INSIGHT | VENTILATION


Above: Smoke Duct with new Damper Actuators


The axial fans of the egress pressurisation system


will be replaced by fans better adapted to the measured operating conditions of the egress tunnel. The fans will be of the same size as the existing fans to minimise changes to ventilation ducts and installations. It is expected that the new fans will allow for a reduction of installed power and power consumption in normal operation by 50%. The tunnel ventilation control system will be replaced


completely. The new system will include an improved control algorithm for the jet fans in emergency ventilation. It will be based on a PI-controller which – in combination with speed control on two of the six jet fans – will allow faster and more stable airflow control. The ventilation in normal operation will also be


changed from mid-point extraction to longitudinal ventilation with jet fans. Due to the reduction of vehicle emissions since 2004, the ventilation is rarely operated to maintain in-tunnel air quality. The change from mid- point extraction to jet fan operation makes the system even more sustainable. The refurbishment project for the Giswil Tunnel is scheduled for completion in Autumn 2027.


IMMEDIATE ACTION The annual tests of the tunnel equipment showed an increase in communication faults between the tunnel ventilation control system and the damper actuators. As the operation of the smoke dampers is a safety-critical component, it was decided to fast-track the resolution of these issues. The intervention had to be kept at a minimum not to interfere with the regular refurbishment of other system components. As time was critical, small contracts had to be awarded to specific suppliers complying to the regulations for contract tenders.


REFERENCES


● 1Riess I. & Lempp, M. (2005) ‘Ventilation System for the Giswil Tunnel’. TUNNEL 2/2005 ● 2PIARC (2007) ‘Systems and Equipment for Fire and Smoke Control in Road Tunnels’ 05.16.B.


● 3ASTRA (2021) ‘Richtlinie Lüftung der Strassentunnel’. ASTRA 13001 V3.01


It was decided to replace the full signal chain from


the communication gateway in the control system to the damper actuators. The actuators had to be replaced completely as there were no spare parts available for the communication modules. The damper supplier offered the installation of the replacement actuators complete with modifications to the dampers and new protective covers for the damper actuators. The intervention also included the replacement of the optical cable connecting the actuators to the control system. The replacement took place in November 2025 during night-time closures of the tunnel. During the closures, two actuators were exchanged including the modifications to the dampers and the installation of the new actuator covers. The dampers were connected to the new communication fibre and tested before the tunnel was re-opened to morning traffic. With all smoke dampers exchanged, the ventilation system was re-tested for all potential fire sections.


CONCLUSION Refurbishing a tunnel ventilation system requires a multi-pronged approach: ● Analysis of the existing system; ● Deficiencies in reference to current standards; ● Remaining design life of system components (nominal and effective);


● Availability of spare parts; ● Availability of measurements of system performance; ● Coordination with other design disciplines; ● Constraints by the civil construction or other project specific constraints;


● Minimise interruption to normal tunnel operation; and, ● Immediate action for safety deficits.


In the refurbishment project for the ventilation system


of the Tunnel Giswil, we had all the items above. But this is not an exception for a refurbishment project. It is what you expect. It is more complex than the design of a new system. Working in night-time shifts is also not to everyone’s liking. But a refurbishment project is also rewarding as you can learn from everything that worked smoothly the past 20 years.


20 | January 2026


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