escape route quickly, in the certainty that their safety there is guaranteed. That’s also why the fire-resistant sandwich system has been subjected to the heaviest-possible, two-hour fire test. These hydrocarbon fire tests actually take into account situations like those which can occur in tunnels where hazardous materials are being transported. Burning tankers or trucks with chemicals can very quickly cause temperatures of up to 1100 °C in the tunnel. This rapid and extreme heat rise imposes heavy demands on the fire-resistant sealing system.
In contrast to the usual tests which normally take an hour, the ACTIFOAM/ULTRA material was tested successfully for fire resistance over a two-hour period, at a temperature of 1250 °C. The sealing remained intact throughout the fire test, and no gaps appeared in the sealing.
Of vital importance for fire resistance is the fact that even after two hours of exposure to this temperature, the temperature on the other side of the wall only rose by 10 °C.
This not only guarantees fire resistance, but also prevents smoke and toxic fumes being able to spread to escape routes, and the escape route is guaranteed to be passable. The flexibility of the sandwich construction also ensures that the changing loads and weights of the ground and transport movements above are absorbed, and that protection is offered against the water pressure arising from the water table.