Which of the following is a valid step for isolating energy before performing maintenance?

Isolating energy is a critical step in ensuring safety before performing maintenance work. The valid step of bleeding lines to release pressure effectively removes stored energy in the system, which can be dangerous if it is not properly managed. This action ensures that any pressurized fluids or gases in pipelines or cylinders are safely released, eliminating the risk of unexpected releases that could cause harm to workers.

Turning off the lights does not definitively isolate energy sources related to machinery or systems being worked on, as power could still be present in the equipment. Lowering the temperature, while it may affect certain processes, does not guarantee that all energy sources are safely isolated. Using manual overrides can also lead to unsafe conditions if the underlying system is still energized or if it allows for unexpected operation during maintenance. Thus, bleeding lines to release pressure is the most comprehensive step to promote safety in this scenario.