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Explosion protection is important in tunnel construction


Breaking Through Barriers

High up in the mountains or down in the unseen depths of the earth: tunnels break through entire mountain ranges and pass under rivers and seas. They shorten routes and reduce traffic on our roads. They connect cities, countries, or even continents. Pepperl+Fuchs supports its customers when it comes to establishing a safe and easy path to a destination—all over the world. 

The tremor feels like an earthquake, and the noise is deafening. Gigantic machines are eating through the rock piece by piece with brute force. Tunnel construction is often not a fine art. Whether the tunnel is used for vehicles or a rail network, vast quantities of rock must be removed until the workers can see a light at the end of the tunnel. Tunnel-boring machines (TBM) such as those manufactured by Herrenknecht are used for this work. These machines can be several hundred meters long and have impressive diameters of up to 19 m. At a number of different sites, Pepperl+Fuchs has been securing the explosion protection conditions required for using these machines since the introduction of new regulations.

Gigantic tunnel-boring machines are making their way through mountain ranges. © Herrenknecht AG

Underground Challenges

Tunnel construction involves some special conditions: if gaseous rock and soil formations emit a concentration of methane gas that is too high and thus poses an explosion hazard, boring is automatically stopped and the power supply is switched off. This setup not only stops the drill drives; it also switches off all communication systems. However, this is problematic for the important navigation unit and the emergency evacuation system of the TBM since both are crucial for safety.

Enormous Dimensions, Millimeter-Level Precision

The laser-controlled navigation system manufactured by VMT GmbH, part of the Herrenknecht Group, constantly records the exact position and movement pattern of the TBM in real time and therefore provides essential information for the machine operator and for precise control. However, all saved data would be lost in the event of a short, unplanned interruption of the system, which is fatal for the progress of the construction work. To prevent data loss from the navigation unit during a gas leak, an uninterruptible power supply (UPS) serves as an emergency reserve for the machine memory. The UPS keeps the computer running until a controlled shutdown can take place.

The emergency evacuation systems of the TBM are just as important in the event of an explosion hazard. According to regulations, this system must remain switched on for at least 60 minutes to ensure a safe evacuation of the tunnel. As soon as the energy supply is interrupted, another UPS kicks in so that systems like the lighting along rescue routes still function reliably during the hazardous conditions.

Tunnel construction involves some special conditions © Herrenknecht AG

Twice the Level of Safety: Backing Up the Back-Up Plan

Since the UPS itself can represent a potential ignition source in an explosive atmosphere in the tunnel, both companies were looking for a partner experienced in explosion protection methods. Pepperl+Fuchs has the right solution: installed in a robust housing with a flameproof enclosure (Ex d), the UPS is reliably protected. Control stations connected in increased safety (Ex e) enclosures simplify access to terminals and signal cables.

These Ex de combinations were planned, manufactured, and certified at the Solution Engineering Center (SEC) in Bühl, Germany. “When installed in the Ex d housing, the UPS cannot be an ignition source for the surrounding atmosphere in the tunnel. The systems can continue to function and deliver the necessary data or facilitate evacuation,” explains Christian Strohle, Project Consultant at Pepperl+Fuchs in Bühl. Neither personnel nor machine is endangered. “Even if an explosive atmosphere were to penetrate the robust Ex d housing, it would retain the resulting pressure internally in the event of an explosion and prevent transfer to the surrounding environment.” With these systems, machine operators have access to all of the relevant information during the construction process to enable precise control of the machines. At the same time, the emergency evacuation systems function reliably and show workers a safe route to the non-hazardous area.

Ex de combinations from the Solution Engineering Center (SEC) in Bühl, Germany The Ex de combinations were planned, manufactured, and certified at the Solution Engineering Center (SEC) in Bühl, Germany

Globally Unique

From consulting on what type of protection is the most suitable for the individual application, plus solution proposals and project plans, through to production and certification: customized solutions, like the scenario involving the UPS, require local partnerships with customers. On the one hand, this ensures that the necessary project support can be provided. On the other hand, it is necessary to understand and be able to implement regionally specific requirements. 

On-Site in Shanghai

Pepperl+Fuchs confronts these challenges at its 3,000 m² SEC in Shanghai. The resident specialists are authorized to test manufactured solutions themselves on-site and confirm compliance with the NEPSI regulations relevant in China by attaching certified nameplates. This arrangement means that customers do not need to wait until official licensing offices have checked the manufactured system; instead, the SEC gives them a solution that is ready to install from a single source. “Communication with our customers is especially important to us in Shanghai and in general across China,” explains Holger Fink, development manager for electrical explosion protection equipment at Pepperl+Fuchs. “Particularly when it comes to the more unusual solutions, regular discussions between our project engineers and our customers are very important. Working on an explosion protection solution involves teamwork between the SEC and the customer; this approach applies as much in Bühl, Germany, as it does in Shanghai.” This is also a reason why it would be difficult to support the Chinese market from Europe, as Fink continues to explain. With the SEC on-site, the experts can communicate more effectively with customers and exchange ideas. “Just the language barrier and the time difference between Europe and Asia alone would be a major obstacle for communication. With our approach of adapting the SEC to local conditions, we solve these problems,” Fink explains. For instance, visiting customers is much easier. “Companies also often come to visit us at the SEC to find out more about explosion protection. If we were only able to carry out business from Mannheim or Bühl, it would be much more difficult and require much more effort.”

From the Far East to the Wild West

The topic of distance also played an important role when choosing the site for the SEC that opened in Houston, Texas, in 2013. Here, Pepperl+Fuchs tackles the individual needs of its customers in the American market, more than 8,000 km away from the company’s headquarters. Based in close proximity to one of the most important transshipment ports for the oil industry, Pepperl+Fuchs advises and supports plant builders, control system manufacturers, and system integrators on the implementation of regional explosion protection guidelines. This approach is successful only when NEC expertise in addition to local and highly industry-specific requirements are understood and can be implemented. The construction of a new, larger building started in June 2016 to ensure that the SEC is also prepared for future challenges and able to offer even faster customer service. Together with the US distribution center, the SEC in Houston opened in 2017 with a modern, 10,200 m² production and storage facility. 

“The expanded SEC offers a new level of service for our customers,” says David Hohenstein, Head of the SEC in Houston. “While the individual certification of explosion protection solutions can take weeks or months, at the new SEC, we are able to plan, manufacture, and certify solutions based on our international system certificates in just a few days. After all, we have everything under one roof.” Thanks to the connection with the logistics center, solutions that are ready to install can be shipped directly from here to all locations. This is how Pepperl+Fuchs partners with its customers worldwide to protect personnel and machines—regardless of whether it is an oil refinery in North America, a tunnel-boring machine in Europe, or a chemical plant in Asia.