Which of the following actions is most critical before performing maintenance on a boiler?

Before performing maintenance on a boiler, it is crucial to verify that the boiler is shut down and depressurized. This is essential for ensuring the safety of the maintenance personnel and preventing any accidental releases of steam or hot water that could cause serious injuries or accidents.

When a boiler is operating, it is under pressure, and any maintenance work conducted in this state can lead to hazardous situations. For example, if a valve or fitting is accidentally opened while the boiler is still pressurized, it could result in an explosive release of steam or water, posing a significant risk to anyone nearby.

Shutting down the boiler properly involves not only turning it off but also ensuring that it has cooled down and that any residual pressure has been safely released. This often includes following lockout/tagout procedures to ensure that the boiler cannot be accidentally restarted during maintenance.

Other options such as checking the ambient temperature, ensuring the boiler is at full pressure, or recording the water level are important for day-to-day operations but do not prioritize the immediate safety concerns associated with maintenance tasks. Therefore, verifying that the boiler is properly shut down and depressurized takes precedence before any maintenance work can be safely conducted.