Question 63 GLI02 - Mate of Unlimited Tonnage

The Correct Answer is C **Why Option C is Correct:** A flame screen (often part of a flame arrester or fitted in tank venting systems) is a safety device designed to prevent the propagation of a flame front into an enclosed space (like a cargo tank) that might contain an explosive vapor-air mixture. It achieves this by absorbing the heat of the flame as the combustion gases pass through narrow, closely spaced passages (often wire mesh or perforated plates), extinguishing the fire. Crucially, the screen must still allow the free passage of vapor (breathing) under normal operating conditions; therefore, it "permits the passage of vapor but not of flame." **Why Other Options are Incorrect:** * **A) prevents inert gas from leaving a tank:** A flame screen's primary function is fire safety, not gas retention. Inert gas is allowed to leave during off-loading or thermal expansion; the screen doesn't block this flow, it just protects against flashback. * **B) permits vapors to exit but not enter a tank:** This describes a pressure/vacuum (P/V) valve's function in maintaining pressure equilibrium, not the physical principle of a flame screen. A flame screen typically allows flow in both directions, protecting against flame propagation both into and out of the tank. * **D) prevents the passage of flammable vapors:** The screen must allow flammable vapors (or inert gas, or air) to pass freely under normal venting conditions. If it prevented the passage of vapor, the tank would over-pressurize or vacuumize. Its job is to stop the combustion *of* the vapor, not the vapor itself.