When must blocking or marking devices be applied?

Blocking or marking devices must be applied before issuing authorities to occupy the main track because these devices serve a critical safety function by preventing unauthorized access to the main track. They ensure that the area is visibly marked as restricted or being worked on, which protects both train crews and maintenance personnel. This procedure is essential to avoid accidents that could occur if a train were to move onto a section of track that is not clear or is under maintenance.

Additionally, while repairs or requests for blocking devices may occur during other situations, the primary protocol mandates that they be in place specifically before a train is allowed to occupy the track. This adherence to safety ensures that all personnel are aware of the conditions on the track and can operate accordingly without risking an incident.