Which of the listed problems will happen when the water level of a fire-tube type auxiliary boiler approaches the crown sheet?

Correct Answer: Option A — The fusible plugs will melt.

Fusible plugs installed in fire-tube boilers just above the crown sheet contain a core of high-melting-point tin. When water levels drop dangerously close to the crown sheet, the exposed plug melts out, releasing steam into the furnace to warn operators.