Accidental flooding of the engine room bilges through the bilge system is prevented by __________.

Correct Answer: Option A — stop-check valves installed in the bilge suction manifolds

46 CFR 56.50-50 mandates that bilge suction piping must be arranged to prevent accidental flooding. Stop-check valves are essential because they allow flow from the bilge to the pump while automatically preventing backflow from the sea or other tanks into the bilge, maintaining the integrity of the vessel's watertight compartments.