Plan: PTW, risk assessment, and TBT were implemented; however, they were not specific to the task. Check Equipment: The tank was only partially equipped and secured with handrails. Prepare Area: The team did not adequately prepare the area with proper working-at-height controls. Control Energy: The Welder was wearing a safety harness but disconnected the lanyard while discarding the elbow fitting. Communication: A pre-tour meeting was held by the Rig Manager, but no TBT was conducted for this specific out-of-sight activity. Final Check: The team failed to verify that all tank safety controls were in place before starting work. Start Work: The task was initiated without proper planning.