While underway, the boiler water level in a steaming boiler begins dropping rapidly and cannot be kept at the normal level by standard practices. The engineer's next action should be to __________.

Correct Answer: Option B — secure the fires and then secure the main feed stop/check valve to the boiler

A rapidly dropping water level uncorrectable by normal pumping indicates a severe leak or tube rupture; securing fires first prevents immediate overheating, followed by closing the main feed stop/check to isolate the affected unit.