At 18 kilometres-long, the coming connection beneath the Fehmarn Belt will be […]
At 18 kilometres-long, the coming connection beneath the Fehmarn Belt will be world’s largest immersed tunnel for trains and cars. Meanwhile, the combination of design and preparedness will make it the world’s safest underwater passageway. Construction is set to begin as soon as the German permits are in place, and contracts with the developers have been signed.
An immersed tunnel of such length places huge demands on safety. That’s why safety systems and contingency plans are an essential focal point of the tunnel’s design. Safety has been an integral part of the project ever since the first sketches were made back in 2008, until now, when bids for the tunnel’s four large main contracts are being scrutinised by experts and consultants from the project developer, Femern A/S.
– The entire Fehmarn Tunnel is designed with safety in mind. To extent possible, the starting point is naturally to prevent anything at all from going wrong. But should something go wrong anyway, a comprehensive rescue apparatus will be there to intervene in any conceivable situation, says Kim Smedegaard Andersen, a contract director and civil engineer for Femern A/S.
The Construction Act for the project, and thus the environmental regulatory authorisation, was passed by the Danish Parliament on 28 April. Construction can therefore begin as soon as the contracts have been signed and the German permits are in place. According to the project’s schedule, this should happen at some point in 2015.
Tunnel safer than open land
The tunnel consists of five tubes: two for trains, two for cars and one emergency corridor. The roadways have double, one-way lanes, and each has an emergency access lane.
When the tunnel’s design and general safety measures are brought together, we see one of the safest tunnels capable of being built today. As such, the risk of a serious accident on the railway or roadways in the tunnel is actually smaller than on a similar stretch of motorway or railroad on open land.
– This is documented by the risk calculations that Femern A/S has had done by our advisors. The calculations are supported by analyses from the Norwegian Highway Authority and the Norwegian research institute SINTEF, which have shown that the risk of serious accidents in modern tunnels is typically half that of similar stretches of open road, says Andersen, and continues:
– Part of the explanation for the high level of safety is that the traffic isn’t bothered by rain, wind, fog, snow or falling leaves, which is the case outside of the tunnel, and which means there aren’t as many people pulling off the road. There’s also the safety concept and the tunnel’s design, which are based on valid Danish, German and European norms and standards, as well as on the latest international expertise on tunnel safety. For example, the Fehmarn Tunnel only receives traffic in one direction, so that drivers do not face oncoming traffic or collisions.
– One of the most important elements of the safety concept is, however, the fact that the tunnel is monitored on a 24-hour basis, and that the emergency response team is close by, which means we can quickly get an overview of the situation and act immediately in the event of an accident, says civil engineer Finn Ennemark, who is the project manager for safety and emergency preparedness at Femern A/S.
As soon as a fire is detected, a series of systems are activated by the tunnel’s safety personnel. First off, the powerful fans are set in motion so that the smoke is controlled and blown out in the direction of travel. The tunnel is also cleared of traffic and closed off with barriers to prevent additional cars from entering it while the emergency response efforts are underway.
Because only few accidents are expected – no more than 2-4 per year – we’re considering the possibility of stopping traffic in both directions if we have an accident. This way, if necessary, our emergency response team will be able to move in from both sides of the tunnel, both via the emergency lane in the affected tunnel, as well as from the opposite side of the other tube.
The walls and ceiling of the tunnel will be fire-insulated, and the entire tunnel can be fitted with a fire-extinguishing system that is activated directly from the control centre to help keep a fire under control until the fire brigade and emergency response team arrive at the scene.
With fire insulation, all critical constructions will be protected against high temperatures so that they can maintain the load-bearing capacity for which they were originally designed. For example, concrete constructions can withstand large-scale fires with temperatures of up to 1,350 degrees over several hours.
In addition to limiting the fire itself, it is important to keep the development of smoke under control, so that people can quickly flee to a safe and smoke-free area. The tunnel is therefore equipped with powerful ventilation systems which ensure that smoke is blown out in the direction of traffic.
It has not been determined, however, whether the tunnel will be equipped with systems such as sprinklers or water mist extinguishers. Recent experience, tests and technological development has actually shown that such systems depend on the nature of the tunnel and the other safety systems that have been installed in it.
