Final answer:
The correct method to make an outlet gas-tight when an appliance is disconnected is by using a cap or plug. This prevents gas leaks by forming a seal capable of withstanding the pressure of the gas and preventing its escape.
Step-by-step explanation:
When an appliance is removed and not connected to an outlet or piping system, it is essential to ensure that the remaining open connector is made gas-tight to prevent any gas leaks that could pose safety hazards. The correct way to make an outlet gas-tight is by using a cap or plug. This is because caps and plugs are specifically designed to form a seal capable of withstanding the pressure of the gas and preventing any escape of the gas into the environment.
While it's important to mention other methods, sealing with tape is not reliable as tape can degrade over time or may not be suitable for the gas type and pressure. Locking the valve might stop the flow, but it does not guarantee that the outlet itself is sealed. Installing an airtight cover might be effective in some cases depending on the design, but the most consistent and safety-approved method is using a cap or plug.
Reference to scenarios describing the dangers of inadequate sealing, such as gas expanding and overflowing or even rupturing containers, underscores the importance of a proper seal. Air gaps in plumbing are necessary to prevent such situations by allowing expansion and contraction. Similarly, making a gas outlet gas tight with a cap or a plug ensures that no unexpected gas leakage occurs.