Tunnel ventilation

Ventilation is of great importance for the safety of users of road and rail tunnels, both in normal operation and in the event of an incident (fire).

In normal operation, the ventilation ensures the removal of exhaust gases or humid warm air (risk of condensation) or mist. The very corrosive ambient conditions caused by exhaust gases, humidity and salt place high demands on material quality and workmanship.

During incident operation (fire), the tunnel ventilation system must remove toxic, hot fumes and smoke in a targeted manner to allow affected travellers to escape from the tunnel.

As a rule, three concepts are used:

• Smoke extraction via the intermediate ceiling
• Longitudinal ventilation via the portals
• Overpressure ventilation of parallel escape galleries

Smoke extraction via the intermediate ceiling
Heat sensors detect the location of the fire in the tunnel and open 2-3 exhaust flaps to the intermediate ceiling.
Large axial fans draw the smoke gases upwards to a chimney. Flaps and fans are designed redundantly and can withstand fumes of 400°C and more for a longer period of time at full operation.

Longitudinal ventilation via the portals 
Jet fans mounted on the tunnel ceiling generate thrust for smoke evacuation towards the portals or towards exhaust openings.
Depending on the location of the fire, the jet fans can also be operated in reverse. The jet fans must also be able to withstand hot fumes for a certain time at full operation.

Overpressure ventilation of escape galleries
Longer tunnels in particular are equipped with a parallel safety gallery. At regular intervals, it is possible to enter the tunnel via escape doors.
In order to prevent exhaust gases or fumes from entering the escape gallery, fresh air is always fed into the escape gallery from the outside via an overpressure ventilation system.