Tunnel air quality explained
Air quality in the M5 East tunnel is managed by ventilating the tunnel with fresh air. This dilutes the pollutants emitted from vehicles as they travel through the tunnel. Mixing large volumes of fresh air with the vehicle emissions ensures that the concentration of pollutants remain within set limits.
Fresh air is sucked into the tunnel using large fans at an air intake, located in Turrella. Additional fresh air is also drawn into the tunnel at all tunnel entrances and exits by the use of fans, which also move the air along the tunnel at speeds of up to 36 km/h or 10 metres per second.
Monitors in the tunnel measure pollutant levels along the length of the tunnel. Air quality in the tunnel is controlled by adding the right amount of fresh air to dilute the pollutants to the required levels; so high traffic volumes require higher volumes of fresh air.
Once the tunnel air has travelled along the tunnel it is exhausted from the tunnel via a single exhaust stack located in Turrella. This stack contains eight large axial fans which can blow the tunnel air out of the exhaust stack at speeds of more than 100 km/h. A 35 metre high stack ensures tunnel air is well dispersed. This prevents pollutants from accumulating at ground locations around the stack.
Air quality is measured in the tunnel, in the stack and at ground locations around the stack. Ambient air quality readings for locations around the stack can be read on this website.