How should cargo tank hatches be protected when the ullage opening is open and the tank NOT gas free?

Correct Answer: Option B — With flame screens

Flame screens are essential safety devices required by 46 CFR to prevent the flashback of flames into cargo tanks. When ullage openings are used, the screen provides a critical barrier against external ignition sources, ensuring that flammable vapors escaping the tank do not ignite and propagate inward.