Exyte Hargreaves involvement was the manufacture and installation of fans, Saccardo nozzles and their supporting structure, in the service shafts and portal buildings.
Five jet fans were installed, consisting of upline and downline shafts, each with a pattern of five 6m x 6m control dampers (in horizontal and vertical orientation), connecting and isolating the two rail tunnel bores, giving full flexibility of reaction to air movement to various emergency situations.
The air is moved by the 2m diameter flow fans, installed in each of the shafts with attenuators, both on tunnel and atmosphere side; attenuators are 6m x 6m big and connected to the fan by 3m long square to round transformers.
The installation was completed using a crane to access the shaft and included the manufacture and installation of steel access and support floors, and interconnecting cat ladders.
The use of ventilation shafts would have been impractical due to the project located close to the river, hence why a system of Saccardo nozzles were designed to give emergency coverage to the tunnel. These are forced draught ventilation systems inducing a flow in a tunnel over long distances. For each bore of each portal, four 1600mm diameter fans will introduce the air into the tunnel roof via a tapering duct (Saccardo Nozzle) this allows the fans to be outside the tunnel giving easier maintenance.
Along the rail route at shafts and portals service buildings, nine shaft head buildings where built, to provide emergency access to the tunnels housed and to the electrical switch rooms required to run the system. Works included the manufacture and installation of ductwork to ventilate these buildings.