– Water mist and sprinkler systems can keep temperatures down, reduce smoke, keep fires from spreading and limit damages to the construction. Theoretically, however, they can also reduce visibility and be somewhat superfluous if we instead plan on very rapid fire-extinguishing and rescue response measures. So, it’s a matter of accounting for several factors which determine whether we end up deciding to install this type of system, Andersen explains.
Building on experiences from the Great Belt and Øresund projects
The tunnel is being constructed with inspiration from the Øresund and Great Belt tunnel tubes. The two connections, which began their operations in 2000 and 1997, respectively, have proven to be very safe. After nearly 33 years of combined operations, there has not been a single fatal accident in either of the tunnels.
– We’re continuing to build on the positive experiences from Øresund and have added a few elements to our design that can further reduce the risk of accidents, says Ennemark and goes on to clarify:
– For example, we’re establishing emergency lanes along the entire length of the tunnel on both of the double-lane pipes for roadways. There will also be small pull-off areas with access to the technical components that require maintenance. This allows us to prevent constrict or detain traffic on the roads.
Not a Mont Blanc concept
Discussions concerning tunnel safety often focus on the two serious tunnel fires, which occurred in the Alps in the Mont Blanc Tunnel, in 1999, and in the Gotthard Road Tunnel, in 2001. The tunnel concept behind the Fehmarn Belt Fixed Link, however, is very different.
First, both of the tunnels in the Alps had two-way traffic on in the same tubes, with no extra tubes for emergency response teams and without a sufficient number of emergency lanes. Secondly, rescue efforts in the Mont Blanc Tunnel were complicated by insufficient coordination between the emergency response workers on the French and Italian sides of the privately-operated tunnel.
As a result of the two accidents, the requirements for tunnel safety have generally become more stringent, which can be seen in certain aspects of the Fehmarn Fixed Belt Link. In the efforts to develop an optimal safety and rescue concept, Femern A/S has, among other initiatives, worked with drills and simulations in close coordination with the authorities and emergency response personnel from both Denmark and Germany.
Not everything is solved just yet
Shortly before the start of construction, there are still a few loose ends to see to. The German and Danish emergency response and rescue authorities have therefore established a common steering committee and a number of related working groups. For example, one of the working groups is exploring whether physical fire and rescue teams should be established near the tunnel openings on both sides of the Fehmarn Belt Fixed Link.
Because there are no nearby hospitals on either the Danish or German side, a helicopter landing pad and other safety measures must also be established.
Before the tunnel opens, Femern A/S is obligated to develop a detailed emergency rescue and response concept in collaboration with the relevant authorities and rescue services to ensure that solutions have been found for all pending matters.
– The Safety concept and all the details will continue to be polished along the way, all the way up to the day of the tunnel’s opening. Before then, we will have found solutions to every existing problem, and we will have also conducted full-scale drills in the completed tunnel. Only then will the final model be approved by the Danish and German authorities, Ennemark concludes.
Safety concept built on four pillars:
• Accident prevention
24-hour staffed video surveillance and regular road patrols that deploy if e.g. a car breaks down will help prevent accidents. The tunnel’s design also plays a role. Among other features that have been incorporated, there is a slight incline down in the tunnel’s road so that brakes on lorries, campers and other large vehicles do not overheat.
• Minimising consequences
Any accidents will be picked up by the surveillance cameras, after which an emergency response team will be deployed. Traffic can be stopped and the tunnel can be emptied of vehicles with the use of road patrols and a computer-controlled traffic control system with appertaining signage and broadcast connections to car radios and other outlets. Other systems monitor the air quality and temperature inside the tunnel. Emergency lanes have also been established throughout the tunnel, along a specially-designed crash barrier that cars skid along with if they crash. Drivers can also use emergency telephones and fire-extinguishing equipment until help arrives.
• Several escape options
The tunnel is designed so that the distance to the nearest emergency exit is no more than about 50 metres away. In the event of an accident, signs and speakers lead people to safety, and there is access from all of the tunnel tubes to secure neighbouring tubes, where the pressure can be increased to a level higher than that in a tube affected by fire to prevent smoke from penetrating.
• Fast and effective emergency response
In partnership with the relevant Danish and German emergency rescue and response authorities, Femern A/S is currently developing a safety and emergency response concept for the completed tunnel, which will ensure a fast and coordinated rescue response from both the Danish and German sides.
©CFPA EUROPE 2022