Fläkt Woods fans installed as the main ventilation for the Hindhead Tunnel

Fläkt Woods has supplied the main ventilation in the form of 43 of their 1120mm diameter JMTS horizontally mounted smoke vent category: 250 degrees C for 2 hour type jetfans to be mounted within the road tunnels, as well as 34 JM type axial fans for the cross passage sections of the twin bore A3 Hindhead project.


The project has completed the dual carriageway link between London and Portsmouth and removed a major source of congestion, particularly around the A3/A287 traffic signal controlled crossroads. A new road is 4 miles (6.5km) long and includes the 1.2miles (1.8km) twin bored tunnels under the Devil's Punch Bowl Site of Special Scientific Interest.

It is, in fact, Britain’s most ambitious tunnelling project since the Channel Tunnel. It’s actually a pair of record-breaking, 1.3 mile, 70mph road tunnels — one north bound, one south bound — underneath one of southern England’s prettiest beauty spots.

Ventilation in tunnels is required for normal and emergency operation. During normal operation, its purpose is to provide a clean air environment and to maintain reasonable temperatures during congested conditions. During emergency operation, ventilation is needed to influence the flow of smoke and combustion products so as to create a safer environment for tunnel users to escape and for emergency services to intervene.

In an emergency, the smoke is controlled by creating sufficient air velocity to drive it away from the fire. During emergency operation, smoke management is achieved by removal of air, for example by the extraction of air and smoke. Contaminated air is replaced by clean or smoke-free air, which is drawn in through the portals.

Within the tunnel; the cross passage ventilation system draws fresh air into the cross passage via an open motorised fire damper at one end and extracted via a fan and motorised fire damper arrangement at the opposite end. Regardless of the mechanical ventilation equipment, naturally induced airflows are present in the tunnels to a varying extent.

The project includes the closure of the existing A3 around the Devil's Punch Bowl, bringing considerable environmental benefits to an internationally prized area. The centre of Hindhead will be free from the daily gridlock that blights the area, with the result that the project will bring benefits to road users, local residents, and the highly prized environment.

Not only has the tunnel come in ahead of time and slightly below its £371 million budget, it is expected to shave up to half an hour off the time it takes to get from London to Portsmouth and the South Coast.

The 737,000 cubic metres of earth which has been dug out to make the tunnel has stayed on site to create embankments and to bury the present A3. The existing road around the Devil’s Punch Bowl has disappeared completely. It’s all National Trust land and, very soon, the public will have access to a 1,500-acre canyon without having to navigate an overcrowded road carrying 30,000 vehicles per day.

The tunnels feature cross-passages every 100m and state-of–the-art safety and communications systems, including high quality lighting and ventilation, CCTV surveillance and radio-interrupt systems to convey quick appropriate information to tunnel users.

Commenting on the contract, Olivier Auguy of Fläkt Woods said: “One of the first things you see when you enter the tunnel is Flakt Woods fans. The Hindhead contract follows closely on the heels of the Blackwall Tunnel contract, and reinforces our position as the foremost provider of specialist products for emergency high temperature smoke control. No other Company possess the in-house expertise, and the third party certified endorsements that we have”

“We have recently enhanced this by becoming the first fan manufacturer in the world to be able to apply CE marking for the JM HT fan range for 200°C, 300°C and 400°C temperature categories, ensuring that Fläkt Woods has one of the most comprehensive ranges of products available in the Single European Market.”


Tunnelling facts:

The A3 twin tunnels were bored from each end by excavating about a metre per day using diggers, then spraying the walls with concrete. On 26 February 2009, engineers met at the breakthrough point.

Ancillary works included a deep cutting to the south of the tunnel with a new junction for Hindhead and Hammer at its southern end. An equestrian and pedestrian bridge, the Miss James Bridge, crosses the cutting between tunnel and junction, and includes heathland planting to link the habitats on either side of the cutting.

• Fuel consumption rate of the excavators was 528 gallons of low-sulphur diesel per day
• Digging the tunnel took 290,875 man-hours
• 378,599 cubic metres of concrete were made
• 1,399,034 man-hours were worked without an accident
• The tunnel contains 156 miles of cable
• The tunnel has 104 CCTV cameras
• The fire main tank can hold 8,358 gallons of water
• 4,322 people worked on the project

Fläkt Woods:

Fläkt Woods has been active in developing tunnel ventilation fans that are approved in accordance with the requirements of EN 12101-3 at both 300°C and 400°C and has a policy of offering fans certified in accordance with ISO 21927-3 outside Europe.