The correct answer is A) gas tight bulkheads. U.S. regulations require that tank vessels handling grade B liquids (flammable liquids) must have their cargo pumps separated from all sources of vapor ignition by gas tight bulkheads. This is to prevent the possibility of ignition of the flammable vapors from the cargo. The other options, such as areas equipped with power ventilation, cofferdams, or empty cargo spaces, would not provide the necessary gas tight separation to properly isolate the cargo pumps from potential ignition sources.