This document was prepared by UIC Energy and Electrical Traction Experts Group of the Rail System, Forum to provide all the Railways with guidelines to better manage the safety in railway tunnels by appropriate OCL emergency earthing systems. This document describes the systems, technologies, equipments and operations to perform disconnecting, securing against re-connection, verifying the dead status of OCL, carrying out the earthing sequence as well as the procedures to adopt for ascertaining the emergency earthing and the conditions to authorize rescue/emergency services to access tunnels. In order to be applicable in Europe this document has been drafted in accordance with TSI “safety in railway tunnels”. This document is applicable to high speed and conventional rail however not to light/urban rail.