Question 29 QMED03 - Oiler

The Correct Answer is B **Explanation of Option B (Correct Answer):** Option B, "Location of the potable water spigots above the rim of the galley sink," is the correct answer because this arrangement ensures an **air gap**. The air gap is the vertical distance between the lowest point of the water supply outlet (the spigot/faucet opening) and the flood level rim (the highest point water can rise before overflowing) of the plumbing fixture (the galley sink). If the sewage system backs up and fills the sink, the air gap physically prevents the contaminated water from ever reaching and being siphoned back into the potable water supply line. This method is the most reliable form of backflow prevention against severe hazards (like sewage backup) known as atmospheric vacuum breaker or air gap separation. **Explanation of Incorrect Options:** * **A) Check valves in the potable water supply lines delivering water to the galley sink:** Check valves are mechanical devices that rely on seals and springs. They can fail due to wear, debris, or inadequate maintenance. While they provide some protection against backflow (backpressure/backsiphonage), they are not considered reliable enough to protect against high-hazard contamination like sewage backup, especially compared to a physical air gap. * **C) Location of the potable water spigots below the rim of the galley sink:** Placing the spigot below the flood level rim creates a submerged inlet, which is the definition of a cross-connection hazard. If the sink fills with contaminated water (e.g., sewage backup), the supply line is directly vulnerable to backsiphonage and contamination, making this option dangerous and incorrect. * **D) A "P" trap in the drain line draining sewage waste from the galley sink:** A P-trap (or U-trap) is designed to retain a small amount of water to create a seal, preventing sewer gases from entering the building. It has no function in preventing the backflow or backsiphonage of contaminated water into the **potable water supply lines**.