Question 199Motor Plants - 1st Asst/Chief

The correct answer is D) close all manually operated fuel valves. Before performing any work on a burner in an automatically fired auxiliary boiler, it is critical to close all manually operated fuel valves. This is a safety precaution to prevent the unintentional release of fuel, which could result in a fire or explosion. Closing the fuel valves isolates the burner from the fuel supply, reducing the risk of an accident during maintenance or repair work. The other answer choices, while potentially helpful safety measures, do not directly address the need to isolate the fuel supply. Blocking control valves, allowing the boiler to cool completely, and locking safety interlock switches closed are all prudent steps, but closing the fuel valves is the most essential action to take before performing work on the burner.