Balfour Beatty uses Trolex gas detection system in A3 tunnel

Stockport, UK - Sensors and sensing systems manufacturer Trolex has supplied Balfour Beatty with its Sentro 8 integrated gas detection system for use during excavation of the A3 Hindhead Tunnel.

Changes in Workplace Exposure Limits (WEL) since the contract was awarded to Balfour Beatty for the 1.9km tunnel on the A3 in Surrey, meant that environmental monitoring and control was more critical and gas detection devices required a higher level of sensitivity.

The project used 18 Sentro 8 systems each with one pellister for CH4 and 4 fixed electrochemical gas detectors to monitor the level of oxygen, CO, NO and NO2 in the tunnel during construction.

Fixed real-time monitors were required to maintain a safe working environment in the tunnel which comprises two separate bores running in parallel, linked by pedestrian cross-passages at approximately every 100m throughout.

Levels of each gas were monitored and logged at regular intervals by Trolex monitors located at various positions along the tunnel approximately 200m apart. Readings were taken every minute and transmitted to a SCADA display panel in the control room where they were averaged over 24 hour periods. An instantaneous concentration alarm, rather than a time weighted average, was set to sound whenever gas concentration increased above the designated safety limit for each gas.

Commenting on the project, Roger Bridge, Tunnel Construction Manager at Balfour Beatty said, “Trolex has a good reputation in tunnelling and has worked with Balfour Beatty on a number of previous projects. After carrying out technical and commercial tests, the Trolex Sentro 8 system was chosen for its ability to monitor all gases and provide a full package.”

Bridge continued, “The compact units are versatile and can be adapted for other projects in the future. The SCADA package was configured by a Trolex Service Engineer and supported remotely by Trolex via an online link to ensure the system was correct and the software was working efficiently.”