Thrust ventilation in tunnels has the following objectives:

  • Preventing excessive heating of the concrete construction
  • Preventing 'backlayering': the escape of smoke in the opposite direction of the ventilation system
  • Preventing the formation of an explosive mixture in the tunnel tube
  • Keeping the adjacent (safe) tunnel tube smoke free
The operation of the ventilation depends on the incident
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As the longitudinal ventilation plays a major role in combating calamities, it is connected to a standby generator (SG). In the event of a power cut, the standby generator ensures that the detection systems, sprinkler pumps, liquid pumps, ventilation system, emergency lighting and operating systems continue to function. Fire is directly controlled with repressive capacity.

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It should be noted that the eventual shifted amount of air is a multiple of the amount of air that goes through the ventilator. This is called inductive capacity.

The positioning of the ventilators is extremely important with regard to the set-up efficiency.

The set-up efficiency is influenced by –among others- the Coanda effect, the suction conditions and blow out conditions of the ventilator.

The Coanda effect always occurs in practice because ventilators are placed against the ceiling or even at an angle against the wall.

CO/LPG/NOx levels and the spread of smoke in the tunnels are monitored by a PLC or a switch box that is the heart of the ventilation system.

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During normal operation, individually adjustable thrust ventilators ensure a complete mix of air in the tunnel.

In case of a fire, the ventilators create virtual smoke zones that ensure the removal of large volumes of smoke and heat.

If a change in temperature (possible caused by fire) and/or air quality is detected, this information is sent on to the central computer (PLC).

Depending on the place 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.

There are four operational positions:

  1. Continuous ventilation
  2. CO/LPG alarm: this provisionally activates all ventilators
  3. Increased CO/LPG alarm: the air speed and flow rate are increased
  4. Fire/smoke ventilation: heat and smoke are removed in a controlled manner