Transverse & Semi Transverse

In normal operating conditions the Tunnel Ventilation System has to keep the air quality acceptable and the concentration of pollutants within safety levels. In emergency conditions, its role is to control or extract smoke to allow fast and safe evacuation and safe fire fighting activities. This means the fans have to be High Temperature certified by a 3rd Party.

For long tunnels, the ventilation system can be fully transverse or semi-transverse. The fully transverse ventilation system employs centralised exhaust and supply fans with separate ventilation ducts along the length of the tunnel. The fresh air duct normally runs at road level while the polluted air extracts at a higher level.

This system is technically most exact, and is independent of wind and traffic. The cost to built the tunnel is high.

In semi-transverse ventilation system, fresh air is added equally along the tunnel out of an air supply duct, but there is no air extraction. The fresh air is supplied transversely while the polluted air flows longitudinally to the two portals.

This system is technically less exact than fully transverse, it can be affected by wind and traffic, and is still expensive.

Both systems require large axial fans, Unidirectional or Truly Reversible, suitable for smoke extraction at 200/2h, 250/2h,300/2h or 400/2h.

In some cases of very high pressure, an anti-stall device may be necessary.