Question 63

The Correct Answer is A. A flame screen (or flame arrestor) is a safety device typically used on tanks, vents, or pipelines containing flammable materials. Its primary function is to prevent a flame from propagating into the container or system, thereby avoiding an explosion. It achieves this by utilizing materials (usually metal mesh, sintered metal, or perforated plates) with small passages. These passages allow the **passage of vapor or gas** (such as normal ventilation or breathing) but rapidly absorb heat from any incoming flame front, cooling the hot gases below their ignition temperature, thus **quenching the flame** and preventing its passage. Therefore, it **permits the passage of vapor but not of flame**. **Why the other options are incorrect:** * **B) prevents the passage of flammable vapors:** This is incorrect. A flame screen must allow flammable vapors (or air/inert gas mixtures) to pass through for normal tank breathing or operational ventilation. If it prevented vapor passage, it would defeat its purpose as a vent and could cause the tank to over-pressurize or collapse under vacuum. * **C) permits vapors to exit but not enter a tank:** This describes a one-way pressure/vacuum relief valve (or a valve arrangement), not a flame screen. A flame screen typically allows passage in both directions (in and out) while simultaneously blocking a flame from propagating in either direction. * **D) prevents inert gas from leaving a tank:** This is incorrect. If inert gas is being vented (e.g., during cargo loading), the flame screen must permit the inert gas to leave the tank. Its purpose is to stop fire, not prevent gas movement.