Question 501Motor Plants - Assistant Engineer

The correct answer is C) close all manually operated fuel valves. Before any work is to be carried out on a burner in an automatically fired auxiliary boiler, it is crucial to close all manually operated fuel valves. This ensures that the fuel supply to the burner is isolated and eliminated, preventing any unintended ignition or fire hazard during the maintenance or repair work. Closing the fuel valves is a critical safety precaution that must be taken before any work is performed on the burner. The other options are incorrect because: A) blocking control system relays may not completely isolate the fuel supply, B) allowing the boiler to cool completely is not necessary for safety, and D) locking safety interlock switches is not as effective as closing the fuel valves directly.