The project involved the design and construction of 2 cable tunnels running parallel between Hackney and West Ham over a route length of approximately 6km. One tunnel is 4.15 m nominal diameter and connects into National Grid Company (NGC) substations; the other is 2.82m nominal diameter and connects into EDF Energy (EDFE) substations.
For the National Grid Tunnel, Trolex provided a gas detection system to monitor the main shaft, shaft staircases and plant rooms. Junctions of the shaft and tunnel were also monitored and additional carbon monoxide sensors were fixed at the plant room inlet/outlet grills. Methane sensors were fixed at the top of the shafts.
The alarms where the sensors are sited are classed as Zone 1, therefore requiring ATEX Group II equipment. These fed back up to the control panels via intrinsically safe barriers to the non-certified cubicles containing gas racks.
The following gases needed to be monitored:
The monitoring and control panels were located in the control office of each shaft head building. The trip amplifiers located in the controls panels monitored the various gas levels. Control relays were tripped at alarm setpoints to initiate alarms.
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