Thames Tunnel Technology Breathes Fresh Air for M25 Black Spot 

Work is now underway to relieve congestion at the Holmesdale tunnels on the M25. The Highways Agency scheme to refurbish the tunnels involves the removal of jet fans, previously located next to the carriageway.  This has required the engineers to develop new ventilation methods, capable of introducing high volumes of air in an emergency to purge the tunnels of smoke.  Specialist ventilation engineers, Senior Hargreaves, who have previously supplied Saccardo nozzles for the Thames tunnels on the Channel Tunnel Rail Link (CTRL) are playing a crucial role.

The company began installation in October of vital ventilation equipment that has a life-saving role in the event of an accident.  The main contractor, Costain, has created new platforms extending 40 metres over the carriageways at the entrances to each tunnel.  Each platform will carry around 100 tonnes of ventilation equipment to ram air through wedge-shaped chambers to the Saccardo nozzles.  Systems were required to meet a minimum 25 year service life and so structural framework on the giant Hargreaves ducts is galvanised to marine specification.  Ductwork panels are made in maintenance free stainless steel.   

Under normal circumstances, the ventilation systems will be non operational.  However, should an accumulation of carbon monoxide be detected in the tunnels, as may happen when traffic is slow or static, two fans will start to introduce fresh air and dissipate the gas and fumes.  

In the event of a fire or accident in either tunnel, four fans will operate to introduce 370 cubic metres per second of air at high velocity.  This will create airflow away from the tunnel entrance allowing drivers and passengers to evacuate and safer access for emergency services.    

On completion of the installation of air injection equipment, Costain will build enclosures to screen the Hargreaves plant from view, protect it from weather and further reduce noise emission. 

The site programme requires the completion of the ventilation works by April 2007.  To meet this stringent requirement, Senior Hargreaves is prefabricating major elements of ductwork at their Bury factory so that these can be craned into position.  All works are scheduled for completion by December 2007.  

Detailed design of the environmental and emergency ventilation systems was by Capita Symonds.  Mouchel Parkman developed the outline design for the Saccardo ventilation system and is the management contractor supervising the project on behalf of the Highways Agency.  Fans have been supplied by specialists Fläkt Woods.  


More information:
Phil Johnson,  Tel. +44 (0)161 764 5082 Fax. +44 (0)161 762 2336
E-mail: phil.johnson@senior-hargreaves.co.uk  Web: www.hargreaves-ductwork.co.uk
Senior Hargreaves, Lord Street, Bury, Lancashire BL9 0RG, UK

High/low resolution images are on the web at www.ainsmag.co.uk/ha166/4126ha1a.htm

November 15, 2006