Which of the following best describes the role of interlocks in the boiler fuel train?

• A. They regulate water chemistry.
• B. They ensure safe sequencing so fuel is not supplied without proper air or flame.
• C. They adjust feedwater pressure.
• D. They monitor stack emissions.

Answer: (B)

Interlocks in the boiler fuel train are safety devices that ensure the correct sequence of events before fuel can be burned. Their core job is to prevent fuel from flowing unless there is adequate air for combustion and a flame is established. In operation, sensors check that air flow and purge are in place and that a flame detector confirms ignition. Only when these conditions are verified do the fuel valves open. If air isn’t available or the flame isn’t detected, the interlock shuts off the fuel supply to avoid unburned fuel accumulating or a dangerous ignition scenario. This sequencing is what keeps the system safe during startup, operation, and flame failure scenarios. Water chemistry control, feedwater pressure adjustment, and stack emission monitoring are handled by other parts of the system, not by these interlocks.