Question 308Steam Plants - Assistant Engineer

The correct answer is D) close the master fuel oil valve. When a boiler flareback occurs, the immediate action should be to cut off the fuel supply to the boiler by closing the master fuel oil valve. This stops the flow of fuel and prevents the flareback from escalating into a more serious fire or explosion. Closing the master fuel oil valve is the appropriate first response to a boiler flareback, as it isolates the fuel source and helps bring the situation under control. The other options are not the correct responses. Reducing the forced draft blower speed (A) or increasing the fuel oil supply pressure (B) would not address the immediate safety concern of the flareback. Taking the boiler off the line (C) may be a subsequent step, but the priority is to secure the fuel source first.