Question 998 Deck General

The correct answer is B) flame screens. Open ullage holes in tanks that are not gas-free must be protected by flame screens. This is a safety requirement to prevent the ignition of flammable vapors that may be present in the tank. Flame screens act as a barrier to prevent open flames or sparks from entering the tank, which could potentially cause an explosion or fire. The other answer choices are incorrect because: A) Stop-check valves are used to prevent backflow, not to protect open ullage holes. C) PV (pressure-vacuum) valves are used to regulate pressure and vacuum in the tank, not to protect open ullage holes. D) Warning signs alone are not a sufficient safety measure for unprotected open ullage holes in non-gas-free tanks.