Zonegreen
Safety Integrity Level Requirements of a Depot Protection System
Depot Protection Systems are installed in train maintenance facilities to control the safe movement of rail vehicles, protecting staff working in the vicinity. An analysis of the obligations of the safety functions performed by a Depot Protection System in a maintenance facility has concluded that a SIL 2 target level is required.
A system can only be deemed as SIL compliant system if assessed as a whole, rather than relying on compliant COTS (commercial off-the shelf) components in a system using software of unknown pedigree (SOUP). Zonegreen’s DPPS™ has been assessed to meet the hardware and software requirements of SIL 2. DPPS™ uses standardised software and hardware across all installations, resulting in all DPPS™ installations meeting SIL 2.
Introduction to the Depot Personnel Protection System
Zonegreen Smart Depot Personnel Protection System (DPPS™) is installed in maintenance depots to protect personnel who are working in areas such as maintenance sheds or sidings roads, from unauthorised train movements. Each installation is based upon the same core software and hardware, with bespoke configurations that are developed for each customer’s site requirements. The prohibition of train movement is primarily achieved through the deployment of derailers that are typically positioned outside each road at the entrance of a building. The derailers are linked to shunt signals that control trains movements to, from and within the road.
They are also connected to audible and visual alarms that provide an alert to any train movements, authorised or not. Only personnel holding a higher authorisation RFID token (such as depot supervisor, team leader) are allowed to authorise a train movement through the DPPS™ system. Movement of a controlled vehicle is achieved through a controlled logic sequence of procedures by the DPPS™: interlock checking, activating audio visual warning system, lowering derailer and setting inbound/outbound shunt signals.
