The thrust ventilation in tunnels has the following goals:

• Prevent excessive heating of the concrete structure.
• Preventing 'backlayering': creeping smoke against the direction of ventilation.
• Preventing the formation of an explosive mixture in the tunnel tube.
• Keep smoke free from the adjacent (safe) tunnel tube.
• The operation of the ventilation depends on the incident.

Because longitudinal ventilation plays an important role in combating calamities, it is connected to an emergency power generator (NSA).

In the event of a power failure, the emergency power generator ensures that the detection systems, sprinkler pumps, liquid pumps, the ventilation system, the emergency lighting and the control systems continue to function. Fire is immediately tackled with sufficient repressive capacity.

It is important to realize that the final total amount of air moved is a multiple of the amount of air that passes through the fan. We call this the inducing capacity.

The arrangement of the fans is very important in connection with the installation efficiency. The set-up efficiency is influenced by, among other things, the coanda effect, the suction conditions and the blow-out conditions of the fan.

The coanda effect always occurs in practice because fans are placed against the ceiling or even in a corner of the wall.

The CO / LPG / NOx levels and the smoke distribution within the tunnels are controlled by a PLC or a control cabinet, which is the heart of the ventilation system.

In normal operation, individually controllable thrust fans ensure complete mixing of the air in the tunnel.

In the event of a fire, the fans create virtual smoke zones that take care of the removal of large volumes of smoke and heat. If a change in temperature (possibly due to fire) and / or air quality is detected, this information is routed to the central computer (PLC).

Depending on the location and status of any change in air quality in the tunnel, the computer will activate the ventilation system in accordance with the pre-programmed functional diagram.

Four operating modes are possible:

• Continuous ventilation.
• CO / LPG alarm; Here the fans are temporarily activated.
• Increased CO / LPG alarm, whereby the air speed and flow rate are increased.
• Fire / smoke ventilation, in which heat and smoke are removed in a controlled manner