During a boiler inspection, the two main steam stop valves should be?

During a boiler inspection, it is crucial to ensure that the two main steam stop valves are locked closed and tagged out. This practice is vital for safety reasons. Locking the valves closed helps prevent accidental opening during maintenance or inspection activities, which could lead to serious hazards such as steam release or pressure build-up that could jeopardize the safety of personnel working on or around the boiler.

Tagging out the valves serves as a clear warning to anyone who may access the boiler system that maintenance is taking place, ensuring that no one inadvertently operates the system until all safety checks and maintenance work are completed. This practice aligns with safety protocols in the field, ensuring that systems are de-energized, thereby further minimizing risk during inspection processes.

The other options focus on keeping the valves open or undisturbed, which would expose personnel to unnecessary hazards. The use of tags and locks is part of proper lockout/tagout procedures, crucial for maintaining a safe working environment.